Automtaizacion
Automtaizacion
Automtaizacion
Edition 2007
2007
http://theguide.schneider-electric.com
12/2006
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2
chapter
Automation solution guide
From the needs, choose an architecture, then a technology to lead to a product
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1.1 1.2 1.3 1.4 1.5 Introduction The automation equipment Automation architectures Architecture definition Choice of automated equipment
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1.1 1.2
Progress in industrial automation has helped industry to increase its productivity and lower its costs.Widespread use of electronics and powerful, flexible software have given rise to more efficient modular designs and new maintenance tools. Customer demands have also evolved substantially; competition, productivity and quality requirements compel them to adopt a process-based approach.
The process engenders waste which must be collected, transported, treated and discarded.
1.2
v Power control
Controls loads driven by the automatic device, either a contactor is used as a direct on line starter or an electronic controller is used to graduate the power supply of a motor or heater.
v Dialogue
A Fig. 2 Five basic functions
Commonly named man-machine interface, it is the link between the operator and the machine. It is function is to give orders and monitor the status of the process Control is made by push buttons, keyboards and touch screens and viewed through indicator lights, illuminated indicator banks and screens.
v Data processing
The software, part of the automation equipment, fusing the orders given by the operator and the process status measurements is the brain of the equipment. It controls the preactuators and sends information when and where required. The automation engineer has a wide range of options, from the simplest (as a set of push buttons directly controlling a contactor), through programmable logic systems to a collaborative link between the automated devices and computers. Today as simple low-cost automated devices are available, relay diagrams have practically disappeared.
1.2
v Data acquisition
Data acquisition is mandatory to send feedback is to the controller or the PLC. Due to technological progress most of all physical value can now be detected or measured.
b Power links
These are the connections between parts and include cables, busbars, connectors and mechanical protection such as ducts and shields. Current values range from a few to several thousand amperes. They must be tailored to cover electrodynamic and mechanical stress as well as heat stress.
b Control links
These are used to drive and control the automated devices. Conventional cabling systems with separate wires are gradually being replaced by ready-made connections with connectors and communication buses.
b Cost of an equipment
Cost reduction is an issue at every level during the choice and decisionmaking process. Its tightly bound with the customer needs. Though this guide only describes the technical aspects, it has been written with costeffectiveness in mind.
1.2 1.3
To meet these requirements, an offer for reliable and powerful products must include ready-to-use architectures enabling intermediate players such as systems integrators and OEMs to specify and build the perfect solution for any end user. The figure 3 illustrates the relationship between market players and Schneider Electric offer.
A Fig. 3
Architectures add value to the intermediate players, starting with the retailer or wholesaler, panel builder, machine installer or manufacturer. It is a global approach that enables them to respond more reliably, exactly and faster to end customers in different industries such as food, infrastructure or building.
1.3
Automation architectures
In the late 1990s, the conventional prioritised approach both in manufacturing processes (CIM: Computer Integrated Manufacturing) and in continuous processes (PWS: Plant Wide Systems) gave way to a decentralised approach. Automated functions were implemented as close as possible to the process (see the definition of these terms in the software section.) The development of web processes based on Ethernet and the TCP/IP protocol began to penetrate complex automated systems. These gradually split up and were integrated into other functions, thus giving rise to smart devices. This architecture made it possible to have transparent interconnection between the control systems and IT management tools (MES, ERP). At the same time, the components (actuators, speed controllers, sensors, input/output devices, etc.) gradually evolved into smart devices by integrating programming and communication features.
b Smart devices
These include nano-automated devices, automated cells (such as Power Logic, Sepam, Dialpact, etc.) and components with a regulating function, such as speed controllers. These products are smart enough to manage process functions locally and to interact with each other. Transparent communication means that tasks can be reconfigured and diagnoses made these possibilities are perfectly in line with the web process (individual addressing, information formatted to be ready to use, information provider management). The product line of smart devices products are systematically plug and play for power controllers, control bus and sensors. This approach means equipment can be replaced quickly and easily in the event of failure.
1.3
Automation architectures
The integration of browsers into keyboard and screen systems, radio controls and other MMIs has accelerated deployment of web technologies right up to the component level (see chapter 9 for explanations of connection and classes). The integration of control functions into smart devices has reduced the data flow on networks, thereby lowering costs, reducing the power of the automated devices and speeding up response times. There is less need for synchronisation because the smart devices process locally.
b Networks
At the same time, networks have been widely accepted and have converged on a limited number of standards which cover 80% of applications. There are many options open to designers (CANopen, AS-Interface, Profibus, DeviceNet, etc.) but the trend is towards a standard single network. In this framework, Ethernet, which has already won over the industrial computerisation sector, can also address needs for ground buses. A great many elements are now directly network-connectable. This is the result of the combined effects of web-technology distribution, rationalisation of communication standards, the sharp drop in the price of information technology and the integration of electronics into electro-mechanical components. These developments have led to the definition of field buses adapted to communication between components and automated devices such as Modbus, CANopen, AS-Interface, Device Net, Interbus S, Profibus, Fip, etc. The increasing need for exchange prompts customers to give priority to the choice of network ahead of automated equipment.
1.4
Architecture definition
An architecture is designed to integrate, interface and coordinate the automated functions required for a machine or process with the object of productivity and environmental safety. A limited number of architectures can meet most automation requirements. To keep matters simple, Schneider Electric proposes to classify architectures on the basis of two structure levels (C Fig. 4): - functional integration based on the number of automation panels or enclosures, - the number of automated control functions, i.e. the number of control units in e.g. an automated device.
A Fig. 4
Type of architectures
A Fig. 6
1.4
Architecture definition
A Fig. 8
A Fig. 7
A Fig. 11
A Fig. 9
A Fig. 12
Packaging machine
1.4
Architecture definition
A Fig. 14
A Fig. 13
b Collaborative control
Several machines or parts of a procedure have their own controllers (C Fig. 15). They are linked together and collaborate in operating the system. This architecture is designed for large procedures such as in the petrochemical and steel industries or for infrastructures such as airports or water treatment plants (C Fig.16).
A Fig. 16
Water treatment
A Fig. 15 10
1.5
A Fig. 17
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1.5
b Preferred implementations
These implementations are the result of an optimization between the expressed needs and technologies available. The table (C Fig. 18) below shows a summary of them; they are described in greater detail in the documents provided by Schneider Electric.
A Fig. 18
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1.5
A Fig. 19
To assist customers choice, Schneider Electric has drawn up a complete guide with questions divided into four themes given the mnemonic of PICCS (Performance, Installation, Constraints, Cost, Size). An example is given (C Fig. 20 and 21) below. For all the implementations available, please refer to the catalogues. Here we are just illustrating the approach with examples.
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1.5
A Fig. 20
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1.5
A Fig. 21
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1.5
We shall take three different applications and ascertain the most suitable architecture(s) for each of them.
v Tower crane
Notwithstanding its apparent simplicity, this machine (C Fig. 22) has to comply with stringent safety and environmental standards. Market competition forces manufacturers to consider the cost of every element. The features of this type of crane are: - power of the installation from 10 kW to 115 kW depending on the load to hoist (2 to 350 metric tons), - hoisting, rotation, trolleying and translation are driven by three-phase AC motors with two or three gears or AC drives. Braking is mechanical or electric, - the system requires about a dozen of sensors and the man-machine interface can be in the cabin or remote-controlled. The choice of implementation naturally focuses on an optimised compact system in a single panel at the basement of the crane. The highlighted colour coding in the selection table above shows the options at a glance (C Fig. 23).
A Fig. 22
Tower crane
A Fig. 23
The Simple Compact is eliminated because its options are too limited. Both Optimised Compact and Evolutive Optimised Compact are suitable (C Fig. 24 and 25). The latter is even more suitable if the machine is a modular design or if remote maintenance is required.
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1.5
The choice of components naturally depends on the customers constraints and those of the chosen implementation. The figures below illustrate both possible implementations:
A Fig. 24
A Fig. 25
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1.5
A Fig. 26
Revolving table
A Fig. 27
Conveyor
A Fig. 28
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1.5
This leaves the two CANopen field bus solutions. The first, which is more economical (C Fig. 29), ensures the basic requisite functions and the second (C Fig. 30) ensures transparency and synchronisation with automated devices outside the section involved. It is also easy to upgrade: a new configuration can be downloaded whenever a series is changed and so forth.
v Electrical diagram
A Fig. 29
A Fig. 30
CANopen solution
A Fig. 31
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1.5
The choice will focus on a distributed implementation. The table (C Fig. 32) below shows the best one. The most suitable implementation is the Ethernet one (C Fig. 33 and 34), ensuring total transparency in the installation. The ASI bus is limited by its low data exchange capacity. The CANopen ones can be used with a modem but their possibilities are still restricted.
A Fig. 32
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1.5
A Fig. 33
A Fig. 34
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2
2
chapter
Electrical power supply
Reminder of rules, regulations and practices in order to select properly the power supply of the machine. Introduction to the power supply and control functions
Summary
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2.1 2.2 2.3 2.4 2.5 Introduction Power supply to machinery Standards and conventions Power supply functions Power supply to the control circuit
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This section explains how electrical systems in machinery are supplied with electricity. A supply system acts as an interface between the mains installation and the machinery and must meet the technical standards and constraints of both (C Fig.1). It is the latter which is described here and readers are advised to refer to the Electrical installation guide for further information.
A Fig. 1
2.2
A Fig. 2
2.3
2.3
b Machinery
Standards have been brought in line with IEC 60 204-1 to facilitate export and use the same machines through the world. Few countries have retained some specific rules; elements of the main ones are given in the table in (C Fig. 3) below.
TNC diagrams are not permitted in low-voltage installations in buildings (Norway). TT power diagrams are not permitted (USA). The neutral conductor break is mandatory in TN-S diagrams (France and Norway). The distribution of a neutral conductor in an IT diagram is not permitted (USA and Norway). The maximum rated voltage of an AC control circuit is 120V (USA). The minimum gauge of copper conductors is specified in ANSI/NFPA 79 in American sizes (AWG) (USA). Annex G of the standard gives the equivalent in mm2 of the AWG. WHITE or GREY is used to identify neutral earthed conductors instead of BLUE (USA and Canada). Marking requirements for rating plates (USA). A Fig. 3 Specific features of standards and practices in a number of countries
UL508
IEC 60947
JIS-C 8201-4-1
>100A connectors
Lug clamps
>100A A Fig. 4
Parallel wires
2.4
b Supply and cut off the machine power and control units with attention to the following points
v Break capacity
Depending on the power installed, the prospective short-circuit current in the event of an incident can range from a few kA to several hundred kA, so the device must be sized accordingly.
v Short-circuit endurance
A short-circuit downstream of the electrical equipment must not cause destruction of the device.
v Connection capacity
Internal wires in equipment are always in copper but it should be noted that aluminium is used in electrical system distribution. The input device should therefore withstand both types of connection.
b Personal protection
Electrical cabinets are usually locked during operation, so operators do not have access to them. Regulations stipulate personal protection rules for working inside of electrical devices, in particular for starting and maintenance. Personal protection requires compliance with a number of rules: - IP20 protection against contact with internal connections, - disconnection. This function ensures the installation is completely or partly disconnected from any source of electrical power for safety reasons. Insulation Insulation must be ensured when a control device is open, i.e. the leakage current must be below the danger threshold. Padlocking This function is intended to prevent any unauthorised person from switching on electrical devices. Control insulation This must be adequate to protect people and electrical equipment from over-voltage and other electrical pollution. Equipotential connection Installation rules can stipulate earthing or insulation according to the system eathing used.
2.4 2.5
circuit-breaker circuit-breaker
Disconnection Switch-off Short-circuits protection Isulation Short-circuits immunity Padlocking Protection from earth faults A Fig. 5
XX
XX X
XX XX
XX XX XX
XX XX X XX X X
XX XX XX XX XX XX option XX
XX XX X XX XX X XX XX XX XX
XX XX XX
2.5
2.5
A Fig. 6
Upstream power to the transformer can be single or 3-phase; the latter (C Fig. 7) dispenses with the need for smoothing capacitors. Though this solution is more reliable, its immunity to micro-breaks is lessened.
A Fig. 7
2.5
A Fig. 8
A loop feedback controls the high-frequency switch cycle time to ensure the requisite regulation characteristic (C Fig. 9).
A Fig. 9
v Conclusion
The table (C Fig. 10) gives a brief comparison of the two technologies. For more details, see the section on product implementation.
Comparison for a 10A/24V DC source Input voltage range Overall dimensions Weight Efficiency Output voltage adjustment Microbreak immunity Load regulation Line regulation EMC pollution Harmonic pollution Reliability, lifetime A Fig. 10 Regulated switched power Rectified filtered power Wide range of 85 to 264V 3dm2 1.5kg Up to 85% Yes High >20ms 1 to 3% <1% Requires careful design As per EN61000-3-2 with filter Good Set ranges of 110V to 230V 7dm2 6kg Up to 75% No Low <5ms 5% 5-10% depending on mains Naturally low Basically as per standard EN61000-3-2 Very good
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36
chapter
Motors and loads
Introduction to motor technology Information on loads and motor electrical behaviour
Summary
1 2
3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Three phase asynchronous motors Single-phase motors Synchronous motors Direct current motors commonly named DC motors Operating asynchronous motors Electric motor comparison Types of loads Valves and electric jacks
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3.1
This section describes the physical and electrical aspects of motors.The operating principle of the most common types of motors is explained in detail. The powering, starting and speed control of the motors are explained in brief. For fuller information, see the relevant section.
3.1
b Operating principle
The operating principle of an asynchronous motor involves creating an induced current in a conductor when the latter cuts off the lines of force in a magnetic field, hence the name induction motor. The combined action of the induced current and the magnetic field exerts a driving force on the motor rotor.
A Fig. 1
Lets take a shading ring ABCD in a magnetic field B, rotating round an axis xy (C Fig. 1). If, for instance, we turn the magnetic field clockwise, the shading ring undergoes a variable flux and an induced electromotive force is produced which generates an induced current (Faradays law). According to Lenzs law, the direction of the current is such that its electromagnetic action counters the cause that generated it. Each conductor is therefore subject to a Lorentz force F in the opposite direction to its own movement in relation to the induction field. An easy way to define the direction of force F for each conductor is to use the rule of three fingers of the right hand (action of the field on a current, (C Fig. 2). The thumb is set in the direction of the inductor field. The index gives the direction of the force.
A Fig. 2
Rule of three fingers of the right hand to find the direction of the force
The middle finger is set in the direction of the induced current. The shading ring is therefore subject to a torque which causes it to rotate in the same direction as the inductor field, called a rotating field. The shading ring rotates and the resulting electromotive torque balances the load torque.
A Fig. 3
A Fig. 4
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3.1
If we overlay the 3 diagrams, we can see that: - the three anticlockwise fields are offset by 120 and cancel each other out, - the three clockwise fields are overlaid and combine to form the rotating field with a constant amplitude of 3Hmax/2. This is a field with one pair of poles, - this field completes a revolution during a power supply period. Its speed depends on the mains frequency (f) and the number of pairs of poles (p). This is called synchronous speed.
b Slip
A driving torque can only exist if there is an induced current in the shading ring. It is determined by the current in the ring and can only exist if there is a flux variation in the ring. Therefore, there must be a difference in speed in the shading ring and the rotating field. This is why an electric motor operating to the principle described above is called an asynchronous motor. The difference between the synchronous speed (Ns) and the shading ring speed (N) is called slip (s) and is expressed as a percentage of the synchronous speed. s = [(Ns - N) / Ns] x 100. In operation, the rotor current frequency is obtained by multiplying the power supply frequency by the slip. When the motor is started, the rotor current frequency is at its maximum and equal to that of the stator current. The stator current frequency gradually decreases as the motor gathers speed. The slip in the steady state varies according to the motor load. Depending on the mains voltage, it will be less if the load is low and will increase if the motor is supplied at a voltage below the rated one.
b Synchronous speed
The synchronous speed of 3-phase asynchronous motors is proportional to the power supply frequency and inversely proportional to the number of pairs in the stator.
Number of poles 2 4 6 8 10 12 16 A Fig. 5 Speed of rotation in rpm 50 Hz 3000 1500 1000 750 600 500 375 60 Hz 3600 1800 1200 900 720 600 540 100 Hz 6000 3000 2000 1500 1200 1000 750
Example: Ns = 60 f/p. Where: Ns: synchronous speed in rpm f: frequency in Hz p: number of pairs of poles.
The table (C Fig. 5) gives the speeds of the rotating field, or synchronous speeds, depending on the number of poles, for industrial frequencies of 50Hz and 60Hz and a frequency of 100Hz. In practice, it is not always possible to increase the speed of an asynchronous motor by powering it at a frequency higher that it was designed for, even when the voltage is right. Its mechanical and electrical capacities must be ascertained first. As already mentioned, on account of the slip, the rotation speeds of loaded asynchronous motors are slightly lower than the synchronous speeds given in the table.
v Structure
A 3-phase asynchronous squirrel cage motor consists of two main parts: an inductor or stator and an armature or rotor.
v Stator
This is the immobile part of the motor. A body in cast iron or a light alloy houses a ring of thin silicon steel plates (around 0.5mm thick). The plates are insulated from each other by oxidation or an insulating varnish. The lamination of the magnetic circuit reduces losses by hysteresis and eddy currents.
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3.1
The plates have notches for the stator windings that will produce the rotating field to fit into (three windings for a 3-phase motor). Each winding is made up of several coils. The way the coils are joined together determines the number of pairs of poles on the motor and hence the speed of rotation.
v Rotor
This is the mobile part of the motor. Like the magnetic circuit of the stator, it consists of stacked plates insulated from each other and forming a cylinder keyed to the motor shaft. The technology used for this element divides asynchronous motors into two families: squirrel cage rotor and wound slip ring motors.
b Types of rotor
v Squirrel cage rotors
There are several types of squirrel cage rotor, all of them designed as shown in figure 6. From the least common to the most common:
A Fig. 6 Exploded view of a squirrel cage rotor
Resistant rotor The resistant rotor is mainly found as a single cage (see the definition of single-cage motors below). The cage is closed by two resistant rings (special alloy, reduced section, stainless steel rings, etc.). These motors have a substantial slip at the rated torque. The starting torque is high and the starting current low (C Fig. 7). Their efficiency is low due to losses in the rotor. These motors are designed for uses requiring a slip to adapt the speed according to the torque, such as: - several motors mechanically linked to spread the load, such as a rolling mill train or a hoist gantry, - winders powered by Alquist (see note) motors designed for this purpose, - uses requiring a high starting torque with a limited current inrush (hoisting tackle or conveyors). Their speed can be controlled by changing the voltage alone, though this function is being replaced by frequency converters. Most of the motors are self-cooling but some resistant cage motors are motor cooled (drive separate from the fan).
A Fig. 7
Note: these force cooled asynchronous high-slip motors are used with a speed controller and their stalling current is close to their rated current; they have a very steep torque/speed ratio. With a variable power supply, this ratio can be adapted to adjust the motor torque to the requisite traction.
Single cage rotor In the notches or grooves round the rotor (on the outside of the cylinder made up of stacked plates), there are conductors linked at each end by a metal ring. The driving torque generated by the rotating field is exerted on these conductors. For the torque to be regular, the conductors are slightly tilted in relation to the motor axis. The general effect is of a squirrel cage, whence the name. The squirrel cage is usually entirely moulded (only very large motors have conductors inserted into the notches). The aluminium is pressure-injected and the cooling ribs, cast at the same time, ensure the short-circuiting of the stator conductors. These motors have a fairly low starting torque and the current absorbed when they are switched on is much higher than the rated current (C Fig. 7).
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3.1
On the other hand, they have a low slip at the rated torque. They are mainly used at high power to boost the efficiency of installations with pumps and fans. Used in combination with frequency converters for speed control, they are the perfect solution to problems of starting torque and current. Double cage rotor This has two concentric cages, one outside, of small section and fairly high resistance, and one inside, of high section and lower resistance. - On first starting, the rotor current frequency is high and the resulting skin effect causes the entire rotor current to circulate round the edge of the rotor and thus in a small section of the conductors. The torque produced by the resistant outer cage is high and the inrush is low (C Fig. 7). - At the end of starting, the frequency drops in the rotor, making it easier for the flux to cross the inner cage. The motor behaves pretty much as though it were made from a single non-resistant cage. In the steady state, the speed is only slightly less than with a single-cage motor. Deep-notch rotor This is the standard rotor. Its conductors are moulded into the trapezoid notches with the short side on the outside of the rotor. It works in a similar way to the double-cage rotor: the strength of the rotor current varies inversely with its frequency. Thus: - on first starting, the torque is high and the inrush low, - in the steady state, the speed is pretty much the same as with a single-cage rotor.
These rings are rubbed by graphite brushes connected to the starting device. Depending on the value of the resistors in the rotor circuit, this type of motor can develop a starting torque of up to 2.5 times the rated torque. The starting current is virtually proportional to the torque developed on the motor shaft. This solution is giving way to electronic systems combined with a standard squirrel cage motor. These make it easier to solve maintenance problems (replacement of worn motor brushes, maintenance of adjustment resistors), reduce power dissipation in the resistors and radically improve the installations efficiency.
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3.2
Single-phase motors
3.2
Single-phase motors
The single-phase motor, though less used in industry than the 3-phase, is fairly widely used in low-power devices and in buildings with 230V single-phase mains voltage.
v Structure
Like the 3-phase motor, the single-phase motor consists of two parts: the stator and the rotor. Stator This has an even number of poles and its coils are connected to the mains supply. Rotor Usually a squirrel cage.
v Operating principle
Lets take a stator with two windings connected to the mains supply L1 and N (C Fig. 9). The single-phase alternating current generates a single alternating field H in the rotor a superposition of the fields H1 and H2 with the same value and rotating in opposite directions. At standstill, the stator being powered, these fields have the same slip in relation to the rotor and hence generate two equal and opposing torques. The motor cannot start.
A Fig. 9 Operating principle of a single-phase asynchronous motor
A mechanical pulse on the rotor causes unequal slips. One of the torques decreases while the other increases. The resulting torque starts the motor in the direction it was run in. To overcome this problem at the starting stage, another coil offset by 90 is inserted in the stator. This auxiliary phase is powered by a phase shift device (capacitor or inductor); once the motor has started, the auxiliary phase can be stopped by a centrifugal contact. Another solution involves the use of short circuit phase-shift rings, built in the stator which make the field slip and allow the motor to start. This kind of motor is only found in low-power devices (no more than 100W) (C Fig. 10).
A 3-phase motor (up to 4kw) can also be used in a single phase arrangement: the starting capacitor is fitted in series or parallel with the idle winder. This system can only be considered as a stopgap because the performance of the motors is seriously reduced. Manufacturers leaflets give information regarding wiring, capacitors values and derating.
A Fig. 10
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3.2 3.3
It powers up to 1000W and its no-load rotation speed is around 10,000 rpm. These motors are designed for inside use. Their efficiency is rather poor.
3.3
Synchronous motors
b Magnetic rotor synchronous motors
v Structure
Like the asynchronous motor, the synchronous motor consists of a stator and a rotor separated by an air gap. It is different in that the flux in the air gap is not due to an element in the stator current but is created by permanent magnets or by the inductor current from an outside source of direct current powering a winding in the rotor. Stator The stator consists of a body and a magnetic circuit usually made of silicon steel plates and a 3-phase coil, similar to that of an asynchronous motor, powered by a 3-phase alternating current to produce a rotating field. Rotor The rotor has permanent magnets or magnetising coils through which runs a direct current creating intercalated north-south poles. Unlike asynchronous machines, the rotor spins at the speed of the rotating field with no slip. There are thus two distinct types of synchronous motor: magnetic motors and coil rotor motors. - In the former, the rotor is fitted with permanent magnets (C Fig. 12), usually in rare earth to produce a high field in a small space. The stator has 3-phase windings. These motors support high overload currents for quick acceleration. They are always fitted with a speed controller. Motor-speed controller units are designed for specific markets such as robots or machine tools where smaller motors, acceleration and bandwidth are mandatory. - The other synchronous machines have a wound rotor (C Fig. 13). The rotor is connected rings although other arrangements can be found as rotating diodes for example. These machine are reversible and can work as generators (alternators) or motors. For a long while, they were mainly used as alternators as motors they were practically only ever used when it was necessary to drive loads at a set speed in spite of the fairly high variations in their load torque. The development of direct frequency converters (of cycloconverter type) or indirect converters switching naturally due to the ability of synchronous machines to provide reactive power has made it possible to produce variable-speed electrical drives that are powerful, reliable and very competitive compared to rival solutions when power exceeds one megawatt.
A Fig. 12
A Fig. 13
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3.3
Synchronous motors
Though industry does sometimes use asynchronous motors in the 150kW to 5MW power range, it is at over 5MW that electrical drives using synchronous motors have found their place, mostly in combination with speed controllers.
v Operating characteristics
The driving torque of a synchronous machine is proportional to the voltage at its terminals whereas that of an asynchronous machine is proportional to the square of the voltage. Unlike an asynchronous motor, it can work with a power factor equal to the unit or very close to it. Compared to an asynchronous motor, a synchronous one has a number of advantages with regard to its powering by a mains supply with constant voltage and frequency: - the motor speed is constant, whatever the load, - it can provide reactive power and help improve the power factor of an installation, - it can support fairly big drops in voltage (around 50%) without stalling due to its overexcitation capacity. However, a synchronous motor powered directly by a mains supply with constant voltage and frequency does have two disadvantages: - it is dificult to start; if it has no speed controller, it has to be no-load started, either directly for small motors or by a starting motor which drives it at a nearly synchronous speed before switching to direct mains supply, - it can stall if the load torque exceeds its maximum electromagnetic torque and, when it does, the entire starting process must be run again.
v Linear motors
Their structure is the same as that of rotary synchronous motors: they consist of a stator (plate) and a rotor (forcer) developed in line. In general, the plate moves on a slide along the forcer. As this type of motor dispenses with any kind of intermediate kinematics to transform movement, there is no play or mechanical wear in this drive.
Hybrid Bipolar
These are induction motors. At the starting stage, the motor works in asynchronous mode and changes to synchronous mode when it is almost at synchronous speed. If the mechanical load is too great, it can no longer run in synchronous mode and switches back to asynchronous mode. This feature is the result of a specific rotor structure and is usually for lowpower motors.
No. of steps/rev. 8
Step 1
v Stepper motors
The stepper motor runs according to the electrical pulses that power its coils. Depending on the electricity supply, it can be: - unipolar if the coils are always powered in the same direction by a single voltage; - bipolar if the coils are powered first in one direction then in the other. They create alternating north and south poles. Stepper motors can be variable reluctance, magnetic or both (C Fig. 14). The minimum angle of rotation between two electrical pulse changes is called a step. A motor is characterised by the number of steps per revolution (i.e. 360). The common values are 48, 100 or 200 steps per revolution.
Type of stepper motors
Intermediate state
Step 2
A Fig. 14
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3.3 3.4
The motor rotates discontinuously. To improve the resolution, the number of steps can be increased electronically (micro-stepping). This solution is described in greater detail in the section on electronic speed control. Varying the current in the coils by graduation (C Fig. 15) results in a field which slides from one step to the next and effectively shortens the step. Some circuits for micro-steps multiply by 500 the number of steps in a motor, changing, e.g. from 200 to 100,000 steps. Electronics can be used to control the chronology of the pulses and count them. Stepper motors and their control circuits regulate the speed and amplitude of axis rotation with great precision. They thus behave in a similar way to a synchronous motor when the shaft is in constant rotation, i.e. specific limits of frequency, torque and inertia in the driven load (C Fig. 16). When these limits are exceeded, the motor stalls and comes to a standstill. Precise angular positioning is possible without a measuring loop. These motors, usually rated less than a kW, are for small low-voltage equipment. In industry, they are used for positioning purposes such as stop setting for cutting to length, valve control, optical or measuring devices, press or machine tool loading/unloading, etc. The simplicity of this solution makes it particularly cost-effective (no feedback loop). Magnetic stepper motors also have the advantage of a standstill torque when there is no power. However, the initial position of the mobile part must be known and integrated by the electronics to ensure efficient control.
A Fig. 15
A Fig. 16
3.4
A Fig. 17
DC motor
On the other hand, they are not as rugged as asynchronous motors and their parts and upkeep are much more expensive as they require regular maintenance of the collectors and brushes.
b Structure
A DC motor consists of the following components:
v Inductor or stator
This is a part of the immobile magnetic circuit with a coil wound on it to produce a magnetic field, this winding can be replaced by permanent magnets specially in the low power range. The resulting electromagnet has a cylindrical cavity between its poles.
v Armature or rotor
This is a cylinder of magnetic plates insulated from each other and perpendicular to the cylinder axis. The armature is mobile, rotates on its axis and is separated from the inductor by an air gap. The conductors are distributed regularly around it.
3.4
b Operating principle
When the inductor is powered, it creates a magnetic field (excitation flux) in the air gap, directed by the radii of the armature. The magnetic field enters the armature on the north pole side of the inductor and leaves it on the south pole side. When the armature is powered, its conductors located below one inductor pole (on the same side as the brushes) are crossed by currents in the same direction and so are subjected to a Lorentz law force. The conductors below the other pole are subjected to a force of the same strength and in the opposite direction. Both forces create a torque which rotates the motor armature (C Fig. 18). When the motor armature is powered by a direct or rectified voltage U and the rotor is rotating, a counter-electromotive force E is produced. Its value is E = U RI.
A Fig. 18 Production of torque in a DC motor
RI represents the drop in ohm voltage in the armature. The counterelectromotive force E is related to the speed and excitation by E = k where: - k is a constant of the motor itself, - is the angular speed, - , is the flux. This relationship shows that, at constant excitation, the counterelectromotive force E, proportional to , is an image of the speed. The torque is related to the inductor flux and the current in the armature by: T=kI When the flux is reduced, the torque decreases. There are two ways to increase the speed: - increasing the counter-electromotive force E and thus the supply voltage: this is called constant torque operation, - decreasing the excitation flux and hence the excitation current, and maintain a constant supply voltage: this is called reduced flux or constant power operation. This operation requires the torque to decrease as the speed increases (C Fig. 19).
A Fig. 19
Furthermore, for high constant power ratios, this operation requires motors to be specially adapted (mechanically and electrically) to overcome switching problems. Operation of such devices (direct current motors) is reversible: - if the load counters the rotation movement (resistant load), the device produces a torque and operates as a motor, - if the load makes the device run (driving load) or counters slowdown (standstill phase of a load with a certain inertia), the device produces electrical power and works as a generator.
A Fig. 20
46
3.4 3.5
series parallel motor (compound) This technology combines the benefits of the series and parallel excitation motors. It has two windings. One is parallel to the armature (shunt winding) or is a separate excitation winding. It is crossed by a current that is weak compared to the working current. The other is in series. The motor has an added flux under the combined effect of the ampere-turns of both windings. Otherwise, it has a subtracted flux, but this system is rarely used because it causes operating instability at high loads.
3.5
A Fig. 21
47
3.5
Effect on speed The rotation speed of an asynchronous motor is proportional to the frequency of the supply voltage. This property is often used to operate specially designed machines at high speed, e.g. with a power supply at 400Hz (grinders, laboratory or surgical devices, etc.). Speed can also be varied by adjusting the frequency, for example from 6 to 50Hz (conveyor rollers, hoisting equipments, etc.).
v Pole-changing motors
As we have already seen, the speed of a squirrel cage motor depends on the mains supply frequency and the number of pairs of poles. So a motor with two or more speeds can be made by combining windings in the stator to correspond to different numbers of poles. This type of motor can only have1/2 speed ratios (4 and 8 poles, 6 and 12 poles, etc.). It has six terminals (C Fig.22). For one of these speeds, the mains supply is connected to the three corresponding terminals. For the other, these terminals are connected to each other and the mains is connected to the remaining three. Mostly, for both high and low speed, the motor is started direct on line involving no special device (direct starting). In some cases, if the operating conditions require it and the motor allows it, the starting device automatically moves into low speed before changing to high speed or before stopping. Depending on the currents absorbed by the Low Speed (LS) or High Speed (HS) changes, both speeds can be protected by a single thermal relay or by two relays (one for each speed). Such motors usually have low efficiency and a fairly low power factor.
These motors, with two electrically separate stator windings, can produce two speeds in any ratio. However, their electrical characteristics are often affected by the fact that the low speed windings have to support the mechanical and electrical stress of high speed operation. So motors in low speed mode sometimes absorb more current than they do in high speed mode. Three or four speed motors can be made by changing the poles on one or both of the stator windings. This solution requires additional connectors on the coils.
b Slip-ring motors
v Rotor resistance
The resistor externally inserted into the rotor circuit in this kind of motor defines: - its starting torque, - its speed. A resistor permanently connected to the terminals of a slip-ring motor lowers its speed and the higher its value, the more the speed drops. This is a simple solution for speed variation.
48
3.5
Example of slip ring operation. For a variable load exerting a load torque of 0.8 Cn, different speeds can be obtained as represented by the sign in the diagram (C Fig. 23). For the same torque, the speed decreases as the rotor resistance increases.
Its structure makes it a robust system with no wearing parts that can be used for occasional purposes and up to a power of 100kW.
49
3.5 3.6
Ward Leonard motor generator set This device, once very widespread, is the forerunner of DC motor speed controllers. It has a motor and a DC generator which feeds a DC motor (C Fig.25). The speed is controlled by regulating the excitation of the generator. A very small current is used to control powers of several hundred kW in all the torque and speed quadrants. This type of controller was used in rolling mills and pithead lifts. This was the most efficient speed control system before it was made obsolete by the semiconductor.
A Fig. 25
3.6
A Fig. 26
50
3.7
Types of loads
3.7
Types of loads
We can classify the loads in two families: - the active loads which put moving a mobile or a fluid or which change its state like the gas state in the liquid state, - the passive loads which do not get a driving force like lighting or the heating.
b Active loads
This term covers all systems designed to set a mobile object or a fluid in motion. The movement of a mobile object involves changing its speed or position, which implies applying a torque to overcome its resistance to movement so as to accelerate the inertia of the load. The speed of movement is directly related to on the torque applied.
v Operating quadrants
A Fig. 27 The four possible situations for a machine in a torque-speed diagram
The figure 27 illustrates the four possible situations in the torque-speed diagram of a machine. Note that when a machine works as a generator it must have a driving force. This state is used in particular for braking. The kinetic energy in the shaft is either transferred to the power system or dissipated in a resistor or, for low power, in machine losses.
v Types of operation
Constant torque operation Operation is said to be constant torque when the charges characteristics in the steady state are such that the torque required is more or less the same whatever the speed (C Fig.28). This is the operating mode of machines like conveyors, crushers or hoists. For this kind of use, the starter device must be able to provide a high starting torque (1.5 times or more the nominal rate) to overcome static friction and accelerate the machine (inertia). Operation with torque increasing with speed The characteristics of the charge imply that the torque required increases with the speed. This particularly applies to helical positive displacement pumps where the torque increases linearly with the speed (C Fig.29a) or centrifugal machines (pumps and fans) where the torque varies with the speed squared (C Fig.29b). The power of displacement pumps varies with the speed squared. The power of centrifugal machines varies with the speed cubed. A starter for this type of use will have a lower starting torque (1.2 times the motors nominal torque is usually enough).
A Fig. 28
b
A Fig. 29 a/b Variable torque operation curve 51
3.7
Types of loads
Operation with torque decreasing with speed For some machines, the torque required decreases as the speed increases. This particularly applies to constant-power operation when the motor provides a torque that is inversely proportional to the angular speed (C Fig.30). This is so, for example, with a winder, where the angular speed needs to drop as the diameter of the winder increases with the build-up of material. It also applies to spindle motors on machine tools. The constant-power operating range limited by its very nature: at low speed by the available current from the speed controller and at high speed by the torque the motor can provide. The driving torque on asynchronous motors and the switching capacity of DC motors should therefore be checked carefully.
A Fig. 30 Decreasing torque operation
The table (C Fig.31) gives a list of common machines with their torque law depending on speed.
