7.8 Flashcards
detectors should not automatically do what in flight?
should not automatically operate fire extinguishers
where are detector units installed?
locations or zones where there is a grater risk of fire
what are the most common fire detection systems?
thermal switches, thermocouples, continuous loop sensing elements
what do most modern aircraft use for fire detection systems?
continuous loop
what are thermal switches sensitive to?
heat
what happens when temp reaches a certain temperature in a thermal switch system?
the thermal switch closes to completing a light circuit indicating fire or overheat condition
all thermal detectors tend to be connected to what?
one light, may be a thermal switch for each indicator
how is the bulb tested on a thermal switch system?
by pushing it in to cheek auxiliary test circuit
what do some waring lights have?
push to test switch
what does a thermocouple system depend on?
rate of temp change
what does thermocouple not give a waring for?
when engine slowly overheats or when short circuit develops
what does a thermocouple system consist of?
relay box, warning lights and thermocouples
the wiring systems of units are divided in to what circuits?
detector circuit, alarm circuit, test circuit
what is a hot junction on a thermocouple system?
when the metals are joined and expose to heat of a fire
what does number of thermocouple circuit depend on?
size of fire zone and total circuit resistance
when pressing test switch on a thermocouple system what does it pass through?
a heater around the thermocouple
must large commercial aircraft use what for fire/overheat systems?
continuous loop systems
what are continuous loop systems used for?
power plant, pneumatic manifolds and wheel well protection
what are the widely used types of continuous loop systems?
thermistor type detectors (kindle and fenwell systems) and pneumatic pressure detectors
what tube does farewell systems use?
Inconel witch contains thermally sensitive eutectic salt
in frenwell systems where are they operated from?
a control unit
what is the current flow detected by?
the control unit witch produces a signal to output relay and activate the alarms
how does the frenwal system return to stan by?
automatically ready to detect any fire or overheat conditions
what are the two different filing compounds in frenwal and what are the differences?
ceramic beads and are impregnated with eutectic salts ad melting point is low and resistance decrease when hot, aluminum oxide suspended in fiber glass resistance lowers with heat
