ueeneed026b design a computer based control system · reference list ... relay control systems that...

UEE07 Electrotechnology Training Package

Learner Workbook

Version 1

TRAINING AND EDUCATION SUPPORT

INDUSTRY SKILLS UNIT, MEADOWBANK

Product 5495

UEENEED026B

Design a computer based control system

SAMPLE

UEENEED026B Design a computer based control system

Developed by Training & Education Support Industry Skills Unit, Meadowbank

@ TAFE NSW 2011

Acknowledgments

The TAFE NSW Training and Education Support Industry Skills Unit, Meadowbank

would like to acknowledge the support and assistance of the following people in

the production of this learner workbook:

Writers:

Jeffrey Stokes

TAFE NSW

Reviewers:

TAFE NSW

Project Manager:

Steve Parkinson

TAFE NSW

Enquiries

Enquiries about this and other publications can be made to:

Training and Education Support Industry Skills Unit, Meadowbank

Meadowbank TAFE

Level 3, Building J,

See Street,

MEADOWBANK NSW 2114

Tel: 02-9942 3200 Fax: 02-9942 3257

ISBN 978-1-74236-256-4

© The State of New South Wales, Department of Education and

Training, TAFE NSW, Training and Education Support Industry Skills

Unit, Meadowbank, 2011.

Copyright of this material is reserved to TAFE NSW Training and Education

Support Industry Skills Unit, Meadowbank. Reproduction or transmittal in

whole or in part, other than for the purposes of private study or research, and

subject to the provisions of the Copyright Act, is prohibited without the written

authority of, TAFE NSW. Training and Education Support Industry Skills Unit,

Meadowbank.

SAMPLE



@ TAFE NSW 2011

Table of contents

Introduction .................................................................................. 9

1. General introduction ........................................................................... 9

2. Using this learner workbook ................................................................ 9

3. Prior knowledge and experience ......................................................... 11

4. Unit of competency overview ............................................................. 11

5. Assessment ..................................................................................... 16

Section 1: .................................................................................... 17

Control System Architecture ........................................................ 17

1.1 Microprocessor Based Controllers ........................................................ 17

1.2 PC Based Control Systems ................................................................. 21

1.3 Distributive and Hybrid Systems ......................................................... 30

1.4 Safety Considerations in Control System Design ................................... 34

Section 2: .................................................................................... 39

Measurement, Signals and Connections ....................................... 39

2.1 Industrial Sensors ............................................................................. 39

2.2 Controller I/O Electrical Specifications ................................................. 42

2.3 Signal Conditioning and Calibration ..................................................... 46

2.4 Input Protection Methods ................................................................... 48

2.5 Data Signals and Connections ............................................................. 51

Section 3: .................................................................................... 53

Control Programming .................................................................. 53

3.1 PLC Programming ............................................................................. 53

3.2 SCADA Programming ......................................................................... 55

3.2 Data Acquisition Systems ................................................................... 57

Section 4: .................................................................................... 61

SAMPLE



@ TAFE NSW 2011

Introduction to Labview .............................................................. 61

4.1 Labview Installation and Setup ........................................................... 61

4.2 Creating a Virtual Instrument (VI) ....................................................... 66

4.4 Introduction to HMI Design ................................................................ 72

Section 5: .................................................................................... 75

Analogue to Digital Conversion .................................................... 75

5.1 ADC Methods ................................................................................ 75

5.2 Resolution and Sample Rate ............................................................... 77

5.3 Noise Reduction ................................................................................ 78

5.4 Data Logging .................................................................................... 82

Section 6: .................................................................................... 83

Introduction to Visual Basic.net .................................................. 83

6.1 VB.net Installation and Setup ............................................................. 83

6.2 Navigating the IDE ............................................................................ 84

The Default Form ......................................................................... 86

6.3 Components and Properties ................................................................ 87

6.4 Events, Methods and Functions ........................................................... 97

6.5 Data Types and Variable Declarations .................................................. 98

6.6 Testing and Debugging a Program ..................................................... 111

Section 7: .................................................................................. 115

