Automatic smoke detector. Ionization fire detectors: types and principle of operation

fire detector- a device for generating a fire signal. The use of the term "sensor" is incorrect, as the sensor is part of the detector. Despite this, the term "sensor" is used in many industry codes to mean "detector".

Conventions

The symbol of fire detectors should consist of the following elements: IP X1X2X3-X4-X5.
The abbreviation IP defines the name "fire detector". Element X1 - indicates a controlled sign of a fire; instead of X1, one of the following digital designations is given:
1 - thermal;
2 - smoke;
3 - flame;
4 - gas;
5 - manual;
6…8 — reserve;
9 - when monitoring other signs of a fire.
The X2X3 element denotes the principle of operation of the PI; X2X3 is replaced by one of the following numerical designations:
01 - using the dependence of the electrical resistance of the elements on temperature;
02 - using thermo-emf;
03 - using linear expansion;
04 - using fusible or combustible inserts;
05 - using the dependence of magnetic induction on temperature;
06 - using the Hall effect;
07 - using volumetric expansion (liquid, gas);
08 - using ferroelectrics;
09 - using the dependence of the modulus of elasticity on temperature;
10 - using resonant-acoustic methods of temperature control;
11 - radioisotope;
12 - optical;
13 - electroinduction;
14 - using the effect of "shape memory";
15 ... 28 - reserve;
29 - ultraviolet;
30 - infrared;
31 - thermobarometric;
32 - using materials that change optical conductivity depending on temperature;
33 - air ion;
34 - thermal noise;
35 - when using other principles of action.
The X4 element denotes the serial number of the development of a detector of this type.
Element X5 designates the class of the detector.

Classification according to the possibility of reclosing

Automatic fire detectors, depending on the possibility of their reclosing After triggering, they are divided into the following types:

• returnable detectors with the possibility of reclosing - detectors that can return to the control state from a fire alarm state without replacing any nodes, if only the factors that led to their operation have disappeared. They are divided into types:
  • detectors with automatic reclosing - detectors that, after being triggered, automatically switch to the control state;
  • detectors with remote reactivation - detectors that, with the help of a remotely given command, can be transferred to the control state;
  • detectors with manual actuation - detectors that, by means of manual switching on the detector itself, can be switched to the control state;
• detectors with replaceable elements - detectors that, after triggering, can be transferred to the control state only by replacing some elements;
• non-reclosable detectors (without replaceable elements) - detectors that, after triggering, can no longer be switched to the monitoring state.

Classification by type of signaling

Automatic fire detectors according to the type of signal transmission are divided into:

• dual-mode detectors with one output for transmitting a signal both about the absence and the presence of fire signs;
• multi-mode detectors with one output for transmitting a limited number (more than two) types of signals about the state of rest, fire alarm or other possible conditions;
• analog detectors, which are designed to transmit a signal about the magnitude of the value of the fire sign they control, or an analog / digital signal, and which is not a direct fire alarm signal.

Application
Thermal fire detector designed in the 19th century. It consists of two wires a and b, which are connected to each other by washers cc made of non-conductive material. On the side of the device there is a tube d with a capsule e filled with mercury and closed from below with a wax plate. When the temperature rises, the wax melts, mercury is poured into the device and contact is established between the two wires, as a result of which a signal appears
They are used if a significant amount of heat is released at the initial stages of a fire, for example, in warehouses of fuel and lubricants. Or in cases where the use of other detectors is not possible. Use in administrative and amenity premises is prohibited.
The field of the highest temperature is located at a distance of 10...23 cm from the ceiling. Therefore, it is in this area that it is desirable to place the heat-sensitive element of the detector. The heat detector, located under the ceiling at a height of six meters above the fire, will work when the heat release of the fire is 420 kW.

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A detector that reacts to fire factors in a compact area.

multipoint
Thermal multipoint detectors are automatic detectors, the sensitive elements of which are a set of point sensors discretely located along the line. The step of their installation is determined by the requirements normative documents and technical specifications specified in technical documentation for a specific product.

