Control system

  Introduction to Control Systems : 

In modern times, control systems play a very important role in our daily life. The concepts of automatic 

conllOl are fundamental and well mixed in every aspect our life touches. From a simple bread ,toaster to a 

complex modem power plant, there is a series of control principles that affect our life. Elementary acts such ru. 

walking or moving a chalk to a particular point on the blackboard illustrate control principles. Advanced 

examples of launching a satellite, regulating the generation in a power plant, tracking an enemy plane on radar 

etc., show exhaustive application of control principles. Practically an engineer has to deal with-these systems in 

any industry he lands in, and so it is necessary to be familiar with the analysis and design aspects of modern 

control systems. The principles of control theory is applicable to engineering as well as non engin~_ring fields. 

In this chapter we get familiar with elementary definitions, classification, applications and control 

tenninology. 

 $  Important Definitions : 

(1) System : "A system is an arrangement of or a combination of different physical components 

connected or related in such a manner so as to form an entire unit to attain a certain objective". Thuc; 

a system is a collection of objects etc. in such a manner so as to achieve an aim or output. Thus a 

system has an input, an output and a way to achieve this input-output combination. 

(2) Output : "The actual response obtained from a system is C;alled output": 

(3) Input : "The stimulus or excitation applied to a control system from an external source 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". 

Combining the above definitions, 

(5) Control System : "It fs an arrangement of different physical elements  connected  in such  a manner  so as to regulate  direct or command  itself  to achieve a certain  objective 

Requirements of a Good Control System 

1..Accuracy : Accuracy . is very high feedback as any error  arising should  be connected  . Accuracy  can be improved  by  using feedback element, system becomes of feedback  element closed loop system 

improved by using feedback element. Because O · 

system In closed loop control system, steady state error tends to zero. 

2. Sensitivity : A co~trol system senses changes in output due to environmental or parametric changes, 

internal disturbances or any other parameters and corrects the same. Any control system should be 

insensitive to such parameters but very sensitive to the input signals. 

3  Noise : Noise is an undesired input signal. A good control system should be insensitive to such input 

signal. A good control system should be able to reduce the effects of wise or undesired inputs. 

4. Stability : Stability means bounded input and bounded output. In the absence of the inputs, the 

outpu!._ should tend to zero as time increases. A good control system response is stable for all variations. 

5.Bandwidth : Operating frequency range decides the bandwidth of any system. For frequency 

response of good control system, bandwidth should be large. The required output means maximum 

possible output without overshoots and it should be stable for required input frequency range. 

6.Speed : A good control system should have high speed. That is output of system should be as fast 

as possible.

  7..Oscillation : For a good control system, oscillations of output should be constant or sustained 

oscillation which follows the barkhausein's criteria.