[FAQ] Can I use multiple XTR devices if I have multiple DAC outputs or multiple sensors that share a supply and ground?

If you are attempting to use 2-wire transmitters, you will need to isolate the input to each transmitter. The I_RET pin of a 2-wire transmitter needs to float and cannot be tied to other grounds or the I_RET of other transmitters. See the attached articles for further explanation on why I_RET cannot be tied to the loop supply GND, and how to input isolate 2-wire transmitters. Depending on where the isolation needs to occur, you can use a digital isolator such as the ISO7310C or ISO7340C, or an isolation amplifier.

2y-Wire 4-20 mA Sensor Transmitters: Understanding the 2-wire Transmitter GND

2-wire 4-20mA transmitters: Controlling 2-Wire Transmitter Outputs with Externally Powered Sources

2-wire 4-20mA sensor transmitters: Designing Input Isolated 2-Wire Sensor Transmitters

You can use multiple sensors with no input isolation if you are using multiple 3-wire transmitters. However, isolation may be necessary if you are using a microcontroller that is controlling multiple analog outputs that are not referred to the same ground, or the sensors you’re using are referred to different grounds.

The following reference design goes through the theory, component selection, simulation, complete PCB schematic & layout, bill of materials, and measured performance results of a two channel combined voltage and current analog output module features two independent outputs that can source and sink voltage and current over the standard industrial output ranges using 2 XTR300s. Circuit modifications that help to meet alternate design goals are also discussed.

TIPD155