The valve positioner will confront into various kinds of problems when controlling the control valve. Especially, when digital positioner is attached to the control valve with large grand friction, it often invites hunting behaviors due to the integrator in control algorithm. Further, the control valves which operates under the conditions of high pressure and temperature, their grand friction tends to be large since the grand packing is tightened in order to prevent the leakage. Analyzing the behaviors of the system and examining the cntrol scheme, the authors constructed the simulator for practical application. In the consequence of the examination, the authors confirmed that introducing the PI-D control with a gap in the integrator and the minor feedback control of diaphragm pressure to the system would bring out the significant improvement on stability and dynamic response of the system. Moreover, our investigation derived the guideline for tuning the pressure loop-position loop cascading control system.
