Compact Daq noisy signals on laptop until I plug into external monitor

[OKors]

I have a cDaq 9172 which is mostly populated with AI and universal modules. When used with a DELL laptop through USB this device has always been very noisy, but just the other day I had to plug the laptop into an external monitor and low and behold the noise cleaned up considerably. I then realized the cDaq, power supply is 3-prong earth grounded, and so was the monitor. The laptop's power 'brick' however is 2-pronged and floating ground. It made sense the signal cleaned up once the VGA cable touched the laptop but the issue still exists; I wont always be using an external monitor. So how do you eliminate this ground loop issue?

BTW, I found this white paper on laptop noise and grounding but I've always referenced the signal to AIGND. This is how I got the signal to be tolerably "less" noisy. When reference grounded through the monitor the signal cleans up again twofold.

[stockson]

Hi, this thread discusses a similar issue. I believe it will be a solution for you too:

http://forums.ni.com/t5/Multifunction-DAQ/Can-we-connect-the-earth-ground-on-a-cDAQ-chassis-to-the-g...