XTR112

Hello Adam,

Is it possible that you're applying GND referenced signals to the inputs as well as the IRET signal of the XTR112?  In order for the XTR112 to properly operate as a remote 2-wire transmitter the inputs and IRET signals must be completely floating.  

Figure 9 displays a circuit where all voltage potentials on the inputs of the XTR112 are derived from the reference currents which flow out of the IR1 and IR2 pins, through the bridge, and return into the IRET pin.  If you've connected a GND referenced lab tool anywhere in the circuit to simulate a sensor, then you will have issues because the inputs are no longer allowed to float properly above the potential on the IRET pin which will vary based on the output current and load resistor. 

If it is not an issue with aGND reference the please check that the loop supply, measured between pins 10 and 7, is between 7.5 and 36V and that the output transistor is connected properly.

You are correct that if you have the circuit properly configured, removing RG should produce a 4mA output current.  If this does not occur, then there is likely a connection error or issue mentioned above fouling up the results.

Please let us know what you find.

Regards,
Collin Wells
Precision Analog