How to do FFT of vibrations signal?

[Y.Yang]

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

[Che_T.]

Hi Y. Yang.  Can you also post a screenshot of what you're seeing?  Without looking at that, I can make a speculation based off of what you wrote.

Since your FFT graph looks like a line, we can modify the 'Spectral Measurements' result to function in a logarithmic scale instead of a linear scale.  Maybe that is what you're looking for.

[Yue Yang]

Hello, 

I've attached a word document with the screenshot of my problematic FFT and a picture of what it should like for my application. 

Thank you. 

Y.Yang

[Che_T.]

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.