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Regarding this paper, I first tried to wire single-ended floating sources to a diff ended data acquisition board. But because of some power supply related issues and not wanting to make another interface for bias resistors I want to try another configuration by converting floating sources(0 10V DC outputting transducers like humidity, temperature ect) to grounded sources. So basically my sources are single-ended(not bipolar) and the DAQ board is diff ended.

To make it clear what I mean here are the general configurations from the paper:

enter image description here

In above table, I was using the the one on the top left with bias resistor and now I want to try the encircled one in red.

My questions are:

Here I made a more practical drawing:

enter image description here

As you see above the Figure 1 represents my current wiring scheme. And in that there is no earth ground involved. But still I'm having issues. And now I want to change this to "grounded sources to diff ended" scheme like the one encircled in red.

Regarding the red encircled configuration from the original paper:

1-) Can I do this floating to grounded scheme by using earth? Is my Figure 2 correct?

2-) No extra wire needed to be wired to AIGND?

3-) I wired the DC- to earth ground, but is this correct? I'm not sure whether DC- or SGND must be wired to earth ground. Because sometimes I observed wiring DC- to the earth reduces 50Hz interference.

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1 Answer 1

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You have to ask yourself what common mode voltage might appear between "earth" and AIGND: -

enter image description here

Then you have to check whether your DAQ differential inputs can handle this voltage both safely (without destruction) and without unacceptable performance degredation.

I wired the DC- to earth ground, but is this correct? I'm not sure whether DC- or SGND must be wired to earth ground.

If both are internally connected inside the transducer (as per the dotted red line above) then it won't matter.

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  • \$\begingroup\$ Thanks but I have some lack of knowledge when I look at these figures. 1-) For example in your drawing AIGND is not connected to earth ground right? 2-) Can I measure that common-mode voltage by a multimeter AC setting? 3-) If the commonmode voltage is high what can be the workaround for this config? \$\endgroup\$
    – floppy380
    Commented Mar 13, 2018 at 11:16
  • \$\begingroup\$ I don't know what AIGND connects to - I would assume it connects through to "earth" at some point but this is down to you. Measuring it on a good day might convince you it will work but, on a bad day it could be several volts peak to peak. You need to estimate/calculate what it might be worst case. Again, I can't help you with this because I know nothing about your plant/factory/installation set-up. If CM voltage is high then you have to use isolation methods. Measuring with a meter doesn't tell you anything about any RF/high frequency CM noise unless you have a suitable meter. \$\endgroup\$
    – Andy aka
    Commented Mar 13, 2018 at 11:25

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