What is the Difference between E/P Positioner and I/P
positioner in a control valve? In which applications the
respective positioners are used in?
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Answer Posted / william z butryn
An I/P convertor is a device that converts an electronic
input signal (typically 4-20 MA @ 24 VDC) to a pneumatic
output signal(usually 3-15 or 6-30 PSI) depending on the
control pressure required. The output must be calibrated to
provide the desired percentage of span as the input span.
The output of this convertor will do NOTHING until it is
connected to another device. The other device can be an
actuator, positioner or other device requiring a pneumatic
control signal.
If an actuator is used, the actuator can be connected to a
valve stem, a damper or a lever. The actuator can then be
used to set the position of the connected device by moving
a shaft up and down corresponding to the pressure applied
by the output of the I/P convertor. An E/P can be construed
to mean a device that converts a voltage or electronic
input signal to a pnematic output signal. A P/I convertor
does the reverse and converts a pneumatic input signal to
an electrical or electronic output signal.
An EPP as it really should be designated, is an electro-
pneumatic positioner (which can also be a smart positioner)
that can provide a position feedback to itself through the
use of a lever connected between the positioner and the
controlled device that will move proportionately up or down
with the shaft movement of the control valve, lever or
damper to which it is connected. When the position feedback
signal has reached the corresponding percentage of span of
travel, the output signal will be adjusted accordingly and
stabilized to maintains and hold the desired position of
the device.
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