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JuddJones

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I took some data today on a fan motor that I thought was interesting. The spectrum on the NDE bearing showed 1x with harmonics with a pronounced 4x harmonic in velocity. The long range acceleration reading showed rotor bar pass frequency with several 7200 cpm sidebands and harmonics of RBPF with sidebands. The part that was interesting was the SPM filter 3 data with symptom enhancement. I can count all 58 rotor bars in the circular plot! The waveform is also quite impressive. It is amazing the difference in quality in the data over the data collector I was using before. This makes it too easy, I think the new guys we bring up should have to start out on the old equipment!

2018-05-15 13_54_47-baghouse fan circle.png

 
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Vibe-Rater

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Yes it is nice stuff

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Danny Harvey

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It's even prettier is you don't have the running speed correct.

Like a spirograph and equally as useful.
JuddJones

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The running speed is dead on. Here is a zoomed in view of the same time waveform with the cursors on 1order. I believe your seeing the modulation. Please advise if I am mistaken (that happens a lot [smile]) .> Edit 1 order, not 4, and it isn't modulation...Maybe something to do with their Symptom enhancement algo?2018-05-16 08_43_42-Spectrum -  190       -01  Motor NDE_ filter 3 (5_.jpg
Danny Harvey

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I wasn't implying that yours was incorrect. Move the running speed just a hair and you'll see what I'm talking about.
JuddJones

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I have been playing with it, even .01 of a RPM + or - and the tips start getting wider with no improvement to the middle portions that don't line up. Is it just minute differences in amplitude that don't fall right in the middle of the bin? Some of the points on the waveform have more energy on one side than the other. My reply came off as defensive, that wasn't my intent...I am just interested in learning.
Danny Harvey

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As I understand it, autocorrelation is like taking a twf of a certain length and laying one over the other.  The result is a factor of how much it repeats.  So if your twf length is off just a hair from the actual running speed, then the sample gets chopped up and overlayed in something other than the proper length so the peaks are still there, they just don't have a high correlation factor because the repeat at another frequency. Hence the spirograph effect when you put the autocorrelated twf into a circular format.

...i think.
RustyCas

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Reply with quote  #8 
So what does the pretty picture mean? Does it represent a problem? If so, what?
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Vibe-Rater

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Hi Rusty, mine was from a gear with 3 broken teeth - confirmed after replacement and inspection of the old gear - from a right angle pulper gearbox. Horizontal input, vertical output shaft.  It was the output gear that was damaged. rgds
JuddJones

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Quote:
Originally Posted by RustyCas
So what does the pretty picture mean? Does it represent a problem? If so, what?

I believe the rotor is loose on the shaft. I will follow it to the rebuild house to learn all I can. I would love to hear others thoughts.
fburgos

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Reply with quote  #11 
Quote:
Originally Posted by Vibe-Rater
Hi Rusty, mine was from a gear with 3 broken teeth - confirmed after replacement and inspection of the old gear - from a right angle pulper gearbox. Horizontal input, vertical output shaft.  It was the output gear that was damaged. rgds


In the plot I see 48 spikes, is it related to 48 teeth? your plot also show a big spikes on top (yellow area), I think this is just because is near the load zone, also noted some spikes are a little "flat" do they mean something.

broken pulper.png

Vibe-Rater

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Reply with quote  #12 
The polar plot indicates several broken gearteeth on a pulper gearbox.  The broken teeth are what you show in yellow. rgds
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