Hi there,
I have been working with a USB-6363 for some time now. Today I have been having a problem with data acquisition on the analog inputs.
I am sampling AI0 at a moderate rate of 1 kHz in differential mode, +/-10V with a continuous trigger.
for troubleshooting I am shorting the leads between AI0+ and AI0- andtheAIGNDisconnectedtotheUSB-6363case
When I start an acquisition (through a vi or in NI-MAX) everything starts OK, reading 0 voltage.
at some time later the voltage drifts up to 3.07 V over a period of seconds and stays there
Looks like a capacitor charging.
If I connect AI0- to AI GND this floating up behavior goes away and my signal goes back to 0V differential. I ultimately want to measure a small differential signal and it was my understanding that I did not want to tie the ground of AI- to AIGND because of ground differences between my signal source and the USB-6363
If I measure AI1 (differential, +/-10V) along with AI0 I see the same behavior, i.e. AI1 and AI0 will both float up to 3.07 V.
However, if I ground AI1- to AI GND it brings both AI0 and AI1 back to ground.
I have not ever seen this problem before and my system has been working for over a year. I did recently updrade DAQmx to 9.6.2, but I do not see how this could affect anything.
Can someone explain what is happening here? Any help is much appreciated!
