Practical SCADA for Industry Titles in the series Practical Cleanrooms: Technologies and Facilities (David Conway) Practical Data Acquisition for Instrumentation and Control Systems (John Park, Steve Mackay) Practical Data Communications for Instrumentation and Control (John Park, Steve Mackay, Edwin Wright) Practical Digital Signal Processing for Engineers and Technicians (Edmund Lai) Practical Electrical Network Automation and Communication Systems (Cobus Strauss) Practical Embedded Controllers (John Park) Practical Fiber Optics (David Bailey, Edwin Wright) Practical Industrial Data Networks: Design, Installation and Troubleshooting (Steve Mackay, Edwin Wright, John Park, Deon Reynders) Practical Industrial Safety, Risk Assessment and Shutdown Systems (Dave Macdonald) Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems (Gordon Clarke, Deon Reynders) Practical Radio Engineering and Telemetry for Industry (David Bailey) Practical SCADA for Industry (David Bailey, Edwin Wright) Practical TCP/IP and Ethernet Networking (Deon Reynders, Edwin Wright) Practical Variable Speed Drives and Power Electronics (Malcolm Barnes) Practical SCADA for Industry David Bailey BEng, Bailey and Associates, Perth, Australia +J]OT=XOMNZ MIPENZ, BSc(Hons), BSc(Elec Eng), IDC Technologies, Perth, Australia Newnes An imprint of Elsevier Linacre House, Jordan Hill, Oxford OX2 8DP 200 Wheeler Road, Burlington, MA 01803 First published 2003 Copyright 2003, IDC Technologies. All rights reserved No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1T 4LP. Applications for the copyright holder's written permission to reproduce any part of this publication should be addressed to the publisher British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 07506 58053 For information on all Newnes publications, visit our website at www.com Typeset and Edited by Vivek Mehra, Mumbai, India (vivekmehra@tatanova.com) Printed and bound in Great Britain Contents Preface xiii 1 Background to SCADA 1 1.1 Introduction and brief history of SCADA 1 1.2 Fundamental principles of modern SCADA systems 2 1.5 Landlines for SCADA 6 1.6 SCADA and local area networks 7 1.7 Modem use in SCADA systems 7 1.8 Computer sites and troubleshooting 8 1.9 System implementation 9 2 SCADA systems, hardware and firmware 11 2.2 Comparison of the terms SCADA, DCS, PLC and smart instrument 12 2.2 Distributed control system (DCS) 15 2.3 Programmable logic controller (PLC) 15 2.5 Considerations and benefits of SCADA system 17 2.3 Remote terminal units 17 2.2 Analog input modules 19 2.3 Typical analog input modules 26 2.6 Counter or accumulator digital inputs 29 2.7 Digital output module 31 2.8 Mixed analog and digital modules 33 2.10 Power supply module for RTU 33 2.11 RTU environmental enclosures 33 2.12 Testing and maintenance 34 2.13 Typical requirements for an RTU system 35 2.5 PLCs used as RTUs 36 2.2 Basic rules of ladder-logic 38 2.3 The different ladder-logic instructions 40 2.6 The master station 46 2.1 Master station software 48 vi Contents 2.2 System SCADA software 48 2.3 Local area networks 48 2.5 Token ring LANs 51 2.6 Token bus network 52 2.7 System reliability and availability 52 2.1 Redundant master station configuration 52 2.8 Communication architectures and philosophies 54 2.4 CSMA/CD system (peer-to-peer) 59 2.9 Typical considerations in configuration of a master station 61 3 SCADA systems software and protocols 64 3.2 The components of a SCADA system 64 3.1 SCADA key features 65 3.3 The SCADA software package 67 3.2 System response time 72 3.3 Expandability of the system 72 3.4 Specialized SCADA protocols 72 3.1 Introduction to protocols 73 3.3 High level data link control (HDLC) protocol 78 3.4 The CSMA/CD protocol format 80 3.1 Causes of errors 83 3.2 Feedback error control 84 3.6 Distributed network protocol 87 3.4 IEC and IEEE 88 3.12 Application layer 97 Contents vii 3.7 New technologies in SCADA systems 97 3.1 Rapid improvement in LAN technology for