CST 01
CST 01
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Sourav Choubey
Asst. Professor,
Electrical Engineering
SRICT, Ankleshwar
Mob:- +919726785727
Email id: Sourav.choubey@srict.in
PSO2: To develop the capability to comprehend the technological advancements in the usage of modern design
tools to analyses and design Electrical Engineering systems/processes for the various applications.
Control
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Theory
The goal of ICSs is to make daily operations more efficient and autonomous, with minimal input from human
workers. Additionally, ICSs can come in various forms and types, such as supervisory control and data
acquisition systems, distributed control systems, and process control systems.
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Shroff S.R. Rotary Institute of Chemical Technology CST Sourav Choubey
Types of Industrial Control System
Process Control Systems
• Accuracy
• Sensitivity
• Noise Reduction
• Stability
• Bandwidth
• Speed
• Oscillation
Control Systems can be classified as open loop control systems and closed loop control systems based on
the feedback path.
In open loop control systems, output is not fed-back to the input. So, the control action is
independent of the desired output.
In closed loop control systems, output is fed back to the input. So, the control action is dependent on the
desired output .
Open loop control system can be converted in to closed loop control system by providing a feedback. This
feedback automatically makes the suitable changes in the output due to external disturbance. In this way
closed loop control system is called automatic control system.
The error detector produces an error signal, which is the difference between the input and the
feedback signal. This feedback signal is obtained from the block (feedback elements) by considering the
output of the overall system as an input to this block. Instead of the direct input, the error signal is
applied as an input to a controller.
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CST Sourav Choubey
Practical Examples of Closed Loop Control
System
• Automatic Electric Iron – Heating elements are controlled by output temperature of the iron.
• Servo Voltage Stabilizer – Voltage controller operates depending upon output voltage of the system.
• Water Level Controller – Input water is controlled by water level of the reservoir.
• Missile Launched and Auto Tracked by Radar – The direction of missile is controlled by comparing the
target and position of the missile.
• An Air Conditioner – An air conditioner functions depending upon the temperature of the room.
• Cooling System in Car – It operates depending upon the temperature which it controls.
The air conditioner is the example of the closed-loop system. The air conditioner regulates the
temperature by comparing it with the surrounding temperature. The comparison of temperature is
done with the help of the thermostat. When the AC provides the error signal which is the difference
between the surrounding temperature and room temperature the thermostats turn on or off the
compressor.
Feedback Advantage
Automatically reduce errors
Closed-loop systems are continuously feeding back the actual output and analyzing against the desired output.
As a result, your machinery can react automatically to whatever the data is telling it. All of this is done within
the device itself and requires no manual action.
Improve stability
A feedback device means you have total access to key data and information in real time, meaning you can
remain in control and improve the stability of your movement. Insight into performance can provide significant
support in ensuring stability, control and consistent precision of the movement.
Increase robustness against external disturbances
Often, control systems are used in hazardous and difficult environments. But no matter where you’re operating
your machinery, a feedback device will enable you to gain control of your equipment’s output. It also means
that your machinery can auto-adjust depending on the external situation it is in.
Reliable and repeatable
Having access to information from a feedback device means you can ensure your machinery is reliable, letting
you continue to deliver consistent, accurate movements, time after time.
Shroff S.R. Rotary Institute of Chemical Technology
A feedback device sounds like a good CSTidea right now, doesn’t it? Well, like everything, there are a few
Sourav Choubey
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Disadvantage
Changes
• Using a feedback device means that there will be a lot of commands and signals passing
to and from the controllers, at all times. If a system is too sensitive to changes in the
commands or signal, it can produce unreliable movements. This is because the
controller will try to over-correct itself. To combat this, you must enter some pre-defined
limits and tell the system exactly how you want it to behave. It will adjust accordingly
from there.
Complexity
• To provide a high level of information, control and consistent feedback to a machine, a
closed-loop system must have one or more feedback paths. This can be complex,
impacting cost, space and installation.
Block diagrams of some of the systems turn out to be complex, such that the evaluation of their performance
required simplification (or reduction) of block diagrams which is carried out by block diagram rearrangements.
• Block diagram does not include any information about the physical construction of the system.
• Source of energy is generally not shown in the block diagram, so block diagram for a given system is not
unique.
The basic components of block diagram are block, branches, summing point, arrows.
Comparator or Summing Block Although blocks are used to identify many types of mathematical
operations, operations of addition and subtraction are represented by a
circle, called a summing point. A summing point may have one or several
inputs. Each input has its own appropriate plus or minus sign
Take Off Point The take-off point is a point from which the same input signal
can be passed through more than one branch. That means with
the help of take-off point, we can apply the same input to one
or more blocks, summing points.
In the figure below, there are two elements with
transfer function Gone(s) and Gtwo(s). Where Gone(s) is
the transfer function of first element and Gtwo(s) is the
transfer function of the second element of the system.
Feedback
In addition to that, the diagram also shows there is a
feedback path through which output signal C(s) is fed
back and compared with the input R(s) and the
difference between input and output
is , which is acting as the
actuating signal or error signal.
In each block of the diagram, the output and input are related together by a transfer function. Where the
transfer function is:
Where C(s) is the output and R(s) is the input of that particular block.
H2
H1
Cascade Blocks
When several systems or control blocks are connected in cascaded manner, the transfer function of the
entire system will be the product of transfer function of all individual blocks. Here it also to be
remembered that the output of any block will not be affected by the presence of other blocks in the
cascaded system.
Rule 4: Moving Pick off from right side of the Block to Left side or Moving in Reverse Direction
Block Diagram Reduction Technique
Rule 5: Moving Pick off from Left side of the Block to Right side or Moving in Forward Direction
Rule 6: Moving of Summing Point from right side of the Block to Left side or Moving in Reverse Direction
For the two systems to be equivalent the input and output of the system should be the same. For the left hand
side system, we have,
Solving the feedback path & Moving the take off point after the block
Step 3
Most feedback control systems contain mechanical Newton’s law of motion states that the algebraic
as well as electrical components. From a sum of forces acting on a rigid body in a given
mathematical viewpoint, the descriptions of direction is equal to the product of the mass of the
electrical and mechanical elements are analogous. body and its acceleration in the same direction.
The law can be expressed as
The motion of mechanical elements can be Σforces = Ma
described in various dimensions as translational,
rotational, or a combination of both. The
equations governing the motions of mechanical
systems are often directly or indirectly formulated
from Newton’s law of motion.
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List of Symbols
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Rotational Friction Coefficient (B)
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Obtaining Transfer Function
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At Node 1