Digital PID process control apparatus

Claim 1

A digital PID process control apparatus comprising digital PID controlling means (12) for calculating a control signal as a process input signal in accordance with PID control parameters and a difference between a set-point signal and a process signal as a process output signal so as to supply the control signal to a process (10), identifying means (30) for identifying a pulse transfer function of the process (10) in accordance with the process input signal and the process output signal while superposing a persistently exciting signal as an identification signal on the control signal and supplying a superposed signal to the process (10), and for calculating an S-transfer function of the process in accordance with the identified pulse transfer function, tuning means (40) for tuning the PID control parameters of said digital PID controlling means (12) in accordance with the S-transfer function, characterized by further comprising identification-complete detecting means (42) for detecting a convergence of the S-transfer function so as to stop generating the persistently exciting signal by said identifying means (30), characteristic change detecting means (44) for detecting a model error of the process (10) in accordance with the process input signal, the process output signal and the pulse transfer function, and for changing the set point signal in a pulse form, and restarting means (52) for detecting a change in the model error when the set point signal is changed in the pulse form and for restarting generation of the persistently exciting signal by said identifying means (30).