Valve stiction in control loops — A survey on effective methods of detection and compensation

In many industrial manufacturers, the quality of product heavily depends on control loop performance. Oscillations in control loop decreases performance of their systems. This is made worse with the increased number of control loops in a control process. There are several reasons for oscillations such as poor controller tuning, oscillating load or disturbances with a high-frequency. However, the most common reason for oscillations is friction in the valve. This paper presents a brief summary of some effective methods of detection of stiction in control loops and the compensation techniques to mitigate this effect. The aim is to determine the appropriate model of stiction in order to design a proper controller to prevent oscillations in the control loops. Based on the literature, Data Driven model with fewer parameters provides simpler solution and is the most common method used in comparison with physical based model which presents a number of unknown physical parameters. Moreover, previous methods (even in data-driven models) were based on some assumptions and thus their judgments are not reliable when the assumptions were not satisfied. From this study too, it is seen that numerous methods of stiction detection are available. Hence, it is suggested that the future research emphasis should be more on compensation of stiction especially for nonlinear processes.