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IntroductionControl systemLecture 1

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Lesson Objectives:

1. To define a control system.2. Open loop and closed loop systems

Lesson

Objectives:

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Lesson Objectives 01

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To define a controlsystem

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Control System DefinitionControl System DefinitionControl System DefinitionControl System Definition

A control system consists of subsystems and processes (or plants)assembled for the purpose of obtaining a desired output with desired

performance, given a specified input.

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Systems: collections of subsystems/components

Input: reference value/actuation signal/set point

Output: measured response/actual result

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Example

Consider an elevator

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A control system inits simplest form

The inputrepresents adesired output

When the eighth-floor button is pressed on the first floor, the elevator rises to the eighthfloor with a speed and floor levelling accuracy designed for passenger comfort

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Control system

The performance of the elevator can be seen from the elevator response

curve in the figure. Two major measures of performance are apparent: (1) the transient

response and (2) the steady-state error.

In our example, passenger comfort and passenger patience are dependent

upon the transient response. If this response is too fast, passenger comfort

is sacrificed; if too slow, passenger patience is sacrificed.

The steady-state error is another important performance specification

since passenger Safety and convenience would be sacrificed if the

elevator did not properly level.

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What is a control system?

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A control system consists

of subsystems and plantassembled for the purpose

of controlling the outputs

of the plants. Norman S.Nise

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Elements of a control system?

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Any control system consist of four elements:

1. The input is the desired response of acontrol system

2. The output is the actual response of acontrol system

3. Subsystem is any system that helps

controlling the output of the controlsystem

4. A plant is a system in which its output isthe one to be controlled

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Example of a control system

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Desiredlight

ActualLightOn-Off

Switch Bulb

Control System

Room

Desiredtemp

Actual

temp

Temp

Settingknob

AirConditioned

Control System

Room

On

OffSwitch

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Lesson Objectives 02

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Open loop and closed

loop system

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Control system types

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Two types:

1. Open loop control system

2. Closed loop control system.

Also called Feedback control

system or Automatic controlsystem

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Open loop system

Open loop system is also known as non feedback system

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For example, the plant can be a furnace or air conditioning system, where the output

variable is temperature. The controller in a heating system consists of fuel valvesand the electrical system that operates the valves.

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Control System Configurationsa. Open-loop system

Examples:

Toaster

Mechanical System with Mass and Spring

Characteristics: Simple, less complicated configuration

Could not compensate for any disturbances

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Closed loop system

Closed-Loop Control Systems utilizes feedback tocompare the actual output to the desired output response.

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Closed loop system: Example

Speed control of car

Objective: To keep moving atconstant speed

Activities in controlling car

Reading speedometer

Deciding to increase or decreasespeed

Acting on the gas pedal

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(a) Automobile steeringcontrol system.

(b) The driver uses thedifference between theactual and the desired

direction of travel to generatea controlled adjustment ofthe steering wheel.

(c) Typical direction-of-travelresponse.

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Closed loop system: Example

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Control System ConfigurationsClosed-loop system

Characteristic:

Compensates disturbances to the system for greater accuracy

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Control system types

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Open-loop control system?

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Desiredlight

ActualLight

On-OffSwitch

Bulb Room

Sun Light orBlocked light

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Closed-loop control system?

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Desiredlight Actual

Light

On-Off

Switch Bulb Room

Sun Light or blocked light

Light

sensor

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Open-loop control system?

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Desiredtemp

ActualtempTemp

Settingknob

On-Offswitch

Room

People in the room

Airconditioned

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Closed-loop control system?

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Desired

temp

Actual

tempTempSettingknob

OnOff

switch

Room

People in the room

Airconditioned

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Control systems Introduction

Why Control?

Modern society have sophisticated control systems whichare crucial to their successful operation.

Reasons to build control systems: Power amplification

Remote control

Convenience of input form

Compensation for disturbance

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Control systems Introduction

Feedback

Feedback is a key tool that can be used to modify thebehavior of a system.

This behavior altering effect of feedback is a keymechanism that control engineers exploit deliberately to

achieve the objective of acting on a system to ensure that

the desired performance specifications are achieved.

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Control systems Introduction

What is the Control System

Engineer trying to achieve?

First, understand the broader picture of the

application to best apply a suitable control system.

A good control system is a system that will

generate a response quickly and without oscillation(good transient response),

have low error once settled (good steady-state response),

and will not oscillate wildly or damage that system(stability).

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Control systems Introduction

Control System DesignCycle

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Next lecture

Review of Laplace transform Modeling

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