Type of machine Conveyor Rotary press Helical displacement pump Metering pump Centrifugal pump Fans and blowers Screw compressor Scroll compressor Piston compressor Cement kiln Extruding machine Mechanical press Winders, unwinders Pulpers Sectional machine Crusher Mixer Kneader, calender Centrifuge Machine tool spindle Hoist A Fig. 31 Torque law depending on speed Constant Constant Torque increasing linearly with speed Constant Torque increasing with the speed squared Torque increasing with the speed squared Constant Constant Constant Constant Constant or decreasing linearly with speed Constant Constant or decreasing linearly with speed Constant Constant Constant Torque increasing linearly with speed Constant or decreasing linearly with speed Torque increasing with the speed squared Constant or decreasing linearly with speed Constant
Torque characteristic per machine
When a machine starts, it often happens that the motor has to overcome a transitory torque, such as in a crusher when it starts with a full hopper. There can also be dry friction which disappears when a machine is running or a machine starting from a cold stage may needs a higher torque than in normal operation when warm.
b Passive loads
There are two types of passive charge used in industry: - heating, - lighting.
52
3.7
Types of loads
v Heating
Heating is a costly item for industrial premises. To keep these costs down, heat loss must be reduced; this is a factor which depends on building design and is beyond the scope of this guide. Every building is a specific case and we cannot allow ourselves to give vague or irrelevant answers. That said, proper management of the building can provide both comfort and considerable savings. For further information, please see the Schneider Electric Electrical Installation Guide or the Cahier Technique 206 available from the Schneider Electric website. If necessary, the best solution may be found by asking the advice of the electrical equipment suppliers experts.
v Lighting
Incandescent lighting Incandescent lighting (trademarked by Thomas Edison in 1879) was an absolute revolution and, for many years afterwards, lighting was based on devices with a filament heated to a high temperature to radiate visible light. This type of lighting is still the most widely used but has two major disadvantages: - extremely low efficiency, since most of the electricity is lost in heat consumption, - the lighting device has a lifetime of a few thousand hours and has to be regularly changed. Improvements have increased this lifetime (by the use of rare gases, such as krypton, or halogen). Some countries (Scandinavian ones in particular) plan to ban this type of lighting eventually. Fluorescent lighting This family includes fluorescent tubes and fluocompact lamps. The technology used is usually low-pressure mercury. Fluorescent tubes These were introduced in 1938. In these tubes, an electric discharge makes electrons collide with mercury vapour, which excites the mercury atoms and results in ultraviolet radiation. The fluorescent matter lining the inside of the tube transforms the radiation into visible light. Fluorescent tubes dissipate less heat and last longer than incandescent lamps but require the use of two devices: one to start them and one called a ballast to control the current of the arc once they are switched on. The ballast is usually a current limiting reactor connected in series with the arc. Fluocompact lamps (C Fig.32) These work to the same principle as a fluorescent tube. The starter and ballast functions are performed by an electronic circuit in the lamp, which enables the tubes to be smaller and to be folded. Fluocompact lamps were developed as an alternative to incandescent lamps: they save a significant amount of power (15W instead of 75W for the same brightness) and last much longer (8000 hours on average and up to 20,000 for some).
A Fig. 32
53
3.7
Types of loads
Discharge lamps (C Fig.33) Light is produced by an electric discharge created by two electrodes within a gas in a quartz bulb. Such lamps all require a ballast, usually a current limiting reactor, to control the current in the arc. The emission range depends on the gas composition and is improved by increasing the pressure. Several technologies have been developed for different functions. Low-pressure sodium vapour lamps These have the best lighting capacity but they have a very poor colour rendition because they radiate a monochrome orange light. Uses: motorway lighting, tunnels. High-pressure sodium vapour lamps These emit a white light tinged with orange. Uses: urban lighting, monuments.
A Fig. 33
Discharge lamps
54
3.7
Types of loads
This constraint applies equally to ordinary and halogen lamps. It requires reducing the maximum number of lamps that can be powered by the same device such as a remote control, modular contactor or relay on ready-made circuits. Light dimming This can be achieved by varying the RMS voltage powering the lamp. Voltage is usually adjusted by a triac used to vary the triggering angle in the mains voltage cycle. The waveform of the voltage applied to the lamp is illustrated (C Fig. 34). Gradual powering of the lamp also reduces, or even eliminates, the power surge when it is switched on. Note that light dimming: - alters the colour temperature, - shortens the life of halogen lamps when low voltage is maintained for long periods. The filament is not regenerated so efficiently at low temperature. Some halogen lamps are powered at low voltage through a transformer. Magnetisation in a transformer can produce power surges 50 to 75 times greater than the nominal current for a few milliseconds. Suppliers also offer static converters which do away with this disadvantage. Powering fluorescent lamps and discharge lamps Fluorescent tubes and discharge lamps require control of arc intensity. This function is performed by a ballast device inside the bulb itself. The magnetic ballast (i.e. limiting current reactor (C Fig.35) is commonly used in domestic appliances.
A Fig. 34
Current waveform
A Fig. 35
Magnetic ballast
A magnetic ballast works in conjunction with the starter device. It has two functions: to heat the electrodes in the tube and to generate a power surge to trigger the tube. The power surge is induced by triggering a contact (controlled by a bimetal switch) which breaks the current in the magnetic ballast. When the starter is working (for about 1 sec.), the current absorbed by the light is about twice the nominal current.
t (s)
(V) 600 400 200 0 -200 -400 -600 0 0,02 0,04 0,06
As the current absorbed by the tube and ballast together is mainly inductive, the power factor is very low (0.4-0.5 on average). In fixtures with a large number of tubes, a capacitor must be used to improve the power factor. This capacitor is usually applied to each light appliance. Capacitors are sized to ensure that the overall power factor exceeds 0.85. In the most common type, the parallel capacitor, the average active power is 1F for 10W for all types of lamp. The parallel capacitor layout creates stress when the lamp is switched on.
t (s)
(A) 300 200 100 0 -100 -200 -300 0 0,02 0,04 0,06
As the capacitor is initially discharged, switching on creates causes a power surge (C Fig.36). There is also a power surge due to oscillation in the power inductor/capacitor circuit. The electronic ballast (C Fig. 37), first introduced in the 1980s, does away with these disadvantages. The electronic ballast works by powering the lamp arc by an electronic device generating a rectangular alternating voltage. There are low frequency or hybrid devices, with frequency ranging from 50 to 500Hz, and high frequency devices with frequency ranging from 20 to 60kHz. The arc is powered by high frequency voltage which completely eliminates flickering and strobe effects.
A Fig. 36
A Fig. 37
55
3.7 3.8
The electronic ballast is totally silent. When a discharge lamp is heating up, it supplies it with increasing voltage while maintaining a virtually constant current. At continuous rating, it regulates the voltage applied to the lamp independently of fluctuations in the mains voltage. As the arc is powered in optimal voltage conditions, 5-10% of power is saved and the lifetime of the lamp is increased. Furthermore, the output of an electronic ballast can exceed 93%, whereas that of a magnetic device is on average only 85%. The power factor is high (> 0.9). An electronic ballast does however have some constraints with regard to the layout used (C Fig. 38), since a diode bridge combined with capacitors leads to a power surge when the device is switched on. In operation, the absorbed current is high in third harmonic (C Fig. 39), resulting in a poor power factor of around 55%. The third harmonic overloads in the neutral conductor. For more information, see Cahier Technique 202: The singularities of the third harmonic. Electronic ballasts usually have capacitors between the power conductors and the earth. These anti-interference capacitors induce a constant leakage current of about 0.5-1mA per ballast. This limits the number of ballasts that can be powered when a residual current device (RCD) is installed (see the Cahier Technique 114 Residual current device in LV).
A Fig. 38
A Fig. 39
3.8
b Electric scewjacks
Linearly driven applications require heavy-duty electric screwjacks that are powerful, fast, long-lived and reliable. Manufacturers offer wide ranges of electric screwjacks for practically all requirements.
56
3.8
This is a fairly cost-effective design with useful properties: plastic and metal can work together well without catching. The acme screw works quietly, so it is suitable for offices, hospitals, etc. Another of its assets is its high friction coefficient. This design is particularly well suited to screwjacks used in applications where they must be self-locking, i.e. with no recoil against the mass of the load. For instance, when a screwjack is used to adjust the height of a table, one with an acme screw enables the table to withstand heavy loads without altering its vertical position. This means that no brake or other locking mechanism is required to maintain the load in place when it is idle. The ball screw system is used for high performance purposes (C Fig.41). The ball screws in the screwjack are made of steel and have a row of ball bearings in a closed system between the nut and the screw. This design gives a very low friction coefficient between the nut and the screw due to the rolling contact between the ball bearings, nut and tracks. Wear is low compared to an acme screw, so the ball screw has a lifetime 10 times longer in identical operating conditions. This lifetime also implies that a ball screw can withstand heavy loads and long operating cycles. Its low friction coefficient makes the ball screw especially efficient because it does not overheat. The ball screw is therefore highly suited for situations requiring lengthy operation at high speed. A screwjack with a ball screw system has very little play, so its precision is significantly better in applications where position and precision are crucial.
A Fig. 41
v Product family
Electric screwjacks can be made in many different shapes and sizes to fit easily into machines. Manufacturers also offer control units to make it easier to operate them. The photo (C Fig.42) gives a view of some products offered by one manufacturer (SKF).
Document SKF
v Selection guide
Choosing the right electric screwjack often requires detailed knowledge of the application and some calculation. However, manufacturers catalogues can help in making the initial choice of screwjacks meeting the basic criteria such as load and speed.
A Fig. 42 Electrical screwjacks from SKF
57
3.8
b Valves
Valve operating systems do not enter into the scope of this guide. That said, as valves can be part of industrial control systems such as regulation loops or speed controllers, it is useful to have some idea of their structure and what happens when they work. v Valve structure A valve (C Fig.43) consists of a body and a throttle which presses against a seat. Fluid movement is controlled by an operating rod. This rod is actuated by electric or pneumatic devices. Many valves are pneumatically controlled, others are electrically controlled (solenoid valves). There are many different valve designs (butterfly, spherical, diaphragm, etc.) for different types of use, fluid and progression rates (output in relation to the position of the throttle or the control signal in regulation valves). The throttle usually has a specific shape to prevent or mitigate any unwanted effects such as water hammer or cavitation. Water hammer This can occur in hydraulic pipes when the valve is closed. The flow through the pipe is suddenly stopped and causes this phenomenon known as water hammer.
A Fig. 43
58
3.8
Dh
+C
As an example (C fig. 44a et 44b)), here is a description of a pumping station feeding a reservoir above the feed pump. When the emptying valve is closed, the water drained from the reservoir via the pump below the fluid column tends to pursue its movement while there is no more output from the pump. This movement causes elastic deformation of the pipe which contracts at a point near the valve.
0<t<T
This phenomenon makes the mass of fluid temporarily available and maintains it in movement. Depression occurs and spreads throughout the pipe at the speed of elastic waves C until the entire pipe is affected by it, i.e. after a time T=L/c, where L is the length of the pipe between the valve and the outlet. The result is that the pressure where the pipe goes into the reservoir is lower than the pressure in the reservoir and causes backflow. The wave spreads from the reservoir to the pumping station and reaches the valve throttle after a time 2T from the start of the phenomenon.
A Fig. 44a
Dh -C
-Q
The fluid column continues its descent and hits the closed valve again, causing the pipe to swell and reversing the movement of the fluid. Water hammer would occur indefinitely if the effects of load loss, depression and overpressure are not gradually dampened.
T < t < 2T
To overcome this potentially destructive phenomenon, valve closing can be controlled by a system based on a slow closing law to keep overpressure and depression within reasonable limits. Another procedure involves gradually slackening the speed of the feed pump to enable the valve to close the pipe. In the case of pumps running at constant speed, the most suitable device is a soft start device such as Altistart by Telemecanique or Altivar for speed-controlled pumps. Cavitation Closing a valve results in restricting the section available for fluid flow (C Fig.45). Applying the Bernoulli theorem, restricting the flow section left by the valve accelerates the flow and lowers static pressure at that point. The amount of static pressure drop depends on: - the internal geometry of the valve, - the amount of static pressure downstream of the valve. The pressure when the valve is open is shown on (C curve 1). Flow is restricted at the point of the closing valve throttle, causing a drop in pressure and accelerated flow (Venturi effect); When the throttle closes, the Venturi effect increases and curve 1 is gradually deformed (C curve 2). When the static pressure in the fluid vein reaches the value of the vapour tension at the flow temperature, vapour bubbles form in the immediate vicinity of the restricted flow. When the static pressure rises again downstream of the valve (pressure P2), the vapour bubbles condense and implose. Cavitation has the following undesirable effects: - unacceptably loud noise, rather like pebbles rattling in the pipes, - vibrations at high frequencies which loosen the valve nuts and other parts, - rapid destruction of the throttle, seat and body by removal of metal particles. Surfaces subject to cavitation are grainy, - the flow through the valve is related to valve opening. Regulation valves are often required to operate for a long time in conditions where cavitation can occur and their lifetime will be seriously affected by it. Ways of limiting or preventing cavitation do not enter into the scope of this guide.
59
A Fig. 44b
Water hammer
A Fig. 45
Cavitation phenomenul
4
60
chapter
AC motors starting and protection systems
Presentation : AC motors starting and braking systems AC motors protection devices and failure analysis Protection devices selection guide
Summary
1 2
4.1 4.2 4.3 4.4 4.5 4.6 4.7 Asynchronous motor starting systems Electrical braking of 3-phase asynchronous motors Multifunction motor starter units Motors protection Motor losses and heating Causes of faults and their effects Protection functions
62
3 4 5 6 7 8 9 10 11 12 M
69
74
76
77
77
83
61
4.1
This section is devoted to starting and braking systems and the protection of asynchronous motors of all types. Motor protection is required to ensure the installations work properly and to protect machines and equipments. Technology, starting and speed control are mentioned briefly. Please refer to the relevant sections with detailed descriptions in this guide. Personal protection is not discussed in this section. For information on this, please refer to specific works on the topic. Details of this important aspect can be found in the Electrical installation guide published by Schneider Electric.
4.1
A Fig. 1
62
4.1
v Star-delta starting
This starting system (C Fig.2) can only be used with a motor where both ends of its three stator windings are fitted to a terminal board. Furthermore, the winding must be done so that the delta connection matches the mains voltage: e.g. a 380V 3-phase supply will need a motor with 380V delta and 660V star coiling. The principle is to start the motor by connecting the star windings at mains voltage, which divides the motors rated star voltage by 3 (in the example above, the mains voltage at 380V = 660V / 3). The starting current peak (SC) is divided by 3: - SC = 1.5 to 2.6 RC (RC rated Current). A 380V / 660V motor star-connected at its rated voltage of 660V absorbs a current 3 times less than a delta connection at 380V. With the star connection at 380V, the current is divided by 3 again, so by a total of 3. As the starting torque (ST) is proportional to the square of the supply voltage, it is also divided by 3: ST = 0.2 to 0.5 RT (RT Rated Torque) The motor speed stabilises when the motor and resistive torques balance out, usually at 75-85% of the rated speed. The windings are then deltaconnected and the motor recovers its own characteristics. The change from star connection to delta connection is controlled by a timer. The delta contactor closes 30 to 50 milliseconds after the star contactor opens, which prevents short-circuiting between phases as the two contactors cannot close simultaneously. The current through the windings is broken when the star contactor opens and is restored when the delta contactor closes. There is a brief but strong transient current peak during the shift to delta, due to the counterelectromotive force of the motor. Star-delta starting is suitable for machines with a low resistive torque or which start with no load (e.g. wood-cutting machines). Variants may be required to limit the transient phenomena above a certain power level. One of these is a 1-2 second delay in the shift from star to delta. Such a delay weakens the counter-electromotive force and hence the transient current peak. This can only be used if the machine has enough inertia to prevent too much speed reduction during the time delay. Another system is 3-step starting: star-delta + resistance-delta. There is still a break, but the resistor in series with the delta-connected windings for about three seconds lowers the transient current. This stops the current from breaking and so prevents the occurrence of transient phenomena. Use of these variants implies additional equipment, which may result in a significant rise in the cost of the installation.
A Fig. 2
Star-delta starting
63
4.1
A Fig. 3
A Fig. 4
64
4.1
v Autotransformer starting
The motor is powered at reduced voltage via an autotransformer which is bypassed when the starting process is completed (C Fig.5). The starting process is in three steps: - in the first place, the autotransformer is star-connected, then the motor is connected to the mains via part of the autotransformer windings. The process is run at a reduced voltage which depends on the transformation ratio. The autotransformer is usually tapped to select this ratio to find the most suitable voltage reduction value, - the star connection is opened before going onto full voltage. The fraction of coil connected to the mains then acts as an inductance in series with the motor. This operation takes place when the speed balances out at the end of the first step, - full voltage connection is made after the second step which usually only lasts a fraction of a second. The piece of autotransformer winding in series with the motor is short-circuited and the autotransformer is switched off. The current and the starting torque vary in the same proportions. They are divided by (mains V/reduced V2). The values obtained are: SC = 1.7 to 4 RC ST = 0.5 to 0.85 RT The starting process runs with no break in the current in the motor, so transient phenomena due to breaks do not occur. However, if a number of precautions are not taken, similar transient phenomena can appear on full voltage connection because the value of the inductance in series with the motor is high compared to the motors after the star arrangement is open. This leads to a steep drop in voltage which causes a high transient current peak on full voltage connection. To overcome this drawback, the magnetic circuit in the autotransformer has an air gap which helps to lower the inductance value. This value is calculated to prevent any voltage variation at the motor terminals when the star arrangement opens in the second step. The air gap causes an increase in the magnetising current in the autotransformer. This current increases the inrush current in the mains supply when the autotransformer is energised. This starting system is usually used in LV for motors powered at over 150kW. It does however make equipment rather expensive because of the high cost of the autotransformer.
A Fig. 5
Autotransformer starting
A Fig. 6
4.1
For example, for a starting torque equal to 2 RT, the current peak is about 2 RC. This peak is thus much lower and the maximum starting torque much higher than with a squirrel cage motor, where the typical values are about 6 RC for 1.5 RT when directly connected to the mains supply. The slip ring motor, with rotor starting, is the best choice for all cases where current peaks need to be low and for machines which start on full load. This kind of starting is extremely smooth, because it is easy to adjust the number and shape of the curves representing the successive steps to mechanical and electrical requirements (resistive torque, acceleration value, maximum current peak, etc.).
A Fig. 7
A Fig. 8
66
4.1
Direct on-line
Star-delta
Part windings
Resistors
Soft starter
Standard + 5 to 10 RC
Standard ++ 2 to 3 RC
6 windings ++ 2 RC
Standard +++ 4 to 5 RC
Voltage dip
High
Low
Low
Low
Low
Low
High
Moderate
Moderate
Moderate
Moderate
Low
High
High
Power factor
Low
Low
Moderate
Moderate
Low
Moderate
Low
High
Restricted
3-4 times more 3-4 times more than DOL than DOL
Limited
High
Available torque
Approx. 2.5 RT
0.2 to 0.5 RT
2 RT
RT
Approx. 0.5 RT
Approx. 2 RC
Approx. 0.5 RT
1.5 to 2 RT
Very high
High
Moderate
High
Moderate
Moderate
Moderate
Low
Trs lev
Moderate
Low
Low
Any
No-load
Any
Any
Yes*
No
Yes
Yes
* This starting system requires the motor to be specifically sized. A Fig. 9 Summary table
A Fig. 10
4.1
A 3-phase motor (230/400V) can be used with a 230V single-phase supply if it is fitted with a starting capacitor and an operating capacitor permanently connected. This operation lessens the working power (derating of about 0.7), the starting torque and the thermal reserve. Only low-powered 4-pole motors of no more than 4kW are suitable for this system. Manufacturers provide tables for selecting capacitors with the right values.
A Fig. 12 68
4.2
When braking, the current and torque peaks are noticeably higher than those produced by starting. To brake smoothly, a resistor is often placed in series with each stator phase when switching to countercurrent. This reduces the torque and current, as in stator starting. The drawbacks of countercurrent braking in squirrel cage motors are so great that this system is only used for some purposes with low-powered motors.
A Fig. 14
4.2
The movement of the rotor is a slip in relation to a field fixed in space (whereas the field spins in the opposite direction in the countercurrent system). The motor behaves like a synchronous generator discharging in the rotor. There are important differences in the characteristics obtained with a rectified current injection compared to a countercurrent system: - less energy is dissipated in the rotor resistors or the cage. It is only equivalent to the mechanical energy given off by masses in movement. The only power taken from the mains is for stator energising, - if the load is not a driving load, the motor does not start in the opposite direction, - if the load is a driving load, the system brakes constantly and holds the load at low speed. This is slackening braking rather than braking to a standstill. The characteristic is much more stable than in countercurrent. With slip ring motors, the speed-torque characteristics depend on the choice of resistors. With squirrel cage motors, the system makes it easy to adjust the braking torque by acting on the energising direct current. However, the braking torque will be low when the motor runs at high speed. To prevent superfluous overheating, there must be a device to cut off the current in the stator when braking is over.
b Electronic braking
Electronic braking is achieved simply with a speed controller fitted with a braking resistor. The asynchronous motor then acts as a generator and the mechanical energy is dissipated in the baking resistor without increasing losses in the motor. For more information, see the section on electronic speed control in the motor starter units chapter.
70
4.2
v Reversing
3-phase asynchronous motors (C Fig.16) are put into reverse by the simple expedient of crossing two windings to reverse the rotating field in the motor. The motor is usually put into reverse when at a standstill. Otherwise, reversing the phases will give countercurrent braking (see the paragraph on the Slip ring motor). The other braking systems described above can also be used. Single-phase motor reversing is another possibility if all the windings can be accessed.
b Types of duty
A Fig. 16 Principle of asynchronous motor reversing
For an electrical motor, number of starting and braking per unit of time have a large incidence on the internal temperature. The IEC standard : Rotating electrical machines - Part 1: Rating and performance (IEC 60034-1:2004) gives the service factors which allow to calculate the heat generated ad size correctly a motor according to the operation. The following information is an overview of these service factors. Additional information will be found in the relevant IEC standard and the manufacturers' catalogues.
71
4.2
Series of identical cycles, each with a period of operation and a pause. The starting current in this type of duty is such that it has no significant effect on heating.
A Fig. 19
Duty D3
A Fig. 20
Duty D4
A Fig. 21
Duty D5
72
4.2
A Fig. 22
Duty D6
A Fig. 23
Duty D7
A Fig. 24
Service D8
A Fig. 25
Duty D9
A Fig. 26
Duty D10
73
4.3
A Fig. 27
Tesys U
It ensures total coordination, meaning the device cannot fail to restart after a trip. Compared to a conventional solution, the number of references is divided by 10, savings in wiring are 60% and the space gain is 40%. The illustration (C Fig.27) shows Tesys U with some of its options. Like Integral, it offers the major functions of motor starter units, and in addition has advanced dialogue and switching functions which can be used for outstandingly economical new diagrams. Tesys U has a power base with disconnection, switching and protection functions. It is this base element which performs the following basic function.
b Forward operation
The diagram (C Fig.28) shows how the product is built inside. The power base includes all the components required for disconnection, protection against short circuits and overload and power switching. The power base is used to build the classic diagrams below with no additional components: - 3-wire control (C Fig.29), Pulse control with latch, - Or 2-wire control (C Fig.30), 2-position switch control.
A Fig. 28
A Fig. 29
3-wire control
A Fig. 30
2-wire control
74
4.3
A Fig. 31
A Fig. 32
A Fig. 33
75
4.4
Motors protection
Every electric motor has operating limits. Overshooting these limits will eventually destroy it and the systems it drives, the immediate effect being operating shutdown and losses. This type of receiver, which transforms electrical energy into mechanical energy, can be the seat of electrical or mechanical incidents. Electrical - power surges, voltage drops, unbalance and phase losses causing variations in the absorbed current, - short circuits where the current can reach levels that can destroy the receiver. Mechanical - rotor stalling, momentary or prolonged overloads increasing the current absorbed by the motor and dangerously heating its windings. The cost of these incidents can be high. It includes production loss, loss of raw materials, repair of the production equipment, non-quality production and delivery delays. The economic necessity for businesses to be more competitive implies reducing the costs of discontinuous output and nonquality. These incidents can also have a serious impact on the safety of people in direct or indirect contact with the motor. Protection is necessary to overcome these incidents, or at least mitigate their impact and prevent them from causing damage to equipment and disturbing the power supply. It isolates the equipment from the mains power by means of a breaking device which detects and measures electrical variations (voltage, current, etc.). Every starter motor unit should include - protection against short circuits, to detect and break abnormal currents usually 10 times greater than the rated current (RC) as fast as possible, - protection against overloads to detect current increase up to about 10 RC and open the power circuit before the motor heats up, damaging the insulation. These protections are ensured by special devices such as fuses, circuit breakers and overload relays or by integral devices with a range of protections.
Ground fault protection, which covers personal protection and fire safety, is not dealt with here because it is normally part of the electrical distribution in equipment, workshops or entire buildings.
76
4.5 4.6
These losses depend on use and working conditions (see the section on motor starting) and lead to motor heating. Faults due to the load or the power supply voltage or both are likely to cause dangerous overheating.
b Insulation categories
Most industrial machines come into the F insulation category. See the table (C Fig.36). Category F permits heating (measured by the resistance variation method) up to 105K and maximum temperatures at the hottest points of the machine are limited to 155C (ref IEC 85 and IEC 34-1). For specific conditions, in particular at high temperature and high humidity, category H is more suitable. Good quality machines are sized so that maximum heating is 80 in rated operating conditions (temperature of 40C, altitude less than 1000m, rated voltage and frequency and rated load). Derating applies when exceeding these values.
T max 125C 155C 180C
A Fig. 35
Losses in a AC motor
For a category F, this results in a heating reserve of 25K to cope with variations in the region of the rated operating conditions.
4.6
77
4.6
Windings are the motor parts most vulnerable to electrical faults and operating incidents
the motors operating conditions - overload states, - excessive number of starts or braking, - abnormal starting state, - too high a load inertia, - etc. the motors installation conditions - misalignment, - unbalance, - stress on shaft, - etc.
A Fig. 38
Protection against overload is thus mandatory to prevent overheating and reduce the risk of motor failure due to a break in winding insulation.
v Voltage surges
Any voltage input to plant with a peak value exceeding the limits defined by a standard or specification is a voltage surge (cf Cahiers Techniques Schneider-Electric 151 and 179). Temporary or permanent excess voltage (C Fig. 40) can have different origins: - atmospheric (lightning), - electrostatic discharge, - operation of receivers connected to the same power supply, - etc.
A Fig. 40 Example of a voltage surge
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4.6
Very short (1 10s) Very high (1000 kV/s) Very short (ns) Short (1ms) Long (>1s) High (10 MHz) Medium (1 to 200 kHz) Mains frequency
A Fig. 41
These disturbances, which come on top of mains voltage, can apply in two ways: - regular mode, between active conductors and the ground, - differential mode, between active conductors. In most cases, voltage surges result in dielectric breakdown of the motor windings which destroys the motor.
v Unbalanced phases
A 3-phase system is unbalanced when the three voltages are of unequal amplitude and/or are not phase-shifted by 120 in relation to each other. Unbalance (C Fig. 42) can be due to phase opening (dissymmetry fault), single-phase loads in the motors immediate vicinity or the source itself.
A Fig. 42 3 phase unbalanced voltages
Unbalance can be approximated by the following equation: Unbalance(%) = 100 x MAX where: Vmax is the highest voltage, Vmin is the lowest voltage, (V1 + V2 + V3) Vmoy = 3 The result of unbalance in the voltage power supply is an increase of current for the same torque, invert component, thereby overheating the motor (C Fig.43 ). The IEC 60034-26 standard has a derating chart for voltage unbalance (C Fig. 44) which should be applied when the phenomenon is detected or likely in the motor power supply. This derating factor is used to oversize a motor to take into account the unbalance or to lower the operating current of a motor in relation to its rated current.
Unbalance value (%) Stator current (A) Loss increase (%) Heating (%) A Fig. 43
0 In 0 100
2 1,01 x In 4 105
5 1,075 x In 25 128
A Fig. 44
79
4.6
A micro drop or brake is one that lasts about a millisecond. Voltage variations can be caused by random external phenomena (faults in the mains supply or an accidental short circuit) or phenomena related to the plant itself (connection of heavy loads such as big motors or transformers). They can have a radical effect on the motor itself. Effects on asynchronous motors When the voltage drops, the torque in an asynchronous motor (proportional to the square of the voltage) drops suddenly and causes a speed reduction which depends on the amplitude and duration of the drop, the inertia of rotating masses and the torque-speed characteristic of the driven load. If the torque developed by the motor drops below the resistant torque, the motor stops (stalls). After a break, voltage restoration causes a re-acceleration inrush current which can be close to the starting current. When the plant has a lot of motors, simultaneous re-acceleration can cause a voltage drop in the upstream power supply impedances. This prolongs the drop and can hamper re-acceleration (lengthy restarting with overheating) or prevent it (driving torque below the resistant torque). Rapidly repowering (~150ms) a slowing down asynchronous motor without taking precautions can lead to an phase opposition between the source and the residual voltage maintained by the asynchronous motor. In this event, the first peak in current can be three times the starting current (15 to 20 Rated Current) (cf. Cahier Technique Schneider Electric n161). These voltage surges and resulting drop can have a number of effects on a motor: - further heating and electrodynamic stress in the windings likely to break insulation, - inching with abnormal mechanical stress on couplings or premature wear or breakage. They can also affect other parts such as contactors (contact wear or welding), cause overall protection devices to cut in bringing the manufacturing chain or workshop to a standstill. Effects on synchronous motors The effects are more or less the same as for asynchronous motors, though synchronous motors can, due to their greater general inertia and the lower impact of voltage on the torque, sustain greater voltage drops (about 50% more) without stalling. When it stalls, the motor stops and the starting process must be run again, which can be complex and time consuming.
80
4.6
Effects on speed-controlled motors The problems caused by voltage drops in speed controllers are: - inability to supply enough voltage to the motor (loss of torque, slow down), - dysfunction of mains-powered control circuits, - possible overcurrent on voltage restoration due to the smoothing capacitors built into the drive, - overcurrent and unbalanced current in the mains supply when voltage drops on a single phase. Speed controllers usually fault when the voltage drop exceeds 15%.
v Harmonics
Harmonics can be harmful to AC motors. Non-linear loads connected to the mains supply causes a non sinusoidal currant and voltage distortion. This voltage can be broken down into a sum of sinusoids:
h total (h1+h5)
h1
h5
A Fig. 46
Harmonic distortion (C Fig. 46) is a form of pollution in the electricity network likely to cause problems at rates over 5%. Electronic power devices (speed controller, UPS, etc.) are the main sources that create harmonics into the power supply. As the motor is not perfect either, it can be the source of rank 3 harmonics. Harmonics in motors increase losses by eddy currents and cause further heating. They can also give rise to pulse torques (vibrations, mechanical fatigue) and noise pollution and restrict the use of motors on full load (cf. Cahiers Techniques Schneider-Electric n 199).
81
4.6
v Rotor locks
A Fig. 47
Starting time based on the ratio of starting current to rated current
Motor locks from mechanical causes lead to an overcurrent approximately the same as the starting current. But the heating that results is much greater because rotor losses stay at their maximum value throughout the lock and cooling stops as it is usually linked to rotor rotation. Rotor temperatures can raise to 350C.
b Summary
The summary in the table in figure 48 shows the possible causes of each type of fault, the probable effects and inevitable outcome if no protection is provided. In any event, motors always require two protections: - protection against short circuits, - protection against overload (overheating).
Causes
Effects Current surge Electrodynamic stress on conductors Dielectric breakdown in windings Decrease of the available torque Increased losses Decrease of the available torque Increased losses Decrease of the available torque Increased losses
Phase-to-phase, phase-to-ground , winding to winding Lightning Voltage surge Electrostatic discharge Disconnection of a load Unbalanced voltage Phase opening Single-phase load upstream of motor Instability in mains Voltage drop voltage and dip Connection of high loads Mains supply pollution Harmonics by non linear loads Starting too long
Effects on the motor Windings destroyed Windings destroyed by loss of insulation Overheating(*) Overheating(*)
Overheating(*)
Too high a resistant Increase in Overheating(*) torque starting time Voltage drop Locking Mechanical problem Overcurrent Overheating(*) Increase in resistant Higher current Overheating (*) Overload torque consumption Voltage drop (*) And in the short or long run, depending on the seriousness and/or frequency of the fault, the windings short-circuit and are destroyed.
A Fig.48
82
4.7
Protection functions
83
4.7
Protection functions
v Fuses
Fuses perform phase-by-phase (single pole) protection with a high break capacity at low volume. They limit I2t and electrodynamic stress (I ).
crte
Break and closing capacities for circuit breakers by the IEC 60947-2 standard
They are mounted: - on special supports called fuseholders, - or on isolators in the place of sockets and links (C Fig. 50). Note that trip indicator fuse cartridges can be wired to an all-pole switching device (usually the motor control contactor) to prevent singlephase operation when they melt. The fuses used for motor protection are specific in that they let through the overcurrents due to the magnetising current when motors are switched on. They are not suitable for protection against overload (unlike gG fuses) so an overload relay must be added to the motor power supply circuit. In general, their size should be just above the full load current of the motor.
A Fig. 50
These circuit breakers protect plant from short circuits within the limits of their breaking capacity and by means of magnetic triggers (one per phase) (C Fig. 51). Magnetic circuit breaking is all-pole from the outset: one magnetic trigger will simultaneously open all the poles. For low short-circuit currents, circuit breakers work faster than fuses. This protection complies with the IEC 60947-2 standard. To break a short-circuit current properly, there are three imperatives: - early detection of the faulty current, - rapid separation of the contacts, - breakage of the short-circuit current. Most magnetic circuit breakers for motor protection are current-limiting devices and so contribute to coordination (C Fig.52). Their very short cut-off time breaks the short-circuit current before it reaches its maximum amplitude.
A Fig. 51
This limits the thermal and electrodynamic effects and improves the protection of wiring and equipment.
A Fig. 52
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4.7
Protection functions
The values in the table above are for information only, as the derating of a motor depends on its size, insulation category, structure (self-cooling or fan-cooled, protection level IP 23, IP 44, etc.) and varies with the manufacturer. Note: The rated power value usually stamped on a motors plate is set by the manufacturer for continuous duty D1 (steady state operation long enough to reach thermal balance). There are other standard duties, such as temporary duty D2 and periodical intermittent duties D3, D4 and D5, for each of which the manufacturer sets a working power different from the rated power. A Fig. 53
Motor derating factors according to their operating conditions
Depending on the level of protection required, overload protection can be provided by relays: - overload, thermal (bimetal) or electronic relays, which provide minimum protection against: - overload, by controlling the current absorbed on each phase, - unbalanced or missing phase, by a differential device, - positive temperature coefficient (PTC) thermistor probe relays, - overtorque relays, - multifunction relays.
85
4.7
Protection functions
Reminder: A protection relay does not break a circuit. It is designed to open a breaking device with the requisite breaking capacity for the faulty current, usually a contactor. For this purpose, protection relays have a fault contact (NC) fitted in series with the contactor coil.
v Overload relays (thermal or electronic) Overview These relays protect motors against overload but must sustain the temporary overload of starting and only trip when starting lasts too long. Depending on its use, motor starting can range from a few seconds (no-load starting, low resistant torque, etc.) to a few dozen seconds (high resistant torque, high inertia of the driven load, etc.). Hence the necessity for relays adapted to the starting time. To meet this need, the IEC 60947-4-1 standard has several categories of overload relay each defined by its tripping time (C Fig.54).
Tripping time from: Cold Warm to 1.05 x Ir to 1.2 x Ir Classe 10 A 10 20 30(*) Warm to 1.5 x Ir Cold to 7.2 x Ir
Lower tolerance (band E)
2 s < tp < 10 s 4 s < tp < 10 s 5 s < tp < 10 s 6 s < tp < 20 s 10 s < tp < 20 s 9 s < tp < 30 s 20 s < tp < 30 s
(*) category little used in Europe but widespread in the USA. Cold : initial state with no previous load Warm : thermal balance reached at Ir Ir : overload relay current setting A Fig. 54
Main categories of overload relay tripping according to the IEC 60947-4-1 standard.
