Basic and Advanced Regulatory Control: System Design and Application, Third Edition

Harold Wade

• Publisher: International Society of Automation
• Year: 2017
• Print ISBN: 9780876640135
• eBook ISBN: 9781643310909
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

This intermediate-level book explains the application of basic and advanced regulatory control strategies for the wet process industries. Rather than mathematical systems theory, the book builds upon the engineer or technician's own experience and knowledge of processes to demonstrate the application of successful control strategies.Following a summarization of the characteristics of processes and feedback control loops, attention is given to the application of advanced regulatory control (ARC) strategies to provide significant economic benefit. The latter portion of the book gives an overview of the next level of control, advanced process control (APC). New topics include an expanded coverage of set-point weighting controllers, an amplified discussion of valve problems, a control algorithm for dead-time processes, expanded coverage of cross-limiting control systems, and a new heuristic procedure for improving "as-found" tuning. End of chapter exercises have been added. Suitable for the beginning or experienced engineer or technician.

1

Introduction

The term process control implies that there is a process for which there is a desired behavior and that there is some controlling function that acts to elicit that desired behavior. This broad concept can embrace everything from societal processes governed by some regulatory control authority to automated manufacturing processes. In practically all cases, however, a common thread is that some measure of the actual process behavior is compared with the desired process behavior. This feedback action then generates a control policy that acts to minimize or eliminate the difference between desired and actual behavior.

This book focuses on a particular segment of automated process control that is applied to chemical, refining, pulp and paper, power generation, and similar types of processes. Even within this limited scope of applications, the discussion is restricted primarily to processes that are operated continuously for long periods of time and within a narrow region of the operating variables. In other words, the book excludes such important operating modes as batch processing, start-ups, and grade changes. Many of the control techniques to be presented here, however, can be adapted to these other modes of operation.

The behavior of the processes in this book is often characterized by measured values of process variables, such as temperatures, flow rates, and pressures. The desired behavior is stated to be the set points of those process variables. Until fairly recent times, most applications of industrial process control used simple feedback controllers that regulated the flow rates, temperatures, pressures and other process variables. These controllers required a form of adjustment called tuning to match their controlling action to the unique requirements of individual processes.

As long as most of the control systems were implemented with analog hardware, applications were limited to simple regulatory control. This was due to the cost of additional components and additional interconnections that more advanced control required, along with the burden of additional maintenance and the vulnerability to failure of many devices in the control loop. With the advent of digital control systems, however, more sophisticated loops became feasible. Advanced regulatory control techniques, such as ratio, cascade, and feedforward control, as well as additional forms such as constraint (selector) control and decoupling, could readily be implemented simply by configuring software function blocks.

With this additional capability, however, a need developed for a systematic approach toward using it. This is called control strategy design. In order to design a technically successful and economically viable control strategy, the control system engineer must be well grounde...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Contents
• About the Author
• Preface to the Third Edition
• Chapter 1: Introduction
• Chapter 2: Mathematical Background, Diagrams, and Terminology
• Chapter 3: Process and Control Loop Characteristics
• Chapter 4: PID Control
• Chapter 5: Modifications to Standard PID Controllers
• Chapter 6: Tuning Feedback Control Loops
• Chapter 7: Self-Tuning
• Chapter 8: Advanced Regulatory Control
• Chapter 9: Cascade Control
• Chapter 10: Ratio Control
• Chapter 11: Feedforward Control
• Chapter 12: Override (Selector) Control.
• Chapter 13: Control for Interacting Process Loops
• Chapter 14: Dead-Time Compensation and Model-Based Control
• Chapter 15: Multivariable Model Predictive Control
• Chapter 16: Other Control Techniques
• Appendix A: Derivation of Equations for Installed Valve Characteristics
• Appendix B: Signal Scaling
• Appendix C: Exercise Answers
• Bibliography
• Index