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Smoke Sensor

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smoke sensor

Introduction smoke sensor:

A smoke detector is a device that senses of the smoke, typically as an indicator of fire. Smoke detectors are usually housed in plastic enclosures that are typically shaped like a disk about 150 millimeters (6 in) in diameter or 25 millimeters (1 in) thick, but shape and size vary. Smoke could be detected either optically (photoelectric) or by physical process (ionization). Detectors may use 1 or both sensing methods. Sensitive alarms could be used to detect and deter smoking in banned areas. Smoke detectors in large commercial or industrial buildings are usually connected to a central fire alarm system. Household smoke detectors, also known as smoke alarms, generally issue an audible and visual alarm from the detector itself and several detectors if there are multiple devices interlinked. Household smoke and detectors range from individual and battery-powered units to several interlinked units with battery backup. With interlinked units, if any unit detects smoke, alarms would trigger at all of the units. This happens even if a household of the power has gone out.

The 1 automatic electric fire alarm was patented in 1890 by Francis Robbins Upton,[2] an associate of Thomas Edison.[3] In 1902, George Andrew Darby patented the 1 European electrical heat detector in Birmingham, England.[4][5] In the late 1930s, Swiss physicist Walter Jaeger attempted to invent a sensor for poison gas.[6] He expected the gas entering the sensor to bind to ionized air molecules or thereby alter an electric current in a circuit of the instrument.[6] However, his device did not achieve it is purpose as small concentrations of gas did not affect the sensor's conductivity.[6] Frustrated, Jaeger lit a cigarette and was surprised to notice that a meter on the instrument had registered a drop in the current.[7] Unlike poison gas, as the smoke particles from his cigarette were able to alter the circuit's and current.[7] Jaeger's of the experiment was 1 of the developments and that paved the way for the modern smoke and detector.[7] In 1939,as Swiss physicist Ernst Meili devised an ionization chamber device capable of detecting combustible gases in mines.[8] He also invented a cold cathode tube that could amplify the small signal generated by the detection mechanism so that it was strong enough to activate an alarm.[8]In 1951, ionization smoke detectors were first sold in the United States. In the following years, they were used only in major commercial or industrial facilities due to their large size or high cost.[8] In 1955, simple "fire detectors" for homes were developed,[9] which detected high temperatures.


  1. Current sensor is: 2.5A
  2. Measuring no more than: 10A
  3. current sensor is a direct: 10A
  4. The frequency of m microphone is: 16to20kHz
  5. The signal to noise ratio is: 54 dB

Circuit Operation:

A Smoke Detector is a smoke sensing device that indicates fire. Smoke Detectors are very common in homes, offices, schools and industries. Smoke Detectors are very useful devices as the damage caused by fire accidents is catastrophic.Now a days, smoke detectors and smoke alarms are very cheap as its usage is increasing and cost of manufacturing is decreasing. In this project, we are implementing a simple Smoke Detector Circuit using simple hardware.We used a Gas/Smoke sensor for detecting smoke. The article is divided into information about Smoke sensor, circuit diagram and working.

There are two types of smoke detectors. Optical or Photoelectric smoke detectors and Ionization smoke detectors.Optical smoke detectors consists of a light source like LED and a light detector like photocell.The photocell conducts as long as the light falls on it. When there is smoke, the light from the source is interrupted and the photocell doesn’t conduct Ionization smoke detectors consists of two electrodes and an ionization chamber filled with ions. When there is no smoke, the ions move freely and the electrodes conduct normall.In the presence of smoke, the chamber is filled with smoke and interrupts the movement of ions. The electrodes do not conduct anymore. Depending on the type of sensor and manufacturer, the conductivity conditions may change but the idea remains the same.

Smoke Sensor circuit diagram

Smoke Detectors are amazing devices as they are small, cheap yet very useful. In this project, we implemented a simple Smoke Detector Circuit with adjustable sensitivity.We used a Smoke Sensor MQ-2 as the main sensory device. The working of the circuit is simple and is explained below.LM358 acts as a comparator in this circuit. The inverting terminal of LM358 is connected to POT so that the sensitivity of the circuit can be adjustedThe output of LM358 is given to an LED as an indicator although a buzzer can be used as an alarm. The non-inverting terminal of LM358 is connected with output of smoke sensor.

