FFT Power spectrum

[JBadon]

It appears that the project I'm working on will end up teaching me a lot about labview because the project is complicated.  Using labview, I am spinning two objects at two different speeds, which makes up the signal.  One object is being spun at 1200rpms and the other at 2400rpms.  This should yield a spike at 20Hz and one at 40Hz.  I have a spectrum analyzer which is giving me the results I expect, but I can't seem to get it with labview.  I tried using FFT and then taking the real portion of the signal and graphing it, which didn't work.  I then tried the power spectrum, which also didn't work.  I need some help/suggestions.  Any and all are appreciated. 

Thanks,

JB

[johnsold]

JB,

To help you, we need some help. Specifically, some specifics about your application.

How are you acquiring the signals from your spinning objects? What is your sampling rate? Are the signals sinusoidal, pulses from an encoder, something else?

What did not work? Did you not get any spectrum, was the frequency wrong, was the amplitude wrong, was the resolution poor?

If you post your VI with some typical data saved as default (because we do not have your spinning objects), someone will probably be able to help you.

Lynn