A position transmitter is a device used on a
valve actuator that sends a feedback signal to indicate what the actual valve position is.
On a control valve, it sends a signal which is ranged from 4 to 20 mA where 4 mA is closed, to the DCS or PLC that allows the control system to verify that the valve positioner has moved the valve according to the signal sent to the positioner.
Position transmitters, when used, are usually an integral part of either the valve positioner or limit switch devices.