This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Can the 2-wire 4-20mA load resistor connect to loop(+) ?

Other Parts Discussed in Thread: XTR116

Hello everyone!

Don't know if this is the right forum t o discuss this topic, sorry if i am wrong.

According to  Collin Wells' blog ,  when using chip like XTR116, I can't  connect sensor GND to Vloop GND. (https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/12/09/part-2-two-wire-4-20-ma-transmitters-background-and-common-issues)

But in my design, I use the 'High-Side' method to ensure the load is shorted to GND, so R_shunt is connected to Vloop(+), left sensor GND connect to  Vloop(-).

How can i solve this problem that Collin mentioned above? Can I simple add a resistor between Vloop(-) and sensor GND so to lift up a potential? Does this way work?

Thanks!

  • Also, does Rload and Rshunt the same thing?

    In my understand, Rshunt is used as sensing the current,  Rload can be either sensing or rising up the potential so to distinguish from Vloop(-). So, can I put Rshunt any series place of the loop, as long as there is a Rload connect to the Vloop(-)?

  • Hi Benjamin,

    I will move your question to the Precision amplifiers forum. I believe that's Collin's group, hopefully you could get direct support from him or other apps engineer on his group.
  • It's nice to have the topic in the proper place, thank you!

  • Hi Benjamin,

    Thanks for reading the blogs and for double-checking your design.

    The blog states that the 2-wire GND (IRET) can't be connected to the VLoop GND. The 2-wire GND is a different schematic node than the Io (4-20mA current output) node. It is perfectly acceptable to connect the Io node to the VLoop GND. Doing so still allows the 2-wire GND (IRET) node to float up and down as the output current changes. Take a look at the images in the blog and you'll notice that there is a resistance (~25 Ohms) between the IRET and IO pins on the XTR116.
  • Hi Collin,

    I notice the 25 Ohms resistor there, and I think this also means the Rshunt can be anywhere along the loop.

    I'll built the circuit and update the result later, thank you very much!