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, he contracts with Emerson DeltaV R&D via CDI Process & Industrial in Austin and consults for MYNAH Simulation Technologies in Saint Louis. Greg 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.
Anti-reset windup (ARW) protection is a standard feature of industrial PID controllers. In some DCS, ARW limits are adjustable besides output limits. The ARW limits may not be at their best values. ARW default values may not match up with output limits as output scale and engineering units change.
This last checklist may help you get the most out of your career and your life. Our accomplishments and our humanity are tightly related. The checklist is a summary of an understanding gained of an attitude and philosophy that has helped me be a better engineer and person. The checklist...
Contrary to common conceptions, bioreactors have more sophisticated analysis and control and with the advent of at-line analyzers more extensive opportunities than chemical reactors. The specialty chemical industry can get a preview of the future from the biopharmaceutical industry.
Nearly every process input is a flow, whether directly via a material input flow or indirectly via an energy input (e.g., utility flow). Good flow control is important for achieving the desired material and energy balance and stoichiometric ratio for reaction rates.
Nearly all of the deadtime in pressure loops comes from the automation system. For gas pressure there is a process time constant or integrating process gain that becomes slower as the volume increases and the throughput decreases.
Compressor surge is the fastest gas dynamic phenomena. A precipitous drop in flow occurs in 0.05 seconds and subsequent flow reversals occur every 1 to 2 seconds. The speed of response requirements for control valves, measurements, and controllers are extraordinary.
The maximum level controller gain for stability is one or two orders of magnitude higher than expected. The main limit to how high you can go in controller gain is often measurement noise and control objective.
pH is the most common analytical measurement. pH is important for product purity and environmental compliance. The most stringent pH control requirements occur in bioreactors for biopharmaceuticals where a deviation of 0.05 pH can cause a noticeable degradation in mammalian cell growth rate and product formation rate.
Batch processing is a critical part of many high value added biological and chemical processes. Batch processes are capable of higher conversions than continuous processes because there is no discharge flow until the batch is deemed complete.
Flow feed-forward control is the most utilized and underutilized advanced regulatory control technique. Proper implementation involves the use of ratio control and cascade control. Processes can be started up and moved quickly to new operating points by achieving a new flow ratio. Temperature and composition loops have a particular ratio...