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What is the function of positioner in control valves? does the control valve operate without positioner?
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No...valve can only be used as on/off purpose..not for control without positioner.
A positioner is a device put into a valve to ensure that it is at a correct position of opening as per the control signal. An I/P converter only sends the opening/closing request to valve but can not confirm its position.
Positioner senses the valve opening through a position feedback link connected to valve stem which is its input signal. I/P converter output is its setpoint input. The difference between these two is the error signal based on which the positioner positions the valve to correct position to reduce error to zero. Hence positioner is nothing but a pneumatic feedback controller. Controlled external supply air to positioner provides power to positioner to position a valve. Also positioner is used in a valve when valve operating signal range is different from I/P converter output range.
In recent days software configurable digital positioner are being used in valves which do not require I/P converter and has many features like advanced valve diagnostics, partial stroke testing, remote communication etc.
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