SCADA: Supervisory Control and Data Acquisition, Fourth Edition

Stuart Boyer

• Publisher: International Society of Automation
• Year: 2010
• Print ISBN: 9781936007097
• eBook ISBN: 9781941546178
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Supervisory control and data acquisition (SCADA) technology has evolved over the past 30 years as a method of monitoring and controlling large processes. This reference book offers overviews of SCADA's component technologies, as well as details necessary to understand the big picture. SCADA processes cover areas that may be in the thousands of square miles, and have dimensions that may be hundreds, occasionally thousands, of miles long. Now a mature technology, SCADA includes, but is not limited to, software packages that can be incorporated into a system of hardware and software to improve the safety and efficiency of the operation of these large processes. After completing these 15 self-study units, readers should be conversant with SCADA nomenclature and architecture, understand the basic technology of the system's building blocks, understand its limitations, understand how it can benefit particular operations, and have a basis for selecting appropriate SCADA technology for their operational requirements. This Fourth Edition includes a unit about improving the security of SCADA systems and has been rearranged to provide a more logical presentation of the subject.

UNIT 1

Introduction and Overview

Welcome to the ISA’s text on SCADA, Supervisory Control And Data Acquisition. This unit provides an overview of the book and the information you will need for independent study.

Learning Objectives—When you have completed this unit you should:

A.    Understand the general organization of the material in this course.

B.    Know the course objectives.

1-1.    Text Coverage

This text provides introductory technical material about SCADA systems. It addresses the basic layout of SCADA systems and the parameters for system selection. Communications and the basic building blocks of SCADA systems are dealt with in some detail. System security methods and the need for security are considered. Applications examples are provided and discussed. Economic evaluations are mentioned.

No recommendations about specific equipment types or methods are provided; however, techniques that will help the reader to make such selections are included.

1-2.    Purpose

The purpose of this text is to introduce the student to the basics of SCADA by providing overviews of relevant topics where appropriate and details where necessary. SCADA consists of the elements of several different technologies and it is sometimes difficult to know where to stop when describing some of these technologies. The text will focus on such technologies to the extent that doing so makes SCADA more understandable. This text will also attempt to identify major differences between the SCADA systems of different industries, but because the basics of SCADA are much the same from one industry to another, examples from many industries have been included throughout the text.

1-3.    Audience and Prerequisites

This text is designed for those who wish to learn the basics of SCADA by themselves at their own pace. It will be useful to managers, supervisors, engineers, operators, and technicians who contemplate coming in contact with SCADA systems. It will also be useful to students of technical schools and colleges as an introduction to the subject. For any technical people who have a personal interest in the subject, it should serve as a source of overview information about SCADA.

1-4.    Study Materials

This text is the only required study material for learning the basics of the subject. For those who want or need to learn additional details about some aspects of the subject, Appendix A provides a comprehensive list of readings and other study material.

1-5.    Organization and Sequence

This text is divided into fifteen separate units. Unit 2 is an overview of SCADA that provides some definitions and describes elements and some of the limits of SCADA systems. It will focus the student’s attention on those factors that make SCADA what it is.

Unit 3 provides a sketch of the technology and defines it in the context of related technologies. Unit 3 also discusses analog and digital measurement and nomenclature.

Unit 4 considers the effect of time on a SCADA system. Certain functions must be completed before other functions are started. In addition, a definition of Real-Time Systems is discussed and methods of calculating scan times are introduced.

Unit 5 talks about control system elements. Sensors, used to measure what the process or equipment is doing; and actuators, used to make changes to the process, are introduced in this unit. Control algorithms are discussed to the extent needed for an understanding of how they can be used in SCADA.

Unit 6 addresses the specific needs of communication between field sensors/actuators and RTUs.

Unit 7 is about one of the main pieces of hardware unique to SCADA systems, the Remote Terminal Unit (RTU). The necessary functionality of RTUs is described, and several hardware methods to achieve this functionality are presented.

Of course, for a SCADA system to work, the RTUs must also be able to communicate with Master Terminal Units. Unit 8 discusses how this happens and the problems that must be defeated for this to happen. Developments in this form of communication are among the things affecting the way SCADA systems are now being designed and built. This is the unit where protocols are detailed.

Master terminal units, the other equipment unique to SCADA, are explained in Unit 9. Their functionality, layouts, and particular requirements are discussed in some detail in this unit.

Unit 10 discusses methods of communication between the system and the human operator. Because SCADA systems are often being integrated into corporate enterprise systems, Unit 10 also discusses some advantages and disadvantages of doing so.

