Approaches for efficient stiction compensation in process-control valves

Limit cycles caused due to valve nonlinearity such as stiction can be eliminated with proper valve maintenance. Valve maintenance is undertaken during production stops, which are scheduled once every 6 months to 3 years. The loss of energy and product quality during this intermediate period can be quite high. Stiction compensation algorithms can mitigate this problem to a large extent. In this paper, two novel approaches for stiction compensation are proposed: (a) a simple two-move approach and (b) an optimization based approach much in the spirit of predictive control strategies. Both the approaches are based on a data-driven model for stiction. The merits and demerits of both these approaches are discussed. The results are illustrated using simulation case studies. The two-move approach is also validated on a liquid level system. (C) 2007 Published by Elsevier Ltd.