Where Is the Ground Reference on NI-9223?

Updated May 13, 2024

Reported In


  • NI-9223
  • NI-9222
  • NI-9224
  • NI-9225
  • NI-9229
  • NI-9238
  • NI-9239
  • NI-9251

Issue Details

In the Field Wiring and Noise Considerations for Analog Signals  it is suggested to use bias resistors between the signal lines (AI+ and AI-) and ground reference of the channel (AI GND or COM) when differential configuration is used with floating sources. However, the NI-9223 does not have a GND or COM connection available. Where to connect the bias resistors in this case?


The information provided in the document above is a general recommendation, a specific module's wiring recommendation for different configurations can be found in the Getting Started Guide of the module. For the NI-9223 we do not need to use bias resistors, the signal source can be connected directly to the AI channel. 

Additional Information

The purpose of the bias resistors is to ensure that the common-mode voltage level of the signal with respect to the measurement system ground remains in the common-mode input range of the measurement device. If we check the datasheet of the NI-9223, we do not find a specification for common-mode voltage range, while for the other modules (those that require bias resistors in differential input with floating sources) we do. In case of NI-9223 the ground reference of the internal ADC is internally connected to the AI- input of the channel which eliminates the need for bias resistors. The same applies to the other modules with channel-to-channel isolation and the NI-9251 which has no isolation.