G02020
APU Tachometer Generator Installation 540
49-61-61Page 402 Figure 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Feb 01/74
5. Restore Airplane to Normal
A. Position lower shroud against upper shroud and close shroud latches.
CAUTION: MAINTAIN A MINIMUM CLEARANCE OF 0.18 INCH BETWEEN ENGINE PLUMBING, FIRE DETECTOR, CLAMPS AND INSIDE SURFACE OF LOWER SHROUD.
EXERCISE EXTREME CARE NOT TO DAMAGE SHROUD DRAIN LINES WHEN HANDLING SHROUD.
B. Disengage APU compartment access door support rods and stow rods. Close and latch access door.
C. Close the circuit breaker on M280 module-APU accessory unit on E3-3 electronic shelf.
D. Position BATTERY SWITCH to ON and remove placards.
E. Operate APU to check tachometer generator (Ref 49-11-0, Maintenance Practices).
540
Jan 20/83 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-61-61 Page 403
INDICATING - DESCRIPTION AND OPERATION
1. General
A. The APU exhaust gas temperature (EGT) indicating system and the APU indicating system comprise the APU indicating. The APU EGT indicating system provides means of monitoring the turbine EGT on an indicator in the control cabin. The APU indicating system provide means for monitoring the engine overspeed and the elapsed time of the engine operation. The overspeed light is located on the forward overhead panel. The elapsed time indicator is located on the APU engine. For detail description of the APU indicating, refer to 49-71-0, APU Exhaust Gas Temperature Indicating System and 49-72-0, APU Indicating System.
500
May 15/67 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-70-0 Page 1
APU EXHAUST GAS TEMPERATURE INDICATING SYSTEM -
DESCRIPTION AND OPERATION
1. General
A. The APU exhaust gas temperature (EGT) indicating system measures the APU engine EGT and displays the temperature value on an indicator in the control cabin. The system consists of a temperature sensing probe, system balancing resistor, harness balancing resistor, and an exhaust gas temperature indicator (Fig. 1). Copper and constantan wires are used in the airplane wiring; chromel and alumel wires are used inside the APU shroud where higher temperatures are encountered.
B. Engine EGT is sensed by the thermocouple probe. The heat of the exhaust gases causes the thermocouple to generate dc electrical signals which actuate the meter movement of the EGT indicator. The balancing resistor is included in the circuit to provide a means of adjusting the system.
2. Exhaust Gas Temperature Thermocouple Probe
A. The thermocouple probe is a temperature sensing device, mounted on the turbine exhaust flange, that senses the temperature of the engine exhaust gases. It consists of two stud terminals, a head, and a thermocouple measuring junction and leads enclosed in a cylindrical shield (Fig. 1). The thermocouple junction leads and studs are made of chromel and alumel material. The alumel stud terminal (-) is larger than the chromel stud terminal (+).
3. Exhaust Gas Temperature System Balancing Resistor
A. The EGT system balancing resistor permits adjustment of the system circuit resistance. The resistor consists of a spool of No. 24 constantan wire, coarse adjustment terminals and vernier adjustment terminals. Since primary adjustment of the resistance is made by cutting off lengths of the wire, a spare resistance spool is included. The resistor is located on the control cabin structure directly under the right No. 3 window (Fig. 1). The total circuit resistance is 13.5 ohms excluding the engine harness, EGT thermocouple probe, and the EGT indicator.
4. Harness Balancing Resistor
A. The harness balancing resistor is matched to the individual engine during final test. Do not replace with any other resistance value.
500
Feb 20/91 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-71-0 Page 1
G02030
APU EGT Indicating System Component Location 500
49-71-0 Figure 1 (Sheet 1) Feb 15/73
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
540 APU EGT Indicating System Component Location
Feb 20/91 Figure 1 (Sheet 2) 49-71-0
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