Noisy strain channel on 9237

[OKors]

I have a single uniaxle strain gage connected to channel 0 of a Dsub 9237. Using external bridge completion and in software calling it a full-bridge. Internal Excitation of 3.3V. Shunt cal is fine and strain linearity appears to be fine but it'm getting a TON of noise; several hundred microstrain noise at zero load.

Is there a common or chassis ground I should be connecting my signal leads to?

I should also note; this is in a cDAQ- 9172 chassis and I'm also logging 2 analog voltage signals from 9215 module connected in defferential mode.

Below is how the module is wired.
Green AI+

White AI-

Red Ex+

Black Ex-

blue in the diagram are jumpers at the Dsub solder connectors.

[afrowizard]

Hello OKors,

Hope you're having a great week!  If you are only using one active element (strain gauge), I recommend going with a Quarter Bridge setup.  We have a white paper dealing with the various strain gauge configurations we support, it begins with Quarter Bridge configurations in Section 4:

http://www.ni.com/white-paper/4172/en/

This would be a great setup for measuring uniaxial strain using your single gauge and you won't have to rely on any external circuitry or resistors (since the 9237 uses and internal resistor to complete this setup)!

[OKors]

So I was able to clean up this signal considerablyby connecting a grounding wire between the COM of the adjacent 9215 module and the hold down screw for the Dsub connector on the 9237. So far no smoke got let out but could someone with a little better understanding of this hardware explain why/how its a cleaner signal?  

[Karl-G]

Sounds like you have a workable solution in place, but I agree that the wiring is a bit suspicious. Are you still using external bridge completion or did you switch to the module bridge completion?