International Journal of Engineering and Technology

Stiction in control valves is an extremely nonlinear and one of the long-standing problems in a closed loop control system, since the controller will push the control valve to move until the controlled variable reaches the desired value. Stiction moves the control valves to extreme positions so that the process output will force to produce overshoot. Then, the action gets repeated as the controller output reverses its direction. The limit cycle generated, when the control valve sticks and slips during a change in input signal is called stick/slip cycle, will induce vibrations. As the control loops in an industrial plant are interlinked each other; these oscillations will be propagated to the entire system. In this critical situation the only option is to go for maintenance of the faulty valves, which may be recommended/ possible only during process shut down. But, shutting down the process for maintenance of defective valves is not an economical option. Hence, it is very important to provide an efficient technique to compensate the nonlinear effect of the stiction in faulty control valve, especially when it is not under maintenance. This paper proposes a new compensation approach using sinusoidal signal for the stiction nonlinearity present in such faulty control valves.