Meggitt Safety Systems - smart engineering for extreme environments

Thermistors

Meggitt's fire/overheat detection sensor is a 0.070 inch diameter semiconductor cable with a flexible and rugged double metal sheathing, allowing any configuration down to a 1/2 inch bend radius.

The Fire/Overheat Detection Cable has a negative temperature coefficient. As the ambient temperature increases, the cable resistance decreases. When the resistance of the cable drops to the predetermined value (typically 100 ohms), whether from a fire or from an overheat condition, the control unit will activate either a light or aural alarm in the cockpit. A fire condition is defined as a short section (1 foot) of cable heated to a high temperature. An overheat condition is defined as the entire cable length heated to a temperature which is higher than ambient, but lower than the fire alarm temperature.

The sensor is installed in a loop configuration with both ends connected to the control unit, allowing a severed sensor cable to provide undegraded protection.

Features:

Low cost
Light weight
Simple design
High reliability - selected for many high performance military and civil aircraft
Easily survives repeated flame and mechanical stress
Fast response rate of less than five seconds under fire condition
TSO-C11d and TSO-C11e certified
MIL-C-7872C Qualified