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Welcome to the official blog of the International Society of Automation (ISA).

This blog covers numerous topics on industrial automation such as operations & management, continuous & batch processing, connectivity, manufacturing & machine control, and Industry 4.0.

The material and information contained on this website is for general information purposes only. ISA blog posts may be authored by ISA staff and guest authors from the automation community. Views and opinions expressed by a guest author are solely their own, and do not necessarily represent those of ISA. Posts made by guest authors have been subject to peer review.

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How to Get the Most out of Your PID Controller

 

This post was written by Greg McMillan, industry consultant, author of numerous process control books, 2010 ISA Life Achievement Award recipient and retired Senior Fellow from Solutia Inc. (now Eastman Chemical).

 

One of the objectives of the ISA Mentor Program is to increase the number of papers and presentations by users to share plant expertise and best practices to advance the automation profession. The paper Effective Use of Key PID Features co-authored with Hector Torres is an excellent example of what is possible from the ISA Mentor Program participants and in the evolving automation profession.

 

Hector Torres is a senior process and control engineer for Eastman Chemical Company in Tlaxcala, Mexico, with more than 20 years of experience.

 

The PID controller has evolved over the decades to include a large number of features to address common application opportunities. Many of the features are not effectively used due to lack of a consolidation of functional understanding and best practices. The number of options and parameters can seem overwhelming and the best choices unknown.

 

The capability of the PID is experiencing a renaissance triggered by the advent of smart wireless instrumentation. A particularly key advancement is an enhancement for wireless that has unexpected benefits for simplifying and stabilizing tuning for loops with large and highly variable update times from at-line and off line analyzers, stopping limit cycles, reducing interactions, and recovering from failures. An emerging capability for smart reset action offers the ability to specify when a PID output comes off an output limit and to prevent overshoot or faltering in an approach to setpoint.

There is also an increasing recognition that a key feature where the controller output cannot change faster than the manipulated variable can enable the user to tune for maximum disturbance rejection and still meet other objectives such as coordination and decoupling of loops. Furthermore the PID can be easily extended to unit operation optimization problems usually reserved for model predictive control.

This paper offers guidance for getting the most out of your PID, extending its functionality from basic control to advanced control by the use of important existing and new features for applications encountered in the process industry. The goal is not only to show the flexibility but also how an understanding of the functionality and synergism of features can result in a simplification of tuning the PID.

Greg McMillan
Greg McMillan
Greg McMillan has more than 50 years of experience in industrial process automation, with an emphasis on the synergy of dynamic modeling and process control. He retired as a Senior Fellow from Solutia and a senior principal software engineer from Emerson Process Systems and Solutions. He was also an adjunct professor in the Washington University Saint Louis Chemical Engineering department from 2001 to 2004. Greg is the author of numerous ISA books and columns on process control, and he has been the monthly Control Talk columnist for Control magazine since 2002. He is the leader of the monthly ISA “Ask the Automation Pros” Q&A posts that began as a series of Mentor Program Q&A posts in 2014. He started and guided the ISA Standards and Practices committee on ISA-TR5.9-2023, PID Algorithms and Performance Technical Report, and he wrote “Annex A - Valve Response and Control Loop Performance, Sources, Consequences, Fixes, and Specifications” in ISA-TR75.25.02-2000 (R2023), Control Valve Response Measurement from Step Inputs. Greg’s achievements include the ISA Kermit Fischer Environmental Award for pH control in 1991, appointment to ISA Fellow in 1991, the Control magazine Engineer of the Year Award for the Process Industry in 1994, induction into the Control magazine Process Automation Hall of Fame in 2001, selection as one of InTech magazine’s 50 Most Influential Innovators in 2003, several ISA Raymond D. Molloy awards for bestselling books of the year, the ISA Life Achievement Award in 2010, the ISA Mentoring Excellence award in 2020, and the ISA Standards Achievement Award in 2023. He has a BS in engineering physics from Kansas University and an MS in control theory from Missouri University of Science and Technology, both with emphasis on industrial processes.

Books:

Advances in Reactor Measurement and Control
Good Tuning: A Pocket Guide, Fourth Edition
New Directions in Bioprocess Modeling and Control: Maximizing Process Analytical Technology Benefits, Second Edition
Essentials of Modern Measurements and Final Elements in the Process Industry: A Guide to Design, Configuration, Installation, and Maintenance
101 Tips for a Successful Automation Career
Advanced pH Measurement and Control: Digital Twin Synergy and Advances in Technology, Fourth Edition
The Funnier Side of Retirement for Engineers and People of the Technical Persuasion
The Life and Times of an Automation Professional - An Illustrated Guide
Advanced Temperature Measurement and Control, Second Edition
Models Unleashed: Virtual Plant and Model Predictive Control Applications

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