A control system is a system of devices or a set of devices that manages, orders, directs or regulates the behaviour of other devices or systems to achieve desired results. In other words the definition of control system can be rewritten as a control system is a system, which controls another system. As human civilisation is modernised day by day the demand for automation is increasing accordingly. Automation highly requires device control. In recent years, control systems have played a major role in the development and advancement of modern technology and civilisation. Virtually every aspect of our daily lives is less or more affected by some control system. A bath tank, a refrigerator, an air conditioner, a geezer, an automatic iron, a car are all control system. These systems are also used in industrial processes to obtain more power. We found the control system in product quality control, weapons system, transportation systems, power system, space technology, robotics and many more. The principles of control theory are applicable to both engineering and engineering.


Characteristics of the control system

The main feature of the control system is that there must be a clear mathematical relationship between the input and the output of the system. When the relationship between the input and the output of the system can be represented by a linear proportionality, the system is called a linear control system. Again when the relation between input and output can not be represented by a single linear proportionality, rather the input and output are related by some nonlinear relationship, the system is called a nonlinear control system.

Requirement of a good control system

Accuracy: Accuracy is the measurement tolerance of the instrument and defines the limits of errors made when the instrument is used under normal operating conditions. Precision can be improved by using feedback elements. To increase the accuracy of any error detector of the control system must be present in the control system. 
Sensitivity: The parameters of the control system are always changing with the change in surrounding conditions, internal disturbance or any other parameter. This change can be expressed in terms of sensitivity. Any control system must be insensitive to such parameters but sensitive to input signals only. 
Noise: An unwanted input signal is known as noise. A good control system should be able to reduce the noise effect for better performance. 
Stability: This is an important feature of the control system. For the bounded input signal, the output must be delimited and if the input is zero, then the output must be zero, then said control system is said to be a stable system.
 Bandwidth: An operating frequency range decides the bandwidth of the control system. The bandwidth should be as large as possible for the frequency response of a good control system. Speed: It is the time it takes the control system to achieve its stable output. A good control system has high speed. The transitional period for this system is very small. 
Oscillation: A small number of oscillation or constant oscillation of the output tends to the system to be stable.