NI 9221 Measuring voltage difference between two analog inputs

[Wakeel]

Is it possible to measure the voltage difference between two analog inputs without using the com pin in the circuit as seen in the attached photo.

Also if I have two circuits that have different grounds, can I use the attached photo?

[MitchBrown · Accepted solution]

Hey Wakeel,

From the datasheet, the NI 9221 is a single ended analog input module and so it cannot perform a differential measurement as you describe in the second picture with the DC source.

The NI 9221 supports only Referenced Single Ended, and this is shown in the following diagram.

For the second question, you could connect the hardware in this manner and I would expect AI1 to measure 7 V, and AI0 to measure 12 V, as both are measuring relative to ground.

Some useful links:

Field Wiring and Noise Considerations for Analog Signals

NI-9221 Datasheet

Hopefully this helps!

Mitch