(a)
The BITE does a test on sensors and compensators by looking for these malfunctions:
-
The electrical resistance of the sensor or compensator is not in a satisfactory range
-
The sensor or compensator circuit is shorted
-
The sensor or compensator circuit is open.
(2)
The line maintenance person can use the CMC to do a system test. In this test a signal equivalent to 1022 degrees F (550 degrees C) is added to the system. This causes the BRAKE TEMP indication to come into view on EICAS. The gear synoptic will show each brake temperature equivalent to 5 or more for 2 +/- 0.2 seconds after the test signal stops. The brake indications will be amber during the test.
D.
When power is applied to the system and the BTMU is not operating in the BITE mode, a built in test (BIT) continuously monitors the components and necessary functions for correct system operation. Data on malfunctions is stored in non-volatile memory for access during maintenance operations.
E.
Line maintenance operations on the BTMU include a test, and a removal and installation. All adjustments and repairs on the BTMU are done during shop maintenance.
3. Brake Temperature Sensor (Fig. 2)
________________________
A. One brake temperature sensor is installed in each of the 16 landing gear brakes. The sensor contains a chromel-alumel thermocouple in a stainless steel sheath. The thermocouple will supply a voltage that is directly proportional to the temperature of the thermocouple. A mounting bracket and connector are attached to the thermocouple. The connector has a chromel pin attached to the chromel side of the thermocouple and an alumel pin attached to the alumel side of the thermocouple. These pins mate with pins made of the same material which are connected to thermocouple wire made of the same material. This wire is installed in conduits that go to the junction box on each gear.
B. Sensors are removed and installed using procedures in this section. Tests on the sensors are done using the BTMU and the central maintenance computer. No other line maintenance is done on brake temperature sensors.
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A
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MAINTENANCE MANUAL
SHOCK STRUT
TRUNION
DRAG STRUT
J6 (LH BODY GEAR)
J5 (RH BODY GEAR)
SEE B
SEE A SEE A
AXLE
WASHER SENSOR(2 LOCATIONS)
BOLT
(2 LOCATIONS)
CONNECTOR
CONDUIT
NUT
LOCK HOUSING
BRAKE PISTON WASHER
BRAKE A
TEMPERATURE COMPENSATOR
J BOX
B
Brake Temperature Sensor and Compensator Location Figure 2
J8 (LH WING GEAR)
J7 (RH WING GEAR)
SEE B
LOCK WASHER
WASHER
LUG
TERMINAL STRIP
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747-400
MAINTENANCE MANUAL
4. Brake Temperature Compensator (Fig. 2)
_____________________________
A. One brake temperature compensator is installed in the junction box of each wing and body gear and supplies an ambient temperature reference for the system. It is connected to the negative lead from each brake temperature sensor on the gear and to the BTMU. The brake temperature compensator is a platinum resistive element. The electrical resistance of the element changes proportionally with changes in temperature.
5. Operation (Fig. 3)
_________
A. Signals from the brake temperature sensors come into the BTMU on input sensing circuit cards. The signal is compared with the brake temperature compensator through a differential amplifier. The signal from the amplifer goes to a digital analog converter where it is changed to the digital equivalent. It then goes to a central processing unit where it is changed into single digit equivalents of brake temperature and transmitted to the EIUS for display on EICAS.
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