usb 6009 - low frequency problems

[student09]

Hello all,

I am reading a signal from a function generator into one of the analog inputs of the usb 6009 device through labview.  For sine waves of larger frequencies, generally greater than 10kHz or so, i'm getting a clear undisrupted signal.  However, at lower frequencies ( and the range i'm interested in could be as low as 10^-3Hz - 1Hz), I'm observing an abnormal and distorted sinewave.  I've tried messing with the sampling rate, but haven't had any luck.  Any help would be appreciated.

Thanks

[dthess]

I noticed the same thing.  Log sampling rates (in the Hz range) can result in odd spikes in the data.

I've personally worked around it by using a 1000Hz base sampling rate, then bunching the points together for an average.

[JoeFriedchicken]

Hi,

dthess's suggestion is good practice for removing unwanted noise and should work in this case.

I'd like to ask some simple troubleshooting questions to get an understanding of the behavior you're seeing:

1. Does the same problem occur on all channels?
2. If you generate a DC output voltage on one of the device's analog output channels and read this back into the analog input channels, do you see the same voltage abnormalities?
3. What voltage input range are you using? If you change the range do you see a significant change in the noise level?
4. Do you see the same problem when using the device in both differential and single-ended mode?
5. If possible, could you try connecting the USB-6009 to another computer and seeing if the same problem occurs?
6. Finally, if you could provide screenshots of what you're observing, then that will help me understand the behavior you're observing.