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(5) Underwater Locator Beacon
(a) The underwater locator beacon is powered by a self contained battery. The ULB is activated when its water switch is immersed in water. The water switch is part of a low-current trigger circuit that turns on the oscillator circuit. The oscillator output drives a transducer that is mechanically coupled to the units case, radiating 37 kHz acoustic energy into the surrounding water. It sends out acoustic rf pulses when it is immersed in water up to 20,000 feet. It has a detection range of 2,000 to 4,000 yards.
B. BITE and TEST (Fig. 2)
(1)
DFDR Status Signal and Display
(a)
During normal operation, the system fault and DFDR fault signals are generated at a logic 0. This causes in turn, the output of the OR gate to go to logic 0 and relay K1 to be de-energized. The logic 0 output of the OR gate enables the output of the NOR gate to be a logic 1 causing relay K2 to be energized. This enables the 28-volt dc input to be applied through the relay contacts of K1 and K2 and to the fault relay in the control panel. If the solid state switch in the DFDAU is on (no DFDAU fault), the fault relay in the control panel is energized. Consequently, the ground return for the OFF light is removed and the OFF light is turned off.
(b)
When a system fault occurs, the fault signal is logic 1. The NOR gate output is logic 0, and relay K2 is de-energized. Consequently, the 28-volt dc is removed which de-energizes the fault relay. The ground signal is then applied through the fault relay to turn on the OFF light.
(c)
If the DFDR malfunctions, the DFDR fault signal is generated as a logic 1. The NOR gate output is a logic 0, and relay K2 is de-energized. The fault signal also energizes relay K1 and turns on the BITE fault indicator. In addition the 28-volt dc is removed from the fault relay on the control panel to turn on the OFF light. A discrete is also sent to the EICAS to display FLT DATA REC, a status/maintenance message (Ref 31-41-00), and to the DFDAMU to turn on the DFDR FAULT indicator.
(2)
DFDAMU Status and Display
(a) For a no-fault condition, the solid state switch in the DFDAMU provides a ground to the off relay in the flight recorder control panel. This energizes the relay which removes the 28 volts dc from the OFF light. In addition, the FDAU FAULT indicator on the front panel of the DFDAMU remains off.
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(b) If the DFDAMU malfunctions, the CPU generates a high FDAU FAULT signal. It turns on the solid state switch which removes the ground from the fault relay on the flight recorder control panel to turn on the OFF light. The fault signal also enables the logic gate which turns on the FDAU FAULT light on the front panel of the DFDAMU. A descrete signal is also sent to the EICAS to display the FLT DATA ACQ level C caution message (Ref 31-41-00). 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：757 AMM 飞机维护手册 仪表 CHAPTER 31 - INSTRUMENTS 1(52)
