TM 5-6675-316-14
(5) The data and timing tracks are divided into 112 segments, as are the
Each data segment is divided into 18 parts which are bits of
alphanumerics.
information. These bits are approximately 0.0008 in. (0.020 mm) in width, and are
either transparent (clear) or non-transparent (black).
(6) Located at the outside perimeter of the disc is a detector assembly which
picks up data from the tracks on the edge of the disc. The detector assembly
consists of a large light emitting diode, approximately 1/4 in. (6.35 mm) in
diameter, which projects infrared light across the three tracks, through the disc
and onto a 45-degree mirror where the light is turned through 90 degrees. A small
lens focuses the beam of light through a slit mounted on the font pickup lens tube.
Three photodetectors are mounted in line with the slit, and each corresponds to a
data track on the disc. With the disc in rotation, pulse patterns representative of
the three data tracks are developed and detected by the photodetectors. The three
pulse trains are then converted by the font interface logic into binary data which
is representative of the data encoded on the three tracks of the disc.
(7) To expose an individual character, the program determines at which point
in the font disc rotation the xenon flash will fire. The xenon flash freezes the
selected character and projects it through the lens system and onto the film.
(8) A font change is accomplished by moving the whole disc laterally so that
the adjacent character is positioned opposite the flash window. The track data
detection system moves with the disc assembly.
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