Programming Structures ........................................................... 115

7.1 If... Then... Else .............................................................................. 115

7.2 Select... Case ................................................................................. 117

7.3 For... Next ..................................................................................... 118

7.4 Do... While and Do... Until ............................................................... 119

7.5 Writing Function, Moving Objects ...................................................... 120

SAMPLE



@ TAFE NSW 2011

Section 8: .................................................................................. 131

Advanced Maths Techniques ...................................................... 131

8.1 Order of Operations......................................................................... 131

8.2 Trigonometric Functions ................................................................... 132

Section 9: .................................................................................. 133

Graphical Methods and Techniques ........................................... 133

9.1 Drawing in a Picture Box .................................................................. 133

9.4 Form and Component Opacity .......................................................... 136

Section 10: ................................................................................ 139

Control Programming Techniques .............................................. 139

10.1 Accessing I/O Devices .................................................................... 139

10.2 The Basic Control Loop .................................................................. 139

10.3 Timing Functions ........................................................................... 140

10.4 Counting External Events ............................................................... 141

Reading and Scaling Analogue Values ..................................................... 144

Section 11: ................................................................................ 147

Software Design Planning ......................................................... 147

11.1 Top-Down Methodology.................................................................. 147

11.2 Project Planning ............................................................................ 148

11.3 Modular Programming .................................................................... 150

11.4 Documenting Software Design Projects ............................................ 151

Section 12: ................................................................................ 153

Software Design Implementation – Project ............................... 153

12.1 Control Algorithms ........................................................................ 153

12.2 Data Logging Features ................................................................... 155

12.3 Programming Alarms ..................................................................... 156

SAMPLE



@ TAFE NSW 2011

12.4 Programming Access Control .......................................................... 158

12.5 Managing Project Changes ............................................................. 159

Section 13: ................................................................................ 161

Beta Testing and System Commissioning .................................. 161

13.1 Testing Modules of Code ................................................................ 161

13.2 Safety Testing and System Commissioning ....................................... 161

13.3 Commissioning Documentation ....................................................... 161

13.4 Operating Manuals and Training ...................................................... 161

Section 14: ................................................................................ 163

Data Communications Features ................................................. 163

14.1 Networks ..................................................................................... 163

14.2 Network Topologies ....................................................................... 173

14.3 Network Standards and Protocols .................................................... 174

Section 15: ................................................................................ 177

Computer Based Control System Project ................................... 177

15.1 System Planning ........................................................................... 177

15.2 System Implementation ................................................................. 178

15.3 System Problem Solving ................................................................ 179

15.4 System Completion ....................................................................... 180

Reference list ............................................................................ 183

Resource Evaluation Form ......................................................... 185

SAMPLE


Page 17 of 188

Section 1:

Control System Architecture

1.1 Microprocessor Based Controllers

Control System History

Early in the history of what we would call modern industrial

development, control systems were manually operated. They

relied on human measurement and decision making. This

means that they were flawed.

Over a period of time many

manual systems, especially

simple ON/OFF control

systems, were replaced with

relay control systems that

were capable of a level of

automation.

These were more reliable and saved money

because of the lower labour cost. Relay

operation is still relatively slow to respond to

process changes when compared with

electronics and systems still broke down often,

due to the electromechanical nature of the

devices used. We still use relays today but only

to isolate and control loads. They are not as

part of the control. If a relay operation takes 15

milliseconds and there are 10 stages in the

control circuit where one relay drives another,

the propagation of the signal might be greater

than 150 milliseconds. This is inadequate for

many applications today.

With the invention and introduction of

electronic devices, some relay control systems

were replaced by dedicated digital systems.

These systems were able to respond more

quickly and required less maintenance as the

devices were “solid state”, an old fashioned

term meaning that they had no moving parts.

They were essentially still hard-wired though,

and process modifications and fixes meant that

part of the system had to be re-designed and

re-wired. It was not until the arrival of the

microprocessor, that programmable control

was made possible.

