By Bob Rice1 and Doug Cooper Integrating (or non-self regulating) processes display counter-intuitive behaviors that make them surprisingly challenging to control. In particular, they do not naturally settle out to a steady operating level if left uncontrolled. To address this distinctive dynamic character, we modify the controller design and tuning recipe to include a FOPDT […]
By Bob Rice1 and Doug Cooper As has been discussed elsewhere in this e-book, it is best practice to follow a formal recipe when designing and tuning a PID controller. A recipe lets us move a controller into operation quickly. And perhaps most important, the performance of the controller will be superior to one tuned […]
By Bob Rice1 and Doug Cooper The case studies on this site largely focus on the control of self regulating processes. The principal characteristic that makes a process self regulating is that it naturally seeks a steady state operating level if the controller output and disturbance variables are held constant for a sufficient period of […]
When considering the range of control challenges found across the process industries, it becomes apparent that very different controller behaviors can be considered “good” performance. While one process may be best operated with a fast and aggressive control action, another may be better suited for a slow and gentle response. Since there is no common […]
A fairly common stumbling block for those new to controller tuning relates to step 2 of the controller design and tuning recipe. Step 2 says to “collect controller output (CO) to process variable (PV) dynamic process data around the design level of operation.” But suppose disturbance rejection is our primary control objective (example studyhere). Shouldn’t […]
The controller design and tuning recipe we have used so successfully on this site requires that we bump our process and collect dynamic data as the process responds. For the heat exchanger and gravity drained tanks study, we generated dynamic data using a step test while the controller was in manual mode. One benefit of […]
Ziegler and Nichols first proposed their method in 1942. It is a trial-and-error loop tuning technique that is still widely used today. The automatic mode (closed-loop) procedure is as follows:
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. […]
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 […]
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.