Understanding Beam Detectors
How do optical beam detectors work?
Optical beam detectors work on the principle of light obscuration.
This means that it works by measuring how much beam light is being obscured by other particles blocking the beam path.
A transmitter sends out an infra-red beam of light to a receiver, which determines the amount of IR light received.
When there is an obstruction from flame or smoke particles, the amount of IR light received should be less. This will indicate that a fire is present.
There are two types of beam detector; projected and reflected.
Where can an optical beam detector be used?
Beam detectors are designed to provide large area detection for a minimal cost. They’re often used in situations where it’s inefficient or inappropriate to install a wired unit.
The standard beam detector has a range of 100m with a 15m coverage area. This keeps a 1500m2 area covered. Plus, they’re suitable for installation in heights well above the operational limits of standard detectors.
Typically, you might find them in museums, large warehouses, factories and similar environments.
What is a projected (end to end) beam detector?
With projected (end to end) beam smoke detectors, the transmitter and receiver face each other from opposite ends of the protected area. The beam travels directly from the transmitter to the receiver.
What is a reflected (single ended) beam detector?
With reflected beam detectors, the transmitter and receiver are contained together in one unit, called a transceiver. This unit is at one end of the protected area, sending beams to a reflectors prism which is at the other end. The reflector prism will send the beam back to the transceiver.
Which is better, reflected or projected?
Reflected flame beam detectors (single ended) are easier to install because the reflector prism will reflect beams coming from various angles. However, this does mean that they can be affected by obstructions or by stray reflections from nearby objects.
Projected (end to end) beam detectors don’t have this problem as there is no reflector. This means they’re suitable for installation in smaller, narrower areas with potential nearby obstructions. However, they are harder to install as the transmitter and receiver need to be exactly perpendicular.
The benefits of auto-alignments
Many beam detectors will advertise an auto-alignment or compensation facility. It basically means that after installation, if the building or beam that the unit is mounted on moves, the sensor will realign itself.
This is a feature to look out for as any building movements could affect the functioning of your detector or make you susceptible to false alarms.
The benefits of drift compensation
This is where a detector monitors signal degradation caused by build ups of dust and dirt. The detector will compensate for this to ensure the sensitivity level remains stable.
This is another benefit to look out for.
This is the maximum distance between the transmitter and receiver (end to end) or transceiver and reflector (single ended).
The transmitter is the part of the detector that emits the light beam.
This is part of the detector that receives the beam of light, and measures for obscuration.
This is the amount by which a beam is obscured by other particles.
This is the level of obscuration that will lead to the detector being activated.