**ON A/C ALL
LOW PRESSURE COMPRESSOR ROTOR SPEED (NL) INDICATING SYSTEM −
DESCRIPTION AND OPERATION
1.
General
Refer to Figure 1.
The speed indicating system for the low pressure compressor rotors of both engines consists
of a speed sensor for each engine connected by electrical wiring to a dual indicator which
serves both engines.
2.
Description and Operation
A.
Low Pressure Compressor Rotor Speed (NL) Sensor
A low pressure compressor rotor speed sensor is mounted on, and supplied as part of,
the basic engine. The sensor (magnetic pickup) is located in a boss on the
intercompressor case on the left side of the engine. The output of the sensor is 0 to 9233
Hz signal (0 to 5 volts peak to peak), which is equivalent to 0 to 100% rotor speed. The
signals from both engines are applied as separate inputs to the dual indicator. For details
of the speed sensor, refer to the Engine Maintenance Manual. For location of NL speed
sensor, see ENGINE INDICATING − GENERAL, Figure 2.
B.
NL Dual Indicator
The low pressure compressor rotor speed (NL) indicator for both engines is mounted on
the engine instrument panel in the flight compartment.
The indicator contains separate circuits and indicating mechanisms for engine No. 1 and
engine No. 2, which receive separate inputs from the associated speed sensor. The
circuits are separately powered from the 28 V dc essential buses, circuits for engine No.
1 from the left bus, protected by the ENG 1 NL IND circuit breaker (L5) and circuits for
engine No. 2 from the right bus, protected by the ENG 2 NL IND circuit breaker (H4).
Lighting for the indicator is from the 5 V dc lighting system (refer to Chapter 33).
The indicator circuits compute the ac signal from the associated sensor and provide an
equivalent indication of NL speeds by means of moving pointers against a fixed dial. The
pointers for engines No. 1 and No. 2 are mounted on concentric shafts and identified 1
and 2 by a marking on each pointer.
A 0 to 5 V dc signal proportional to 0 to 100% NL is relayed from each separate circuit to
the flight data recorder (refer to Chapter 31).
The indicator dial is marked NL % RPM and the scale is graduated with major
graduations in increments of 10% NL from 10 to 110% NL with minor graduations of 5%
NL.
The scale is provided with a green arc from 40 to 100% NL.
In the event of indicator power supply failure, the pointer(s) of the affected circuit(s)
move off scale below zero.
D
SERIES 100
AIRCRAFT MAINTENANCE MANUAL
MASTER
EFFECTIVITY: See Pageblock 77−14−00 page 1
77−14−00
Page 1
Dec 20/2004