How to measure differential analog signal

[abdel2]

I have read the manual and measuring differential and single-ended signals but I'm still not sure if one method suits my applications. Basically I connect a BNC to one of the analog channels. The BNC has the actual signal in one wire (inner pin) and ground in the other wire (outer shield). I am connecting different components to different analog inputs so they might not share the same ground (or negative terminal). What is the best way to acquire that kind of data. It seems the differential settings on the panel (BNC 2090A) records different between, let's say, ai1 and ai9. I don't want that because I want to record difference between two wires that are connected to ai1.

[Dennis_Knutson]

You don't have two wires connected to ai0. You have a single wire connected there - the center conductor. Depending on the switches of the 2090, the shield of the bnc connector is connected to ai8 (for diff), to ai gnd (for RSE), or ai sense (for nrse).

Have you read the manual about the various connections available?

[abdel2]

Hmm, it doesn't make much sense to have a differential signal using two different BNC connectors. Currently, I'm using a pressure sensor which provides a differential output using one BNC. I just want to be able to connect that BNC to the DAQ board and read signal from it properly.

I actually just tried acquiring a differential signal on channel A0 using one BNC. if the ground (outer shell) of floating, the signal obtained is not good but when I connect the ground to the actual transducer's ground (this time it's a pulse oximeter), I get a good signal. Wouldn't it mean the outer shell on the BNC panel is actually connected to something?

[Dennis_Knutson · Accepted solution]

Who ever said that a differential signal is connected to two different BNC's? Did you bother to look at the manual? The schematic of figure 2-2 is pretty clear about the connections on how the shield is connected in differential mode.

[abdel2]

My bad, I didn't look at it in details. From the initial scan, it looked like it used inputs from a0 and a8 to record differential voltage. Didn't know it was only for the card. The BNC panel itself uses one BNC. This is great! Thank you!