The Control Talk Blog provides guidance from a user's viewpoint on the design of automation systems, equipment, and piping for process control improvement. Details are offered on the selection and installation of PID controllers, control valves, variable speed drives, and measurements to maximize loop performance. The blogs are often more intensive and extensive and less vendor specific than a white paper. The goal is an advancement of the profession by sharing conceptual principle based knowledge.
Greg McMillan is a retired Senior Fellow from Solutia/Monsanto and an ISA Fellow. At present, McMillan is a part time modeling and control consultant in Technology for Process Simulation for Emerson Automation Solutions specializing in the use of the Virtual Plant for exploring new opportunities. He spends most of his time writing, teaching and leading the ISA Mentor Program he founded in 2011. He received the ISA Kermit Fischer Environmental Award for pH control in 1991, received the Control magazine Engineer of the Year Award for the Process Industry in 1994, was inducted into the Control magazine Process Automation Hall of Fame in 2001, was honored by InTech magazine in 2003 as one of the most influential innovators in automation, and received the ISA Life Achievement Award in 2010.
When is a controller in automatic not able to do anything to reduce an oscillation? When will a controller amplify an oscillation? In both of these cases, the controller is doing more harm than good by wearing out valves and upsetting other loops.
Sensor lags, transmitter damping, and PID signal filters can make oscillations look better but is this really a good a thing? Here we look at how these dynamics affect what you see and how much of a problem it can be.
What comes at you too fast? How do people know you are a process control engineer? What is more disturbing than talk shows? Is a flea market indicative of a project behind schedule? These and other questions you have not asked will be answered.
Before the 1990s relatively few choices in PID structure were offered. There were also various supplier specific rules as to how to set the proportional mode and integral mode tuning settings to get proportional-only and integral-only control. A different model controller may have been needed for a different structure.
Not knowing the implications of the PID Form in an existing control system being migrated or the PID Form learned in a University course can cause gross errors in the tuning parameters and potential instability. The PID Form predominantly used today is not the Form in most of the controllers...
The question for the day is where to locate measurements. My first choice would be a Caribbean island but if the plant is not there, the sensing or sample lines and the associated transportation delays would be quite long.
Batch processes pose particular challenges for closed-loop control and optimization due to inherent process nonlinearity and non-self-regulation. At the same time there is a greater potential for increasing capacity in batch than in continuous processes. Solutions need to address the interrelationship between yield, capacity, quality, and repeatability.
The highest value added products use batch operations. Batches can take days to complete and be worth millions of dollars. In many cases bad batches cannot be fixed downstream. Bad batches must be avoided. There are many techniques for making batches more repeatable and faster by better monitoring and control.
Software for auto tuning and adaptive control provide the opportunity to identify key loop dynamics besides providing a sound fundamental and automated basis for getting the best PID settings. Presented are uses of the knowledge gained and the setup of the automation system and testing/monitoring of PID performance to get...
Automating any process can yield big improvements by eliminating human error and adding repeatability and predictability. The benefits are greatest when the best technology and practices are automated, the novice is protected against mistakes, and the specialist is enabled to capitalize on creativity and expertise.