Linear (thermal cable)
There are several types of linear thermal fire detectors that are structurally different from each other:

• semiconductor - a linear thermal fire detector, in which the wire coating with a substance having a negative temperature coefficient is used as a temperature sensor. This type The thermal cable only works in conjunction with an electronic control unit. When temperature is applied to any section of the thermal cable, the resistance at the point of impact changes. Using the control unit, you can set different temperature response thresholds;
• mechanical - as a temperature sensor of this detector, a sealed metal tube filled with gas is used, as well as a pressure sensor connected to the electronic control unit. When temperature is applied to any part of the sensor tube, the internal pressure of the gas changes, the value of which is recorded by the electronic unit. This type reusable linear thermal fire detector. The length of the working part of the metal tube of the sensor has a length limit of up to 300 meters;
• electromechanical - a linear thermal fire detector, in which a temperature-sensitive material is used as a temperature sensor, applied to two mechanically stressed wires (twisted pair). Under the influence of temperature, the heat-sensitive layer softens, and two conductors are short-circuited.

Smoke detectors - detectors that react to combustion products that can affect the absorbing or scattering ability of radiation in the infrared, ultraviolet or visible spectral ranges. Smoke detectors can be point, linear, aspiration and autonomous.

Application

The symptom to which smoke detectors react is smoke. The most common type of detector. When protecting administrative and amenity premises with a fire alarm system, only smoke detectors should be used. The use of other types of detectors in administrative and amenity premises is prohibited. The number of detectors protecting the premises depends on the size of the premises, the type of detector, the availability of systems (fire extinguishing, smoke removal, equipment blocking) controlled by the fire alarm.
Up to 70% of fires arise from thermal microfoci that develop in conditions with insufficient access to oxygen. This development of the focus, accompanied by the release of combustion products and proceeding for several hours, is typical for cellulose-containing materials. It is most effective to detect such foci by registering combustion products in small concentrations. This allows you to make smoke or gas detectors.

Optical

Smoke detectors using optical means of detection react differently to smoke different colors. At present, manufacturers provide limited information on the response of smoke detectors in the technical specifications. Information about the detector's reaction only includes the nominal values ​​of the reaction (sensitivity) to gray smoke, not black. Often a range of sensitivity is given instead of an exact value.

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Activated smoke detector (red LED continuously on)

Smoke detectors must be closed during repairs in the room to avoid dust ingress.
The point detector responds to fire factors in a compact area. The principle of operation of point optical detectors is based on the scattering of infrared radiation by gray smoke. They respond well to the gray smoke emitted during smoldering in the early stages of a fire. Responds poorly to black smoke that absorbs infrared radiation.
For periodic maintenance of the detectors, a detachable connection, the so-called "socket" with four pins, is required, to which the smoke detector is connected. To control the disconnection of the sensor from the loop, there are two negative contacts that are closed when the detector is installed in the socket.

Smoke chamber and point smoke detector electronics
In all point smoke optical fire detectors IP 212-XX, according to the classification of NPB 76-98, the effect of diffuse scattering of LED radiation on smoke particles is used. The LED is positioned in such a way as to exclude direct exposure of its radiation to the photodiode. When smoke particles appear, part of the radiation is reflected from them and enters the photodiode. To protect against external light, an optocoupler - an LED and a photodiode - are placed in a smoke chamber made of black plastic.
Experimental studies have shown that the detection time of a test fire source when smoke detectors are located at a distance of 0.3 m from the ceiling increases by 2..5 times. And when the detector is installed at a distance of 1 m from the ceiling, it is possible to predict an increase in the time for detecting a fire by a factor of 10..15.
When the first Soviet optical smoke detectors were developed, there was no specialized element base, standard LEDs and photodiodes. In the photoelectric smoke detector IDF-1M, an incandescent lamp of the SG24-1.2 type and a photoresistor of the FSK-G1 type were used as an optocoupler. This determined the low specifications detector IDF-1M and weak protection against external influences: the response time at an optical density of 15 - 20% / m was 30 s, the supply voltage was 27 ± 0.5 V, the current consumption was more than 50 mA, the weight was 0.6 kg, the background illumination was up to 500 lx, air flow speed up to 6 m/s.
In the combined smoke and heat detector DIP-1, an LED and a photodiode were used, moreover, they were located in a vertical plane. Instead of continuous radiation, pulsed radiation was used: duration 30 μs, frequency 300 Hz. To protect against interference, synchronous detection was used, i.e. the input of the amplifier was open only during the emission of the LED. This provided higher protection against interference than in the IDF-1M detector and significantly improved the characteristics of the detector: the inertia decreased to 5 s at an optical density of 10%/m, i.e. 2 times smaller, the weight decreased by 2 times, the allowable background illumination increased by 20 times, up to 10,000 lux, the allowable air flow speed increased to 10 m/s. In the "Fire" mode, the red LED indicator turned on. A relay was used to transmit an alarm signal in the DIP-1 and IDF-1M detectors, which determined significant consumption currents: more than 40 mA in standby mode and more than 80 mA in alarm, with a supply voltage of 24 ± 2.4 V and the need to use separate signal circuits and power circuits. The maximum time between failures of DIP-1 is 1.31 104 hours.

