6. Inlet Pressure Sensor (Fig. 1)
_____________________
A. The inlet pressure sensor (P1) has a silicone sensing element covered with a protective coating for corrosion resistance. The sensor port is mounted on the aft face of the inlet plenum and faces downwards to avoid water and fluids reaching the sensor.
7. Serial Number Identification Unit (Fig. 1)
_________________________________
A. The identification unit is similar to the trim box and incorporates a number of resistors and jumpers which permits 1024 steps. The APU controller reads the unique resistance values which represents the APU serial number and transmits the information to the cockpit EICAS display screen.
8. APU Control Switch (Fig. 2)
__________________
A. The APU control switch is installed on the P5 pilots overhead panel. With the APU control switch, the APU can be started, operated, and stopped.
9. APU Start Source Switch (Fig. 2)
_______________________
A. The APU start source switch is installed on the P461 pilots overhead maintenance panel. With the APU start source switch, the APU can be started using main battery power or external ground power.
10. Current Transformer (Fig. 3)
___________________
A. The current transformer is used to monitor the current drawn from the third phase of the 90 KVA, three phase, 400 HZ generators mounted on the APU. The third phase wiring is placed through the hollow core of the current transformer. The current pulsating through the wiring induces a similar signal on the current transformer windings. This signal is sent to the APU controller to determine the status of the generator load.
11. APU Controller (Fig. 3)
______________
A. The APU controller is a microprocessor based control unit. It is designed to allow for automatic control and constant monitoring of the APU for unattended operation. This is accomplished by precise speed governing of high speed and power turbines and through extensive fault detection, indication and accommodation. The APU controller controls the load compressor inlet guide vane actuator, the diverter valve control and the fuel metering unit. This allows for efficient and surge-free operation of the APU. An extensive built-in-test capability allows for fault isolation to the lowest level possible. Fault codes are stored in non-volatile memory and are transmitted to the maintenance computer via ARINC 429 bus. The high fault detection coverage and the exercising of the protection functions during normal shutdown eliminates the need for manual pre-start checks.
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A
747-400
MAINTENANCE MANUAL
APU CONTROL SWITCH
APU START SOURCE
TR
APU BATTERY
SWITCH FOR THE APU START SOURCE
APU Controls Component Location
Figure 2
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
SEE B
ASEE AFT EQUIPMENT CENTER, E8
CSEE APU CONTROLLER A FWD AFT EQUIPMENT CENTER, E8
FWD
FWD
APU CONTROLLER
B
C
APU Airframe Controls Component Location
Figure 3 (Sheet 1)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
C77144
A
747-400
MAINTENANCE MANUAL
BULK CARGO COMPARTMENT,
BULK CARGO COMPARTMENT
823R
NO. 2 CURRENT TRANSFORMER, T1504 NO. 1 CURRENT TRANSFORMER, T1503
RIGHT STATION 2160 BULKHEAD LEFT STATION 2160 BULKHEAD
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