Control Talk Blog
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...
Tight reactor temperature control enables the optimization of capacity and yield. What happens upfront in the reaction sets the stage for downstream processing and what ultimately ends up in the final product. Generally, increasing reactor temperature will increase reaction rate (capacity) but if the temperature is too high, side reactions...
Cascade control is an effective way of providing better feedback and feedforward control. The peak error in the primary loop can be reduced by more than an order of magnitude for disturbances originating in the secondary loop.
What is the most effective type of simulation? What is the fidelity needed? How can you automatically increase fidelity? How can you help operators deal with abnormal situations? How can you have a laboratory that behaves like the real plant to learn how the process responds, demonstrate creative control solutions, and quantify the benefits?
Deadband and resolution cause sustained equal amplitude oscillations called limit cycles that cannot be eliminated by controller tuning. A resolution limit causes limit cycles if there is integrating action at just one point in the control loop either in the process (e.g. level), positioner, or the process controller (e.g. PID).