This document discusses orbit plot analysis for analyzing vibrations. It was written by four authors and discusses various topics related to orbit plot analysis including: - How orbit analysis measures vibration in an X-Y plot using proximity probes - How polar and orbit plots can determine unbalance and faults in machines - The different types of orbits including floating, absolute, filtered, and overall - Common causes of vibration that can be identified using orbit plots like unbalance, misalignment, rotor rub, oil whirl/whip - How full spectrum plots provide additional information on orbit direction and can differentiate between issues like rubs and fluid instability - Other analysis methods like cascade plots to show vibrations at different speeds and waterfall plots

1. Orbit Plot
Analysist
Of Vibrations

2. Writer by :
• Aji Candra Lestari (14/366701/TK/42148
• M. D. Nashrullah (14/366988/TK/42275)
• Bayu Hari Santoso (14/366989/TK/42276)
• Achdzul Abizar A A (14/366795/TK/42212)

3. Orbit Plot Analysist of
Vibration
• Figure (1) Vibration Pickups in Orbit
Analysis Application. Orbit analysis is the vibration
measure of any rotor system in an X–Y plot (Figure
1). In most applications, the unit of measurement is
displacement which is measured directly using
proximity probes. These types of measurements are
relative vibration readings.

4. • Polar Plot and Orbit Plot analysis
are methods to determine the
unbalance in the machine. By the
nature of the plots, one can easily
determine the type of fault in the
machine and can take remedial
action immediately in order to
prevent any catastrophic effects
on the machine.

5. Unbalance is defined as an unequal distribution of mass causing the mass axis to differ from the bearing axis. During rotation, the
unequal mass along with the radial acceleration due to rotation create a centrifugal force. This results in force on the bearings and/or
vibration of the bearings. Balancing is a procedure in which the mass distribution of a rotor is assessed and if necessary, adjusted via
addition or subtraction of weight to ensure that the vibration of the journals and/or forces on the bearings are within specified limits.
Vibration is a mechanical movement where an object oscillates about an equilibrium point. It commonly produces unwanted sound
and wastes energy. Vibration in rotating equipment can greatly reduce the life of the equipment and the bearings.
Before studying the basic principles of balancing, one must keep in mind that there are many causes of vibration other than
unbalance. In some cases, balancing may result in only a partial or temporary reduction in vibration, while in other cases balancing is
the only effective course of action. Mechanical unbalance, which produces a force at 1 X RPM, has been found to be one of the most
common causes of machinery vibration, present to some degree on nearly all rotating machines. Polar Plot and Orbit Plot analysis are
methods to determine the unbalance in the machine. By the nature of the plots, one can easily determine the type of fault in the
machine and can take remedial action immediately in order to prevent any catastrophic effects on the machine.

6. Types of Orbit Plots
• Orbits can be divided into main categories, that is floating orbit and absolute orbit.
And also can be devided into filtered orbit dan overall orbit. Floating orbit analyses
is one of method to analyse orbits that don’t use keyphasors, hence the orbit
direction is floating and starting point differ from another. . Referenced or absolute
orbits have fixed starting point due to the use of keyphasors. Nowdays, many
modern vibration analysis and monitoring system uses keyphasors.
• The filtered orbit is the method that normally track one order and utilize the
keyphasor signal for synchronous filtering as well as reference point. The filtered
orbits are useful to track a certain order and neglecting other orders which may
cause unclear orbit plot. But, the overall orbit orbit do not use any filter and it is
useful to obtain the actual shaft movement.

7. CHARACTERISTIC AND CAUSES
So many thing can be causes a vibration. But there are causes, we can
solve with orbital plot analysis :
1. Unbalenced
2. Missalignment
3. Rotor Rub
4. Oil Whirl
5. Oil Whip

8. Unbalanced
Unbalance condition is happen because the
weight of the rotating part isn’t perfectly same or
balance. So that can causes unbalanced spin and
make vibration to the system. Unbalance will
generally produce 1xRPM vibration with 90° phase
shift between the horizontal and vertical directions.
This will result is ellipse-shaped.

9. Missalignment
Missalignment is the incorrect arrangement or
position of something in relation to something else. That
problem can be happen on assambley of shaft, gear, etc. When
radial preloads due to misalignment, gravity, fluid forces and
other causes increase in magnitude, the orbit will become
acutely ellipsoid. And the position of the center can be
changing. A bearing preload due to a cocked assembly can also
cause the orbit to have lower amplitude in one axis that makes
the ellipse look thinner. And suddenly, if the preloading
increases further, it will result in the orbit’s shape to resemble
a number 8 character. But If the trajectory of our imaginary
point on the trace of the orbit is continued, one can visualize
that precessions keep changing continuously.

10. Rotor Rub
Rotor rub can be happen if the rotor of motor is have
a contact with strator. Orbit analysis is a good tool to identify
rubs. As mentioned earlier, partial or complete rubs can occur
when a rotating shaft comes in contact with stationary parts
like seals or in abnormal cases of bearing (and/or
instrumentation) failures. The rub causes the orbit to take on
different shapes.

