Abstract: A process control apparatus for use in a control system includes a controller (40) for coupling to a process in a closed loop of the control system and for controlling a process variable having predetermined set point and measured values. A deviation signal is generated by comparing the set point and measured values to generate a deviation signal and the controller (40) is responsive to the deviation signal to control at least one operating parameter of the process to reduce the deviation signal. An identification section (60) is provided which is responsive to the deviation signal and which provides a measured value of at least one characteristic of the closed loop response of the control system from the deviation signal by integrating the deviation signal with time.