5-10
Chadwick-Helmuth Company, Inc.
Chapter 5
- Balance Measurement and Solutions
signal by locking onto the velocimeter pulse at the designated balance frequency. If a vibration signal
is acquired, the 8500C/C+ then indicates that the Strobex has been activated and that the balance
measurement may continue (see Figure 5-7).
Figure 5-7. Strobex Activation Screen
If a vibration signal is not present, the measurement terminates, and an error message is displayed
(Figur e 5 -8). In this case, use the
SPECTRUM
key to display the acquired spectral balance data to help
determine the cause of the failure. Usually, the problem is a preset balance frequency that is not within
range of the actual vibration signal. The 8500C/C+ can only analyze those frequencies that are within
±6.25 percent of this designated value.
Figure 5-8. Strobex: No Balance Frequency Signal Error Screen
If the 8500C/C+ indicates that a vibration signal has been found, press the Strobex trigger and aim it at
the rotor disc. The retro-reflective target then appears frozen at some angular position or clock angle,
relative to the rotor's reference azimuth. The azimuth is usu ally at12:00, and the actual position is
usually indicated on the balance chart. Use the Leftand Rig htArr owkeys to modulate the Strobex
pulse rate so that the target appears to rotate toward the azimuth. A single keystroke changes the target
position by one degree. Holding the key down changes it more quickly. The target may be rotated in
either the clockwise or counter-clockwise direction. When the target stabilizes at the designated
position, press the
STOP
key to complete the balance measurement and display the solution. Onc
STOP
has been pressed, the
SPECTRUM
key can be used to display the spectral data acquired during
the balance measurement. The plot is automatically centered about the balance frequency.
NOTE: When the retro-reflective target has been visually moved to its designated position, it
may appear to fluctuate or “jitter” without ever becoming completely stable. This
fluctuation does not affect the balance solution. If the mean position of the target can be
judged to be stable, the computed solution does not suffer any appreciable loss of accuracy.
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