How Does a Smoke Detector Work?

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What is a Smoke Detector?

  • A smoke detector is an electronic device that was originally invented in 1890 by Francis Robert Upton and Fernando J. Dibble. Essentially this electronic device is designed to detect the presence of smoke and alert anybody nearby of the potential danger of fire. A smoke detector should not be mistaken for a fire detector. A fire detector, though physically similar as they are both round disk-like objects that come in plastic shells often placed on the ceilings of private dwellings and offices, only alerts anybody nearby to the danger of a fire which has already grown to such a degree as to raise the temperature of the environment beyond the fire detector's programmed safe level. A smoke detector is much more effective in that it, by emitting a loud siren-like noise, can alert people to the danger of a fire in time to evacuate the building or stop the fire before it has a chance to grow. It is a device designed to prevent serious harm to people's property and persons. To date there are two types of smoke detector; the photoelectric smoke detector and the ionization smoke detector.

How Does a Photoelectric Smoke Detector Work?

  • A photoelectric smoke detector is comprised of a few simple parts; a T-shaped chamber with a small light bulb or LED aimed toward the top of the T, a lens to focus the light into a concentrated beam, and a photodiode which detects the presence of the beam. When functioning normally the LED emits light in a steady beam at the photodiode. The sides of the T-shaped chamber are vented and open. As smoke rises, it would rise up to the smoke detector and seeps into the vents of the chamber. By doing so the smoke obscures the light, preventing it from striking the photodiode. When this happens the alarm is triggered.

How Does an Ionization Smoke Detector Work?

  • An ionization smoke detector is cheaper and more effective than a photoelectric smoke detector, but some people are bothered by keeping them in their homes as the detectors make use of a radioactive substance. This substance is called americium and is not considered to be dangerous given the infinitesimally small amount used, though some people are still skeptical. The device is comprised of an air filled chamber with vents. Each vent contains a tiny amount of americium. This chamber contains two electrodes which are slightly separated, though a small amount of current is still able to continually jump that gap and close the device's circuit. When smoke enters the chamber, even microscope particles of smoke, it carries with it some of the americium. This americium makes the air in the chamber less prone to carrying an electric current and prevents the electricity from jumping the gap between electrodes. This breaks the circuit and triggers the alarm.

  • Photo Credit democrats.assembly.ca.gov
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