11. Oil Whirl
Oil whirl is present bearing clearances are excessive.
can occur when clearances become excessive. An oil wedge is
formed that is held in place by the rotation of the shaft. The
friction of the shaft against the wedge then pushes the shaft
around the housing. Fortunately (for the analyst), it occurs in a
very precise sub-synchronous frequency range.

12. Spectrum
Calculation of Full Spectrum Plot
• First
• Waveform and its half spectrum
• Second
• Waveform and its half spectrum
• Combined orbit and its full spectrum

13. Spectrum
Circular Orbits and Their Full Spectra
• Forward Precession
• Spectrum on forward side of plot
• Reverse Precession
• Spectrum on reverse side of plot
• Direction of rotation – CCW
• Forward Precession
• Spectrum on forward side of plot
• Direction of rotation – CW
• Reverse Precession
• Spectrum on reverse side of plot
• Direction of rotation - CW

14. Spectrum
Full Spectrum of Elliptical Orbit
• Orbit is generated by two counter rotating vectors
• Forward spectrum length is twice the length of forward
rotating vector
• Reverse spectrum length is twice the length of reverse
rotating vector
• Major axis of ellipse = a +b
• Minor axis of ellipse = a - b
• Original orbit cannot be reconstructed from full spectrum
because there is no phase information.

15. Spectrum
Circular & Elliptical 1x Orbits
• Direction of precession is indicated by dominant line of
“Forward” and “Reverse” components.
• Flatness of ellipse is determined by the relative size of
forward and reverse components
• When orbit is circular there is only one spectrum line
• When orbit is a line the spectrum components are equal.
• Therefore, the smaller the difference between components,
the more elliptical the orbit.

16. Spectrum
Orbit and Spectrum of a ½x Rub
• Orbit and spectrum of a steam turbine with a ½ x rub
• Full spectrum clarifies the complex orbit which is a sum of ½
x, 1x and their harmonics.
• From the ratio of forward ad reverse components
• 1x is the largest, forward and mildly elliptical
• ½ x and 2x orbits are nearly line orbits
• Small component of 3/2 x is third harmonic of ½ x
fundamental

17. Spectrum
Half and Full Spectrum Display of a ½ x Rub
Differentiating ½ x Rub and Fluid Instability from Ful
Spectrum Plots
• Half and full spectrum display of a ½ x rub (red data) and fluid induced
instability (blue data)
• Note similarity in appearance of the two half spectrum plots
• The full spectrum plots clearly show the difference in the subsynchronous
vibration
• The ½ x rub orbit is extremely elliptical – small difference between forward
and reverse components
• The fluid induced instability orbit is forward and nearly circular – large
difference between forward and reverse 1x and ½ x components.
• The unfiltered orbits are at the bottom

18. Spectrum
Full Spectrum Cascade Plot of Machine Start Up
• Horizontal axis represents precession frequency
• Rotor speed is to the left and amplitude scale is on the right
• Order lines drawn diagonally from the origin show vibration
frequencies that are proportional to running speed

19. Spectrum
• Display of spectra plots taken at different speeds during start up
• Base of each spectrum is the rotor speed at which the sample was
taken
• Diagonal lines are “Order” lines. Usually 1x, 2x and ½ x are plotted
• Resonances and critical speed can be seen on 1x diagonal line
• Sudden appearance of ½ x indicates rub which can produce
harmonics.
• Phase relationships cannot be seen on cascade plot.
• Many harmonics at low speed usually due to scratches on shaft

20. Spectrum
• Horizontal ellipse shows rub second balance resonance
(critical)
• Vertical ellipse shows ½ x rub frequency is almost equal to
first critical. Slight shift to right is due to stiffening of rotor
system from rub contact.

21. Spectrum
Full Spectrum Waterfall Plot
• Displays spectra with respect to time
• Used for correlating response to operating parameters
• Time on left and Running Speed on right. Amplitude scale is
at extreme right
• Plot of compressor shows subsynchronous instability
whenever suction pressure is high (red). 1x component is
not shown on plot.
• Full spectrum shows subsynchronous vibration is
predominantly forward.

22. Spectrum
Waterfall of Motor with Electrical Noise Problem
• High vibration at mains frequency (60 Hz) during start up.
• Vibration reduces when normal speed and current are
reached (green)
• When motor is shut down (blue) 60 Hz component
disappears suddenly.
• 1x component reduces gradually with speed.

23. Spectrum
• Summary
• Conventional spectrum is constructed from the output
waveform of a single transducer
• Full Spectrum is constructed from the output of a pair
of transducers at right angles.
• Displays frequency and direction of precession
• Forward precession frequencies are shown on right
side
• Reverse Precession frequencies are shown on left side
• Full spectrum is the spectrum of an orbit
• Ratio of forward and reverse orbits gives
information about ellipticity and direction of
precession
• However, there is no information about orientation
of orbit
• Cascade and Waterfall plots can be be constructed
either from half or full spectra

24. Reference
• Alsalaet Jaafar, Orbit Analysis, University of Basrah
• http://www.marinediesels.info/2_stroke_engine_parts/Other_i
nfo/oil_whip_and_whirl.htm
• http://www.jaafarali.info/files/orbit_analysis.pdf
• http://freevibrationanalysis.blogspot.co.id/2011/08/full-
spectrum-plots.html

25. Thank You