07-12-2010 04:23 AM
I try to measure a sinus signal from a oscillator with a DAQCard 6062E in the Measurement&Automation Explorer. If the cDAQ-9172 system is disconnected (disconnected usb-plug), all looks fine. Now I connect the usb-plug and the signal will be disturbed in the graph-view. A look on the signal with a Tekscope shows no problem. It doesn't matter if the cDAQ-system is switched on or off. If I disconnect the usb-plug, the disturbance will disappear after a while. I attached a screenshot from the sinus-signal.
A measurement with the cDAQ-System (NI9215 an NI9205) is mostly not possible, but not always.
Any hints? It looks to me like a nice software problem. Ni Measurement&Automation Explorer has the version 4.6.0f1.
07-13-2010 03:50 AM
to me, this looks like a grounding problem. What kind of measurement did you configure? Referenced Single Ended, Non-Referenced Single Ended or Differential? Did you establish a common ground between your 6062E and the Signal Source?
Maybe you create a ground loop when physically connecting the USB cable. Make sure that the ground of your 6062E, Signal Source and cDAQ are all on the same potential. Keep the ground connection as short as possible.
Please have a look at these documents:
Noise Reading on the NI 9205
Field Wiring and Noise Considerations for Analog Signals
My Laptop is Reading a Floating Voltage from a Grounded Source in Differential Mode
Please let me know if you could fix the problem.
08-06-2010 08:48 AM
You are right, it was a simple groundling problem.
Thanks for Your help.
Sorry for my late reply, it's summer time :-).