9205 differential zero volts

[rich24]

I am using a 9205 to measure several voltage signals. Some of these voltage signals come from relays inside my instrumentation (to signify that the instrument is ready to take measurements for instance). When the relays are on, there is no problem reading the voltage out (say 5 V), however, when the relay goes off, there is a random noise that floats around and is not near zero volts. Any help here would be great!!!

[OA1]

Hi Rich the behaviour you're seeing is expected of multiplexed modules, when the relay goes "off" the channel you're reading from effectively becomes open and as a result you see voltage spike in all connected channels. You'll most likely need a digital input card. Getting digital output to work on an analog input is tricky.