Frequency vs. Acceleration using Time-based Data

[Will_S.]

I've searched around and haven't found a definitive answer to my question. I have acquired time-based Acceleration data with an accelerometer. I have a specific requirement to determine Frequency vs. Acceleration (m/s^2), therefore observing the frequencies contributing most to the vibration AND determining the magnitude of acceleration those frequencies contribute. 

I assumed an FFT would do the trick, but I am struggling to find a definitive answer to which FFT method will show me Frequency vs. m/s^2. I am aware that FFTs provide magnitude data, but how does that magnitude correspond to the acceleration units? This article: https://www.ni.com/en/shop/labview/using-fast-fourier-transforms-and-power-spectra-in-labview.html (Section 4 figure 16) indicates that a Fourier Analysis with an FFT should do it, but my results fail to match the white paper. Please see attached VI as an example. 

Hopefully I am blind or simply blanking on a piece of FFT understanding. Any suggestions would be appreciated.

[Henrik_Volkers]

May I ask what your task behind requirement is?

For most of these tasks there are standards defined (human body vibration, vibration emmisions to buildings etc...)

[Will_S.]

Hi Henrik,

Thank you for your reply. This is for testing small machinery with a compressor. I have looked into defined standards like ISO 18431-1:2005 but I can't find any method description other than needing to purchase the standard itself. Regardless, that description will be in the form of a mathematical formula(s), which is not always directly available in the help documentation for various sound & vibration analysis functions in LabVIEW. So I am concerned I'll just be back asking what functions will implement those formulas, rather than how to obtain specific units. 

Thanks,

[Will_S.]

I believe I found the solution. It requires a few steps:

1. SVL Scale Voltage to EU.vi.
   This VI scales the voltage input from the accelerometer to the appropriate engineering units (EUs).
   Use the specs on the accelerometer to know what to specify.
2. SVFA FFT Spectrum (Mag-Phase).vi.
   If you don't want dB reported, deselect dB On in the View settings.
   This VI generates the FFT spectrum as an RMS. 
3. (Optional) SVT Weighting Filter (frequency).vi
   Applies dB weighting (Such as A-Weighting) to the frequency spectrum.