A Performance Monitoring Tool to Quantify Valve Stiction In Control Loops

The paper presents main features of a performance monitoring system, which allows stiction quantification. It implements a methodology which permits one to reproduce the unknown stem position, without requiring any additional knowledge, based only on data normally registered in industrial plants (controller output OP, controlled variable PV and set point SP). A general procedure is proposed to discard data for which quantification is very likely to give wrong indications and to restrict the application to appropriate cases. Simulations show that several sources of perturbations can be eliminated; on the contrary, the presence of external disturbances may alter the reliability of stiction evaluation and then stiction diagnosis techniques must be applied firstly. Results are confirmed by application to industrial valves for repeated acquisitions, in the framework of a performance monitoring system implemented for continuous supervision of control loops and valve maintenance scheduling and checking.