TM 55-1520-240-23-7
8-1
ENGINE INSTRUMENTS
(Continued)
8-1
POWER TURBINE INLET TEMPERATURE AND
CONTINGENCY POWER INDICATING SYSTEM WITH
74
Description
Except for component locations, the power turbine inlet
temperature (PTIT) and contingency power indicating
circuits are the same for both engines. The PTIT system
uses ten T4.5 thermocouples and a harness to measure
the temperature at the inlet to each engine power
turbine section. The power turbine inlet temperature
signal is sent to the digital electronic control unit
(DECU). An output signal is sent from the DECU to the
PTIT indicators on the center instrument panel. The
indicators are hermetically sealed and powered by 28
vdc. The indicator has a high impedance so that the
wiring harness resistance does not have an effect on
the indication of the PTIT.
NO BREAK - WORK HARDER
The contingency power indicating system is operated
from the PTIT indicators. When the power turbine inlet
reaches a temperature of greater than 894ºC on either
engine, a switched ground circuit is completed at the
indicator. This causes the amber ENG CONT PWR light
on the Master Caution Panel to come on. When the
PTIT drops below the contingency level, the ENG CONT
PWR light goes out.
NO BREAK - WORK HARDER
Ten T4.5 thermocouple probes are mounted in tubes
around the power turbine nozzle. The probes extend
into the gas stream between the vanes of the third
turbine nozzle. The probes are connected to a harness.
Heat at the power turbine inlet causes the probes to
generate a voltage proportional to the heat. The voltage
is sent to the DECU and then to the PTIT indicator. The
indicator displays the temperature on a scale calibrated
0 to 1,200ºC.
8-3
