Industrial Training Report: Sri.B.Sharanappa
Industrial Training Report: Sri.B.Sharanappa
Industrial Training Report: Sri.B.Sharanappa
ON
COURSE IN INDUSTRIAL AUTOMATION USING PLC-SCADA
Submitted in partial fulfilment of the requirement for the award in
DIPLOMA IN
APPLIED ELECTRONICS & INSTRUMENTATION ENGINEERING
Under the esteemed guidance of
Sri.B.SHARANAPPA
NATIONAL SKILL TECHNICAL INSTITUTE, RAMANTHAPUR
Submitted by
K.DHRUVA
16030-AEI-021
CERTIFICATE
This is to certificate that the industrial report in “National skill
technical institute” submitted by k.DHRUVA bearing pin number
16030-aei-021 in fulfilment for the award in of DIPLOMA IN
APPLIED ELECTRONICS AND INSTRUMENTATION
ENGINEERING of state board of technical education & training,
AMARAVATHI is a record of bonafide work carried out during the 6
month industrial training.
EXTERNAL EXAMINER
2
ACKNOWLEDGEMENT
3
CONTENTS
TOPIC Pgs.
1. Abstract
2. Introduction to Programmable Logic Controllers……………… 7
4. Characteristics………………………………………………….. 8
5. System Scale……………………………………………………. 9
6. User Interface……………………………………………………. 10
4
15. Liquid level control Trainer
Introduction……………………………………………………37
Description of the Instrument………………………………….38
Liquid level control program with explanation……………...39-40
16. Conclusion………………………………………………………….41
17. Bibliography………………………………………………………..42
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ABSTRACT
This projectwork is divided into two parts. The first part deals with the history and
development of Programmable Logic Controllers and its subsequent applications in
different industries. In The second part PLC was implemented to control 3 different
processes namely lift car controller, Liquid level controller, Temperature controller.
Before, a programmable logic controller would have been programmed in ladder logic,
which is similar to a schematic of relay logic. A modern programmable logic controller is
usually programmed in any one of several languages, ranging from ladder logic to Basic
or C. Typically, the program is written in a development environment on a personal
computer (PC), and then is downloadedonto the programmable logic controller directly
through a cable connection. The program is stored in the programmable logic controller
in non-volatile memory.
There are several different types of interfaces that are used when people need to interact
with the programmable logic controller to configure it or work with it. This may take the
form of simple lights or switches or text displays, or for more complex systems, a
computer of Web interface on a computer running a Supervisory Control and Data
Acquisition (SCADA) system.
Programmable logic controllers were first created to serve the automobile industry, and
the first programmable logic controller project was developed in 1968 for General Motors
to replace hard-wired relay systems with an electronic controller.
The lift controller controls the movement of the lift. The program is designed to make the
lift car move to the correct floor based on floor request. The temperature controller
controls the temperature of the fluid based on a set point.The level controller controls the
level of a liquid in a tank.
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Introduction
Fast and Easy PLC Control The object of a PLC simulator is to 'fake out' the input into a
PLC so that the programmer can test and debug the program before installation into it's
operating environment. Our patent pending PLC simulators achieve this by mounting on
the existing terminal strip of the PLC card and providing easy controls to turn digital
inputs on/off or adjust analog signals. If you are a engineer who programs PLCs or even a
technician in need of a quick way to test a PLC functionality then these devices are for
you. Save time, money and embarrassment by fixing problems before they start. These
PLC simulators are for sale in our products section.
History
The PLC wasinvented in response to the needs of the American automotive industry.
Before the PLC, control, sequencing, and safety interlock logic for manufacturing
automobiles was accomplished using relays, timers and dedicated closed-loop controllers.
The process for updating such facilities for the yearly model change-over was very time
consuming and expensive, as the relay systems needed to be rewired by skilled
electricians. In 1968 GM Hydramatic (the automatic transmission division of General
Motors) issued a request for proposal for an electronic replacement for hard-wired relay
systems.
