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Launching Advanced Medium-Range Air-to-Air Missiles from jet fighters requires a sophisticated power system in the aircraft. Specialized power supplies, located in the pylons of the fighter, provide the power and control for launching a variety of missiles.
These supplies include high voltage outputs to ignite the missile's propellant and arm the warheads. Audio signals are processed by the supplies to keep the pilot appraised of the missile status. A complex arrangement of relays and launch control signals interlocks and releases the missile at the appropriate command.
Testing these supplies requires a full featured tester plus specialized applications modules to simulate the launch command sequence. Precise voltage pulses must be applied and measured to determine correct operation of the power supplies. Real time testing is critical to prevent destructive test cycles.
AUTOTEST offers a solution:
A dedicated Launch Command Control Card in the application
fixture. The card is a state machine that, once triggered by
computer command, initiates a precisely timed sequence of applied
voltages and multiplexed triggered measurements.
Multiple test results are obtained from limited test data. Voltages applied and measured yield timing data and voltage drop data. Extrapolated from this data is verification of proper control sequencing and component values within the supplies.
The state machine consists of a debounced solid-state switch to start the sequence. A variable clock provided the time base to increment a state counter.
The state counter steps through consecutive addresses in a PROM. Each address holds a 7-bit binary mask. Three bits are used to control an eight-channel multiplexer to route signals to the DMM. One bit triggers the DMM trough an opto-isolated buffer driver to preserve the digital circuit ground.
Voltage drops set up by series resistor combinations produce the target voltages used to calculate the precise values of the embedded resistors in the supplies. Comparison of the measured values to expected norms verifies contact closure and conductivity of the relays and paths in the supplies.
In addition to controlling applied voltages and thus relay closures, the successive PROM address masks set the multiplexer channel and trigger the DMM to read and store the appropriate voltage in the next memory location. Later, the readings are extracted and analyzed by the computer program.
The ability to vary the state clock timing permits minor adjustment to resolution of state time base. Manipulation of the bits between successive state masks allows for a high degree of flexibility in adjusting and modifying the sequence timing.
The concept proved to be high stable, reliable and versatile. Currently there are five separate implementations of this application. Minor PROM variations also make it possible to implement this design in similar applications. This approach provided a cost-effective solution to a complex testing requirement.
Copyright © 1995-2002, Autotest Company, All Rights Reserved.
10.18.2007