Showing posts from March, 2019


Positioner  Identify the Positioner Parts and Their Function Introduction In previous unit, you have learned about valves and actuators. Figure 1 below, shows how a controller is connected to an actuator to drive a valve to close and open a piping system.                                                   Figure 1     Control Valve without a Positioner   As in any control situation, instability is one of many problems in process system.   Instability is caused when time lags, causes the control loops to react too late to any disturbance.   Time lags also occurred in control loops where large actuator is being used.   A large actuator is like a capacitance in the process.   Valves do not change position when airflow starts to enter in the diaphragm chamber of the actuator.   Valves will move only when enough air accumulates to build up pressure inside the diaphragm chamber and cause motion to actuator stem. To overcome time lags due to actuator capaci