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Incorrect voltage reading on USB-6229 DAQ

Hi,

 

I am attempting to read an analog voltage using a USB-6229 DAQ. 

 

I have a voltage at ~6.7V that I read with a DMM (nothing connected to the DAQ). 

 

When I try to read that same signal through AI0 (or AI1) and AIGND I read a steady 10.6V using Measurement & Automation Explorer. 

 

When I have this signal connected to AI0/AIGND and read the same signal using the DMM, the DMM reading jumps to ~13V.

 

I assume there is some sort of grounding issue here somewhere.  Can anyone help me diagnose this problem I'm seeing?

 

Thank you,

Seth

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Hi Seth,

 

What is the signal source that you are reading?  Is this a grounded signal source (like a power supply) or is this a floating source (like a battery)? How do you have your signal wired?  Are you reading single ended or differential in MAX? The document below is a good reference for signal connections (take a look at Table 1):

 

Field Wiring and Noise Considerations

 

 

 

Regards,
Jim Schwartz
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