0044-023-01 14.11.08
2
1. System Description.
The Detector comprises a Transmitter and Receiver contained within one enclosure.
The Detector installs to the building fabric between 0.3 and 0.6 metres from the ceiling.
The Transmitter emits an invisible infrared light beam that is reflected via a prism(s) mounted directly opposite
and with a clear line of sight. The reflected infrared light is detected by the Receiver and analysed.
The Detector has maximum lateral detection of 7.5 metres either side of the beam.
2. System Operation.
Smoke in the beam path will reduce the received infrared light proportionally to the density of the smoke. The
Detector analyses this attenuation or obscuration of light and acts accordingly.
Alarm thresholds of 25%, 35%, and 50% can be selected to suit the environment, where 25% is the most
sensitive. If the received infrared signal reduces to below the selected threshold, and is present for
approximately 10 seconds, a Fire condition is activated.
The Detector will continue to show a Fire condition until the panel is reset. If the panel is reset and a Fire
condition is still present, the Detector will return to a Fire condition after 60 seconds.
If the infrared beam is obscured rapidly to a level of 90% or greater for approximately 10 seconds a Fault
condition is activated.
This condition can be entered in a number of ways, for example, an object being placed in the beam path,
transmitter failure, loss of the prism(s), or sudden misalignment of the Detector. The fault condition will reset
within 5 seconds of the condition being rectified.
The Detector monitors long term degradation of signal strength caused by component ageing or build up of dirt
on optical surfaces. This operates by comparing the received infrared signal against a standard every 15
minutes; differences of less than 0.7dB/Hour are corrected automatically.
3. Detector Positioning.
It is important that the Detector is positioned correctly to minimise the detection time.
Experiments have shown that smoke from a fire does not rise directly upwards, but fans out or mushrooms due
to air currents and heat layering effects. The time to signal a fire condition depends on the location of the
Detector within the premises, the volume of smoke produced, construction of the roof, and ventilation
arrangements.
The maximum distance either side of the beam axis is found to be typically 7.5 metres for satisfactory detection
under flat ceilings.
Smoke layering, where smoke does not reach the ceiling level due to layers of static hot air is overcome by
mounting the Detector at the recommended height below the ceiling of between 0.3 and 0.6 metres, bringing
the infrared beam below the heat layer and into the smoke layer.
However, in all installations the latest national fire standards must be consulted. If there is any doubt on the
correct mounting height, positioning may be determined by smoke tests.
Single Beam
15 m 15 m
0.5 ↔7.5 m
Multiple Beams
0.3 ↔0.6 m
0.5 ↔7.5 m