Figure 1 Manual Valve

Figure 2 3000 Type relays used for control

Figure 3 Early transistor circuits in computers

SAMPLE


Page 18 of 188

Eventually the PLC was invented. It came about because of the needs of the

automotive manufacturers who needed to make changes to designs and build

new models.

PLCs became popular for control and are

still currently the most common solution

used by control engineers and electricians.

They grew in size and power until their

complexity made them too slow for some

applications. It is now more common to use

several small PLCs that communicate with

each other than one very large PLC with a

lot of processing power.

Activity box – A1.1

Using the Internet links below, complete the following

activities and respond in the space provided.

http://en.wikipedia.org/wiki/Programmable_logic_controller

http://www.machine-information-systems.com/PLC_History.html

http://www.plcs.net/chapters/links.htm

1.

In what year was the

very first PLC

designed?

2.

Why is it that PLC

programs have a

“ladder” like layout

rather than being

written in a normal

programming

language?

3.

List four well known

PLC manufacturers.

Figure 4

A shoebox PLC

SAMPLE

http://en.wikipedia.org/wiki/Programmable_logic_controller



http://www.plcs.net/chapters/links.htm


Page 19 of 188

Microprocessor Control

There are a number of choices in regard to a control system

solution. The decision to utilise a specific type of controller

and control system architecture is often based on the

number of inputs and outputs required and the complexity of

the control algorithms and therefore the processing power

required to do the calculations. Other considerations might

be the development time available, the lifecycle of the

project, the likelihood of process changes and limits on the

cost of system implementation.

Some of the choices are;

An embedded system (a dedicated system) such as is used for TV remote

controls, simple alarm systems and pool chlorination systems. In such

systems, a microprocessor or microcontroller executes a program that is

stored as “firmware” in EPROM memory. Costs for these systems are very

low because of mass production. If large production numbers are not

required, this sort of system is often not viable.

A single PLC, or a number of PLCs,

(a programmable system) where

changes are easily made and the

costs of both equipment and

development time are relatively

low. These systems are capable of

some analogue measurement but

only in a limited way. If a large

number of analogue channels are

required or very high sample rates,

then other solutions might be more

effective.

A third option is to use what is popularly called a single board computer.

This is something that has a PC operating system but is a limited

configuration in terms of computing power, memory and communications

capabilities. The benefits of a single board computer are that its power

consumption is low and

physically, it can be incorporated

in pieces of equipment. Flash

memory is used instead of a

hard drive. Graphics processors

are limited compared with a

normal PC and the processor is a

low power (slower) version of

standard CPU. Even today, it is

often a Pentium 4, not dual core

PC architecture. Software can be

developed easily as it is still

essentially a PC platform.

Figure 5 Embedded System

Figure 6 PLCs with SCADA control

Figure 7 Single Board Computer with onboard graphics,

Ethernet, expansion bus and USB ports

SAMPLE


Page 20 of 188

Ever since the advent of the personal computer, a PC based control

system has been an option. The processing power available in such a

system makes it perfect for complex measurement, analysis and advanced

control systems. The use of a PC along with data acquisition hardware, is

common in scientific circles. It is less commonly used in industry because

of the relatively high cost. As industrial process control becomes more

sophisticated and the price of PC technology continues to fall, this is

becoming less of a constraint. This type of control is the focus of this unit

of competency.

Technology Change

1. Why answer questions about historically irrelevant technology? Simply to

bring into focus the fact that technology will not stop changing. The

control solutions that are common today may not meet the needs of

tomorrow‟s industry.

Activity box – A1.2

Try to guess what year each of the two computers above

is from. The first is a relatively early PC. You will notice

the two floppy drives. There was no hard drive. Each time

you booted the PC you had to load the operating system

from a floppy disk.

The second PC is fairly recent. The flat LCD monitor

places it within the last five years.

Write your responses

to the right.

PC 1 PC 2

Figure 8 Two computers from different generations

SAMPLE

ueeneed026b design a computer based control system · reference list ... relay control systems that...

Documents