Smoke detectors save lives. Make your home is safe.
There are two types of technology used in the working of a smoke alarm, which runs from either 9 volt alkaline battery, a lithium battery, or from the 120 volt AC main house hold power. The detectors work either by optical detection, which is essentially a photo-electric device, or by chemical reaction, which follows the principle of ionization. There is some smoke detecting devices that you can buy which use both the technologies in order to provide a greater sensitivity in detection.
Optical detector smoke alarm:
The technology used in such devices is based on photo-electric principle. The smoke alarm device consists of a light sensor, which senses light from a built-in light source. This light source falls in front of the sensor in a straight line as long as there is no smoke. In case of a fire, the smoke from the fire enters the smoke alarm device and scatters the light from the light source, with the result the sensor detects the presence of light and sets off the alarm. This is how do smoke alarms work with photo-electric principle.
The other type of smoke alarm that you can buy works on the same principle but with an infra-red light source. This is how do the infra-red smoke alarms work. The light source falls directly on to the infra-red sensor, and as long as there is no smoke, the light beam is not disturbed. As smoke enters the device, the intensity of the light falling on the sensor gets scattered, with a result that the light falling on the sensor is of much lower intensity. This is detected by the sensor which in turn sets off the alarm. The light falling on the infra-red sensor is fine tuned to the intensity of the light falling on it. Therefore, any variation in the intensity of the light is detected by the sensor.
Ionization detector smoke alarm:
This is how do ionization smoke alarms work. Smoke alarm devices working on principle of ionization consists of an ionization chamber, where a potential from a battery source is applied to two plates, kept one on to top of the other, separated by about one centimeter. This chamber also has a minute quantity of americium-241 in the order of approximately 1/5000th of a gram. This is a radioactive material and is a good source for alpha particles. The battery in the smoke alarm applies a voltage to the two plates, charging the two to a positive and a negative potential. The alpha particles constantly knock the electrons off the atoms in the air, which ionizes the oxygen and nitrogen atoms in the chamber.
The positively charged oxygen and nitrogen atoms get attracted towards the negatively charged plate, while the electrons move towards the positively charged plate. This process generates a constant flow of a small current. In case of fire, smoke travels into the ionization chamber of the smoke alarm, and the particles from the smoke attach themselves with the ions, which start to get neutralized. This prevents the ions from reaching the plate and there is a drop in the current which sets off the alarm.
The radioactive element, americium-241, has a half-life of 432 years and has been fund to be a good source of alpha particles. The technology used in smoke alarm is unique and the devices have proved to be quite reliable in providing alert signals in case of fire. There are varieties of these detectors on sale in the market, which can run either on batteries or on the main electrical power of the building.
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