The following discussion is part of an occasional series showcasing the ISA Mentor Program, authored 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). Greg will be posting questions and responses from the ISA Mentor Program, with contributions from program participants.
The following question by Greg McMillan, ISA Mentor Program co-founder, is designed to start a conversation on what practitioners can do to increase innovation in all aspects of PID control, including the use of better measurements and valves, PID options, and control strategies.
What can be done to stem the decline in innovation in PID control as seen in the increasing prevalence of copy jobs and overwhelming emphasis on budgets and schedules rather than more productive control? How can we encourage and facilitate individual efforts to take advantage of the remarkable increases in the capabilities and opportunities in today’s measurements, valves, and PID controllers and the wealth of knowledge of industry experts?
This is a good question, and one that might be addressed in a variety of ways. For new and especially for novel plants/processes, value can be added and many commissioning problems can be avoided by engaging the control systems/process control specialist in the process design review process, including HAZOP and risk assessments. Engaged in this way, the control systems specialist can anticipate the use of features available with contemporary PID controllers to provide the required performance, including any requirements for procedural control, override strategies, action augmentation, and control priorities for “normal” and upset conditions.
A good example of this kind of involvement contributing to a successful project is the integration of a co-generation unit and steam distribution system where only with a broad understanding of the process interactions, operating strategies, and probable upset conditions can advantage be taken of the features of the PID controller for turbine load control and header pressure control.
I also wonder if the described situation indicates that practitioners understand the component functions of the PID controller well enough but find that the closed loop behavior is a mystery and that loops are commonly put into service and perform poorly, not taking advantage of all that the digitally implemented PID algorithm can offer.
Goodness knows the power of the PID control algorithm. Why is it not exploited more effectively? My experience points to a lack of understanding. How can one take advantage of something one doesn’t understand? All the control systems have the major algorithms at the engineer’s fingertips, but they often hardly get touched. The lack of understanding is due partly to a lack of mentoring. Mentoring is more than teaching a specific task, it is motivating and inspiring the pupil to study, practice, and progress in a craft. Controls systems are no exception.
As difficult as it is to implement an efficient, optimal control scheme it can be more difficult to dispel the fear if this is a new venture. When the customers and managers do not understand the power of the PID, when they do not give the practitioner tools and resources to become proficient in its use, then the implementer fails to implement these improvements effectively. This confirms the culture of “don’t touch it.” All the while, advanced process control, particularly model predictive control, is the solution that management sees to cover up these sins.
It does take real time and effort to implement and optimize good regulatory controls. A culture of poor communication and keeping things close to the vest on the part of the controls engineer can breed mistrust and a “wizard of Oz” persona. This eventually leads to a loss of knowledge and capability in the organization.
Some of the problem, too, is that there are so few control engineers. At my mill, for instance, there are only three, with a couple highly trained technicians. We all have our own large area of responsibility, with mostly project management and systems management expectations for our roles. This makes a focus on regulatory controls a case-by-case basis for a motivated individual.
In these days of greater emphasis on the bottom line by management with little or no interest in or understanding of process control, the approval and delivery of optimization projects is challenging at best. In the process industry—with the possible exception of refining and petrochemicals—it's difficult to even start a conversation with executives on process control and optimization. The need is greater than ever due to advances in software and instrumentation. The retirement of experts that know and can take advantage of the opportunities adds urgency.
We have an excellent, practical, insightful, and entertaining example from Michel Ruel, ISA Fellow and co-chair of the ISA 5.9 Technical Report on PID Algorithms and Performance in the Control Talk column, “Want to be a hero?” The follow-up column with Michel, “Keys to optimization project success” gives detailed examples of the preliminary work, remediation, and assessment tasks needed.
Maybe we can simplify the message to the decision makers. They need to be aware that the PID has proven to potentially provide, with minimal effort, the best response to unmeasured disturbances and setpoint changes. The capability of the PID has greatly increased, as seen in the ability of external reset feedback to inherently suppress oscillations from slow final control elements and secondary loops in the PID structure to enable a good setpoint response with tuning done to maximize disturbance rejection in the Control Talk column, “The concealed PID revealed, part 3” with Sigifredo Nino.
Unfortunately, the PID capability is underutilized due to lack of advocates, often stemming from missing knowledge and poor tuning. This is partly addressed in Appendix B – Basics of PID Controllers in the ISA book Advances in Reactor Measurement and Control.
Most importantly this better performance can translate to more efficient operation (lower raw material and energy costs) and greater capacity (higher production rate and onstream time), especially for changes in product mix. Simple monetarized metrics can be implemented online and demonstrated in simulations in a digital twin to show the bottom-line impact of the possible improvements in efficiency and capacity from better PID control and better operator performance. The metrics with dynamic compensation can provide the performance for the last hour, last shift, and last batch. The metrics can be done monthly and formularized to provide Real Time Accounting (RTA). Simulations provide a visual relatable experience and training that gets everyone on board, leading to better operator performance and technical support. Furthermore, the simulations help you develop and test the PID control strategies.
For more on how simulation can help, see the Control Talk article, “Simulation enhances career and system performance” with Chris Stuart, and “Getting innovation back into process control.” For how to get the most out of your PID, see “Best practices for PID” with Hunter Vegas. The human factor in getting everyone on board is significant and is extensively addressed by Mentor Program resource Luis Navas and co-founder Hunter Vegas in “Motivating, inspiring and directing automation professionals.”
A strong history and a leader who can push for the best can make a huge difference as seen in the Control Talk column with Mentor Program resource Bart Probst, “An ‘entitlement’ approach to continuous process control improvement,” where he explains the “entitlement” view, the evolution of the opportunity assessment sheet, the use of new tools, the documentation of the theoretical maximum, and the value of each incremental improvement that has led to his group focusing on these improvements expanding in size from six to eleven.
For an inside look at the history and key aspects of the opportunity sizing and assessment process, the importance of involvement of all people (including accounting), and monthly cost sheet analysis for production units, see the Control Talk article “The Human Factor” with Glenn Mertz. The Process Control Improvement group at Solutia achieved an average of a 4% reduction in the cost of goods in dozens of production units.
For more details on metrics, including real-time accounting and the opportunity assessment and sizing process, see Chapter 11 - Improving Process Performance in Process/Industrial Instruments and Controls Handbook Sixth Edition 2019.
In May, I am going to start a monthly weekend WebEx presentation and discussion on each chapter in my Momentum Press book, Tuning and Control Loop Performance Fourth Edition 2014. People who commit to attending the weekend sessions will be offered a complementary copy of the book for those in North America and Europe. Be on the lookout for more details in my April Control Talk column.
When there is so much material available now to young engineers to develop their skills, including attractively priced simulation software for personal learning, it disappoints us that so few take advantage of opportunities to learn. Unfortunately, too many folks enter our field, and engineering in general, as an opportunity to advance up the management ladder rather than becoming subject experts. Companies would do well to create greater incentives to encourage young engineers to “keep the faith” by adopting corporate structures that recognize the value of in-house engineering expertise.
The automation profession is incredibly interesting and rewarding. What we see in the process and how we affect the process all depends upon measurements, final control elements, and control systems, all of which have greatly increased in capability that is largely underutilized. Practitioners have the advantage in knowing the application and the relevance of solutions.
We suggest you take the time to read technical articles and books by professionals in the automation industry. We suggest two hours each weekend. If you would like to be part of a group that gets together one weekend a month to discuss articles or books, please send a note to mentor@ISA.org and ask to join the “Automation Reading Gathering.” I think that you will find the synergy of talking about important technical aspects of how you make automation systems better both energizing and motivating.