Line detectors

Linear - a two-component detector consisting of a receiver unit and an emitter unit (or one receiver-emitter unit and a reflector) reacts to the appearance of smoke between the receiver and emitter unit.

The device of linear smoke fire detectors is based on the principle of attenuation of the electromagnetic flux between a radiation source spaced apart in space and a photodetector under the influence of smoke particles. A device of this type consists of two blocks, one of which contains an optical radiation source, and the other a photodetector. Both blocks are located on the same geometric axis in the line of sight.
A feature of all linear smoke detectors is the self-test function with the transmission of a "Fault" signal to the control panel. Due to this feature, it is correct to use it only in alternating loops at the same time as other detectors. Inclusion linear detectors into permanent loops leads to blocking the signal "Fault" signal "Fire", which is contrary to NPB 75. Only one linear detector can be included in a fixed-sign loop.
One of the first Soviet linear detectors was called DOP-1 and used an SG-24-1.2 incandescent lamp as a light source. A germanium photodiode was used as a photodetector. The detector consisted of a receiving-transmitting unit used to emit and receive a light beam, and a reflector installed perpendicular to the directed light beam at the required distance. The nominal distance between the receiving-transmitting unit and the reflector is 2.5±0.1 m.
The Soviet-made photobeam device FEUP-M consisted of an infrared beam emitter and photodetector.

Aspiration detectors

The aspirating detector uses forced air extraction from the protected volume, monitored by ultra-sensitive laser smoke detectors, and provides ultra-early detection of a critical situation. Aspirating smoke detectors allow you to protect objects in which it is impossible to place a fire detector directly.
The fire aspiration detector is applicable in the premises of archives, museums, warehouses, server rooms, switching rooms of electronic communication centers, control centers, "clean" production areas, hospital rooms with high-tech diagnostic equipment, television centers and broadcasting stations, computer rooms and other rooms with expensive equipment . That is, for the most important premises where material values ​​​​are stored or where the funds invested in equipment are huge, or where the damage from stopping production or interrupting operation is great, or the loss of profit from the loss of information is great. On such objects, it is extremely important to reliably detect and eliminate the source at the earliest stage of development, at the stage of smoldering - long before the appearance of open fire, or if overheating of individual components occurs electronic device. At the same time, given that such zones are usually equipped with a temperature and humidity control system, air is filtered in them, it is possible to significantly increase the sensitivity of the fire detector, while avoiding false alarms.
disadvantage aspiration detectors is their high cost.

Autonomous detectors

Autonomous - a fire detector that reacts to a certain level of concentration of aerosol products of combustion (pyrolysis) of substances and materials and, possibly, other fire factors, in the case of which an autonomous power source and all components necessary for detecting a fire and direct notification of it are structurally combined. An autonomous detector is also a point detector.

Ionization detectors

The principle of operation of ionization detectors is based on the registration of changes in the ionization current resulting from exposure to combustion products. Ionization detectors are divided into radioisotope and electrical induction.