The winning proposal came from Bedford Associates of Bedford, Massachusetts. The
first PLC, designated the 084 because it was Bedford Associates eighty-fourth project,
was the result. Bedford Associates started a new company dedicated to developing,
manufacturing, selling, and servicing this new product: Modicon, which stood for
Modular Digital Controllers. One of the people who worked on that project wasDick
Morley, who is considered to be the "father" of the PLC. The Modicon brand was sold in
1977 to Gould Electronics, and later acquired by German Company AEGand then by
French Schneider Electric, the current owner.
One of the very first 084 models built is now on display at Modicon's headquarters in
North Andover, Massachusetts. It was presented to Modicon by GM, when the unit was
retired after nearly twenty years of uninterrupted service.
Theautomotive industry is still one of the largest users of PLCs, and Modicon still
numbers some of its controller models such that they end with eighty-four. PLCs are used
in many different industries and machines such as packaging and semiconductor
machines. Well known PLC brands are Siemens,Allen-Bradley,ABB,Mitsubishi,Omron,
and General Electric.
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Characteristics
The main difference from other computers is that PLCs are armored for severe condition
(dust, moisture, heat, cold, etc) and have the facility for extensive input/output(I/O)
arrangements. These connect the PLC to sensorsand actuators. PLCs read limit
switches,analog process variables (such as temperature and pressure), and the positions of
complex positioning systems. Some even use machine vision. On the actuator side, PLCs
operate electric motors,pneumaticor hydrauliccylinders, magnetic relaysor solenoids, or
analog outputs. The input/output arrangements may be built into a simple PLC, or the
PLC may have external I/O modules attached to a computer network that plugs into the
PLC.
PLCs were invented as replacements for automated systems that would use hundreds or
thousands of relays,cam timers, and drum sequencers. Often, a single PLC can be
programmed to replace thousands of relays. Programmable controllers were initially
adopted by the automotive manufacturing industry, where software revision replaced the
re-wiring of hard-wired control panels when production models changed.
Many of the earliest PLCs expressed all decision making logic in simple ladder
logicwhich appeared similar to electrical schematic diagrams. The electricians were quite
able to trace out circuit problems with schematic diagrams using ladder logic. This
program notation was chosen to reduce training demands for the existing technicians.
Other early PLCs used a form of instruction listprogramming, based on a stack-based
logic solver.
The functionality of the PLC has evolved over the years to include sequential relay
control, motion control, process control,distributed control systemsand networking. The
data handling, storage, processing power and communication capabilities of some modern
PLCs are approximately equivalent to desktop computers. PLC-like programming
combined with remote I/O hardware, allow a general-purpose desktop computer to
overlap some PLCs in certain applications.
System Scale:
A small PLC will have a fixed number of connections built in for inputs and outputs.
Typically, expansions are available if the base model does not have enough I/O.
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Modular PLCs have a chassis (also called a rack) into which is placed modules with
different functions. The processor and selection of I/O modules is customised for the
particular application. Several racks can be administered by a single processor, and may
have thousands of inputs and outputs. A special high speed serial I/O link is used so that
racks can be distributed away from the processor, reducing the wiring costs for large
plants.
PLCs used in larger I/O systems may have peer-to-peer (P2P) communication between
processors. This allows separate parts of a complex process to have individual control
while allowing the subsystems toco-ordinate over the communication link. These
communication links are also often used for HMI(Human-Machine Interface) devices
such as keypads or PC-type workstations. Some of today's PLCs can communicate over a
wide range of media including RS-485, Coaxial, and even Ethernet for I/O control at
network speeds up to 100 Mbit/s.
Programming in PLCs
Early PLCs, up to the mid-1980s, were programmed using proprietary programming
panels or special-purpose programming terminals, which often had dedicated
functionkeys representing the various logical elements of PLC programs. Programs were
stored on cassette tape cartridges. Facilities for printing and documentation were very
minimal due to lack of memory capacity. More recently, PLC programs are typically
writtenin a special application on a personal computer, then downloaded by a direct-
connection cable or over a network to the PLC. The very oldest PLCs used non-volatile
magnetic core memorybut now the program is stored in the PLC either in battery-backed-
up RAMor some other non-volatile flash memory.
