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MIL-PRF-83419 Altimeter, Servo Controlled, Automatic Pressure StandbyThis specification covers integrally-lighted altimeters that have an electromechanically servo driven pointer and a digital display of corrected altitude. The altimeters operate in the normal mode to display altitude transmitted by altitude computers or central air data computers. The altimeters incorporate an integral pressure sensor with electronic outputs to aid operation in the normal mode and to provide altitude inputs for the electronic display of pressure altitude when operated in the standby mode. The altimeters also incorporate an electrical output of barometric pressure setting which is required by some aircraft. A method is provided on the bezel of the altimeter for the selection of barometric setting to be displayed in either inches of mercury \(in. hg\) or millibars \(mb\). The altimeters are designed to operate from the following power sources: 115V, 400Hz \(primary\), 28V DC \(secondary\), and 18V DC \(battery mode\) from an optional rear mounted battery module. Altimeters meeting the requirements of this specification are interchangeable with AAU-19/A, AAU-19A/A, and AAU-19B/A, AAU-34/A, and AAU-37/A Altimeters.

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MIL-PRF-83419E
to FIGURE 1 and FIGURE 3.
3.5.7.1 Battery Module Pin Assignment. The following pin assignments apply to the
altimeter receptacle for the battery module interface:
Pin 1. Battery discharge status. The battery module transmits a bi-level output
signal indicating the battery state-of-charge to this pin. The altimeter shall sense
and display a "B Err" message as specified herein when a logical high (>3.5V)
signal is present indicating a potentially depleted battery. When in the inactive
low state, the output impedance of the state-of-charge signal shall be no greater
than .5KΩ.
Pin 2. Battery clock. The altimeter shall output a digital signal on Pin 2 as
required for incrementing the state-of-charge counter of the battery module. A
pulsed signal (0 to 5V) having a frequency of 9.25Hz shall be supplied to the
state-of-charge counter of the battery module. When the altimeter battery module
function is initially armed ("A") by setting of the altimeter control lever as
specified herein, a single pulse shall be transmitted by the altimeter. The
altimeter shall provide the signal continuously when the 18DC power derived
from the external 28V DC power source for the altimeter is (<18V) DC and the
altimeter is operating in the battery ("B") mode. The altimeter clock input to the
battery module counter is also terminated to ground in the module through a
1OKΩ±5% resistance. The altimeter shall detect the installation of a module by
monitoring for the presence of the resistance.
Pin 3. Battery power output. Provides an input of battery module power, (13.5V-
l8V), for operation of the altimeter in the battery mode. The battery output shall
be protected in the module by a fuse having a value not exceeding 0.5 Amp.
Pin 4. Battery power return.
Pin 5. Battery fuse test (6V tap). A 6V positive battery tap input from the battery
module is provided for use in verification of the battery tap fuse of the module.
The battery tap fuse has a value not exceeding .5 Amps. The 6V interface signal
is supplied as a means of fuse verification only and shall not be subjected to
positive (charging) currents or a steady state discharging load. The battery
module design shall use enhancement devices for developing the state-of-charge
signal. As a result, when the state-of-charge electronics are not powered, the state
of charge shall not be terminated to ground.
3.5.7.2 Module fuses. The altimeter shall sense the failure of the fuses in the module. A
"B Err" shall be displayed when a fuse has opened and a BIT test is performed or the altimeter is
initially armed. Under power-up and normal operating conditions, the altimeter shall not cause
the battery module fuses (thermal actuated type) to open. The altimeter shall not subject the
module to positive charging currents or steady state discharging load except as required for
normal operation in the battery mode.
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