There are multiple reasons for a Beam of any kind to false alarm and the types of reasons are listed below. The 3 LED version of the F5000 Controller has an Event Log which can be used for fault finding. At present, this is the only FFE with an Event Log.
Dust/Mist: As a rough rule of thumb if your eye can see something, the Beam can too. So, a site which has a lot of dust up in the roof space where the Beams are can trigger false alarms. Similarly, if the site is not sealed for the outside world, mist can form in the roof space and trigger a false alarm. To a Beam, both dust and mist will appear as smoke as they attenuate (reduce) the Beams signal.
Condensation: Any moisture which forms on the lens of the Reflectors of a Beam can cause the Beam’s signal to drop below the Fire Threshold and cause an alarm. Since the moisture can evaporate quickly, this type of False Alarm can be hard to detect. I will usually occur at colder times of the year and hot during the warmer months. FFE make heaters for Detectors and Reflectors, but these may need an extra power supply.
Building Movement: Ideally, you should always use a solid surface to mount a Beam on. If the surface moves, then it is not suitable for a Beam. If it holds the building up, brickwork, steels in the roof space, it is good to use. Remember – the longer then Beams run, the more important the solid surface becomes. Over 100m, 1 degree of movement at one end is nearly 2m at the opposite end of the building. If you have a brick wall and a plaster board wall, always put the Detector or Transmitter on the Brick wall and the Reflector or Receiver on the plaster board wall. This is because both the Reflector and Receiver can tolerate move movement before it affects the Beam’s signal than the Detector or Transmitter.
Obstructions: Anything that can block the path of a Beam can cause a False Alarm. This can be people, a temporary structure or most commonly, a pallet on the top of a rack. Again, a pallet blocking a Beam can be removed before the Fire Alarm Engineer has seen it and this can lead to confusion about the cause of the alarm.
Sunlight: The older Beam designs are False Alarmed by sunlight shining directly onto either the Detector or Receiver. Sunlight passing through the Beam is not a problem. Thought needs to be given when using Beams in areas with lots of glass as reflected sunlight can also False Alarm older designs. Newer Beams have LCT (Light Cancellation Technology) which will not False Alarm because of the sun.
Poor Manual Alignment: If a Beam is manually aligned, the skill of the Engineer setting the Beam up will have a crucial impact on the long-term performance. A poorly aligned Beam may not go wrong for a few weeks of months, but this combined with a not so solid mounting can end up with the Beam False Alarming. So, with a manually aligned Beam, the Engineer needs to follow the manual and or watch the training video to get the best possible Alignment of the Beam.