master stations 97 3.2 Man machine interface 97 3.3 Remote terminal units 98 3.8 The twelve golden rules 98 4 Landlines 100 4.2 Background to cables 100 4.3 Definition of interference and noise on cables 101 4.4 Sources of interference and noise on cables 102 4.5 Practical methods of reducing noise and interference on cables 107 4.1 Shielding and twisting wires 107 4.4 Earthing and grounding requirements 111 4.5 Specific areas to focus on 111 4.6 Types of cables 112 4.1 General cable characteristics 112 4.2 Two wire open lines 114 4.3 Twisted pair cables 114 4.6 Theory of operation 116 4.7 Modes of propagation 118 4.8 Specification of cables 120 4.10 Limitations of cables 121 4.7 Privately owned cables 121 4.1 Telephone quality cables 121 4.2 Data quality twisted pair cables 122 4.3 Local area networks (LANs) 122 4.5 Assessment of existing copper cables 125 4.8 Public network provided services 125 4.9 Switched telephone lines 126 4.3 DC pulses 128 viii Contents 4.4 Dual tone multifrequency — DTMF 128 4.10 Analog tie lines 128 4.2 Four wire E&M tie lines 129 4.3 Two wire signaling tie line 130 4.4 Four wire direct tie lines 131 4.5 Two wire direct tie lines 131 4.11 Analog data services 131 4.2 Point-to-point configuration 132 4.3 Point-to-multipoint 132 4.5 Switched network DATEL service 134 4.6 Dedicated line DATEL service 134 4.12 Digital data services 135 4.13 Packet switched services 136 4.15 ATM 141 5 Local area network systems 142 5.2 Bus topology advantages 144 5.3 Bus topology disadvantages 144 5.3 Media access methods 146 5.5 10BaseF 153 Contents ix 5.5 MAC frame format 154 5.6 High-speed Ethernet systems 155 5.1 Fast Ethernet overview 156 5.2 100Base-TX and FX 157 5.8 Fast Ethernet design considerations 159 5.1 UTP Cabling distances 100Base-TX/T4 159 5.2 Fiber optic cable distances 100Base-FX 159 5.3 100Base-T repeater rules 160 5.9 Gigabit Ethernet 1000Base-T 160 5.1 Gigabit Ethernet summary 160 5.2 Gigabit Ethernet MAC layer 161 5.3 1000Base-SX for horizontal fiber 162 5.4 1000Base-LX for vertical backbone cabling 163 5.5 1000Base-CX for copper cabling 163 5.6 1000Base-T for category 5 UTP 163 5.7 Gigabit Ethernet full-duplex repeaters 163 5.10 Network interconnection components 164 5.11 TCP/IP protocols 169 5.1 The TCP/IP protocol structure 170 5.2 Routing in an Internet 170 5.3 Transmission control protocol (TCP) 171 5.12 SCADA and the Internet 172 5.1 Use of the Internet for SCADA systems 173 5.2 Thin client solutions 173 5.5 Conclusion 175 x Contents 6 Modems 176 6.2 Review of the modem 176 6.1 Synchronous or asynchronous 178 6.2 Modes of operation 179 6.3 Components of a modem 180 6.3 The RS-232/RS-422/RS-485 interface standards 182 6.1 The RS-232-C interface standard for serial data communication 182 6.2 Electrical signal characteristics 183 6.3 Interface mechanical characteristics 185 6.4 Functional description of the interchange circuits 185 6.5 The sequence of asynchronous operation of the RS-232 interface 186 6.7 Disadvantages of the RS-232 standard 188 6.8 The RS-422 interface standard for serial data communications 188 6.9 The RS-485 interface standard for serial data communications 190 6.4 Quadrature amplitude modulation (or QAM) 193 6.6 Error detection/correction and data compression 196 6.1 MNP protocol classes 196 6.2 Link access protocol modem (LAP-M) 197 6.3 Data compression techniques 198 6.7 Data rate versus baud rate 201 6.10 Troubleshooting the system 207 6.1 Troubleshooting the serial link 207 6.2 The breakout box 208 6.4 Troubleshooting the modem 209 6.11 Selection considerations 210 7 Central site computer facilities 212 7.2 Recommended installation practice 212 7.1 Environmental considerations 212 Contents xi 7.2 Earthing and shielding 213 7.1 Typical control room layout 215 7.5 Colors of equipment 217 7.4 Design of the computer displays 217 7.1 Operator displays and graphics 218 7.2 Design of screens 219 7.5 Alarming and reporting philosophies 220 8 Troubleshooting and