Orbit Explanation

Motorman1969 posted:

Very little knowledge here concerning orbits-but just enough to comprehend.

Attached is a filtered orbit showing the 1st-4th order.  Can someone explain the phase shift? And what is occuring? 

I would suggest you start by reviewing the attachment at http://www.maintenance.org/topic/orbit-tutorial and then come back and be more specific as to your questions.  I for one am not sure what you are asking about "phase shift".  Do you anticipate that phase shift would not vary 1st order to 2nd order or are you asking why the difference in the way the orbit is orientated?   

Motorman1969 posted:


Why the change in orientation from 1-2-3-4 orders.  Maybe i am stating it wrong saying phase shift.  But the question is why the orientation change between orders.

Also, what is the shape of the first order telling us?

Why not?  Relating the relative phases and amplitudes of different orders may not mean anything.  The orientation relates to the relative amplitudes and phases for these signal components; this has many similarities to what Bently calls the Full Spectrum.  If Bently displayed relative phases (or absolute for orders like this), one could produce these types of plots from their Full Spectral plots (which I showed Don a long time ago). 

One can break down these orbit components in a number of ways.  The data in these could yield components of the Full Spectrum, or it could be displayed as x vs. y,  like you did.  As far as the individual frequency components, not much can be said about their meaning. These components can be manipulated to gain further information, like a digital representation of the inclination angle, an ellipticity ratio, or the forward/backward sense of the frequency components for the x-y pair of signals.

I think as well you need to start with a data "quality" issue and then proceed to understanding what the data may mean.  If I look at your data, I see an arrow on each orbit.  Normally one associates that with direction of rotation, but in your case I see on the 1X a CCW rotation, on the 2X a CW rotation, the 3X a CCW rotation, and on the 4X a CCW rotation.  One could conclude that the arrow represents precession, a term you likely are not familiar with.  But most software packages that I'm familiar with show rotation, not precession.  What software package generated the plots?  Rotation by the way is usually defined by a convention as viewing from driver to driven.

Now, on the amplitudes...is the scale utilized in a plot representative of amplitude in mils (as the plots are labeled)?  If so the 1X plot, with a scale going from approximately ±12 would then show vibration of roughly 15 to 20 mils, certainly something I would not expect from a 2-pole motor.

The plots don't indicate where your transducers are mounted?  Can you supply this information?

I see a very small "Y2 [mils]" in the top left corner of each plot and also "Y1 [mils]" in the lower right corner.  Any idea what these designations mean?  Is there something indicated by where they are positioned?  Normally if they designated transducer angles they would be at 90°, not diagonally opposite.


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