1) Power for the PMC connector J2 is supplied by the N2 control alternator speed sensor on the accessory gearbox. AC voltage is supplied to the PMC through an internal variable reactor which serves as a coarse DC regulator. A solid-state fine regulator then supplies the constant DC reference voltage for all internal computation.
(b)
Throttle Scheduling
1) The basic flat-rated N1 fan speed demand signal is computed as a scheduled function of sensed power lever angle (PLA). The PMC provides excitation to and signal demodulation of a rotor position transducer in the MEC.
(c)
Altitude Compensation
1) The corrected N1 fan speed set by the power lever position is adjusted as a function of sensed PS12 pressure to give the required altitude bias. The PMC has a self-contained pressure transducer which is supplied from the PS12 manifold from the fan inlet.
(d)
Speed Correction
1) Physical N1 fan speed is sensed from a sawtoothed wheel in the forward sump (immediately in front of the No. 2 bearing) and combined in the PMC with a function of sensed T12 to provide a signal proportional to corrected N1 fan speed. The T12 sensor is a resistance element installed at the fan inlet. This corrected fan (LP rotor) speed is compared to the computed demand speed and torque motor current adjusted to null the error. Input signals for fan speed (N1), T12 and power demand (PLA) and output signal for the torque motor are transmitted through connector J3.
(e)
Temperature Limiting
1) When T12 temperatures are beyond the flat-rated point, the demand corrected speed is reduced to give a calculated maximum gas temperature. The computed demand speed from thrust schedule and altitude bias, PS12, is compared to a computed T12 function and the minimum demand speed selected for use in the torque motor amplifier.
(f)
Deactivation
1) The PMC ON switch controls the PMC through connector J4 and can be used to deactivate the PMC utilizing the torque motor override signal to the MEC. All functions of the PMC stay energized and active except for the output current to the MEC torque motor.
2) During normal operation, the PMC ON switch is white. With the PMC ON switch depressed to deactivate the PMC, the switch light extinguishes and the amber PMC INOP light illuminates along with the MASTER CAUTION and FUEL annunciator lights on the light shield.
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73-21-00
ALL ú ú C02 Page 30 ú Nov 12/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / /
CFM56 ENGINES
737-300/400/500/ /MAINTENANCE MANUAL ////////////////////////
(g) Sensor or Control Failure
1) A contact closure is provided at J4 that automatically closes if a failure occurs in the control or in a sensor used by the control. This closure will remain until the fault is cleared and manual disable is reset.
2) In the event of a failure, the PMC INOP light, MASTER CAUTION lights and ENG annunciator light will illuminate with the PMC ON switch remaining illuminated.
(h) Monitor 1) A monitor connection, J5, is given for testing of the PMC.
D. AIRPLANES WITH THE INDICATION CIRCUIT FOR THE 45% N1 ENGINE IDLE; Engine Idle Control System (Fig. 11)
(1)
Power for the engine idle control circuit is provided by the IDLE CONT and MASTER CAUTION circuit breakers located on the P6-2 circuit breaker panel (WDM 73-23-11). The indication system monitors engine fan speed (N1), thrust lever angle (TLA), start lever position and the state of the idle reset solenoids.
(2)
The Eng Idle Ind circuit breaker supplies power to the engine idle indication relays (WDM 73-23-12). The indication circuit also monitors engine start switch position, engine core speed (N2) and radio altitude.
(3)
The LOW IDLE light is illuminated in these cases:
(a)
Start lever is set to IDLE and respective engine speed (N1) is less than 25%
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