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please tell me five types of fault of
control valve and positioners?please
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Answer Posted / carl_ellis
1) Actuator loses air supply or diaphragm leaks
2) Positioner loses control signal input
3) Positioner mechanical feedback is damaged or disconnected
4) Air supply does not meet instrument air requirements,
dirt and moisture accumulate and cause positioner shuttle
valve to stick
5) Stiction - valve internals are sticky, stem does not move
smoothly through its range
6) Poor positioner tuning creates overshoot
7) Mechanical backlash creates deadband that causes poor
control action
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Q1: Consider part of a control loop, which excludes the transmitter, consisting of a process, a controller and a control valve which may be represented by two dead times of 0.5 min each and three exponential lags of 0.8 min., 1.0 min. and 1.5 min. respectively. We wish to express this system as an overall first order plus dead time (FOPLD) model ie gain, time constant and process dead time. (We will see later that this is often done, to simplify controller tuning). For this exercise, gain is considered to be 1.0. (A) If the transmitter is a flow transmitter whose behaviour can be described by a dead time of 0.2 min. and an exponential lag of 0.5 min. in terms of the overall dead time and overall first order lag how can the system behaviour be approximated ? Overall dead time = Overall time constant = (B) If the transmitter is a temperature transmitter with a temperature sensor in a protecting well whose behaviour can be described by a dead time of 0.7 min. and an exponential lag of 15 min. how can the overall system behaviour be approximated now? Overall dead time = Overall time constant =
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