Early PLCs were designed to replace relay logic systems. These PLCs were programmed
in "ladder logic", which strongly resembles a schematic diagram of relay logic. Modern
PLCs can be programmed in a variety of ways, from ladder logic to more traditional
programming languages such as BASIC and C. Another method is State Logic, a Very
High Level Programming Languagedesigned to program PLCs based on State Transition
Diagrams.
Recently, the International standard IEC 61131-3has become popular. IEC 61131-3
currently defines five programming languages for programmable control systems: FBD
(Function block diagram), LD (Ladder diagram), ST (Structured text, similar to the
Pascal programming language), IL (Instruction list, similar to assembly language) and
SFC (Sequential function chart). These techniques emphasize logical organization of
operations.
While the fundamental concepts of PLC programming are common to all manufacturers,
differences in I/O addressing, memoryorganization and instruction sets mean that PLC
programs are never perfectly interchangeable between different makers. Even within the
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same product line of a single manufacturer, different models may not be directly
compatible.
User Interface
PLCs may need to interact with people for the purpose of configuration, alarm reporting
or everyday control. A Human-Machine Interface(HMI) is employed for this purpose.
HMI's are also referred to as MMI's (Man Machine Interface) and GUI (Graphical User
Interface).
A simple system may use buttons and lights to interact with the user. Text displays are
available as well as graphical touch screens. Most modern PLCs can communicate over a
network to some other system, such as a computer running a SCADA(Supervisory
Control And Data Acquisition) system or web browser.
10
Fig. Operation of a PLC in basic stages
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– Condition Sensors
– Encoders
• Pressure Switches
• Level Switches
• Temperature Switches
• Vacuum Switches
• Float Switches
Output Devices
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– Valves
– Motor Starters
– Solenoids
– Actuators
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a specific custom-built controller design. On the other hand, in the case of mass-produced
goods, customized control systems are economic due to the lower cost of the components,
which can be optimally chosen instead of a "generic" solution, and where the non-
recurring engineering charges are spread over thousands of places.
For high volume or very simple fixed automation tasks, different techniques are used. For
example, a consumer dishwasherwould be controlled by an electromechanical cam
timercosting only a few dollars in production quantities.
Very complex process control, such as used in the chemical industry, may require
algorithms and performance beyond the capability of even high-performance PLCs. Very
high-speed or precision controls may also require customized solutions; for example,
aircraft flight controls.
PLCs may include logic for single-variable feedback analog control loop, a "proportional,
integral, derivative" or "PID controller." A PID loop could be used to control the
temperature of a manufacturing process, for example. Historically PLCs were usually
configured with only a few analog control loops; where processes required hundreds or
thousands of loops, a distributed control system(DCS) would instead be used. However,
as PLCs have become more powerful, the boundary between DCS and PLC applications
has become less clear-cut
Digital and Analog Signals:
Digital or discrete signals behave as binary switches, yielding simply an On or Off signal
(1 or 0, True or False, respectively). Pushbuttons, limit switches, and photoelectric
sensorsare examples of devices providing a discrete signal.
Discrete signals are sent using either voltageor current, where a specific range is
designated as Onand another as Off. For example, a PLC might use 24 V DC I/O, with
values above 22 V DC representing On, values below 2VDC representing Off, and
intermediate values undefined. Initially, PLCs had only discrete I/O.
Analog signals are like volume controls, with a range of values between zero and
fullscale. These are typically interpreted as integer values (counts) by the PLC, with
various ranges of accuracy depending on the device and the number of bits available to
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store the data. As PLCs typically use 16-bit signed binary processors, the integer values
are limited between -32,768 and +32,767.
Pressure, temperature, flow, and weight are often represented by analog signals. Analog
signals can use voltageor currentwith a magnitude proportional to the value of the process
signal. For example, an analog 4-20 mAor 0 - 10V input would be convertedinto an
integer value of 0 - 32767.
Current inputsare less sensitive to electrical noise (i.e. from welders or electric motor
starts) than voltage inputs.As an example, say the facility needs to store water in a tank.
The water is drawn fromthe tank by another system, as needed, and our example system
must manage the water level in the tank.