The relay size should be chosen on the basis of the motors rated current and the estimated starting time. Limits of use are characterised by curves (C Fig. 55) based on the time and value of the current setting (in multiples of Ir). These relays have a thermal memory (apart from some electronic ones, indicated by their manufacturers) and can be connected: - in series with the load, - or, for high powers, to current transformers fitted in series with the load. v Bimetal thermal overload relays (C Fig. 56 and 57) These are linked to a contactor to protect the motor, the power supply and the equipment against low prolonged overload. They are thus designed to enable the motor to start normally without tripping. However, they must be protected from strong over currents by a circuit breaker or fuses (see protection against short circuits).
A Fig. 55
A Fig. 56
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4.7
Protection functions
The operating principle of a thermal overload relay is based on the distortion of its bimetal strips heated by the current that crosses them. As the current crosses them, the strips distort and, depending on the setting, cause the relay contact to open suddenly.
A Fig. 57 Thermal relay diagram
The relay can only be reset when the bimetal strips have adequately cooled down. Thermal overload relays work with alternating and direct current and are usually: - 3-pole, - compensated, i.e. insensitive to ambient temperature variations (same tripping curve from 0C to 40C on a standard gauge (C Fig.58), - graduated in motor amperes: current indicated on the motor plate displayed on the relay. They can also respond to a loss of a phase: this is the differential. This feature prevents the motor from working in single-phase and complies with standards IEC 60947-4-1 and 60947-6-2 (C table Fig. 59).
Tripping time >2h >2h A Fig. 59 Multiple of current setting value 2 poles : 1.0 Ir 1 pole : 0.9 Ir 2 poles : 1.15 Ir 1 pole : 0
Widely used, this relay is very reliable and cost-effective. It is especially recommended if there is a risk of rotor locking. It does however have the disadvantages of imprecision with regard to the thermal status of the motor and sensitivity to the thermal conditions where it is installed (housing ventilation, etc.). v Electronic overload relays (C Fig. 60)
A Fig. 58
Operating limit of a differential thermal overload relay (responding to loss of a phase)
These relays have the advantages of electronic systems and build a more detailed thermal image of the motor. Using a template with the motors thermal time constants, the system continuously calculates the motor temperature based on the current crossing it and operating time. Protection is hence closer to the reality and can prevent inadvertent tripping. Electronic overload relays are less sensitive to the thermal conditions where they are installed. Apart from the usual functions of overload relays (protection against motor overload, unbalance and lack of phase) electronic overload relays can include options such as: - PTC probe temperature control, - protection against locking and overtorques, - protection against phase inversion, - protection against insulation faults, - protection against no-load operation, - etc.
A Fig. 60
87
4.7
Protection functions
v PTC thermistor probe relays These protection relays control the actual temperature of the motor to be protected. Probes are imbedded into the motor and because they are small, their thermal inertia is very low, ensuring a very short response time and hence a very accurate temperature reading. They directly control the temperature of the stator windings so can be used to protect motors against: overload, increase in ambient temperature, ventilation circuit faults, too frequent starting processes, inching, etc. They consist of: - one or more Positive Temperature Coefficient (PTC) thermistor probes in the windings themselves or at any other point likely to heat (bearings, etc.). These are static components with resistance that increases suddenly when the temperature reaches a threshold called the Nominal Operating Temperature (NOT) as shown by the curve (C Fig.61). An electronic device An electronic device powered by alternating and direct current for continuous control of the resistance of the probes linked to it. If the NOT is reached, the strong increase in resistance is detected by a threshold circuit which then orders a change in the status of the output contacts. Depending on the probes chosen, this protection mode can be used to: - set off an alarm without stopping the machine (NOT of the probes lower than the maximum temperature set for the element to be protected), - or order the machine to stop (the NOT has reached the maximum level) (C Fig.62). This protection system should be organised upfront because the probes have to be set in the windings when the motor is manufactured, though they can be included when new windings are fitted after an incident. The choice of PTC probes depends on the insulation category and motor structure. It is usually made by the motor manufacturer or winding fitter who are the only ones with the requisite skills. These two conditions mean that PTC probe protection really only applies to high-end equipment with expensive motors or processes.
A Fig. 61
An overtorque relay can be used to protect motors against overload when their starting process is long or very frequent (e.g. inching).
v Multifunction relays
Electromechanical or electronic relays Electromechanical or electronic relays protect the motor using the current flowing into the motor. The are perfectly suitable for regular operation. However, they are not able to take into consideration multiple potential problems due to voltage temperature or specific application. Furthermore users requirements as maintenance or production management has become a major concern and electrical manufacturers has introduced to the market new products which can be tailored to the application and offer a global protection for the motor and the driven load.
A Fig. 63
88
4.7
Protection functions
Features These relays has been developed using the following technologies: voltage and current sensors, the latters use ironless devices (Rogowsky sensors) which are fast and offer an outstanding linearity: - an electronic combining numerical and analogic technologies, the result being a good capacity for treatment and data storage, - use of field buses to exchange data to and from the PLCs and other devices, - use of accurate motor modelisation algorithms, - use of embedded programmes whose parameters can be defined. This new generation of product allow to reduce the costs from the design of the equipment, as PLCs programming are made simple, to the operation as maintenance cost and downtime are dramatically cut down. The following is a brief description of the possible solutions and a basic selection guide. Readers should consult Schneider Electric technical documentation which give more in depth information. The whole product line can be broken down in three families Solution 1: The multifunction relay is embed into the motor starter (CFig. 64). The benefit of this all in one solution is a very compact product with a limited number of connections. The upper limit is 32 Amps.
A Fig. 65
Multifunction relay is separated from the motor starter
A Fig. 64
Solution 2: the multifunction relay is separated from the motor starter and uses the same components as the all in one solution (CFig. 65). The benefit is a possible connection to any motor starter. Solution 3: the multifunction relay is segregated from the motor starter and offer multiple inputs / outputs. It is the most versatile solution. (CFig. 66) Protection relay selection guide Main functions are given in the table bellow (CFig. 67). More in depth information can be found in the manufacturer data sheets.
A Fig. 66
Multifunction relay with multiple I/O
89
4.7
Protection functions
Overtorque relay
Muntifunction relay
Built in the starter Type of control Current Protection classes Overcurrent Ground fault Phase imbalance Mechanical locking during / after starting No load operation Votage and power supply Voltage imbalance Phase loss Phase inversion Undervoltage Overvoltage Power an power factor Temperature PTC probes PT100 probes Numerical functions Truth table Timer Starting mode Direct on line Reversing Star delta Part winding - two speed motors Operation / maintenance Diagnostics Log Links / communication Local display Remote display (communication bus) Remote control (communication bus) A Fig. 67
Motor protection table
10 et 20 ++ +++
5 to 20 +++
5 to 20 +++
5 to 30 +++
++ + ++
++ ++ module
++ ++ module
module module
module module
+++ +++
3 I/O
10 I/O
10 to 20 I/O ++
+ module
+ module
+++ +++
90
4.7
Protection functions
A Fig. 68
The thermal elements (protection against overload) are compensated for fluctuations of the ambient temperature. The thermal protection threshold can be adjusted on the front of the unit. Its value must correspond to the rated current of the motor to be protected. In all these circuit breakers, coordination (type II) between the thermal elements and short-circuit protection is built into the device. Moreover, in the open position, the insulation distance (between contacts) in most of these units is adequate to ensure isolation. They also have a padlocking device.
v Tripping curves
A motor trip switch is characterised by its tripping curve, which represents the time it takes to trip based on the current (multiple of Ir). This curve is divided into four zones (C Fig. 69) : - lc normal operating zone . As long as I < Ir, there is no tripping, - thermal overload zone . Tripping is ensured by the thermal feature; the greater the overload, the less time it takes to trip. The standards refer to this as inverse time, - strong high current zone , monitored by the instant magnetic or short-circuit feature which works instantaneously (less than 5ms), - and on some circuit breakers (electronic), an intermediate zone monitored by a timed-delay magnetic feature with a delay function (0 to 300ms). The standards refer to this as definite time-lag. This prevents accidental tripping at switch-on with magnetising peak currents. Their limits are: Ir: setting current for protection against overload; should correspond to the rated current value (In) of the motor to be protected, Im: tripping current of timed magnetic protection, Iinst: tripping current of instant magnetic protection. This can range from 3 to 17 times Ir but is usually close to 10 Ir, Ics: service rated breaking capacity in short circuit, Icu: ultimate (maximum) breaking capacity in short circuit.
A Fig. 69
b Conclusion
Motor protection is an essential function for ensuring the continuity of machine operation. The choice of protection device must be made with extreme care. The user would be wise to select devices that include electronic communication features to foresee and prevent any faults. These greatly improve the detection of abnormalities and the speed with which service is restored.
91
5 - Dparts moteurs
5
92
chapter
Motor starter units
Presentation: Mandato functions to built a motor starter Selection table
Summary
1 2
5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11 5.12 5.13 5.14 5.15 Forward The basic functions of motor starter units An additional function: communication Motor starter units and coordination Speed controllers Structure and components of starters and electronic speed controllers Controller regulator for DC motors AC drives for asynchronous motors Voltage controller for asynchronous motors Synchronous motor-speed controller Stepper motor controllers Additional functions of speed controllers Speed controllers and energy assessment Speed controllers and savings in power and maintenance Choice table for motor starters
94
3 4 5 6 7
94
97
98
101
106
110
112
119
8 9 10 11 12 M
121
122
123
125
127
128
93
5.1 5.2
5.1
Forward
A motor starter unit has four basic functions: - isolating the load from mains, - protection against short-circuits, - protection against overload, - commutation or control (start - stop). Each motor starter unit can be enhanced with additional functions depending on its purpose. These can be: - power: speed controller, soft starter, phase reversal, etc, - checking: auxiliary contacts, time-delay, communication, etc. According to the structure of a motor starter unit, the functions can be distributed in different ways (C Fig. 1) shows the possible arrangements.
A Fig. 1
5.2
94
5.2
b Protection
v Protection against short-circuits
For this, it is necessary to detect the overcurrents following the short circuits (generally more than 10 times the rated current) and open the faulty circuit. It is filled with fuses or magnetic circuit breakers.
b Commutation or control
v The control function
The word control means closing (making) and opening (breaking) an electrical circuit on-load. The control function can be ensured by a load break switch or by motor starting device, soft starters or speed controllers. But a contactor is mostly used to carry out this function as it allows for remote control. With motors, this control device must allow for a large number of operations (electrical durability) and must comply with standards IEC 60947-4-1. These standards stipulate that, for this material, manufacturers must clarify the following points: Control circuit: - type of control current and its frequency, in the case of alternating current, - rated control circuit voltage (Uc) or supply voltage control (Us). Power circuit: - rated operational power (Ue): generally shown by voltage between phases. It determines the utilisation of the circuits which contribute to the making and breaking capacity, the type of service and the starting characteristics.
95
5.2
- rated operational current (Ie) or rated operational power: this characteristic is defined by the manufacturer based on the nominal operational conditions and especially taking into account the rated operational voltage and the conventional thermal current. In the case of equipment for direct control of one motor, the indication of the rated operational voltage can be replaced or completed by that of the assigned maximum available power. This information can, in some cases, be completed by: - the assigned service, mentioning the intermittent service class, if there is one. The classes define different operational cycles, - the powers assigned to making and/or breaking. These are maximum current values, set by the manufacturer, that device can adequately make (closing) or break (opening) in specific conditions. The assigned powers of making and breaking are not necessarily specified by the manufacturer but standards require the minimum value for each utilisation category.
Typical uses Non inductive or slightly inductive load, resistance furnace. Power distribution (lighting, generators, etc.). Brush motor: starting, breaking. Heavy duty equipment (hoisting, handling, crusher, rolling-mill train, etc.). Squirrel cage motor: starting, switching off running motors. Motor control (pumps, compressors, fans, machine-tools, conveyors, presses, etc.). Squirrel cage motor: starting, plugging, inching. Heavy-duty equipment (hoisting, handling, crusher, rolling-mill train, etc.). Non inductive or slightly inductive load, resistance furnace. Shunt wound motor: starting, reversing, counter-current breaking, inching. Dynamic breaking for direct current motors. Series wound motor: starting, reversing, counter-current breaking, inching. Dynamic breaking for direct current motors.
* Category AC-3 can be used for the inching or reversing, counter-current breaking for occasional operations of a limited length of time, such as for the assembly of a machine. The number of operations per limited length of time normally do not exceed five per minute and ten per 10 minutes.
A Fig. 3
Contactor utilisation categories based on the purposes they are designed for, according to IEC 60947-1
The following is also taken into consideration: - circuit making and breaking conditions, - type of load (squirrel cage motor, brush motor, resistor), - conditions in which making and breaking take place (motor running, motor stalled, starting process, counter-current breaking, etc.).
96
5.2 5.3
v Choosing a contactor
The utilisation categories defined in the standard allow for initial selection of a device that can meet the demands of the purpose the motor is designed for. However, there are certain constraints to take into consideration and which are not all defined by the standard. These are all the factors which have nothing to do with the purpose itself, such as climatic conditions (temperature, humidity), geographical setting (altitude, sault mist), etc. In certain situations, the reliability of the equipment can also be a critical factor, especially if maintenance is difficult. The electrical life (durability of contacts) of the device (contactor) therefore becomes an important feature. It is thus necessary to have detailed and accurate catalogues to ensure the product chosen complies with all these requirements.
5.3
A Fig. 4
97
5.4
5.4
A Fig. 5
This covers a wide power range. The combination calls for a compatibility study to choose the devices and an installation study to see if they should be panel mounted or enclosed. This work (compatibility, choice and installation) may not be straightforward for users as they must establish all the features of the devices and know how to compare them. This is why manufacturers first study and then offer the device combinations in their catalogues. Likewise, they try to find the most efficient combinations between protections. This is the notion of coordination.
A Fig. 6
98
5.4
A Fig. 7
99
5.4
Multifunction
A Fig. 8
b Selectivity
In an electric installation, the receivers are connected to mains by a series of breaking, protection and control devices. Without a well-designed selectivity study, an electrical defect can trig several protection devices. Therefore just one faulty load can cut off power to a greater or lesser part of the plant. This results in a further loss of power in fault-free feeders. To prevent this loss, in a power distribution system (C Fig. 9), the aim of selectivity is to disconnect the feeder or the defective load only from the mains, while keeping as much of the installation activated as possible. Selectivity therefore combines security and uptime and makes it easier to locate the fault. To guarantee a maximum uptime, it is necessary to use protection devices which are coordinated amongst themselves. For this, different techniques are used which provide total selectivity if it is guaranteed for all the fault current values up to the maximum value available in the installation or partial selectivity otherwise.
A Fig. 9
Selectivity between two circuit-breakers D1 and D2 fitted in a series and crossed by the same fault current ensures that only the D2 circuit-breaker placed downstream from D1 will open
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v Selectivity techniques
There are several types of selectivity: amperemetric, using a differential between the tripping thresholds of the circuit-breakers fitted in series; chronometric, with a delay of a few dozen or hundred milliseconds before the upstream circuit breaker trips, or using the normal operation characteristics linked to the device ratings. Selectivity will may therefore be ensured between two overload relays by respecting the condition Ir1 > 1,6. Ir2 (with r1 upstream of r2); Sellim ou energy , in the power distribution area, where a limiting upstream circuit-breaker opens for the time it takes for the downstream circuit-breaker to work and then closes; logic, by passing on from one circuit breaker to another the information of the threshold reached to allow the circuit-breaker the furthest downstream to open. For more information of selectivity, see the Schneider-Electric Cahier Technique n 167.
v Process selectivity
For process control equipment (manufacturing chain, chemical production units, etc.), the commonest selectivity techniques between the motor starter units and power distribution to the process are usually amperemetric or chronometric. In most cases, selectivity is ensured by a power limiter or ultra-limiter in the motor starter units.
5.5
Speed controllers
This section describes the details of all the aspects of speed controllers. Some very specific technologies such as cycloconverters, hyposynchronous cascade, current wave inverters for synchronous or asynchronous motors, to name but a few, will not be discussed.The use of these speed controllers is very specific and reserved to special markets.There are specialised works dedicated to them. Speed control for direct-current motors, though widely replaced by frequency changer speed control, is nonetheless described because the understanding of its operating principle smoothes the approach to certain special features and characteristics of speed control in general.
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Speed controllers
Historically, the first solution brought to the market was the electronic speed controller for direct-current motors. Progress in power semiconductors and microelectronics has led to the development of reliable and economical AC drives. Modern AC drives enable of the shelves asynchronous motors to operate at performances similar to the best DC speed controllers. Some manufacturers even offer asynchronous motors with electronic speed controllers incorporated in an adapted terminal box. This solution is available for low power assemblies (a few kW). Recent developments in electronic speed controllers are discussed at the end of this section, along with the trends seen by the manufacturers. These elegant developments considerably widen the offers and possibilities of controllers.
The precision of the regulator is generally expressed as a % of the rated value of the values to regulate. Controlled deceleration When a motor is slowing down, its deceleration is solely due to the machine load torque (natural deceleration). Starters and electronic speed controllers are used to control deceleration with a straight or S-shaped ramp, usually independent of the acceleration ramp.
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Speed controllers
This ramp can also be regulated for a delay time to change from steady state to intermediary or zero speed: - if the desired deceleration is faster than natural deceleration, the motor must develop a braking torque which is added to the machine load torque. This is often referred to as electronic braking and can be done either by sending the energy back to the mains network, or dissipation in a dynamic brake resistor, - if the desired deceleration is slower than natural deceleration, the motor must develop a load torque higher than the machine torque and continue to drive the load until it comes to a standstill. Reversing Reversing the supply voltage (direct-current motor controllers) or reversing the order of the motor powering phases is done automatically either by reversing the input settings, or by a logical order on a terminal, or by using information sent by a field bus. This function is standard on most of the current controllers for AC motors. Braking to a standstill This braking involves stopping a motor without actually controlling the deceleration ramp. For asynchronous motor starters and AC drives, this is done in an economical way by injecting direct current in the motor with a special operation of the power stage. All the mechanical energy is dispersed in the machines rotor, so braking can only be intermittent. On a direct current motor controller, this function can be fulfilled by connecting a resistor to the armature terminals. Built-in protections Modern controllers generally ensure thermal protection of the motors and their own protection. Using the current measure and information on the speed (if motor ventilation depends on the rotation speed), a microprocessor calculates the increase of the motor temperature and gives an alarm or trip signal in the event of excessive overheating. Controllers, especially AC drives, are also usually equipped with protection against: - short circuits between phase-to-phase and phase-to-ground; - voltage surges and drops; - phase unbalances; - single-phase operation.
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Speed controllers
Reversibility is achieved either by sending the power a running motor back to the mains (reversible input bridge) or by dissipating this power in a resistor with a braking chopper or, for low power, in machine losses. The figure 12 illustrates the four possible situations in the torque-speed diagram of a machine as summed up in the table below. One-direction controller This type of controller, is made for: - direct-current motors, with a DC converter or controlled rectifier (AC => DC) with a diode and thyristor mixed bridge (C Fig.12 I), - an AC motor with an indirect converter (with intermediate transformation in direct current) with a diode bridge at the input followed by a inverter which makes the machine work with the 1 quadrant (C Fig. 12 II). In certain cases this assembly can be used as two-direction controller (quadrants 1 and 3). An indirect converter with a braking chopper and a correctly sized resistor is perfectly suitable for momentary braking (in slowing down or on a hoisting appliance when the motor must develop a braking torque when going down to hold back the load). For prolonged use with a driving load, a reversible converter is essential as the charge is then negative, e.g., on a motor used as a brake on a test bench. Two-direction controller This type of controller can be a reversible or non-reversible converter. If it is reversible, the machine runs in all four quadrants (C Fig. 11) and can be used for permanent braking. If it is not reversible, the machine only runs in quadrants 1 and 3. The design and the size of the controller or the starter are directly affected by the nature of the driving load, especially with regard to its capacity to supply an adequate torque enabling the driven motor to gather speed. The families of machines and their typical curves are dealt with in section 4: Technology of loads and actuators.
A Fig. 11
II
Working diagrams (I) DC converter with mixed bridge; (II) indirect converter with (1) input diode bridge, (2) braking device (resistor and chopper), (3) frequency converter
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Speed controllers
Controlled rectifiers for direct-current motors This supplies direct current from an AC single-phase or 3-phase power supply. The semiconductors are arranged in a single-phase or 3-phase Gratz bridge (C Fig. 13). The bridge can be a combination of diodes/thyristors or thyristors only.
A Fig. 13 LDC bridge for a DC motor
The latter solution is the most frequent as it allows for a better form factor in the current drawn from the mains. A DC motor is most often of the wounded field type, except in low power where permanent magnet motors are quite common. This type of speed controller is well adapted to any purpose. The only limits are imposed by the DC motor, particularly the difficulty of reaching high speeds and the maintenance requirement (brush replacement). DC motors and their controllers were the first industrial solutions. In the last ten years, their use has steadily diminished as people are turning more to AC drives. Furthermore, the asynchronous motor is more robust and more cost-effective than a DC motor. Unlike DC motors, standardised in the IP55 envelope, it is hardly affected by the environment (rain, dust, dangerous atmospheres, etc.). AC drive for asynchronous motors This supplies AC 3-phase voltage with an RMS value and variable frequency (C Fig. 14). The mains power supply can be single-phase for low power (a few kW) and 3-phase for higher power. Some low power controllers take single- or 3-phase voltage indifferently. The output is always 3-phase as asynchronous single-phase motors are poorly adapted to frequency changer supply. AC drives power standard cage motors, with all the advantages linked to them: standardization, low cost, ruggedness, sealing and maintenance free. As these motors are selfventilated, their only limit is being used for a long period of time at a low speed because of a decrease in ventilation. If such an operation is required, a special motor equipped with an independent blower should be provided. Voltage controller to start asynchronous motors This type of controller (commonly known as a soft starter) is basically exclusively used to start motors. In the past, combined with special motors (resistant squirrel cage motors), it was used to control the speed of these motors. This device provides an alternating current from an AC power supply at a frequency equal to the mains frequency, and controls the RMS voltage by modifying the triggering of the power semiconductors. The most common arrangement has two thyristors mounted head to tail in each motor phase (C Fig. 15).
A Fig. 14
A Fig. 15
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v Control module
On modern starters and controllers, all the operations are controlled by a microprocessor which takes into account the settings, the commands transmitted by an operator or a processing unit and the feedbacks for the speed, current, etc. The calculation capacity of the microprocessors and dedicated circuits (ASIC) have led to the development of powerful command algorithms and, in particular, recognition of the parameters of the driven machine. With this information, the microprocessor manages the acceleration and deceleration ramps, controls the speed and limits the current and generates the command of the power components. Protection and security are dealt with by a special circuit (ASIC) or built into the power modules (IPM). The settings (speed limits, ramps, current limitation, etc.) are done either by a built-in keyboard or with PLCs via a field bus or with a PC to load the standard settings. Furthermore, commands (start, stop, brake, etc.) can be given through MMI dialogue, by the programmable PLCs or via a PC. The operational parameters and the alarm and defect information can be visualised by lights, by light emitting diodes, by a segment or liquid crystal display or sent to supervisors via field buses. Relays, which are often programmable, give information about: - defects (mains power, thermal, product, sequence, overload, etc.), - supervision (speed threshold, pre-alarm, end of starting). The voltage required for all the measurement and control circuits is supplied by a power supply built into the controller and separated electrically from the mains network.
The power module mainly consists of: - power components (diodes, thyristors, IGBT, etc.), - voltage and/or current measurement interfaces, - often a ventilation system. Power Components The power components are semiconductors and so comparable to static switches which can either be in a closed or off-state. These components, arranged in a power module, form a converter which powers an electric motor with a variable voltage and/or frequency from a fixed voltage and frequency network. The power components are the keystones of speed controllers and the progress made in recent years has led to the development of electronic speed controllers. Semiconductor materials, such as silicon, have a resistance capacity which may change between that of a conductor and that of an insulant.
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Their atoms have 4 peripheral electrons. Each atom combines with 4 neighbouring atoms to form a stable structure of 8 electrons. A P type semiconductor is obtained by incorporating into the silicon a small proportion of a body whose atoms have 3 peripheral electrons. Therefore, one electron is missing to form a structure with 8 electrons, which develops into an excess of positive loads. An N type semiconductor is obtained by incorporating a body whose atoms have 5 peripheral electrons. There is therefore an excess of electrons, i.e. an excess of negative loads. Diode (C Fig.17a) A diode is a non-controlled semiconductor with two regions P (anode) and N (cathode) and which only lets the current pass in one direction, from anode to cathode. Current flows when the anode has a more positive voltage than that of the cathode, and therefore acts like a closed switch. It blocks the current and acts like an open switch if the anode voltage becomes less positive than that of the cathode.
A Fig. 17 Power components
The diode had the main following characteristics: in a closed state: - a voltage drop composed of a threshold voltage and an internal resistance, - a maximum admissible permanent current (up to about 5000A RMS for the most powerful components). in an off-state: - a maximum admissible reverse voltage which may exceed 5000 V. Thyristor (C Fig.17b) This is a controlled semiconductor made up of four alternating layers: P-N-P-N. It acts like a diode by transmission of an electric pulse on an electrode control called gate. This closing (or ignition) is only possible if the anode has a more positive voltage than the cathode. The thyristor locks itself when the current crossing it cancels itself out. The ignition energy to supply on the gate is not linked to the current to switch over. And it is not necessary to maintain a current in the gate during thyristor conduction.
A Fig. 17b
The thyristor has the main following characteristics: in a closed state: - a votage drop composed of a threshold voltage and an internal resistance, - a maximum admissible permanent current (up to about 5000A RMS for the most powerful components). in an off-state: - an invert and direct maximum admissible voltage, (able to exceed 5000 V), - in general the direct and invert voltages are identical, - an recovery time which is the minimum time a positive anode cathode voltage cannot be applied to the component, otherwise it will spontaneously restart itself in the close state, - a gate current to ignite the component. There are some thyristors which are destined to operate at mains frequency, others called fast, able to operate with a few kilohertz, and with an auxiliary extinction circuit. Fast thyristors sometimes have dissymmetrical direct and invert locking voltage. In the usual arrangements, they are often linked to a connected antiparallel diode and the manufacturers of semiconductors use this feature to increase the direct voltage that the component can support in an off-state. Fast thyristor are now completely superseded by the GTO, power transistors and especially by the IBGT (Insulated Gate Bipolar Transistor).
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A Fig. 17c
The GTO thyristor (Gate Turn Off thyristor) (C Fig.17c) This is a variation of the rapid thyristor which is specific in that it can be locked by the gate. A positive current sent into the gate causes conduction of the semiconductor as long as the anode is at a more positive voltage than the cathode. To maintain the GTO conductor and the limit the drop of potential, the trigger current must be maintained. This current is generally very much less than is required to initialise conduction. Locking is done by inverting the polarity of the gate current. The GTO is used on very powerful converters as it is able to handle high voltages and currents (up to 5000V and 5000A). However, progress in the IGBT has caused their market share to drop. The GTO thyristor has the main following characteristics: in a closed state: - a voltage drop composed of a threshold voltage and an internal resistance, - a holding current designed to reduce the direct drop of potential, - a maximum admissible permanent current, - a blocking current to interrupt the main current in the device. in an off-state: - invert and direct maximum admissible voltages, often dissymmetrical, like with fast thyristors and for the same reasons, - an recovery time which is the minimum time during which the extinction current must be maintained, otherwise it will spontaneously restart itself, - a gate current to switch on the component. GTOs can operate with low kilohertz frequencies. Transistor (C Fig.17d) This is a controlled bipolar semiconductor made up of three alternating regions P-N-P or N-P-N. The current can only flow in one direction: from the emmiter to the collector in P-N-P technology and from the collector to the emmiter in N-P-N technology. Power transistors able to operate with industrial voltages are the N-P-N type, often Darlington assembled. The transistor can operate like an amplifier. The value of the current which crosses it therefore depends on the control current circulating in the base. But it can also operate like a static switch, i.e. open in the absence of a base current and closed when saturated. It is the latter operating mode which is used in controller power circuits. Bipolar transistors cover voltages up to 1200V and support currents up to 800A. This component is now supplanted by IGBT converters. In the operations which interest us, the bipolar transistor has the main following characteristics: in a closed state: - a voltage drop composed of a threshold voltage and an internal resistance, - a maximum admissible permanent current, - a current gain (to maintain the transistor saturated, the current injected in the base must be higher than the current in the component, divided by the gain). in an off-state: - a maximum admissible direct voltage. The power transistors used in speed controllers can operate on low kilohertz frequencies.
A Fig. 17d
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IGBT (C Fig.17e) This is a power transistor controlled by a voltage applied to an electrode called grid or gate and isolated from the power circuit, whence the name Insulated Gate Bipolar Transistor. This component needs very little energy to make strong currents circulate. Today it is the component used in discrete switch in most AC drives up to high powers (about a MW). Its voltage current characteristics are similar to those of bipolar transistors, but its performances in energy control and switching frequency are decidedly greater than any other semiconductor. IGBT characteristics progress very rapidly and high voltage (> 3 kV) and large current (several hundred amperes) components are currently available.
A Fig. 17e L
The IGBT transistor has the main following characteristics: voltage control: - allowing for conduction and locking of the component. in a closed state: - a voltage drop composed of a threshold voltage and an internal resistance, - a maximum admissible permanent current. in an off-state: - a maximum admissible direct voltage. IGBT transistors used in speed controllers can operate on frequencies of several dozen kilohertz. MOS transistor (C Fig.17f) This component operates in a completely different way from the previous one, altering the electric field in the semiconductor by polarising an isolated grid, hence the name Metal Oxide Semiconductor. Its use in speed controllers is limited to low voltage (speed controllers powered by battery) or low power, as the silicon surface required for a high locking voltage with a small voltage drop in a closed state is economically unfeasible. The MOS transistor has the main following characteristics: a voltage control : - allowing for the conduction and the locking of the component. in a closed state: - internal resistance, - a maximum admissible permanent current.
A Fig. 17f
in an off-state: - a maximum admissible direct voltage (able to go over 1000 V). The MOS transistors used in speed controllers can operate at frequencies of several hundred kilohertz. They are practically universal in switching power supply stages in the form of discrete components or as built-in circuits with the power (MOS) and the control and adjustment circuits.
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Structure and components of starters and electronic speed controllers Controller - regulator for DC motors
LIPM (Intelligent Power Module) It is not strictly speaking a semiconductor but an assembly of IGBT transistors. This module (C Fig.18) groups an inverter bridge with IGBT and low-level electronics to control the semiconductors. In the same compact package are: - 7 IGBT components, six for the converter bridge and one for braking resistor, - the IGBT control circuits, - 7 power diodes combined with IGBT to allow for circulating current, - protections against short circuits, overload and temperature overshooting, - electrical insulation of the module. The input diode rectifier bridge is mostly built into this module. The assembly allows for a better control of the IGBT wiring and control constraints.
A Fig. 18
5.7
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5.7
b Regulation
Regulation consists of exactly maintaining the speed at the imposed speed despite interference (variation of load torque, power voltage, temperature). However, during acceleration or in case of overload, the magnitude of the current must not reach a dangerous value for the motor or the power devices. A control loop built in the controller limits the current at an acceptable value. This limit can be accessed for adjustment according to the characteristics of the motor. The speed reference is set by an analogue or digital signal sent by a field bus or any other device which gives an information corresponding to the requisite speed. The reference can be set or vary during the operating cycle of the driven machine. Adjustable acceleration and deceleration ramps gradually apply the voltage reference corresponding to the requisite speed. The setting of the ramps defines the time for acceleration and deceleration. In a closed loop, the actual speed is permanently measured by a tachymetric dynamo or a pulse generator and compared to the reference. If a differential is noticed, the electronic control corrects the speed. The speed ranges from several revolutions per minute to the maximum speed. In this variation range, it is easy to achieve precision better than 1% in analogue regulation and better than 1/1000 in digital regulation, by combining all the possible variations (empty/load, voltage variation, temperature, etc). This regulation can also be done by measuring the motor voltage taking into account the current crossing it. In this case performance is clearly lower with regard to speed range and precision (a few % between run-free and load operation).
Each one of these bridges can invert the voltage and the current as well as the sign of energy circulating between the mains and the load.
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5.8
b Structure
Usually the power circuit consists of a rectifier converting the power supply to a DC voltage feeding an inverter which produces an alternative voltage at a variable frequency (C Fig. 20). To comply with the EU (European Union, CE label directive) and relevant standards, a network filter is placed upstream of the rectifier bridge.
A Fig. 20
v The rectifier
In general the rectifier is equipped with a diode rectifier bridge and a filter circuit composed of one or several capacitors depending on the power. A limitation circuit controls the value of the inrush current when the unit is connected to mains. Some converters use a thyristor bridge to limit the inrush current of these filter capacitors which are charged at a value virtually equal to the peak value of the sine wave network (about 560V in 400V 3-phase).
Note: despite the presence of discharge circuits, these capacitors are likely to continue having a dangerous voltage even if there is no mains voltage. Any intervention within such products should only therefore be made by trained people who know exactly what essential precautions to take (additional discharge circuit or knowledge of waiting time).
v The inverter
The inverter bridge, connected to the capacitors, uses six power semiconductors (usually IGBTs) and associated diodes. This type of controller is designed for powering asynchronous squirrel cage motors. Therefore Altivar, a Telemecanique brand, creates tiny electronic networks which have variable voltage and frequency capable of powering a single motor or several motors in parallel. It has: - a rectifier with a filter capacitor, - an inverter with 6 IGBTs and 6 diodes, - a chopper connected to a braking resistance (in general on the outside of the product), - IGBT transistor control circuits, - a control unit around a microprocessor, to ensures control of the inverter, - internal sensors to measure the motor current at the capacitor terminals and in certain cases the voltages at the rectifier bridge and the motor terminals as well as the values required to control and protect the entire motor controller, - a power supply for the low-level electronic circuits. This power supply is made by a switching circuit connected to the filter capacitor terminals to profit from the power reserve. This arrangement allows Altivar to be unaffected by mains fluctuations and short-term voltage disappearance, which gives it remarkable performance in power supply conditions with high interference.
b Speed variation
Generation of the output voltage is obtained by switching the rectified voltage with pulses where the time length, and therefore width, is modulated so that the resulting alternating current is as sine waved as possible (C Fig.21). This engineering, known under the name of PWM (Pulse Width Modulation) conditions regular rotation at low speed and limits overheating. The modulation frequency retained is a compromise as it must be high enough to reduce the current ripple and the acoustic noise in the motor without at all increasing losses in the inverter bridge and in the semiconductors. Two ramps set the acceleration and deceleration.
A Fig. 21
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b Built-in protections
The controller protects itself and the motor against excessive overheating by locking itself until the right temperature is restored. The same thing happens for any sort of interference or fault which could alter the overall functioning, such as over- or under-voltage, or the disappearance of an input or output phase. In certain ratings, the rectifier, inverter, chopper, control and protections against the short circuits are built into a single IPM model Intelligent Power Module .
b AC drive operation
Former AC drives made use a voltage frequency law, named constant U/F ratio or scalar operation. At that time it was the only economical choice. Introduction of microcontrollers opens the door to flux vector control and outstanding performances. Today, leading manufacturers offer in the same pacakge enhanced scalar operation allong with sensor and sensorless vector control operation.
v U/f operation
In this type of operation, the speed reference imposes a frequency on the inverter output and consequently, on the motor, which determines the rotation speed. The power voltage is in direct relationship to the frequency (CFig.13). This operation is often called a U/f operation or scalar operation. If no compensation is made, the real speed varies with the load, which limits the operating range. A crude compensation can be made taking the internal impedance of the motor into consideration to limit the speed variation.
