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Tuning and Control Loop Performance, Fourth Edition

Book Description

The proportional-integral-derivative (PID) controller is the heart of every control system in the process industry. Given the proper setup and tuning, the PID has proven to have the capability and flexibility needed to meet nearly all of industry’s basic control requirements. However, the information to support the best use of these features has fallen behind the progress of improved functionality. Additionally, there is considerable disagreement on the tuning rules that largely stems from a misunderstanding of how tuning rules have evolved and the lack of recognition of the effect of automation system dynamics and the incredible spectrum of process responses, disturbances, and performance objectives. Tuning and Control Loop Performance, Fourth Edition provides the knowledge to eliminate the misunderstandings, realize the difference between theoretical and industrial application of PID control, address practical difficulties, improve field automation system design, use the latest PID features, and ultimately get the best tuning settings that enables the PID to achieve its full potential.

Table of Contents

  1. Cover
  2. Title Page
  3. Copyright
  4. Abstract
  5. Contents
  6. List of Figures
  7. List of Tables
  8. Acknowledgments
  9. Preface
  10. 1 Fundamentals
    1. 1.1 Introduction
      1. 1.1.1 Perspective
      2. 1.1.2 Overview
      3. 1.1.3 Recommendations
    2. 1.2 PID Controller
      1. 1.2.1 Proportional Mode
      2. 1.2.2 Integral Mode
      3. 1.2.3 Derivative Mode
      4. 1.2.4 ARW and Output Limits
      5. 1.2.5 Control Action and Valve Action
      6. 1.2.6 Operating Modes
    3. 1.3 Loop Dynamics
      1. 1.3.1 Types of Process Responses
      2. 1.3.2 Dead Times and Time Constants
      3. 1.3.3 Open Loop Self-regulating and Integrating Process Gains
      4. 1.3.4 Deadband, Resolution, and Threshold Sensitivity
    4. 1.4 Typical Mode Settings
    5. 1.5 Typical Tuning Methods
      1. 1.5.1 Lambda Tuning for Self-regulating Processes
      2. 1.5.2 Lambda Tuning for Integrating Processes
      3. 1.5.3 IMC Tuning for Self-regulating Processes
      4. 1.5.4 IMC Tuning for Integrating Processes
      5. 1.5.5 Skogestad Internal Model Control Tuning for Self-regulating Processes
      6. 1.5.6 SIMC Tuning for Integrating Processes
      7. 1.5.7 Traditional Open Loop Tuning
      8. 1.5.8 Modifed Ziegler–Nichols Reaction Curve Tuning
      9. 1.5.9 Modifed Ziegler–Nichols Ultimate Oscillation Tuning
      10. 1.5.10 Quarter Amplitude Oscillation Tuning
      11. 1.5.11 SCM Tuning for Self-regulating Processes
      12. 1.5.12 SCM Tuning for Integrating Processes
      13. 1.5.13 SCM Tuning for Runaway Processes
      14. 1.5.14 Maximizing Absorption of Variability Tuning for Surge Tank Level
    6. 1.6 Test Results
      1. 1.6.1 Performance of Tuning Settings on Dead Time Dominant Processes
      2. 1.6.2 Performance of Tuning Settings on Near-Integrating Processes
      3. 1.6.3 Performance of Tuning Settings on True Integrating Processes
      4. 1.6.4 Performance of Tuning Settings on Runaway Processes
      5. 1.6.5 Slow Oscillations from Low PID Gain in Integrating and Runaway Processes
