TEMPERATURE CONTROL OF A WATER BATH BY SELF-TUNING-PI-CONTROLLER

Although there have been several reports of various self-tuning propor tional-plus-integral (STPI) schemes and proportional-plus-integral-plu s-derivative (STPID) schemes for controllers in recent years, their th eory and practice are still immature. The capabilities of this type of controller to control real physical processes need to be proven in mo re detail. In this light, the paper presents an application of an STPI controller proposed by Cameron and Seborg (1983) to a microcomputer-c ontrolled water bath system. The water bath is an example of an import ant component in many industrial chemical processes. Experiments are c onducted to test the STPI controller and to compare its performance wi th two other controllers, namely a self-tuning controller (STC) due to Clarke and Gawthrop (1975, 1979) and a conventional PI controller. Th e reliability of the STPI controller is tested by artifically adding l oad disturbances, simulating a change in the process dynamics, and art ificially adding a variable delay element in the control loop of the p rocess. The results prove that the performance of the STPI controller is as good as a self-tuning controller with the added advantage of hav ing a PI-like structure. Moreover, the STPI controller performs better than the conventional PI controller, especially when there are change s in the process dynamics.