Power Spectrum no longer working correctly after upgrading to 8.0.1

[Babs]

Recently, I installed Labview 8.0.1 to correct a problem I was experiencing in 8.0.  The installation resolved my problem, but now the Power Spectrum no longer gives the correct result.  My program has not changed other than the update.  I checked my circuit and everything is functioning properly.  Before changing to 8.0.1 the power spectrum peaked at 40Hz and 80Hz,  which was correct, and now it peaks at 0Hz and 10Hz.  On top of everything, the peaks are much higher than they should be.  I expect peaks with a max of 2.5millivolts and now they are 1volt.  I don't understand what is going on. Nothing changed, but the software version.  Can someone please help me? 

[altenbach]

Can you attach a simplified VI containing typical data?

How do you calculate the power spectrum (Spectral measurments express VI, auto power spectrum.vi, power spectrum.vi, etc.)

[Mark_W]

In addtion to Altenbach's comments - 

I'd recommend trying another VI function to get the power spectrum for your signal to see if the behavior is the same.  You can find some examples of VIs using the power spectrum functions using the NI Example Finder.

You can go to LabVIEW's Example Finder by going to Help >> Find Examples. Then search for FFT. There should be some results that include FFT and Power Spectrum Units.vi, Power Spectrum Measurement.vi, Basic Spectral Measurements.vi,  and Spectrum Measurements.vi. Try opening and running these examples to see if the VIs are returning the proper results.


Mark Walters
Application Engineer
National Instruments