Radioisotope detectors

A radioisotope detector is a smoke fire detector that is triggered by the impact of combustion products on the ionization current of the detector's internal working chamber. The principle of operation of a radioisotope detector is based on the ionization of the chamber air when it is irradiated with a radioactive substance. When oppositely charged electrodes are introduced into such a chamber, an ionization current arises. Charged particles "stick" to heavier particles of smoke, reducing their mobility - the ionization current decreases. Its decrease to a certain value is perceived by the detector as an "alarm" signal. Such a detector is effective in fumes of any nature. However, along with the advantages described above, radioisotope detectors have a significant drawback, which should not be forgotten. We are talking about the use of a source of radioactive radiation in the design of detectors. In this regard, there are problems of compliance with safety measures during operation, storage and transportation, as well as disposal of detectors after the end of their service life. Effective for detecting fires accompanied by the appearance of the so-called "black" types of smoke, characterized by high level light absorption.
In Soviet radioisotope detectors (RID-1, KI), the source of ionization was the radioactive isotope of plutonium-239. The detectors are included in the first group of potential radiation hazard.

Radioisotope smoke detector RID-1
The main element of the RID-1 radioisotope detector is two ionization chambers connected in series. The connection point is connected to the control electrode of the thyratron. One of the chambers is open, the other is closed and acts as a compensating element. Air ionization in both chambers is created by plutonium isotope. Under the action of the applied voltage, an ionization current flows in the chambers. When smoke enters an open chamber, its conductivity decreases, the voltage on both chambers is redistributed, resulting in a voltage on the control electrode of the thyratron. When the ignition voltage is reached, the thyratron begins to conduct current. An increase in current consumption will trigger an alarm. The sources of radiation built into the detector are not dangerous, since the radiation is completely absorbed in the volume by the ionization chambers. Danger can arise only if the integrity of the radiation source is violated. The detector also uses a thyratron TX11G with a small amount of radioactive nickel, the radiation is absorbed by the volume of the thyratron and its walls. Danger may arise if the thyratron is broken.
The assigned service life of radioactive sources of detectors was:
RID-1; KI-1; CI-1 - 6 years;
RID-6; RID-6m and the like - 10 years.
The radioisotope smoke detector of the RID-6M type has been serially produced for more than 15 years at the Signal plant (Obninsk, Kaluga region) with a total output of up to 100 thousand pieces. in year. The RID-6M detector has a limited designated service life of alpha sources of the AIP-RID type - 10 years from the date of their release. There is a technology for installing new alpha-sources of the AIP-RID type in fire detectors of previous years of production, which allows the detectors to continue to operate for another 10 years, instead of their forced dismantling and disposal.
High sensitivity allows the use of radioisotope detectors as an integral component of aspiration detectors. When pumping air through the detector in protected premises, it can provide a signal when even an insignificant amount of smoke appears - from 0.1 mg / m³. At the same time, the length of the air intake pipes is practically unlimited. For example, it almost always registers the fact of ignition of a match head at the inlet of an air sampling tube 100 m long.

Electroinductive detectors

The principle of operation of the detector: aerosol particles are sucked in from environment into a cylindrical tube (gas duct) using a small-sized electric pump and enter the charging chamber. Here, under the influence of a unipolar corona discharge, the particles acquire volume electric charge and, moving further along the gas duct, they enter the measuring chamber, where an electric signal is induced on its measuring electrode, which is proportional to the volume charge of the particles and, consequently, their concentration. The signal from the measuring chamber enters the preamplifier and then to the signal processing and comparison unit. The sensor selects the signal by speed, amplitude and duration and provides information when the specified thresholds are exceeded in the form of a contact relay closing.

Electric induction detectors are used in the fire alarm systems of the Zarya and Pirs modules of the ISS.

Flame detectors

Flame detector - a detector that reacts to electromagnetic radiation flame or smoldering hearth.
Flame detectors are used, as a rule, to protect areas where high detection efficiency is required, since fire detection by flame detectors occurs in the initial phase of a fire, when the temperature in the room is still far from the values ​​​​at which the thermal fire detectors are triggered. Flame detectors provide the ability to protect areas with significant heat exchange and open areas where the use of heat and smoke detectors is not possible. Flame detectors are used to control the presence of overheated surfaces of the units in case of accidents, for example, to detect a fire in the car interior, under the casing of the unit, to control the presence of solid fragments of overheated fuel on the conveyor.