A Fig. 22
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In most modern controllers, this device is factory built. Knowledge or estimation of the machine parameters permits one to dispense with a speed sensor for most uses. In this case a standard motor can be used with the usual limitation of prolonged operations at low speed. The controller processes the information from the values measured at the machine terminals (voltage and current). This control mode ensures correct performance without increasing the cost. To achieve such a result, certain machine parameters must be known. Upon commissioning, the machines debugger must in particular introduce the characteristics stamped on the motor in the settings for the controller such as: - rated motor voltage, - rated stator frequency, - rated stator current, - rated speed, - motor power factor. With these values, the controller calculates the rotor characteristics: Lm, Tr. (Lm: magnetising inductance, Tr: torque moment). On powering up, a controller with a flux vector control and no sensor (type ATV58F Telemecanique) self-tunes to enable it to determine the stator parameters Rs, Lf. The length of time varies according to the power of the motor (1 to 10 s). These values are memorised and enable the product to process the control profiles. The oscillogram (C Fig.23) shows a motor gathering speed, loaded with a rated torque and powered by a controller without a sensor. We can note the speed at which the rated load is reached (less than 0.2 s) and the linearity of acceleration. The rated speed is obtained in 0.8 seconds.
A Fig. 23
LCharacteristics of a motor fed by a sensorless flux vector controller (e.g. ATV58F Telemecanique)
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A Fig. 24
The maximum transient torque is equal to 2 or 3 times the rated torque depending on the motor type. Moreover, the maximum speed often reaches twice the rated speed, or more if the motor has enough power.
A Fig. 25 LOscillogram of the acceleration of a motor loaded with a rated torque and powered by a controller with a sensor flux vector control (e.g. ATV58F Telemecanique)
This type of control also allows for very high frequency bandwidths and performances comparable to or higher than the best DC controllers. This is why the motor is not of standard manufacturing owing to the presence of a sensor, or sometimes an external ventilation blower. The oscillogram (C Fig.25) shows the acceleration of a motor loaded with a rated torque and powered by a controller with a flux vector control with a sensor. The time scale is 0.1 seconds per division. Compared to the same product without a sensor, the performance increase is obvious. The rated torque is achieved in 80ms and the time for speed increase in the same load conditions is 0.5 seconds. To conclude, the table (C Fig.26) compares the respective performances of a controller in the three possible configurations.
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v Case 2: inversion of the order the semiconductors operate in preceded by deceleration with or without a ramp
If the load torque of the machine is such that natural deceleration is faster than the ramp set by the controller, it will continue to power the motor. The speed gradually decreases and reverses itself. But, if the load torque of the machine is such that natural deceleration is weaker than the ramp set by the controller, the motor acts like a hypersynchronous generator and restores the energy to the controller. But the presence of diode bridges prevents the energy being sent to the network, so the filter capacitors charge themselves, the voltage increases and the safety devices built in the controller locks itself. To avoid this, it is necessary to have a resistance connected to the capacitor terminals through a chopper so as to limit the voltage to a suitable value. The braking torque is only limited by the capacity of the speed controllers as the speed gradually decreases and reverses itself. For this use, the controller manufacturer supplies braking resistors sized to match the power of the motor and the energy to be dissipated. Since, in most cases, the chopper is included in the controller, only the presence of a dynamic braking resistor distinguishes a controller that can ensure controlled braking. This braking method is therefore particularly economical. It goes without saying that this operation mode can slow down a motor to a standstill without necessarily reversing the rotational direction.
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However prolonged operation at the rated torque at low speed is only possible if the motor is externally fan cooled, and this requires a special motor. Modern controllers have protection circuits which build a thermal image of the motor based on the current, operational cycles and rotation speed to ensure its protection.
A Fig. 27b
LTorque of an asynchronous motor powered by a frequency converter (b) constant power operation zone
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5
A Fig. 28 LAsynchronous soft starter and current shape A Fig. 29 LAvailable torque in an asynchronous motor powered by variable voltage and with a receiver with a parabolic resistant torque (fan) (a) squirrel cage motor (b) resistant cage motor
These asynchronous motors are mostly 3-phase, and sometimes singlephase for low powers (up to about 3kW). Most of the time used as for soft starting and decelerating, insofar as a high starting torque is not necessary, a voltage controller limits the inrush current, the subsequent drop of potential and mechanical shocks due to the sudden emergence of the torque. Its most common uses include starting of centrifugal pumps, belt conveyors, escalators, rollover carwash systems, machines equipped with belts, etc. and in speed controllers on very low power motors or on universal motors as in portable electric tools. But for certain uses, such as speed controllers in small fans, voltage controllers have pretty well given way to AC drives, which are cheaper to operate. In pumps, the deceleration function does away with water hammer. But certain precautions must be taken when choosing this device for speed controllers. When a motor slips, the losses are proportional to the resistant torque and inversely proportional to the speed. Therefore, the operating principle of a controller involves reducing the motor torque by reducing the voltage in order to balance the resistant torque at the requisite speed. The high resistance cage motor must therefore be able, at a low speed, to dissipate losses (small motors up to 3kW usually are). Beyond this, a fan cooled motor must be used. In slip ring motors, the resistors must be sized to match the operation cycles. The decision should be taken by a specialist who can select the right motor for the operation cycles. There are three types of starter on the market: controlled single-phase with low power, controlled 2-phase (the third being a direct connection) and with all phases controlled. The first two systems should only be used for operation cycles that are low-strain due to a higher rate of harmonics.
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b General principle
The power circuit has 2 thyristors mounted head-to-tail per phase (C Fig. 28). Voltage variation is obtained by varying the conduction time of these thyristors. The longer turn on is delayed, the lower the value of the resulting voltage. Thyristor control is managed by a microprocessor which also ensures the following functions: - ramp control to increase and decrease adjustable voltage. The deceleration ramp can only be followed if the natural deceleration time of the driven system is longer, - current limitation, - starting torque adjustment, - braking control by injection of direct current, - protection of the controller against overloads, - protection of the motor against overheating due to overloads or too frequent startings, - detection of phase unbalance or absence of a phase and thyristor faults. An instrument panel displaying operation parameters helps implementation, use and maintenance. Some controllers, such as Altistart (Telemecanique) can control the starting and deceleration of: - a single motor, - several motors together, within the limits of its rating, - several motors successively by commutation. This type of operation is common in pumping stations, as only one starter is used to bring to speed an additional pump according to the needs of the application network. In the steady state, each motor is powered directly by the mains supply through a contactor. Only Altistart has a patent allowing for estimation of a driving torque for linear acceleration and deceleration and, if necessary, to limit the driving torque.
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ESC ENT
stop reset
RUN
Motor-speed controller units are designed for specific markets such as robots or machine tools where smaller motors, acceleration and bandwidth are prerequisites.
b Motor
The motors rotor is fitted with permanent magnets in rare earth to produce a high field in a small space (see the section on motors for detailed explanations). The stator has 3-phase windings (C Fig.31). These motors support high overload currents for fast acceleration. They have a sensor to indicate the angular position of the motor poles to the controller to manage winding commutation (C Fig.32).
A Fig. 30 LPhoto of a synchronous motor-speed controller (Lexium controller + motor, Schneider Electric)
A Fig. 31
A Fig. 32
LSimplified representation of a permanent magnet synchronous stator motor - "brushless motor" with a sensor showing the angular position of the rotor
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5.10 5.11
b Controller
Basically, the controller is like an AC drive and works in a similar way. It also has a rectifier and a pulse width modulation (PWM) GTO bridge to produce an output current in a sine waveform. Several controllers of this type are often powered by a single source of direct current. Thus on a machine tool, each controller operates one of the motors linked to the machine axes. This type of installation enables the entire set to use the energy resulting from the braking of one of the axes. As in frequency changers, a braking resistor combined with a chopper is used to dissipate surplus braking energy. Electronic interlocking functions and low mechanical and electrical constants enable acceleration and, more generally, high bandwidths together with high speed dynamics.
5.11
b Motor
Stepper motors can be variable reluctance, magnetic or both (C see the section on motors for more detailed explanations).
b Controller
In structure, the controller is like a AC drive (rectifier, filter and bridge made up of power semiconductors). However, its performance is fundamentally different in that its purpose is to inject constant current into the windings.
A Fig. 33
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5.11 5.12
Sometimes it uses pulse width modulation (PWM) to enhance performance, especially in current access time (C Fig. 34), and widen the scope of its operating range. Operation (C Fig.35) in micro-steps (see the section on motors for more details) artificially multiplies the number of possible rotor positions by generating a succession of graduations in the coils in each sequence. The currents in the two coils behave like two alternating currents offset by 90.
A Fig. 34
A Fig. 35
LDiagram, current curves and graduation principle for micro-step control of a stepper motor-speed controller
The resulting field is the vectorial composition of the fields created by the 2 coils. The rotor therefore takes on all possible intermediary positions. The schema represents the supply current of coils B1 and B2. The rotor positions are represented by the vector.
5.12
123
5.12
b Built-in functions
To cover a good number of uses efficiently, the controllers have many adjustments and settings such as: - acceleration and deceleration ramp times, - ramp shapes (linear, S- or U-shaped), - ramp switching for two acceleration or deceleration ramps for, e.g. coasting speed, - decrease of maximum torque controlled by a discrete input or instruction, - jog operation, - management of brake control for hoisting, - choice of preselected speeds, - summing inputs to total speed references, - switching of references at the controller input, - PI regulator (e.g. speed or flow rate), - automatic stop following a loss of power supply allowing the motor to brake, - automatic catch on-the-fly restart function with search for motor speed, - thermal protection of the motor based on an image generated in the controller, - connection of PTC sensors built into the motor, - machine resonance frequency skipping (the critical speed is inhibited to prevent permanent operation at this frequency), - timed locking at low speed in pumping systems where the fluid helps to lubricate the pump and prevent it seizing up. On advanced controllers, these functions are already standard features as in Altivar (ATV71) Telemecanique.
b Optional cards
For more complex applications, manufacturers offer optional cards either for specific functions, such as a flux vector control with sensor, or for a specific industry. These cards include: - pump switching cards for a cost-effective pumping station with just one controller successively powering several motors, - multi-motor cards, - multi-parameter cards, to toggle the preset parameters in the controller automatically, - custom cards developed at the request of an individual. Some manufacturers also offer PLC cards built into in the controller for simple applications. The operator can use programming, input and output instructions for small automated systems where a full PLC would be too expensive.
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5.13
5.13
v Case 1: the circuit entry consists of semiconductors controlled by thyristors: e.g. a direct-current motor controller. The outphasing factor is obviously equal to the cosine of the triggering delay angle. In other words, if the output voltage is low (low speed), the cosine is low. If the output voltage is high (high speed) the cosine is close to one.
In a reversible speed controller, the cosine becomes negative if the controller restores energy to the mains.
b Power factor
v Reminder
The power factor is the ratio of the apparent power S and the active power P. Fp = P/S The active power P is the product of the fundament voltage multiplied by the fundament current and the cosine. P = U x I x cosine The apparent power S is equal to the product of the RMS value of the voltage multiplied by the RMS value of the current. If the voltage and the current are distorted, the quadratic sum of the RMS value of each item must be calculated. If mains impedance is low (which is generally the case), the voltage supply will be close to the sine wave, but the current absorbed by the semiconductors is rich in harmonics, and all the richer the lower mains impedance is. The RMS value of the current is shown in the following way: Ieff = (I1_ + I2_+ I3_+ In_) 0.5 And the apparent S power by: or more or less: S = Veff x Ieff S = V x Ieff
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5.13
A low P/S ratio signifies a mains supply overload due to the harmonics likely to overheat the conductor which must be designed accordingly.
v Case 1: the circuit entry consists of semiconductors controlled by thyristors: e.g. direct-current motor controller.
Current sampling is approximately square. The power factor is low at low output voltage and improves when the output voltage increases to reach a value of about 0.7.
A Fig. 36
v Converter losses
When considering the efficiency of a drive, one should take into account the losses in the drive (the converter) and losses into the driven motor. Semiconductors are the main source of energy losses in two ways: - conduction losses due to residual voltage of about one volt and the internal resistance, - losses by commutation linked to the switching frequency. Semiconductors with rapid switching times have the smallest commutation losses; this is the case with IGBTs, which enable high switching frequencies. Due to this, the converters have excellent efficiency exceeding 90%.
v Motor losses
A Fig. 37 LPWM operation
Motors with converters suffer additional losses due to switching of the working voltage. However, as the switching frequency is high, the current absorbed is nearly sinusoidal and additional losses may be considered insignificant (C Fig.38).
A Fig. 38
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5.14
5.14
b Load types
Ac drices are best for pump and fan output control. A detailed explanation is given in section 4. Compared to discrete systems or control systems requiring valves, flaps or shutters, speed controllers ensure substantial power savings. These savings can only be assessed with perfect knowledge of the application; manufacturers experts have this knowledge to guide users in their choice.
b Reduced maintenance
AC drives and electronic soft starters (see the section on starting motors) eliminate the mechanical stress on the machine so it can be directly optimised at the design stage. For multi-motor control (e.g. a pumping station), adequate monitoring of the motors regulates the operating hours of each and increases the uptime and sustainability of the plant.
b Conclusion
The choice of a starter or speed controller being contingent on the type of load driven, the performance demanded and the protections required, the definition and choice must be based on an analysis of functional requirements for the equipment then the performance required for the motor itself. Other widely-mentioned features in the documentation of speed controller suppliers are constant torque, variable torque, constant horsepower, flux vector control, reversible speed controller, etc. These terms describe all the data required to choose the most suitable type of controller. It is advisable to ask for detailed advice from manufacturers experts who can help choose the speed controller with the best performance/price ratio. The wrong choice of controller can lead to disappointing operating results.
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5.15
5.15
Product
Fonction
Disconnect
Breaking capacity
Overload
Additional functions Commutation (DOL, star delta) Soft start Variable speed drive
128
129
6
130
chapter chapitre
Data acquisition: Acquisition de detection donnes : dtection
Presentation: Prsentation : Fonctions features and technologies Detection et des technologies de dtection Tableau de choix Selection table
Summary
1 2
6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 Introduction Electromechanical limit switches Inductive proximity detectors Capacitive proximity detectors Photoelectric detectors Ultrasonic detectors RFID -Radio Frequency IDentification-detection Vision Optical encoders Pressure switches and vacuum switches Conclusion Technology selection guide
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3 4 5 6 7
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8 9 10 11 12 M
154
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6.1
Introduction
A Fig. 1
Sensors functions
The field of data capture is divided into two families.The first, called detection, comprises products that can detect a threshold or limit or estimate a physical measurement.The second measurement or instrumentation measures a physical measurement to a given level of accuracy. In this section, we shall only describe sensors and detection devices for machines and their related automation systems. Sensors designed for machine safety are dealt with in appropriate section. For those who are interested, there are many works on machine safety describing all the devices available on the market. These products have three essential functions as shown in the figure 1. The diversity of these functions requires manufacturers to produce a great number of product variants to cover all the requirements. Recent innovations in product modulation enable Schneider Electric to offer smaller ranges with more versatile applications.
6.1
Introduction
b Detection: an essential function
The detection function is essential because it is the first link in the data chain (C Fig. 2) of an industrial process. In an automatic system, detectors ensure that data is captured: - on all the events needed for operation that are used by the control systems according to a preset program; - on the progress of all the process phases when the program is running.
b Detection functions
A Fig. 2
The basic ones are: - controlling the presence, absence or position of an object, - checking the movement, flow or obstruction of objects, - counting. These are usually dealt with by discrete devices, as in typical parts detection applications in manufacturing chains or handling operations and in the detection of persons or vehicles. There are other more specific needs such as detection of: - presence (or level) of a gas or fluid, - shape, - position (angular, linear, etc.), - a label, with reading and writing of encoded data. There are many additional requirements, especially with regard to the environment, where, depending on their situation, detectors must be able to resist: - humidity or submersion (e.g.: higher water-tightness), - corrosion (chemical industries or agricultural installations, etc.), - wide temperature variations (e.g. tropical regions), - soiling of any kind (in the open air or in the machines), - and even vandalism, etc. To meet all these requirements, manufacturers have developed all kinds of detectors using different technologies.
b Detector technologies
Detector manufacturers use a range of physical measurements, the main ones being: - mechanical (pressure, force) for electromechanical limit switches, - electromagnetic (field, force) for magnetic sensors, inductive proximity detectors,
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6.1 6.2
light (light power or deflection) for photoelectric cells, capacitance for capacitive proximity detectors, acoustic (wave travel time) for ultrasound detectors, fluid (pressure) for pressure switches, optic (image analysis) for viewing.
These systems have advantages and limits for each type of sensor: some are robust but need to be in contact with the part to detect, others can work in hostile environments but only with metal parts. The description of the technologies used, outlined in the following sections, is designed to help understand what must be done to install and use the sensors available on the market of industrial automation systems and equipment.
6.2
b Detector movements
A probe or control device can have different kinds of movement (C Fig. 3) so it can detect in many different positions and easily adapt to the objects to detect: - rectilinear, - angular, - multi-directional.
A Fig. 3 Illustration of movements in commonlyused sensors
Use for safety purposes requires devices with positive opening operation.
133
6.2 6.3
6.3
b Principle
The sensitive component is an inductive circuit (L inductance coil). This circuit is linked to a C capacitor to form a circuit resonating at frequency Fo usually ranging from 100kHz to 1MHz. An electronic circuit maintains the oscillations of the system based on the formula below:
These oscillations create an alternating magnetic field in front of the coil. A metal shield set in the field is the seat of eddy currents which induce an extra load and alter the oscillation conditions (C Fig.6). The presence of a metal object in front of the detector lowers the quality factor of the resonant circuit. Case 1, no metal shield: Reminder:
Detection is done by measuring variation in the quality factor (approx. 3% to 20% of the detection threshold). The approach of the metal shield causes the quality factor to drop and thereby a drop in the oscillation range.
A Fig. 6 Operating principle of an inductive detector
134
6.3
l l l l l l l l
Shaping stage: this consists of a peak detector monitored by a twothreshold comparator (Trigger) to prevent untimely switching when the object to detect nears the rated range. It creates what is known as detector hysteresis (C Fig.7bis). Power input and output stages: this powers the detector over wide voltage ranges (10VDC to 264VAC). The output stage controls loads of 0.2A in DC to 0.5A in AC, with or without short-circuit protection.
b Specific functions
Detectors protected against magnetic fields generated by welding machines.
A Fig. 7bis Detector hysteresis
Detectors with analogue output. Detectors with a correction factor of 1* where the detection distance is independent of the ferrous or non-ferrous metal detected. Detectors to select ferrous and non-ferrous metals. Detectors to control rotation: these under-speed detectors react to the frequency of metal objects. Detectors for explosive atmospheres (NAMUR standards).
*When the object to detect is not made of steel, the detection distance of the detector should be proportional to the correction factor of the substance the object is made of. DMat X = DSteel x KMat X Typical correction factor values (KMat X) are: - Steel = 1 - Stainless steel = 0.7 - Brass = 0.4 - Aluminium = 0.3 - Copper = 0.2 Example: DStainless = DSteel x 0.7
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6.4
b Principle
The sensitive surface of the detector constitutes the armature of a capacitor. A sinusoidal voltage is applied to this surface to create an alternating electric field in front of the detector. Given that this voltage is factored in relation to a reference potential (such as an earth), a second armature is constituted by an electrode linked to the reference potential (such as a machine housing). The electrodes facing each other constitute a capacitor with a capacity of:
A Fig. 8 No object between electrodes
where 0 = 8,854187.10-12 F/m permittivity of vacuum and r relative permittivity of substance between the 2 electrodes. Case 1: No object between electrodes (C Fig.8)
Case 2: Isolating substance between electrodes (C Fig.9) => (r = 4) In this case, the earth electrode could be, e.g. the metal belt of a conveyor.
A Fig. 9 Presence of an isolating object between electrodes
When mean r exceeds 1 in the presence of an object, C increases. Measurement of the increase in the value of C is used to detect the presence of the isolating object. Case 3: Presence of a conductive object between electrodes (C Fig.10)
where r 1 (air) => The presence of a metal object also causes the value of C to increase.
These work directly on the principle described above. A path to an earth (reference potential) is required for detection. They are used to detect conductive substances (metal, water) at great distances. Typical application: Detection of conductive substances through an isolating substance (C Fig.11).
A Fig. 11
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6.4
A Fig. 12
v Detection distance
This is related to the dielectric constant or relative permittivity of the objects substance. To detect a wide variety of substances, capacitive sensors usually have a potentiometer to adjust their sensitivity.
Substance Acetone Air Ammonia Ethanol Flour Glass Glycerine Mica Paper Nylon Petroleum Silicone varnish Polypropylene Porcelain Dried milk Salt Sugar Water Dry wood Green wood A Fig. 13
r
19.5 1.000264 15-25 24 2.5-3 3.7-10 47 5.7-6.7 1.6-2.6 4-5 2.0-2.2 2.8-3.3 2.0-2.2 5-7 3.5-4 6 3.0 80 2-6 10-30
v Substances
The table (C Fig.13) gives the dielectric constants of a number of substances.
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6.5
Photoelectric detectors
These work on a principle suiting them to the detection of all types of object, be they opaque, reflective or virtually transparent. They are also used for human detection (door or safety barrier opening).
b Principle (C Fig.14)
A light-emitting diode (LED) emits luminous pulses, usually in the close infrared spectrum (850 to 950nm).
A Fig. 14 Principle of a photoelectric detector
The light is received or otherwise by a photodiode or phototransistor according to whether the object to detect is present or not. The photoelectric current created is amplified and compared to a reference threshold to give discrete information.
b Detection system
v Through-beam (C Fig.14bis)
The emitter and receiver are in separate housings.
A Fig. 14bis Through-beam detection
The emitter, a LED in the cell of a converging lens, creates a parallel light beam. The receiver, a photodiode (or phototransistor) in the cell of a converging lens, supplies a current proportional to the energy received. The system issues discrete information depending on the presence or absence of an object in the beam. Advantage: The detection distance (range) can be long (up to 50m or more); it depends on the lens and hence detector size. Disadvantages: 2 separate housings and therefore 2 separate power supplies. Alignment for detection distances exceeding 10m can be problematic.
v Reflex systems
A Fig. 15 Principle of photoelectric reflex detection
There are two so-called Reflex systems: standard and polarised. Standard reflex (C Fig.15) The light beam is usually in the close infrared spectrum (850 to 950nm). Advantages: the emitter and receiver are in the same housing (a single power supply). The detection distance (range) is still long, though less than the through-beam (up to 20m). Disadvantage: a reflective object (window, car body, etc.) may be interpreted as a reflector and not detected. Polarised reflex (C Fig.16) The light beam used is usually in the red range (660 nm). The emitted radiation is vertically polarised by a linear polarising filter. The reflector changes the state of light polarisation, so part of the radiation returned has a horizontal component. The receiving linear polarising filter lets this component through and the light reaches the receiver. Unlike the reflector, a reflective object (mirror, sheet metal, glazing) does not alter the state of polarisation so the light it reflects cannot reach the receiving polariser (C Fig.17). Advantage: this type of detector overcomes the drawback of the standard reflex. Disadvantages: this detector is more expensive and its detection distances are shorter: IR reflex -->15m Polarised reflex ---> 8m
A Fig. 16
A Fig. 17
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6.5
Photoelectric detectors
Direct reflection with background suppression (C Fig.19) This detection system uses triangulation. The detection distance (up to 2m) does not depend on the reflectivity of the object but on its position, so a light object is detected at the same distance as a dark one and a background beyond the detection range will be ignored.
v Optic fibres
Principle The principle of light wave propagation in fibre optics is based on total internal reflection. Internal reflection is total when a light ray passes from one medium to another with a lower refractive index. The light is reflected in totality (C Fig. 20) with no loss when the angle of incidence of the light ray is greater than the critical angle [c]. Total internal reflection is governed by two factors: the refraction index of each medium and the critical angle. These factors are related by the following equation:
A Fig. 19
If we know the refractive indexes of the two interface substances, the critical angle is easy to calculate. Physics defines the refractive index of a substance as the ratio of the speed of light in a vacuum (c) to its speed in the substance (v).
A Fig. 20
The index of air is considered as equal to that of a vacuum 1, since the speed of light in air is almost equal to that in a vacuum. There are two types of optic fibres: multimode and single-mode. There are two types of optic fibres: multimode and single-mode (C Fig.21) - Multimode These are fibres where the diameter of the core, which conducts light, is large compared to the wavelength used ( 9 to 125 m, Lo = 0.5 to 1 mm). Two types of propagation are used in these fibres: step index and graded index. - Single-mode By contrast, these fibres have a very small diameter in comparison to the wavelength used ( <= 1 m, Lo = usualy 1.5 m). They use step-index propagation. They are mostly used for telecommunication. This explanation illustrates the care that has to be taken with these fibres when, for example, they are pulled (reduced tensile strength and moderate radii of curvature, according to manufacturers specifications). Multimode optical fibres are the most widely used in industry, as they have the advantage of being electromagnetically robust (ECM ElectroMagnetic Compatibility) and easy to implement.
A Fig. 21
139
6.5 6.6
Detector technology The optic fibres are positioned in front of the emitting LED and in front of the receiving photodiode or phototransistor (C Fig.22). This arrangement is used to: - position electronic components away from the monitoring point, - operate in confined areas or at high temperature, - detect very small objects (of around 1mm), - depending on the configuration of the fibre ends, operate in throughbeam or proximity mode,
A Fig. 22 Principle of an optic fibre detector
Note that extreme care must be taken with the connections between the emitting LED or receiving phototransistor and the optic fibre to minimise light signal losses.
6.6
Ultrasonic detectors
b Principle
Ultrasonic waves are produced electrically with an electroacoustic transducer (piezoelectric effect) supplied with electrical energy which it converted into mechanical vibrations by piezoelectricity or magnetostriction phenomena (C Fig. 23). The principle involves measuring the time it takes for the acoustic wave to propagate between the sensor and the target.
A Fig. 23
The speed of propagation is 340m/s in air at 20C, e.g. for 1m the measuring time is about 3ms. This time is measured by the counter built in a microcontroller. The advantage of ultrasonic sensors is that they can work over long distances (up to 10m) and, above all, detect any object which reflects sound, regardless of its shape or colour.
b Application (C Fig.24)
Excited by the high-voltage generator, the transducer (emitter-receiver), generates a pulsed ultrasonic wave (100 to 500kHz, depending on the product) which travels through the ambient air at the speed of sound. As soon as the wave meets an object, a reflected wave (echo) returns to the transducer. A microprocessor analyses the incoming signal and measures the time interval between the emitted signal and the echo. By comparing it with preset or ascertained times, it determines and monitors the status of the outputs. If we know the speed at which sound is propagated, we can calculate a distance using the following formula: D = T.Vs/2 where D: distance between detector and object, T: time elapsed between mission and reception of the wave, Ss: speed of sound (300m /s). The output stage monitors a static switch (PNP or NPN transistor) corresponding to an opening or closing contact, or provides an analogue signal (current or voltage) directly or inversely proportional to the measured distance of the object.
A Fig. 24
140
6.6
Ultrasonic detectors
A Fig. 25
Through-beam mode: the through-beam system consists of two separate products, an ultrasonic emitter and a receiver, set opposite each other.
141
6.7
b Overview
Radio Frequency IDentification (RFID) is a fairly recent automatic identification technology designed for applications requiring the tracking of objects or persons (traceability, access control, sorting, storage). It works on the principle of linking each object to a remotely accessible read/write storage capacity. The data are stored in a memory accessed via a simple radio frequency link requiring no contact or field of vision, at a distance ranging from a few cm to several metres. This memory takes the form of an electronic tag, otherwise known as a transponder (TRANSmitter + resPONDER), containing an electronic circuit and an antenna.
A Fig. 27 Layout of a RFID system
b Operating principles
A RFID system consists of the following components (C Fig.27 and 28): - An electronic tag, - A read/write station (or RFID reader).
v The reader
Modulates the amplitude of the field radiated by its antenna to transmit read or write commands to the tag processing logic. Simultaneously, the electromagnetic field generated by its antenna powers the electronic circuit in the tag.
v Tag
This feeds back its information to the reader antenna by modulating its own consumption. The reader reception circuit detects the modulation and converts it into digital signals (C Fig.29).
A Fig. 28 View of components in a RFID system (Telemecanique Inductel system)
b Description of components
v Electronic tags
Electronic tags consist of three main components inside a casing. Antenna (C Fig.30): This must be adjusted to the frequency of the carrier and so can take several forms: - coil of copper wire, with or without a ferrite core (channelling of field lines), or etched on a flexible or rigid printed circuit, or printed (with conductive ink) for frequencies of less than 20MHz; - dipole etched onto a printed circuit, or printed (with conductive ink) for very high frequencies (>800MHz).
A Fig. 29
A Fig. 30
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6.7
Logical processing circuit This acts as an interface between the commands received by the antenna and the memory. Its complexity depends on the application and can range from simple shaping to the use of a microcontroller (e.g. payment cards secured by encryption algorithms). Memory Several types of memory are used to store data in electronic tags (C Fig.31). Type
ROM
Advantages
Good resistance to high temperatures Inexpensive
Disadvantages
Read only
EEPROM
Fairly long read/write access time Number of write operations limited to 100,000 cycles per byte
RAM
FeRAM (ferroelectric)
A Fig. 31
6
a b Active tags contain a battery to power their electronic components. This configuration increases the dialogue distance between the tag and the antenna but requires regular replacement of the battery.
v Casing
Casings have been designed for each type of application to group and protect the three active components of a tag: (C Fig.32a) - credit card in badge format to control human access, - adhesive support for identification of library books, - glass tube, for identification of pets (injected under the skin with a syringe), - plastic buttons, for identification of clothing and laundry, - label for mail tracking. There are many other formats, including: key ring, plastic nails to identify wooden pallets, shockproof and chemical-resistant casings for industrial applications (surface treatment, furnaces, etc.) (C Fig.32b).
A Fig. 32 a et b
a - RFID formats designed for different uses b - RFID industrial (Telemecanique Inductel)
v Stations
A station (C Fig.33a) acts as an interface between the control system (PLC, computer, etc.) and the electronic tag via an appropriate communication port (RS232, RS485, Ethernet, etc.). It can also include a number of auxiliary functions suited to the particular application: - discrete inputs/outputs, - local processing for standalone operation, - control of several antennas, - detection with built-in antenna for a compact system (C Fig.33b).
A Fig. 33a
A Fig. 33b
6.7
v Antennas
Antennas are characterised by their size (which determines the shape of the zone where they can exchange information with the tags) and the frequency of the radiated field. Ferrite cores are used to concentrate the electromagnetic field lines to increase the reading distance (C Fig.34) and reduce the influence of any metal bodies in the vicinity of the antenna. The frequencies used by the antennas cover several distinct bands, all of which have advantages and disadvantages (C Fig.35).
A Fig. 34 Influence of a ferrite antenna on electromagnetic field lines
Frequency
125-134 khz (LF) 13.56 Mhz (HF)
Advantages
Immune to the environment (metal, water, etc.) Standard antenna/tag dialogue protocols (ISO 15693 ISO 14443 A/B)
Disadvantages
Small storage capacity Long access time Sensitive to metallic environments
Typical applications
Identification of pets Library book tracking Access control Payment systems
Very low-cost tags Frequency ranges differ Product control in retailing Long dialogue range (several metres) with the country Interference in dialogue zones caused by obstacles (metal, water, etc.) Very high speed of transfer between tag and antenna Long dialogue range (several metres) Dips that are hard to control in the dialogue zone Cost of reading systems Vehicle tracking (motorway tollgates)
A Fig. 35
Power ratings and frequencies used vary with the applications and countries. There are three major zones: North America, Europe and Rest of World. Each zone and each frequency has an authorised emission spectrum range (CISPR standard 300330) within which every RFID station/antenna must operate.
b Advantages of RFID
Compared to barcode systems (labels or marks and readers), RFID has the following advantages: - data in the tag can be modified, - read/write access through most non-metallic materials, - insensitive to dust, soiling, etc., - several thousand characters can be recorded in a tag, - data confidentiality (tag data access lock). These advantages all contribute to its development in the service sector (e.g. ski run access control) and retailing. Furthermore, the ongoing fall in the cost of RFID tags will probably result in their replacing conventional barcodes on containers (boxes, parcels, baggage) in logistics and transport and also on products in the industrial manufacturing process. It should be noted however that the appealing idea of using these systems for automatic identification of trolley contents without having to unload them at supermarket checkouts is not yet feasible for physical and technical reasons.
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6.8
Vision
b Principle
The eye of a machine which gives sight to an automation system. A camera takes a photo of an object and digitises its physical characteristics to provide information on (C Fig.36): - its dimensions, - its position, - its appearance (surface finish, colour, brightness, any defect), - its markings (logos, characters, etc.). The user can also automate complex functions such as: - measurement, - guidance, - identification.
A Fig. 36 Inspection of a mechanical component. The arrows indicate the zones checked by the system
v Lighting systems
Lighting technologies - LED (Light-Emitting Diode) Now the most widely-used system: it provides uniform lighting and has a very long lifetime (30,000 hours). It is available in colour, but then only covers a field of about 50cm. - High-frequency fluorescent tube This gives off a white light and has a long lifetime (5000 hours). The area illuminated (field) is large, though this obviously depends on the power used. - Halogen This also gives off a white light. It has a short lifetime (500 hours) but a very high lighting power so can cover a large field.
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6.8
Vision
These lighting technologies can be used in different ways. Five main systems (C Fig.37) are used to highlight the features to check: Systems
Ring light LEDs arranged in a ring Very powerful lighting system: Lights an object in its axis from above Precision, inspection such as markings
ring light, back lighting, direct front light, dark field, coaxial. Applications type
Characteristics
Back lighting Lighting behind an object and facing the camera Highlights the contours of an object (shadowgraph) Measuring the dimensions of an object or analysing opaque items
Direct front lighting Highlights a detail of an object to check and creates a heavy shadow Finding specific defects, checking screw threads, etc.
Dark field Detects the edges of an object Checks markings Detects flaws on glass or metal surfaces Checking printed characters, surface finish, detecting scratches, etc.
Coaxial Highlight smooth surfaces perpendicular to the optical axis by reflecting the light to a semi-reflective mirror surface Inspecting, analysing and measuring smooth metal surfaces and other reflective surfaces
A Fig. 37
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6.8
Vision
Industrial cameras use a number of sensor formats (C Fig.38) defined in inches: 1/3, 1/2 and 2/3 (1/3 and 1/2: camcorder, 2/3 and over: industrial high resolution, television, etc.). There are specific lenses for each format to ensure full use of the pixels. - CMOS Gradually being superseded by CCD Inexpensive > basic applications - Vidicon (tube) Now obsolete. Scanning The cameras are either interlaced image or progressive scan/full frame types.
A Fig. 39
Interlaced scan
Where vibration or image capture on the fly is common, it is recommended to use progressive scan (for reading on the fly) or full frame sensors. CCD ensures exposure of all the pixels at the same time. Interlaced scan This system derives from video. It analyses an image by scanning odd and even lines alternately (C Fig.39). It is designed to save half the bandwidth, at the cost of a few defects hardly visible on screen, notably flicker. One frame, represented by black lines, analyses the odd lines and the other, green, analyses the even lines. Progressive scan This is the type of image analysis used in information technology. It works by describing all the lines of an image at the same time (C Fig.40). It has the advantage of eliminating flicker and providing a stable image (C Fig.41). Lens - C and CS screw mounts with a diameter of 25.4mm are the most commonly used in industry. - The focal length (f in mm) is calculated from the height of the object to frame (H in mm), the distance between the object and the lens (D in m) and the height of the image (h in mm): f= D x h/H (C Fig.42). There is also a field angle = 2 x arctg (h/(2xf)). Therefore, the shorter the focal length, the larger the field.
A Fig. 40
Progressive scan
A Fig. 41
- The type of lens is therefore chosen according to the distance D and the size of the field viewed H.
v Processing unit
Its electronic system has two functions: format the image and then analyse the enhanced image.
