LAUSR

Control valves are very important actuators in the process industry. Due to friction in the stem, they present a nonlinear behavior, which can generate errors in the stem position and oscillations in control loops. This paper presents five control algorithms based on feedback linearization technique, to deal with pneumatic control valves affected by high friction in their stems. These control algorithms measure the valve position and manipulate the actuator pressure, acting as a valve positioner. The paper also shows practical results with a control valve operating in a real flow control loop.