How to do FFT of vibrations signal?

Hello,
I'm trying to measure the time and frequency spectrum of a vibrations signal.
My time plot seems to be ok, but my FFT graph doesn't look right.
An expected vibration FFT graph of a bearing should look like peaks at various frequencies, but my FFT graph looks only like a linear line.
Does anyone know what's wrong with my attached program?
Thank you.
Y.Yang
Attachments:
3 axis white and green sensors v2.vi ‏122 KB

Your code looks fine.  I double checked how you're acquiring data, and it seems fine.  I'm pretty sure that you are acquiring an FFT and the graph is just not scaled correctly.  Do the following:
Right Click Waveform Graph 2 >> X Scale >> AutoScale X
Right Click Waveform Graph 2 >> Y Scale >> AutoScale Y
I've also attached an example of what I've done to get the FFT from a simulated signal.
Che T.
Applications Engineer
National Instruments
Attachments:
FFT.vi ‏67 KB
fft.png ‏43 KB

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