Interturbine Temperature Sensing System; Interturbine Temperature Indicators - De Havilland DASH8 100 Series Maintenance Manual

**ON A/C ALL
INTERTURBINE TEMPERATURE INDICATING SYSTEM − DESCRIPTION AND OPERATION
1. General
Refer to Figure 1.
The interturbine temperature (ITT) indicating system provides visual indication of operating
temperature in the interturbine zone between the low pressure turbine rotor and the first stage
of the power turbine rotor. For location and details of the interturbine zone refer to the Engine
Maintenance Manual.
The indicating system consists of an interturbine subsystem supplied with each engine and
two turbine temperature indicators located on the engine instrument panel, in the flight
compartment. The temperature sensing components of the subsystem for each engine and its
corresponding indicator are joined by chromel (positive) and alumel (negative) leads, between
the indicators and thermocouple harness terminals on the associated engine. For location of
T6 sensor junction block, see ENGINE INDICATING − GENERAL, Figure 2.
2. Description and Operation
A.

Interturbine Temperature Sensing System

The interturbine (ITT) temperature (T6) sensing system consists of parallel−connected
chromel/alumel thermocouples, the output of which is a millivolt signal proportional to the
average temperature sensed in the interturbine zone. For details of the temperature
sensing system, refer to the Engine Maintenance Manual.
B.

Interturbine Temperature Indicators

The interturbine temperature indicators are powered from the 28 V dc essential buses,
engine No. 1 indicator from the left bus, protected by the ENG 1 ITT IND circuit breaker
(F5) and engine No. 2 from the right bus, protected by the ENG 2 ITT IND circuit breaker
(F5).
Indicator lighting is white powered from the 5 V dc lighting system (refer to Chapter 33).
The indicators each receive a millivolt signal, proportional to temperature (T6) from the
corresponding interturbine sensing system. Circuits in the indicators compute the signals
to provide temperature readings and a 0 to 5 V dc output signal proportional to T6
temperatures to the flight data recorder (refer to Chapter 31). The temperature readings
are obtained by an indicator driven pointer against a fixed dial and an equivalent digital
display.
The indicator fixed dial is marked ITT degrees C × 100 and the scale is graduated in
major graduations in increments of 100 degrees C, between 0 and 1200 degrees C, with
minor graduations in increments of 50 degrees C.
The scale is provided with a green arc 350 to 785 degrees C, a red radial at 785 degrees
C, a yellow arc 785 to 816 degrees C, a dashed red radial at 816 degrees C and a red
triangle at 950 degrees C.
The digital display is of the 4−digit liquid crystal display (LCD) type. Pre mod 8−1/1101
aircraft incorporate a heater associated with LCD operation, located one in each
indicator, powered from the 28 V dc secondary buses; engine No. 1 indicator heater from
the left bus (S2), and engine No. 2 indicator heater from the right bus (A1) (refer to
ENGINE INDICATING − GENERAL).
An overtemperature lamp in each indicator is operated by a switch, which is calibrated to
operate and turn on the lamp when interturbine temperature sensed by the indicator
MASTER
EFFECTIVITY: See Pageblock 77−20−00 page 1
D
S ERIES 100
AIRCRAFT MAINTENANCE MANUAL
77−20−00
Dec 20/2004
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