Manual Chapter 5

5-27
Alignment Data
Data Quality
When using Auto Sweep, Manual Sweep, or Dual Pass a sine curve is fit to
the data points to determine what the projected data would be at each of
the clock positions mentioned above in the 4 Point Auto method. If the fit
of the curve to the data points is marginal, then the data can be automati-
cally 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 suit-
ably, then a message “UNFIT DATA” will appear on-screen warning the
user to retake data or change data collection methods. There is always some
variability introduced into data due to shaft clearances, bearing faults, base
deterioration, etc. If this variability becomes significant compared to the
amount of misalignment, 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 method from the Align-
ment Options menu and retake the last set of data.
When using any 4 point method the data is always checked for validity. In
theory, subtracting any third measurement from the sum of two opposing
measurements will give the value of the 4th measurement (the one opposite
the third measurement). For example, add the left and right measurements
together, then subtract the top measurement. The results should approxi-
mately equal the value of the bottom measurement. If this comparison
varies by more than 20%, a message will be displayed warning of a “Data
Validity Error, Reading Error Above 20%”. When this happens you should
retake the last readings to check for accuracy, before proceeding. There is
always some variability introduced into data due to shaft clearances,
bearing faults, base deterioration, etc.