A Fig. 42
Focal length
147
6.8
Vision
Image formatting algorithms Preprocessing changes the grey scale value of the pixels. Its purpose is to enhance the image so it can be analysed more effectively and reliably. The most common preprocessing operations are: - binarisation, - projection, - erosion/dilation, - opening/closing. Image analysis algorithms The table (C Fig.43) shows a number of image analysis algorithms. Note the image processing operations prior to analysis in the Prerequisites column.
Prerequisite
Binarisation and exposure adjustment if necessary Binarisation and exposure adjustment if necessary None Binarisation and exposure adjustment if necessary None and position adjustment if necessary Binarisation and explosure adjustment if necessary
Advantage(s)
Limits
Binarisation can affect image stability Binarisation can affect image stability
Binary window
Fast (ms)
Binary edge
Pixel-accurate at best.Binarisation can affect image stability Sub-pixel accuracy possible. Grey scale projection possible by preprocessing Many results extracted, versatile. Repositioning by 360 possible Easy to implement Requires accurate repositioning Pixel-accurate at best. Binarisation can affect image stability. Slow (>10..100 ms) Recognition limited to 30. Slow (> 10.. 100 ms) if large template and/or search zone Stability of mark to inspect can deteriorate over time. (ex stamped parts)
Shape extraction
Counting, object detection, measurement and geometrical parameter reading Positioning, repositioning, measurement, sorting, identification. Shape recognition, positioning, re-positioning, measurement, sorting, counting, identification
Advanced comparison
None
OCR/OCV
A Fig. 43
148
6.9
Optical encoders
A Fig. 44
v Principles
Rotation of a graduated disc generates identical pulses at the optical sensor output dependent on the movement of the object to inspect. The resolution, i.e. number of pulses per revolution, corresponds to the number of graduations on the disc or to a multiple of this number. The higher the number is, the more the number of measurements per revolution more accurately divides the movement or speed of the moving part connected to the encoder. Typical application: cutting to length. The resolution is expressed by distance covered in 1 revolution number of points For example, if the product to cut drives a measuring wheel of 200mm in circumference, for a precision of 1mm the encoder resolution must be 200 points. For a precision of 0.5mm the encoder resolution must be 400 points.
A Fig. 45
Incremental encoders are designed for applications to position moving parts and monitor their motion by incrementing and decrementing the pulses they generate.
149
6.9
Optical encoders
The disc of an incremental encoder has two types of track: - an outer track (channels A and B) divided into "n" alternately opaque and transparent intervals with equal angles, "n" being the resolution of number of periods. Two out-of-phase photodiodes behind this track generate square wave signals A and B every time the light beam crosses a transparent zone. The 90 electrical degree (1/4 of a period) phase shift of signals A and B defines the direction of rotation (C Fig.47). When rotating in one direction B is equal to 1 when A changes from 0 to 1 when in the opposite direction of rotation B is equal to 0, - an inner track (Z) with a single transparent window. The Z signal, called the zero marker, with a period of 90 electrical degrees, is synchronised with signals A and B. It defines a reference position and is used to reinitialise with every revolution. Operation of channels A and B Incremental encoders provide three levels of operating accuracy: - using the rising edge of channel A only: single operation corresponding to the encoder resolution, - using the rising and falling edges of channel A only: operating accuracy is doubled, - using the rising and falling edges of channels A and B: operating accuracy is quadrupled (C Fig.48). Elimination of interference Any counting system can be disrupted by interference on the line, which is counted along with the pulses generated by the encoder. To prevent this risk, most incremental encoders generate complementary signals A, B and Z in addition to the regular signals . If the processing system is designed to support them (numerical controls, for example), these complementary signals can be used to differentiate between encoder pulses and interference pulses (C Fig.49), to prevent them from being counted or to reconstruct the emitted signal (C Fig.50).
A Fig. 47
v Absolute encoders
Design principle Incremental encoders are designed for applications to position moving parts and monitor their motion.
A Fig. 48 Increase in number of points
A Fig. 49
A Fig. 50
150
6.9
Optical encoders
These rotary encoders work in a similar way to incremental sensors, but differ by their disc, which has several concentric tracks divided into equal alternating opaque and transparent segments (C Fig.51). An absolute encoder continuously generates a code which is the image of the actual position of the moving part monitored. The first inner track is half opaque and half transparent. It is read to ascertain the location of the object to the nearest half-revolution (MSB: Most Significant Bit).
A Fig. 51
The next tracks, from the centre to the edge of the disc, are divided into alternately opaque and transparent quarters. Reading the second track along with the preceding one (the first) ascertains in which quarter (1/4 or 1/22) of a revolution the object is located. The following tracks successively ascertain in which eighth (1/8 or 1/23), sixteenth (1/16) etc. of a revolution it is located. The outer track corresponds to the lowest-order bit (LSB: Least Significant Bit). The number of parallel outputs is the same as the number of bits or tracks on the disc. The image of the movement requires as many diode/ phototransistor pairs as bits emitted or tracks on the disc. The combination of all the signals at a given moment gives the position of the moving part. Absolute encoders emit a digital code, the image of the physical position of the disc, where a single code corresponds to a single position. The code produced by rotary absolute encoders is either natural binary (pure binary) or reflected binary, also called the Gray code (C Fig.52). Advantages of absolute encoders Absolute encoders have two major advantages over incremental encoders: - they are power failure-tolerant because, on start-up or after a power failure, the encoder supplies data on the actual angular position of the moving part that can be used by the processing system immediately. An incremental encoder has to be reset before the signals can actually be used, - they are impervious to line interference. Interference can alter the code generated by an absolute encoder but it returns automatically to normal as soon as the interference stops. An incremental encoder takes interference data into account, unless complementary signals are used. Using signals For each angular position of the shaft, the disc supplies a code, which can be binary or Gray: - pure binary code. Used to perform 4 arithmetical operations on numbers expressed in this code, so processing systems (PLCs) can use it directly to run calculations. It does however have the drawback of having several bits which change their status between two positions and could give rise to ambiguous readings. To overcome this, absolute encoders generate an inhibit signal which blocks the outputs at each change of status. - the Gray code, where only one bit changes status at a time, also avoids this ambiguity. But to be used by a PLC, this code must first be converted to binary (C Fig.53). Using an absolute encoder In most applications, the pursuit of greater productivity demands rapid movements at high speed, followed by deceleration to obtain accurate positioning. To achieve this objective with standard I/O cards, the MSBs must be monitored when the speed is high, so that deceleration is triggered at the nearest half revolution (C Fig.54).
A Fig. 52
A Fig. 53
A Fig. 54
151
6.9
Optical encoders
v Encoder variants
Many variants have been designed and several different types are available to answer different purposes, such as: - multi-revolution absolute encoders, - tacho-encoders and tachometers, - solid-shaft encoders, - hollow-shaft encoders, - through-shaft encoders.
Processing unit
Encoder Incremental Signal frequency (kHz) =< 0,2 =< 40 > 40 Parallel connection X X Absolute
PLC
X X
X X
b Speed sensors
-c a -b' c' b -a
The encoders above are able to provide speed data by a process suited to the output signal.
c -b
This description would not be complete without mentioning analogue speed sensors. These are mainly used for speed control and in particular in direct current motor speed controllers. To operate frequency converters in a closed loop, modern speed controllers use a virtual speed sensor, which uses the electrical quantities measured in the controller to recalculate the actual speed of the machine.
N
b' -c'
a'
v Tachometer alternator
This speed sensor (C Fig.56) consists of a stator with several windings and a rotor with magnets. This machine is similar to an alternator. Rotation induces alternating voltages in both stator windings. The amplitude and frequency of the signal generated is directly related to the speed of rotation. The user can either use the voltage (rms or rectified) or the frequency to control or set speed. Rotation direction can easily be detected by using winding phase displacement.
-a'
A Fig. 56
v Tachometer dynamo
This speed sensor consists of a stator with a fixed winding and a rotor with magnets. The rotor is equipped with a collector and brushes (C Fig.57).
A Fig. 57 Diagram of a tachometer dynamo
152
6.9
Optical encoders
This machine is similar to a direct current generator. The collector and the type of brush are chosen to limit threshold voltages and voltage discontinuity as the brushes pass. It can operate in a very wide range of speeds. Rotation induces direct voltage where the polarity depends on the rotation direction and has an amplitude proportional to the speed. The data on amplitude and polarity can be used to control or set speed. The voltage produced by this type of sensor ranges from 10 to 60 volts/1000rpm and can, for some dynamos, be programmed by the user.
A Fig. 58
153
6.10
Atmospheric pressure is expressed in hpa (hectopascal) or mbar. 1hP = 1mbar. The international unit of pressure is the Pascal (Pa): 1 Pa = 1N/1m2 A more practical unit is the bar: 1bar = 105Pa = 105N/m2 = 10N/cm2 Pressure switches, vacuum switches and pressure transmitters are used to monitor, control or measure pressure or a vacuum in hydraulic or pneumatic circuits. Pressure switches and vacuum switches convert a change in pressure into a discrete electrical signal when the displayed set-points are reached. Their technology can be electromechanical or electronic (C Fig.59). Pressure transmitters (also called analogue sensors), which use electronic technology, convert pressure into a proportional electrical signal.
A Fig. 59
Example of pressure detectors (Telemecanique), A: XML-B electromechanical pressure switch B: XML-F electronic pressure switch C: XML-G pressure transmitter
Telemecanique electronic pressure detectors are equipped with a piezoresistive ceramic cell (C Fig.61). The distortion caused by the pressure is transmitted to the thick-film resistors on the Wheatston bridge screenprinted onto the ceramic diaphragm. The variation in resistance is then processed by the built-in electronics to give a discrete signal or a signal proportional to the pressure (e.g. 4-20mA, 0-10V, etc.). Pressure control or measurement is the result of the difference between the prevailing pressures on both sides of the element under pressure. Depending on the pressure reference, the following terms are used: Absolute pressure: measurement relative to a sealed value, usually vacuum. Relative pressure: measurement in relation to atmospheric pressure. Differential pressure: measurement of the difference between two pressures. Note that the electrical output contacts can be: - power, 2-pole or 3-pole contacts, for direct control of single-phase and 3-phase motors (pumps, compressors, etc.), - standard, to control contactor coils, relays, electrovalves, PLC inputs, etc.
A Fig. 61
v Terminology (C Fig.62)
General terminology - Operating range The interval defined by the minimum low point (LP) adjustment value and the maximum high point (HP) adjustment value for pressure switches and vacuum switches. It corresponds to the measurement range for pressure transmitters (also called analogue sensors). Note that the pressures displayed on the device are based on atmospheric pressure.
A Fig. 62 Graphic illustration of commonly-used terms
154
6.10
- Rating Maximum value of the operating range for pressure switches. Minimum value of the operating range for vacuum switches. - High set-point (HP) The maximum pressure value, selected and set on the pressure switch or vacuum switch, at which the output will change status when the pressure rises.
- Low set-point (LP) The minimum pressure value, selected and set on the pressure switch or vacuum switch, at which the output will change status when the pressure drops. - Differential The difference between the high (HP) and low (LP) set-points.
- Fixed differential devices The low point (LP) is directly linked to the high point (HP) by the differential. - Adjustable differential devices The differential can be adjusted to set the low point (LP). Electromechanical terminology (C Fig.63)
A Fig. 63
- Accuracy of set-point display (C Fig.63a) The tolerance between the displayed set-point value and the actual value at which the contact is activated. For an accurate set-point (first installation of a product), use the reference of a rating device (manometer, etc.). - Repeatability (R) (C Fig.63b) The variation in the operating point between two successive operations. - Drift (F) (C Fig.63c) The variation in the operating point over the entire lifetime of the device. Electronic terminology - Between pressure values measured by the transmitter. It ranges from 0 bars to the pressure corresponding to the transmitter rating. - Accuracy comprises linearity, hysteresis, repeatability and adjustment tolerances. It is expressed as a percentage of the measuring range of the pressure transmitter (% MR).
A Fig. 64
- Linearity is the greatest difference between the actual and rated curves of the transmitter (C Fig.64a). - Hysteresis is the greatest difference between the rising and falling pressure curves (C Fig.64b). - Repeatability is the maximum scatter band obtained by varying the pressure in specified conditions (C Fig.64c). - Adjustment tolerances are the tolerances for zero point and sensitivity adjustment specified by the manufacturer (curve gradient of the transmitter output signal). - Temperature drifts The accuracy of pressure detector is always sensitive the operating temperature. It is proportional to it and is expressed as a percentage MR/C. - Zero point and sensitivity drift (C Fig.65a et b)
A Fig. 65
155
6.10
- Permitted maximum pressure in each cycle (Ps) The pressure a detector can withstand in each cycle with no adverse effect on its lifetime. It is equal to at least 1.25 times the device rating. - Permitted maximum accidental pressure The maximum pressure, excluding pressure surges, which the detector can withstand occasionally without causing damage to the device. - Break pressure The pressure beyond which the detector risks developing a leak or bursting. All these definitions of pressure are essential for choosing the right sensors for an application, in particular for ensuring they can be used in hydraulic circuits where severe transitory phenomena can occur, such as water hammer.
b Choice criteria
The paragraphs below give some examples of criteria which, though not central to the basic function, are advantageous for implementation and operation.
v Electrical characteristics
Supply voltage, AC or DC, the range of which varies.
A Fig. 66 2-wire and 3-wire connections
2-wire or 3-wire load switching techniques (C Fig.66). 2-wire technique: the detector is powered in series with the load, so it is subject to a residual current in the open state and a voltage drop in the closed state. The output can be normally open or normally closed (NO/NC). The maximum intensity of the switched current at the AC or DC output can be higher or lower, with or without short-circuit protection. 3-wire technique: the detector has two wires for power supply and one for transmitting the output signal (or more for products with more than one output). The output can be transistorised PNP or NPN. Both techniques are used by many manufacturers, but it is important to pay special attention to residual currents and voltage drops at the detector terminals: low values ensure greater compatibility with all types of load.
v Environmental conditions
Electrical: - immunity to - immunity to - immunity to - immunity to line interference, radio frequencies, electrical shocks, electrostatic discharge.
Thermal Usually from -25 to +70 but can be as much as -40 to +120C. Moisture/dust Degree of protection of the enclosure (seal): e.g. IP 68 for cutting oil in machine tooling.
156
6.10 6.11
v Options/ease of use
geometrical shape (cylinder or parallelepiped), metal/plastic casing, flush-mountable or not in metal frame, fastening devices, connection by cable or connector, self-teaching functions.
6.11
Conclusion
b What does the future hold?
The performance of electronic sensors is bound to improve with developments in electronics, with regard to both the electrical characteristics of the components and their size. With the boom in telecommunications (Internet, mobile phones), the operating frequencies of electronics have increased from a few hundred MHz to the GHz range. This will make it easier to measure wave propagation speed and do away with local physical phenomena. Moreover, technologies such as Bluetooth and Wi-Fi have opened the way to wireless sensor with radio links at frequencies of around 2.4GHz. Digital processing of the signal is another advantage of modern electronics: the falling cost of microcontrollers means that simple sensors can be equipped with advanced functions (automatic adjustment to the environment with detection of moisture, smoke or nearby metallic objects, intelligent sensors with self-testing capacity). This technical progress will make electronic sensors better suited to their initial requirements and more easily adaptable to process changes, without any significant alteration in price. But such innovation demands a heavy outlay that only the big sensor manufacturers are currently able to invest.
157
6.12
Dtection distance By contact 0 to 400mm (by levier) --> 60mm --> 100mm
Environment
Technology
Transfert and formating Electromechanical contact Discrete or analogue static Reed contact
Advantages Intuitive, high-power dry contact Positive contact Robust, sealed Not easily disrupted Detects through all non-ferrous metals Wide range Detects all types of object
Inductive Magnetic
All parts
--> 60 mm
Dry
Capacitive
Detects through all non-conductive substances Robust Detects transparent substances and powders
--> 15m
Ultrasonic
Sensitive to metal
Radio-frequencies
--> 1m
Optical
A Fig. 67
158
159
7
160
chapter
Personnal and machines safety
Reminder of European legislation regarding safety for people and environment. Reminder of IEC regulation for machines and products. Examples of application, products and safety networks
Summary
1 2
7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 Introduction Industrial accidents European legislation Concept of safe operation Certification and EC marking Safety principles Safety functions Network safety Example of application Safety-related functions and products Conclusion
162
3 4 5 6 7
163
165
172
173
175
176
178
179
8 9 10 11 12 M
181
182
161
7.1
Introduction
After presenting and defining the rules which govern safety, we shall focus on the machinery and the product technologies to meet customer requirements and comply with constraints.
7.1
Introduction
b Safety scope and definition
Legislation requires us to take preventive action to preserve and protect the quality of the environment and the human health. To achieve these objectives, there are European Directives which must be applied by plant operators and by manufacturers of equipment and machines. It also assigns the responsibility for possible injury. Notwithstanding the constraints, machine safety increases productivity by: - preventing industrial accidents, - ensuring the health and safety of all personnel by suitable safety measures that take into account the machines application and the local environment. Cutting direct and indirect costs by: - reducing physical harm, - reducing insurance premiums, - reducing production loss and delay penalties, - limiting harm and cost of maintenance. Safe operation involves two principles: safety and reliability of operation (C Fig.1) - Safety is the ability of a device to keep the risk incurred by persons within acceptable limits. - Reliability of operation is the ability of a system or device to perform its function at any moment in time and for a specified duration. Safety must be taken into account from the design phase and kept in place throughout all stages of a machines life cycle: transport, installation, adjustment, maintenance, dismantling. Machines and plants are sources of potential risk and the Machinery Directive requires a risk assessment for every machine to ensure that any risk is less than the tolerable one. Risk is defined in accordance with EN 1050 as follows (C Fig. 2): seriousness multiplied by the probability of occurrence.
A Fig. 1
Severity Risk
related to potential hazard A Fig. 2
Probability of occurrence
Of the harm - frequency and duration of exposure - possibility of avoiding or limiting the harm - Probability of the occurrence of an event which may cause harm
Definition of risk
162
7.1 7.2
The European Standard EN1050 (Principles of Risk assessment) defines an iterative process to achieve safety in machinery. It states that the risk for each individual hazard can be determined in four stages. This method provides the basis for the requisite risk reduction using the categories described in EN954. The diagram (C Fig. 3) shows this iterative process which will be detailed further on.
7
A Fig. 3 Machine safety process
7.2
Industrial accidents
An industrial accident occurs through work or in the workplace and causes minor to serious injury to a person operating or working on a machine (fitter, operator, maintenance worker, etc.).
163
7.2
Industrial accidents
Machine-related factors - Inadequate guards. - Sophisticated type of control and supervisory systems. - Inherent machine hazards (reciprocal motion of a machine, sudden starting or stopping). - Machines not suited to the application or environment (sound alarms deadened by the noise of surrounding machinery). Plant-related factors - Movement of personnel (automated production line). - Machinery from different sources and using different technologies. - Flow of materials or products between machines.
b The consequences
- Varying degrees of physical danger to the user. - Stoppage of the machine involved. - Stoppage of similar machine installations for inspection, for example by the Health and Safety Inspectorate. - Alterations to make machines comply with regulations where necessary. - Change of personnel and training new personnel for the job. - Damage to the company brand image.
b Conclusion
Damages for physical injuries are equivalent to about 20 billion euros paid out each year in the European Union. Decisive action is required to reduce the number of accidents in the workplace. The first essentials are adequate company policies and efficient organisation. Reducing the number of industrial accidents and injuries depends on the safety of machines and equipment.
b Types of hazards
The potential hazards of a machine can be classified in three main groups, as illustrated (C Fig. 4).
A Fig. 4
164
7.3
European legislation
The main purpose of Machinery Directive 98/37/EC is to compel manufacturers to guarantee a minimum safety level for machinery and equipment sold within the EU. To allow free circulation of machinery within the European Union, the EC marking must be applied to the machine and an EC declaration of compliance issued to the purchaser. This directive came into effect in January 1995 and has been enforced since January 1997 for all machines requiring compliance. The user has obligations defined by the health and safety directives 89/655/EEC which are based on all standards.
b Standards
v Introduction
The harmonized European safety standards establish technical specifications which comply with the minimum safety requirements defined in the related directives. Compliance with all applicable harmonized European standards ensures compliance with the related directive. The main purpose is to guarantee a minimum safety level for machinery and equipment sold within the EU market and allow the free circulation of machinery within the European Union.
A Fig. 5
Safety standards
165
7.3
European legislation
EN ISO 12100-1, -2
Machinery safety - basic concepts, principles for design Part 1 Terminology Part 2 principles Two-handed control devices - design principles Emergency stop equipment - design principles Safety-related parts of control systems - design principles Minimum gaps to avoid crushing of human body parts Safety distances to prevent danger zones being reached by the upper limbs Safety distances to prevent danger zones being reached by the lower limbs Machinery safety - Principles for risk assessment Machinery safety - Electrical equipment of machines Part 1: general requirements Positioning of protective equipment in respect of approach speeds of body parts Locking devices associated with guards - design and selection principles Electro-sensitive protective equipment Part 1 general requirement Part 2 particular requirement for light barrier Prevention of unexpected start-up Switching for LV electromechanical control circuits Visual danger signals - General requirements, design and testing Safety requirements for injection moulding machines for plastics and rubber Safety requirements for mechanical presses Safety requirements for hydraulic presses Safety requirements for moulding machines by compression and by transfer Safety requirements for design and construction of moulding machines by metal blowing Manipulating industrial robots - safety requirements Packaging machines Part 4: palletisers - safety requirements Safety and EMC requirements for equipment for mechanical handling of unit loads Safety and EMC requirements for fixed belt conveyors for bulk material Industrial thermo processing equipment Part 2: Safety requirements for the generation and use of atmosphere gases Safety requirements for portable disc cutting machines with thermal motor
EN 574 EN 418 EN 954-1 EN 349 EN 294 EN 811 EN 1050 EN 60204-1 EN 999 EN 1088 EN 61496
B B B B B B B B B B B
EN 1037 EN 60947-5-1 N 842 EN 201 EN 692 EN 693 EN 289 EN 422 EN 775 EN 415-4 EN 619 EN 620 EN 746-3
B B B C C C C C C C C C C
EN 1454
A Fig. 6
166
7.3
European legislation
Risk graph According to the definition of risk, standard EN 954-1 defines a practical method for selecting a category of control system and covers: - S : Seriousness of injury. - F : Frequency and/or exposure to a hazard. - P : Possibility of preventing accident. Resulting categories define resistance to faults and the behaviour of control systems in the event of a fault (C Fig. 8).
S Accident result
S1 Slight injury S2 Serious or permanent injury to or death of a person F Presence in the danger zone F1 Rare to fairly frequent F2 Frequent to permanent P Possibility of preventing accident P1 Possible in certain circumstances P2 Virtually impossible A Fig. 8 Choice table
167
7.3
European legislation
To illustrate those concepts we present an assessment of risk in a hydraulic press with manual materiel feeding (C Fig. 9). - Seriousness of injury: S2 since serious permanent injury could occur. - Frequency and exposure time: F2 since the operator is permanently present. - Possibility of avoiding the hazard: P2since it is virtually impossible to avoid. The result on the risk graph is category 4. To supplement this example we will select the guard locking devices (EN 1088 standard). In this example (C Fig. 10) the diagram conforms to category 4. When faults occur, they are detected in time to prevent loss of the safety function.
A Fig. 9
A Fig. 10
168
7.3
European legislation
Definition of Functional Safety according to IEC/EN 61508 Functional safety is a part of the overall safety of equipment under control (EUC). It depends on the correct functioning of safety-related systems which include electrical, electronic and programmable electronic parts and other external risk reduction devices. Safety Integrity Level (SIL) There are two ways to define the SIL, depending on whether the safety system is run in low demand mode or in continuous or high demand mode (C Fig. 11). The scale of functional safety is on 4 levels, from SIL1 to SIL4, the latter having the highest level of safety integrity.
A Fig. 11
Risk reduction
Safety is achieved by risk reduction (IEC/EN 61508) (C Fig.12). The residual risk is the risk remaining after protective measures have been taken, Electrical, Electronic and Programmable Electronic safety-related systems (E/E/EP) contribute to risk reduction.
A Fig. 12
Safety integrity levels estimate the probability of failure. For machinery, the probability of dangerous failure per hour in a control system is denoted in IEC/EN 62061 as the PFHd (C Fig.13).
169
7.3
European legislation
PFDaverage > = 10-5 to 10-4 > = 10-4 to 10-3 > = 10-3 to 10-2 > = 10-2 to 10-1
> = 10 to 10
-6
-5
IEC 61508 considers two modes of operation: - high demand or continuous mode where the frequency of demand made on a safety-related system is greater than one per year or greater than twice the proof test frequency, - low demand mode where the frequency of demand made on a safety-related system is no greater than one per year and no greater than twice the proof test frequency. IEC/EN 62061 does not consider the low demand mode to be relevant for machinery safety. SIL 4 is not considered in IEC/EN 62061, as it is not relevant to the risk reduction requirements normally associated with machinery. Safety integrity levels are calculated by the probability of failure l which is expressed as follows: = s+dd +du where: s rate of safe failures dd rate of detected dangerous failures du rate of undetected dangerous failures In practice, dangerous failures are detected by specific functions. The calculation of the PFHd, for a system or subsystem depends on several parameters: - the dangerous failure rate (d) of the subsystem elements, - the fault tolerance (i.e. redundancy) of the system, - the diagnostic test interval (T2), - the proof test interval (T1) or lifetime whichever is smaller, - susceptibility to common failures (). The graph (C Fig. 14) illustrates IEC/EN 61508-5 and the graph (C Fig. 15) the risk parameters.
A Fig. 14 170
Risk graph
7.3
European legislation
Comments 1 The classification system has been developed to deal with injury and death to people. Other classification schemes would need to be developed for environmental or material damage 2 For the interpretation of C1, C2, C3 and C4, the consequences of the accident and normal healing shall be taken into account 3 See comment 1 above
Frequency of, and exposure time in, the hazardous zone (F)
W1 A very slight probability that the unwanted occurences will come to pass and only a few unwanted occurrences are likely W2 A slight probability that the 6 If little or no experience exists of the EUC, or the EUC control system, or of a unwanted ocurences will come similar EUC and EUC control system, the estimation of the W factor may be to pass and few unwanted made by calculation. In such an event a worst case prediction shall be made occurrences are likely W3 A relatively high probability that the unwanted occurrences will come to pass and frequent unwanted occurrences are likely
4 This parameter takes into account: operation of a process (supervised (i.e. operated by skilled or unskilled persons) or unsupervised), rate of development of the hazardous event (for example suddenly, quickly or slowly), ease of recognition of danger (for example seen immediately, detected by technical measures or detected without technical measures), avoidance of hazardous event (for example escape routes possible not possible or possible under certain conditions), actual safety experience (such experience may exist with an identical EUC or a similar EUC or may not exist). 5 The purpose of the W factor is to estimate the frequency of the unwanted occurrence taking place without the addition of any safety-related systems (E/E/PE or other technology) but including any external risk reduction facilities
A Fig. 15
A Fig. 16
Assessment process
171
7.4
172
7.5
b Machinery Directive
The Machinery Directive is an early example of the New Approach to technical harmonisation and standardisation of products and is based on: - mandatory essential health and safety requirements (which must be met before machinery is placed on the market), - voluntary harmonised standards drawn up by the European Committees for Standardisation (CEN) and Electro-technical Standardisation (Cenelec), - compliance assessment procedures tailored to the type and level of risks associated with machinery, - EC marking, affixed by manufacturers to signify compliance with all relevant directives. Machinery bearing this marking may circulate freely within the European Community. The directive has greatly simplified the national laws that preceded it and thus removed many barriers to trade within the EU. It has also reduced the social cost of accidents. New Approach directives apply only to products which are marketed or commissioned for the first time.
b Harmonised standards
The easiest way to prove compliance with the Directive is to comply with Harmonised European Standards. When, for products in appendix 4, there are no Harmonised Standards, existing standards are not relevant for covering all essential safety requirements or when a manufacturer considers them inappropriate for his product, he must seek approval by an independent third party, a (Notified Body). These are appointed by the Member States after having proven that they have the relevant expertise to provide such an opinion. (TV, BGIA, INRS, HSE, etc.) Although a Notified Body has various responsibilities under the Directive, the manufacturer (or authorised representative) always remains responsible for the compliance of the product.
173
7.5
b Conformity assessment
According to article 8 of the Machinery Directive the manufacturer (or his authorised representative established in the Community) must draw up an EC declaration of conformity for all machinery (or safety components). This must be done to certify that machinery and safety components comply with the Directive. Before a product goes on the market, the manufacturer, or his authorised representative, must draw up and submit a file to the Notified Body (C Fig. 14).
b EC marking
The manufacturer or his authorised representative established in the Community must affix EC marking to the machine. This marking has been mandatory since 1 January 1995 and can only be applied if the machine complies with all relevant EU Directives such as: - machinery Directive 98/37/EC, - electromagnetic Compatibility Directive (EMC) 89/336/EEC, - low Voltage Directive 73/23/EEC. There are other directives e.g. for personal protective equipment, lifts, medical devices which may also be relevant. The EC marking on a machine is like a passport for the European countries, because such machines can be sold in all EU member states without considering their respective national rules. The EC marking process is described (C Fig. 17) below.
A Fig. 17
EC marking process
174
7.6
Safety principles
Below are examples of devices for electrical systems (C Fig.18): - switches with positive mode actuation, - emergency stop equipment (according to EN 60947-5-5), - power switch, - main contactor (only when the additional requirements of the norm are fulfilled), - auxiliary contactors with mechanically linked contacts (only when the additional requirements of the norm are fulfilled), - electromagnetic valve. Below are some explanations of technical principles which are usually the province of experts.
b Positive actuation
This is direct opening (IEC 60947-5-1) whereby contacts are separated as the result of switch movement by a non-resilient (rigid) device. The figure 19 shows how opening of N/C contacts is ensured by the rigid link and is independent of the springs.
A Fig. 19 Principle of positive actuation
Every element of direct opening contact must be indelibly and legibly marketed on the outside with the symbol the figure 20.
Relays, contactors and switches usually consist of a set of contacts. For safety applications, the position of every safety related contact in the circuit must be known in all possible switching conditions. This makes it possible to determine the behaviour of the circuit under fault conditions. Mechanically linked contacts are an answer to this requirement (C Fig.21).
A Fig. 21
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Definition of mechanically linked contacts (IEC/ EN 60947-5-1): [] a combination of n N/C contact element(s) and b N/O contact element(s) designed so that they cannot be closed simultaneously. When an N/C contact is maintained in the closed position a minimum gap of 0.5mm between all N/O contacts is ensured when the coil is activated. When an N/C contact is maintained in the closed position a minimum gap of 0.5mm between all N/O contacts is ensured when the coil is de-energised.
7.7
Safety functions
Based on the risk assessment, safety can be ensured by adapting existing functions (C Fig.22). As previously explained, this can be done in one of two ways: - redundancy or self-testing, - increased component safety. Unlike the classical approach where automation systems are divided into functions and treated individually, safety needs to be viewed holistically. To make it easier to build an automation system, component manufacturers offer specific certified products with integrated sets of functions. The figure 23 shows the generic solutions for the first four categories (B,1,2,3). We shall describe their use in standard applications and then give a more complex one. An example of a safety module designed for the requirements of category 4 is given at the end of the section.
A Fig. 22
A Fig. 23
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b Emergency stop
The emergency stop (C Fig.24) is designed to warn or reduce the effects of a potential hazard on humans, the machine or the process. The emergency stop is manually enabled. Requirements for the emergency stop: - for stop category 0: immediately stop the machine actuators or disconnect mechanically. If necessary, non-controlled stopping can be used (e.g. mechanical brake), - for stop category 1: controlled stop at the power rate of the actuators concerned then power disconnection when standstill is reached. The type of control component and its actuator must be positive mechanical (standard EN 2922). The emergency stop function must be available and operational at all times whatever the operating mode. The diagram (C Fig.25) shows a typical case of emergency stop:
A Fig. 24
Emergency stop
7
A Fig. 25 Typical emergency stop diagram
If the emergency stop device has to work on more than one circuit, the safety diagram is much more complex. This is why it is advisable to use a safety module. The diagram (C Fig.26) represents an emergency stop function for 2 circuits.
A Fig. 26
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The diagram (C Fig.27) shows how an emergency stop is linked to a speed controller (stop category 1).
A Fig. 27
7.8
Network safety
Technological progress, improved reliability and new standards have helped to change industrial networks so they can be used for applications with high safety demands. Most networks have a secured version; here we shall describe the ASI network used for components. For more information on networks, (see the section on Industrial networks).
b AS-Interface (ASI)
The Actuator-Sensor Interface (AS-Interface), a system which can be connected with the power on, is the successor to conventional wiring. This network is easy to use and extend. Speed, shorter installation time, cost saving, simplified maintenance and high availability are the defining features of this standardised network. The ASI network is ideal for fast sure transmission of small amounts of data in a hostile industrial environment.
v Data integrity
Invulnerability to interference in data transmission is an important feature in a network of sensors and actuators in the industrial environment. By using specific APM coding (alternating pulse modulation) and permanent monitoring of the signal quality, the ASI network delivers the same data integrity as other field buses.
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A Fig. 28
Operators of hazardous machines can be exposed to serious injury. Such machines are found in all means of production and are most common in the hydraulic press group: presses, punching machines, folding machines, etc. The machine is often manually fed by an operator. At this stage in the work, the risk is heightened by familiarity and routine. Two-handed controls (C Fig.28) are devices that require the operator to start the hazardous process by using two distinct controls simultaneously with each hand. These two-handed controls include the controls themselves and an emergency stop device. The four output contacts are monitored (C Fig.29) to control their interdependence. The time lapse between the actions on the two controls must not exceed 0.5 seconds and the controls must be in operation throughout the entire length of the hazardous machine process.
A Fig. 29
7
7.9 Example of application
The application described and illustrated (C Fig.30) is a practical example of some safety functions.
A Fig. 30
Example of application
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Example of application
The system has a mid-range PLC which controls up to 6 speed controllers, each of which powers a motor. Every speed controller is protected by a circuit breaker and every motor has its own contactor. The speed controllers can run with the factory settings or else be reconfigured with Power Suite software. Power supply: 3-phase 400V and single-phase 230V distributed to the components (3-phase 400V for the speed controllers and 230V for the Phaseo supply). All the speed controllers are hard-wired to the PLC. The speed controllers are monitored via a graphic touch-screen terminal and programmed with VijeoDesigner software. The graphic terminal is connected to the PLC via a Uni-Telway link. The PLC is configured and programmed with PL7 Pro software. An illuminated indicator bank gives the actual status of the system (power on or off, motor(s) running, awaiting confirmation, and emergency stop). The main switch is connected so that if the system is disconnected the PLC will still be powered and enable diagnostic operations to be run. As the speed controllers are used with the factory settings, the application program in this example is at its most basic. The equipment however was chosen to control further inputs/outputs. Options: The system reaches safety level 4 with the Preventa module to drive the speed controller contactors. This module not only protects the controllers but also keeps account of the emergency stop. The system also has another safety option for safety level 3 which automatically stops the motors if any box is open.
Note: the speed controller safety module has its own power supply. If there is a safety stop, starting again will require confirmation.
A gateway (TSX ETZ) to the next level up can be added to communicate via TCP/IP. The options are framed with dotted lines. This diagram can be used for the following typical applications: - small and medium automatic machines, - packaging machines, textile machines, conveyor belts, water distribution, wastewater treatment, etc, - automated standalone subsystems relating to medium to large machines.
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E Fig. 31
Safety-related controllers Examples of solution The controller governs the following functions Emergency stop Protection of persons by protective barrier Positioning movement
Category 4
Category 4 XPS MF Protection of operator accessing a danger zone Safety-related PLC Programmable software
Category 4
category 4
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A Fig. 32
7.11
Conclusion
Machine safety is an essential requirement in the European Union and a precondition for circulation of the products in member states. Designers would be well advised to use analysis tools such as FMECA to help find the most appropriate and cost-saving solutions. If this analysis is done, risk assessment to comply with standards in force will be faster and further-reaching. The methodical approach described above will help guarantee successful risk assessment. It will lead to the best-devised safety diagram and the best choice of components to perform the function. Suppliers such as Schneider Electric offer a full range of products and solutions perfectly designed for building safety functions. If required, experts can step in to help find solutions for difficult cases.
