Linear heat detection
| Typical Detecting Temperature | 68°C[1] (building) | 180°C (plant) |
|---|---|---|
| Maximum Length | 3000m[1][2] |
Linear Heat Detection (LHD) (also known as Linear Detection Wire or Linear Heat) is a very commonly used method of fire detection. It can detect a fire any where 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 (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:
- Open-circuit - Effectively an infinite resistance
- Normal Operating Condition - Apparent resistance will be the same as the end-of-line resistor
- Fire Detection - zero resistance (0Ω)
Advantages and Disadvantages
Advantages
- Simple in construction
- Controller complexity is low
- Easily deployed
- Can cover a large area
- Small and Compact
- Supported by the majority of fire controller panels
Disadvantages
- Very slow response time - up to 30 seconds
- Lack of information about fire
See also
- ^ a b c "Linear Heat Detection cable information" (PDF). Retrieved 26 April 2014.
- ^ "Safe Fire Detection, LHD Information". Safe Fire Detection. Retrieved 26 April 2014.