BNC-2090A AI GND

[alexkane]

I am using an X series DAQ  to measure the output voltage of a SR570 current preamplifier. I have found that I can measure a signal without any modifications, but I need to reduce noise, and I wonder if the signal needs to be tied to the DAQ AI GND as directed by the manual.  This would essentially be connecting the ground of the preamp to the DAQ AI ground. Would this help reduce noise, and do I have the right procedure below?

Measurement details:

• DAQ: PCIe-6374
• Mode: Differential
• Coupling: DC
• Connector: BNC-2090A
• SR570 output ground (shield): Fully floating
• SR570 output impedance: 50 Ohms

The X series manual, pg. 4-43 says that a low-impedance floating source must be referenced to AI GND, most easily done by connecting "the positive side of the signal to the positive input of the DAQ and the negative side of the signal to AI GND as well as to the negative input of the instrumentation amplifier, without using resistors."

The preamp is noninverting, and so I think that the way to make the connection to AI GND on the BNC-2090A is to short position B (R31) to AI GND in the diagram below. This would connect the preamp ground directly to the AI ground.

[VA.KI]

Hello alexkane,

It should, so does it helps?

Also if possible could you share noise spectrum?

[alexkane]

We have not detected a significant difference.