Ziegler-Nichols Tuning Poor Choice For Production Processes
ABSTRACT: Ziegler and Nichols first proposed their method in 1942. It is a trial-and-error loop tuning technique that is still widely used today. Many process control books and articles propose a variety of tuning correlations using Ku and Pu that provide improved performance over that provided by the original Z-N correlations listed above. Of course, the definition of "improved" can vary widely depending on the process being controlled and the operations staff responsible for a safe and profitable operation.
Controller Tuning Using Set Point Driven Data
ABSTRACT: 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 this "open loop" step test is that we can analyze the response graph by hand to compute first order plus dead time (FOPDT) dynamic model parameters. These parameter values are then used in rules and correlations to complete the controller design and tuning.
Do Not Model Disturbance Driven Data for Controller Tuning
ABSTRACT: 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 study here). Shouldn't we then step or pulse (or "bump") our disturbance variable to generate the step 2 dynamic process test data?