AIRPLANES WITH THE HARNESS BALANCING RESISTOR AIRPLANES WITHOUT THE HARNESS BALANCING RESISTOR
APU EGT Indicating System Schematic Figure 2
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITHOUT THE ETC ú
49-71-00
ú CONFIG 1 ú 01 Page 6 ú Mar 15/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
EXHAUST GAS TEMPERATURE INDICATING SYSTEM - DESCRIPTION AND OPERATION
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1. General (Fig. 1)
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A. The EGT indicating system measures the temperature of the APU engine exhaust. This temperature is shown on the EGT indicator on the P5 forward overhead panel. The EGT indicating system has two ETC thermocouple probes, an EGT resistor, and an EGT indicator. The airplane wires are copper and constantan. The wires in the APU shroud are chromel and alumel because of the high temperatures.
B. The two ETC thermocouple probes measure the EGT of the APU engine. The heat of the exhaust gases makes the ETC thermocouple probes send dc signals to the ETC. The ETC sends a signal to the EGT indicator, on the P5 forward overhead panel, to show the correct temperature. The EGT resistor is part of the circuit. The EGT resistor adjusts the EGT indicating system.
C. The electronic temperature control (ETC) is part of the circuit between the two ETC thermocouple probes and the EGT indicator. The ETC is not a part of the EGT indicating system. For a more detailed description of the ETC, refer to AMM 49-61-00/001.
2. ETC Thermocouple Probe
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A. The two ETC thermocouple probes measure the temperature of the exhaust gases from the APU engine. The ETC thermocouple probes are installed in the turbine exhaust port. The two ETC thermcouple probes have four stud terminals and four measurement junctions. The thermocouple leads and studs are made of chromel and alumel materials.
3. EGT Resistor
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A. The EGT resistor permits the adjustment of the circuit for the EGT indicating system. The EGT resistor has a spool of No. 24 constantan wire, coarse adjustment terminals, and vernier adjustment terminals. The primary adjustment for the resistance removes wire from the resistance spool. Because of this, the EGT resistor has an extra spool of wire. The EGT indicator is found in the control cabin directly below the right No. 3 window. The total resistance is 13.5 ohms without the EGT indicator, ETC thermocouple probes and APU engine harness.
4. EGT Indicator
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A. The EGT indicator is a millivoltmeter in a hermetically sealed case. The EGT indicator has an electrical plug on the rear side. The electrical plug connects the EGT indicator to the circuit for the EGT indicating system. The dial of the EGT indicator shows temperatures from 0 to 850°C. There are color bands to show the usual and dangerous temperature ranges.
5. Operation (Fig. 2)
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A. The EGT indicating system has the two ETC thermocouple probes connected to the EGT indicator on the P5 forward overhead panel. The airplane electrical system supplies the power for the EGT indicating system.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH THE ETC ú
49-71-00
ú CONFIG 2 ú 01 Page 1 ú Jul 15/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FORWARD OVERHEAD PANEL, P5
SEE B
SEE A
FLIGHT COMPARTMENT
100 15050 200 AC AMPERES AVAILABLE GRD POWER GRD OFF PWR 100 15050 200 AC AMPERES
ON
OFF BUS BUS OFF TRANSFER F F O BUS TRANS O T U A OFF BUS BUS OFF TRANSFER
RESISTOR EGT BUS OFF GEN OFF OFF BUS APU GEN GEN OFF OFF BUS
GEN 1 ON APU APU GEN ON GEN 2
1 PRESSURE LOW OIL 2 SPEED OVER
A FWD INDICATOR EGT 6 C X 100 EXH 8 7 5 4 3 2 0 1 TEMP 100 50 150 AC AMPERES 200
1 OR "MAINT" LIGHT "LOW OIL QUANTITY" LIGHT FORWARD OVERHEAD PANEL, P5
2 "HIGH OIL TEMP" LIGHT OR "FAULT" LIGHT B
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