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AMLCD
require maximum illumination above the clouds where
sunlight is particularly bright
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Night
conditions produce little ambient light requiring less
illumination gain for readibility
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One
of 13 Boeing 777 cockpit instrumentation systems that
utilize Marlow Ind.s' TECs.
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Active
matrix liquid crystal display (AMLCD) panels are used to display
data, images, symbols, and text for human-readable screens. One of
the many applications for this technology is commercial aviation.
The ability to clearly view instrumentation in varied lighting
conditions is critical to the safe operation of the aircraft.
Thermoelectrics are employed to provide an effective automated means
of contrast and brightness adjustment to improve instrumentation
readability in bright daylight or pitch
darkness.
An AMLCD
needs a source of illumination to give the display sufficient
contrast and brightness to be readable. Since the characters are
usually imbedded on a flat screen, a display's readability depends
on the light that comes through it in the transmission mode. One way
to provide the back-lighting is to suspend a serpentine mercury
vapor tube behind the AMLCD display panel. The amount of
illumination depends on the amount of mercury vapor in the tube.
The
thermoelectric cooler (TEC) makes contact with the tube through a
"cold shoe" that controls the temperature of a spot on the
tube. By increasing and decreasing the temperature of that spot,
mercury condenses or vaporizes on the spot with the increase or
decrease in temperature. More vapor in the tube causes the tube to
glow brighter. The TEC is controlled by an automatic gain control
that senses the amount of ambient illumination. Above the clouds,
where sunlight is particularly
bright, the AMLCD requires maximum brightness; at night on the
ground it needs little.
Marlow
provides the holding bracket that is soldered to the TEC. Electronic
components are mounted on the bracket and a wire harness and
connector are attached to the TEC. The cold shoe that makes contact
with the tube is attached to the TEC. The TEC is potted with epoxy
to prevent condensation in it when it gets cold. The unit is tested
separately and the customer can plug it in to the AMLCD box, attach
the connector, and operate the system.
Advantages of
Thermoelectrics for this Application
Thermoelectric
coolers are lightweight, small, and rugged. They operate with good
power efficiency, have no moving parts, and provide solid-state
semiconductor reliability. Thermoelectric cooling produces no
vibration and makes no noise.
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Specific Marlow
Advantages
Marlow
has engineered combinations of materials that enable our devices to
withstand wide temperature variations without failure due to
coefficient of thermal expansion (CTE) mismatch of materials and
joints.
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