TM 10-1670-305-23&P
0005 00-4
TEST CHAMBER ASSEMBLY
0005 00
THEORY OF OPERATION - CONT
THEORY OF OPERATION (MODEL 453)
The AR2 is installed inside the transparent altitude chamber during testing. The JUMP/OFF
switch and piston rod of the AR2 engage fittings inside the chamber which enable the switch to
be operated and the AR2 to be recocked after actuation without opening the chamber lid or
returning the unit to ground level. The ON and OFF position of the JUMP/OFF switch are
electrically monitored by magnetic sensors in the bottom wall of the chamber. An infrared LED
emitter/detector switch mounted inside the air cylinder senses movement of the piston rod
assembly at the instant the AR2 actuates. Signals from these sensors are transmitted to the
control assembly through an electrical connector in the left side wall of the control assembly near
the front.
The combination vacuum pump/air compressor enables the operator to raise and lower the air
pressure inside the sealed altitude chamber and thereby simulate the entire functional altitude
range of the AR2. The compressor also provides regulated pressure to the air cylinder to cock
the mechanism of the AR2. The necessary pneumatic plumbing connections between the
pump/compressor unit, control assembly, and altitude chamber are located along the bottom left
side wall of the control assembly. Power for the pump/compressor is supplied through a separate
electrical connector, also located in the left side wall of the control housing. Routing and
connections for all external electrical wiring and pneumatic plumbing are shown in schematics.
The control assembly is a self-contained, independently calibrated, completely interchangeable
modular unit. It contains a precision calibrated pressure sensor, a printed circuit board
incorporating signal conditioning and complete system operating logic, digital displays which
feature a preprogrammed microprocessor for making pressure-to-altitude conversion, pneumatic
valve and regulators to control altitude, regulated power supplies to run associated electronic
circuits and devices, and operational controls and indicator lights to perform and monitor the
various test functions. A quick disconnect port is located in the front wall of the control assembly
to permit attachment of a precision pressure standard during periodic altimeter calibration. A
separate auxiliary chamber used for calibrating wrist altimeters may also be connected through
this port.
WP 0007 00 shows the configuration of the control panel. The altitude and fall rate displays are
placed at the upper left with their respective setting controls at the right. The chamber can
simulate altitudes greater than 35,000 feet MSL. The fall rate may be set to any value between
approximately 10 and 240 feet per second, except that rates between 65 and 85 feet per second
cannot be selected because actuation at these rates will cause increased wear to internal
components of the AR2. The altitude display reads to the nearest foot, and the fall rate display
reads to the nearest 0.1 foot per second with positive values indicating a descent and negative
values indicating a climb. Although the displays are updated approximately two times per
second, the internal circuitry of the altimeter is designed to instantaneously capture and hold the
pressure sensor signal as soon as piston rod movement is detected by the infrared switch. The
altitude corresponding to this pressure is then locked in and displayed as the actuation altitude at
the next update interval.
Six (6) push button controls and seven (7) indicator lights are located on the control panel. In
addition to their primary functions, several of the controls are provided with interlocking logic
circuitry to preclude operations which are out of sequence or which might damage the AR2.
The description and function of the controls and lights are summarized in WP 0007 00.
