Chapter 4 - Installation
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13841 Rev A
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NOTE: Generally, for helicopter main rotor
installations, the user may install a magnetic pickup
assembly to provide the Vibrex unit with a necessary
azimuth signal. This signal provides a baseline for
taking vibration measurements, in the same way as the
photocell system does for propeller balance operations.
Note that the Vibrex unit uses only a single interrupter.
If the user does not have an applicable Vibrex unit checklist and
require one, contact Customer Support and order it (see Section
1.2 “Product Support”).
Photocell Mounting - The photocell’s distance from (gap
between) the target (interrupter) is anywhere from 7 in. to 7 ft.
What they do not say is the size target required to use it at 7 ft. In
most aviation applications the target tape would have to be so
big you couldn't find anywhere to put it, and it would throw the
item out of balance a good amount.
Photocell Tape Width - Try to stay in a range of between 5
in. to 18 in. Also, since the photocell requires the target to be in
the beam for a specific time period, try to stay at a small radius.
A target tape placed on the back of the spinner at the 6-in. radius
might be 0.5 in. long (width of tape passing through the beam)
for an RPM of 2400. The same target to provide the same dwell
(length of time) in the beam at the 30-in. station would have to
be approximately 2 in. long.
For details on calculating photocell tape length, see “Appendix
A: Photocell Taping”.
4.5 Sample Installations
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