      6. 1.6.6 Performance of Tuning Methods on Various Processes
    7. Key Points
  11. 2 Unified Methodology
    1. 2.1 Introduction
      1. 2.1.1 Perspective
      2. 2.1.2 Overview
      3. 2.1.3 Recommendations
    2. 2.2 PID Features
      1. 2.2.1 PID Form
      2. 2.2.2 External Reset Feedback
      3. 2.2.3 PID Structure
      4. 2.2.4 Split Range
      5. 2.2.5 Signal Characterization
      6. 2.2.6 Feedforward
      7. 2.2.7 Decoupling
      8. 2.2.8 Output Tracking and Remote Output
      9. 2.2.9 Setpoint Filter, Lead-Lag, and Rate Limits
      10. 2.2.10 Enhanced PID for Wireless and Analyzers
    3. 2.3 Automation System Diffculties
      1. 2.3.1 Open Loop Gain Problems
      2. 2.3.2 Time Constant Problems
      3. 2.3.3 Dead Time Problems
      4. 2.3.4 Limit Cycle Problems
      5. 2.3.5 Noise Problems
      6. 2.3.6 Accuracy and Precision Problems
    4. 2.4 Process Objectives
      1. 2.4.1 Maximize Turndown
      2. 2.4.2 Maximize Safety and Environmental Protection
      3. 2.4.3 Minimize Product Variability
      4. 2.4.4 Maximize Process Effciency and Capacity
    5. 2.5 Step-by-Step Solutions
    6. 2.6 Test Results
    7. Key Points
  12. 3 Performance Criteria
    1. 3.1 Introduction
      1. 3.1.1 Perspective
      2. 3.1.2 Overview
      3. 3.1.3 Recommendations
    2. 3.2 Disturbance Response Metrics
      1. 3.2.1 Accumulated Error
      2. 3.2.2 Peak Error
      3. 3.2.3 Disturbance Lag
    3. 3.3 Setpoint Response Metrics
      1. 3.3.1 Rise Time
      2. 3.3.2 Overshoot and Undershoot
    4. Key Points
  13. 4 Effect of Process Dynamics
    1. 4.1 Introduction
      1. 4.1.1 Perspective
      2. 4.1.2 Overview
      3. 4.1.3 Recommendations
    2. 4.2 Effect of Mechanical Design
      1. 4.2.1 Equipment and Piping Dynamics
      2. 4.2.2 Common Equipment and Piping Design Mistakes
    3. 4.3 Estimation of Total Dead Time
    4. 4.4 Estimation of Open Loop Gain
    5. 4.5 Major Types of Process Responses
      1. 4.5.1 Self-regulating Processes
      2. 4.5.2 Integrating Processes
      3. 4.5.3 Runaway Processes
    6. 4.6 Examples
      1. 4.6.1 Waste Treatment pH Loops (Self-regulating Process)
      2. 4.6.2 Boiler Feedwater Flow Loop (Self-regulating Process)
      3. 4.6.3 Boiler Drum Level Loop (Integrating Process)
      4. 4.6.4 Furnace Pressure Loop (Near-integrating Process)
      5. 4.6.5 Exothermic Reactor Cascade Temperature Loop (Runaway Process)
      6. 4.6.6 Biological Reactor Biomass Concentration Loop (Runaway Process)
    7. Key Points
  14. 5 Effect of Controller Dynamics
    1. 5.1 Introduction
      1. 5.1.1 Perspective
      2. 5.1.2 Overview
      3. 5.1.3 Recommendations
    2. 5.2 Execution Rate and Filter Time
      1. 5.2.1 First Effect via Equation for Integrated Error
      2. 5.2.2 Second Effect via Equations for Implied Dead time
    3. 5.3 Smart Reset Action
    4. 5.4 Diagnosis of Tuning Problems
    5. 5.5 Furnace Pressure Loop Example (Near-integrating)
    6. 5.6 Test Results
    7. Key Points
  15. 6 Effect of Measurement Dynamics
    1. 6.1 Introduction
      1. 6.1.1 Perspective
      2. 6.1.2 Overview
      3. 6.1.3 Recommendations
    2. 6.2 Wireless Update Rate and Transmitter Damping
      1. 6.2.1 First Effect via Equation for Integrated Error
