Duplicate signals on NI 9205 module

[Cameron.Andersen]

I am having difficulty with a NI 9205 ±10V AI module installed in a 9112 chassis for use with a 9024 controller.  I am using a 9264 module to generate a steady 5V signal (verified with voltmeter) and would simply like to verify correct operation of the 9205 in picking up the signal.  I've wired the common from the 9264 to the common on the 9205, and the 5V signal to the AI0 terminal on the 9205. 

Prior to making any connections at all to the 9205 (even with the DSUB 37 disconnected), Distributed Systems Manager shows roughly -3V on every input channel of the 9205 (first unexpected observation). 

As soon as I make the connection between the 5V signal from the 9264 to the AI0 terminal on the 9205, every channel on the 9205 jumps up in value.  The first eight channels show 5V.  The remaining channels jump to approximately 3-4V, in roughly four groupings centered around 3.7, 4.2, and 3.5V.  As I move the 5V signal to successive input channels, the remaining channels up to AI7 stay at 5V, but the ones I've left behind (AI0, AI1, etc.) drop to about 3.9V.  In this setup, it appears to be very repeatable.

My expectation was to simply see a noisy zero volts on every channel but the one I've wired to, which would show the signal voltage...

I don't have a tremendous amount of experience with cRIO, so any help or suggestions would be appreciated!  Thanks in advance!

[Zach J]

Hi Cameron.Andersen,

The 9205 module has Channel-to-Earth Ground isolation but does not have Channel-to-Channel isolation.  There may be noise introduced on all channels when a signal is recieved on one of them.  This is expected with a data acquisition module that does not have Channel-to-Channel noise isolation.  In regard to the measurement you are taking with nothing connected, this is also expected.  There is no reference for the device to measure by and a disconnected terminal could potentially read anything.  Try connecting the positive and negative terminals of an input channel together (basically shorting the measurement) and see if the value is near zero.  

At what rate are you taking measurements?  It could be possible that the measurements you are taking are ghosting between the channels.  Hopefully that helps!  If you have any further questions, please feel free to ask away and we can answer them!