Answer / carl_ellis

An E/P transducer is a voltage to position transducer, so
its input signal from the control system is a voltage
signal, like 0-5Vdc. Its output is a proportional pneumatic
signal.

An I/P transducer is a current to position transducer, so
its input signal from the control system is a current
signal, like 4-20mA. Its output is a proportional
pneumatic signal.

E/P and I/P are not positioners and are not called
positioners because each is a transducer that converts an
input signal to a proportional pneumatic signal.

A positioner is a much more than a transducer; a positioner
is a controller.

A positioner senses valve position and regulates its
pneumatic output to control the valve position to the
setpoint defined by the input signal.

Where an E/P or an I/P is mounted is a matter of opinion,
plant standard or convenience, it is not dependent on its
function.

A positioner must receive a valve position feedback signal,
so a positioner must be mounted so mechanical linkage can
sense valve position or when mounted remotely from the valve
(like in high ambient temperature applications) a remote
position sensor is used to feed a signal to the positioner.

Carl Ellis
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