PRESENTED BY:
Nanda Dulal Maity

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SMOKE DETECTOR
 Description
A smoke detector is a device that detects smoke, typically as an indicator of fire. Commercial, industrial, and mass residential devices issue a signal to a fire alarm system, while household detectors, known as smoke alarms, a smoke alarm is often powered only by a single disposable battery.
 Design
Smoke Detector system can be classified by manufacturing Technology.
1. Optical
2. Ionization
3. Air-sampling
4. Carbon monoxide and carbon dioxide detection
 Optical
An optical detector is a light sensor. When used as a smoke detector, it includes a light source (incandescent bulb or infrared LED), In the absence of smoke, the light passes in front of the detector in a straight line. When smoke enters the optical chamber across the path of the light beam..
A wall-mounted unit sends a beam, which is e received by a separate monitoring device or reflected back via a mirror. When the beam becomes less visible to the "eye" of the sensor, it sends an alarm signal to the fire alarm control panel.
 Ionization
An ionization type smoke detector is generally cheaper to manufacture than an optical smoke detector; however, it is sometimes rejected because it is more prone to false (nuisance) alarms than photoelectric smoke detectors. It can detect particles of smoke that are too small to be visible.
 Also these alarms are somewhat prone to nuisance alarms because small particles such as kitchen or cooking smoke may activate the alarm.
 Air-Sampling
An air-sampling smoke detector is capable of detecting microscopic particles of smoke. Most air-sampling detectors are aspirating smoke detectors,
 Carbon monoxide and carbon dioxide detection
Some smoke alarms use a carbon dioxide sensor or carbon monoxide sensor in order to detect extremely dangerous products of combustion.
 Performance Differences
Optical or "toast-proof" smoke detectors are often considerably quicker in detecting particulate (smoke) generated in the smoldering (cool, smoky) stage of a fire.
Ionization smoke detectors are usually only marginally quicker in detecting particulate (smoke) generated in the flaming (hot) stage of a fire.
Only photoelectric smoke detectors are regarded as suitable for detecting fire in both the smoldering and flaming stages.
 Commercial smoke detectors
Commercial smoke detectors are two types
 Conventional
 Analog Addressable
These are the most common type of detector, and usually cost a lot more than a household smoke alarms.
They exist in most commercial and industrial facilities, such as high rises, ships and trains.
• Conventional
These detectors are connected in parallel to the signaling path.
The resulting increase in current flow is interpreted and processed by the control unit as a confirmation of the presence of smoke and a fire alarm signal is generated.
• Addressable
Analog addressable detectors provide information about the amount of smoke in their detection area.
These are usually more expensive than autonomous deciding detectors.
 Batteries
Most residential smoke detectors run on 9-volt alkaline or carbon-zinc batteries. When these batteries run down, the smoke detector becomes inactive.
Common NiMH and NiCd rechargeable batteries are use in smoke detectors.
 Installation & Placement
Installation and placement process of the Smoke detector is so easy.
In the High rise building, shopping mall, Convention Center are gradually install the smoke detector for Public security..
 Benefits of Installing Smoke Alarm in the House
1.Early detection can save lives. . It is also valuable in the safety of your home. Detection of a threat early on will help save lives
2. You can respond to the alarm immediately. You can try to stop the fire from spreading. The detectors will point you to the area where the smoke is detected. This will enable you to find out the flame
3. The device will notify everyone in the family right away. There are also devices that you can connect with the local rescue unit so that they can respond right away as soon as your alarm system sounds.

SMOKE DETECTOR
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INTRODUCTION



A smoke detector is an important safety device in homes, offices and other enclosed structures. It can save lives especially when fires occur during the most unexpected times. Thousands of people are killed every year as a result of suffocation from thick smoke caused by fires.
Smoke detectors in homes can either be the hard wired or the battery-powered units. Most states, however, require the installation of hard wired smoke alarms which are more reliable. This type is powered by 120-volt electricity in the home and is interconnected with other smoke detector units in the house. They are normally wired into the electrical system of the home. Most homes install several units with each room and hallways having a separate alarm to make sure that all members of the family are warned in case a fire occurs.



