Improved Critical point estimation and its application to temperature control system

The ultimate gain and ultimate period (Critical point) is used for tuning the PID Controller in process industry. An experimental method is proposed for improved estimation of the ultimate gain and period by conducting the relay feedback test for two different hysteresis bands. Simulation results show that the ultimate gain and period estimated by the proposed method is superior to conventional relay feedback method, and very close to the actual one. Usefulness of the proposed method is demonstrated through a laboratory scale practical temperature control system under both set-point change and load disturbance.