Government Engineering College, Modasa

Control System Engineering

Module I : Introduction to Control System

Created by : Kazim Marfatiya

Contents

• Introduction• Important terms• Types of Systems 1) Open loop system 2) Close Loop system• Comparison of Systems• Requirements of a good control system• Feed Forward system• Design Process

Introduction

• Control system are an integral part of our lives and play very important role.

• From a simple bread toaster to complex power plant, control system are all around us and inseparable part of modern society.

• Launching a satellite in orbit, regulating a power plant, tracking enemy on radar are some of man made control system..

• Control system occur in nature also. Human body is a great example of complex Control system, because we've so many control system by nature i.e. respiratory, Digestive system etc.

Important terms

• Control system : A control system is an arrangement or a combination of various physical components, also called sub-systems, connected in such a manner so as to attain a certain objective.

• Input : The excitation applied to the system from an external source to attain a output is called input signal

• Output : The actual signal attain from system is called output signal.

• Control action : is a quantity responsible for activating the system.

Control systemInput Outpu

t

Fig.(1) Basic Block Diagram of Control System

Must have things in the control system:1. Inputs 2. Outputs3. An arrangement of subsystems to achieve the input-output

combination

There are two types of systems depending on the configuration of components:

1) Open loop system 2) Close loop system

Open loop system

• Those systems in which the output has no effect on the control action are called open-loop control systems. i.e. It doesn’t automatically correct the changes in the output

• A system in which control action is independent of the output of the system is called as open loop system.

• In open loop system, the output remains constant for a given input provided the external conditions are the same.

• There is no connecting action taking place in an open loop system i.e. No Feedback

Controller PlantInput Signal

Output

• Examples of Open loop system Electric Hand Drier Automatic Washing Machine Bread Toaster

• Advantages 1) Simple Construction & Design 2) Economic 3) Easy maintenance 4) Stability• Disadvantages 1) Incorrect and unreliable 2) Internal Disturbance 3) Recalibration is required time to time

Close loop system

• A system in which the control action is dependent on the output is called close loop system. In close loop system the output is constantly monitored and adjusted to the required value by the system.

• The output signal is fed back and compared to the reference input.

• Depending upon the difference between the output signal and reference input, corrective actions can be taken by the controller to adjust the output.

• i.e. Air-conditioning unit

Transducer

Controller

Sensing device/Feedback element

PlantInput

Output

• Example of close loop system Automatic Electric Irons Voltage Stabilizer DC motor speed control by Tachometer Missile Launcher• Advantages 1) Accuracy is high 2) Reduced effect of non-linearties 3) High Bandwidth 4) Facilitates Automation • Disadvantages 1) Complicated in design and maintenance costlier 2) Problem of Stability

Comparison of Open loop and Close loop system

Sr. No. Open Loop System Close loop System

1. No feedback. Hence feedback element is absent.

Feedback exists. Hence feedback elements are exists.

2. No error detector. Error detector is present.

3. It is inaccurate. It is accurate.

4. Highly sensitive to parameter changes.

Less sensitive to parameter changes.

5 Small bandwidth. Large bandwidth.

6. Stable. May become unstable.

7. Economical. Costly.

8. Examples: Coffee maker, hair drier

Example: Guided missile, servo voltage stabilizer

Feed forward System

• In feed forward systems the output of one stage of control system is sent to improve the overall performance of control system. It is used whenever there is disturbance.

Feed Forward System

System

Sensor

Disturbance

Input signal

Outputsignal

The Design Process

Physical system

Draw a functiona

l block diagram

Convert into a

schematic

Obtain a precise block

diagram or signal

flow chart

Get a transfer Function

Analyze by checking

for stability and see if

specifications are met

Thank You