If I use 500 meters 4-20mA current loop in an outdoor environment, does it matter whether I use single ended or differential ended data acquisition inputs?

I know that for voltage signals differential ended inputs are good to reject common mode interference.

Below is the current loop measurement I'm talking about with a shunt resistor:

enter image description here

As in the above diagram, if the sensor is a 4-20mA loop and converted to voltage at the DAQ side by a 250 Ohm shunt resistor and coupled to the DAQ input as voltage, is there any advantage to using differential ended inputs?


Here is the two options single and diff ended inputs for several current loops:

enter image description here

Above there are 3 current sensors hooked up for both single ended(Figure1) and diff ended(Figure2) data acquisition board channels. If I have many sensors that way, would using diff ended make any difference in this case in terms of interference noise immunity? (I know if the signals were transmitted as voltage it would have big impact but I dont know the current case)

  • \$\begingroup\$ High noise immunity? \$\endgroup\$ – Long Pham May 7 '18 at 10:29

As drawn in your Figure 1 everything should be fine as the sources are isolated from ground. All three circuits are grounded at only one point.

The original circuit concerns me a little in that there is a different ground present at each end and this implies that a variation in potentials is possible. With one circuit as show this would be the same as introducing a voltage source on the ground / return line but due to the current drive you would still get the correct voltage drop across the shunt resistor. The problem is that with three such circuits and a common ground (as in Figure 1) you're going to get circulating earth currents and it will rapidly get difficult to figure out what's going wrong.

Stick with Figure 1 and isolate your sources, if possible.

  • \$\begingroup\$ The data acquisition multiplexing board can be set to diff ended and single ended inputs. If I set to single ended I can use more(double the diff ended scheme) channels. Thats why I wanted to use single ended. So seems like using diff ended for these current signals is redundant? (sources are isolated from ground) \$\endgroup\$ – floppy380 May 7 '18 at 12:54
  • \$\begingroup\$ It seems that your single-ended design should be OK. \$\endgroup\$ – Transistor May 7 '18 at 13:06

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