maintenance 223 8.2 Troubleshooting the telemetry system 225 8.1 The RTU and component modules 225 8.2 The master sites 227 8.3 The central site 227 8.4 The operator station and software 227 8.4 The maintenance unit system 230 9 Specification of systems 232 9.7 Future trends in technology 234 9.1 Software based instrumentation 234 9.2 Future trends in SCADA systems 235 Appendix A Glossary 237 Appendix B Interface standards 258 Appendix C CITECT practical 262 Index 273 1 Background to SCADA 1.1 Introduction and brief history of SCADA This manual is designed to provide a thorough understanding of the fundamental concepts and the practical issues of SCADA systems. Particular emphasis has been placed on the practical aspects of SCADA systems with a view to the future.
Formulae and details that can be found in specialized manufacturer manuals have been purposely omitted in favor of concepts and definitions. This chapter provides an introduction to the fundamental principles and terminology used in the field of SCADA. It is a summary of the main subjects to be covered throughout the manual. SCADA (supervisory control and data acquisition) has been around as long as there have been control systems.
The first ‘SCADA’ systems utilized data acquisition by means of panels of meters, lights and strip chart recorders. The operator manually operating various control knobs exercised supervisory control. These devices were and still are used to do supervisory control and data acquisition on plants, factories and power generating facilities. The following figure shows a sensor to panel system.1 Sensors to panel using 4–20 mA or voltage 2 Practical SCADA for Industry The sensor to panel type of SCADA system has the following advantages: • It is simple, no CPUs, RAM, ROM or software programming needed • The sensors are connected directly to the meters, switches and lights on the panel • It could be (in most circumstances) easy and cheap to add a simple device like a switch or indicator The disadvantages of a direct panel to sensor system are: • The amount of wire becomes unmanageable after the installation of hundreds of sensors • The quantity and type of data are minimal and rudimentary • Installation of additional sensors becomes progressively harder as the system grows • Re-configuration of the system becomes extremely difficult • Simulation using real data is not possible • Storage of data is minimal and difficult to manage • No off site monitoring of data or alarms • Someone has to watch the dials and meters 24 hours a day 1.2 Fundamental principles of modern SCADA systems In modern manufacturing and industrial processes, mining industries, public and private utilities, leisure and security industries telemetry is often needed to connect equipment and systems separated by large distances.
This can range from a few meters to thousands of kilometers. Telemetry is used to send commands, programs and receives monitoring information from these remote locations. SCADA refers to the combination of telemetry and data acquisition. SCADA encompasses the collecting of the information, transferring it back to the central site, carrying out any necessary analysis and control and then displaying that information on a number of operator screens or displays.
The required control actions are then conveyed back to the process. In the early days of data acquisition, relay logic was used to control production and plant systems. With the advent of the CPU and other electronic devices, manufacturers incorporated digital electronics into relay logic equipment. The PLC or programmable logic controller is still one of the most widely used control systems in industry.
As need to monitor and control more devices in the plant grew, the PLCs were distributed and the systems became more intelligent and smaller in size. PLCs and DCS (distributed control systems) are used as shown below. Background to SCADA 3 PLC or DCS PC Sensors A fieldbus Figure 1.