A Research on the Stiction and Detection in the Control Valves

Abstract

Stiction is a common problem in spring-diaphragm type valves, which are widely used in the process industry. A non-invasive method for detecting and quantifying stiction in control valve has been presented in this paper. Although there have been many attempts to understand and detect stiction in control valves, none of the current methods can simultaneously detect and quantify stiction. The method first detects nonlinearity in a control loop by the use of the sensitivity of the normalized bispectrum or bicoherence to the nonlinear interactions that may be present in the control error signal.If nonlinearity is detected, then controlled variable(pv) and controller output(op) signals are filtered using frequency domain wiener filter to obtain filtered pv and op signals.This work describes a model free method that can detect and quantify stiction that may be present in control valves using routine operating data obtained from the process. No additional excitation or experimentation of the plant is required.