Hi-Endurance Switching, Sensing
& Linear Position Sensors

Aircraft Fire Detection

The X2003 thermal switch belongs to a class of stand alone Rod & Tube style, bi-metal Thermal Switch products where contact movement is achieved via differences in the coefficients of expansion of two materials, in this case the outer tube and the inner rod. This family of switches is characterized by very rapid response time and very high temperature sensing.which operate completely independently of any external control system. The switch has seen many deployments in aircraft over the years, where remote sensors and control systems are not a good or reliable option.

These thermal switches can be procured in multiple rod lengths and multiple contact configurations. They have been used in helicopter engine exhaust, plastics extrusion, aircraft brake applications, among many other demanding applications for the industrial, aerospace, and military industries.

Thermal Switch Uses in Modern Aircrafts

All modern aircraft employ a number of thermal sensing elements for various systems. So called Spot Fire Detection Systems refer to systems where overheat conditions are monitored at a specific point in a compartment or LRU bay.  In order to receive FAA approval, these systems must demonstrate superior detection performance and have the proven ruggedness to survive in the harsh thermal and vibrational environment of modern aircraft.

Typical zones on aircraft that employ spot fire detection include:

  1. Auxiliary power unit (APU)
  2. Engine compartments
  3. Cargo and baggage compartments
  4. Lavatories on transport aircraft
  5. Electronic bays
  6. Wheel wells

Several detectors, or sensing devices, are available to solve these detection challenges, encompassing a number of different technologies. Many modern aircraft have some type of thermal switch system or thermocouple system. A thermal switch system has one or more indicator lights or audible alarms that trip when a thermal limit is reached.

Thermal Switch Fire Detection Circuit

They are sometimes connected in parallel with each other but in series with the indicator lights. If the temperature rises above a set value in any one section of the circuit, the thermal switch closes, completing the light circuit to indicate a fire or overheat condition. No set number of thermal switches is required; the exact number is usually determined by the aircraft manufacturer. On some installations, all the thermal detectors are connected to one light; on others, there may be one thermal switch for each indicator light.