Indian Journal of Science and Technology

Abstract

Control valves are an increasingly vital component of modern manufacturing around the world, since control valves are mechanical devices, their performance is less than ideal, and degrades over time. For a plant to perform optimally control valve performance must be tracked and maintained. Backlash is one of much invertible nonlinearity present in control valve, if a valve has some backlash, the loop will have a tendency to oscillate, which will get bigger and bigger as time goes by and will also make the loop slower to respond. At present, pneumatic valve Positioner is used which uses mechanical cam to correct the non-linear nature of control valves. Pneumatic valves Positioner typically are very simple and do not implement integral control. In this project a novel low cost Smart Positioner is designed and developed to improve the performance of control loops. A rotary potentiometer with a linear actuator is used to give feedback signals to the controller of the current position of the control valve. A specially designed control system which is cascade in nature increases the performance of the control system. The Position sensor control being a slave controller acts faster to position the valve and thereby avoiding backlash problem. The developed design is implemented in the Second Order Two Tank Level control system and the performance metrics such as Rise time, Settling time and Steady state errors evaluated found improved after implementing smart Positioner. The oscillation of control valve was found minimum compared to pneumatic Positioner which clearly an indication of reduced backlash in the system. The low cost smart Positioner is RVDT which fixed on a pinion rack and interfacing the proposed second order system using MATLAB for error analysis and LabVIEW software and NI DAQ6008 to run the proposed second order system.
Keywords: Control Valve, FCE, RVDT, Second Order, Smart Positioner