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  • 1.  BUMP TEST results Validation

    This message was posted by a user wishing to remain anonymous
    Posted 08-18-2023 02:22
      |   view attached
    This message was posted by a user wishing to remain anonymous

    Hi Everyone,
    We have been facing a high-vibration issue in one of the equipment structure support.
    The machine is vibrating at a maximum vibration or 4.1 mm/s RMS but the attached structure vibrates at 70 mm/s RMS. To identify the natural frequency of the structure support we have performed the bump test. I have attached the results, I would like your expert opinion to validate if the bump test spectrum and waveform seem correct or if I have to reperform the test for better results.
    I really appreciate any help you can provide.


    Bump test.docx   101 KB 1 version

  • 2.  RE: BUMP TEST results Validation

    Posted 08-19-2023 09:36

    please attach a pic of the structure.  Probably very easy  fix.

    Ron Brook

  • 3.  RE: BUMP TEST results Validation

    Posted 08-20-2023 06:07

    In order to provide any meaningful results some additional information is required:

    • what is the spectrum showing on the equipment (V and H)?
    • What is the spectrum of your structure (V and H)?
    • What instrument did you use to perform the bump test?
    • Does your instrument have the capability to display coherence or perform only a "poor man" bump test?

    Alex Jablonski

  • 4.  RE: BUMP TEST results Validation

    Posted 08-21-2023 09:47
    Edited by Kristan Sears 08-21-2023 09:48

    In addition to Alex's comments, I would also want to know how the structure is supported or suspended when you did the bump test.  As Ron mentioned, a picture of the structure would be helpful.  Looking at your results, there's still considerable energy after 1 sec, including the pretrigger. 

    • What kind of window are you using for your bump test? 
    • What is the sensitivity of your transmitter?
    • What Fmax did you use? 
    • How many lines or samples are you collecting?

    This resolution leads me to believe that there are other peaks in here that aren't visible because the frequency resolution is too large.

    That may change where the natural frequencies really are, compared to what's shown in your spectrum.

    Another thing that stands out to me: the initial spike, the impact, in the time waveform is almost 12G's.  That's quite a bit. 

    Typically, you don't need that much force to detect the natural frequencies.  Unless this is a large piece of industrial equipment, a small impact hammer should do the trick. 

    Pictures of the test setup and some details on your measurements would be really helpful.

  • 5.  RE: BUMP TEST results Validation

    Posted 08-21-2023 04:38

     I can assume that  this a 2-pole machine?

    Din Ellias