It sometimes happen that after some time measuring with my DAQ-2120, the signal appears noisy, like its baseline is changing between two values. Someone told me it's because I'm using the ground of the DAQ device, and this ground is not connected to earth and therefore what I see is the charging and discharging of my AO "ground". If I connect with a cable the AO ground to earth, the noise increases (because of a ground loop?).
An important thing to note is that I use the same ground for the transducer circuit, the filter and faraday cage; all of them are not connected to any other ground.
I need to use the AO ground because I need to use the signal from the analog outputs.
I would like to know what can I do to solve this problem and also to ask: Is the AO ground connected to earth? Does it really matter?
(note: I use a PCI-6036E)