Gas detectors

Gas detector - a detector that reacts to gases released during smoldering or burning materials. Gas detectors may react to carbon monoxide (carbon dioxide or carbon monoxide), hydrocarbon compounds.

Flowing fire detectors

Flowing fire detectors are used to detect fire factors as a result of the analysis of the medium propagating through the ventilation ducts exhaust ventilation. The detectors should be installed in accordance with the operating instructions for these detectors and the manufacturer's recommendations, agreed with authorized organizations (having permission for the type of activity).

Manual call points

Fire manual call point - a device designed to manually turn on the fire alarm signal in fire alarm and fire extinguishing systems. Manual fire detectors should be installed at a height of 1.5 m from the ground or floor level. Illumination at the installation site of the manual fire detector must be at least 50 lx.
Manual fire detectors should be installed on escape routes in places accessible for their inclusion in the event of a fire.
In structures for ground storage of flammable and combustible liquids, manual call points are installed on the bund.
By 1900, 675 manual call points were installed in London with a signal output to the fire department. By 1936, the number had increased to 1,732.
In 1925, there were manual call points in Leningrad at 565 points; in 1924, they transmitted about 13% of all messages about fires in the city. At the beginning of the 20th century, there were manual call points included in the ring loop of the recording device. When turned on, the detector produced an individual number of closings and openings and thus transmitted a signal to the Morse device installed on the recording device. Manual call points of the design of that time consisted of a clock mechanism with a pendulum escapement, consisting of two main gears and a signal wheel with three rubbing contacts. The mechanism is actuated by means of a tape coil spring, and the detector mechanism, when actuated, repeats the signal number four times. One spring winding is enough to supply six signals. The contact parts of the mechanism, in order to avoid oxidation, are covered with silver. This type of signaling was proposed in 1924 by the Head of the Workshops of the Fire Telegraph Ryulman A.F. Comrade Lenin. The operation of the alarm system was discovered on March 6, 1924. After a ten-month trial operation, which showed that there was no case of non-receipt of a signal and that the operation of the alarm system was completely trouble-free and accurate, the system was recommended for widespread use.

Application in hazardous areas

When protecting explosive objects with fire alarm systems, it is necessary to use detectors with explosion protection equipment. For point smoke detectors, the type of protection "intrinsically safe circuit (i)" is used. For heat, manual, gas and flame detectors, the types of protection "intrinsically safe circuit (i)" or "flameproof enclosure (d)" are used. A combination of protections i and d is also possible in one detector.

Ionization fire detector - it's high tech automatic device to register a fire source by the appearance in the gas-air environment of the protected room of volatile products of the combustion process - the smallest particles of soot, burning. This detection method is based on the property of ionized air to attract smoke particles, which gave rise to such a name.

In terms of its effectiveness, this is one of the latest stages of technical development, comparable in sensitivity, speed / inertia of detection characteristic features combustion process with the formation of fumes, only with gas, aspiration, flow sensors; exceeding the indicators of optical-electronic devices intended for the same purposes.

Ionization fire detectors are able to detect a fire not only at the earliest stage by the appearance of volatile particles of the combustion reaction, but also react to any size; as well as the color depending on the physical and chemical parameters of the fire load in the protected premises, the so-called gray and black smoke; which is not available to most other automatic devices that detect the formation of a smoke stream.

Due to the complexity of production, technical control when creating such devices; the need for disposal / decontamination of expired ionization fire detectors only at specialized enterprises of the nuclear industry, prerequisites for the high cost of products have been created.

Due to the presence in them, albeit within the permissible state norms, of a small amount of radioactive substances inside miniature radioisotope emitters, which are an integral element of the design in most product models; partly due to the formed prejudiced public opinion in our country, they are not mass-produced.

However, their production continues abroad, and certified in in due course products can be purchased at Russian market fire-technical products.

