wiring difference between the usb-6009 and usb-6211 For differential input.

[griff32]

I have a working system for measuring a differential analog input using a usb-6009. The wiring for the channel is using AI1for the + and AI5 for the -. The power supply - is connected to the GND. This configuration works fine for the usb-6009. I purchased a usb-6211 and want to us it inplace of the 6009. I wired the channel like this: AI1 is the + and AI9 is the -. The power supply - is connected to the AI GND. This cofigurations has a large amount of noise and also has drift. Any help in figuring this out would be appreciated.

Thanks in advance

[KyleTTU]

Hi griff32, 

This is odd, you say everything worked in the same configuration on the USB-6009?  Did you also tie the power supply ground the the AI-GND on the 6009?  In addition, did you set the DAQmx task to be a differential measurement in LV or MAX?

Regards,

Kyle S

[griff32]

Thanks for the reply Kyle,

The 6009 Ground was also the power supply ground. Also I was reading the differential through Max using the test panels. The 6211 response acts like a capacitor discharging, while the 6009 is very clean and precise. I thought this would be an easy fix, but it seems there is a hardware difference between the 2 modules that I cannot figure out.

[AnalogKid2DigitalMan]

I do know that the input impedance of the 6009 is orders of magnitude lower than most other DAQ cards (144Kohm versus 100's Mohms to GigOhms).

This may account for the difference. Try putting a few 100Kohms resistor across the analog input terminals of the 6211 to see if it helps.

-AK2DM