Analog Input NI USB 6009

[hughes265]

I am using a USB 6009 differential analog input channel to read a voltage from a load cell amplifier. I am however unsure if it is ground referenced or floating signal output. The power supply to the amplifier is 24Vdc and grounded. The output is +-10Vdc but not sure if floating/isolated. I have measured resistance from power supply negative to signal output negative terminal and have a reading of 5 MOhms. Can i presume the output is isolated from ground?  If I cannot determine which is correct should i use a floating or ground referenced connection as default?

[AlastairUK · Accepted solution]

Hi,

I have done a little bit of looking and I can confirm that the analogue inputs on a USB-6009 are not isolated.

To ensure correct grounding I would consider the following tie the power supply ground the AI-GND on the 6009. The following link gives you good information on grounding for this specific device. Namely page 10 and 12-15
http://www.ni.com/pdf/manuals/371303n.pdf

The following KB is also great for giving a quick overview of the grounding that you need.
http://digital.ni.com/public.nsf/allkb/4A441BC4E49541F4862573A000789203?OpenDocument

If you can have a read through this and let me know if this answers your question or if you have any more then please ask.

Alastair

[hughes265 · Accepted solution]

Hi Alastair,

Thanks for response.

I agree with all you have said and have read the notes previously. I was aware the NI USB 6009 was not isolated, I use an isolated NI USB 6215 in a different application. At the time of writing i was not aware which type of output i had from my amplifier and therefore my input type to the NI USB 6009. I managed to talk to someone there and they have confirmed that it has a common ground plane. Therefore if I supply the amplifier with a 24vdc grounded power supply then the output is ground referenced. Where as if i supply with a isolated brick type psu then the output is floating. I supply using a 24vdc grounded psu, 0v is tied to ground and therefore use the ground referenced diff configuration as described in the manual which has no connection to analog gnd. Does this make sense?

Do you know of any papers on describing how to identify the type of input to an A/D?  For future reference.

Thanks again

Paul

[AlastairUK · Accepted solution]

Hi,

I believe this article will help you understand the wiring required. Should be quite detailed.

http://www.ni.com/white-paper/3344/en/

Alastair

[hughes265 · Accepted solution]

Thanks.