Practical Model and Detection Algorithm for Valve Stiction

Stiction is the most common problem in pneumatic control valves, which are widely used in the process industry. Stiction causes fluctuation of process variables, which lowers productivity. Therefore, developing a method to detect stiction and distinguish it from other causes is crucial to help operators take an appropriate action for improving control performance. The present work proposes a valve stiction model and new stiction detection algorithms. Using only two parameters, the proposed model can describe the stiction phenomenon with sufficient accuracy. The usefulness of the proposed detection methods are demonstrated by comparing them with a conventional method. The proposed methods are shown to successfully detect valve stiction, distinguish it from bad tuning or disturbances, and quantify the degree of stiction, by using simulation data sets and real operation data sets of several chemical processes. Copyright c ©2004 IFAC