×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Constant Displacement v. Grms

Constant Displacement v. Grms

Constant Displacement v. Grms

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

RE: Constant Displacement v. Grms

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

RE: Constant Displacement v. Grms

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

RE: Constant Displacement v. Grms

(OP)
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

RE: Constant Displacement v. Grms

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources