Where to Use Beam Detectors
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Fire detectors are designed to detect one or more fire criteria like smoke, heat, flame, spark, etc. The spot-type smoke detectors sense an alarm when the smoke enters their chamber. However, since smoke travels from bottom to top, it may take a long time for the typical smoke detector to detect the fire if the height of the ceiling is high. In such cases, special detectors are to be used.
As per IS 2189 guidelines, spot-type smoke detectors can be used only up to 10 Mtrs of ceiling height. When the ceiling height exceeds 10 Mtrs, line type detectors like Beam detectors or Aspiration type smoke detectors should be used if the fire hazard is smoky.
There are two basic types of beam detectors, viz., Reflective beam detector and transmitter-receiver type or end to end type, both operate on the principle of light obscuration.
An infrared light beam is projected from transmitter to receiver, and the signal strength will be monitored for smoke. The range of these detectors will be from 50 to 100 Mtr from transmitter to receiver.
Recently there is a new technology in beam detection using imaging technology with a CMOS Imager which uses dual-wavelength for UV and IR particle detection. It supports a long range up to 150 Mtrs.
The transmitter receiver type requires power on both ends. In contrast, in the reflective type detector, only one end is powered as both receiver, and transmitter electronics sit inside the same enclosure. As a result, the reflective mirror reflects the light to the receiver.
The IR beam detector will not respond to changes in environmental conditions such as dust and dirt accumulation on the transmitter and receiver’s optical assemblies. These are compensated for by automatic drift compensation. When the detector is first turned on through the setup program, it assumes the current light signal level as a reference point for a normal condition. The sudden and total obscuration of the light beam is not the typical smoke signature, so crossing a crane or similar objects will not be considered an alarm. Beam detectors require visible smoke to detect alarms.
The Image sensing Beam detector is easier to install and commission and minimize drastically false alarms from foreign object intrusion and sunlight saturation compared to IR beam detector.
High ceiling areas such as atriums, lobbies, sports arenas, museums, places of worship, factories, and warehouses might be the candidates for beam smoke detectors.
Written by Kanchana R.