NI DAQ boards have different grounds that are used depending on the application: Analog Input Ground (AI GND), Analog Output Ground (AO GND), and Digital Ground (D GND). They are all referenced to a single point on the module itself. But they have different ground pins on the module to minimize noise and cross-talk. Especially, digital ground is particularly noisy because of the high frequency content of digital signals. Most of In case of COM, It is the ground reference used in dedicated modules, such as Analog Input module (ex. NI 9205). This is same as the pin for DAQ AI GND. But, case of AI SENSE is different. It is not connected to any ground anywhere else and floating with respect to AIGND, AOGND, and DGND. AI SENSE is a line that makes the reference of all single-ended AI channels common to each other; they all share a common reference
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