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why two ground types?

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Hello, 

 

I am a teaching assistant in charge of a couple lab sessions where mechanical engineering students are using MyDAQ modules to learn about measurements. In one experiment we use both the 5V and +/- 15V sources to power a wheatstone bridge connected to an amplification IC (INA126). I assumed that since AGND is the reference for the 15V sources and DGND is the reference for the 5V source, it will best to connect both AGND and DGND to the common ground rail of our circuit, assuming that I want accurate supply voltages. However, would doing so lead to any more or less noise being introduced to the circuit by the MyDAQ, versus just connecting one of the ground (AGND or DGND but not both)? We know the circuit will "work" with only one of the grounds connected, as a DMM resistance measurement on the myDAQ unit by itself indicates that AGND and DGND are connected together internally anyway. A colleague of mine suggested that it would cause less noise to only connect AGND, but not DGND to this circuit. I was thinking AGND and DGND should be both be connected to the common rail of the circuit to prevent a possible ground bias/loop. Thanks for any advice you can give me!

 

Brian

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Accepted by topic author BrianMendo

Hi Brian, 

 

AGND and DGND are connected to the same ground. They are similar to a COM port. They should be no concerns about ground loops because the two ports are the same ground. 

 

If you do see different behaviors when using the two different ground ports, let me know. 

 

Best Regards

T. Le
Vision Product Support Engineer
National Instruments
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