FEEDBACK-CONTROL OF A 2-INPUT, 2-OUTPUT INTERACTING PROCESS

A model for a two-input, two-output interacting process is described which characterizes the four open-loop responses by six time constants and two interacting gain factors. The system parameters are reformulated in terms of the normalized amplitude ratio and critical frequency of each loop. Proportional-integral controllers are used in two feedback control loops. The optimum behavior for a step input disturbance in one loop is determined where the criterion function is the sum of the integrals of the square of the error for each loop. The Continuous Cycling Method of controller tuning is applied to the model. A simultaneous and several sequential schemes are tested and the results are compared with those of the optimum settings. Tuning parameters for gain and reset time are suggested. The gain parameter is about the same as that suggested by Ziegler and Nichols (1942) for single loops, but the reset time parameter is one-fourth as large. © 1979, American Chemical Society. All rights reserved.