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A presentation by Siemens and the Canadian Fire Alarm Association reports that the ionization detector is the best at detecting incipient-stage fires with invisibly small particles, fast-flaming fires with smaller 0.01–0.4 micron particles, and dark or black smoke, while more modern photoelectric detectors are best at detecting slow ...
Ionization-type smoke detectors are gaseous ionization detectors in widespread use. A small source of radioactive americium is placed so that it maintains a current between two plates that effectively form an ionisation chamber. If smoke gets between the plates where ionization is taking place, the ionized gas can be neutralized leading to a ...
An optical beam smoke detector is a device that uses a projected beam of light to detect smoke across large areas, [1] typically as an indicator of fire. [2] They are used to detect fires in buildings where standard point smoke detectors would either be uneconomical [ 3 ] or restricted for use by the height of the building.
In a photoionization detector, high-energy photons, typically in the vacuum ultraviolet (VUV) range, break molecules into positively charged ions. [2] As compounds enter the detector they are bombarded by high-energy UV photons and are ionized when they absorb the UV light, resulting in ejection of electrons and the formation of positively charged ions.
The alarm's circuitry detects this drop in the current and as a result, triggers the piezoelectric buzzer to sound. Compared to the alternative optical smoke detector, the ionization smoke detector is cheaper and can detect particles which are too small to produce significant light scattering. However, it is more prone to false alarms.
The ionization chamber has found wide and beneficial use in smoke detectors. In an ionisation type smoke detector, ambient air is allowed to freely enter the ionization chamber. The chamber contains a small amount of americium-241, which is an emitter of alpha particles which produce a constant ion current. If smoke enters the detector, it ...