pci-6111 dc voltage dropping to zero

[Fuqface]

Hi,

 We have a PCI-6111 Daq card.  When we put a DC voltage across any of the AI channels the voltage drops to zero after a split second. We have checked
the channel voltage with an oscilloscope and it is indeed 5 volts high.  Upon applying the 5V the DAQ card reads a sharp spike usually less than 5V then drops to zero volts.
It seems that the card can't hold a voltage.

ALso, on the AO channels we put out a sine wave to an oscilloscope and we get a sine wave that has its negative peaks truncated.  So the bottom wave peaks are flattened.

Is this indicative of a bad card?

Thanks.

[AnalogKid2DigitalMan]

Ff:

Your description of the 5V spiking and then going to 0 sounded like AC coupling to me. I looked at the manual, and indeed the card does support AC and DC coupling so you may want to make sure you are set to DC coupling. Here's a link to an older manual: http://www.ni.com/pdf/manuals/321759e.pdf

There are newer manuals available here: http://sine.ni.com/manuals/main/p/sb/navsRel?q=pci-6111

Regarding analog ouputs, that does seem odd. You may want to try running diagnostics, here's a link to that, do not know what version DAQmx you are using so you may have to use an older version (links on that page): http://joule.ni.com/nidu/cds/view/p/id/566/lang/en

Let us know the results.

[Fuqface]

Actually we were measuring the voltage with reference to the AI ground.  Changing it to the AI0- fixed the problem.

Thanks.

[AnalogKid2DigitalMan]

Very good. Are the analog outputs behaving properly when reference to the proper ground level?