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Presentation : Man machine dialog according to machine operation Command and interface solutions (push buttons or terminals) Screens configuration software
8. Human-machine interface
Summary
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8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 Human-machine interface setup Human-machine interfaces Discrete control and indicator units Schneider Electric Discrete Control and Indicator Unit offer Advanced human-machine interfaces Exchange modes Development software Conclusion
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Operators play an important part in the human-machine dialogue.They must use the information they have to perform actions that make the machines and installations run properly without endangering safety and availability. It is therefore crucial that the interfaces and dialogue functions are designed to ensure that operations can be performed reliably in all circumstances.
8.1
v Independent
Because their content can be on different levels. The levels are defined by the designer of the automation system according to the requirements of the process and what the user wants, such as discrete signals from the operator to the machine, alphanumerical or animated diagram messages from the machine to the operator.
v Linked
Because the automation system interprets an operator action on a control interface as a specifically defined action and, in return, emits information that depends on whether the action was properly performed or not. The operator can either act by his own decision (stop production, modify data, etc.) or in response to a message from the machine (alarm, end of cycle, etc.).
A Fig. 1
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The scope of these tasks shows how important the operators role is. Depending on the information he has, he may have to take decisions and perform actions that fall outside the framework of the regular procedures and directly influence the safety and availability of the installation. This means the dialogue system should not be confined to mere exchange of information between human and machine but should be designed to facilitate the task of the operator and ensure that the safety of the system in all circumstances.
v Detect
Any change in a machines operating conditions is usually seen by a change in or display of information on an indicator, display unit or screen. The operator must, above all, be able to detect the event in any environmental conditions (ambient lighting, etc.). Different means can be employed to attract attention: flashing information, colour change, sound signal, anti-reflection devices, etc.
v Understand
To prevent any action that might endanger safety, the information the operator sees must be legible and accurate enough to be immediately understood and used. This is as much a matter of the ergonomics of the components as of the function design: - for a pilot light: use of the standard colour, fast and slow flashing clearly differentiated, etc.; - for a display unit: clear texts in the language of the user, adequate reading distance, etc.; - for a screen: use of standard symbols, zoom giving a detailed view of the area the message involves, etc.
v Respond
Depending on what message the machine sends, the operator may have to act swiftly by pressing one or more buttons or keys. This action is facilitated by: - clear markings to identify buttons and keys easily, such as standard symbols on buttons; - clever ergonomics with large buttons, touch keys, etc.
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8.2
8.2 8.3
Human-machine interfaces
The human-machine interface has made outstanding progress over the last few years. The basic function of the push button has been enhanced by interfaces using electronics to improve and customise the dialogue and add new features, such as custom settings and diagnostics. The table (C Fig.2) shows the offer and functions of human-machine interfaces
DESIGN
COMMISSIONING
OPERATING
MAINTENANCE
Product PB Integrated dialogue Operator Dialogue Supervision Function Operation PB, Supervision, PB, Supervision, Operator Operator dialogue dialogue
Integrated dialogue (Supervision and Operator dialogue possible)
Integrated dialogue (Supervision and Operator dialogue possible)
Diagnostic
Adjustment
Integrated dialogue Operator, Supervision software Offer and functions of human machine interfaces
PC adjustment software
A Fig. 2
8.3
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Note : the IEC 60204-1 standard stipulates the colour codes that pilot lights and push buttons must be: - red light: emergency hazardous situation requiring immediate action (pressure not within safety limits, over-travel, broken coupling, etc.); - yellow light: abnormal an abnormal situation likely to lead to a hazardous situation (pressure not within normal limits, tripping of protection device, etc.); - white light: neutral general information (supply voltage, etc.); - red push button: emergency - action to counter danger (emergency stop, etc.); - yellow push button: abnormal - action to counter abnormal conditions (intervention to restore an automatic cycle run, etc.).
The push button interface is used for general stop and start control and safety circuit control (emergency stops). They exist in diameters of 16, 22 and 30mm (NEMA standards) and different designs (C Fig 3): - chromium-plated metal bezel, for all heavy-duty applications in harsh industrial environments; - plastic for harsh environments: chemical and food industries. Operating head There is a wide range of control heads: - flush, protruding, recessed or booted; - mushroom; - double-headed; - mushroom with latching; - emergency stop; - switch with toggle, handle, key, 2 or 3 set or pull-off positions; - metal pin (multidirectional control); - flush, protruding or booted pilot lights. The modular design of control and indicator units offers great flexibility of use. Pilot lights and illuminated buttons are fitted with filament lamps or LEDs. They are mains powered and have a voltage reducer or built-in transformer. The control units can hold 1 to 6 NO or NC contacts compatible with 24V PLC inputs. Ruggedness and reliability Push buttons and pilot lights are subject to harsh environmental conditions. Life time of a push button is around 1 million of operations. They must be designed to withstand shock tests according to the IEC 60947-5-5 standard. As an example, according to the standard, an emergency stop button must withstand 5.5 Joules without failure, the Harmony push button range can withstand 17 Joules.
A Fig. 3
A Fig. 4
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Square-headed key buttons and pilot lights These devices are mounted at intervals of 19,05 mm (3/4 ) in holes 16 mm in diameter. They are used to make compact control units when space is at a premium and they can be linked to input keyboards. Key buttons are touch-sensitive. They can have a silver or gold contact. LED pilot lights (C Fig 5) LEDs for 0.8 and 12 mm mountings are especially recommended when space is limited or when there are a lot of indicating elements (low power dissipation). They have many advantages: - excellent resistance to shocks, vibrations and voltage surges, - long lifetime (>100,000 hrs), - low consumption making them directly compatible with PLCs outputs.
A Fig. 5
Flashing lights - For distinction or specific information: - Attract more attention - Call for immediate action - Indicate discordance between the instruction and the actual status - Indicate a change in cycle (flashing during transition). Flash and rotating mirror beacons - A more powerful signal for top priority information or longer distance signalling (conforming to IEC 60073). Buzzer and sirens - Recommended in environments subject to considerable light or sound interference or when the presence of the operator is of higher importance.
v Joysticks (C Fig.7)
Joysticks usually use contactors to control movement through one or two axes, such as travel/direction or raising/lowering on small hoisting equipment. They usually have 2 to 8 directions, with 1 or 2 contacts per direction, with or without return to zero. Some joysticks have a dead man contact at the end of the lever.
A Fig. 7
Telemecanique joysticks
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8.4 8.5
Schneider Electric Discrete Control and Indicator Unit offer Advanced human-machine interfaces
A Fig. 8
Harmony offer
8.5
v Main features
- Graphic screen with custom display. - Plain text entry with 6 languages available (Chinese, English, French, German, Italian and Spanish) and others on option. - Browse button to navigate the menus easily. - Simply Start menu for a quick start to get the most from Altivar 71 performance immediately. - Function keys for shortcuts, online help or to configure for applications. - Permanent display of motor operation settings.
A Fig. 9
v Main advantages
- Clear display with text on 8 lines and graphic views. Legibility up to 5 m (C Fig.10). - Flexibility through remote operation: on a cabinet door avec with IP 54 or IP 65 protection for multipoint connection to several speed controllers. - Storage 4 configurations can be stored for transfer to other speed controllers.
A Fig. 10
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- Ease to use with function keys for shortcuts, direct access and online help, maximum and minimum parameter display. - Ergonomic browse button. Navigate the dropdown menu quickly and easily with just one finger. - Custom parameters, viewing screens, monitor bar, user menu creation, etc. - Protection of parameters, visibility control, password protection for safe and easy access to custom configurations. Many macro-configurations already integrated. They ared designed for a wide range of uses and applications: handling, hoisting, general use, connection to field bus, PID regulation, master, slave, etc. They are easy to modify. A wealth of varied services is available through the graphic terminal to help tune and diagnose machines.
b Screen/keyboard terminals
Unlike embedded terminals, screens and keyboards are generic products that adapt to any application. As we saw in the table above (C Fig.2), screen terminals are used in both commissioning and operation. Depending on their type and software, they can play an important part in maintenance operations. Terminals communicate with the process via the appropriate communication bus and are an integral part of the dialogue and data chain. To illustrate what screen/keyboard terminals can do, we shall take a look at the Telemecanique Magelis offer. These graphic terminals (with an LCD touch screen of 5.7 to 12.1 and keyboard or touch screen of 10.4) provide simple access to graphic solutions for controlling and/or supervising automated units. Communication performance are guaranteed by a direct connection to an Ethernet TCP/IP network.
v Important features
Designed for harsh industrial environments - rugged and compact; - reliable ergonomic control by keyboard or touch screen; - highly contrasted screens for excellent legibility. Maintenance & diagnostics via the web - remote control via Internet Explorer; - access to operator console diagnostic information via HTML pages; - remote diagnostics; - automatic emailing. Compatible and upgradeable - API connection available (several manufacturers); - OPC communication (several manufacturers (OPC server); - TCP/IP network integration; - Embedded VB Script. Innovating HMI concepts - decentralised control stations; - centralised access to local stations, small control rooms; - usable throughout the world over as many languages are supported.
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Terminal device family figure 11. Magelis XBT R, S Compact matrix operator terminals: - 4 to 8 lines with 5 to 20 prints, - semi-graphic symbols, - touch pad and password. ZENSHIN Touch screen graphic terminals available in 5.7 - 7.5 - 10.4" dimensions. Magelis XBT GK Graphic man machine operating terminals available in 5.7 - 7.5 - 10.4" dimensions. Magelis XBT GT Touch screen colour graphic terminals available in 3.8-5.7-7.4-10.412.1-15 dimensions.
A Fig. 11
Magelis XBT G touch screen graphic terminals - Display LCD screen size 5.7 7.4 10.4 12.1 - Functions - representation of variables: alphanumeric, bitmap, bargraph, gauge, - button, light, clock, flashing light, keypad; - curves with log; - incorporated alarm log. - Communication - embedded Ethernet: 10BASE-T (RJ45); - downloadable protocols: Uni-Telway, Modbus, Modbus TCP/IP. - Compatible with Schneider Electric controllers and PLCs: Twido, Nano, Modicon TSX Micro, Modicon Premium, Modicon Quantum. - Configuration software Vijeo Designer VJD SPU LFUCD V10M (on Windows 2000 and XP). - Compact Flash card slot - Supply voltage 24V = Magelis XBT F graphic terminals - Display LCD screen size 10.4 Format 256-colour TFT - Data entry keypad - 10 dynamic function keys with LEDs; - 12 static function keys with LEDs + legends; - 12 service keys; - 12 alphanumeric keys + 3 alphanumeric access.
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- Touch screen data entry option - Functions - representation of variables: alphanumeric, bitmap, bargraph, gauge, potentiometer, selector; - recipes: 125 records maximum with 5000 values; - 16 curves; - alarm log. - Communication - embedded Ethernet: 10BASE-T/100BASE-TX (RJ45); - buses and networks: Fipway, Modbus Plus, and third-party protocols; - downloadable protocols: Uni-Telway, Modbus, Modbus TCP/IP. - Compatible with Schneider Electric controllers and PLCs Twido, Nano, Modicon TSX Micro, Modicon Premium, Modicon Quantum - Configuration software XBT L1003M (on Windows 98, 2000 and XP) - Supply voltage 24 V =
b Industrial PCs
v Characteristics
Industrial PCs are characterised by their rugged design enabling them to work without failure in industrial environments with electromagnetic interference and harsh climatic conditions. Industrial PCs can be compact or modular to fit closely the users needs. The illustrations (C Fig.12a) shows part of Schneider Electric offer.
A Fig. 12a
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8.5 8.6
Magelis Modular iPC Easy commissioning with 12 or 15 colour TFT LCD screens, with or without touch screen, with or without a QWERTY keyboard. Magelis IDisplay 12, 15, 19 touch screen with a USB port optimising the man / machine interface.
A Fig. 12b
8.6
Exchange modes
Conventional communication modes such as serial and bus links are naturally used on most products. They work through drivers embedded in the configuration software. Networks can also be used.
b Protocols supported
All the core protocols in the =S= offer can be used: - Uni-TE (Uni-Telway), Modbus, Modbus TCP-IP, FipWay, Modbus Plus; - third-party protocols are also available; - features: control graphic and ergonomics, types of automation system action.
v FactoryCast HMI
Same diagnostic functions as FactoryCast + new HMI functions embedded in a PLC module: - real-time database and PLC data acquisition (1000 variables); - calculations for pre-processing data; - advanced alarm management with emailing; - data archived in relational databases (SQL, Oracle, MySQL); - a web server the user can customise for an interface suited to requirements.
A Fig. 13
v FactoryCast Gateway
New offer of intelligent all-in-one web gateways in a standalone box containing: - network communication interfaces and Modbus or Uni-Telway serial links; - remote access server (RAS); - alarm notification by email; - a web function the user can customise.
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8.7 Development software
8.7
Development software
In addition to the terminal hardware, software is also offered to configure and adapt the terminals to their requisite application. Below is a description of the Telemecanique Magelis offer. Hardware and software are combined in a consistent package enabling the user to build the requisite application in the shortest possible time. The software can also be used to communicate with third-party products to gain optimal flexibility and open-endedness.
v Configuration
The XBTL1001/L1003 configuration software is an user friendly package to create several family of pages: - application pages (eventually linked to each other); - alam pages; - help pages; - recipe pages.
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A Fig. 15
b Vijeo Citect
Vijeo Look 2.6 a SCADA (Supervision ControlAnd Data Acquisition) aimed to stand alone terminals (C Fig.15). If offer a perfect symbiosis between Web and MMI (Man Machine Interface). Information are available in the Schneider Electric documentation.
A Fig. 14
8.8
Conclusion
Human-machine interface is probably the sector in automation which has made the greatest progress in the last few years. This progress is due to increasingly sophisticated and user-friendly electronics and signal processing. With the right choice of interface and its configuration, users can control processes with ever greater exactness and undertake diagnostics and preventive maintenance to increase productivity by reducing downtime.
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Presentation: Needs and available components Technologies Schneider Electric policy
9. Industrial networks
Summary
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9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 Introduction History Market requirements and solutions Network technologies Networks recommended by Schneider Electric Ethernet TCP/IP Web services and Transparent Ready CANopen bus Ethernet and CANopen synergy AS-Interface (AS-I) Bus Conclusion
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9.1 9.2
Introduction History
In this part we discuss the electrical links required for operating automation equipment.These usually involve two categories: - High current links connecting the power components between the mains supply and the load.We shall not be dealing with this topic here but refer the reader to the sections on power supply and implementation. - Low current links connecting all the capture, dialogue, processing and power control components with the machine and process environment.
9.1
Introduction
Electrical equipment systems are traditionally hard wired. The international machine standard IEC 60 204-1 and individual country standards have precise stipulations for sections, the quality of the insulating agent and colour markings. Most of these links are made from flexible wire units with a section of 1.5-2.5 mm2 (AWG 16 and 14), protected at each end. Until a decade ago, these solutions covered all requirements, both for discrete signals and analogue signals for servocontrol, the latter sometimes requiring shielded cables to prevent electromagnetic interference. Influenced by IT and automotive industry standards, the advent of digital technologies in other industries has had a considerable impact on the design and construction of electrical equipment. Digital data exchange entails links by communication networks requiring the use of connectors and ready-made connections. This makes it much simpler to build electrical equipment as wiring errors are reduced and maintenance is more straightforward. As conventional link technologies are already well known, we shall devote this section to the communication networks used in industry.
9.2
History
In 1968, the company Modicon invented the concept of the programmable logic controller, a single unit to handle a wide range of needs and provide economies of scale. Its high flexibility in use offers many advantages throughout every stage in the lifetime of a plant. Networks came in gradually, initially as serial links. Exchanges were formalised by protocols, such as Modbus (1979, short for MODicon Bus), which has become a standard by its very existence. Within the last few years, many applications have adopted the field bus. This backbone of automation system architecture is an extremely powerful means of exchange, visibility and flexibility in the devices connected to it. The field bus has gradually led to an overhaul in architecture: - input/output wires eliminated; - input/output interfaces superseded or decentralised; - intelligence decentralised and distributed; - Internet interconnection.
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The 1970s saw the emergence of the Xerox PARC Ethernet a contraction of ether and net(work) which 10 years later became the international standard native equipment in practically all computers. Its initial applications were file and message transfer and web page transmission. The spread of information technology to all parts of industry by the 1990s led to the need for industry-wide connection. The World Wide Web invented by the CERN in 1989 was originally developed to enable different work teams scattered throughout the world share information. The WWW system involves sharing documents and links using HTTP, a simple protocol used by a browser to access web pages stored on a server. These pages are programmed with languages such HTML or XML. The World Wide Web Consortium (W3C) was set up in 1994 to manage technical web developments (see the site http://www.w3.org). In 1996 Schneider Electric promoted the industrial Ethernet to connect the management and shop floor sides of businesses by PLCs and then developed the Transparent Ready concept based on the addition of industrial tools and protocols, including Modbus, to existing standard Ethernet elements.
9.3
A Fig. 1
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Before analysing communication network technologies, there should be a breakdown of the main requirements for which these levels provide a relevant solution. The characteristics in the table in fig. 2 are detailed in the paragraphs which follow.
Level Requirement Volume to data Response to transmit time Files Mbits 1 min Distance World Network topology Bus, star Number of addresses Unlimited Medium Electrical, optic, radio
Management Data exchange. Computer security . Standards between software packages. Shop floor Synchronisation of PLCs in the same data exchange automation cell in client/server mode with the control tools (HMI, supervision). Real-time performances. Distributed architecture. Embedded functions and exchange. Transparency. Topology and connection costs. Simplification of distribution wiring for power supply to sensors and actuators. Optimised wiring costs.
Data Kbits
50-500 ms
2-40 Km
Bus, star.
10-100
Machine
Data Kbits
10 m to 1K m Bus, star
10-100
Sensor
Data Bits
1- 100m
No constraint 10-50
Electrical, Radio
A Fig. 2
An initial approach is to adopt the two main focuses from this table of requirements: - the amount of information to transmit; - the response time needed. This helps to position the main networks (C Fig.3).
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9.4
Network technologies
9.4
Network technologies
The concepts are described in brief; for further reading, there are many works devoted to this subject.
b Network topology
An industrial network is made up of PLCs, human-machine interfaces, computers and I/O devices linked together by communication links such as electric cables, optic fibres, radio links and interface elements such as network cards and gateways. The physical layout of a network is the hardware topology or network architecture. For the circulation of information the term used is software topology. Topologies are usually divided as follows: - bus, - star, - tree, - ring, - hub. Bus topology This is one of the simplest layouts; all the elements are wired together along the same transmission line. The word bus refers to the physical line. This topology is easily implemented and the failure of a node or element does not prevent the other devices from working. Machine and sensor level networks, otherwise known as field buses, use this system. The bus topology is implemented by linking devices together in a chain or to the main cable via a connection box (TAP) (C Fig.4). Star topology This is the Ethernet topology, the most common at management and shop floor levels (C Fig.5). It has the advantage of being very flexible to run and repair. The end stations are linked together via an intermediate device (repeater, switch). Failure of a node does not prevent the network as a whole from working, though the intermediate device linking the nodes together is a point of weakness. Other topologies (C Fig.6) - The ring topology uses the same hardware layout as the star topology but ensures greater network availability. - The hub topology is not very widespread in industry and has the disadvantage of a large number of links.
Ring Hub
A Fig. 4
Network topology
A Fig. 5
The ring topology uses the same hard- The hub topology is not very widespread ware layout as the star topology but in industry and has the disadvantage of ensures greater network availability. a large number of links. A Fig. 6 Other topologies network
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b Protocol
A communication protocol specifies a set of rules for a given type of communication. Initially, protocol was the word meaning what was used to make dissimilar devices communicate on the same level of abstraction. The term now extends to the rules of communication between two layers on the same device. The OSI (Open System Interconnection) model was created by ISO (International Standards Organisation) which published standard ISO 7498 to provide a common basis for all computer network descriptions. In this model, the suite of protocols in a network is divided into 7 parts called OSI layers, numbered 1 to 7. OSI layers work on the following principles: - every layer supports a protocol independently of the other layers; - every layer provides services to the layer immediately above it; - every layer requires the services of the layer immediately below it; - layer 1 describes the communication medium; - layer 7 provides services to the user or an application. In a communication, the network user calls on the services of layer 7 via a program. This layer formats and enriches the data the program gives it according to its protocol and sends it to the layer below it when a service is requested. Each layer formats the data and adds to it according to the protocols used. Finally it is sent to the medium and received by another network node. It goes back through all the layers of this node and ends up in the correspondents program, divested of all the protocol-related additions. The OSI 7-layer model (C Fig.7) has been implemented by several manufacturers but was never a commercial success as the market preferred the 4-layer TCP/IP model which is easier to understand and use and which had already been implemented in the mobile domain. The model does however have a certain theoretical advantage, even though the frontiers of the 4 TCP/IP layers do not have an exact equivalent in OSI. These layers will be described in the subsection on Ethernet.
N 7 6 5 4 3 2 1
Function of layer The interface with the user; sends requests to the presentation layer.
Defines how data will be represented. Converts data to ensure that all systems can interpret it. HTML, XML. Ensures correct communication and links between systems. Defines session opening on network devices. Manages end-to-end communication, data segmentation and reassembly, controls flow, error detection and repair. Routes data packets (datagrams) through the network. Creates an error-free link from the hard medium. Defines the protocols for the bit stream and its electrical, mechanical and functional access to the network. ISO8327, RPC, Netbios. TCP, UDP, RTP, SPX, ATP. IP, ICMP, IPX, WDS. ARCnet, PPP, Ethernet, Token ring. CSMA, RS-232, 10 Base-T, ADSL.
A Fig. 7
OSI layers
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9.4 9.5
b Frame
A frame (C Fig.8) is a set of data sent via a network in a single block. It is also known as a packet. Every frame has the same basic layout and contains control information such as synchronisation characters, workstation addresses, an error control value and a variable amount of data.
A Fig. 8
Format of a frame
9.5
A Fig. 9
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b CANopen
CANopen is the industrial version of the CAN bus developed for automotive purposes. This network has proved its flexibility and reliability for over 10 years in a wide range of applications such as medical equipment, trains, lifts and many machines and plant installations. Schneider Electrics choice of this network is upheld by its widespread distribution.
b As-Interface
Modern machines have a great many actuators and sensors and often have safety constraints as well. AS-Interface is the network at sensor level which meets industrial automation requirements. It has the advantage of fast connections and a single cable to convey data and power.
9.6
Ethernet TCP/IP
b General description
Ethernet works on the principle of media access controlled by a collision detection mechanism. Each station is identified by a unique key, or MAC address, to ensure that every computer on an Ethernet network has a different address. This technology known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD) ensures that only one station can transmit a message on the medium at a time. Successive Ethernet upgrades have given rise to the IEEE 802.3 standard (see www.ieee.org) which only defines the characteristics of the physical layers; the way the data accesses the network and the data frame must be defined by further layers. As these notions often get confused, figure 10 places them and the protocols mentioned are explained in the following paragraphs. For many years, Ethernet was present in industry but had little success. Suppliers and customers felt it was non-deterministic. Their need for realtime control made them prefer proprietary networks. It was the combination of industry and Internet protocols that finally led them to accept it.
A Fig. 10
Ethernet topology
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Ethernet TCP/IP
b Physical layer
The physical layer describes the physical characteristics of communication such as the type of medium conventionally used (electric cables, fibre optic or radio links) and all related details like connectors, types of encoding and modulation, signal levels, wavelengths, synchronisation and maximum distances.
b Network layer
In its original definition, the network layer solves the problem of conveying data packets across a single network. Further functions were added to it when networks became interconnecting, especially data transmission from a source network to a target one. In general this means that packets are routed across a network of networks, otherwise known as Internet. In the suite of Internet protocols, IP transmits packets from a source to a target anywhere in the world. IP routing is made available by defining an IP addressing principle to ensure and enforce the uniqueness of every IP address. Each station is identified by its own IP address. The IP protocol also includes other protocols, such as ICMP used for transferring IP transmission error messages and IGMP which manages multicast data. ICMP and IGMP are located above IP but join in the functions of the network layer, thereby illustrating the incompatibility of the Internet and OSI models. The IP network layer can transfer data for many higher level protocols.
b Transport layer
The transport layer protocols can solve problems such as the reliability of data exchange (Did the data reach the target?), automatic adaptation to network capacity and data stream control. It also ensures that the data arrive in the right order. In the suite of TCP/IP protocols, transport protocols determine which application each data packet is to be delivered to. TCP is a connection-oriented transport protocol which delivers a reliable stream of bytes ensuring the data arrive unaltered and in order, with retransmission in the event of loss and elimination of duplicate data. It also handles urgent data to be processed in random order (even though they are not technically emitted out of band). TCP tries to deliver all the data correctly and in order this is its purpose and main advantage over UDP, even though it can be a disadvantage for real-time transfer applications, with high loss rates in the network layer. UDP is a simple, connection-free, unreliable protocol. This does not mean it is actually unreliable, but that it does not check that the packets have reached their target and does not guarantee they arrive in order. If an application requires these guarantees, it has to ensure them itself, or else use TCP. UDP is usually used for broadcasting applications such as Global Data or multimedia applications (audio, video, etc.) where there is not enough time for managing retransmission and packet ordering by TCP, or for applications based on simple question/ answer mechanism like SNMP queries, where the higher cost of making a reliable connection is disproportionate to needs. TCP and UDP are used for many applications. Those that use TCP or UDP services are distinguished by their port number. Modbus TCP uses TCP services. UDP can be used for the Factorycast plug-in.
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Ethernet TCP/IP
b Application layer
Most network application functions are located in the application layer. These include HTTP (World Wide Web), FTP (file transfer), SMTP (messaging), SSH (secured remote connection), DNS (matching IP names and addresses) and many others. The applications generally work below TCP or UDP and are usually linked to a well-known port. Examples: - HTTP port TCP 80 or 8080; - Modbus port 502; - SMTP port 25; - FTP port 20/21. These ports are allocated by the Internet Assigned Numbers Authority.
v BOOTP/DHCP
It automatically provides product IP address settings. This avoids having to find the individual address of each device by offloading the task onto a dedicated IP address server. The DHCP protocol (Dynamic Host Configuration Protocol) automatically allocates device configuration parameters. DHCP is an extension of BOOTP. The BOOTP/DHCP protocol has 2 components: - the server to provide the IP network address; - the client which requests the IP address. The Schneider Electric devices can be: - BOOTP/DHCP clients which automatically retrieve the IP address from a server; - BOOTP/DHCP servers for the device to distribute the IP addresses to network stations. The standard BOOTP/DHCP protocols are used to provide the faulty device replacement service (FDR).
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v COM/DCOM (Distributed Component Object Model) or OLE (Object Linking and Embedding)
It is the name of the Windows object component technology used for transparent communication between Windows applications. These technologies are used in OFS data server software (OLE for Process Control Factory Server).
9.7
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9.7
A Fig. 11
These communication services are divided into three classes: - Class 10: basic Ethernet communication; - Class 20: Ethernet communication management (network and device levels); - Class 30: advanced Ethernet communication. Table 12 gives a brief summary of the services.
A Fig. 12
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9.7
Its simplicity enables any field device, such as an I/O module, to communicate via Ethernet without requiring a powerful microprocessor or a lot of internal memory. Ethernet Modbus TCP has a very simple protocol and high output of 100 Mbps which guarantee its excellent performance enabling this type of network to be used for real-time applications such as I/O scanning. As the application protocol is identical on Modbus serial link, Modbus Plus and Ethernet Modbus TCP, messages can be routed from one network to another without having to change protocols. Modbus is implemented above the TCP/IP layer, so users also benefit from IP routing which enables devices anywhere in the world to communicate regardless of the distance between them. IANA (Internet Assigned Numbers Authority) has assigned the Ethernet Modbus TCP with the fixed port TCP 502, thus making Modbus an Internet group standard. The maximum data size is 125 words or registers in read mode and 100 words or registers in write mode.
A Fig. 13
In operation, the module ensures: - management of TCP/IP connection IP with each remote device; - product scanning and I/O copying in the configured word zone; - feedback of status works to monitor service operation from the PLC application: - use of preconfigured default values in the event of communication problems. An offer for hardware and software to implement the I/O Scanning protocol on any device that can be connected to Ethernet Modbus TCP can be found on the Modbus-IDA website (www.modbus-ida.org).
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9.7
Transparent Ready devices support 2 SNMP network management levels: - MIB II Standard interface: a basic network management level is accessible via this interface. The manager uses it to identify architecture component devices and retrieve general information on the configuration and operation of Ethernet TCP/IP interfaces; - Transparent Ready MIB interface: this interface enhances Transparent Ready device management. The MIB has a set of information enabling the network management system to supervise all the Transparent Ready services. It can be downloaded from the FTP server of any Transparent Ready Ethernet module on a PLC.
A Fig. 14
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v Class A
Transparent Ready devices with no web services.
v Class B
Basic web level for managing static web pages pre-configured in a Transparent Ready device. It offers device diagnostic and monitoring services using a standard web browser.
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v Class C
Configurable web level for customising the website of a Transparent Ready device with web pages defined by the user for the needs of an application. The client procedure diagnostic and monitoring can be run from a standard web browser. The Factorycast offer includes this level of web functionality as well as tools to facilitate management and modification of embedded websites:
v Class D
Active web level for running specific processes in the Transparent Ready Web Server device itself. This processing capacity can be used for precalculation, real-time database management, communication with relational databases and sending e-mails. Communication between the browser and the server is thus reduced and optimised. The Factorycast offer includes this level of web functionality as well as tools to configure processes to run in the Web Server device.
9
A Fig. 15 Web services
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9.7 9.8
The services offered by a higher class include all those supported by a lower one. The range of Transparent Ready devices is divided into 4 major families: - field devices (simple or intelligent) like sensors and pre-actuators. - controllers and PLCs; - HMI (Human/Machine Interface) applications; - dedicated gateways and servers. The selection table in figure 16 can be used to choose Transparent Ready devices according to the requisite service classes.
A Fig. 16
Selection table
9.8
CANopen bus
b General description
CAN (Controller Area Network) is a serial system bus developed by Bosch for the automotive industry. It was presented with Intel in 1985 and designed to reduce the amount of wiring in a vehicle (there can be as much as 2 km of wires in a car) by making control organs communicate via a single bus rather than dedicated lines, thereby reducing the weight of the vehicle. High immunity to electromagnetic interference combined with reliable real-time transmission caught the attention of industrials. In 1991, the CiA (CAN in Automation) consortium was set up to promote the use of CAN in industry (see the site: http://www.can-cia.de/). In 1993 the CiA published the CAL (CAN Application Layer) specifications describing transmission mechanisms without giving details on when and how to use them. In 1995 the CiA published DS-301 communication profile: CANopen. Several applications level 7 layers as in figure 17 are defined to the CAN standard: - CANopen; - DeviceNet; - CAL; - SDS; - CAN Kingdom.
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9.8
CANopen bus
In 2001 the CiA publication of DS-304 enabled integration of level 4 safety components on a standard CANopen bus (CANsafe). A description of CANopen technical features follows.
A Fig. 17
b Advantages of CANopen
v CANopen uses short frames
Because it has high immunity to electromagnetic interference (EMI), CANopen enables a machine or plant to work with precision, even in an atmosphere of high interference. The short CANopen frames and CANground connection offer the same capacities for every device connected to the network and protect them from electromagnetic interference (EMI).
When the network detects an error condition, first device status monitoring feature is the watchdog. Each diagnostic message contains the source and cause of the error, thus enabling a rapid response and a less time lost. A further diagnostic is developed to improve complex CANopen device diagnostics and uphold the network. In addition, there is an error log to help detection of random errors.
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9.8
CANopen bus
A Fig. 18
CAN operation
A Fig. 19
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9.8
CANopen bus
A CAN frame (C Fig.20) starts with a start of frame bit (SOF) followed by eleven identification bits, from the most to the least significant. The next bit is the remote transmission request bit, followed by 5 control bits and up to 8 bytes of working data. The control bits are: ID extension (IDE), a reserve bit and 3 bits of working data length code (DLC) in bytes. A frame check sequence (FCS) of up to 8 bytes follows the working data. The transmitter sends a recessive acknowledgement bit (ACK) which is replaced by a dominant bit by receivers which have received the frame with no error.
A Fig. 20
CAN Frame
The end of frame (EOF) bit denotes the end of frame transmission. The buss intermission frame space (IFS) bit must be recessive before the next frame starts. If no node is ready to transmit, the bus stays as it is. Bit codes have 2 values, dominant and recessive. If 2 nodes transmit at the same time, the receiver will only see the dominant value. In binary code, '0' is dominant and '1' is recessive. When a node transmits, it is always heard on the bus. If it transmits a recessive bit and receives a dominant one, it stops transmitting so it can continue receiving the dominant bit. This simple system prevents collisions on the CAN bus. The message with the smallest identifier has priority on the bus. CAN is a system bus with carrier sense multiple access, collision detection and arbitration of message priority (CSMA/CD+AMP). As collisions never occur, the CAN bus is often said to be CSMA/CA (carrier sense multiple access and collision avoidance). The message frame described in figure 21 is the base frame. For applications requiring more identifiers, there is the CAN extended frame format. The extended frame has 18 extra identifier bits in the header, after the control bits. This extends the range from 211 to 229 different identifiers. The two frame types can coexist in a single bus.
A Fig. 21
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CANopen bus
CAN has several means of detecting wrong messages: - the frame check sequence (FCS) contains the frames cyclic redundancy check (CRC). The receiver checks the frames CRC and compares the result against the FCS. If they are not the same, the frame has a CRC error; - the receiver detects errors in the frame structure. If the frame structure is faulty, the frame has a format error; - the receiver of a frame publishes a dominant acknowledgement bit (ACK) if it has received an error-free frame. If the transmitter does not receive this bit, it sends an error acknowledgement; - CAN uses non return to zero (NRZ) coding with bit stuffing. If the sender has to transmit 5 consecutive bits of the same type, it inserts another bit of the opposite type. Bit stuffing enables the receiver to synchronise with the bit chain. The receiver removes the stuffing bits from the data frame. If there are more than 5 consecutive bits of the same type, the receiver detects a stuffing error. There are several levels of protocol application that can be used with CAN, such as DeviceNet and CANopen. CAN itself does not define a protocol application level.
b Overview of CANopen
CANopen defines an application layer and a communication profile based on CAN.
v Properties
serial data transmission based on CAN; up to1 Mbps; efficiency approx. 57%; up to 127 nodes (devices); several masters allowed; interoperability of devices of different brands.
v Object dictionary
The object dictionary (C Fig.22) is an interface between the application program and the communication interface.
A Fig. 22
Object dictionary
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9.8
CANopen bus
Process data object (PDO) Process data objects (PDO) are used for their speed of process data transmission. A PDO can carry up to 8 bytes of working data, the maximum for a CAN frame. PDO transmission uses the CAN producer/consumer model extended by synchronised transfers. Synchronised PDO transfer relies on SYNC message transfer on the CAN bus. A PDO is sent in cyclic mode after a number (configurable from 1 to 240) of SYNC messages received. It is also possible to await availability of application process variables and send a PDO after the next SYNC message is received. This is called acyclic synchronised transfer. Service data objects (SDO) Service data objects (SDO) transmit parameters. SDOs give remote devices access to the object dictionary. There is no limit for the length of an SDO. If the working data cannot adapt to the CAN frame, they are divided into several CAN frames. Each SDO is acknowledged. SDO communication uses the point-to-point mode, with one point acting as server and the others as clients. Network management (NMT) Network management objects (NMT) change or check the status of CANopen devices (C Fig.23). An NMT message has a CAN 0 identifier. This gives NMT messages top priority. An NMT message always has 2 bytes of working data in the CAN frame. The first byte contains the encoded NMT command and the second the ID of the addressed node. A CANopen device starts at initialisation status when the ON button is pressed. When the device has completed its initialisation, it delivers a starting NMT object to notify the master. The collision detection protocol for monitoring device status is implemented with NMT objects.
