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RickP330

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Reply with quote  #1 
Wow,
1.4 on the Tangential exactly at 11X.  Could be gear mesh, but this on the Motor free end, drive end this magnitude is lower.  Unless the data was taken backwards.  Any Ideas?
Much Thanks
Rick

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Sinski

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Reply with quote  #2 
Is there a cooling fan on the back of the motor?
Vibe-Rater

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Reply with quote  #3 
For some reason I think it is a DLI system.....? Maybe..? I get confused by all the vertical lines.  Why not just look at the spectrum. rgds
Vibe-Rater

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Reply with quote  #4 
Quote:
Originally Posted by Sinski
Is there a cooling fan on the back of the motor?


Hi Sinsk, 11 is an unusual number for me. Fans will have even numbers, 4,6,8,10 etc.  But you never know.  I would be going back to basics and figuring out running speeds accurately first and then looking at the spectra which hopefully can be displayed better quality and without the silly vertical lines.  You and I know what we are looking for, no lines required. rgds
RickP330

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Reply with quote  #5 
Hello all,
I am using an older Azima DLI / DCX collector and EA.  Please take it easy on me.  This is an older system and the only reason I have it is because I found it in an unused corner of the Laboratory.  If it weren't for this collector I would have no vibration analyst program at all.  I am sorry about the low quality of the print - its a screen capture of an output file.  I am not sure of a better way to export the data.
The vertical lines are because I compressed the Low end of the spectrum since there is really nothing at all to look at there.  I expanded it here for you to see.
I have two of these motors and on the other one I also see an 11X signature but the amplitude is very small.  It is also stronger on the free end of the motor Bearing 1.  On the drive end of the motor is a positive displacement oil pump.  It would make more sense if this were bearing #2 and this was a signature of the oil pump.  There are 10 fan blades on the rear of the motor.
I took these measurements myself, I am very sure I took them in the right order - but I'll do it again for good measure and recheck the fan blade number on the free end.
Much Thanks for the insight.  I assume you feel that 11X is too low a number to be a Bearing issue or shaft looseness?
Kind regards,
Rick


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Noknroll

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Reply with quote  #6 
I wouldnt consider it that unusual to see 11t GMF transmitting to motor NDE.
Stranger things have happened with vibration
Edit
I was assuming 11t pinion on gbox when you said gmf but i Just read your last post, 11 pistons/vanes also quite plausible and again not unusual to see it at motor nde
Beatnik

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Reply with quote  #7 
I agree with Nok, vibrations are often transmitted in a weird way. It can be because of lower rigidity or local resonnance.


I would take a high resolution to make sure it's really 11.00x. If it is, it's not a bearing frequency. 10.95x or 11.05x can happoened but I never seen a bearing frequency being a direct multiple of the rotation frequency. Most of us also like to track the amplitudes found in the acceleration timewaveform to evaluate and follow bearing conditions, do you have the TWF??
RickP330

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Reply with quote  #8 
Well,
I have velocity time waveform.  Let me fool with it to see if I can get acceleration units.  I'll go down now and also get another reading set.
RP



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Vibe-Rater

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Reply with quote  #9 
Quote:
Originally Posted by RickP330
Hello all,

 assume you feel that 11X is too low a number to be a Bearing issue or shaft looseness?
Kind regards,
Rick

I think it is too high to be a bearing given that typical motor bearings are 63**, 62** with BPFO's of 3.1x or 4.1x or there abouts.  If you are 99.99% sure of the speed and it is precisely 11x then it is not bearing because as pointed out bearing frequencies are non synchronous. (rare exception axial thrust bearings with an even number of rolling elements) See attached.

So my call is that it is pump related. If indeed the speed is precise.  11 teeth on an input pinion is on the low side. In my experience 13 is about as low as I have seen and I assume there isn't a gearbox here anyway. rgds 




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Walt Strong

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Reply with quote  #10 
Looking at the waveform plots, there appears to be about 6 periods (beats) per 0.2 seconds. This is a frequency of 1800 cpm or 30 Hz. The plots indicate shaft speed is 1785 rpm, so the fault is shaft speed related.

Walt
electricpete

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Reply with quote  #11 
What are the bearings involved (part numbers). 

Do you have more details about the pump. I have seen the rotary piston pumps with swashplate that create oddball harmonics of running speed.

Any other details about the train may provide a clue.

What are the other frequencies shown in the first attachment?  This is a key to narrowing down the cause of a peak... is it part of a pattern. In particular are there harmonics of this mystery 11x. Also are there any families of harmonics present. Are there any regular sideband spacings.  Please label the peaks or give us word description.

Personally I don't rule out bearing (Unless you are sure it is EXACTLY 11.00 orders). BPFI pattern in TWF often appears modulated by 1x (and will have spectral 1x sidebands around BPFI and around BPFI harmonics). The TWF doesn't show the impacting we expect but we normally look in acceleration. The velocity display of TWF tends to suppress the higher frequency components and may tend to make the waveform look smoother rather than impactful.




RickP330

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Reply with quote  #12 
Guys,
This occurs exactly at 11X.  Tomorrow mourning I will take another data set and use a strobe to get the exact RPM.  This is 45 year old equipment.  All I know is that it is 11kw = 14.7HP and it drives a fixed displacement (Gear) pump through a rubber coupling.  I have no drawings of the pump and have never taken it apart, so I don't know how many lobes there are.  I mentioned earlier that I see an 11X signature on the second motor, but the amplitudes are much more behaved.

In the first attachment the other two larger spikes occur at 21.98X and 31.98X  I've attached screen shots with the peaks highlighted so you can see the harmonics below.



  IMG_9970.JPG    IMG_9968.JPG    IMG_8297.JPG  VibrationChartControl35021.jpg  VibrationChartControl35022.jpg  VibrationChartControl35023.jpg 

Vibe-Rater

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Reply with quote  #13 
My guess it is the number of lobes/whatever in the pump. Do you have a history? If so is this deteriorating or has it always been like this.  Levels don't seem high to me.  History will tell. Rule out bearing this motor will have 63** or 62**, possibly one of each. rgds
MarkL

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Reply with quote  #14 
Snap Vibe, I was going to ask has the coupling fingers or elements and how many?
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