Emerson 2130 RBM Consultant Pro, Справочное руководство

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3-127 Laser Address Selection
If the data correlation can not be brought into the acceptable level but the peak-
peak amplitude is too high, then a message will be displayed advising you to check
the system for looseness and then repeat the measurement. Another possible
reason for this condition could be due to data points lying too far away from the
sine fit curve. To verify this condition, it will be necessary to check the sine fit curve
for points which might lie far away from the sine fit curve and either edit the sine
fit and remove the measurement points which might lie far away from the curve or
change to a four point method and acquire new data.
Bearing faults, rubs, and looseness are all problems which can cause points not to
fall on the curve. These mechanical problems can cause all data to have some low
levels of variability. This variability may appear as randomness, or “noise”. This noise
is not generally of much concern when the level of misalignment is high; however,
as the amplitudes measured from misalignment decrease then the ratio of noise to
the signal increases and the percentages of fit may worsen. Although the program
automatically conditions the data for an improved fit in such a circumstance, there
may be times when the user chooses to change methods or to manually condition
the data using the edit data function. Refer to the Display Sine Fit section on page
3-168 for more information.
Data Quality
When using Auto Sweep, Manual Sweep, or Dual Pass a sine curve is fit to the data
points. This sine curve is analyzed to determine what the projected data would be
at each of the clock positions mentioned above in the Auto 4 Point method. If the
fit of the curve to the data points is marginal, then the data can be automatically
conditioned to improve the sine fit. The resultant fit may be viewed and can be
manually conditioned if desired. This procedure is discussed in the application
chapter.
If the analyzer is unable to condition the data suitably, then a message will be dis-
played warning of an “Unfit Data” condition. There is always some variability intro-
duced into data due to shaft clearances, bearing faults, base deterioration, etc. If
this variability becomes significant compared to the amount of misalignment (for
example, due to the presence of too much background vibration), it may become
necessary to look at the sine fit curve in order to determine the cause of the unfit
sine fit and take corrective action. Alternatively, it may become necessary to use a 4
Point or Manual Sweep Method to acquire data. Changing methods does not
require the job to be redefined. Merely select a new alignment method from the
Alt Main screen and retake the last set of data.