[b]Finding amplitude from PSD data?[/b]
[b]Finding amplitude from PSD data?[/b]
(OP)
A question to those of you who probably have a far greater knowledge about this than me!
I have a PSD plot (g2/Hz) against frequency, there are very distinct peaks at certain frequencies. Very simply I want to find out what the displacement of the object would be at these frequencies.
I am sure this must be easy but.....
Thanks alot in advance
Parsnip
I have a PSD plot (g2/Hz) against frequency, there are very distinct peaks at certain frequencies. Very simply I want to find out what the displacement of the object would be at these frequencies.
I am sure this must be easy but.....
Thanks alot in advance
Parsnip





RE: [b]Finding amplitude from PSD data?[/b]
What do you mean, the travel of the vibration head or the deflection on the part due to Fn?
Tobalcane
"If you avoid failure, you also avoid success."
RE: [b]Finding amplitude from PSD data?[/b]
Basically the accelerometer was mounted on the vertical axis of the excited part, the PSD was 0.004 g2/Hz at 504Hz, what I want to try and find out is how much has that part moved. Does that make sense?
Cheers
Parsnip
RE: [b]Finding amplitude from PSD data?[/b]
BUT, unless the random background is VERY low, the total random displacements might exceed the contribution from any single line.
TTFN
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RE: [b]Finding amplitude from PSD data?[/b]
TTFN
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RE: [b]Finding amplitude from PSD data?[/b]
a~0.6 m/s^2 rms
x~5*10^-6 m rms
Cheers
Greg Locock
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RE: [b]Finding amplitude from PSD data?[/b]
How do we convert that PSD into acceleration in g's?
I would assume two steps:
1 - Integrate over a certain frequency band.
2 - Take the square root.
What frequency band should be used for step 1?
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RE: [b]Finding amplitude from PSD data?[/b]
So for instance, in this case, suppose the sample rate was 8192 pts/sec and the frame length was 1024 points, then the frequency resolution would be 8192/1024 = 8 hertz. Then, using the OP's data:
Average amplitude = sqrt[.004 g2/hz* 8 hz] = .179 g
Peak Displacement = (.179 * 386 )/((2*pi*504)**2) = .00000689 inches
RE: [b]Finding amplitude from PSD data?[/b]
that should be m/Hz
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: [b]Finding amplitude from PSD data?[/b]
Cheers
Parsnip