2. CREATED BY
Bagas Alqadri : 15/379035/TK/42977
Emil Hakim : 15/379042/TK/42984
Bimo Adiartha D. : 15/379036/TK/42978
Evelyn Patriciana : 15/379044/TK/42986
3. VIBRATION
• Why do we need vibration analysis ?
• Having a general overview of engine condition after long period time of operation.
• Vibration analysis is needed to know whether the engine are in good condition or not.
• Vibration analysis will give the engineer early warning to failure in engine.
4. ORBIT PLOT ANALYSIS
What is Orbit Plot Analysis ?
• Orbit Plot is on of vibration analysis method to measure problems in engine by analyzing the
vibration.
• Orbit Plot analysis is not the only one methode to know the problems in engine, but because some
of the part of the engine is an rotating (moving) part, they are a non-contact installation so orbit
plot analysis is needed to know the vibration level in axial direction.
• Thus a complete measurement recommendation with the direction of axial vibration can not be
performed.
• For non-contacts are generally fixed permanently to detect direct vibrations on the shafts of
machines with critical use, installation of radial (horizontal and vertical) probes that are separated
by 90 degree angles.
5. ORBIT PLOT ANALYSIS
What is Orbit Plot Analysis ?
• Orbit Plot is used as addition in spectrum analysis. Many researcher has conducted
experiments about the purpose of orbit plot analysis.
• The experiments shows the relationship between the shape of the orbit and the failure of
engine part.
• This method work by creating an orbital line that will be translated into types of vibration
that happened.
• The orbital line is the path from the center point of the shaft that moves not on its axis
due to the bearing slit, etc.
7. ORBIT PLOT ANALYSIS
Construction of Orbit Analysis
• XY transducers observe the vibration of a rotor shaft
• A notch in the shaft (at a different axial location) is detected by
the Keyphasor transducer.
• The vibration transducer signals produce two time base plots
(middle) which combine into an orbit plot (right)
8. TYPES OF ORBIT PLOTS
Orbits may be divided into two main categories:
• Floating Orbits
• Absolute Orbits.
9. TYPES OF ORBIT PLOTS
• FLOATING ORBITS
Floating orbit analyses do not use keyphasors, hence, the orbit direction is floating
and starting point may differ from cycle to another.
• ABSOLUTE ORBITS
Referenced or absolute orbits have fixed starting point due to the use of keyphasors.
10. TYPES OF ORBIT PLOTS
• THE FILTERED ORBIT
A normally track one order such as 1xRPM, 2xRPM… etc. 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.
• THE OVERALL ORBIT
Do not use any filter and it is useful to obtain the actual shaft
movement
Most modern vibration analysis and monitoring system possess keyphasors.
Orbits may also be divided into filtered and overall.
11. CHARACTERISTICS
A. UNBALANCE
• Unbalance will generally produce 1xRPM vibration with 90° phase shift between the horizontal
and vertical directions. This will result is ellipse-shaped orbit
• Unbalanced orbit shape.
12. B. MISALIGNMENT
• The orbit will become acutely ellipsoid.
• 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.
• The average shaft centerline will move from the normal position to the upper left quadrant.
• Heavy preloading due to misalignment can cause the shaft to go into reverse precession.
Forward precession is normal, reverse is not.
• If the trajectory of our imaginary point on the trace of the orbit is continued, one can visualize
that precessions keep changing continuously.
CHARACTERISTICS
13. • For example, all points on the orbit are moving clockwise (which is the same as the direction
of rotation) and therefore the orbit is still in forward precession.
• If the preloading increases further, it will result in the orbit’s shape to resemble a number 8
character.
• In this case, it is also interesting to follow the average shaft centerline position, which has now
moved further upwards into the left quadrant
CHARACTERISTICS
15. C. OIL WHIRL
• Oil whirl is basically a sub-synchronous fluid instability.
• When viewed in the orbit domain, it is shown with the characteristic two dots.
• When viewed with an oscilloscope, the two dots do not appear stationary, but seem to be
rotating instead. This is because the frequency is marginally less than 0.5×.
• An oil whirl phenomenon generates a vibration precession, which is always forward
CHARACTERISTICS
17. CHARACTERISTICS
D. Rotor Rub
• 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.
18. CHARACTERISTICS
• The rub causes the orbit to take on different shapes. From a number 8 to a full circle to
something like the orbit
19. CHARACTERISTICS
E. Oil Whip
• Occurs when the rotor is passing through its critical speed.
• Oil whip is a destructive bearing defect.
• The precession of vibration is in the forward direction in this case, but some reverse 1× and
sub-synchronous components are present due to anisotropy (changes in response when
operating conditions change) of the bearing pedestal stiffness.
• The period of this self-excited defect may, or might not, be harmonically related to the
rotating speed of the shaft.
• When it is not harmonically related, the dots appear to be moving randomly. When it is
harmonically related they appear stationary
20. SPECTRUM
First Waveform and its half spectrum
Second Waveform and its half spectrum
Combined orbit and its full spectrum
Creating of Full Spectrum Plot
21. SPECTRUM
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
Circular Orbits and Their Full Spectra
22. 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.
3 possible orbits are shown
23. 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.
