How do I tell DAQmx to give me differential voltage readings?

[ngp12]

We have wired our PXI-6221 card with differential voltage inputs.  I can't figure out how to configure the DAQmx voltage reading to supply 8 channels of differential voltage instead of 16 channels of single ended voltage.

thanks,

ngp12

[David L.]

Hi Ngp,

For a differential measurement, the analog input channels are in pairs of 8 (X, X+8) but are assigned according to the first channel in the pair. Ex – A differential measurement for AI0 would use AI0 & AI 8 as the differential pair. The same could be said for 1&9, 2&10, etc.

When you create a task in Measurement and Automation Explorer (MAX), the software knows of this rule and allows you to choose the ‘terminal configuration’ appropriately. Therefore, for the 6221, channels 0-7 can be configured as differential OR all channels 0-15 can be configured as single ended. Please see the pictures below as example in MAX and LabVIEW.

Single Ended in MAX (notice channel 8 is selected)




Differential in MAX (Channels 0-7)


Differential Task in LabVIEW




Regards,

Message Edited by David L. on 10-23-2007 02:20 PM