What is Control Systems & Types of Control systems

What is Control System?

          Let us study about a new type of engineering study which is called as Control Systems Engineering.It’s very interesting subject and has a lot of calculation part.Control system theory evolved as an engineering discipline and due to the universality of the principles involved, it is extended to various fields like economy, sociology, biology, medicine etc.In this, you will learn about open and closed loop control system and also their differences. 

      Control System theory has played a vital role in the advance of engineering and science.The automatic control has become an integral part of modern manufacturing and industrial processes.For example, numerical control of machine tools in manufacturing industries, controlling pressure, temperature, humidity, viscosity and flow in the process industry.

             When a number of elements or components are connected in a sequence to perform a specific function, the group thus formed is called a system.In a system when the output quantity is controlled by varying the input quantity, the system is called control system.The output quantity is called controlled variable or response and input quantity is called command signal or excitation. 

                                           

                                         

Types of Control systems:

Control systems are of two types.They are 

1)Open Loop System

2)Closed Loop System

1)Open loop control system:

Any physical system which does not automatically correct the variation in its output is called an open loop system or control system in which the output quantity has no effect upon the input quantity are called open loop control system.This means that the output is not feedback to the input for correction.

                          

                                 

In open loop control system, the output can be varied by varying the input.But due to external disturbances, the system output may change.When the output changes due to disturbances, it is not followed by changes in input to correct the output.In open loop systems, the changes in output are corrected by changing the input manually.

2)Closed loop control system: 

Control systems in which the output has an effect upon the input quantity in order to maintain the desired output value are called closed loop systems.

                The open loop system can be modified as closed loop system by providing a feedback.The provision of feedback automatically corrects the changes in output due to disturbances.Hence the closed loop system is also called automatic control system.The general block diagram of an automatic control system is shown in the figure below.It consists of an error detector, a controller, plant (open loop system) and feedback path elements.

                        

                      

                   The reference signal (or input signal) corresponds to the desired output.The feedback path elements sample the output and convert it to the same type as that of the reference signal.The feedback signal is proportional to the output signal and it is fed to the error detector.The error signal generated by the error detector is the difference between the reference signal and the feedback signal.The controller modifies and amplifies the error signal to produce better control action.The modified error signal is fed to the plant to correct its output.

Advantages of Open loop control system: 

1.The open loop systems are simple and economical.

2.The open loop systems are easier to construct.

3.Generally, the open loop systems are stable.

Disadvantages of open loop systems:

1.The open loop systems are inaccurate and unreliable.

2..The changes in the output due to external disturbances are not corrected automatically.

Advantages of closed loop systems:

1.The closed loop systems are accurate.

2.The closed loop systems are accurate even in the presence of non-linearities.

3.The sensitivity of the systems may be made small to make the system more stable.

4.The closed loop systems are less affected by noise.

Disadvantages of closed loop systems:

1.The closed loop systems are complex and costly.

2.The feedback in closed loop system may lead to an oscillatory response.

3.The feedback reduces the overall gain of the system.

4.Stability is a major problem in closed loop system and more care is needed to design a stable closed loop system.