Smoke detectors record fire or flue gas and sound an alarm as soon as a certain (usually very low) concentration of smoke is registered.
However, not all smoke detectors work the same. Three types of smoke detectors are distinguished from each other:
- Foto-optical smoke detectors
- Thermo-optical smoke detector
Photo-optical smoke detector
Photo-optical smoke detectors – sometimes referred to as photo-electronic smoke detectors – are the most common variant. In her smoke chamber, a diode is used. This emits an infrared beam. Under normal circumstances, this infrared beam passes unbroken through the chamber, as the light is not reflected in clear air.
On the other hand, if there is a sufficient concentration of smoke particles in the chamber, this light beam is broken and scattered. When this occurs, the rays of the scattered infrared signal strike a sensor in the chamber. This sensor will not be illuminated under normal circumstances when there is no smoke in the chamber. Consequently, the beam can only hit the sensor if it is broken. Once this is the case,
In order to avoid external interference by light sources from the outside and thus false alarm, the sensor is installed so that it can not be illuminated from the outside. This is usually achieved by a surrounding construction of non-reflective material. This shields the sensor from external light sources.
Some photo-optical smoke detectors use a laser beam instead of an infrared diode, but in principle, they work the same way.
Thermo-optical smoke detector
Thermo-optical smoke detectors combine the functions of photo-optical smoke detectors and heat detectors. So you not only visually detect any smoke concentrations but also react when the ambient temperature increases rapidly or exceeds a certain maximum value.
The optical component of this fire detector works in the same way as with the photo-optical smoke detectors described above. In addition, they record the ambient temperature via the thermistor. Thermistors are made of the electrically conductive material that conducts electricity better at high temperatures than at low temperatures. Thus, if the room temperature rises quickly enough, the thermistor also heats up and changes occur in its power line. In heat detectors always two thermistors are installed: a so-called Messheißleiter and a Vergleichheestleiter. The measuring heat conductor is used to detect the ambient temperature based on its own conductivity and the reference hot conductor is used as a reference to compare and confirm the measurement results. If a fast rising temperature is detected during such a measurement, A heat detector triggers an alarm. Likewise, an alarm is triggered as soon as a previously configured room temperature is exceeded.
Pure heat detectors are completely unsuitable for private households as they react too slowly to an existing fire. Until a pure heat detector responds to an open fire, there is certainly a very high and potentially lethal smoke concentration in the air. For this very reason, pure photo-optical smoke detectors are also more widely used than thermo-optical smoke detectors. Although the combination of smoke and heat detectors is a nice kinkerlitzchen, makes practically no difference, since the thermo-optical smoke detector reacts to smoke, long before its heat detection function comes into play. For a thermo-optic smoke detector to sound the alarm earlier than a photo-optical smoke detector, a fire would have to be virtually smoke-free. And that’s almost impossible with almost all fire causes and processes.
Ionisation smoke detectors are already reliable at the lowest smoke concentrations. So they can be considered particularly sensitive and sound an early warning.
They work as follows: Between two metal plates inside a radioactive radiating element is implemented. This emits alpha and beta rays, which ionize between the metal plates and thus bring about a flow of electric current. If even the smallest amounts of smoke enter between the metal plates, some of the ionic compounds are bound to this smoke by electrostatic attraction, whereby the current flow decreases. When this happens, the ionization smoke detector will immediately alarm.
Despite their sensitivity, ionisation smoke detectors are rare in this country. Although the radiation inside these smoke detectors are harmless, as long as they are not opened. However, they must be disposed of separately. This has a dramatic effect especially if a house with installed ionisation smoke detector burns down. Then its remains are buried somewhere in the fire debris, which under certain circumstances may result in a special disposal of the entire fire, if these remains can not be detected.
In comparison, it is easy to understand why the photo-optical smoke detector is the most widely used in our fields. Although the thermo-optical smoke detector is also more common, but offers relatively little added value, since the smoke detection function usually strikes much faster than the heat detection function, which makes him in use usually not more effective than a photo-optical smoke detector.
The ionization smoke detector, on the other hand, is a remarkably reliable smoke detector that reacts even with very small amounts of smoke. But by the consistent provisions regarding its disposal, it is rarely installed here. Different in the USA. There you can dispose of Ionisationsrauchmelder namely simply in the trash. But whether that is better, is left undone.