Using only digital signals, the PLC has two digital inputs from float switches(tank empty
and tank full). The PLC uses a digital output to open and close the inlet valveinto the
tank.When the water level drops enough so that the tank empty float switch is off
(down),the PLC will open the valve to let more water in. Once the water level raises
enough so that the tank full switch is on (up), the PLC will shut the inlet to stop the water
from overflowing.
| |
| Low Level High Level Fill Valve |
|------[/]------|------[/]----------------------(OUT)---------|
| | |
| | |
| | |
| Fill Valve | |
|------[ ]------| |
| |
| |
An analog system might use a water pressure sensoror a load cell, and an
adjustable (throttling)dripping out of the tank, the valve adjusts to
slowly drip water back into the tank.
In this system, to avoid 'flutter' adjustments that can wear out the valve, many PLCs
incorporate "hysteresis" which essentially creates a "deadband" of activity. A technician
adjusts this dead bandso the valve moves only for a significant change in rate. This will in
turn minimize the motion of the valve, and reduce its wear.
A real system might combine approaches, using float switches and simple valves to
prevent spills, and a rate sensor and rate valve to optimize refill rates and prevent water
hammer. Backup and maintenance methods can make a real system very complicated.
PLC Software:
The PLC software is manufacturer dependent and even when the manufacturer is the
same, it may vary for the different models of the same brand.
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For, instance for a manufacturer like Allen Bradley the software may vary for its PICO
Controller models and other models. For example, the software used for these controllers
is PICOSoft whereas for its higher models it is RSLogix.
Moreover, the HMI Interface may also vary for the different controllers.
PLC APPLICATIONS:
Automotive Industry
Our industrial automation and control solutions span the entire automotive supply chain
and can help you address these challenges while staying focused on improving quality,
reducing costs, increasing responsiveness and ultimately improving time-to-customer
throughout your supply chain.
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components, in the right quantities, at exactly the right time and place. The result: faster
time-to-customer forthe entire industry.
Your requirements are unique. So are our solutions. We listen to you then apply our
resources to build cost-effective, results-based solutions for the automotive industry. We
are committed to your success. Whatever your automation challenges, you'll find the
answer by partnering with us.
Beverage Industry
Our focus on beverage production optimization addresses these issues and every phase of
your operation so you can meet cost, quality, flexibility and regulatory challenges across
the entire life cycle - from raw materials through final shipment.
Because of the diversity of beverage production processes, it can be challenging for you
to meet customer demand, document regulatory compliance and identify production
inefficiencies. Through our domain knowledge and production experience, we offer a
variety of solutions to help you satisfy your demanding consumers and retailers.
We understand the beverage industry, and can help you turn our solutions and
servicesinto a competitive advantage. Your requirements are unique, so whatever
production challenges you have, partnering with us will help you overcome them.
Entertainment Industry
From the initial conceptualization of the system architecture through the implementation
and commissioning of a specific solution, we will receive the skills and experience to
fulfill your project requirements through:
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• Superior support, everything from integrated engineering and support solutions on
multi-vendor platforms, to software and MRO asset management services.
• Global parts availability for localized support.
• Depth and breadth of products.
• Migration with easy upgrades to the newest technology to protect your investment
long-term.
• Essential Componentswith exceptional value to give you the assurance that the
machines and systems you build will have the optimum levels of quality and
performance.
• Integrated Architecturefor seamless integration of control, communication, and
visualization across multiple platforms.
Marine Industry
Packaging Industry
At the same time, customers demand customization with greater speed and accuracy —
and shortened lead times.
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We help you meet these challenges through a single hardware and software solutionand
programming templates and tools.
Everything we offer, from components to turnkey systems, is designed to save time and
reduce your customers' total cost of ownership. And our support doesn't stop there.
Through remote diagnostics, predictive maintenanceand a network of global support, we
can help your customers — no matter where they put their packaging machines to work.
Improve your process performance with precise speed and torque control and save money
with energy efficient operation.
