(3)
The monitor unit has its own Built-In Test Equipment (BITE) circuits self contained for testing the brake temperature system. A monitor test and sensor test are included and are defined as follows:
(a)
By selecting the MONITOR TEST position with the selector switch of the monitor unit (Fig. 1), a simulated high temperature condition signal is generated for all brake locations. If the system is normal, the nine LED indicators will illuminate on the face of the monitor unit, the EICAS indicators will all show uniform unit values of 7 or above and the flight deck BRAKE TEMP light indicator will illuminate. In this test the sensors themselves are not a part of the circuit that is tested.
(b)
By selecting the SENSOR TEST position with selector switch, a simulated signal is applied across each of the eight brake sensor thermocouples. If either the sensor or its cabling is open or shorted to ground the simulated signal will not be received by the monitor unit. The loss of signal in any of the sensors will be indicated by a dark LED for that sensor and the monitor unit. Normally, all eight sensor LED's will be illuminated in the sensor test and the monitor LED will also remain illuminated.
C. EICAS Computers and Display Units (Fig. 1 and 3)_________________________________
(1) Two EICAS computers are connected in parallel to provide system redundancy. A 0 to 5 volt signal corresponding to a 100 to 650°C (212 to 1202°F) brake temperature is provided to the EICAS computer(s) for each of the sensors. The EICAS system then displays unit values of 0 to 9 on the corresponding to these brake temperatures.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. GUN 051 ú
32-46-00
ú ú 09 Page 4 ú Dec 20/93
A
757
MAINTENANCE MANUAL
FLT COMPT
BRAKE TEMP
W
INDICATOR LIGHT
EICAS DISPLAY
C
Brake Temperature Monitoring System Indication Figure 2
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. GUN 051 ú
32-46-00
ú ú 04 Page 5 ú Dec 20/93
A
757 MAINTENANCE MANUAL
(2) The temperature ranges for EICAS unit values vs. brake temperature (approximate) are as follows:
NOTE: Increasing and decreasing brake temperature ranges overlap to
____ eliminate the rapid flip-flop between numbers that would occur if a brake temperature input was at the switch point with non-overlapping ranges.
Temperature ranges are approximate and may vary slightly due to EICAS and brake temperature monitor unit tolerances.
EICAS BRAKE TEMPERATURE BRAKE TEMPERATURE
INDICATION (Increasing) (Decreasing) 0 Up to 138° C Below 116°C 1 139 to 193 170 to 116 2 194 to 248 225 to 171 3 249 to 303 280 to 226 4 304 to 358 335 to 281 5 359 to 413 390 to 336 6 414 to 468 445 to 391 7 469 to 523 500 to 446 8 524 to 578 555 to 501 9 Over 578 Down to 556
(3)
The indications are grouped by the left and right trucks.
(4)
Displayed temperature values and surrounding boxes may be displayed in either a white or blue (cyan) color in different conditions. The color of the readouts and boxes are as follows:
(a)
Normal condition - all readouts ranging from 0 to 2 units. The boxes and numerals will be blue (cyan) in color.
(b)
Threshold condition - any readout showing 3 or 4 units. The box will be white and the numeral will be blue. Only one box in each group can be white in the threshold condition. The first box to reach the highest readout (3 or 4) in each group shall be white in color.
(c)
High temperature condition - any readout with a value of 5 or above. All readouts 5 and above will have the numeral and it's surrounding box white in color.
(5)
Refer to 31-41-00 description and operation for information on the internal logic and function of EICAS.
3. Operation_________
A. Functional Description (Fig. 3)
(1) The system is operational when 28 vdc from the left DC bus is supplied to the monitor unit through the BRAKE TEMP circuit breaker on the flight compartment P11 panel.
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