Smoke-ionization fire detector

According to the definition given in, this is an automatic fire detection device, the method of operation of which is based on a change in the values ​​​​of the electric current passing through artificially ionized air, when smoke particles appear in them, formed during the combustion of solid, liquid materials.

According to the controlled sign of fire, product design, technical device of sensitive elements of sensors, method of detecting smoke particles, ionization fire detectors include two types:

• Radioisotope.

This is a smoke fire detector that is triggered due to the impact of combustion products on the ionization current of the detector's internal working chamber. The principle of operation of a radioisotope detector is based on the ionization of the chamber air when it is irradiated with a radioactive substance. The principle of operation of a radioisotope detector is based on the ionization of the chamber air when it is irradiated with a radioactive substance. When oppositely charged electrodes are introduced into such a chamber, an ionization current arises. Charged particles "stick" to heavier particles of smoke, reducing their mobility - the ionization current decreases. Its decrease to a certain value is perceived by the detector as an "alarm" signal.

Such a detector is effective in fumes of any nature. However, along with the advantages described above, radioisotope detectors have a significant drawback, which should not be forgotten. We are talking about the use of a source of radioactive radiation in the design of detectors. In this regard, there are problems of compliance with safety measures during operation, storage and transportation, as well as disposal of detectors after the end of their service life. Effective for detecting fires accompanied by the appearance of the so-called "black" types of smoke, characterized by a high level of light absorption.

• Electroinduction.

Aerosol particles are sucked from the environment into a cylindrical tube (gas duct) using a small-sized electric pump and enter the charging chamber. Under the influence of a unipolar corona discharge, the particles acquire a volumetric electric charge and, moving further along the gas duct, enter the measuring chamber, where an electrical signal is induced on its measuring electrode, which is proportional to the volumetric charge of the particles and, consequently, their concentration. The signal from the measuring chamber enters the preamplifier and then to the signal processing and comparison unit. The sensor selects the signal by speed, amplitude and duration and provides information when the specified thresholds are exceeded in the form of a contact relay closing.

1. high voltage modulator.
2. Voltage regulator.
3. Power Supply.
4. Amplifier.
5. Block of information processing.
6. Charging chamber, electrode ring.
7. Charging chamber, electrode needle.
8. Capacitor.
9. Resistor.
10. Resistor.
11. Zener diode.
12. induction electrode.
13. Light-emitting diode.
14. Aerosol consumption booster.
15. F - Output signal.

Structurally, the measuring line is a cylindrical gas duct, at the inlet of which there is a charging chamber of the needle-cylinder type, and at the outlet there is a measuring electrode-ring and an air mixture flow stimulator.

The main parameter of an electrically inductive fire detector, which allows the use of a floating threshold, is its sensitivity, which makes it possible to provide a stable level of an electrical signal proportional to the aerosol weight concentration over its entire possible range of change.

In, on the requirements for the design of APS, AUPT systems, it is recommended to select point smoke fire detectors in accordance with their sensitivity to various types of smoke. According to this characteristic indicator, ionization fire detectors are out of competition among similar devices, incl. effectively detect "black" smoke.

The principle of operation of ionization fire detectors

The history of the invention of the smoke radioisotope detector is amazing. In the late 1930s physicist Walter Jaeger was developing an ionization sensor for detecting poison gas. He believed that the ions of air molecules formed under the action of a radioactive element (scheme A, B) would be bound by gas molecules and due to this, the electric current in the device circuit would decrease. However, small concentrations of poisonous gas had no effect on the conductivity in the measuring ionization chamber of the sensor. Walter lit a cigarette in frustration and soon noticed with surprise that a microammeter connected to the sensor recorded a drop in current. It turned out that cigarette smoke particles reproduced the effect that poison gas could not provide (scheme B). This experiment by Walter Jaeger paved the way for the first smoke detector.

It is based on fixing, registering changes in the indicators of the electric current passing through the ionized molecules of the air in the sensitive element of the sensor, when exposed to them small particles volatile combustion reaction products.