PowerFlex®Family of AC Drives
Because we have a wide range of control needs, PowerFlex AC drives offer a variety of
motor control technologies, from Volts/Hertz Control for the simplest applications, to
Vector Control with patented FORCE™ Technology, which provides excellent low
speed/zero speed performance for both induction and permanent magnet motors. For
motor control applications from low to medium voltage, and from simple to complex, the
PowerFlex family of drives range from 0.2 kW (0.25 hp) to 25.4 MW (34000hp).
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LIFT CONTROL MODULE
1) Introduction
This trainer is intended to demonstrate the operation of a Lift car using a PLC. Using this
trainer one can understand the concepts of data logging and the control operation of Lift
control system. There are various types of controllers to do the control action. Here we
are using a PLC to achieve this. This trainer has all the necessary instrumentation like
roller switches to sense the position of the lift car, Stepper motor to simulate the
movement of the lift either upward or downward directions.
Using the hardware available with the setup various types of control actions can be done
using PLC Trainer Model IM-29. In this manual a general LIFT CONTROL PROGRAM
is described. Depending upon the logic one can use various programs and test the control
operations.
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2) HARDWARE
2.1 Description of the front panel
1. Floor sensors
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3. Stepper Motor
Stepper motor is a DC motor. It differs with conventional motors in the sense that stepper
motor is used for positioning the rotor at a specified position. A sequential magnetization
and demagnetization enables the rotor of the motor to rotate on its axis by a fixed angle.
If this is so it should be possible to rotate only a few steps either in clockwise or
anticlockwise direction. For example in a printer a stepper motor controls the print head
movement. A Stepper Motor can be used in any place where, a precise mechanical
movement is desired.
A Stepper Motor has 4 different windings. These windings are placed strategically around
a rotor. By sending current (up to 800mA per phase) into these windings in pairs, and in
selective manner, magnetization takes place around those windings. While in other pair
current is switched OFF hence demagnetization takes place. Due to this a physical
movement of rotor takes place causing a small rotation of the rotor. The angular motion
isof the order of 1.8 degrees pershift. It is possible to make this angular rotation to 0.9
degrees by changing the sequence of current flow in these windings.
4-TTL Outputs of PLC are used for generating control signals by power driver
electronics. The binary state logic from these TTL signals is used by power driver
electronics to switch high power transistors to ON or OFF state. During ON state the
Stepper motor winding connected to these power drivers output will allow high current to
pump into these windings. As a result ofthis magnetization takes place. Due to this effect
a mechanical rotation takes place in the Stepper Motor.
General instructions:
The following bit pattern must be provided in the same order, to make the Stepper Motor
to rotate either in clockwise direction or in anti-clockwise direction.
For Clockwise Rotationprovide the bit pattern in the same order as indicated below:
For example your flow chart must follow the sequence as shown here
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For Clockwise Rotation For Anti-Clockwise Rotation
4. Interfacing Connector
A 15-pin connector is provided on the
front panel of the Lift Simulator Setup.
Lift car sensors outputs and the stepper
motor feed points are connected to this
connector. This can be connected to
the ‘CON-C’ of PLC Trainer Model
IM-29 using a l5pin to 9pin connector
cable provided with the trainer setup.
There are three different states in this program. All these states are loaded in the
Registor#0.
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2. Floor request. This state is indicated as ‘1’ in Register#0.
3. Lift car Movement (Either up or down).This state is indicated as ‘2’ in
Register#0.
.
The Lift Car position feedback is stored in Register#2 and the position of the lift
is indicated by annunciators 0 to 2 respectively Floor request is stored in
Register#1.
Keys 0, 1 arid 2 are used as request keys at Floor Level and Keys 4, 5 and 6 are
used as request keys in the lift car for Ground Floor to Second Floor.
Stepper motor movement is simulated in two registers.
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Explanation
Step#1 Lift Car Position Feed Back
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Step#2 Floor Request
There are three rungs as per the above manner for this step. The following table describes
the tags to be assigned for each instruction in these rungs. Here PLC will collect the data
from the request keys and stores the floor number in Register#1. Once any key is pressed
Register#0 will be loaded with 1. This state of Register#0 is Floor Request State.
