Converting a "differential" connection to an "RSE" connection

[Aleksi-]

Hi,

I am dealing with a measurement system that previously used a "RSE" connection to measure certain voltage signals and it worked ok. Now there's a new DAQ (NI USB 6353) and the "differential" connection is used. However the measurements are no more correct.

I know that it would be possible to change the connection method to "RSE" as it used to be by modifying the VI used but in this case that would be difficult since I do not have an easy acces to the DAQ device anymore.

So the question is this:

Is it possible to manually change a "differential" connection to an "RSE" connection just by disconnecting the GND signal cables now used and connect those input ports to the GND ports of the NI USB 6353? Wouldn't this kind of connection practically be the same thing as using "RSE"?

All help is appriciated.

[crossrulz]

Sounds like you should have been using RSE anyways if the negative sides were all ground.

RSE just does measures relative the the Analog ground.  So just tying the grounds together should do it for you.

[Aleksi-]

Thanks for your reply.

And yes, as I already mentioned I SHOULD have used RSE. And that's what  I am now trying to do without changing the VI.

Anyway what do you exactly mean by "tying the grounds together"? Do you mean that I just connect the DAQ ground reference to the negative signal input terminals of the "differential" inputs that I am using?

[crossrulz · Accepted solution]

Didn't you previously say your negatives were all ground?  So you just need to make sure the ground for your signal matches the ground for the DAQ.  And for that to happen, you need to connect a ground from your UUT to the DAQ (ie tying your grounds together).

[Aleksi-]

Thanks, I just wanted to make sure.

[A.E.M]

Hi Aleksi.

Great that you already got the answer you were looking for. I just quickly wanted to show you two great articles that might be helpfull for you later on.

Field Wiring and Noise Considerations for Analog Signals (especially see table 1)

Five Tips to Reduce Measurement Noise