valve position transmitter Vs DVC inbuilt position feedback


Is there a difference between using independent position transmitter for valve position feedback and using DVC inbuilt position feedback  in terms of giving no error between command and feedback even though small errors? Do independent position transmitters create errors and need to be calibrated frequently ? Appreciate your comments from experience please.

Thank you

  • 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:
  • In reply to Jonas Berge:

    In continuation to good points on Jonas response, on saving extra hardware cost of Position transmitter, mounting complexity (two devices on small valve), Single calibration for both, less maintenance headache due to reduced components etc., please note that microprocessor based device provides equal performance.
    In past independent position transmitter were used, specifically for SIS application, where Cause Effect Matrix of Logic Solver require completely independent AI (Analog Input) for voting arrangements. Good news is that DVC in built position transmitter is completely Independent of positioner function and AI is SIL suitable.
    Hope this helps