A control system uses feedback to regulate physical components and achieve a desired output from a given input. It has an input, output, and control action to achieve objectives. Control systems can be open-loop or closed-loop. Open-loop systems do not measure or feedback output, so accuracy depends on input calibration. Closed-loop systems compare input to measured output and use error signals to maintain output at the desired level, making them more accurate but also more complex and expensive.

1. z
Basics of
Control
System

2. z
 Let’s divide the word into Control and System
so it’ll be easy to understand the meaning of it.
 Control: Meaning of control is to regulate,
direct or command to a system so
that the desired objective is obtained.
 System: System is arrangements of different
physical components that gives the proper
output for given input.
 Control System: Arrangement of different physical
components such that it may give
desired output from given input by
means of regulate or control either
by direct or indirect method.

3. A control system must have :
 Input
 Output
 Ways to obtain i/p and o/p objectives
 Control action
Any system can be characterised mathematically by
1. Transfer Function
2. State Model
Laplace transform of o/p
Transfer Function=
Laplace transform of i/p Initial
condition=0
L[c(t)]
L[r(t)]
=
C(s)
R(s)

4. z
Classification of Control
System
 Open loop C.S.
 Closed loop C.S.
1.Positive Feedback C.S.
2.Negative Feedback C.S.

5. z
Open Loop Control System
Reference
i/p
Controller Process Output
 Reference i/p controls the o/p through a control action process.
 From the diagram it can be observed that i/p has no control on o/p.
Such a system is called as open loop C.S.
 O/p is neither measured nor fed back to compare with i/p.
 Faithfulness of such system is depends on accuracy of i/p
calibration.
Ex. Traffic lights, fans any system without having sensor.

6. z
Advantages of Open Loop
C.S.
 Simple in construction and design.
 Economic
 Easy from maintenance point of view.
 Not much troubled with problems of stability.
 Convenient to use when o/p is difficult to
measure.

7. z
Disadvantages of Open Loop
C. S.
 Not accurate and reliable because is depends
on accuracy of calibration.
 Inaccurate results obtained with parameter
variation i.e. Internal disturbances.
 Recalibration is required time to time to
maintain quality and accuracy.

8. z
Closed Loop Control System
Reference
i/p
Controller Process Output
Feedback
Network
 Output has an effect on control system through feedback network.
 Control action is actuated by an error signal which is difference
between i/p and o/p signal.
 This process of comparison maintain o/p at desired level.
 Ex. Air conditioner

9. z
Advantages of Closed Loop
C.S.
 Accuracy is very high due to correction of any
arising error.
 Reduced effect of non-linearity.
 High bandwidth i.e high operating frequency
zone.
 Facilities of automation in these systems.

10. z
Disadvantages of Closed
Loop C. S.
 Complicated in design, hence costlier.
 May be unstable.