vibration conversion

[mannypons]

how do i convert a vibration reading in dB and G's to Hz? This is reading of the floor slab on grade.

 

[IRstuff]

You don't. dB and g's relate to amplitude and acceleration, while Hz relates to frequency

TTFN

 

[mannypons]

thank you for clarifying that. however i have a client who would like to convert the vibration reading in G's to dB. is there an equation to convert such G number to dB.

 

[IRstuff]

Not without some reference level. dB is a ratio relative to some reference value. g is a reference to 9.8 m/s².

TTFN

 

[MikeyP]

For acceleration levels I have always used 10^-6 ms^-2 ie 20*log_10(accel_in_SI_units/10^-6). I don't think it is a standard though.

M

--
Dr Michael F Platten

 

[GregLocock]

There was a draft ISO standard for a reference level, but can't remember what they came up with. I typically use 1g RMS or 1 m s-2 RMS, since that gives sensible numbers for engine vibration.

Cheers

Greg Locock

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

 

[tomirvine]

Floor vibration standards are typical defined in terms of velocity.

Furthermore, some ISO standards require the floor velocity in terms of a one-third octave spectrum. The amplitude in each band is represented in terms of RMS velocity.

This format is called "Generic Vibration Criteria (VC) for Vibration-Sensitive Equipment."

Tom Irvine

http://www.vibrationdata.com

 

[Rob45]

Manny:
Try using 1 G for your reference level; in the eqn L = 20 log G's
That is, G's = 10^(dBg/20)

 

[Tobalcane]

I look at this that you want the difference (dB) between the acceleration levels from one reading (before a fix) compared to another (after fix) at a certain frequency (Hz). Thus a phrase would be “ the fix is good the difference between the G levels dropped 6 dBs at 500 Hz”. Is this what you are asking?

Good Luck!

Go Mechanical Engineering
Tobalcane

 

[Tmoose]

wilcoxon has a vibration calculator/converter to download.


AdB is re: 1 micro g

then there's pk vs RMS, ISO vs ??

 

[McVibe]

You can download a vibration units conversion program here:

http://www.dliengineering.com/section.asp?nID=19

This one has a unit of "AdB" for acceleration and "VdB" for velocity in decibles.