Beam type smoke detectors are mostly used in places with high ceilings like basketball courts, warehouses, movie theatres etc. Detection with optical smoke detector can be slow in these places. Because smoke has to reach the detector mounted to the ceiling. In EN 54-14 standard, maximum level suitable for optical smoke detectors is 11 meters. However beam type smoke detectors are recommended for places with ceilings higher than 7 meters.
What is the detection principle of beam type smoke detectors?
There are two types of beam detectors: Receiver-transmitter type and reflector type. First type consists of receiver and transmitter unit. In normal state, IR light beams sent from transmitter reach the receiver unit. In case of fire, smoke obstruct the IR light beams and some of light rays can not reach receiver unit. The distance between two units can be between 5-100 meters.
Second type consists of reflector and a unit that works as both receiver and transmitter. In normal state, IR light beams sent from receiver-transmitter unit reflect from reflector and reaches the unit. In case of fire, smoke obstruct the IR light beams and some of light rays can not reach receiver-transmitter unit. If there are 4 reflectors, the distance between reflector and the unit can be between 5-50 meters. If there is 1 reflector, the distance between reflector and the unit can be between 5-35 meters.
What happens if a solid object interrupts IR light beam?
If a solid object interrupts IR light beam instantaneously, nothing will happen. No fire alarm, no fault alarm. However, if a solid object interrupts IR light beam for 6-8 seconds, beam detector will give fault alarm. Beam detector can recognize the difference of smoke and solid object by evaluating the percentage of IR light rays that is blocked.
Sources:
1. Mavili Project Notes
2. EN 54-14 Standards
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