Control System Basics

What is Control System?

 Is it like a system which can be controlled?

Yes, Right. That it is. A system in which the output is controlled by varying the input. The first control system device was James Watt's Flyball governor, which was invented in 1767. The aim of inventing Flyball governor was to keep the speed of the engine constant by regulating the supply of the steam to the engine.

As above shown system, change in input will bring changes in output.

 Terminology in control system:

State: The state of a system is the set of parameters that describe it at a given point in time.

Model: A set of expressions which represent the behavior of the system.

 There are two types of control system.

1) Open loop control system

An open-loop control system is a system in which the control action is independent of the desired output signal. In this system, the output signal is not compared with the input signal which means there is no feedback signal in this system. The open-loop control system is also known as a non-feedback control system or control system without feedback.

Let’s learn it with example :-

Automatic washing machine - In this system, the operating time is set manually. After the completion of the set time, the machine stops whether the desired cleanness is obtained or not because there is no feedback signal which the machine can sense.

Advantages: Simple, Economical, Low maintenance

Disadvantages: Inaccurate, Not-reliable, slow, optimization is not possible.

2) Closed loop control system

A closed loop control system is a system in which control action is dependent on the desired output. In this system, the output signal is compared with the reference input signal, and an error signal is produced then this error signal is fed to the controller to reduce the error to obtain the desired output.

Let’s learn it with example :-

An Air Conditioner – In this system  the heated enclosure air is drawn into the air conditioner by a powerful blower where heat and moisture are removed as it passes through an evaporator coil and forced back into the enclosure, As per temperature you set, you will get your desired output state.

Advantages: More reliable, faster, optimization possible, more variables can be handled

Disadvantages: Expensive, Maintenance difficulty, Installation difficulty