A Fig. 23 Network management
Special function objects (SYNC, EMCY, TIME) CCANopen must have a SYNC producer to synchronise CANopen node actions. The SYNC producer periodically transmits the SYNC object. The SYNC object identifier is 128. This can lead to a delay caused by the priority of this message. An internal device error can trigger an emergency message (EMCY). The response of EMCY clients depends on the application. The CANopen standard defines several emergency codes. The emergency message is transmitted in a single CAN frame of 8 bytes. A CAN frame with the ID CAN 256 and 6 bytes of working data can be used to transmit the time to several CANopen nodes. The TIME message contains the date and time in an object of Time-OfDay type. Watchdog systems CANopen has 2 device status monitoring methods. One is a network manager which regularly scans every device at configured intervals. This method is called "Node guarding" and has the drawback of consuming a lot of bandwidth. The other is a message sent regularly by each device. This method uses up much less bandwidth than node guarding.
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9.8
CANopen bus
Network length and output rate The length is restricted by the output rate due to the bit priority procedure (C Fig.24).
Output (Kbps) Max. length (m) A Fig. 24 1000 20 800 25 500 100 250 250 125 500 50 1000 20 2500 10 5000
In documents on CANopen, the most common maximum length mentioned for an output rate of 1 Mbps is 40 metres, calculated without electrical insulation such as is used in Schneider Electric CANopen devices. When this insulation is included, the minimum bus length is 4 metres at 1 Mbps. However, experience shows that, in practice, the maximum length is 20 metres.
A Fig. 25
Limitations on branching devices must be taken into account and are set by the parameters in figure 25. (1) L max.: maximum length of branching device. (2) EL max. local star: maximum value of total length of branching devices at the same point when a multiport distribution box is used to create a local star topology. (3) Interval min.: Minimum distance between 2 distribution boxes. Maximum length of branching devices at the same point. This value can be calculated individually for each device: the minimum interval between two branching devices is 60% of the total length of devices at the same point. (4) EL max. (m) of total bus: maximum value of the total length of all intervals and branching devices on the bus.
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9.8
CANopen bus
A Fig. 26
CANopen compliance
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Table 27 shows the best possible product combinations based on the compliance classes.
Compliance class M10 M20 M30 A Fig. 27 Product combinations S10 Possible combination S20 Usage restriction S30
It is however possible to use a slave device with a master of a lower compliance class (e.g. S20 with M10) or a master device with a slave of a higher compliance class (e.g. M10 with S20), by using only devices supported by the lower compliance class.
9.9
A Fig. 28
Access to information on a CANopen device is available in read/write mode for a great many device control functions.
9.10
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9.10
A Fig. 29
AS-Interface
1 2 1 2
1 2 1 2
AS-Interface is identify by a yellow cable (C Fig.30) of a particular shape which makes inversion impossible. This cable is self sealing and sensors / actuators are equipped with punch through connectors allowing tool less connection or displacement. AS-Interface is exclusively a field bus of the master / slave type, master being a PC, a PLC or a controller which receives information form sensors and controls the actuators thorough the installation. AS-Interface has other benefits as a free topology which allows to operate in a star , point to point, line, tree, ring technology network.
9
A Fig. 30 AS-Interface components
During 10 years, AS-Interface was only suitable for discrete I/O. A few vendors had slow analogue devices i.e. temperature sensors; level sensors, but any time these were proprietary products and the number of addresses 0 to 31 was a major restriction. AS-Interface consortium has launched a new version (V2). With this one, the number of addresses has doubled with a possibility of 62 discrete I/Os per master. But the major change is the capacity to connect any analogue sensors / actuators to any master, trough an AS-Interface. Its is also possible to mix discrete and analogue devices. Although the number of slaves will be reduced, operation is still manageable.
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9.10
This new version introduced changes at the diagnostic level. The former version was only able to detect faults of the network. V2 version takes into account all defects including defects into the devices. Obviously, V2 and V1 operating on the same network are compatible.
Cost reduction
Safety
A Fig. 31
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9.10
b AS-Interface components
These are grouped into families (C Fig.32) For more information, please refer to the Schneider Electric product catalogues.
These enable any standard device (sensor, actuator, starter, etc.) to be connected to the AS-Interface. They offer wide freedom of choice and are especially suited to machine modifications and improvements previously done by conventional wiring. These interfaces are available for mounting in housings (IP20) or directly on the machine (IP67). Dedicated interfaces (communication modules, etc.) are used for communication with the AS-Interface cable. Dedicated components are embedded in an interface and can be connected directly the AS-Interface cable. This makes short work of wiring but the choice is not as wide as with generic components. This is the central component in the system; its function is to manage data exchanges with the interfaces and components (also called slaves) throughout the plant. It can take: - 31 interfaces or components in version V1 (cycle time 5 ms); - 62 interfaces or components in version V2 (cycle time 10 ms). The master is: - either embedded in a PLC, e.g. as an extension, - or connected the field bus, where it acts as a gateway. Extra-low voltage of 29.5 to 31.6V for interfaces and components powered via the AS-Interface cable. It is protected against over-voltage and short circuits. This is the only type of supply that can be used on an AS-Interface line. As the AS-Interface cable has restricted current, it is sometimes necessary to add a further supply for some circuits, in particular for actuators. The yellow cable connected to the power supply ensures two functions: - data transmission between master and slaves; - powering sensors and actuators. The black cable connected to the auxiliary 24V supply powers the actuators and the sensors with insulated inputs. The mechanical profile of the cables makes polarity inversion impossible; the materials used allow for fast reliable connection of the components. When a device is disconnected, e.g. for alteration purposes, the cable recovers its initial shape by self-sealing. These cables support 8A maximum and are available in two versions: - rubber for standard applications; - TPE for applications where the cable may be splashed with oil.
Flat cable
Safety solutions Standard process information can be transmitted at the same time and by the same media as information safety AS-Interface up to level 4 of standard EN 60954-1. (See section 6 on safety) Integration into AS-Interface by adding a monitor and safety-related components connected to the yellow AS-Interface cable. Safety information is only exchanged between the safety monitor and its components and is transparent for the other standard functions. This means a safety system can be added to an existing AS-Interface network. Addressing terminal As the components are connected in parallel on the AS-Interface bus, a different address must be assigned to each. This function is ensured by a terminal connected individually to each components.
A Fig. 32
AS-Interface components
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v Signal modulation
A Fig. 33 AS-Interface connection
AS-Interface has been designed to run without a terminal plug in any configuration. Operation principle uses current modulation based on Manchester encoding. Two chokes, inserted in the power supply convert this current in a sine wave. The shape of the generated signal avoid the use of shielded cables (C Fig.34).
A Fig. 34
A Fig. 35
AS-Interface limits
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v Protocol principle
Protocol principle is base on a single master protocol. The master send a request to all slaves in a row, these ones send the requisite data (C Fig.36). When all slaves have send an answer, a new cycle begins and so on. Cycle time depends upon the number of slaves and is easy to calculate.
A Fig. 36
AS-Interface use several means to guaranty the dependability of the data transmission. The signal is checked by the receiver; if the form is incorrect, the message is discarded. A check sum bit, added to a short message (7 and 14 bits), secure the logic content of the information. The master dead time causes the acknowledgement (C fig.37).
A Fig. 37
Length of a bit is 6 ms. At a rate of 166.67 Kbits/s, adding all the dwell bits, the cycle time cannot exceed 5082 s. Each cycle can be divided in 3 parts - data exchange, - system supervision, - updating / slave insertion. Masters AS-Interface profile tailors its actual capabilities. In general, it has the following functions: - initialise the system, - identify the connected slaves, - send the slaves parameters to the slaves, - check the integrity of the process data with the slaves, - monitor the system diagnostics (status of the slaves, status of the power supply etc.), - transmit all detected fault to the system supervisor (PLC, etc.), - reconfigure the system if any modification is made to it. Slaves decipher requests issued from the master and sent the answer with no delay. However, as slave will not answer to an incorrect or inappropriate request. Functional capacity of a slave is defined by its AS-Interface profile.
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A Fig. 38
System configuration
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Compatible Compatible
v Master profiles
Master profiles define individual capacities of every AS-Interface master. There are four profile types: M1, M2, M3, M4, the last one is compatible with the former versions.
v Slave profiles
All slaves have a profile, which means they are seen as ASIC equipped AS-Interface peripheral devices. Dedicated products as smart actuators, interfaces connecting traditional devices to the AS-Interface network are in this family. Profiles, similar to ID cards, have been defined to sort actuators and sensors in large categories. This is particularly useful when a slave has to be replaced i.e. tow actuators made by different manufacturers can be installed on the network with no change in the program or the address.
9.11
Conclusion
The use of networks for communication in industrial automation architectures increases their flexibility so they can fulfil the requirements for adapting machines or plants. To do so involves making choices necessitating specific knowledge of the right solutions out of a wide range of communication networks. Simple criteria should be used: products should be open, standardised and suitable. - An open network, as opposed to a proprietary one, leaves one free to choose suppliers of automation devices. - An internationally standardised network guarantees durability and upgradeability. - A suitable choice balanced between machine or plant requirements and network performance is the way to optimise the investment. The last point is the one which evidently requires exact knowledge of what is offered for communication networks, which have long been thought of as complicated to select, implement and maintain. Schneider Electric has decided to focus its offer on genuinely open networks based on international standards and adapted to requirements at all levels of automation architecture by defining implementation classes which keep choices simple and optimal.
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chapter
Data treatment and software
Presentation of actual architecture examples (schematics, products and softwares) Presentation of an application generator in a collaborative environment
Summary
1 2
10.1 10.2 10.3 10.4 10.5 10.6 Dfinition Introduction Programming, configuration and languages Application categories UAG: Application generators Definition of the main abbreviations used
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3 4 5 6 7 8 9 10 11 12 M
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236
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10.1 10.2
Definition Introduction
This section deals with the processing function discussed in the first section and includes a description of industrial software and its interaction with automation system processes. Unlike other sections, we shall not go into details about concepts such as systems, programming languages, etc. Many publications are available to the readers.
10.1
Definition
Programmable Logic Controller (PLC) is the name used for a programmable electronic device for controlling industrial systems by sequential processing. It sends operators (Operating Section or OS) commands based on input data (sensors), setpoints and a program. A PLC is a device similar to a computer and is used for instance to control machines on an industrial assembly line. A single PLC is enough to do what older automation systems did with hundreds or thousands of relays and cams. The people who program PLCs are called automated systems engineers.
10.2
Introduction
Programmable Logic Controllers (PLCs) were first developed in the 1970s. They were initially designed to deal with the sequential logic required to run machines and processes. At first with, their cost confined them to large systems. Major technological developments have radically restructured the processing function: - the languages have been unified and standardised; the IEC 61131-3 standard defines the different types; - the system approach is now widespread and the diagram principle has been superseded by function blocks; - digital systems are now widely used to process digital values as well as analogue values with prior analogue-to-digital conversion; - the cost of electronic components has dropped so much that PLCs can now be used instead of relays even in simple systems; - the communication buses used for data exchange are a competitive alternative to conventional wiring; - the software technology used in offices and business are increasingly used in industrial automation systems; - human-machine interfaces have also progressed in becoming programmable for greater flexibility.
234
10.3
b Standard languages
The International Electrotechnical Commission (IEC) has developed the standard IEC 61131 for Programmable Logic Controllers. Part 3 of this standard (IEC 61131-3) defines the programming languages: IL (Instruction List) is very similar to assembler language, working in close touch with the processor by using the arithmetical and logical unit, its registers and accumulators; ST (Structured Text) is similar to C language used in computing; LD (Ladder Diagram) resembles electrical diagrams and can quickly convert an old electromechanical relay program. This way of programming gives a visual approach to problems; FBD (Function Block Diagram) is a suite of blocks which can be linked together and perform any type of function from the simplest to the most advanced; GRAFCET (acronym for GRAphe Fonctionnel de Commande Etapes/Transitions or Step/Transition Control Function Chart) is an automation system representation and analysis mode particularly well adapted to sequential systems because it can be broken down into steps. In PLC programming, SFC can be used in a very similar way to G (Grafcet IEC848 became an international standard in 1988 with the name of Sequential Function Chart (SFC)). Behind each action there is an associated program written in IL, ST, LD or FBD.
10
235
10.4
Application categories
Technological progress impelled by user requirements has given rise to a wide range of PLCs which can feature: - hardware such as processing power, the number and characteristics of inputs/outputs, execution speed, special modules (axis control, communication, etc.); - software which, apart from the programming language, has higher functions and capacities for communication and interaction with other business software. These will be described through typical applications to help direct the readers choice. Our advice is then to refer to the individual documentation of each product. In the introduction to this guide, we looked at the principle of automation system architecture and implementation based on the customer profile. The solutions described can be divided into four categories. A - Electrician solutions Applications are simple, standalone and fixed. The choice criteria should be based on products that are easy to use, inexpensive and undemanding in maintenance. B - Automated/mechanical systems engineer solutions Applications are demanding with regard to mechanical performance (precision, rapidity, movement control, range changes, etc.). Their architecture and processing systems will largely be chosen for performance. C - Automated systems engineer solutions Automated systems are made complex by the volume and variety of the information to process such as adjustment, interconnections between PLCs, number of inputs/outputs, etc. D - Automated/production systems engineer solutions Automated production systems must be integrated into the plants management system architecture. They must interface with each other and exchange data with production and management software, etc. In figure 1, these categories are positioned over the implementations described in section 1 of the Guide to Industrial Automation Systems.
A Fig. 1
236
10.4
Application categories
b Electrician solutions
Simple solutions use a few electromechanical relays to run automation sequences. The latest generation of small PLCs are easy to use, competitively priced starting from a few inputs/outputs and offer new capacities without requiring any expertise in programming. Typical applications are in the following sectors: - industry: simple machines and additional functions in decentralised systems; - buildings and services: lighting management, access, control, premises surveillance, heating, ventilation, air-conditioning.
Automatic gate
Electric window
A Fig. 2
A Fig. 3
In the diagram (C Fig. 3), motor operation is governed by a speed controller. For discrete control, all it requires is a contactor linked to its thermo-relay. This unit comprises: - a Zelio Logic PLC; - 24V DC Phaseo power supply; - an Altivar 11 speed controller; - a GV2 motor circuit breaker; - an XVB light tower; - a Vario VCF switch. The variables of the speed controller (time, speed, control) can be set directly on the Altivar 11 or with Powersuite software. The Zelio can be programmed directly on the module or with Zeliosoft software installed on a PC. The latter option is illustrated by the screenshot in figure 4 which shows a logical process run by FDB (Function Block Diagram).
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A Fig. 4
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10.4
Application categories
Ventilation
Control of a ventilation system in an industrial building. Temperature measurement governs the starting and stopping of the system. Heating system control in a building.
Heating
Control of a fountain infrastructure of a service company. The system is remote controlled via a modem.
Control of filter cleaning The application controls in a water distribution and cleans the filter in a plant. water distribution plant with an air-cleaning sequence followed by clean water. The system can also be remotely controlled via a modem.
A Fig. 5 Examples with Twido PLC
v Typical diagram
The system is developed from a Twido PLC (C Fig.6) and controlled and viewed via a Magelis keyboard/screen. Security is ensured by an emergency stop on the main switch. The system is hardwired and the PLC controls the starter and the messages from the alarm module.
A Fig. 6
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Application categories
The following components make up the system: Hardware: - Twido Modular (PLC); - Phaseo power supply (PS); - TeSys-U Starter Controller (SC); - Magelis XBT-N (HMI); - Standard 3-phase motor. Software: - Twidosoft Version 2.0; - Magelis XBTL1003M V4.2. The screenshot in figure 7 of the Twidosoft program illustrates programming in Ladder which can be switched to List. The software includes a large set of instructions and an embedded browser is used to access all the objects directly.
A Fig. 7
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Application categories
A Fig. 8
v Applications
This configuration is suited to the following applications (C Fig 9).
Exemple
Dedicated machines
Conveyors
A Fig. 9
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Application categories
v Typical diagram
To make the illustration of this solution clearer, the power section and its supply are not shown figure 10. In the diagrammatic illustration, the system comprises:
A Fig. 10
Hardware - Controller Inside card installed in an Altivar 71; the speed controller is the master on a CANopen bus; - ATV31 and ATV71 speed controllers with built-in CANopen interface; - Lexium05 servo-drive with built-in CANopen interface. The HMI is managed by a Magelis XBT-GT graphic terminal and linked to the production cell by a Modbus link; - Advantys STB distributed input/output production cells. Software - PS1131 (CoDeSys V2.3); - PowerSuite for ATV31, ATV71 and Lexium05; - Vijeo-Designer V4.30 for Magelis; - Advantys Configuration Tool V2.0.
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Application categories
This type of automation solution is used in industrial processes where several machines are linked together or in infrastructures. Some examples are shown in the table figure 11.
Application Description Example
Handling equipment.
Used in a process with several conveyor systems and which uses external information.
Used for cutting and folding machines integrated into a production line.
Used for water circulation and refrigeration systems governed by external measurements such as output rates.
A Fig. 11
v Applications
We do not intend to describe an application from end to end, but to illustrate its working principle we will make a description of a significant part of it. A Premium PLC is used to control a local production cell (C Fig.12). This is a platform made up of Advantys STB inputs/outputs, four speed controllers and external input/output modules. Each element is connected to a CAN bus. This implementation can easily be expanded by adding more speed controllers and inputs/outputs. The PLC is linked to the production cell by a Modbus/TCP bus. The controllers and motors are powered from a 230VAC network. Another source is used for a 24VDC supply.
A Fig. 12
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Application categories
- 3-phase squirrel cage motors. Software: - Unity Pro V2.0.2 (PLC), - Advantys configuration software V1.20 (I/O cell), - PowerSuite V2.0 (ATV31 speed controller configuration).
A Fig. 13
Main features of Unity Pro - Windows 2000/XP graphic interfaces; - Custom icons and toolbars; - user profiles; - graphic design of hardware configurations; - integrated PL7 and Concept converters; - automatic generation of synchronisation variables on Ethernet (Global Data); - 5 native IEC61131-3 languages supported with graphic editors; - integration and synchronisation of program editors, data, user function blocks; - drag & drop reuse of library objects; - XML import/export and automatic data reassignment; - automation of repetitive tasks by VBA macros; - plug & play Hot Standby redundancy system. Unity Pro offers a comprehensive set of functions and tools to match the structure of the application to the structure of the process or the machine. The program is divided into functional modules which, assembled with hierarchical priority, form the functional view and contain: - program sections; - animation tables; - operator screens; - hyperlinks. The basic functions, used repetitively, can be encapsulated into user function blocks (DFB) in IEC61131-3 language. To create an application reference database, Unity Pro supports project and application libraries locally or on server. It has around 800 standard function, and can be enhanced with customers standards (variables, data types, function blocks).
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Application categories
It also includes: - symbolic variables independent of the physical memory; - structured user-defined data types (DDT); - DDT and DFB function block version management in the library; - a library of pre-animated graphic objects for operator screens; - read/write protection of programming data to prevent any modification; - function block development available in C++ with the Unity EFB Toolkit option. Put in libraries on a local PC or a remote server, the application objects and their properties are used and shared by all programs and any changes made to an object in a library is effective in the programs that use it: - the functional modules can be used in the application or between projects by XML import/export; - function blocks are instantiated by drag & drop from the library; - all instances automatically inherit library changes (as the user chooses); - graphic objects for operator screens are selected and configured by drag & drop. A PLC simulator on PC is integrated into Unity Pro and is used to finetune the application as much as possible before it is commissioned on site. It exactly reproduces the behaviour of the target program. All the debugging tools can be used in simulation: - step by step program execution; - sreak and view point; - dynamic animations to view the status of variables and the logic in execution. Operating screens facilitate debugging by views representing variable status in graphic object form: indicators, trend curves, etc. The same as for configuration, application-specific modules have special screens to debug them: the functions available are adapted to the type of module implemented (discrete, analogue, counter, communication I/Os, etc.). Operator actions are logged and archived in a standard secured Windows file. Hypertext links are used to link the application to all the documents and tools required for operation and maintenance. Diagnostics tools Unity Pro provides a library of application diagnostic DFBs. These are integrated into the program and, depending on their function, are used to monitor the permanent safety conditions and the progress of the process. A viewing window displays any system and application defects explicitly and chronologically in real time from the source. A click on the window opens the editor of the program where the error was triggered (search for conditions missing at the source). Online changes can be grouped consistently in local mode on a PC and transferred directly to the PLC in one operation to be included in the same cycle run. Hypertext links integrated into the application give remote or local access to working resources (documentation, additional tools, etc.) to cut stopping time. There is a full range of functions to control operations: - unity Pro operator action log in a secured file; - user profile with a choice of accessible functions and password protection.
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Application categories
Operating screens and functional views for direct graphic access to application elements (C Fig. 14). The Unity client/server architecture gives access to the software resources via programming interfaces in VBA, VB or C++; here are two examples: - automation of repetitive tasks (input, configuration, translation, etc.); - integration of specific applications (code generator, etc.). Cross-software exchange The XML format, the universal W3C standard for data exchange via the internet, is used as the source format for Unity applications such as variables, programs, inputs/outputs, configurations, etc. (C Fig. 15). Simple import/export is used to exchange all or part of the application with other software in the project (CAD, etc.). Unity Developer's Edition (UDE) and its programming interfaces in C++, Visual Basic and VBA can be used to develop custom solutions such as interfaces with electrical CAD, a variables generator, a PLC program or repetitive design task automation. Many software publishers use UDE to simplify data exchange with Unity Pro; here are some examples (C Fig. 16).
A Fig. 14
Domain Electrical CAD Electrical CAD Electrical CAD Electrical CAD Electrical CAD Process Simulation Change Management Application Generator SCADA/Reporting SCADA SCADA Graphical User Interface SCADA SCADA MES Historian/RtPM Web Services A Fig. 16
Company ECT EPLAN IGE-XAO AutoDesk SDProget Mynah MDT Software TNI Iconics EuropSupervision Arc Informatique ErgoTech Areal Afcon Tecnomatix/UGS OSISoft Anyware Sofware publisher using UDE
Product Promise EPLAN SEE Electrical Expert AutoCAD Electrical SPAC Automazione Mimic AutoSave Control Build GENESIS BizViz Suite Panorama PCVue32 ErgoVU Topkapi P-CIM XFactory PI PLC Animator
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A Fig. 15
10.4
Application categories
Compatibility with existing applications PL7 and Concept IEC61131 applications are imported into Unity Pro by an integrated converter as a standard feature. Operating system update provided with Unity Pro is available for most Premium and Quantum PLC processors. Existing I/O peripherals, application-specific, communication and field bus modules remain compatible with Unity Pro.
A Fig. 17
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10.4
Application categories
the corporate level is characterised by a very large flow of information. Office automation and internet standards are now basic requirements. The software is run on PC or on more powerful servers; the shop floor level is mainly characterised by supervisory tools and the PLCs which govern the process. Ethernet is now the standard means of communication between the computer and PLC domains; the machine level where the principle of real time conditions the choice of communication tools. Tasks are allotted to industrial PCs and PLCs, links are made by field buses (CANOpen for Schneider Electric) or by Ethernet associated to specific application layers; the sensor level where hardwired links compete with the ASi bus which is particularly well suited to this kind of use.
A Fig. 18
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The Unity Pro software workshop has already been described so we will devote the next paragraph to UAG and how it works.
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10.4
Application categories
Several additional software tools have been developed to ensure collaboration. The table figure 19 describing their functions is followed by a brief explanation of how they work. The main computing standards such as Ethernet TCP/IP, Web, OPC, SOAP, XML, etc. are used to facilitate vertical collaboration at every corporate level and offer: - more visible information in real time; - interoperability between the process and the information systems (MES, ERP, etc.); - exchange with design tools such as CAD.
Components Unity Pro UAG Unity Application Generator UDE Unity Developer Edition OFS OPC Factory System Factory Cast Web Environnement CITEC SCADA AMPLA Ethernet card Organisation of additional configuration and setting software XBT L1000 Vijeo designer Vijeo Look Power Suite A Fig. 19 HMI creation HMI creation Mini SCADA Configuration of Altivar speed controllers and Altistart and Tesys U starter units Complementary software tools Function Single PLC application development workshop in a collaborative environment Object-oriented multiple PLC application development and SCADA Complies with standard ISA S88 Software for development in VBA, VB and C++ programming languages Schneider OPC server to interrelate the desktop and PLC environments Ensure that information passes between a PLC environment and a desktop environment SCADA software MES software Cards using Factory Cast services
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Application categories
Ethernet cards
The ranges of Ethernet cards offer modern architectures open to different current software technologies and provide users with tools to build their own functions. This makes it possible to organise objects in a way fully compatible with MES and ERP IT environments.
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A Fig. 20
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b UAG operation
Unity Application Generator is made up of three tools (C Fig.21). Tool SCoD Editor. Field Libraries. Library Specification of control modules, DFB or EFB import, attribute specification and screen configuration definition (within UAG). Definition of user profiles in a project including: naming rules, hardware specification catalogues, libraries. Project design, functional analysis and application generator.
Projet
UAG tools
Control modules are defined and used in type libraries; the SCoD editor is the tool which creates, updates and groups specific customer controls in the objects (Smart Control Device). Definition of rules and properties in the SCoD editor based on the DFB/EFB interface includes: - graphic user interface (GUI); - mandatory configuration of the SCoD instance; - optional configuration of the SCoD instance; - SCoD instance inheritance; - simple and complex relations inherited by the selected module and other ScoDs; - definition of data transmitted to and from the HMI; - definition of data related to the topological model; - specific HMI information such as alarm texts, measurement units; - access levels: - per module reference to specific HMI information such as ActiveXs and symbols; - per module reference to specific PLC information such as DFBs/EFBs; - SCoD documentation.
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An example of a Smart Control Device could be a valve. A valve is generally used as a cut-off device to prevent or allow the flow of a fluid or gas in a pipe. It is usually linked to three digital signals: - limit switch open or closed (2 signals); - the signal for the actuator. There are many different standard valves ranging from the smallest actuated by solenoids to the largest actuated by motors.
A Fig. 23 Screen shot of UAG editor
The properties are assigned for the type of valve from the PLC interface (API). The default valve insert mode is Energise-to-Open, though the user can specify Energise-to-Close. The Travel Time-out operating time must be within the [min Value.. max Value] interval. Figure 23 shows a screenshot of the editor.
A Fig. 24
v Application generator
Unity Application Generator is a design and functional analysis program generating applications for PLCs and SCADAs (C Fig. 25).
A Fig. 25
Screen shot UAG physical model and control model parameter setting
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There are two independent tasks to generate the physical and topological models: - The physical model describes the process in a tree structure of elements as shown figure 25. - The typological model describes the hardware of the automation process, including the PLCs, inputs/outputs, networks, PCs, etc. as shown figure 26.
A Fig. 26
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chapter
Equipment manufacturing
Presentation: Step by step manufacturing Quality rules Relevant standards
Summary
1 2
11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 Equipment design Choice of supplier Drafting diagrams and programs Programming methodology Choice of technology Equipment design Building an equipment Mounting Device fitting tools
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11.1
Equipment design
Automated systems use equipment that implements products to facilitate the installation, wiring and connection of automation components.These products have to comply with local and international standards as well as safety standards for the protection of people and property. Equipment is built in 3 stages: - design (diagram, program writing, choice of material, installation study); - construction (assembly, wiring, tests, housing); - installation (wiring, connections, commissioning). To complete these three stages satisfactorily, thought must previously be given to: - the understanding of potential problems which could have an impact on the safety and/or availability of the equipment; - implementation of preventive actions and/or alterations to the initial automation diagram; - the capacity of any subcontractors to comply with the requirements; - the compliance of the equipment with the requirements. The purpose of this section is to describe the rules for implementing automation system components and the Schneider Electric products which can be used to build them. A methodology and good engineering practice based on experience for each of the three stages make it possible to build reliable and cost-effective equipment.
11.1
Equipment design
Successful construction of automation system equipment basically depends on the understanding of exact specifications. The design tools, diagram drawings, choice of components and their installation can differ according to the complexity of the system and the choices made by the service provider. Besides this, while a simple standalone machine may be adequately equipped by a mechanic and an electrician or automation system engineer, equipping more complex machines for production cells or process runs often requires the work of multidisciplinary teams. This implies project management and is beyond the scope of this publication.
b Specifications
Specifications for the control section must include all the requisite elements for the project. They are closely tied to the specifications for the operating section (mechanics and actuators). The information they contain is used to: - choose the solution to implement; - build the equipment itself; - run operating tests; - define costs and schedules; - refer to for acceptance. To clarify customer requirements, it is preferable to structure the specifications as follows: - general aspects: overview of the application, standards and recommendations, any material constraints; - characteristics of the power supply, etc.; - use: layout of control devices, operating modes, frequency of use, etc.; - functional features: functions to perform, possible extensions, manmachine dialogue, peripheral devices, etc.; - environment: temperature, hygrometry, vibrations, shocks, corrosive atmosphere, dust, etc.; - special software: diagnosis help programs, supervision, communication protocols, etc.; - adjustment: type, procedures, identification; - on-site acceptance test procedures; - accompanying documents; - any other information which could affect the equipment-building process, such as packaging for transport.
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11.2
Choice of supplier
To build equipment, the order initiator is advised to select a panel builder with ISO9000 certification. Using a certified supplier will simplify discussions, cut down on checks, ensure an up-to-date equipment file and problem-free commissioning and facilitate maintenance. This helps to control costs.
b ISO9000 standard
Equipment is increasingly sophisticated, technologies ever more critical and statutory requirements more and more severe. All this can make it much harder to control events by reason of their complexity. The order initiator must be certain that when the equipment is built, it will correspond exactly to the specifications and that all the requisite precautions have been taken. In particular, the inevitable changes occurring during the manufacturing must be perfectly understood and applied by the panel builder, the staff involved in the process must be properly trained and non-compliant products must be identified and set aside. This implies the development of an ongoing Customer-Supplier relationship. The supplier must provide the customer with proof of competency and skill regarding the quality of the offer and control of the production process. The customer must be assured of the suppliers capacity to perform these undertakings which only stringent organisation can ensure. The ISO9000 standard and certifications are designed to facilitate this customer-supplier relationship by quality management.
b Quality management
Quality management means what an organisation does to ensure that the product, in this instance the equipment built to the customers specifications, complies with requirements when it leaves the suppliers workshops. The way an organisation manages its processes cannot fail to affect the final product. The ISO 9000 series focuses on knowing whether everything has been done to ensure a product meets customer requirements. The international ISO9000 standard is a generic one covering ISO 9001, 9002 and 9003. The difference between ISO 9001, ISO 9002 and ISO 9003 is confined to the field of application: - ISO 9001 sets requirements for organisations with a business ranging from design and development to production, installation and related services; - ISO 9002 is the standard for organisations that do not design or develop. It sets the standards for production, installation and related services; - ISO 9003 is the standard for organisations that basically use inspections and tests to ensure that end services meet specified requirements. The order initiator will choose the panel builder whose organisation best matches the services required. An ISO 9002 certification is usually the requisite minimum. The choice of the order initiator will be made after examining the Quality Manual of the supplier(s) involved. This describes the organisation and management system adopted by the company.
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11.3
b Stop/start modes
The stop/start modes of an automation system are analysed by the AIADA and classified in a graphic guide called GDOSM which is used, regardless of the control technology, to define the operating modes or statuses of the system based on a specific vocabulary, possible links between the modes or statuses and upgrading conditions.
b Failure procedures
These cover the operation of the machine in the event of a problem: - emergency stop; - degraded operation, etc.
b Operating safety
v Standard requirements
The operating safety of an automated system is its capacity to operate: - without danger to people and property (safety); - without hindering production when a failure occurs (availability). Safety should be viewed as an aspect of risk analysis, legislation and relevant standards. It is examined through a risk evaluation procedure applied successively to the product, the process (operation and control) and utilisation. For further information on this topic, please refer to Machine safety Parts 1 and 2 distributed by Schneider Training Institute. European legislation is based on the machine directive (89/392/EEC) defining basic requirements in design and construction of industrial machines and installation for free circulation of these goods in the European Community.
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11.3
v Analysis tools
Analysis tools such as FMECA (Failure Modes, Effects and Criticality Analysis) can provide a systematic approach to all aspects of failure and provide suitable solutions. FMECA is designed for evaluating the impact or criticality of failure modes in system components on the reliability, sustainability, availability and safety of the system. The FMECA method lists the failure modes of components and sub-units and evaluates the effects on all the functions in a system. It is widely recommended throughout the world and consistently used in all hazardous industries (nuclear power, space, chemical, etc.) for making preventive analyses of operating safety. Before an FMECA analysis can be run, the system and its environment must be accurately understood. This information is usually obtained in the results of the functional analysis, risk analysis and any feedback. Next, the effects of the failure modes must be evaluated. To find the effects on a specific entity, the components directly interfaced with it are examined first (local effect), and then gradually out to the system and its environment (global effect). It is important to note that when a specific entity is examined for a specific failure mode, all other entities are assumed to be in their rated operating condition. FMECA is based on the well-established fact of non-simultaneous failures. The third step is to classify the failure mode effects by their level of criticality in relation to certain operating safety criteria predefined for the system according to the requisite objectives (reliability, safety, etc.). The failure modes of a component or sub-unit are grouped by the criticality level of their effects and prioritised accordingly. This typology helps to identify the most critical elements and propose the strictly necessary actions and procedures to remedy them. This process of results interpretation and recommendation implementation is the final step in FMECA. To keep FMECA to the strictly necessary and control the number of entities to examine, it is advisable to run functional FMECA analyses. This helps to detect the most critical functions and thus confine the physical FMECA to the components that perform all or part of the functions. FMECA methodology ensures: - a different view of the system; - means of thought, decision and improvement; - information to use in operating safety examinations and remedial action.
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11.4
Programming methodology
Programming methodology
b Programming organization
Industry uses more and more software programs for its production purposes. There is such a wide variety of these applications that understanding the place of each in its environment is a very complex matter. The need to interface programs requires a collaborative approach from the outset of new production unit design. The design must be analysed throughout as it is intended to implement a series of activities which, starting from a request for process automation (which can range from a simple vocal question to full specifications) to devise, write and finalise software programs ready for their delivery to the customer. Generally speaking, software design involves 3 major phases: - functional analysis or design (C Fig.3); - specifications; - design.
v Programming tools
All these constraints lead to the creation of a modern, innovating software workshop designed to achieve the required results. The term integrated development environment (IDE) is used to mean a set of software programs which can themselves produce industrial automation programs. The activities an IDE covers are usually: - general project design, building stages or phases; - data and program subset naming conventions; - data structuring; - assistance for writing programs in different languages; - compiling or generation; - assistance for tests and correction monitoring; - subset libraries that can be reused in other projects; - documentation; - management of successive versions or variants of individual programs; - assistance for commissioning. An IDE facilitates collaboration between programmers and subsequent program maintenance by promoting the use of common methods.
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11.5
Choice of technology
The technologies available for building automation system equipment are mainly electromechanical, pneumatic or electronic (PLCs, microcomputers, standard or specific electronic cards). Networks and field buses have gained ground in equipment construction and have a great effect on the choice of materials. For more information, please refer to Field buses distributed by Schneider Training Institute or Cahier Technique N CT197: Field bus: a user approach. There are three choice criteria: - feasibility criteria to eliminate technologies which could not meet the specifications; - optimisation criteria designed to minimise overall costs during the equipments lifecycle (procurement, implementation, flexibility, fixed assets, production management, maintenance, etc.); - financial criteria for building the equipment at optimal cost. Eventually, preliminary FMECA can be used to help select the best suited technology.
b Choice of components
A range of constraints should be considered: - ambient temperature (which may derate the material), dust, vibrations, etc.; - coordination of devices making up the power outputs; - discrimination between protection devices up to the main circuit breaker; - requisite machine cycle time; - number of operating cycles; - category of use (AC-1, AC-3, etc.); - standards (petrochemical, electrical, marine, etc.).
