Loopback Test for USB DAQ Device Shows Unexpected Data

Updated Jan 24, 2018

Reported In


  • USB-6212
  • USB-6341


  • NI-DAQmx

Issue Details

To test my USB DAQ device, I have looped an analog output to an analog input. I am getting distortion and DC offset in my analog input data. For example, my AO is outputting 5V, but my AI is only reading 2V. Why is this happening?


This unexpected measurement usually means that the analog input task is configured to be differential. When performing loopback test between analog input and output pins on a USB DAQ device, you must configure the analog input task as reference single-ended (RSE). Changing the configuration from differential to RSE should yield expected measurements.

Additional Information

For more information about the different input terminal configurations (e.g. RSE, NRSE, Differential) and when to use each, see Field Wiring and Noise Considerations for Analog Signals.


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