11.8 Flashcards
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
Where are pneumatic continuous loops used
Engine overheat and fire detection
What is a discrete temperate sensor filled with and the range
Hydrogen filled core
1100 degrees C for 5 seconds
Are averaging and discrete functions reversible
Yes both are
What are linberg , Systron-dinner and meggitt systems tubes filled with
Stainless steel tube filled with helium gas and length of titanium wire
What does titanium wire do
Acts as gas absorption material
When must a lavatory smoke detector be used
When 20 or more pax are being carried
What system of fire detection does cargo use
Optical smoke detector which uses leds to monitor photodiodes
How is the lavatory smoke detector powered
28v dc from left/right main DC bus
How do you cancel the smoke indications in the lavatory
Pushing the lavatory call reset switch
What makes the optical smoke detector go off
If the air has smoke , smoke reflect more light on the scatter detector which causes an alarm signal
What is the photoelectric system
Light reflects onto the photocell which decreases the circuits resistance which allows output to the logic test systems
What does the ionisation type smoke detector have on one side of the smoke detection chamber?
An electrode with a very small amount of radioactive material
Radioactive Material
What happens when smoke comes into the chamber of the ionisation type smoke detector?
It affects the amount of ionisation and reduces the current flow between the electrodes
What turns on the warning device in the cockpit when the current flow falls below a pre-set value?
A solid-state sensor
