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dB in vibration PSD specification
3

dB in vibration PSD specification

dB in vibration PSD specification

(OP)
Hi,

 Recently I received PSD data input.

 In that PSD input 5 to 20 Hz, some constant PSD input was specified. Then between 20 to 200 Hz, the input was mentioned as negative slope of 6dB per octave.

  To my understanding 6 dB per octave indicates the vibration level will reduce half per doubling of frequency (Octave).

Say at 20 Hz, the PSD level is 'x'. Then at 40 Hz it is 'x/2' as per 6dB per octave concept.Whether am I right?

 If not pl. correct me.
 
 Is there any specific reason to charactize the input with slope of dB per octave.

 Thanks for going through this thread.

 Regards,
 Logesh.E

RE: dB in vibration PSD specification

Yes, you have it right. 6 dB/octave roll off is a typical first order response.

I think you'll find it gives constant energy per octave as well.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: dB in vibration PSD specification

(OP)
Hi,

Thanks Greglocock.

I got it.

Regards,
Logesh.E

RE: dB in vibration PSD specification

(OP)
Hi Tom,

  Thanks for posting the conversion utility.

 Based on the conversion utility,the PSD value reduces quadrupally.

 Earlier, I calculated the conversion based on the following formula,

  dB = 20 log (X/Xref)

 With Xref = PSD value in G^2/Hz. Therfore I thought X = 2*Xref (For positive slope of 6dB per octave).

whether the above formula is right!

 If not, Can you specify the formula!

 With Thanks and Regards,
 Loganathan.E



 

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