Introduction of Control systems:
In modern times, control systems play a very important role in our life daily. The concepts of automatic control are fundamental and well mixed in every aspect of our life touches.
From a simple bread toaster to a complex modern power plant, there is a series of control principles that affect our life.
The principle of the control systems is applicable to engineering as well as non-engineering fields.
In this lecture, we will study the definition of some important terms, types of control systems, applications, and advantages and disadvantages of control systems.
1. System: A system is an arrangement of or a combination of different physical components connected or related n such a manner so as to form an entire unit to attain a certain objective.
2. Output: The actual response obtained from the system is called output.
3. Input: The stimulus or excitation applied to control systems from external sources in order to produce the output is called input.
4. Control: It means to regulate, direct or command a system so that the desired objective is attained.
5. Control Systems: It is an arrangement of different physical elements connected in such a manner sp as to regulate, direct or command itself to achieve a certain objective (or command some other systems to achieve a certain objective)
Thus control systems must have the following:
- An input or inputs
- An output or outputs
- An arrangement to achieve these input-output combinations.
what is a requirement of Good Control systems:
- Accuracy is very high as any error is arising should be corrected.
- Accuracy can be improved by using the feedback element. Because of the feedback element, the system becomes a closed-loop system.
- In closed-loop control systems, the steady-state error tends to zero.
- The control systems sense changes in output due to environmental or parametric changes, internal disturbances, or any other parameters and correct the same.
- Any control system would be insensitive to such parameters but very sensitive to the input signals.
- Noise is an undesired input signal.
- A good control system would be insensitive to such input signals.
- A good control system should be able to reduce the effect of wise or undesired inputs.
- Stability means bounded input and bounded output.
- In the absence of inputs, the output should be tends to zero as time increases,
- A good control system response is stable for all variations.
- The operating frequency range decides the bandwidth of the control systems.
- For the frequency response of a good control system, bandwidth should be large.
- A good control system would have high speed.
- That is the output of the control system should be as fast as possible.
- For a good control system, oscillations of output should be constant air sustained oscillations that follow the Barkhauseein’s criteria.
what are the types of Control systems:
“Control action is that quantity responsible for activating the system to produce the output.”
Depending on whether such control actions s dependent on the status of output, control systems are classified into two categories:
- Open-loop Control System
- Closed-loop Control System
What is Open-loop Control system:
Definition: “A system in which the control action is totally independent of the output of the system is called as open-loop control system”.
Example of Open-loop Control system:
- Automatic hand driver
- Automatic washing machine
- Bread toaster
- automatic coffee server
- electric lift
- traffic signal
- theater lamp dimer etc.
Advantages of Open-loop Control system:
- They are simple in construction and design
- They are economic
- Easy for maintenance
- Not much problem of stability
- Convenient to use when output is difficult to measure
Disadvantages of Open-loop Control system:
- Inaccurate and unreliable because accuracy is dependent on the accuracy of the calibration.
- Inaccurate results are obtained with parameter variations, internal disturbances.
- To maintain quality and accuracy, Recalibration of the controller is necessary from time to time.
What is Closed-loop Control system:
Definition 1: “A system in which the control action is somehow dependent on the output is called as closed-loop control system”.
Definition 2: “Feedback is that property of the system which permits the output to e compared the reference input so that appropriate control action is formed”.
Example of Closed-loop Control system:
- Automatic electric iron
- DC motor speed control by tacho feedback
- railway reservation status
- missile launched
- servo voltage stabiliser
- human perspiration system
- water level controller etc.
Advantages of Closed-loop Control system:
- Accuracy is very high as any error arising is corrected
- It senses changes in output due to environmental or parametric changes, internal disturbances, etc., and corrects the same.
- Reduced effect of non-linearities
- High bandwidth
- Facilitates Automation
disadvantages of Closed-loop Control system:
- Complicated in design and maintenance costlier
- The system may become unstable
Comparison of Open and Closed-loop Control systems:
|Sr. No||Open-Loop System||Closed-Loop System|
|1.||No feedback. Hence feedback elements absent||Feedback exists. Hence feedback elements present.|
|2.||No error detector||Error detector is present|
|3.||It is inaccurate||It is accurate|
|4.||Highly sensitive to parameter changes||Less sensitive to parameter changes|
|5.||Small bandwidth||large bandwidth|
|6.||Stable||May become unstable|
|8.||Example: Coffee maker, toaster, hand drier, etc.||Example: Guided-missile, Oven, stabilizers, etc.|
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