Curve Fitting for Detecting Valve Stiction

In this chapter, a curve-fitting method is introduced for detecting valve stiction. It is assumed that the loop in question is known to be oscillating by using any of the oscillation detection methods presented in Chap. 4. The stiction-detection method is based on the curve-fitting results of the output signal of the first integrating component located after the valve, i.e. the controller output for self-regulating processes or the process output for integrating processes. In this chapter, we answer important questions such as which signal should be looked after, and why that signal takes a certain shape in the presence of valve stiction. A metric referred to as the stiction index (SI), is introduced based on the proposed method to facilitate the automatic detection of valve stiction. The effectiveness of the proposed method is demonstrated using both simulated and real industrial data sets.