Input configuration, cabeling and ground loops

[tnemitz]

I read the "field wiring and noise considerations for Analog signals" with great interest. However, I'm having a bit of a understanding problem when trying to transfer the contents of the article to my current setup, so I want to make sure I understood it correctly.

As can be seen in the picture, I have signals from a microphone (electret), which are amplified, filtered and processed with a NI 9205 ADC (sitting in a cRIO Chassis). Microphones, amplifier and filter are powered by a pair of 12V-batteries, while the cRIO is powered by a different battery. There is no connection to Building or Earth Ground anywhere.

Setup:

My questions:

1) Can the signal source type be considered to be a floating signal source in this setup, as it is powered by batteries?
2) Did I produce a ground loop because of the wiring of the microphone, filter and amplifier? As you can see, at the moment, there are two ground connections each the amplifier and the filter
3) At the moment, the input configuration in the NI 9205 is "RSE". Should I switch to "NRSE" to improve the signal quality?

[Christoph_D]

Hi,

regarding the use of your NI hardware you can also have a look at the follwing guide:

http://download.ni.com/evaluation/pxi/Grounding_Considerations.pdf

Regarding your first question: I would consider the inputs to the 9205 as from a floating source since the NI 9205 and your setup can not possibly share a common ground, so no ground loops possible.

Also have a look at the X Series User Manual and read the section When to Use Non-Referenced Single-Ended (NRSE) Connections with Floating Signal Sources (page 4-12).

Best regards,
Christoph