510 noise

[ULEng]

Recently I installed Labview 8.2 and have since been detecting a 510Hz signal regardless of the input used on either of two PXI-4662 cards.  After eliminating all external noise sources I have determined that this signal seems to be internal to the PXI-1000B.  I have adjusted the speed of the cooling fans and that has had no effect on the detected signal.  I have determined that placing a 15.6kohms input resistor on the inputs pratically eliminates the signal.  Any suggestions?

[stilly32]

Hi ULEng,

Do you mean a PXI-4462? To my knowledge we don't sell a 4662. How are you connecting this signal - are you just reading an open connection, or reading a known source? What is the amplitude of the signal (Screenshots are useful) and at what rate are you sampling? Also, how did you determine that its at 510hz - FFT? 

If you're reading off of an open channel the noise shouldn't be too unexpected, you'd be reading a floating signal with no path to bleed off any charge that accumulates. Open connections are very susceptible to noise - is the noise still there if you read a signal from a battery, power supply or function generator?

I was a little confused about how LabVIEW 8.2 played into this - did you upgrade from another version or are you just getting started?

Hope this helps, please post back if the troubleshooting doesn't help.

Cheers,

Andrew S

National Instruments

[ULEng]

Yes, I meant two 4462 cards and I upgraded from Labview 8.0 to 8.2.  I have surmised that the there are two signals from an FFT (1kHz and 1.5Hz) which, after testing equipment in the lab and shielding the inputs to the card, are not being picked up externally.  I am aware that an open connection acts as an antenna, but the level of signals being detected are larger than expected (3.3mV) and previous experience shows that the signals should be <1mV.

[stilly32]

Hi ULEng,

Did you not see this noise before with LabVIEW 8.0, or is this just when you noticed it? Do you still see this noise when you input a known signal? What is your concern with this - the fact that you're seeing the signal, or that it showed up after an upgrade? I want to make sure that I adress your issue rather than getting side tracked on something irrelevant.

thanks,

Andrew S.