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11.6
Equipment design
b Computer-Aided Design
Software tools can be of great assistance in the field of automation system design. Apart from building the diagram, the designer can use them throughout the project, from the record of the customers request for a quotation to commissioning and maintenance assistance. This way of proceeding not only boosts productivity in system design, it also improves the quality of the diagrams and programs and facilitates their upgrading. The main features of CAD software are:
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v Computer-aided
This is more aimed at services specialising in automation system equipment studies. The installation tool in the CAD software offers overall dimension transfers based on the diagram and a Hardware Database.
v Manufacturing file
The complete file should be compiled before manufacturing starts. It defines: - the list of all documents in the contents; - boxes: installation, drillings, parts, etc.; - cabinets: installation, framework plan, drillings, etc.; - control stations: drillings, parts, etc.; - electrical diagrams; - programs; - hardware list; - overall dimension.
11.7
Building an equipment
Many electrical equipment manufacturers develop auxiliary components to implement their products. This is the case of the Telequik system offered by Telemecanique (C Fig.1). This system contains all the products required for building equipment and ensures that the components of an automation system are quick and easy to implement. Given their features, we have classified the products in it into four different functions to Enclose, Structure, Distribute and Connect.
b Enclose function
To protect the hardware from shocks, severe weather and ensure it can resist the most stringent conditions of use in industry, the equipment must be housed in boxes or cabinets. These should have all the features required for cutting down assembly and maintenance time. Depending on the degree of protection needed, enclosures comply with defined standards and IP (International Protection) codes. The IP code is described in the 60529 document published by the International Electrotechnical Commission.
A Fig. 1 Telequick pre-slotted plate by Telemecanique
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It uses an alphanumerical method to define the level of protection the enclosures provide against the approach of dangerous parts, penetration of solid foreign bodies and the detrimental effects of water.
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11.7
Building an equipment
The first figure from 0 to 6 indicates simultaneously the protection of persons from dangerous parts and protection from penetration of foreign bodies. The second figure, also 0 to 6, indicates protection from water splashes. The additional letters indicate further protection such as internal baffles. Cahier Technique CT 166 Enclosures and levels of protection gives a detailed description of the codes and the stringency of the corresponding tests. The builder is responsible for end product compliance with standards, but the enclosure manufacturer documentation must specify where the hardware must be fitted to ensure the stated levels of protection are maintained. The installer who connects (wiring) and attaches the cabinets and in some cases adapts the auxiliary components (push buttons, measuring devices, etc.) must also ensure the specified level of protection is maintained. Schneider Electric offers an entire range of boxes, cabinets and parts compliant with IP standards (C Fig.2).
b Structure function
A Fig. 2 Telemecanique AA3 cabinet
To bind the components together mechanically, there is a range of perfectly adapted products to assemble and attach automation system components firmly. Put together, these products make up the structure of the equipment and their assembly systems provide great flexibility of use, a wide choice of assembly options and significant cost savings in implementation.
b Distribute function
v Electrical power distribution
When building equipment, product implementation must comprise safety, simplicity and fast assembly and wiring. Maintenance and any modification to the equipment must be easy to perform, with the least possible impact on operating continuity. To meet these criteria, there are distributors basically designed to shift the main current to a number of secondary circuits (see the Schneider Electric general catalogue for more information). Some models are designed as product supports so it is possible to intervene on live equipment (e.g. connection or disconnection of a motor starter unit). This is notably the case with the Telemecanique TegoPower technology (C Fig.3).
A Fig. 3
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11.7
Building an equipment
v Connect function
A Fig. 4 Interface ABS2
This function covers the products required for wiring and connecting equipment. Terminal blocks (C Fig.5) These comply with TEU standards and the major certification requirements. They are made of coloured nylon enabling them to be used at temperatures ranging from -30 to + 10C. Their fire-resistance complies with the standard NF C 20-455. They are identified by characters on clip-on strips and are designed for connecting conductors with a maximum section of 240 mm2. They cover all needs: - a wide range of currents, from a few amperes (control, signal electronic circuits, etc.), to several hundred amperes (power connections); - fixed or detachable single- or multiple-pole blocks; - screwed, bolted, clipped, welded or spring connections; - blocks for special functions such as fuse or electronic component holders, draw-out terminals, overload conductor connection, etc.; - mounting on rails, pre-slotted plates or printed circuits. Cable ends Cable ends have a number of advantages: - easier wiring, as the copper sleeve is crimped automatically when the connection is fitted in the terminal; - perfect resistance to vibration; - wire strands cannot creep; - timed saved in connection work; - the same marker tag holders and markers for all cable sections. Each holder can take up to 7 marking rings (letters or digits). Telemecanique cable ends also have: - a different collet colour for each section; - 3 sleeve lengths depending on the model. There are insulated cable ends: to standard NF C 63-023 - without tag holders for sections from 0.25 to 6 mm2; - with built-in tag holders for sections from 0.25 to 6 mm2; - with removable tag holders for sections from 4 to 50 mm2; to standard DIN 46228 - collet colour per section different from the French standard; - without tag holders for sections from 0.25 to 50 mm2. Cable clips and ducts Cable clips and ducts are designed to channel wires into horizontal and vertical layers on the same plane as the devices. All the wiring is on the front facing, so repair work and alterations are made easier. They are made of PVC and have no metal parts that can come into contact with the conductors they hold.
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A Fig. 5
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Ducts (C Fig.6) These have open slots in the sides and perforations at the back. They are fitted vertically or horizontally on feet with quarter-turn fixing devices. These can be clipped to combination or omega rails of 35 mm and to preslotted plates. Ducts are available in several sizes and can hold up to 700 wires of 1.5 mm2. They are closed with covers that slot into them. The same tag holders can be used for ducts and cable clips.
A Fig. 6
Telemecanique duct
11.8
Mounting
Automation system and distribution components are designed to be mounted on chassis or frame structures. This sub-section describes a few definitions, useful tips or rules and draws attention to the precautions to take in mounting work.
b Chassis
This consists of two pre-drilled vertical uprights, with or without notches. The device, depending on its mounting system, is either clipped or screwed to: - horizontal rails; - pre-slotted plates; - solid plates; - a combination of plates and rails. Depending on the dimensions of the rails or plates and, above all, the mass of the device, it is advised to use: - combination or omega rails of 35 mm; - omega rails of 75 mm; - "C" uprights to support the devices instead of horizontal rails; - pre-slotted plates stiffened at the back with a horizontal rail. Chassis are usually mounted in monoblock cabinets or boxes.
b Frame
This is a unit consisting of one or more chassis side by side or back to back, held to the floor by a cross piece/foot or hung on the wall by the top of an upright. It can also be installed in and linked to a cabinet the upper part of which is equipped with horizontal busbars to power each chassis.
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11.8 11.9
b Device mounting
The following general rule should apply when mounting and attaching devices to chassis and frames: attachment should always be possible from a front access. Since equipment is nearly always in a box or cabinet, such access makes it much easier to carry out any alterations or additions to it.
K M2
A Fig. 7a
A Fig. 7b
11.9
b Wiring
The wiring procedure by explanatory circuit diagram works by systematic use of the device terminal markings represented on the circuit diagram. It applies to the power and control circuit wiring of all equipment with contactors, regardless of complexity. This wiring procedure saves time for the user. The circuit diagram is noted for: - execution speed: time saved in design; - clarity: simple illustration of electrical circuits; - easy understanding: intuitive wiring; - operational efficiency: easy comprehension, searches, modifications and servicing. It can be accompanied by a hardware layout and installation plan to help locate components and by an external connections diagram.
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The purpose of platform tests is to correct any errors made when building the equipment and make adjustments prior to commissioning. The following points must be checked: - the hardware is the same as specified in the plans and is correctly mounted; - the wiring is the same as in the diagrams; - operation complies with the specifications. Some of these checks must be made with live equipment, so the following points are mandatory: - platform tests must always be run by trained personnel qualified to work with live electrical equipment; - all the requisite precautions must be taken to ensure the safety of persons in compliance with current legislation..
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b Insulation test
The quality of insulation is measured in meg-ohms (= 106 ) with a megger. Insulation is measured: - between two conductors insulated from each other; - or between a conductor insulated from the earth and frames and from earthed frames. Sensitive devices and circuits are disconnected before checking the insulation of each circuits wiring between terminals and between terminals and the earth. Likewise, the insulation of break device conductors is checked on both sides. The figure 8 gives the voltage values for measuring insulation and the isolation resistance to be reached.
Rated voltage of circuit < 48 V Voltage from 48 to 500 V Voltage higher than 500 V A Fig. 8 Insulation voltage test Insulation test direct voltage 250 V 500 V 1 000 V Isolation resistance 1n M Equal to or higher than 0.25 Equal to or higher than 0.5 Equal to or higher than1
b Dielectric tests
These are designed to test the dielectric rigidity of a device unit at an alternating voltage defined according to the circuits rated insulation voltage. Dielectric rigidity is expressed by resistance to a test voltage applied between active conductors and the chassis frame. The test is considered satisfactory when there is no breakdown or flashover. The device used is a flashover bridge delivering an alternating voltage that can be adjusted to a frequency between 45 and 55Hz. It can provide high voltage with a very weak current. When it is applied, the test voltage must not exceed 50% of the value indicated in figure 9.
Rated insulation voltage < = 60 V Voltage from 61 to 300 V Voltage from 301 to 660 V A Fig. 9 Dielectric voltage test Dielectric test voltage (RMS voltage) 1 000 V 2 000 V 2 500 V
It is then gradually increased until it reaches the specified value a few seconds later. This voltage is maintained for one minute. When the equipment includes electronic devices, dielectric tests cannot be run afterwards but must be run during the mounting and wiring process to prevent any destruction.
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v General test
The general test involves simulating all the operating phases of a machine or process in the order they are supposed to run and checking the servosystems and safety. An adequate power supply must be provided and the interconnections and connections made with the test benches which replace the external control auxiliaries by switches, push buttons, etc. The purpose of the general test is to ensure that the equipment operates as described in the specifications. It is also designed to check the effect of an operating error in machine or process control, of an impaired external control element (limit switch, detector, etc.). The programs are loaded in the PLCs and tested as fully as possible by simulating discrete inputs by contacts and analogue inputs by signals. This simulation is used to correct any programming error and substantially reduce the time required for commissioning. For equipment with electronic speed controllers, simulation should include a dynamic test using the installations motors or, failing this, a test motor, preferably with comparable ratings. It is advisable to draft a test report mentioning the adjustments (values) and alterations (programs and hardware) made, as well as any elements that could not be tested or were only partly tested. This document will help to make commissioning work easier. The diagrams, listing and product lists should be altered to give an exact description of the equipment that is to be commissioned. Cabinets and boxes are unwired before shipping. If necessary, heavy parts are wedged to prevent frames and cabinets from warping during transport. The bases of cabinets should be thoroughly cleaned to prevent any foreign bodies (washers, wires, etc.) from getting into the devices.
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b Installation
v Upon receipt of equipment
Check that: - the enclosures have not received any shocks; - the mobile part of the rotating contactors has not been warped or shifted; - no foreign bodies have entered the air gap in the magnetic circuit, between the contacts or terminals; - the mobile part of the contactors and disconnectors and the overload relay trip devices work freely; - the closing devices (boxes, cabinets) work properly; - seals are tight (for proofed hardware); - the control and signalling auxiliaries and the measuring devices on the doors are in good condition; - the shipment includes up-to-date diagrams, commissioning instructions, operator manuals and any platform test reports. Before connecting external conductors: - check the voltage and frequency of the power supply to the power and control circuits; - check that the type and gauge of fuses and protection relays are properly adapted to the receivers to protect.
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Thermal overload relays are compensated, so there is no need to make adjustments for ambient temperature within the limits indicated on the technical data sheets. These adjustments are usually made on the platform and are indicated in the test report. When the power line and all the external power and control circuits are connected, general tests of the equipment can be made. These are run in two steps:
b No-load test
This test is run to check that all the connections (control and signalling auxiliaries, sensors, safety switches, etc) have been made correctly and in compliance with the diagram. To run it, the power to all the receivers must be cut off: - by removing the fuse cartridges protecting the power circuit from their base; - or by powering the control section only and leaving the power section off. When the control circuit is powered, an action on the starter control auxiliary should stop the contactor(s) it governs and, on more complex equipment, start the automatic cycle. At this point, it is advised to operate external devices manually (particularly safety devices) or simulate their operation, then deliberately and methodically trigger every control and operation anomaly to check the efficiency of the control, servosystem, safety and signalling circuits.
b On-load test
Now, turn on the power circuit to run a general on-load test to check the exactness of the connections and receiver operation. This test can be completed by a series of further ones to check the automatic equipment governs the installations mechanical functions properly. Successful commissioning is the result of the operators experience along with the contents of the equipment file (automation system lists, commissioning instructions, device manuals, etc.).
b Troubleshooting
The wide variety of automation equipment makes it impossible to define a troubleshooting procedure that applies to all diagrams. Experience and knowledge of the equipment and its functions are indispensable to an efficient troubleshooting. Knowledge of the FMECAs carried out at the design stage can be very useful when seeking the reason for failures.
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Equipment maintenance
At the design stage, FMECAs are used to define maintenance operations and their intervals: - motor brush replacement when applicable; - filter cleaning; - wear part replacement; - consumable item provisions, etc. Electronic and electromagnetic devices require practically no maintenance. However, a few important points should be noted.
v Contactor coil
If a coil has to be replaced (such as when the control circuit voltage changes), the new coil must be defined according to the actual control circuit voltage. It then ensures: - closing of the contactor when the voltage reaches 85% of its rated value; - opening of the contactor when the voltage drops below 65% of its rated value; - permanent tolerance of voltage corresponding to 110% of the rated value. A coil can be damaged due to: - incomplete closure of the magnetic circuit caused by a mechanical incident or a control circuit voltage of less than 85% of the rated value. In alternating current, this lowers the reluctance of the magnetic circuit and, in direct current, destroys the efficiency of the consumption control system where the contact has not opened. It also prevents there being adequate pressure on the poles, which overheat and can weld if the current crossing them is the one absorbed by a motor during starting; - a poorly adapted control circuit; - a power voltage greater than 110% of the rated value. In all cases, the coil will deteriorate if the energy dissipated by Joule effect is higher than normal. To prevent such incidents, use coils adapted to the voltage measured at the equipments power supply terminals.
v Contactor poles
Knowledge of controlled power and the category of use (such as disconnecting a running squirrel-cage motor) helps to ascertain the electrical durability of the contacts in an individual contactor or to choose a contactor on the basis of the intended operations.
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Equipment maintenance
v Block contactor
Block contactor poles need no maintenance. For example, in category AC-3, a contactor powering a compressor motor that starts 6 times in an hour and operates 24 hours a day will have a lifetime of: 2,500,000 = 17,360 days, i.e. about 50 years without maintenance. Contacts that have made many breaks may appear to be worn. Only regular checks of the compression rate or monitoring, with some calibres, of the general wear indicator can ensure the wear rate is properly ascertained. When in use, never adjust the compression rate. When this ranges from 20 to 50% of the initial rate, the contacts must be changed. After this operation: - the contacts must be aligned according to the initial compression rate; - it is advised to scrape the sides of the blow-out chambers; - it is indispensable to check the screw tightening torque.
v Thermo relays
No maintenance. The only possible intervention is adjustment of the trip current value which depends on the current absorbed by the receiver.
v Enclosures
Grease hinges and the closing device from time to time. On sealed boxes and cabinets, check the efficiency of sealing devices (seals, cable glands, cable boxes). Clean filters with a vacuum cleaner, never use compressed air.
b NEVER
- file or grease contacts; - alter a part or replace it with an improper spare; - rearm an overload relay without having found and eliminated the cause of tripping; - replace a fuse and repower the equipment without having remedied a fault; - leave a cabinet or box open unnecessarily, especially in a dusty atmosphere; - use inappropriate solvents.
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Eco-design
Environment concern shall take into account several requirements as: selection of raw materiel at the design stage, energy consumption during operation, recycling capability at the end of lifetime.
12. Eco-design
Summary
1 2
12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 Foreword Concepts and main directives Standards Eco-design Lifecycle Main rules of eco-design Conclusion Applications
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12.1
Foreword
12.1
Foreword
The term eco-design means products (goods and services) designed with the environmental factor in mind. It implies that this factor is included with the rest of the conventional design ones (customer requirements, cost control, technical feasibility, etc.) (C Fig.1). This policy involves different players in the economy suppliers, producers, distributors, consumers, and private buyers who wish to offer or choose products that offer the same service but are more environment-friendly. Because is it upstream of the decision-making process, eco-design is a preventive policy. It is based on a global attitude, a multicriteria approach to the environment (water, air, soils, noise, waste, energy, raw materials, etc.) encompassing all the stages in the lifecycle of a product: raw material extraction, production, distribution, use and disposal at the end of the lifetime.
A Fig. 1
Environmental parameters
This double nature of eco-design (multicriteria and multiple stages) is what may be called its signature. Investigation methods can be described as in-depth or simplified depending on the degree to which they keep account of environmental impact throughout the product lifecycle.
Excerpt from the definition of eco-design by Ademe (the French environment and energy agency).
In this guide, we propose a general methodology for eco-design which can be used for any new development of products or services and for new versions of existing ones.
b Introduction
It is Schneider Electrics policy to act as an environmentally responsible company. As regards to products and services, this means that ecodesign has to be part of any new development and any new version of existing ones if we want to mitigate the environmental impact of our products throughout their lifetime. To achieve this goal, this guide must: - state the environmental policy of Schneider Electric, the main object of which is to promote respect for all natural resources and act positively and constantly for a better environment for all; - outline the main European regulations that will soon apply to us, in order to plan ahead; - provide designers with a methodology to help them design ecofriendly products/services; - describe the EIME software available from Schneider Electric for designers to use in eco-friendly design projects
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12.1 12.2
Environmental protection as part of management policy - by taking the requisite steps to make respect for the environment an integral part of Schneider Electrics common culture and a natural approach to all our work and throughout our industry; - by promoting environmental protection within Schneider Electric, through awareness raising, training and communication in line with our environmental policy; - by providing our customers, suppliers and partners with relevant information. Sustainable environment-friendly industrial development - by adopting an ongoing positive approach to mitigate the environmental impact of our products/services throughout their lifecycle; - by developing more environment-friendly new products/services and manufacturing procedures with special attention to forward planning; - by using new techniques that help to conserve natural resources and control our products power consumption; - by designing our products with a view to making them recyclable; - by complying with current directives and anticipating new ones. ISO 14001 certification for all our sites - by adopting an environmental management system based on the international ISO 14001 standard; - by building and running our sites in a way worthy of Schneider Electrics local image, in compliance with rulings in force and going further whenever relevant, - By eliminating or reducing waste and improving its recovery; - by ongoing improvement of current manufacturing processes to optimise their environmental impact.
12.2
v The main objective of the IPP (Integrated Product Policy), a priority of the Action Programme, is: - in relation to the concept of sustainable development, to stimulate environment-friendly product and service supply (eco-design, information on lifecycles) and demand (awareness, communication, provision of raw material and services more environmental friendly).
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12.2 12.3
b Main directives
The main directives based on these concepts, currently in the European discussion stage, are:
v EUP (Energy Using Product): Based on the IPP concept, this aims to standardise the design of electric and electronic equipment to ensure its free circulation and mitigate its environmental impact throughout its lifecycle, ensure more efficient use of resources and protect the environment in a way compatible with sustainable development. v WEEE (Waste of Electrical and Electronic Equipment)
- To reduce waste from electric and electronic equipment and, for this reason, commit the producer to recovering and recycling (70 to 80% in weight) equipment at the end of its lifetime.
12.3
Standards
In addition to the European directives, there are a number of other standards to regulate inclusion of environmental aspects in product design. These include:
As an environmentally responsible company, Schneider Electric develops new, more environment-friendly products/services and manufacturing procedures compliant with the above directives, standards and rules and also plans ahead for them by implementing eco-design.
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12.4 12.5
Eco-design Lifecycle
12.4
Eco-design
Eco-design, an important feature of sustainable development, as we saw in the foreword, is a proactive customer-oriented approach which can be defined as follows: - products/services designed to best satisfy customer requirements and mitigate their environmental impact throughout their lifecycle. It involves ongoing dynamic progress which can, by common upstream thinking (techniques, marketing, training, etc.) change a restriction into an opportunity. This is clearly the strategy manufacturers should strive to follow. This strategy, which should apply as much to design of new products as upgrading of existing ones, implies that the designer must include a further criterion when seeking solutions: minimum environmental impact throughout the entire lifecycle (C Fig.2).
A Fig. 2
As stipulated in the EUP directive, the choice of an optimal solution meeting customer requirements must be consistent with maintaining a reasonable balance between the design criteria: - performance, cost, quality, environment, industrialisation, etc., as well as complying with safety and health criteria.
12.5
Lifecycle
The point of eco-design, as we have seen, is to design products/services with a lesser impact on the environment throughout their entire lifecycle. How can we define this lifecycle? The lifecycle of a product goes from the cradle to the grave, i.e. from the extraction of the raw material to ultimate disposal, via all the stages of manufacture/assembly, distribution, use and recovery at the end of the lifetime. It is obvious that every stage in a products lifecycle has an impact on the environment and it is this impact we must strive to mitigate. This is the aim of eco-design, which has to take into account all the stages together in order to prevent any improvement in the ecological behaviour of one stage having a detrimental effect on that of the others. This requires full detailed analysis of the lifecycle (LCA) so the right choice can be made. This is what EIME software is for. The end-of-lifetime recovery stage can involve major constraints and so must be considered from the outset of product design. To comply with regulations, recovery should cover 70% to 80% of the product (in weight) and can be in the form of: repair/restoration of the product; reuse of parts/sub-units; recycling of materials; energy recovery.
A Fig. 3
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12.6
b Choice of materials
The designer can have an effect on a products environmental impact through the choice of materials. So, in line with the general rules of eco-design described above, this choice should be made using criteria targeting smaller consumption of the raw material and lower environmental impact of the materials used. Reduction of the mass and volume of materials used - optimisation of the volume and mass of parts and products, - reduction in number of parts. Choice of non-toxic or only slightly toxic materials in extraction, production, utilisation and disposal (end of lifetime). Choice of materials based on renewable resources to save natural non-renewable resources. Choice of power-saving materials in raw material extraction, material processing and use. Use of recycled materials, the environmental impact is then due to recycling and not production. Use of recycled materials with a view to product recovery at the end of its lifetime. It goes without saying that compliance with these environmental criteria does not dispense the materials chosen from having to meet the usual requirements for the product with regard to mechanical, electrical, cost and manufacturing (casting, cutting, etc.) factors.
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b Production
The production stage is an important part of the lifecycle and should never be neglected in eco-design. Design choices can have significant effect on industrial processes and therefore on their environmental impact. This is why a certain number of optimisation criteria should be considered from the outset. Reduction in environmental discharges (water, soils, air) - choice of production methods that cut down environmental dumps. Example: wherever possible, avoid surface treatments Reduction in power consumption at all stages of production - choice of power-saving manufacturing, mounting and assembly methods. Reduction in the amount of waste (machining, cutting, casting, etc.) Example: - parts designed to reduce offcuts; - reuse of casting sprues; - reduction of scrap. Reduction in the number of production stages - example: fewer different parts. Less transport between stages - less transport from plant to plant (parts, sub-units), - less power consumed for transport, - use of new production methods, - new methods with a lower environmental impact than conventional methods - BAT (Best Available Technique).
b Distribution
Product distribution is another stage in the lifecycle which can have a substantial impact on the environment. This is why it is necessary to optimise packaging and the distribution system itself from the outset of product design. To this end, in compliance with standards (EN 13428 to 13432) and the decree published 25/07/98, the following criteria should apply. Reduction in the mass and volume of packaging - reduction in volume and mass of products; - optimisation of the packaging function. Fewer packages: packages common to several products Choice of greener packaging minimum heavy metal content (lead cadmium, mercury, etc.) Packages designed to be reused or recovered - recovery of 50 to 65% in weight; - avoid use of different materials (cardboard, foam, etc.). Optimisation/reduction in transport: fewer masses and volumes to transport Choice of means of transport using less fuel As always, compliance with these criteria should not be detrimental to the basic functions of packaging such as protection and safety.
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12.6
b Utilisation
Product utilisation is a stage in the lifecycle which can have a significant effect on the environment, especially with regard to electricity consumption. Here again, there are a number of criteria which can play a decisive part: Lower power consumption when the product is used - consumption in electrical contacts (contact resistance, welds, etc.) and bimetal strips; - consumption by control units (electromagnets, etc.); - power dissipated in electronic components, etc. Reduction in leaks and discharges into the environment - noise reduction; - less leakage (e.g. SF6). Greater product durability Easier maintenance and repairs - greater product reliability; - customer link (pre-alarm, etc.); - modular products. Another important point in this stage is the use of clean renewable fuels but the designers impact on this does not seem decisive.
b End of lifetime
As we have already said, recovery at the end of a products lifetime should be an important part of it (70 to 80% in weight) and should be taken in charge by its producer. If this environmental criterion is to be complied with at reasonable cost, the product must be designed so as to facilitate this operation. This in turn implies a certain number of criteria. Products easy to dismantle - avoid the use of assembly systems that cannot be dismantled; - modular products. Reuse of sub-units/components: preference for modular products Product repair/restoration (2nd hand) Recycled materials - marked plastic parts (see technical directive FT 20 050); - fewer different materials. Choice of non-toxic materials: incineration Easy dismantling of toxic products and/or products requiring special processing Easy access to and quick dismantling of batteries, mercury relays, electronic cards, LCD monitors, etc. Simple product safety devices (tension springs, etc.) End of lifetime guide enclosed with product This short list of design criteria for each stage in a products lifecycle and the examples to illustrate them do not claim to cover all cases of eco-design. They are principally intended as a guide to help the designers thought process. Moreover, dividing the products lifecycle into major stages (choice of material, production, distribution, utilisation and end of lifetime) should not get in the way of the final object, which is to mitigate the overall impact of the product from beginning to end of its lifecycle. It is therefore crucial, as we have already said, that improvement in the ecological behaviour of one stage should not have a detrimental effect on that of the others. To achieve this requires full detailed analysis of the lifecycle (LCA) made. This is what EIME software (see further in this document) is used for.
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12.7 12.8
Conclusion Applications
12.7
Conclusion
The policy of Schneider Electric includes eco-design to: - promote respect for all natural resources; - constantly and positively improve conditions for a clean environment to satisfy its customers and users of its products, its employees and the communities where the company is established. This constant positive progress policy can enhance the companys performance and should be seen as an opportunity. Therefore, eco-design, the purpose of which is to design products/services with a lower impact on the environment throughout their lifetime and which best satisfy customer requirements, will be our general policy for the development of every new product/service, and for new versions of existing ones.
12.8
Applications
b EIME software
EIME (Environmental Information and Management Explorer) is an application to help in the design of environment-friendly products. It is owned and controlled by Alcatel, Alstom, Legrand, Schneider Electric and Thomson Multimedia. It is used to evaluate the environmental impact of a product from beginning to end of its lifecycle and guides designers in their choice of materials and designs. It can be accessed from anywhere in the world; its database (materials, procedures, etc.) is the same for all Schneider Electric designers all throughout the world. The main features of this software are: - help in the choice of materials and procedures; - information on compliance with regulations; - evaluation of environmental impact (LCA); - help in identifying weak points; - comparison of two design options. The environmental profile of a product built with EIME is an essential basis for environmental product communication with customers.
The environmental analysis was made in compliance with standard ISO 14040 Environmental management: lifecycle analysis, principle and framework. It covers all the stages in the product lifecycle.
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12.8
Applications
v Constituent materials
In mass, the products in the range extend from 2680 g to 9000 g The Altivar 71 rated 0.75kW, 500V, weighs 2680g without packaging. The constituent materials are made up as figure 5 :
A Fig. 5
AT71 material constituents (*) Others comprises all elements at less than 1% such as shrinkable tubing, EPDM elastomers, etc.
All our departments, suppliers and subcontractors have been briefed to ensure that materials used in the Altivar 71 0.37 to 18kW range contain none of the substances prohibited by current legislation (list available on request) when it goes on the market. The range is designed to need no batteries or accumulators. The site where this product family was designed is certified ISO 14001 for its eco-design process.
v Manufacture
The range is manufactured at a Schneider Electric production site which has set up an environmental management system certified ISO 14001. Ongoing process enhancement reduces the annual average power consumption on site by 5%. Waste is thoroughly sorted for a recovery rate of 99%.
v Distribution
The packaging is designed to cut down its weight and volume, in compliance with the European packaging directive 94/62/EC. Its overall weight is 1080 g, and it is made mainly of cardboard with a recyclable polyethylene bag. No packing foam or staples are used. The distribution channels are optimised by local distribution centres in the vicinity of the market areas.
v Utilisation
The products in the Altivar 71-0.37 to 18kW range cause no pollution requiring special conditions of use (noise, emissions). Their electricity consumption depends on how they are commissioned and operated. Their power losses spread from 44 W to 620 W. For example the Altivar 71-0.75kW, 500V losses are 44W, i.e. under 6% of the total power circulating in it.
v End of lifetime
At the end of their lifetime, the products in the Altivar 71-0.37 to18 kW range shall be dismantled to recover their constituent materials. Their recycling potential is more than 80%. This includes ferrous metals, copper and aluminium alloys and marked plastics. The products in the range also contain electronic cards which should be withdrawn and sent through special processing channels. The end-oflifetime data is detailed in the relevant data sheets.
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Applications
v Environmental impacts
The Lifecycle Analysis (LCA) was made with EIME (Environmental Impact and Management Explorer) version 1.6 and its database version 5.4 (C Fig.6). The products theoretical duration of use is 10 years and the electrical power model used was the European model. The device analysed was an Altivar 71-0.75kW, 500V. Environmental impacts were analysed in the stages of manufacturing (M) including processing of raw materials, distribution (D) and utilisation (U). The environmental impact analysis was made by comparing the impacts of a non-eco-designed and an eco-designed product. The eco-designed product was 27% less in mass and 19% less in volume than the one from the earlier range. The plastics used are 100% recoverable owing to the choice of materials and the new product architecture.
A Fig. 6 LCA comparison of impacts of Altivar 71-0.75W, 500V with and without ecodesign
These modifications result in an overall reduction in the products impact on the environment.
v Glossary
Raw Material Depletion (RMD) This indicator quantifies raw material consumption during a products lifetime. It is expressed as a fraction of the raw materials depleted every year in relation to their annual overall reserves. Water Depletion (WD) This indicator calculates the amount of drinking water or industrial water consumed. It is expressed in cubicmeters. Global Warming Potential (GWP) Global warming is the result of the increase in the greenhouse effect caused by greenhouse gas absorption of solar radiation reflected by the earths surface. The effect is measured in grams of CO2. Ozone Depletion (OD) This indicator describes the part played by emissions of specifigases in the depletion of the ozone layer. It is expressed in grams of CFC-11. Photochemical Ozone Creation (POC) This indicator quantifies the part played by ozone-producing gases in the creation of smog and is expressed in grams of ethylene (CH2:CH2). Air Acidification (AA) Acid substances in the atmosphere are carried by rainfall. Highly acid rain can destroy forests. The degree of acidification is calculated using the acidification potential of the substance and is expressed in moles of H+.
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Memorandum
Presentation: Fundamental laws which reign in the electrical and mechanical universe. Tables of the main quantities and constants. Measurement units and symbols, and conversion tables with common units. Neutral regimes.
M. Memorandum
Summary
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M.1 M.2 M.3 M.4 M.5 M.6 M.7 M.8 M.9 Quantities and units of measurement Average full-load currents of asynchronous squirrel cage motors Electrical formulae Calculation of starting resistances Mechanical formulae Fundamental formulae Neutral connections Driving machines Conversion tables for standard units
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M.1
M.1
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M.3
Electrical formulae
M.3
Electrical formulae
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Electrical formulae
Ohms Law
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Mechanical formulae
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Mechanical formulae
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Fundamental formulae
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Fundamental formulae
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Neutral connections
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Neutral connections
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Driving machines
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Driving machines
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M.9
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Summary
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Automation solution guide Electrical power supply Motors and loads AC motors starting and protection systems Motor starter units Data acquisition: detection Personnal and machines safety Human-machine interface Industrial networks Data treatment and software Equipment manufacturing Eco-design Memorandum
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Detailed summary
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Detailed summary
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Human-machine interface
8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8 Human-machine interface setup Human-machine interfaces Discrete control and indicator units Schneider Electric Discrete Control and Indicator Unit offer Advanced human-machine interfaces Exchange modes Development software Conclusion
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Industrial networks
9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 Introduction History Market requirements and solutions Network technologies Networks recommended by Schneider Electric Ethernet TCP/IP Web services and Transparent Ready Canopen bus Ethernet and CANopen synergy AS-Interface (AS-I) Bus Conclusion
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Equipment manufacturing
11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 11.10 11.11 11.12 Equipment design Choice of supplier Drafting diagrams and programs Programming methodology Choice of technology Equipment design Building an equipment Mounting Device fitting tools Platform tests Equipment commissioning Equipment maintenance
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Eco-design
12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 Foreword Concepts and main directives Standards Eco-design Lifecycle Main rules of eco-design Conclusion Applications
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Memorandum
M.1 M.2 M.3 M.4 M.5 M.6 M.7 M.8 M.9 Quantities and units of measurement Average full-load currents of asynchronous squirrel cage motors Electrical formulae Calculation of starting resistances Mechanical formulae Fundamental formulae Neutral connections Driving machines Conversion tables for standard units
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Contributors
We would like to give our warmest thanks to all those who have contributed their knowledge and experience to this work and in particular:
For their contribution to information on safety: Armin Wenigenrath Schneider Electric Carsten Dorendorf Schneider Electric Didier Laurent Schneider Electric Schneider Electric Klaus Mickoleit Schneider Electric Martial Patra Schneider Electric Philppe Goutaudier Yves Leonard Schneider Electric For their contribution to information on loads, pre-actuators, actuators and power control: Schneider Electric Michel Bret Schneider Electric Andr Gabagnou Jacques Piriou Jean-Marc Romillon Thierry Passieux Bertrand Guarinos Nuno Dos Santos Schneider Electric Schneider Electric Schneider Electric Schneider Electric Schneider Electric
For their contribution to information on product implementation and application examples: Antonio-Manuel Goncalves-Portelada Schneider Electric Rainer Ritschel Schneider Electric Schneider Electric Yannick Neyret Schneider Electric Thomas Pierschke
For their contribution in information on eco-design: Schneider Electric Claude Jollain Michel Lauraire Schneider Electric Schneider Electric Willy Martin
For their contribution to information on capture, sensors and human-machine interfaces: Andr Gabagnou Schneider Electric Antonio Chauvet Schneider Electric Jean-Marc Romillon Schneider Electric Jean-Marie Cannoni Jean-Michel Carlotti Patrick Mazeau Stig Oprann Schneider Schneider Schneider Schneider Electric Electric Electric Electric
For their overall contribution: Eric Jegu Schneider Electric Fluvio Filippini Schneider Electric Emmanuel Perrin Schneider Electric Franois Bcheret Schneider Electric Stphanie Aug Schneider Electric Richard Blanc Schneider Electric Vronique Fischer Virginie Boutemy Franois Janvier Danielle Ligot Hubert Gourlet Marc Le-Saux Schneider Electric Schneider Electric Schneider Schneider Schneider Schneider Electric Electric Electric Electric
For their contribution to information on links, exchanges and software processing: Andr Gabagnou Schneider Electric Eric Domont Schneider Electric Schneider Electric Boris Suessmann Jacques Camerini Jacques Fighiera Jean-Marc Romillon Jochen Weiland Martyn Jones Patrick Mazeau Philippe Gelin Antonio Chauvet Jrome Firmin Xavier Clenet Bryn Travers Schneider Schneider Schneider Schneider Schneider Schneider Schneider Schneider Schneider Schneider Schneider Electric Electric Electric Electric Electric Electric Electric Electric Electric Electric Electric