Can DGND can be disconnected from the chassis

[neptun]

I have discovered that in NI-6221 USB card all digital grounds (DGND) are connected to Chassis. This is creating ground loops in my application.

Can I untie grounds them from each other.

Also AOGND resistance to DGND and Chassis is only few Ohms. Can I untie them too?

Thank you,

Mikhail 

[Seth_B.]

On the USB 6221, all of the grounds are connected on the circuit board and to chassis ground and cannot be disconnected.  For help with troubleshooting your ground loop issue, I would recommend our Field Wiring and Noise Considerations for Analog Signals tutorial.  It discusses proper wiring to help eliminate ground loops, depending on your wiring setup.  Specifically, the section on "Measuring Grounded Signal Sources"  and Table 1 in the article should point you in the right direction.  It is recommended that you either use Differential mode or Non-Referenced Single Ended (NRSE) mode for measuring grounded signals.

If none of these options are possible for your application, you should considere an isolated DAQ device which will have an isolation barrier between the ground terminals and earth (chassis) ground.

Regards,