how to ground NI BNC-2110 and CB-68LP to my Faraday cage?

[clas004]

I am trying to reduce the noise in my setup. Right now it's at about 0.0002 V, or 200 µV.

Here is my setup: an NI PCI-6229 DAQ card, with its 2 connector blocks being one BNC-2110 and one CB-68LP.

The CB-68LP is generating an analog output voltage, while the BNC-2110 is measuring an analog input voltage. Both are set to RSE terminal configuration. (I tried differential mode and it made no difference to the noise...)

The actual measurements take place inside a Faraday cage, which is grounded. (Incidentally, the CB-68LP block is also within the Faraday cage, but the BNC-2110 block isn't.) What I'd like to do is share a common ground between the Faraday cage and those 2 connector blocks. I am hoping that by doing this, some of the noise can be eliminated.

My problem is that I cannot figure out where to feed in the ground signal from the Faraday cage into the connector blocks to use as their ground signals. 

[clas004]

Actually, now that I look at the PCI-6229 specs, I see the limits of what I'm trying to do... at the minimum voltage range of -200...200 mV, the range sensitivity is about 5 µV:

https://www.ni.com/en-us/shop/model/pci-6229.html

(The accuracy of 112 µV isn't as big of a worry, since I'm interested more in how the signal changes rather than its absolute value.)

So if I could get my noise down from 200 µV to the PCI-6229's sensitivity limits of 5 µV, that'd make me happy.

[lab_boy]

Hey

Connect your signal ground to AI Gnd. Also Check this link. Might make some things more clear

cheers

lab