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OLi

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Reply with quote  #1 
So I have been thrown in to the magic land of relative probe data. Think of 2 large motors, currently one good(er) one in need of work. In 3 bearings out of these 4 the angle at 1xRPM btw. X-Y probes are 80-100 deg. in the 4th that also is the worst it is 30-40 deg also at low speed. Any "normal" reasons for that also possible to shine light on the increased levels 80-90 microns that are found on that bearing? It is load dependent and we have had a history of rub like 1+mm grove in shaft beneath plastic seal etc. Those clearances have been made larger and that made the machine more stable but less than perfect a new inspection will be performed today. So input would be good if this behavior is "normal". 
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vogel

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Reply with quote  #2 
Hi Oli,

A relative phase between X and Y probes of 90 degrees means a circular orbit. As the relative phase decreases (or increases) the orbit becomes more elliptical and at 0 degrees the orbit is flat.
Reasons for an elliptical orbit could be asymmetric stiffness or preloads/static loads (misalignment, pipe strain ...)
Tough to say more without plots.
OLi

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Reply with quote  #3 
Find examples attached.

Attached Images
jpeg Orbit-compensated-DE.jpg (23.42 KB, 7 views)
jpeg Orbit-compensated-NDE.jpg (22.97 KB, 5 views)


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vogel

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Reply with quote  #4 
Any SCL or Bode/polar plots?
John from PA

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Reply with quote  #5 
Your orbit plots are orientated properly for a CCW rotation but are somewhat flattened.  Do you know what type bearings are being used?  Do they perhaps have a lemon bore or some form of anti whirl profile?

Quote:
Originally Posted by vogel
A relative phase between X and Y probes of 90 degrees means a circular orbit. As the relative phase decreases (or increases) the orbit becomes more elliptical and at 0 degrees the orbit is flat. Reasons for an elliptical orbit could be asymmetric stiffness or preloads/static loads (misalignment, pipe strain ...) Tough to say more without plots.


When the relative phase between an X-Y pair is 90° the major axis of the orbit will be directly in line with one of the transducers (marked as X & Y on your orbit plots).  In addition, as this angle difference moves off 90°, the major axis is no longer in line with the transducer.  

OLi

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Reply with quote  #6 
Yes it is a kind of different type bearing but not lemon. I try to get some more data, CL plots look more "normal".
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John from PA

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Reply with quote  #7 
How big a motor is this?  HP or kW and approximate span between bearings?  

On the compensation used for the orbits, do you know if the slow roll was established based on startup or a shutdown?
OLi

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Reply with quote  #8 
38 MW running 37MW 4-5 m btw. bearings.... It was likely run down, run up is messy partly due to no jack oil.... First 2 hours run may be worse pending previous status, hot or cold etc.
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John from PA

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Reply with quote  #9 
The reason I had asked about the size, bearing span, etc. Is I was wondering if the used slow roll compensation is possibly affecting the data. In large motors (like this one) I have found that slow roll has to be acquired on shutdown. Sometimes the rotor moving axially in the magnetic center can also cause issues.
OLi

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Reply with quote  #10 
Yes I have some suspicion on magnetic center as absolute is largest axial DE at 3mm/s p approx and the other "identical" motor we run today had minimal axial vibration absolute and less than 25 microns as long as I saw it. It is connected to a gbx from Texas by a diaphragm coupling that is compressed in mounted state if I understood correctly. The "bad" motor was dropped in transport and brg mount displaced 4.7mm so brg mount and end frame is replaced, still the axial position is given as when it left factory 4 years ago.
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Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
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