Detecting a Voltage Signal

[Fouzaan]

I'm trying to set up a system to monitor a soak test on some ribbon cables. In essence one end of the cable is
not connected to the other end but if the package leaks and saline enters then a connection would be made.

I want to supply a voltage/current to one end of the cable and have labview monitor the
other end for a change in voltage signifying that a leak has occured.

I'm using an SCB-68 breakout box with the PXI 6070E DAQ card. Using the DAQ-mx Assistant
in labview I've set it up to monitor two channels. I'm testing my setup with a DC power
supply, the final setup will use an AC power supply.

I connect the ground to the AI GND pin and then connect and disconnect the +V lead to +V
pin. I'm facing a couple issues. I want the signal to go back to zero when I disconnect
the +V pin and it seems the signal persists at +V even when the lead is disconnected. The
second problem is that when I connect the +V lead to the first channel (ai1 for example),
the second channel that the DAQ Assistant is setup for also reacts to the signal. In
addition, I've added a third channel to the DAQ Assistant and it has made one of the pins
work perfectly, the second pin worked but couples with the other one as before. It makes
no sense to me why adding an extra channel would change the way the first channels
receive signals.

I have the AI GND for each channel connected together. I'm currently using RSE but I'm
not sure if that is correct. I've gotten closer to what I need with RSE. But perhaps I'm
just setting it up wrong for NRSE. I've also tried changing the jumper switches on the
SCB-68 box and am currently using the settings for single ended analog input.

If anything jumps out that I'm doing incorrect let me know. I've spent a lot of
time fiddling with this set up and am stumped as to what I need to get it working.

Thanks.

[Fouzaan]

So I have no idea why this works perhaps someone can explain. But I sampled in the following way and it works exactly as I wanted.

Sample Channel 1 - first signal
Sample Channel 0 - dummy channel
Sample Channel 2 - second signal
Sample Channel 0 - dummy channel

I thought this might be due to crosstalk but when I substituted a different channel as the dummy channel instead of channel ai0 all the channels see the same signal when I connect to one channel. Why is the behavior different for channel 0? I'm beginning to think some hardware might be damaged?

[Fouzaan]

Ok I got it to work with whatever dummy channel is used. The problem was that I had to ground the dummy channel, I just had it unconnected and floating. I'm guessing ai0 is different in some way causing it to not be floating.

[Fouzaan]

I got it working finally. Thanks to anyone who took the time to read my post.