Análise de Vibração e Orbitas

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Orbit and Timebase Plots 
• The Orbit plot shows the path of the shaft centerline. 
 
• The rotor vibration is sensed by two orthogonally mounted 
(XY configuration) Proximity probe transducers. The X and 
Y transducer signals shown in the Timebase plot show the 
vibration with respect to the individual transducer. When 
the two timebase signals are combined, a two dimensional 
picture of the path of the shaft centerline (Orbit) is 
generated. 
 
• The Orbit plot is one of the most powerful machinery 
management plots, because it combines vibration 
amplitude, phase and frequency into a single plot that is 
easy to interpret. 
Orbit and Timebase Plots 
• The Orbit plot shows the path of the shaft centerline. 
 
• The rotor vibration is sensed by two orthogonally mounted 
(XY configuration) Proximity probe transducers. The X and 
Y transducer signals shown in the Timebase plot show the 
vibration with respect to the individual transducer. When 
the two timebase signals are combined, a two dimensional 
picture of the path of the shaft centerline (Orbit) is 
generated. 
 
• The Orbit plot is one of the most powerful machinery 
management plots, because it combines vibration 
amplitude, phase and frequency into a single plot that is 
easy to interpret. 
Trend Plots 
• A presentation in Cartesian format of a measured variable 
versus time. 
 
• The correlation of process related information (flow, load, 
pressure, tank level, etc.) with vibration and position 
information can be a very powerful machinery diagnostic 
tool. 
 
• In many cases the ability to determine the fundamental 
cause of a machine malfunction depends upon process 
information. 
Average Shaft Centerline Plots 
• This plot is constructed from the dc (position) component 
of the Proximity probe signal. 
 
• Two XY Proximity probes are necessary for this two 
dimensional, radial position, measurement. 
 
• Correlation of shaft position measurements: stopped 
versus at speed, cold versus hot, no load versus normal 
load, is an important diagnostic tool. 
 
• This is a very effective indicator of bearing wear and 
changes in the machines alignment state. When the orbit 
plot for a selected point is added to its corresponding dc 
position then a correlation can be made between orbit 
shape changes and the dc position change. 
Average Shaft Centerline Plots 
• When the orbit plot for a selected point is added to its 
corresponding dc position then a correlation can be made 
between orbit shape changes and the dc position change. 
 
• Some applications allow the Shaft Centerline plots to 
provide the option to create Orbit plots for selected points 
and to display these on top of their corresponding DC 
points. This illustrates how the orbit changes as the DC 
position changes. 
Orbit 
Half Spectrum Plots 
• Commonly a presentation of a signal's frequency 
components versus amplitude. 
 
• The Spectrum Plot shows the frequency content of a 
signal. This plot is useful in determining which frequency 
components are included in a complex vibration signal 
Full Spectrum Plots 
• An enhanced spectrum plot produced by using the 
timebase waveforms from XY transducers to calculate the 
amplitudes of the forward and reverse (backward) 
frequency components. 
 
• This plot is very effective at determining the direction of 
precession for various frequency components. 
Half Spectrum Waterfall Plots 
• The Waterfall Plot is generated from a series of spectrum 
plots taken over a period of time or changing load 
conditions. 
 
• The vertical axis is usually time (can be load) and the 
horizontal axis shows the vibration frequency. 
 
• The Waterfall Plot is useful in determining changes to 
various frequency components. 
Full Spectrum Waterfall Plots 
• The full spectrum waterfall plot is constructed from the 
output of two orthogonally mounted Proximity Probe 
transducers. 
 
• It shows the forward and reverse frequency components 
over a time range. 
 
• The Waterfall Plot is generated from a series of spectrum 
plots taken over a period of time or changing load 
conditions. 
 
• The vertical axis is usually time (can be load) and the 
horizontal axis shows the vibration frequency. 
 
• The Waterfall Plot is useful in determining changes to 
various frequency components. 
Half Spectrum Cascade Plots 
• The Spectrum Cascade Plot is a series of spectrum plots 
taken over a speed range, usually at set speed intervals. 
 
• It is a useful plot to determine frequency relationships 
over a speed range. 
Full Spectrum Cascade Plots 
• The Full Spectrum Cascade is constructed from the output 
of two orthogonally mounted Proximity Probe transducers. 
 
• It shows the forward and reverse frequency components 
over a speed range. 
Polar Plots 
• Polar format presentation of the locus of the shaft 1X (or 2X, 
nX…) filtered vibration amplitude and phase lag from a single 
vibration channel as a function of shaft rotative speed. 
 
• The data used in this plot is identical to the data used in the 
Bode plot. 
 
• The polar plot is generated usually during machine startup or 
coast down (transient operation). 
 
• This plot is sometimes incorrectly called a Nyquist plot. 
 
• This plot is useful in determining the slow roll vector, slow roll 
speed range, balance resonant frequencies, synchronous 
amplification factor, heavy spot location and rotor mode 
shape. 
Acceptance Region Plots 
• Trend information of the 1X or 2X vibration vectors (amplitudes 
and phase lag angles) presented in polar or Cartesian format, 
or the shaft average centerline position in Cartesian format. 
 
• The user defines the normal Acceptance Region for each shaft 
radial vibration or position measurement on the machine, 
based on historical data or the machine under all normal 
operating conditions. 
 
• If the vibration vectors or shaft position go outside the 
Acceptance Region hardware and/or software alarms should 
indicate a possible problem. Alarm set points should be set 
independently for maximum and minimum values of 
amplitude, phase and position. 
 
• Acceptance Region information is an important indicator of a 
shaft crack and other machine malfunctions. 
APHT Plots 
• An APHT acronym used to describe the trend plot of 
filtered vibration amplitude and phase angle data. 
 
• This data may be presented in both Cartesian and polar 
formats. 
 
• Commonly used for 1X, 2X and nX vibration data. Under 
constant operating conditions a machine’s vibration 
amplitude and phase lag usually does not change 
appreciably. 
 
• A change in amplitude and phase lag under constant 
operating conditions indicates that something has 
changed inside the machine. 
Bode Plots 
• A pair of graphs in Cartesian format displaying the 1X 
vibration vector (phase lag angle and amplitude) as a 
function of shaft rotative speed. 
 
• The Y axis of the top graph represents 1X phase lag angle, 
while the Y axis of the bottom graph represents 1X 
amplitude. The common X axis represents shaft rotative 
speed. This plot is also used for 2X, 3X, etc. vibration 
vectors. 
 
• The data used in this plot is identical to the data used in 
the Polar plot. 
 
• This plot is useful in determining the slow roll vector, slow 
roll speed range, balance resonant frequencies, 
synchronous amplification factor, heavy spot location and 
rotor mode shape. 
Campbell Plots 
• A diagram used in rotating machinery design. 
 
• A tool for selecting and checking shaft operational rotative 
speeds and other possible forcing function frequencies 
against the spectrum of natural frequencies to avoid 
resonances. 
 
• The X axis represents the various possible excitation 
frequencies, i.e., rotative speed (1X), oil whirl (.40X to .48X), 
blade or vane passing frequencies, gear mesh frequencies, 
etc. 
 
• The Y axis represents the rotor lateral and torsional 
natural frequencies.