PCI-6221: Bad voltage reading when reading all channels at once

[brunoobsomer]

Hi!

We have a PCI-6221 acquisition card which has a very strange behavior. Channels 1 & 2 are connected to an 8V source. When performing an acquisition on those channels only (RSE mode), everything is perfect. But if we perform the acquisition on all the channels at once, there is an offset in the measured voltage.

I include a screenshot of the problem with NI MAX. On one file, only channels 1 & 2 are acquired and we measure 8V. On the other file, all channels are acquired at once and we can see than channel 1 (red line) is around 7.75V, while channel 2 (green line) is correctly at 8V.

Does anybody know why this happens and how to fix this?

Thank you

[Henrik_Volkers · Accepted solution]

Ghosting (settle time error) of multiplexed DAQs!

See spec diagram called 'settle time error' , the scale is in ppm but log!

[brunoobsomer]

Thanks for the hint!