NI-6210 Signal Noise

[CHazel07]

Hello,

I am having an issue with some signal noise and I want to be sure I have made the connections properly. As shown below, I have connected a loadcell amplifier to the NI-USB 6210, and connected the DAQ to a Laptop pc. The Analog Input channel is configured as Differential, and the voltage ranges between 0-5VDC. The amplifier is connected to 120VAC power, and the mains earth ground connected to the shell of the loadcell/device.

The problem I am seeing is that when the laptop is not plugged in to power ( i.e. running only on its battery power), the AI signal is clean. When the laptop is plugged in, signal noise increases drastically. It seems as if there is a floating ground, but I am not sure how to correct it. Do I need to insert pullup resistors from both AI0 and AI8 to AIGND? If the laptop power connection doesn't have a true earth ground pin, how is the AIGND referenced? Do I need to use Referenced Single Ended for my configuration? Thanks.

[PTerro]

Hi CHazeI07,

You should be using a bias resistor between AI0 to AIGND and AI8 and AIGND.  Here is the manual and a picture of the different connections is attached:

http://www.ni.com/pdf/manuals/371931f.pdf

It seems like your laptop is changing from a floating source to ground referenced source and that is throwing off your data.  Let me know if that helps!