When such particles enter the sensor chamber of an ionization smoke detector, they are attached to the ions due to the difference in electrical potentials, which reduces their speed and, as a result, the current strength; with a decrease in their number, removal from the sensitive element of the device, the current strength begins to grow.

The decrease in the strength of the electric current passing through the ionized air to the threshold/critical value set by the product settings is perceived by the device as a sign of the detection of a fire source in the controlled area, the protected room; with the formation, transmission of an alarm message to the receiving and control equipment of the APS installation or the control unit of the automatic fire extinguishing system.

The principle of operation of radioisotope smoke detectors is based on the ionization of the air in the control chamber of the sensitive element located inside the body of the product, with intense radiation from its low-power narrowly directed source of radioactive radiation; in electric induction fire detectors, air ionization is carried out by a unipolar corona discharge of electric current.

The design of the ionization detector

The most widely used in comparison with the electric induction device, the ionization radioisotope smoke detector consists of the following elements:

• Cases made of high-quality plastic, for example, non-combustible polycarbonate with openings for the inlet and outlet of air, flue gases, protected both by a fine metal mesh from insects, and by the shape of the case around them, their location on it to protect against direct air currents.
• Mounting base with electronic printed circuit board, on which two are installed, connected in series in electrical circuit ionization chambers - control and measurement; control unit with a microcontroller for data processing, signal transmission, device addressing; input/output sliding clamp contacts/terminals for connection to the loop of the APS installation.
• Structurally, the control chamber is located inside the measuring chamber, being a closed volume, protected from the penetration of smoke particles; while the measuring chamber is open, it is designed for free penetration, filtration of the gas-air medium to record the changes taking place in it.

• A compact source of radioactive radiation, often containing a negligible amount of the americium-241 isotope, deposited on a metal foil, installed inside the control chamber. Its radiation penetrates through both chambers, forming positively and negatively charged particles in the air - air ions; in this case, the radioisotope radiation source carries a positive charge, and the external measuring chamber carries a negative charge. When power is supplied to the input contacts of an ionization fire detector, an electric field arises inside it.
• When accumulation on the signal electrode, installed at the border of the connection of the control and measuring smoke chambers, a positive charge of sufficient strength, set by the settings of the microcontroller; it is formed through an analog-to-digital converter, which is part of an electronic integrated circuit, into an alarm signal transmitted to the device / unit of the APS installation.

The current strength in the ionized space inside such a fire detector remains stable only while maintaining normal conditions in the control zone.

At the slightest change in the air, ionization fire detectors react sensitively, activating the entire complex of automatic fire protection, which makes it possible, if not immediately, to eliminate the source of ignition; then give an opportunity to localize it, give time before the arrival of fire departments, minimize material damage.

are mandatory engineering system any building. Not only the safety of property depends on their faultless work, but also, most importantly, the health and life of people. Timely and reliable fire detection gives people the opportunity to evacuate to a safe area, and fire brigades - to quickly start extinguishing the fire, preventing its spread.

Types of detectors

Fire detectors in the composition are designed to detect fire. Depending on the principle of action, they are divided into types. It:

• - reacts to the appearance of smoke in the room;
• thermal sensor - triggered when the set temperature is exceeded;
• flame detector - captures the visible or infrared radiation of the flame;
• gas analyzer - registers such as carbon monoxide.

The correct choice of the detector allows you to timely detect the source of the fire.

Fire load and detector type

Premises for various purposes have their own specifics in the development of a fire and the manifestation of its factors. Crucial has a fire load - all objects and materials in the room. For example, the fire of paints or fuel is accompanied by a bright flame, which can be detected by a flame detector. But the same will not be effective in rooms with the storage of materials prone to smoldering; a smoke detector will react to smoke from smoldering materials.

Smoke detectors

The most common and effective tool fire detection is an automatic smoke detector. After all, the release of smoke is characteristic of the combustion process of many substances, such as paper, wood, textiles, cable products, electronic equipment, etc. These sensors are designed to detect fires accompanied by the release of smoke in the early stages of a fire. Detectors of this type are effective when installed in residential buildings, public buildings, production and storage facilities with the circulation of materials prone to smoke during combustion.

