[scilab-Users] vibration test analysis

[Michael J. McCann]

It it's raw vibration data, and very noisy, make a Fast Fourier 
transform of the raw data. The reciprocal of the record length will 
define the frequency resolution you get.
Go through the magnitude of the data looking for values that are 
local peaks relative to their neighbours on either side.
         As a refinement you can use, as the measure, the value of a 
locally weighted magnitude (e.g mostly the a centre frequency with a 
20% or so of the adjacent values) so that if your real peak falls 
between two of the sample frequencies it will get picked up because 
the FFT will give some of the energy to adjacent samples.
         You will need to select the peaks relative to the noise 
level. So generate the magnitude data (or it's locally weighted 
values) and then read off the peaks that come high enough to be 
recognizable. You can calculate a local noise level for the signal 
frequency band for comparison.
         I've used it for raw data from moving vehicle vibration. In 
a laboratory situation the search in frequency can be applied to the 
sweep frequency test data
Mike.
www.mccannscience.com


At 20:02 10/10/2010, you wrote:
>All,
>
>Does somebody has ever wrote/coded (under Scilab but not necessary) 
>a program that analyses the vibration tests results (i.e. 
>automatically find the natural frequencies) ?
>
>I do it manually but studying the transmissibility's and the phase 
>changes but I would like to code it under Scilab and of course there 
>won't be any human appreciation/analysis
>
>The purpose of this email is not to have this code but to have 
>advices/information's on the method / algorithm and so on !
>
>In any way It's a good challenge for me
>
>
>Thanks for any help
>
>Paul
>
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