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ensayospredictivos

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Dear friends.

In past days I attended a conference on wear in bearings. The speaker mentioned the use of the Crest Factor in the wave in the demodulated time:

3.5 Warning
4.5 Alert
5.5 Danger

I have the doubt if the reading was for 10 revolutions or more.

What do you think of this?
What experience have you had detecting wear in bearings?

Regards,
Raul Rios

 
Attached Files
pdf Demod FFT WTF.pdf (1.52 MB, 62 views)


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John from PA

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Quote:
Originally Posted by ensayospredictivos
Dear friends.

In past days I attended a conference on wear in bearings. The speaker mentioned the use of the Crest Factor in the wave in the demodulated time:

3.5 Warning
4.5 Alert
5.5 Danger

I have the doubt if the reading was for 10 revolutions or more.

What do you think of this?
What experience have you had detecting wear in bearings?

Regards,
Raul Rios



Crest factor (CF) is defined as the ratio of the peak value to the RMS value of a waveform.  Although desirable, there isn't really a need for a minimum number of revolutions.  In theory you could establish CF with one complete vibration cycle.

The CF of a pure sine wave is 1.414 since the peak value of a true sinusoid is 1.414 times the RMS value.  You might think of the CF value as a measure of "spikeness".  A relatively smooth waveform will have a CF that is low, near 1.414.  A bearing with spalls will exhibit spikes in the signal and thus have a higher CF.

ensayospredictivos

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Thank a lot John for you imput.

In your experience, does the bearing (DE) of the attached spectra show any signs of wear?
It is a centrifugal ANSI pump with 1X 1755 cpm.
Regards,


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John from PA

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Quote:
Originally Posted by ensayospredictivos
Thank a lot John for you imput.

In your experience, does the bearing (DE) of the attached spectra show any signs of wear?
It is a centrifugal ANSI pump with 1X 1755 cpm.
Regards,



It isn't real clear to me what part of your data is the DE bearing so I guess it all refers to that physical location.  But what I do see, as a single point in time, doesn't seem excessive.  The highest level I see is about 1.3 mm/sec RMS which is equivalent to about 0.08 in/sec pk.  Most specs I'm familiar with allow about 0.15 in/sec.

The signal does seem to be a bit noisy but this may be due to the low indicated level so noise would be more apparent.

Is this machine being trended?  If so has it changed?

OLi

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Reply with quote  #5 
In my world I rarely see a trend in CF it tends to do a step change relatively late in the process but that is only what I see. Curtosis that is sort of the other way around is even more so IMHO. 
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Beatnik

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Reply with quote  #6 
A lot of things outside bearing wear can cause a high crest factor. Electrical vibrations, vibration from gears, etc It's why I gave up on using it.  

With a low frequency Spectrum, a high frequency Spectrum, the TWF and demod, I don't think it's needed to use the CF or Kurtosis. The TWF gives us the severity of the problems and the other tools help identify it.

In your case you have identified the problem, a bearing fault, but the severity still seems low. I'd like to know the settings of your TWF, just to make sure you aren't missing something important.





ensayospredictivos

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Muchas gracias por su aporte.
Muy valores


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