At 50% input transmitter shows 12.3mA .75 and 100% also has variation. Zero reading shows correct, so what to do?
In some brands, this type of hysteresis error is common in Thermocouple input Temp Transmitters, since millivolts are not linear to temp. In old Foxboro pressure, flow, level Transmitters hysteresis error is common and we can’t get rid of it.
in this case, first do zero trim by Hart communicator connected across it. Then go to 100% o/p starting from 0% i.e. from 4-20 ma …then, at last, do span calibration mentioned in Hart ( when 20 mA o/p is reached set it to 100%) …then it will be ok.