Rung No
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Rung#8: (If Reg#0=1 and Register l<Register 2) OR ( Reg#=4 and Timer is Set) then
Latch TTLO/P#16 Latch TTLO/P#78, Unlatch TTLO/P#17, Load Reg#0=2,
Load Reg#3=I and Start Timer.
The above rungs simulate Lift car movement in down ward direction.
Rung#12: (If Reg#0=1 andRegister1 >Register2) OR (Reg#4=4 and Timer is Set) then
Latch TTLO/P#7, Latch TTLO/P#18 Unlatch TTLO/P#16, Load Reg#0=2,
Load Reg#4=1 and Start Timer.
Rung#13:If Reg#4=1 and Timer#0 is Set then Unlatch TTLO/P#18 Latch TTLO/P#1 9,
Load Reg#4=2 and Start Timer.
Rung#l4: If Reg#4=2 and Timer#0 is Set then Unlatch TTLO/P#17 Latch TTLO/P#16.
Load Reg#4=3 and Start Timer.
Rung#15 If Reg#4=3 and Timer#0 is Set then unlatch TTLO/P#19 Latch TTLO/P#6,
Load Reg#3=4 and Start Timer
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Thus the above program can be used to control the movement of lift car based on floor
request
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Temperature Control Trainer
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Description of the Instrument:
This temperature control trainer is a Microprocessor based instrument. You can use 8085
Microprocessor Model MPT-85 or MPT-J-85 or 8086 Microprocessor trainer or PC or
PLC to control this training module. These controllers are not supplied along with this
trainer. It has to be procured separately.
This trainer is designed for the following purposes-
• Learn and experiment how a controller acquires analog data.
• Convert the analog data into a digital value using the ADC.
• Set and upper and lower cut off for the ON/OFF control action.
• Display the converted data in a meaningful form.
It is necessary for you to read the description of the equipments input output terminals,
functions of each block and understand them before actually connecting the instrument.
After this stage it is necessary to read the actual program for understanding software
functions used in the actual program.
READ THE FOLLOWING SECTIONS BEFORE INTERCONNECTIONS ARE
MADE. WE ARE PROVIDING GRAPHICAL EXPLANATION TO ENABLE YOU
TO UNDERSTAND EACH BLOCK.
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Note: When using PLC Trainer Model IM-29, connect the 9-pin ‘D’-type
Connector-to-Connector A of the PLC Trainer. Connector A is available at the rear of the
PLC Trainer. When using PLC Trainer model IM-45, connect the 9-pin ‘D’-type
connector to Digital Output O of the PLC Trainer. These connections are elaborated later
in this manual.
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Actual Experimental Setup:
Please ensure that you have performed the above interconnections properly. After
verifying, switch ON Temperature Control Trainer and PLC Trainer. If you are satisfied
then start entering the actual program and execute your program.
Note: When using PLC Trainer Model lM-29 digital output refers to TTL Output 0 and
when using PLC Trainer Model lM-45, digital output refers to Digital Output 0.The
ladder program for single set point control is shown below.
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Explanation:
• Rung#1:Transfer analog input (voltage equivalent of temperature) from analog
input2to Register#0.
Note: When using PLC trainer model IM-29, ‘Analog Input’ refers to ‘ADO, Channel#0’
When using PLC Trainer model IM-45, ‘Analog Input’ refers to ‘Analog Input’.
• Rung#2: If Register#0 > 65 (set point) reset (turn OFF) the digital output. Else, turn
ON the digital output.
Note: When using PLC Trainer model lM-29, Digital Output refers toTTL Output#0.
When using PLC Trainer model IM-45 ‘Digital Output’ refers to ‘Digital Output#0’.
Experimental Procedure:
1. Fill the beaker with water (around 400ml).
2. Insert the heater and thermocouple into the beaker.
3. Make the circuit connections as mentioned earlier.
4. Run the program.
5. Observe the temperature being displayed on-screen by the Analog Input and
Register#0.
6. Observe that when the measured temperature goes above the set point, the heater
is turned OFF.
