Microprocessor Implemented Sub-Optimum Smith Controllers for Temperature Control

Abstract

The Smith dead time compensator is configured to operate with the Dahlin or the dead-beat controller. The innovation suggested in this paper is to avoid the estimation of the process dead time which is needed in the conventional Smith predictor scheme. This feature is believed to be a practical asset in real life applications where the estimation of the dead time may prove to be difficult. As expected, elimination of the dead time estimation increases the output variance. Further contribution of the paper is to show that the initially designed Smith compensator can always be made stable by placing a low pass filter in the feedback path and adjusting the bandwidth of the filter. The intuitive argument behind this approach is to make the overall system less sensitive to high frequency noise. Finally, these concepts are demonstrated on a pilot scale temperature control system.