Constant Displacement v. Grms

[mbrett]

Is it possible to calculate a relationship between constant displacement within a specific frequency range and Grms. If so how.

 

[dgallagher]

Here is a link to an electronic Vibration Conversion Calculator:

http://www.wilcoxon.com/calculator/wilcoxoncalc.exe

(1,023K download).
NOTE: During download, the file size of the calculator enlarges. (56K modem takes approximately 7 minutes.)

Cheers, DG at

http://www.reliabilitydirect.com

 

[tomirvine]

Constant displacement implies a sine sweep test specification.

The GRMS value at a given sine frequency f is:

GRMS = [ 0.072 ][ f^2 ][ X ]

where X is the zero-to-peak displacement in inches.

On the other hand, GRMS is more commonly used to represent random vibration. If you are trying to compare sine vibration to random vibration, then that brings up a different set of concerns.

Sincerely, Tom Irvine

http://www.vibrationdata.com

 

[VibrationSpecialist]

Dear mbrett,

You can derive the acceleration in G as a function of the frequency in Hz giving the displacement either in mils or mm.
Are you referring to Grms or G's RMS?
In the first it is as stated be Tom is for random vibration (PSD) while the other is the RMS of the acceleration in G's/

Take Care ;-)

 

[mbrett]

Thanks for you quick responses the constant displacement figure is stated as part of a sinusoidal sweep. The rest of the sweep is stated in G. Sorry, not Grms.

Cheers ;-)

 

[dampit]

For Sinusodal motion ONLY

G = Acceleration in g-units
D=inches peak to peak (Double-Amplitude)
F=Frequency in Hz

G=0.0511 F^2 D

Note: Convert this to Grms by

Grms = 0.7071 G

Grms=(0.0511 / 0.7071) F^2 D = 0.072 F^2 D

Converserly,

d0 = Peak Displacement = 9.8 G / F^2 (Zero to Peak Magnitude)

Also, in rms quantities....

drms = 9.8 Grms / Fc^2, where Fc = center frequency of response

Note: Pay particular attention to when using d0 - Peak Amplitude and D - Double Amplitude it obviously makes a big difference.