7. Once the measured temperature is ≤ set point, the heater is turned ON.
8. Dual set point on/off control is an extension of this program.
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Dual Set Point Controller
Explanation:
• Rung#1: Transfer analog input (voltage equivalent of temperature) from analog input
to Register#0.
Note: When using PLC Trainer Model IM-29. ‘Analog Input refers to ADC, Channel#0’.
When using PLC Trainer Model IM-45. ‘Analog Input refers to Analog Input’.
• Rung#2: If Register#2 > 45 (upper limit) unlatch (turn OFF) the digital outputs.
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Note: When using PLC Trainer Model IM-29, Digital Output refers to TTL Output#0’.
When using PLC Trainer Model IM-45 ‘Digital Output refers to ‘Digital Output#0’.
Rung#3: If Register#0 <40 (lower limit) latch (turn ON) the digital output.
Note: When using PLC Trainer Model IM-29,Digital Output refers to TTL
Output#0.When using PLC Trainer Model IM-45, Digital Output refers to Digital
Output#0.
Experimental Procedure:
1. Fill the beaker with water (around400ml).
2. Insert the heater and Thermocouple into the beaker.
3. Make the circuit connections as mentioned earlier.
4. Run the program.
5. Observe the temperature being displayed on-screen by the Analog Input and
Register#0.
6. Observe that when the measured temperature goes above the upper limit, the
heater is turned OFF.
7. Once the measured temperature goes below the lower limit, the heater is turned
ON.
The ladder logic program above works effectively and it can be manipulated accordingly
and used for both single set point controller and dual set point controller.
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In this setup we are having three types of probes. Extreme left probe is the REFERENCE
probe, which will always be immersed in water. Middle one is the LOWER LEVEL
probe. Right side is the UPPER
LEVEL probe.
PUMP will be ON or OFF,
depending on the logic what we
have implemented in the Ladder
Logic program. TTL
OUTPUT#0 gives necessary signal
to the pump either to turn ON or
OFF. Lower level and upper level
are addressed in the instruction set
as INPUTS. Normally
Open symbol Z is used to signify
the water is in contact. This is true
either for lower level probe or
upper level probe.
Thissetup is connected to the level
interface instrument. This interface
instrument is actually connected to
the electronics of the PLC trainer.
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The flowchart for the Level control program
Signals used for the level control from the Level interface instrument to PLC are as
follows.
INPUT:
Lower level and Upper level detection probes of the level interface instrument are
connected at level transducer connector of PLC trainer. This is connected at the front
panel of the PLC trainer. These probes are referred as Lower level detector and Upper
Level detector in PLC programs.
OUTPUT:
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TTL OUTPUT#0 of PLC trainer is connected to PUMP of the Level Interface
instrument. This is connected at the connector, which is behind PLC instrument at
connector — PC, for ON-OFF purposes. To address this pump, use TTL OUTPUT#0,
which is a digital output.
Thus the above ladder diagram applies the logic diagram as shown in the flowchart and
works effectively for controlling liquid level in the tank.
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Conclusion
PLCs are well-adapted to a range of automationtasks. These are typically industrial
processes in manufacturing where the cost of developing and maintaining the automation
system is high relative to the total cost of the automation, and where changes to the
system would be expected during its operational life. PLCs contain input and output
devices compatible with industrial pilot devices and controls; little electrical design is
required, and the design problem centers on expressing the desiredsequence of operations
in ladder logic(or function chart) notation. PLC applications are typically highly
customized systems so the cost of a packaged PLC is low compared to the cost of a
specific custom-built controller design. On the other hand, in the case of mass-produced
goods, customized control systems are economic due to the lower cost of the
components, which can be optimally chosen instead of a "generic" solution, and where
the non-recurring engineering charges are spread over thousands of places
In the second part of the project which deals with the implementation of PLC in lift
control, temperature control and level control, the algorithms were written which were
converted into ladder diagrams and then execution. Upon execution we found that the
programs worked perfectly fine with 100% accuracy. There were no hardware problems
also. The ladder diagram is mentioned in our project report which can also be transferred
to a chip and can be used in real life situations involving control operations.
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Bibliography
http://www.plcdev.com/plc_timeline
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