STUDENT TO ENGINEER

InTech, Oct 2006 by Edgar, Thomas F

Should the teaching of process control be changed?

Part 1 of a two-part series

Let's face it, even under the best circumstances engineering graduates today face a daunting task taking on the massive responsibilities waiting for them in the automation industry. But the underlying debate among academics and those in industry is: Are graduates getting the correct education?

Students trained in chemical engineering are typically not well prepared to support process control in industrial chemical plants, said Eli Lilly's Joseph Alford, especially regarding batch processes, which has been the focus of most of his career. Alford said he checked with engineers who have graduated at different time periods over the past 30 years, and the story is usually the same: Their process control course (typically required for a B.S. chemical engineering degree) is full of content regarding Laplace transforms, frequency domain analysis, Bode diagrams, and root locus, Nyquist, Routh, and other stability algorithms, which they rarely use once they start a job. In addition, these engineers report getting very little practice in practical loop tuning, valve selection, loop diagnostics, and dealing with non-steady state processes in their process control course. It seems most process control courses rely heavily on steady-state continuous kinds of processes (e.g., petrochemicals) that dominated the chemical industry 30 to 60 years ago, but are not a good fit for the extensive use of non-steady state, multi-step batch processes, and also discrete manufacturing processes, in common use today. While Alford's statement reflects the batch industry, it can also apply throughout automation.

In a paper written for the Chemical Process Control 7 conference, my co-authors and I took the position that B.S. chemical engineering graduates don't make the grade if they cannot operate equipment they design, control processes, or understand the dynamic nature of how a process behaves. The following questions capture the important issues:

(1) What is the industrial view of control education?

(2) What control concepts are most important?

(3) Should there be more emphasis on batch control?

(4) What should be the balance of simulation vs. experiments in control education?

(5) How might the future process control course change from its current emphasis?

(6) What topics could be removed?

Traditional process course

One difficulty with the one-semester process control course taught at most schools is its starting point is still the same as it was when the textbook, Process Systems Analysis and Control, by Coughanowr and Koppel first hit the classroom in 1965. In order to incorporate all the advances in control engineering from over the past 40 years (as well as projected developments), considerable streamlining of the existing curriculum must occur. Unfortunately, some instructors still teach the same type of course they had when they were students. We have not adapted the course in a feedforward fashion so it will mesh with technologies encountered in a modern chemical plant.

Topics covered in a typical 15-week undergraduate process control course include dynamic behavior (using Laplace transforms and analytical solutions to ordinary differential equations), physical and empirical modeling, computer simulation, measurement and control hardware technology, basic feedback and feedforward control concepts, and advanced control strategies.

Prior to taking the standard university process control course, students take a mathematics course on solving ordinary differential equations as well as other courses in numerical analysis and mathematical modeling. Laplace transforms are a basic mathematical tool in process control, and the teaching of this subject (along with frequency response) has historically been a major part of a process control course. However, given the emergence of software for linear systems analysis and simulation, the level of emphasis on Laplace transform manipulations should undergo re-evaluation. The early dependence on Laplace transforms arose out of necessity because computational and graphical tools were not available prior to 1990.

Industrial feedback

"While the need for a B.S. graduate to understand Laplace transforms, frequency domain analysis, or relative gain arrays may not appear to be widely applicable, the knowledge of how to control processes using measurement feedback is applicable to most every job a young graduate may encounter and should be considered a basic building block of their education," said Dr. Jim Downs, an engineer at Eastman Chemical. "The new engineer should also understand that process control is a natural extension of material and energy balances, that is, dynamic loops are used to keep the material and energy balances in balance. The practical aspects of process control such as understanding control objectives, how a control strategy fulfills these objectives, how to tune control loops, and understanding dynamic interactions among process variables are often currently learned on the job. The disturbing fact is that many recent graduates feel shortchanged when they learn how critical process control is to their job effectiveness and how little they understand about it from their undergraduate education," he said.