Ignition System; Instrumentation - BOMBARDIER Challenger 601-3A CL-600-2B16 Pilot Training Manual

Fuel metering is controlled by a torque motor,
operating in response to input signals from
the electronic control unit. Fuel is metered to
the combustor so that the power developed by
the APU is equal to the power required, thereby
maintaining a near constant rpm under vary-
ing load conditions.
(For APU fuel supply see Chapter 5, "Fuel
System.")

IGNITION SYSTEM

The APU incorporates a high-energy ignition
system consisting of an APU-mounted ignition
exciter and a single igniter plug in the com-
bustor chamber. The ignition system is fully
automatic and operates in response to inputs
from the electronic control unit. The ignition
system is activated by the ECU at 10% rpm dur-
ing APU starting and remains operative up to
95% rpm.
A
P
U
BLEED ADPTR PWR FUEL
AIR OIL ON/OFF
LO
FAILED
PRESS CLOSED
HI PUMP
OPEN
TEMP
PUSH PUSH
%RPM
100
80
0
60
20
40
Figure 6-5. APU Control Panel
FOR TRAINING PURPOSES ONLY
FlightSafety Canada
CL-600-2B16 PILOT TRAINING MANUAL

INSTRUMENTATION

APU instrumentation consists of rpm and EGT
indicators (Figure 6-5) located on the APU
control panel on the overhead panel, and an
hourmeter located within the APU enclosure
in the rear fuselage compartment. The rpm
gage is calibrated in percentage of design
100% rpm, from 0% to 110%.
The rpm signal is generated by a monopole sen-
sor installed on the planetary gearbox. The
monopole transmits the rpm signal to the elec-
tronic control unit, which in turn supplies the
RPM indicator.
The EGT indicator is calibrated from 0 to 10
in degrees Celsius times 100. EGT, or exhaust
gas temperature, is sensed by a thermocouple
in the APU exhaust duct. EGT signals are sent
to the electronic control unit, which in turn
supplies the EGT indicator.
The hourmeter is located within the APU en-
closure and controlled by the ECU to record
all APU operating time above 10% rpm.
APU START/
OIL STOP
SOV LO
STARTER
PRESS
HI APU
INOP TEMP READY
PUSH
10 EGT
°C X 100
8
6
2
4
C
O
N
T
R
O
0 L
CL 601-3A/R 6-5
Lt é e
Lt d .