Smith predictor implementation in a PLC, a lab experience

Time-delay processes are frequently found in industry and the most common representation is a first order plus delay time (FOPDT) transfer function. The most used controller is the PID and the negative effect of the time delay in the closed loop system response is known. The most common way to attenuate the effects is by selecting a low proportional gain, degrading the response. If the model of the system is known, the Smith predictor allows one to compensate the effect of the time delay on the feedback. In this work we show the implementation of a PID controller with Smith predictor in an industrial PLC, and the results of the experience on a water temperature control loop, designed and constructed in the “Automatic control Lab” of the Facultad Regional San Nicolas - UTN.