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I have multiple sensors going into a DAC with multiple output channels. Can I use multiple XTR devices to transmit the 4-20mA current signals for each sensor?
If you are attempting to use 2-wire transmitters, you will need to isolate the input to each transmitter. The IRET pin of a 2-wire transmitter needs to float and cannot be tied to other grounds or the IRET of other transmitters. See the attached articles for further explanation on why IRET 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.
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