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.
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
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active el ...
(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
), and without which causes the two cores to
short
Short may refer to:
Places
* Short (crater), a lunar impact crater on the near side of the Moon
* Short, Mississippi, an unincorporated community
* Short, Oklahoma, a census-designated place
People
* Short (surname)
* List of people known as ...
. This can be seen as a change in
resistance
Resistance may refer to:
Arts, entertainment, and media Comics
* Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm:
** ''Resistance'' (comics), based on the video game of the same title
** ''T ...
in the wire.
There are a limited states the LHD cable can be in:
# Open-circuit - effectively an infinite resistance
# Normal operating condition - apparent resistance will be the same as the end-of-line resistor
# Fire detection - resistance of the linear heat cable to the short circuit
See also
*
Automatic fire suppression
*
Distributed temperature sensing Distributed temperature sensing systems (DTS) are optoelectronic devices which measure temperatures by means of optical fibres functioning as linear sensors. Temperatures are recorded along the optical sensor cable, thus not at points, but as a cont ...
for linear heat detection using optical fibers
*
Fire alarm
References
{{Reflist
Active fire protection
Safety equipment
Fire detection and alarm
Detectors