Unexpected Offset, Scaling, or Drift on Analog Input Channels of USB R Series

Updated Dec 19, 2017

Reported In

Hardware

  • USB-7845
  • USB-7846
  • USB-7855
  • USB-7856

Issue Details

I see unexpected offset, scaling, or drift on the analog input channels of my USB R Series device when I provide a known voltage source. Does my device need to be replaced or repaired?

 
USB R Series Hardware
USB-7845R
USB-7846R
USB-7855R
USB-7856R


Why is this happening when I provide a known voltage?

Solution

The unexpected measurement may be caused by an incorrect setting of the analog input terminal mode configuration. 

The default analog input terminal mode is differential (DIFF). To correctly measure a differential signal, use the AI+ and AI- pins of the device. For example, use pin 68 and 34 as shown in Figure 1 below to measure a signal on the analog input channel 0 differentially. 

If your application requires single-ended measurements, configure the analog input channels to reference single-ended (RSE) or non-referenced single-ended (NRSE). See the NI R Series for USB Getting Started Part 2: Advanced tutorial for information on how to configure the analog input terminal mode programmatically or through the project explorer.

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