Photoelectric Smoke Detector

A photoelectric smoke detector is a type of smoke detector and alarm initiating device using the scatted light principle and is designed to detect the presence of smoke from fire.

A photoelectric smoke detector comprises an enclosure comprising the following components;

• a fine mesh shield to prevent the ingress of large particles and insects but still allows the ingress of smoke;
• an optical labyrinth extending generally around the entire side wall of the smoke detection chamber. The optical labyrinth of a photo-electric smoke detector is designed to perform several functions that contribute to the accurate detection of smoke, and minimise nuisance alarms. These functions include;
  • Prevent stray light from entering the detection field of the photoelectric receiving diode;
  • Absorb stray light signals from within the detector to reduce background noise;
  • Facilitate the smooth entry of smoke into the detection chamber for reliable and timely smoke detection.
• a light source for emitting light energy;
• a light receiver for providing an output signal at a signal magnitude proportional to the intensity of the light received;
• an electronic circuit that receives the output signal and transmits that signal to the fire detection control and indicating equipment ("FDCIE").

A photoelectric smoke detector operates on the principle that, under normal circumstances in clean air a light wave will travel in a linear direction (straight line) indefinitely. A photoelectric smoke detector leverages the concept that light can be scattered (reflected and refracted) when a light wave is contaminated by the airborne solids suspended in air (smoke).

In this scenario, the light source beam is scattered by the smoke within the chamber of the smoke detector where the light waves that are reflected and refracted are received by the light source receiver.