Emerson Exchange 365

It can be mechanically challenging to put both a positioner and a position transmitter on the same valve. particularly a small valve so using built-in has a mechanical advantage.

You calibrate the built-in position transmitter in one go at the same time as you stroke test the valve after installing the positioner or doing some function check. With a separate position transmitter the stroking and position calibration is done in two separate places which is a more work, particularly if you do it in the field. So again advantage to built-in.

Perhaps the one reason for going with separate position transmitter is if you use wireless position transmitter. A wireless position transmitter would be used if you don't have a separate pair of 4-20 mA wires and DCS AI for position feedback, and you also cannot use HART from the positioner because the DCS AO does not support HART or the 4-20 mA wiring was not made "digital grade" supporting HART in a continuous mode. Particularly interesting if your plant already has WirelessHART network infrastructure.

Learn more about 4-20 mA/HART installation in this essay:
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