Linear heat detection


Linear heat detection is a very commonly used method of fire detection. It can detect a fire anywhere along the length of the cable, and can be of lengths in excess of a kilometer.
Applications can range from building fire alarm systems to mobile plant machinery.

Operation

Linear heat detection cable is essentially a two-core cable terminated by an end-of-line resistor. The two cores are separated by a polymer plastic, that is designed to melt at a specific temperature, and without which causes the two cores to short. This can be seen as a change in [Electrical Electrical resistance and conductance|resistance and conductance|resistance] in the wire.
There are a limited states the LHD cable can be in:
  1. Open-circuit - effectively an infinite resistance
  2. Fire detection - resistance of the linear heat cable to the short circuit
  3. Normal operating condition - apparent resistance will be the same as the end-of-line resistor