Greg: The future of the automation profession depends upon replenishing and revitalizing the expertise in process control. Nearly all of my protégés have retired without an opportunity to mentor and develop their sequels. There was a dearth of hiring automation professionals for 30 years. While there has been a recent increase, many if not most of these engineers new to the profession are not going to work for the plants or associated engineering departments of the process industry manufacturers. They are instead being hired by service providers, either in the application departments of system suppliers or their business partners, or by independent engineering firms. The challenge is how these new engineers go from what they learned in universities to what they have to do on the job. Since they are not starting out gaining extensive plant experience by being stationed at a plant and/or spending significant time checking out, commissioning and starting up the systems throughout their career like Stan and I did, they are challenged to learn what is really going on in the field. Further complicating matters is that university degrees in process automation are rare and the courses offered in control are oriented toward frequency response, emphasizing Laplace and Z transforms and Bode and Nyquist plots. While this knowledge is useful for advanced degrees and a deeper understanding for someone in research and development, the approach has little practical use for the automation engineer in the process industry. The courses in control theory largely reflect an original intent to educate potential aerospace engineers in the 1970s.
The Missouri University of Science and Technology (Missouri S&T) is making a difference principally as a result of the efforts of Dr. Kelvin Erickson. Kelvin worked at Fisher Controls in Marshalltown, Iowa, which was at the time owned by Monsanto. Among other projects, Kelvin helped develop the programmable logic controller (PLC) interface and a large database console for a distributed control system (DCS).
]Kelvin came to Missouri S&T in 1986 where he developed courses and labs that emphasize practical applications in automation. One of the courses is based on the book Plantwide Process Control, which he coauthored with a leading industry expert John Hedrick and focuses on a complete solution to maximize the scope and success of automation in both batch and continuous processes. Kelvin also teaches full and abbreviated lab-based courses onsite and online on using PLCs for automation in and beyond the process industry.
Stan: Kelvin, what is your approach?
Kelvin: Since 80% of the graduates end up providing services to the process industry (e.g., chemical, beverage, and wastewater) and to some extent in packaging, filling, assembly and small parts manufacturing, we developed labs to provide a practical and hands-on education of implementing automation in these industries. The focus is more on practice than the control theory that they can get with traditional courses in process control, which originated based on aerospace. Since PLCs are often used in these manufacturing processes, the labs extensively use PLCs.
Greg: I think this approach is critical because most will not have the advantage that Stan and I had of spending a lot a time onsite in labs and manufacturing plants as we progressed from university graduates full of theory to being specialists and eventually Fellows in process control. Also, the process industry is fraught with nonlinearities and deadtime not typically seen in aerospace.
Kelvin: The feedback we get from graduates and the companies that hire them is that they greatly appreciate the hands-on practical approach providing so many benefits including understanding the terminology and implementation details and seeing the reality of automation in action.
Stan: What do you cover in the labs?
Kelvin: The labs deal more with the operational aspects—controlling the loop mode, setting up the loops and getting the automation system to work. There are a lot of parameters you need to get right. A third of the students do this lab before I cover PID control in the lecture, so I don’t focus on loop tuning.
We have labs on ventilation system pressure/temperature control, pH control, and heat exchanger temperature control. These are all continuous operations. I use only one of these labs in a particular semester. Other lab exercises are discrete sequential in nature.
To support the PID control labs, I spend a few weeks on PID tuning in the second half of the course using a simulator so we can look at more conditions and types of loops. Because it is referenced extensively, I start out with Ziegler Nichols (ZN) tuning but later show how tuning rules developed by H.A. Fertik and described in his paper, “Tuning Controllers for Noisy Processes,” in ISA Transactions Vol 14, No 4, provides more robustness and a compromise between the load and setpoint response.
Greg: ZN tuning is widely recognized as being too aggressive. We have learned to provide robustness with other tuning methods and to minimize setpoint overshoot courtesy of Greg Shinskey, using good load rejection tuning by the simple addition of a setpoint lead/lag with the lag time equal to the reset time and a lead equal to ¼ the lag time. Alternatively, we have learned to set the beta and gamma factors equal to 0.5 and 0.25, respectively, in a two-degrees-of-freedom (2DOF) PID structure.
Stan: How do students get to see what is happening in the process and complete the lab within the limited time available?
Kelvin: The response of the ventilation system is a few seconds and the pH system is about two minutes. The temperature response of the heat exchanger is much slower.
The ventilation system consists of two loops: pressure control by manipulating the variable-frequency drive (VFD) speed and temperature control by manipulating a heater coil through time-proportional control.