      2. 6.2.2 Second Effect via Equations for Implied Dead Time
    3. 6.3 Analyzers
    4. 6.4 Sensor Lags and Delays
    5. 6.5 Noise and Repeatability
    6. 6.6 Threshold Sensitivity and Resolution Limits
    7. 6.7 Rangeability (Turndown)
    8. 6.8 Runaway Processes
    9. 6.9 Accuracy, Precision, and Drift
    10. 6.10. Attenuation and Deception
    11. 6.11. Examples
      1. 6.11.1 Waste Treatment pH Loop (Self-regulating Process)
      2. 6.11.2 Boiler Feedwater Flow Loop (Self-regulating Process)
      3. 6.11.3 Boiler Drum Level Loop (Integrating Process)
      4. 6.11.4 Furnace Pressure Loop (Near-integrating Process)
      5. 6.11.5 Exothermic Reactor Cascade Temperature Loop (Runaway Process)
      6. 6.11.6 Biological Reactor Biomass Concentration Loop (Runaway Process)
    12. 6.12. Test Results
    13. Key Points
  16. 7 Effect of Valve and Variable Frequency Drive Dynamics
    1. 7.1 Introduction
      1. 7.1.1 Perspective
      2. 7.1.2 Overview
      3. 7.1.3 Recommendations
    2. 7.2 Valve Positioners and Accessories
      1. 7.2.1 Pneumatic Positioners
      2. 7.2.2 Digital Positioners
      3. 7.2.3 Current to Pneumatic (I/P) Transducers
      4. 7.2.4 Solenoid Valves
      5. 7.2.5 Volume Boosters
    3. 7.3 Actuators, Shafts, and Stems
      1. 7.3.1 Diaphragm Actuators
      2. 7.3.2 Piston Actuators
      3. 7.3.3 Linkages and Connections
    4. 7.4 VFD System Design
      1. 7.4.1 Pulse Width Modulation
      2. 7.4.2 Cable Problems
      3. 7.4.3 Bearing Problems
      4. 7.4.4 Speed Slip
      5. 7.4.5 Motor Requirements
      6. 7.4.6 Drive Controls
    5. 7.5 Dynamic Response
      1. 7.5.1 Control Valve Response
      2. 7.5.2 VFD Response
      3. 7.5.3 Dead Time Approximation
      4. 7.5.4 Deadband and Resolution
      5. 7.5.5 When is a Valve or VFD too Slow?
      6. 7.5.6 Limit Cycles
    6. 7.6 Installed Flow Characteristics and Rangeability
      1. 7.6.1 Valve Flow Characteristics
      2. 7.6.2 Valve Rangeability
      3. 7.6.3 VFD Flow Characteristics
      4. 7.6.4 VFD Rangeability
    7. 7.7 Best Practices
      1. 7.7.1 Control Valve Design Specifcations
      2. 7.7.2 VFD Design Specifcations
    8. 7.8 Test Results
    9. Key Points
  17. 8 Effect of Disturbances
    1. 8.1 Introduction
      1. 8.1.1 Perspective
      2. 8.1.2 Overview
      3. 8.1.3 Recommendations
    2. 8.2 Disturbance Dynamics
      1. 8.2.1 Load Time Constants
      2. 8.2.2 Load Rate Limit
      3. 8.2.3 Disturbance Dead Time
      4. 8.2.4 Disturbance Oscillations
    3. 8.3 Disturbance Location
    4. 8.4 Disturbance Troubleshooting
      1. 8.4.1 Sources of Fast Oscillations
      2. 8.4.2 Sources of Slow Oscillations
    5. 8.5 Disturbance Mitigation
    6. 8.6 Test Results
    7. Key Points
  18. 9 Effect of Nonlinearities
    1. 9.1 Introduction
      1. 9.1.1 Perspective
      2. 9.1.2 Overview
      3. 9.1.3 Recommendations
    2. 9.2 Variable Gain
      1. 9.2.1 Cascade Control
      2. 9.2.2 Reversals of Process Sign
      3. 9.2.3 Signal Characterization
      4. 9.2.4 Gain Scheduling
      5. 9.2.5 Adaptive Control
      6. 9.2.6 Gain Margin
    3. 9.3 Variable Dead Time
    4. 9.4 Variable Time Constant
    5. 9.5 Inverse Response
    6. 9.6 Test Results
    7. Key Points
