Linear heat detection

Linear heat detection (LHD) (also known as linear detection wire or linear heat detection cable or linear heat) 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.

Typical detecting temperature 68 °C[1] (building) 180 °C (plant)
Maximum length 3000m[1][2]

Applications can range from building fire alarm systems to mobile plant machinery.

Operation

Linear heat detection (LHD) cable is essentially a two-core cable terminated by an end-of-line resistor (resistance varies with application). The two cores are separated by a polymer plastic, that is designed to melt at a specific temperature (commonly 68 °C for building applications[1]), and without which causes the two cores to short. This can be seen as a change in resistance in the wire.

There are a limited states the LHD cable can be in:

  1. Open-circuit - effectively an infinite resistance
  2. Normal operating condition - apparent resistance will be the same as the end-of-line resistor
  3. Fire detection - resistance of the linear heat cable to the short circuit

See also

References
  1. "Linear Heat Detection cable information" (PDF). Retrieved 26 April 2014.
  2. "Safe Fire Detection, LHD Information". Safe Fire Detection. Retrieved 26 April 2014.
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