E. Lockwire universal bolts.
F. Connect electrical connector at receptacle on aft end of switch.
G. During next engine operation, check that switch operates normally.
4. Restore Airplane to Normal Configuration
A. Close Sec 2 and Sec 5 circuit breakers on panel P6.
B. Close engine left cowl panel.
H31460
Low Oil Pressure Switch Installation 540
79-33-11Page 402 Figure 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Aug 15/80
OIL TEMPERATURE INDICATING SYSTEM - DESCRIPTION AND OPERATION
1. General
A. The oil temperature indicating system provides an indication in the control cabin of the oil temperature in each engine. The overall system consists of two oil temperature indicators and two oil temperature sensing bulbs. (See figure 1.)
B. Each oil temperature bulb contains a resistance element which varies its resistance proportionally to changes in temperature. This resistance element controls the current passing through the meter movement in the oil temperature indicator. Electrical power for system operation is 28 volt, 400-cycle ac.
2. Oil Temperature Bulb
A. The oil temperature bulb comprises an enclosed resistance unit whose value changes from approximately 68 ohms at -70oC to 242 ohms at +300oC. The bulb screws into a fitting at the outlet of the fuel/oil cooler. The temperature sensing part of the bulb is in direct contact with the oil flow leaving the cooler.
3. Oil Temperature Indicator
A. The oil temperature indicator is a resistance ratiometer type unit. The indicator is operated by the ratio of currents through two coils in the meter movement. The indicator dial is calibrated in degrees centigrade and reads from -70oC to +150oC. With power off, the dial pointer remains off scale at the low temperature end. Electrical connections are made to the indicator through a quick disconnect plug.
4. Operation
A. The oil temperature indicator and the temperature sensing bulb are electrically connected to form the temperature indicating circuit. The temperature sensing bulb is electrically connected to a deflection coil in the indicator. Since the temperature bulb contacts the engine oil, it will assume the same temperature as the oil, and thus the resistance of the bulb is proportional to oil temperature. Resistance of the bulb controls the current flowing through the indicator deflection coil, and therefore controls the angular position of the pointer.
500
Apr 15/66 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 79-34-0 Page 1
H29455
Oil Temperature Indicating System 500
79-34-0 Figure 1 Apr 15/66
Page 2
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
OIL TEMPERATURE INDICATING SYSTEM - TROUBLE SHOOTING OIL TEMPERATURE INDICATING SYSTEM - ADJUSTMENT/TEST
TROUBLE PROBABLE CAUSE ISOLATION PROCEDURE REMEDY
Indicator reads low Indicator reads high Indicator point-er remains at top of scale Indicator pointer remains at bottom of scale Indicator fluctuates or is erratic Indicator out of tolerance Defective temperature sensing bulb Indicator out of tolerance Defective Temperature Sensing bulb Open circuit in temperature Bulb Short circuit in indicatorNo power supplied to system Short circuit in temperature bulb Open circuit in indicatorNo power supplied to indicator Engine ground stud self-locking nut improperly tightened Defective engine ground Perform Oil Temperature Indicator Test, 79-34-11. (Substitution of test indicator) Perform Oil Temperature Indicator Test, 79-34-11. (Substitution of test indicator) Check that engine oil temperature and pressure indicator circuit breaker on P6 panel is closed and external power is connected Check continuity of wiring between indicator, temperature bulb and power supply Check self-locking nut for proper tightness Check resistance of indi-cating system electrical ground on engine. Ground resistance should not ex-ceed .001 ohm Replace indicator Replace bulb Replace indicator Replace bulb Replace temper-ature bulb Replace indicator Close circuit breaker and connect external power Replace temperature bulb Replace indicator Repair defective wiring Tighten self-locking nut Clean ground stud, terminal lug and bond area
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