How does a smoke deterctor work?

Smoke Detector

Every modern business building nowadays is equipped with smoke detectors (also known as smoke alarms) that have the potential to save millions of lives at very little cost.

The little contraption consists of two basic parts:  a sensor (to detect smoke) and an electronic audible alarm (to rouse people up).  We’ll look into how an optical (photoelectric) smoke detector works.

Have you gone to a place where the glass door automatically opens just before you step inside the building?  The system consists of a light source and a sensor on the other side.  What happens is, when you cross the beam of light, you block it.  the photodetector senses the lack of light and triggers a mechanism that opens the door.

For smoke detectors, however, there is a slight modification.  This type of detector includes a light source, a lens to collimate the light into a beam and a photoelectric sensor at right-angles to the beam.

In the absence of smoke, the light passes in front of the detector but does not fall on it.  when visible smoke enters the beam, some light is scattered by the smoke particles, and some of the scattered light is detected by the sensor.  An increased output from the sensor sets off the alarm.

The other type of smoke detector is the ionization detector that uses radioactive material to detect smoke produced by flaming fires.

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