Hi, devchander and NangSgi,
Thanks very much. Fortuantely, NangSgi is online currently.
I read the recommended link and got more sense on theory. Actually I have read those information in Labview help for at least three times before. However, I don't know how to do it practically.
In terms of my above case, I think my battery power is independent of Building ground. I put the battery pack on the table and didn't use 110V AC power so I think my source signal is non referenced (floating), right?
However, because I use USB6009 digital port to control the CD4051 (multiplelexer) on my circuit board, so I have to connect the USB6009 digital ground with the ground of my circuit board. My output signals are based on the reference of my circuit board ground (which is directly connected to the battery negative terminal). All in all, in my user circuit board system, I have nothing with the building ground, that is Earth Ground.
The signal for measurement is tranported by two wires, one is Vout and another is the ground signal (denoted by VGnd) of my circuit board. I want to use differential measurement for reducing noise so I connect Vout to USB6009 CH1 V+ and VGnd to CH1 V-. The problem is what I should do for the AIGND of USB6009. I found all the AIGND port of USB6009 are connected together by manufacturer. Moreover, the digital port of USB6009 is also connected to the AIGND. Well, you may see that the CH1 v- is actually linked to AIGND via my user circuit board. In this case, how to wire a differential mode?
I tried several wiring mode, for my best understanding of differential and RSE, I found the measured value fluctuate between +-20mV. I measured the battery output too, it seems at the same level.
Could you give me any suggestions? Thanks.