METHOD AND APPARATUS FOR DETERMINING THE ULTIMATE GAIN AND ULTIMATE PERIOD OF A CONTROLLED PROCESS

A method and apparatus determine the ultimate frequency and ultimate gain of a controlled process. The apparatus comprises a process gain and phase lag calculation module, a ultimate gain (K.sub.U) and ultimate period (T.sub.U) calculation module, and a tuning sequence control module. The tuning sequence control module initiates a tuning sequence and the process gain and phase lag calculation module samples the process input signal and the process output signal, and isolates from the process input signal and the process output signal at least one input sample signal and at least one corresponding output sample signal by bandpass filtering the process input signal and the process output signal at at least one observation frequency. The process gain and phase lag calculation module then calculates a phase lag of each output sample signal with respect to a corresponding input sample signal and a signal gain of each output sample signal with respect to a corresponding input sample signal. The ultimate period of the process is calculated from at least one observation frequency and at least one phase lag, and the ultimate gain is calculated based on at least one signal gain.