Unit 11 considers whether SCADA is a remote control system or an automatic control system. This unit will also offer some suggestions about system reliability and how the lack of reliability should affect the way you apply the system.

Security is the subject of Unit 12. Early SCADA systems paid scant attention to this aspect of design. Modern systems pay more attention to this feature. Additionally, methods of improving security are being developed that will result in very secure control and monitoring of the process.

Unit 13 provides a list of applications that are being used by companies now. You may come across an application for your company that you had not thought of, or you may feel that your design is complete if you do not find an application that you have not already included.

Unit 14 outlines some of the directions in which SCADA may move in the near future. As technologies improve, these improvements may be harnessed to push or pull SCADA in different directions.

Unit 15 discusses the economics that must be considered when justifying a SCADA project. The concept of present value is introduced.

Appendix A provides a bibliography of books that the author used in developing this text. Referring to these sources will allow additional information to be gathered to the extent that the reader is interested.

Appendix B provides a glossary of terms from SCADA technology—of course, no such list can be complete. Since SCADA development dates from the time NASA was very active in space exploration, their love affair with acronyms has carried over to SCADA.

Appendix C provides solutions to the exercises that form the last part of each unit. It has been found that the learning process is enhanced by applying what has just been learned to solving a problem using this new knowledge. The reader is encouraged to work these exercises as he or she goes through the book.

Appendix D, the Index, allows the reader to search for instances of particular words throughout the text.

1-6.    Course Objectives

When you have completed this text, you should be able to:

      •  Converse with SCADA nomenclature

      •  Describe the typical architecture of a SCADA system

      •  Identify the limitations of a SCADA system

      •  Describe the basic technology of each of SCADA’s major building blocks

      •  Recognize when a SCADA system would be beneficial to your operation

      •  Select the appropriate SCADA technologies for your operational requirements

In addition to these general objectives, each unit contains a specific set of learning objectives to help direct your study in that unit.

1-7.    Course Length

The basic idea of this book is that students learn best if they proceed at their own pace; consequently, the amount of time individual students will require to complete this text/course will vary significantly. Most students will complete this course in eighteen hours.

Unit 2: SCADA – Purpose, Elements, and Layout

UNIT 2

SCADA – Purpose, Elements, and Layout

SCADA is the technology that enables a user to collect data from one or more distant facilities and to send limited control instructions to those facilities. It is important to note the words “distant” and “limited” in this definition.

SCADA has been developed to monitor and control very large process facilities. SCADA is not normally used to operate a small facility like a factory; although, some factories are large enough to benefit from using SCADA. Control systems like programmable logic controllers (PLC) or distributed control systems (DCS) will do a better job for most factory control and monitoring. An example of a very large process facility is a group of wells that produce and gather the oil and gas from a reservoir beneath fifteen square kilometers (3,700 acres) of farmland or forest. Another example is a transmission system, including wires, switches, and transformers, that moves electrical power across entire states, provinces, or countries.

Note also that the definition does not say, “Control and Data Acquisition.” It says “Supervisory Control and Data Acquisition.” A good supervisor, one who does not micromanage, gives a target to his workers and lets them get on with the job, monitoring them occasionally. A supervisory control system sends a process target to parts of the system, lets those parts attain the target, and monitors them to ensure that the targets are being reached.

Whenever a definition is written down, it is like a challenge to the reader to think of exceptions. Someone might say, “I know of a factory where SCADA is used to measure a flow rate,” or “Our SCADA system does detailed, not supervisory, control.” Please accept the definition as given, at least until you finish reading this t...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• Preface to the Fourth Edition
• Unit 1: Introduction and Overview
• Unit 2: SCADA – Purpose, Elements, and Layout
• Unit 3: Historical Development—Analog and Digital
• Unit 4: Real-Time Systems
• Unit 5: Control System Elements: Sensors, Actuators, and Algorithms
• Unit 6: Field/RTU Communications
• Unit 7: Remote Terminal Units—RTUs
• Unit 8: RTU/MTU Communication
• Unit 9: Master Terminal Units—MTUs
• Unit 10: Operator Interface
• Unit 11: Remote Control—What Not to SCADA
• Unit 12: Security
• Unit 13: Applications
• Unit 14: What’s Next?
• Unit 15: SCADA Economics
• Appendix A: Suggested Readings and Study Materials
• Appendix B: Glossary of SCADA Terminology
• Appendix C: Solutions to All Unit Exercises