  19. 10 Effect of Interactions
    1. 10.1. Introduction
      1. 10.1.1 Perspective
      2. 10.1.2 Overview
      3. 10.1.3 Recommendations
    2. 10.2. Pairing
      1. 10.2.1 Relative Gain Array
      2. 10.2.2 Distillation Column Example
      3. 10.2.3 Static Mixer Example
      4. 10.2.4 Hidden Control Loops
      5. 10.2.5 Relative Gains Less than Zero
      6. 10.2.6 Relative Gains from Zero to One
      7. 10.2.7 Relative Gains Greater than One
      8. 10.2.8 Model Predictive Control
    3. 10.3. Decoupling
    4. 10.4. Directional Move Suppression
    5. 10.5. Tuning
    6. 10.6. Test Results
    7. Key Points
  20. 11 Cascade Control
    1. 11.1. Introduction
      1. 11.1.1 Perspective
      2. 11.1.2 Overview
      3. 11.1.3 Recommendations
    2. 11.2. Confguration and Tuning
    3. 11.3. Process Control Benefts
    4. 11.4. Process Knowledge Benefts
    5. 11.5. Watch-outs
    6. 11.6. Test Results
    7. Key Points
  21. 12 Advanced Regulatory Control
    1. 12.1. Introduction
      1. 12.1.1 Perspective
      2. 12.1.2 Overview
      3. 12.1.3 Recommendations
    2. 12.2. Feedforward Control
      1. 12.2.1 Opportunities
      2. 12.2.2 Watch-outs
    3. 12.3. Intelligent Output Action
      1. 12.3.1 Opportunities
      2. 12.3.2 Watch-outs
    4. 12.4. Intelligent Integral Action
      1. 12.4.1 Opportunities
      2. 12.4.2 Watch-outs
    5. 12.5. Dead Time Compensation
      1. 12.5.1 Opportunities
      2. 12.5.2 Watch-outs
    6. 12.6. Valve Position Control
      1. 12.6.1 Opportunities
      2. 12.6.2 Watch-outs
    7. 12.7. Override Control
      1. 12.7.1 Opportunities
      2. 12.7.2 Watch-outs
    8. 12.8. Test Results
    9. Key Points
  22. 13 Process Control Improvement
    1. 13.1. Introduction
      1. 13.1.1 Perspective
      2. 13.1.2 Overview
      3. 13.1.3 Recommendations
    2. 13.2. Unit Operation Metrics
    3. 13.3. Opportunities
      1. 13.3.1 Variability
      2. 13.3.2 Increasing Capacity and Effciency
      3. 13.3.3 Effective Use of Models
      4. 13.3.4 Sizing and Assessment
    4. 13.4. Key Questions
    5. Key Points
  23. 14 Auto Tuners and Adaptive Control
    1. 14.1. Introduction
      1. 14.1.1 Perspective
      2. 14.1.2 Overview
      3. 14.1.3 Recommendations
    2. 14.2. Methodology
    3. Key Points
  24. 15 Batch Optimization
    1. 15.1. Introduction
      1. 15.1.1 Perspective
      2. 15.1.2 Overview
      3. 15.1.3 Recommendations
    2. 15.2. Cycle Time
    3. 15.3. Profle
    4. 15.4. End Point
    5. Key Points
  25. Appendix A Automation System Performance Top 10 Concepts
  26. Appendix B Basics of PID Controllers
  27. Appendix C Controller Performance
  28. Appendix D Discussion
  29. Appendix E Enhanced PID for Wireless and Analyzer Applications
  30. Appendix F First Principle Process Relationships
  31. Appendix G Gas Pressure Dynamics
  32. Appendix H Convective Heat Transfer Coefficients
  33. Appendix I Interactive to Noninteractive Time Constant Conversion
  34. Appendix J Jacket and Coil Temperature Control
  35. Appendix K PID Forms and Conversion of Tuning Settings
  36. Appendix L Liquid Mixing Dynamics
  37. Appendix M Measurement Speed Requirements for SIS
  38. References
  39. Bibliography
  40. About the Author
  41. Index
  42. Ad page
  43. Backcover