BLOCK DIAGRAM DESCRIPTION

2.1.1 Stimulant
The stimulant here is the smoke which acts as the input to the circuit.The intensity of the smoke determines the activation of the photodiode and in turn affects the working of the circuit.
2.1.2 Sensor assembly
The sensor assembly consists of a photo diode and a white LED. The white LED makes sure that photodiode gets enough intensity of light in the absence of smoke. The photo diode is a photoelectric device and it is connected in the reverse bias mode so as to work in the photoconductive mode of operation.
2.1.3 Switching circuit
The switching circuit consists of an NPN transistor BC549. It switches on the main component, the NE555 timer. The transistor gets on when no smoke is there and it gets off when a smoke of desired intensity gets into the sensor assembly.
2.1.4 Bistable Multivibrator
The bistable multivibrator consists of a NE555 timer which is designed in the bistable mode. The popular timer ICNE555 is used in the Bistable mode to generate the alarm when the sensor assembly detects smoke. The output of IC1 has two states (Bistable), either high or low. This Bistable states are determined by the state of its reset pin4. When the reset pin is high, output turns high and when the reset pin is low, output turns low.


2.1.5 Audiovisual Components
The audiovisual components are mainly aimed at giving the audiovisual response on the detection of smoke. They include a red LED and a buzzer. When smoke is detected, the visual response is first indicated by the glowing of the red LED and then the buzzer sounds for giving the audio response.


3.1 CIRCUIT DESCRIPTION

3.1.1 Power Supply

The supply to the circuit is a 12 v supply. This is provided by connecting either a transformer to the circuit or a battery. When we use a transformer, we have to convert the ac power to dc.This is done by using the two diodes and they perform diode rectification. We can also use a battery as the power supply. As far as a smoke detector is concerned, using a battery is more reliable as current failure may occur due to fire which results in the failure of the circuit.
3.1.2 Photodiode

The major component of the sensor assembly is the PIN Photodiode. Photodiode is a type of light detector capable of converting light energy into either current or voltage, depending upon the mode of operation. Photodiodes are similar to typical semiconductor diodes except that they may be either exposed or packaged with a window to allow light to reach the sensitive part of the device.

Smoke detector

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A smoke detector is a device that detects smoke, typically as an indicator of fire. Commercial, industrial, and mass residential devices issue a signal to a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible and/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 toilets 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.


Ionization



An Americium container from a smoke detector.
An ionization type smoke detector is generally cheaper to manufacture than an optical smoke detector; however, it is sometimes rejected because it is more prone to false (nuisance) alarms than photoelectric smoke detectors.[2][3] It can detect particles of smoke that are too small to be visible. It includes about 37 kBq or 1 µCi of radioactive element americium-241 (241Am),


Air-sampling
An air-sampling smoke detector is capable of detecting microscopic particles of smoke. Most air-sampling detectors are aspirating smoke detectors, which work by actively drawing air through a network of small-bore pipes laid out above or below a ceiling in parallel runs covering a protected area. Small holes drilled into each pipe form a matrix of holes (sampling points), providing an even distribution across the pipe network. Air samples are drawn past a sensitive optical device, often a solid-state laser, tuned to detect the extremely small particles of combustion. Air-sampling detectors may be used to trigger an automatic fire response, such as a gaseous fire suppression system, in high-value or mission-critical areas, such as archives or computer server rooms.
Most air-sampling smoke detection systems are capable of a higher sensitivity than spot type smoke detectors and provide multiple levels of alarm threshold, such as Alert, Action, Fire 1 and Fire 2. Thresholds may be set at levels across a wide range of smoke levels. This provides earlier notification of a developing fire than spot type smoke detection, allowing manual intervention or activation of automatic suppression systems before a fire has developed beyond the smoldering stage, thereby increasing the time available for evacuation and minimizing fire damage.


Carbon monoxide and carbon dioxide detection
Some smoke alarms use a carbon dioxide sensor or carbon monoxide sensor in order to detect extremely dangerous products of combustion.[6][7] However, not all smoke detectors that are advertised with such gas sensors are actually able to warn of poisonous levels of those gases in the absence of a fire.[citation needed]

Performance differences
Photoelectric smoke detectors respond quickly to smoldering fires, which are made up of combustion particles between 0.3 and 10.0 microns. Ionization smoke detectors, however, are superior when detecting flaming fires, which can be characterized by combustion particles between 0.01 and 0.3 microns. Also, ionization detectors are weaker in high air-flow environments, and because of this, the photoelectric smoke detector is more reliable for detecting smoke in both the smoldering and flaming stages of a fire.[8]