How smoke detectors work

The operation of smoke sensors is based on the scattering of light on microparticles of smoke. The emitter of a sensor, usually an LED, operating in the light or infrared range. It irradiates the air in the smoke chamber, when smoked, part of the light flux is reflected from the smoke particles and scattered. This scattered radiation is recorded on a photodetector. A microprocessor based on a photodetector puts the detector into an alarm state. Depending on the concentration of the emitter and receiver, the detectors can be point and linear. The names of devices of this type begin with "IP 212", followed by digital designation models. In the designation, the letters stand for “fire detector”, the first number 2 is “smoke”, the number 12 is “optical”. Thus, the entire marking "IP 212" means: "Optical smoke detector".

Point smoke detectors

In devices of this type, the emitter and receiver are installed in the same housing on opposite sides of the smoke chamber. The perforation of the sensor body ensures unhindered penetration of smoke into the smoke chamber. Thus, the optical-electronic smoke detector controls the degree of smoke in the room only at one point. This type of sensor is compact, easy to install and efficient. Their main drawback is the limited controlled area, not exceeding 80 sq.m. In most cases, point detectors are installed on the ceiling, in increments depending on the height of the room. But it is possible to install them on the walls, under the ceiling.

Linear smoke detectors

In these sensors, the emitter and receiver are made in the form of separate devices installed on different sides premises. Thus, the emitter beam passes through the entire room and controls its smoke. As a rule, the range of this type of detectors does not exceed 150 m. There are variants of devices in which the emitter and receiver are installed in the same housing, and their optical axes are directed in the same direction. For the operation of such a detector, an additional reflector (reflectors) is used, mounted on opposite wall and returning the transmitter beam to the receiver. The linear smoke detector is mainly used to protect long and high spaces, such as halls, indoor arenas, galleries. They are installed on the walls under the ceiling, the emitter on one wall, the receiver on the opposite. In high rooms, such as atriums, sensors are installed in several tiers.

Sensor sensitivity

The most important parameter of smoke detectors is their sensitivity. It characterizes the ability of the sensor to capture the minimum concentration of smoke particles in the analyzed air. This value is measured in dB and is in the range of 0.05-0.2 dB. The difference between high-quality sensors is the ability to maintain their sensitivity when changing orientation, supply voltage, illumination, temperature, and others. external factors. To check the photodetector, special laser pointers or aerosols are used, which allow remote control of the detector's performance.

Analog and address systems

The detectors are connected by a loop to the control panel, which analyzes their condition and, if triggered, issues an alarm signal. Depending on the method of transmitting their state, the detectors are either analog or addressable.

The analog fire smoke detector is connected in parallel to the loop and, when triggered, sharply reduces its resistance, in other words, short-circuits the loop. This is a loop and is fixed by a control panel. As a rule, the connection of analog detectors is carried out by a two-wire loop, through which power is also supplied. But there are options for connecting in a four-wire scheme. The disadvantage of such a system is the inability to continuously monitor the performance of the detector, in addition, sometimes a loop is triggered without indicating the triggered sensor.

The optoelectronic addressable smoke detector is equipped with a microprocessor that monitors the state of the sensor and, if necessary, corrects its settings. Such sensors are connected to a digital loop, in which each detector is assigned its own number. In such a system, control panel not only data on the detector operation and its number are received, but also service information on performance, dust content, etc.

The housings of most modern detectors have built-in LEDs that determine their status by blinking.

Autonomous fire detectors

Often there is no need for installation automatic installation fire alarm, it is enough just to notify people in the same room about the occurrence of a fire. For these purposes, an autonomous smoke detector is intended. These devices combine a smoke sensor and (siren). When the room is filled with smoke, the detector detects the presence of smoke and with its sound signal notifies people about the presence of a dangerous concentration of smoke. Such sensors are self-powered - built-in batteries, the capacity of which is sufficient to operate for three years.

These detectors are ideal for installation in an apartment or small house. Some models allow you to combine sensors into a small network, for example, within an apartment. On the body of such a sensor there is an LED indicator, the color and frequency of flashing of which indicate its condition.