11.8 Flashcards
(38 cards)
What’s necessary for a fire to occur
Oxygen heat fuel
What should detectors not do
Automatically operate fire extinguishers in flight
What happens when overheat warning is detected
Illuminates amber master caution light and audible alarm
Where are overhear warnings used
Engine turbine areas
Nacelles
Wheel well areas
Hot pneumatic manifolds
When do thermal switch circuits complete
Once electrical circuit reaches a certain temperature
How are thermal switches connected
In parallel with eachother but series with the indicators
How does a raise in temperature cause a switch to produce a overheat condition
Once a certain temperature is reached it causes the switch to close which completes the circuit
What principle does thermocouple work on
The rate of temperature change
What’s a thermocouple constructed of
Two dissimilar metals such as chromel and constantan
What is a hot junction
Point 2 dissimilar metals join and exposed to the heat of fire
What resistance does a thermocouple not exceed
5 ohms
Advantage of continuous loop
More coverage of a fire hazard area
Two types of continuous loop systems
Thermistor type and pneumatic pressure
Thermistor type manufacturers
Kidde Fenwal
Pneumatic pressure sensor manufacture
Linberg & meggitt
How does Fenwal system work
Temperature cause resistance to drop with allows current to flow into control unit to produce a signal to output relay
Filling compounds of Fenwal
Ceramic beads impregnated with eutectux slats
Aluminium oxide suspended in fibrous glass
How is the kiddie system constructed
Two wires embedded in an inconel tube filled with thermistor core material
How does the kiddie system detect fire
As the temperate increases the electrical resistance decreases
How does the kiddie system detect fire
As the temperate increases the electrical resistance decreases
How are continuous loop systems tested
Test switch in flight deck
Principe of dual loop system
Both loops must signal in order to generate a fire warning
What’s the logic of a dual loop system and what’s the advantage
‘ AND logic ‘
Advantage is that less change of false fire warnings
Principle of pneumatic continuous loop
Gas expanding due to the application of heat
