output depends on computer power state

[AsaHopkins]

I have two Analog Output cards, PCI-6713 and PCI-6733.  When I tell either one to set the output of analog output 0 to 0V, a multimeter attached to that output reads 0.018V.  When I turn off my computer monitor, that changes to 0.004V.  Of course, I'd like for them to stay at 0.000V all the time, regardless of the monitor state.  This difference from 0V seems to be pretty constant; when I tell it to output 1V, I get 1.018V, etc.

Also installed in this computer is a DIO-32HS digital output card, as well as a non-NI card for driving a camera.

[AsaHopkins]

Upon further investigation, this seems to only happen when using AO0 and AO1, and seems to have something to do with the grounds.  The ground needs to be able to be set by whatever is at the far side of the connection.

Is there some way to make the grounding behavior of AO0 and AO1 the same as the rest of the outputs?  The "floating source" and "ground ref. source" switch doesn't seem to have any effect.

[Jesse_O]

Hello,

All of the analog output should all share a common ground.  When probe an analog output, it should not matter which analog output ground you choose. 

From your post it looks like you are using a terminal block to connect to the 6713/6733.  Which terminal block are you using?  You mention that only channel 0 and channel 1 have this offset, what happens on your other AO channels?  Also, are you able to confirm that the device measuring the output from the 6733 does not have an offset?

If you are using a terminal block like the BNC-2110, can you see the same behavior on a cb-68 or scb-68 (something with screw terminals)?

Regards,

Jesse O.
Applications Engineering
National Instruments

[AsaHopkins]

I traced this down to competing grounds between the analog output groun in the PCi-6733 and the circuit to which it is connected.  I had thought that the 6733 would defer to the other circuit on the ground, but instead I will rework the other circuit to be independent of the ground level on the input from the 6733 board.  (Basically, so the otehr circuit will depend only on the voltage difference from the 6733, not the voltage relative to its own ground.