How does a smoke detector work?

Question

pllz i need it for my homework

Answer 1

A smoke detector or smoke alarm is a device that detects smoke and issues an alarm to alert nearby people that there is a potential fire. Technically, they could also be described as an active fire protection device that is subject to stringent bounding. A household smoke detector will typically be mounted in a disk shaped plastic enclosure about 150mm in diameter and 25mm thick, but the shape can vary by manufacturer.

Because smoke rises, most detectors are mounted on the ceiling or on a wall near the ceiling. To avoid the nusance of false alarms, most smoke detectors are mounted away from kitchens. To increase the chances of waking sleeping occupants, most homes have at least one smoke detector near any bedrooms; ideally in a hallway as well as in the bedroom itself.

Smoke detectors are usually powered by one or more batteries but some can be connected directly to household wiring. Often the smoke detectors that are directly connected to household wiring also have a battery as a power supply backup in case the household wiring goes out. It is usually necessary to replace the batteries once a year to ensure appropriate protection.

Most smoke detectors work either by optical detection or by ionization, but some of them use both detection methods to increase sensitivity to smoke. Smoke detectors may operate alone, be interconnected to cause all detectors in an area to sound an alarm if one is triggered, or be integrated into a fire alarm or security system. Smoke detectors with flashing lights are available for the deaf or hearing impaired. A smoke detector cannot detect carbon monoxide to prevent carbon monoxide poisoning unless it has an integrated carbon monoxide detector.

Answer 2

I can relate...this scared me and my family big time!! This happened to me a couple of times last summer when I had construction going on at my house. Sometimes dust particles will cross over a beam in the smoke detector which makes it go off...In this case, all of them went off like what is happening to you. If you clean the detectors with a vaccum, that should do the trick. Also, I was told to cover the detectors with plastic during construction. Just make sure you uncover your detectors at the end of the day. Hope this helps you. If it doesn't, maybe you need to buy new detectors.

Answer 3

A couple of general types:

Chemical/Gas Detecting:
These detect various chemicals and gasses that are hazaradous and can be assosiated with fire. My smoke detectors do this. If I burn something in the oven, and so much as open it, it only takes 5 seconds for the smoke detector in the other room to go beserk, even though there is no smoke.

Mirrored
These have a simple beam of light that shines on a mirror. If the beam is in tact, the alarm stays off. If the beam is broken somehow by condensation, smoke, steam, etc, it will trigger the alarm.

Many modern smoke detectors incorporate BOTH forms of detection, just to be be thorough.

Answer 4

There are two main types of smoke detectors: ionization detectors and photoelectric detectors. A smoke alarm uses one or both methods, sometimes plus a heat detector, to warn of a fire. The devices may be powered by a 9-volt battery, lithium battery, or 110-240 volt house wiring.
Ionization Detectors
Ionization detectors have an ionization chamber and a source of ionizing radiation. The source of ionizing
radiation is a minute quantity of americium-241 (perhaps 1/5000th of a gram), which is a source of alpha particles (helium nuclei). The ionization chamber consists of two plates separated by about a centimeter. The battery applies a voltage to the plates, charging one plate positive and the other plate negative. Alpha particles constantly released by the americium knock electrons off of the atoms in the air, ionizing the oxygen and nitrogen atoms in the chamber. The positively-charged oxygen and nitrogen atoms are attracted to the negative plate and the electrons are attracted to the positive plate, generating a small, continuous electric current. When smoke enters the ionization chamber, the smoke particles attach to the ions and neutralize them, so they do not reach the plate. The drop in current between the plates triggers the alarm.
Photoelectric Smoke Detectors
In one type of photoelectric device, smoke can block a light beam. In this case, the reduction in light reaching a photocell sets
off the alarm. In the most common type of photoelectric unit, however, light is scattered by smoke particles onto a photocell, initiating an alarm. In this type of detector there is a T-shaped chamber with a light-emitting diode (LED) that shoots a beam of light across the horizontal bar of the T. A photocell, positioned at the bottom of the vertical base of the T, generates a current when it is exposed to light. Under smoke-free conditions, the light beam crosses the top of the T in an uninterrupted straight line, not striking the photocell positioned at a right angle below the beam. When smoke is present, the light is scattered by smoke particles, and some of the light is directed down the vertical part of the T to strike the photocell. When sufficient light hits the cell, the current triggers the alarm.
Which Method is Better?
Both ionization and photoelectric detectors are effective smoke sensors. Both types of smoke detectors must pass the same test to be certified as UL smoke detectors. Ionization detectors respond more quickly to flaming fires with smaller combustion particles; photoelectric detectors respond more quickly to smoldering fires. In either type of detector, steam or high humidity can lead to condensation on the circuit board and sensor, causing the alarm to sound. Ionization detectors are less expensive than photoelectric detectors, but some users purposely disable them because they are more likely to sound an alarm from normal cooking due to their sensitivity to minute smoke particles. However, ionization detectors have a degree of built-in security not inherent to photoelectric detectors. When the battery starts to fail in an ionization detector, the ion current falls and the alarm sounds, warning that it is time to change the battery before the detector becomes ineffective. Back-up batteries may be used for photoelectric detectors.

Answer 5

A smoke detector is a device that senses smoke, typically as an indicator of fire. Commercial and residential security devices issue a signal to a fire alarm control panel as part of a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible or visual alarm from the detector itself.

Smoke detectors are typically housed in a disk-shaped plastic enclosure about 150 millimetres (6 in) in diameter and 25 millimetres (1 in) thick, but the shape can vary by manufacturer or product line. Most smoke detectors work either by optical detection (photoelectric) or by physical process (ionization), while others use both detection methods to increase sensitivity to smoke. Sensitive alarms can be used to detect, and thus deter, smoking in areas where it is banned such as in public restrooms and schools. Smoke detectors in large commercial, industrial, and residential buildings are usually powered by a central fire alarm system, which is powered by the building power with a battery backup. However, in many single-family detached and smaller multiple family housings, a smoke alarm is often powered only by a single disposable battery.

Answer 6

I don't like to do homework, but like to help kids do theirs. I will give you some info and some places to go to learn more.

Some smoke detectors use the ionization principle. Others depend on the photoelectric principle. Still others use condensation neuclei. Don't worry about the last ones. They are not very popular.

howstuffworks.com/smoke.htm
www.consumersearch.com/www/house_and_home/smoke-detectors

Answer 7

The smoke stops a circuit which starts the alarm. See my Wikipedia link.

Also try HowStuffWorks. I'd look but it's a very slow loading site.

Answer 8

Check out How Stuff Works:

http://home.howstuffworks.com/smoke.htm

Answer 9

http://home.howstuffworks.com/smoke.htm

Answer 10

it detects carbon monoxide in the air.