Specifications Explained: FlexRIO Adapter Module DC Offset and ADC Offset

Updated May 16, 2019

Reported In

Hardware

  • NI-5731
  • NI-5733
  • NI-5734
  • NI-5732

Issue Details

In the specifications for my FlexRIO adapter module, I see sections on ADC Offset and DC Coupled Common Mode Output. What do these specifications mean?

Solution

ADC DC Offset is an expected DC offset in the ADC's measurements. For example, on the NI-5733, If the ADC is fed precisely 0V t it will read +/- 7.1 mV. For example, a 100mV signal fed in would have the DC gain error multiplied by the 100 mV signal and then a flat +/- 7.1 mV added on after that.


DC-coupled common mode output is the voltage the ADC will actually drop over a 50 ohm termination. If the devices is attached to a wire with 50 ohm termination onto AI0, a DMM to probed across the connector would read +/- 0.8 mV in DC coupled mode. This would not exist in AC coupled mode.