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We are trying to log a simple voltage and current with an SCXI 1001 and voltage card 1125. The data is good for 5 minutes and then sometimes it doubles the value or cuts it in half. The problems is somewhere in the SCXI (we think) due to monitoring a channel and watching it go out of whack. Any suggestions?
It sounds as if you are running into a grounding issue. Are your signals grounded or floating?
In cases where both signal lines at the transducer end are floating, you'll want to establish an earth connection at the SCXI-1125 by connecting the negative input line to chassis ground in the terminal block. You can directly connect the negative terminal (CH-) to the chassis ground or connect thru a bias resistor. This eliminates noise that may be riding on the floating signal and provides a path to ground for the floating signal.
This information can be found in the SCXI-1125 User Manual on page 2-2. I've linked the manual below.
