Sample Time is a Fundamental Design and Tuning Specification
ABSTRACT: There are two sample times, T, used in process controller design and tuning. One is the control loop sample time (step 4 of the design and tuning recipe) that specifies how often the controller samples the measured process variable (PV) and computes and transmits a new controller output (CO) signal. The other is the rate at which CO and PV data are sampled and recorded during a bump test (step 2 of the recipe). In both cases, sampling too slow will have a negative impact on performance. Sampling fast will not necessarily provide better performance, though it may lead us to spend more than necessary on high-end instrumentation and computing resources.
Parameter Scheduling and Adaptive Control of Nonlinear Processes
ABSTRACT: Processes with streams comprised of gases, liquids, powders, slurries and melts tend to exhibit changing (or nonlinear) process behavior as operating level changes. We discussed the nonlinear nature of the gravity drained tanks and heat exchanger processes in an earlier post. As we observed in that article and explore below, processes that are nonlinear with operating level will experience a degrading controller performance whenever the measured process variable (PV) moves away from the design level of operation (DLO).
Plant-Wide Control Requires a Strong PID Foundation
ABSTRACT: The term "plant-wide control" is used here to describe the use of advanced software that sits above (or on top of) the individual PID controllers running a number of process units in a plant. Depending on the technology employed, this advanced process control software can perform a variety of predictive, scheduling, supervisory and/or optimizing computations. The most common architecture in industrial practice has the plant-wide software compute and transmit set point updates to a traditional platform of individual PID controllers.