×
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

11x vibration frequency

11x vibration frequency

11x vibration frequency

(OP)
I have just done some noise measurements of a bench grinder mounted on a pedestal just to try out analysing frequencies using a microphone ( Just because I got my hands on one). I picked the grinder because it is quite noisy and didn’t have a gearbox.
It rotates at 2918 rpm circa 50 Hz however the largest peak is at 11x. I don’t know the number of balls in the bearing this could be 11 and could account for it. The next largest peak is at 7x.

My question is if the stand has a natural frequency of 11x the forcing frequency will this show up as a higher peak than the forcing frequency.

RE: 11x vibration frequency

That depends on a bunch of things - more helpfully, it depends on the damping of the mode, and the spectrum of the excitation function.

A well balanced rotatry machine might have no first order in its spectrum.

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: 11x vibration frequency

If the ratio of 11x/1x is 0.1 in displacement units, the ratio of 11x/1x for the same vibration would be about 12/1 in acceleration units.  In other words factor of 100 change in relative magnitudes of those two peaks.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: 11x vibration frequency

It could be the motor slot or bar passing frequency.

RE: 11x vibration frequency

Ball bearings do not produce integer multiples of shaft speed. Their fault frequencies can be calculated from their geometry and shaft speed. Motor rotor bar and stator slot frequencies are well above 11x shaft speed. One possible source of 11x shaft speed is motor cooling fan, so count the blades.

Walt

RE: 11x vibration frequency

Every now and then a wayward bearing has had a BPFsomething pretty close to an integer, like 3.06, which required more lines and better yet a synchronous phase reference to really identify as NOT 3X.

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