Additional Features
Mode l8500C/8500C+ Operators Manual
5-17
first rename the chart in order to better identify the history data (see Sec tion5.2.3.3 “Renaming
Charts” on page 5-4). See Secti on10.2.2 “Storing Data to Disk or Memory” on pa ge10-4 for more
information on storing balance histories, as well as Appe ndixC Balance History Files” for a
description of the balance history file format.
NOTE: It is best that 8500C/C+ distribution chart disks not be used to store balance
measurement and solution data files. Instead, use a backup copy of the chart disk and store
the original chart disk in a safe place. Instructions for making a backup disk are located in
Secti on10.2.4 “Copying Balance Charts” on p age10-6.
5.6.1.4 Clearing Histories
Balance histories are stored in 8500C/C+ static memory. As a result, they are always available, even i
power to the instrument is turned off. Only one balance history can be associated with a particular
balance chart. Selecting that chart always invokes its history and begins the balance procedure from
the last run in the series. It may become necessary, therefore, to discard histories, either to begin a new
History or to free up static memory for other balance data.
To clear a balance history, first select the balance chart whose history you wish to delete. Call up th
Balance Run Start-up screen and press
MORE KEYS
. Press
CLEAR HIST
to clear the history for the
current chart (see Figur e 5 -13 on page 5 -15).
Since multiple balance charts can be stored in static memory, it is also possible to store multipl
balance histories there as well. Histories can be deleted one at a time by selecting a chart and pressing
the
CLEAR HIST
soft key. They can also be deleted all at once by using the
CLR CHARTS
soft key (see
Secti on5.2.3.5 Clearing Chart Memory” on pa ge5-5). Since a balance history is always associated
with a particular chart, removing that chart always removes the history.
NOTE: The
CLR CHART
soft key clears all charts and all histories from static memory.
5.6.2 Chart Corrections
As explained in Sectio n2.2.2 Balance Charts” on pa ge2-7, balance charts represent an experimental
averaging of vibrational characteristics for a particular type of rotor system. Actual rotors within the
group, however, often vary from individual to individual. Consequently, some systems may exhibit
characteristics that deviate from the balance chart predictions for that rotor type. The 8500C/C+ has
the ability to detect these differences, and through the technique of chart correction, modify th
balance chart to more accurately reflect the state of the individual rotor system.
Chart correction compares the expected behavior of a vibrating rotor system, as predicted by its
balance chart, with its observed behavior, as measured by the 8500C/C+. You can simplify this
comparison by making a single adjustment at a single test point then analyzing the differences between
the expected and observed behaviors. Using
one
of the adjustments that appear in the Solution screen,
for example, provides a (theoretical) solution for that particular blade, that is, balancing it so that no
more adjustments are required. Consequently, the next run produces a move line whose direction
(phase angle) and magnitude (vibration amplitude) accord with the solution. For an uncorrected chart,
however, the move line values for direction and magnitude that are actually measured very likely differ
from the values that were predicted. The 8500C/C+ uses these differences to calculate correction
factors for phase angle and vibration amplitude. The correction is added to the balance chart and used
to adjust all further measurements of phase angle and vibration amplitude.
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