A CLOSED-LOOP REACTION-CURVE METHOD FOR CONTROLLER TUNING

This article proposes a closed-loop, reaction-curve method to provide a procedure for establishing controller settings on the classical three-mode (P1D) controllers. It uses the partial extreme data available during the early period of step set-point change under porportional control mode to determine the ultimate period and the ultimate gain of the open-loop process. The resulting ultimate data are critical for subsequent controller settings according to Ziegler-Nichols rules. Simulation examples and test on a pilot-scale stirred-tank reactor demonstrate that the method can provide adequate critical process data, and that it is applicable to processes that are underdamped, characterized by large dead-times, open-loop unstable or with inverse-response.