Hysteresis compensation loaded in digital positioner for pneumatic control valve with tightened grand packing

This paper analyzes the behavior of a control valve-digital positioner system that has a large grand friction and examines its control scheme for the performance improvement. The authors have confirmed that introducing the PID control with a gap in the integrator of position control loop and the minor feedback control of the diaphragm pressure is an effective way to ensure the stability and dynamic response of the system. In order to further improve the behavior under this cascade control to small changes of the set point, this paper proposes hysteresis compensation for the control valve with tightened grand packing and confirms its effectiveness experimentally.