The Pneumatic Continuous Loop Fire Wire from Advanced Aircraft Extinguishers, Ltd is a continuous length, temperature sensitive, pneumatic device operating on gas law principles (pressure increases with a rise in temperature).
When the ambient temperature of the sensors entire environment increases (Overheat), or a short section of the sensor is exposed to a high intensity flame (Fire), internal pressure within the tube and responder increases in proportion to the increase in temperature. When the pressure increases to the set value, the alarm switch inside the responder closes and sends an alarm to the aircraft alarm system.
Subsequent to an alarm, if the temperature decreases, the internal gas pressure will also decrease and the alarm switch inside the responder will close. The discrete “fire” condition causes a rapid release of gas from the sensors core material in the tubing, which in turn causes a rapid increase in the internal pressure.
A second pressure sensitive switch (integrity) in the responder housing is kept closed by the helium gas pressure in the sensor tube. Leakage of this gas and the subsequent pressure decrease will cause the integrity switch to open, signaling a malfunction.