Hi,
I've already posted this in the "Multifunction DAQ" section but I think the "Signal Sources" category is closer to my problem:
"I've been trying to measure a source signal that is floating (a voltage around 1V). I'm using the Sc 2345 and I've got the signal coming through a low pass filter module (scc-LP02). I've set up the DAQ board to read in NRSE. When my data aquisition board and laptop are plugged into a battery power supply I have no problem reading the signal correctly. The problem arises when I connect my laptop OR data aquisition board to the AC outlet. When I do this I get a reading of -5V. I believe this is because I'm actually grounding everything to
building ground when I use the AC outlet. I've tried plugging my DAQ board into the AC outlet without grounding it, and I get a signal close to what I'm looking for but with a lot of noise. The SCC-LP02 manual says that the internal circuitry does have bias resistors that are required for floating points, so I'm not sure if I'm still forgetting about something. I've read other liturature suggesting that I need to connect the ground reference of the floating point to the DAQ device analog input ground, but I'm not sure how to physically do this (is there a screw terminal on the board for AIGND?). I've tried connecting the ch- to AISENSE but it didn't seem to help. I have limited electrical knowledge, but I would think that if I referenced the floating ground to the board, it would essentially ground everything to building ground.
Hopefully I've overlooked something relatively simple. Thanks,
Chris"
