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.
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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.
Sat in on a Web presentation this morning over the phone. (Love the Webexes of the world. Much better than burning days in an airport boarding lounge.)