73-21-00
ALL ú ú C02 Page 5 ú Oct 25/86
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
SEE A
CIT SENSOR SEE B
P6 CIT SENSOR
P6 SHROUD DRAIN
FITTING
PB FITTING
FWD
PB SHROUD DRAIN
A
COIL GUARD
MOUNTING FLANGE
P FITTING
6
HOUSING
P FITTING
B
CIT SENSOR REMOVED
B
Compressor Inlet Temperature Sensor Location
Figure 3
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73-21-00
ALL ú ú C01 Page 6 ú Jun 25/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / /
CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
B. The compressor inlet temperature (CIT) sensor consists of a guarded, constant volume, gas filled coil, and a metering valve which controls or meters fuel across the orifice. The sensor is mounted into a port between the 5 and 6 o'clock struts on the fan frame with the coil projecting into the high pressure compressor (HPC) inlet airstream, just forward of the inlet guide vanes (IGV).
NOTE: Clock positions are to be used when locating items only when
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viewed looking forward.
C. The temperature sensing coil has a constant volume; therefore, the gas pressure inside the coil is proportional to the temperature. The coil is connected to the sensing bellows so that any change in gas pressure within the coil changes the force on the feedback bellows and spring. The feedback bellows force is a result of the fuel pressure inside the bellows which is controlled by the metering valve.
D. When CIT changes, the gas pressure inside the sensing bellows varies, thereby opening or closing the metering valve. The metering valve changes the fuel pressure which alters the force on the feedback bellows, thus balancing the sensing bellows force. The differential fuel pressure, thus, is proportional to the temperature at the sensing coil. This fuel pressure is then used by the MEC as a scheduling parameter.
5. T12 Temperature Sensor (Fig. 4)
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A. The T12 temperature sensor, on the inlet cowl at the 2 o'clock position, senses inlet air temperature which is used as fan-air temperature by the PMC.
6. T2 Temperature Sensor (Fig. 1)
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A. The T2 temperature sensor, on the inlet cowl at the 10 o'clock position, senses inlet air temperature. The T2 sending unit is directly above the accessory gear box (AGB) at the 10 o'clock position. The T2 sending unit provides a hydraulic signal pressure, which is a function of inlet air temperature, to the MEC using fuel as a medium. The MEC uses the hydraulic signal to establish parameters to control low and high idle power schedules.
7. CFMI Wiring Harness (Fig. 5)
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A. The CFMI wiring harness is made up of two cable assemblies: the control parameter wiring harness and the N2 control alternator speed sensor cable. These cables provide power from the N2 control alternator speed sensor to the PMC, provide signal information from the N1 speed sensor, power lever angle (PLA) and T12 temperature information to the PMC, and PMC signals to the MEC torque motor power lever angle.
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