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I'm trying to use an absolute shaft encoder with an NI MyDAQ. I'm powering the encoder using the 5VDC pin on the DAQ. Does the ground pin--AGND vs. DGND--I connect the shaft encoder to matter?

I started with the DGND since I was powering the encoder with DC, but my angle reading steadily "floated" down. For example, I would initially read a angle max of "-170" and an angle "min" of -130. However, the two extremes would then begin to float down to -171 and -131, -172 and -132, -173 and -133, and so on.

I switched over to AGND, but I experienced the same phenomenon. I realize my problem is independent of ground pins, but I'd like to know which GND pin is the correct pin for my application or if it truly doesn't matter.

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  • \$\begingroup\$ You should have both grounded, at least that's what my intuition would be. There might be an application schematic shown in the datasheet for your part. \$\endgroup\$ – Nick Williams Jun 18 '15 at 16:48
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    \$\begingroup\$ It depends on the sensor and quite possibly the DAQ card, both of which are proprietary items and therefore this question should be raised with their support personnel. \$\endgroup\$ – Andy aka Jun 18 '15 at 16:51
  • \$\begingroup\$ "floating down" may be caused by being AC coupled. OT your scope is \$\endgroup\$ – Russell McMahon Jun 24 '15 at 18:55
  • \$\begingroup\$ What does "OT your scope is" mean? What does OT stand for? \$\endgroup\$ – techSultan Jun 25 '15 at 19:12
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DGND and AGND are both ok grounds to use. Depending on MyDaq breakout box configuration they are most likely coupled together internally and there is no harm tying them together under most set ups. The difference is there to avoid mixing signals with different noise sensitivity by splitting up their current return paths. Digital signals are noisy and the voltage they generate across small impedance in the ground return path can couple into sensitive analog signals sharing the same ground.

In more complex set ups, for instance where you are using your Daq to measure voltage levels as well as control digital logic, you would need to think about your ground wiring to make sure everything operates with minimal noise and error.

Otherwise please review your manual since they will have application suggestions and typical wiring diagrams.

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Check is there any noise in data.It may also possible due to irregular supply spikes or supply lines passing near to data lines.If you are really facing problems in choosing grounds then short it with an ferrite beed (inductor).I think grounding is not a problem.

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