CSP-HMI-3MD Helicopters, Inc.
MAINTENANCE MANUAL
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95-30-00
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Neither this document nor any part hereof may be reproduced or transferred to
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purpose except as specifically authorized in writing by MD Helicopters, Inc.
Copyright © 1999−2016 by MD Helicopters, Inc.
POWER TRAIN INSTRUMENTS
DESCRIPTION AND OPERATION
1. Power Train Instruments Description and
Operation
Description and Operation for the Power Train
Instruments are as follows:
NOTE: For specific helicopter instrument limit
markings, refer to applicable PFM (RFM)
(Ref. Sec. 01-00-00, Table 201).
2. Tachometer Indicating System (369D/E/FF
− 500N)
(Ref. Figure 401) The N
1
tachometer indicator
indicates speed of the gas producer turbine, in
percent of RPM. The N
2
and rotor tachometer
indicator provides two indications: actual RPM
of the main rotor is indicated on inner scale
with the small (R) pointer; engine power
turbine speed is indicated in percent of RPM
on outer scale with the long pointer.
Three phase, two pole, synchronous tachome
ter generators produce voltages that energize
the power turbine RPM (N
2
), gas producer
turbine RPM (N
1
) and main rotor RPM (N
R
)
indicators. N
2
and N
1
tachometer generators
are on the front of the engine accessories
gearcbox and the N
R
tachometer generator is
near the tail rotor drive output shaft on the
accessory section of the main rotor transmis
sion. Tachometer generators are connected
through individual wiring circuits to indica
tors.
3. Digital N
1
Tachometer Indicator (600N)
The digital N
1
tachometer indicator provides
percent of rpm of the gas producer or centrifu
gal compressor. The four digital LEDs provide
the exact percent of rpm reading. Corrections
occur two times per second. A magnetic speed
sensor, located on the engine accessory gear
case, produces an electrical signal for the
indicator. The system receives 28 Vdc power
from the INSTR circuit breaker located on the
circuit breaker panel. The indicator is an
internally lighted instrument. A red LED light
in the center of the indicator illuminates when
rpm is less than 55% N
1
and greater than
105% N
1
.
4. N
2
/N
R
Dual Tachometer Indicator (600N)
The N
2
/N
R
tachometer indicator is a dual
gauge instrument. The N
2
, long needle,
pointer provides power turbine speed informa
tion measured in percent of rpm, while the N
R
indicator, short needle, provides exact main
rotor speed rpm. A magnetic speed sensor
located on the engine accessory gear case
produces an electrical signal for the N
2
indicator. A separate rotor speed sensor,
located on the main transmission, produces an
electrical signal for the N
R
rpm
.
The indicator
receives 28 Vdc power from the INSTR circuit
breaker located on the circuit breaker panel.
The indicator is internally lighted.
5. N
R
/N
P
Dual Tachometer Indicator (600N)
The N
R
/N
P
tachometer indicator is a dual
gauge instrument. The N
R
indicator, long
needle, provides exact main rotor speed rpm,
while the N
P
, short needle, pointer provides
power turbine speed information measured in
percent of rpm. A magnetic speed sensor
located on the engine accessory gear case
produces an electrical signal for the N
P
indicator. A separate rotor speed sensor,
located on the main transmission, produces an
electrical signal for the N
R
rpm
.
The indicator
receives 28 Vdc power from the INSTR circuit
breaker located on the circuit breaker panel.
The indicator is internally lighted.
6. TOT Indicating System (369D/E/FF −
500N)
(Ref. Figure 403) The TOT indicator indicates
temperature of gases moving from the engine
gas producer turbine to the power turbine. The
indicator is calibrated in major units from 0 -
12; reading is in degrees centigrade times one
hundred (0
° - 1200°C). The indicator is
energized by electrical power generated by an
8 ohm thermocouple harness mounted on the
engine.
7. Analog/Digital Torque Indicator (600N)
The analog/digital torque indicator is driven
by an oil pressure transducer. The transducer
contains a pressure diaphragm and a strain
gauge bridge. As pressure on the diaphragm is
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