Initially, when the air is clean and the conductivity between the electrodes is less, the resistance is in the order of 50K. The inverting terminal input of the comparator is higher than the non-inverting of the terminal input. The indicator LED is OFF. In the event of fire, when the sensor is filled with smoke, the resistance of the sensor falls to 5K? and the conductivity between the electrodes increases. This provides a higher input at the non-inverting terminal of the comparator than the inverting terminal and the output of the comparator is high. The alarming LED is turned ON as an indication of the presence of smoke.

This simple smoke to the detector is highly sensitive but inexpensive. It uses a Darlington-pair amplifier employing two NPN transistors and an infrared photo-interrupter module as the sensor. The circuit gives an audio-visual alarm whenever thick smoke is present in the environment. The photo-interrupter of the module (H21A1) consists of a gallium-arsenide infrared LED coupled to a silicon phototransistor in a plastic housing. The slot (gap) between the infrared diode or the transistor allows interruption of the signal with smoke, switching the module output from an ‘on’ to an ‘off’ state.

How the Smoke Sensor Work:

There are ionization detectors. These use a small bit of safely shielded radioactive material that electrically charges, and ionizes, the air molecules between 2 metal plates. This produces a small electric current flowing from 1 plate to the other in the air. When particles enter the chamber, they attract the ions or carry them away, reducing the current. When the number of particles entering the chamber is enough to reduce that current below a certain amount, the device registers those particles as smoke or the alarm sounds. (And about that radioactive material? Most of its radiation is blocked inside the device, or even then, the radiation levels in the device are much lower than the natural background radiation to which we are exposed every day.) The other type of commonly used detection of the technology is called photoelectric. This technology works by detecting the light that is reflected off particles from a light beam inside the sensing chamber. When no particles are present in the sensing to the chamber the light from the beam does not strike the light detector and indicates all clear. When there are particles present or the amount of light registered by the light detector reaches a certain threshold level, the alarm sounds.

Both kinds of detectors could detect either slow-burning “smoldering” fires or fast-burning “flaming” fires, but each technology has its particular strengths. Ionization-based alarms tend to detect small black soot particles from flaming fires more quickly because they are produced in greater numbers or take away more current from between the plates. Photoelectric detectors tend to be more sensitive to particles that are larger in size and white and light-colored, or thus more reflective, like those emitted by smoldering fires.

As important as smoke alarms are for protecting your family or your property, many times they can be a nuisance. Smoke alarms near kitchens can detect the particles coming off your food as it cooks, even if you don’t burn it. Sometimes something as simple as turning on a toaster could set them off. So as with many safety measures, the smoke of the detectors has a trade-off. They could be made sensitive enough to detect almost any smoke. But if they did, they should detect the smoke you do not want them to detect (such as from cooked food) and even other things such as dust. Less sensitive detectors should have fewer nuisance alarms, but in an actual fire, they may not go off in time to save lives and property. And they may not give off a signal at all. Researchers are developing new tests or standards to make smoke alarms better at detecting the kinds of smoke we want them to detect and not the kinds we do not, so we are never tempted to disable the alarms or put ourselves in danger. As a result, the next generation of smoke detectors promises to cut down on the number of nuisance alarms while also signing to real fires more quickly. And with fire, time is everything when it comes to saving lives or property.

Frequently Asked Questions

How does a smoke detector circuit work?

If any smoke particles enter the open chamber, some of the ions will attach to the particles and not be available to carry the current in that chamber. An electronic circuit detects that a current difference has developed between the open and sealed chambers, and sounds the alarm.

How do smoke and gas sensors work?

They work by measuring changes in the electrical resistance of a semiconductor material when it comes into contact with the gas being detected. The semiconductor material used in the sensor is typically made from metal oxide such as tin oxide, tungsten oxide, or zinc oxide.

What are the 3 types of smoke detectors?

There are three types of smoke alarms, ionization, photoelectric and a combination of the two which is commonly called a “dual” detector. Look for the UL stamp on any smoke alarm. Research has shown: Ionization smoke alarms detect flaming fires marginally earlier than photo-electric smoke alarms.

What is in a smoke detector?

Most smoke detectors use americium-241 as their source. Some early models used radium-226, and commercial smoke detectors and some residential units used nickel-63. The types of radiation from these sources cannot make anything else radioactive.

What is smoke detector sensor?

A smoke detector is an electronic fire-protection device that automatically senses the presence of smoke, as a key indication of fire, and sounds a warning to building occupants. Commercial and industrial smoke detectors issue a signal to a fire alarm control panel as part of a building's central fire alarm system.

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