Control System

What is Control System?

When a number of devices or elements are combined together to produce a desired output then such a system is said to be control system. Each device or element has its own effect on the output. So we can define the Control System as;

Definition of Control System

A control system is a system of devices or set of devices, that manages, commands, directs or regulates the behavior of other device or system to achieve desire results.

Fig. 1

Use of Control Systems in daily life

In recent years, control system plays an important in automation of daily used products and things. For example a refrigerator, an air conditioner, a geezer, an automatic iron, an automobile all are control system.These systems are also used in industrial process for more output. We find control system in weapons system, power system, transportation systems,  space technology, robotics and many more. The principles of control theory is applicable to engineering and non engineering field both.

Feature of Control System

It is feature of control system that is has clear mathematical relation between its input and output. If the relation between input and output is represent by linear proportionality then the control system is called linear control system. When the relation between input and output is represent by non-linear proportionality then the control system is called non linear control system.

Control System Requirements

Good control system has following requirements;

1. Accuracy: High Accuracy
2. Sensitivity: Sensitive to input signals only
3. Noise: A good control system should be able to reduce the noise effect for better performance
4. Stability: It Should be stable
5. Bandwidth: Bandwidth should be large as possible for frequency response of good control system
6. Speed: A good control system possesses high speed
7. Oscillation: A small numbers of oscillation or constant oscillation of output tend to system to be stable

Types of Control System

There are basically two main types of control system i.e Open Loop control system and Closed Loop control system.

• Open Loop Control System : If the control action of the control system is independent of the output then the system is called open loop control system (see Fig.2a).

Fig.2a

     

    . Advantages of Open Loop Control System:       Following are the advantages of open loop control system;

1. Its construction is easy.
2. Its design is simple
3. It is economical as its price is low.
4. Easy to maintain.
5. Generally stable.

  . Disadvantages of Open Loop Control System:

     Following are the disadvantages of open loop control system;

1. These are inaccurate.
2. Reliability is less.
3. Output cannot be correct automatically.

• Closed Loop Control System : If the output of the control system has effect on its input quantity in such a way that input can adjust in accordance with that output is called closed loop control system (see Fig.2b).

Fig.2b

    . Advantages of Closed Loop Control System:       

                                                                                 Following are            the advantages of closed loop control system

1. More accurate.
2. Facilitates the automation.
3. Bandwidth is large
4. Less effected by noise.

   . Disadvantages of Open Loop Control System:

                                                                                  Following are          the disadvantages of open loop control system

1. Complex in design.
2. Cost is high.
3. Maintenance is difficult.