Multiple Switching Relay for Identification of Frequency Responses

Abstract We discuss a new method for relay-auto tuning of a closed-loop control system. Sustained oscillations are obtained by putting relays in the feedback loop and they provide ultimate periods and gains of processes for tuning PID controllers. The ultimate periods obtained by the conventional relays have relative errors up to 5% for first order plus time delay processes. To improve the estimation of ultimate periods, modified relays such as a saturation relay and a relay with preload can be used. However, these modifications lose the binary (on-off) property of the conventional relay. Here relays with multiple switching which produce pulse-width-modulation (PWM) signals are proposed. They retain the binary property and show improved identification accuracies of ultimate data.