Unfortunately, far from everyone in our country understands the advantages that analog addressable systems provide, and some generally reduce their advantages to "taking care of smokers." Therefore, let's also just look at what the addressable analog systems give us.

It is important not only to detect in time, but also to warn in time.

Let me remind you that there are three classes of fire alarm systems: conventional, addressable, addressable analog.

In non-address and address systems, the "fire decision" is taken directly by the detector itself and then transmitted to the control panel.

Address-analogue systems are inherently telemetry systems. The value of the parameter controlled by the detector (temperature, smoke content in the room) is transmitted to the control panel. The control panel constantly monitors the state of the environment in all areas of the building and, based on this data, makes a decision not only to generate a "Fire" signal, but also a "Warning" signal. We especially emphasize that the "decision" is made not by the detector, but by the control panel. The theory says that if you build a graph of the intensity of a fire depending on time, then it will look like a parabola (Fig. 1). At the initial stage of fire development, its intensity is low, then it increases and then an avalanche-like cycle begins. If you throw an unextinguished cigarette butt into a basket of papers, they will first smolder with the release of smoke, then a flame will appear, it will spread to the furniture, and then an intensive development of a fire will begin, which is no longer easy to cope with.

It turns out that if a fire is detected at an early stage, it is easy to eliminate it with a glass of water or a conventional fire extinguisher and the damage from it will be minimal. This is exactly what address-analogue systems allow you to do. If, for example, a conventional (or addressable) heat detector provides the formation of a "Fire" signal at a temperature of 60 ° C, then until this value is reached, the duty officer does not see any information on the control panel about what is happening in the room. And yet, this already implies a significant source of fire. A similar situation is observed with smoke detectors, where the required level of smoke must be achieved.

Addressable does not mean addressable analog

Address-analogue systems, constantly monitoring the state of the environment in the room, immediately detect the beginning of a change in temperature or smoke and issue a warning signal to the duty officer. Therefore, analog addressable systems provide early fire detection. This means that the fire can be easily extinguished with minimal damage to the building.

We emphasize that the "watershed" is located not by non-address systems, on the one hand, and by address and address-analog systems, on the other, but by address-analog and other systems.

In real addressable analog devices, there is a principle. the ability to individually set not only the levels of generating "Fire" and "Warning" signals for each detector, but also determine the logic of their joint operation. In other words, we get a tool in our hands that allows us to optimally form an early fire detection system for each object, taking into account its individual characteristics, i.e. we have a principle. the ability to optimally build the fire safety system of the facility.

Along the way, a number of important tasks are also solved, for example, monitoring the performance of detectors. So, in the analog addressable system, in principle, there cannot be a faulty detector that is not detected by the control panel, since the detector must transmit a certain signal all the time. If we add to this the powerful self-diagnostics of the detectors themselves, automatic dust compensation and the detection of dusty smoke detectors, it becomes obvious that these factors only increase the efficiency of addressable analog systems.

Key Features

An important component of addressable analog devices is the construction of alarm loops. the protocol of the loop is the know-how of the company and is a trade secret. However, it is he who largely determines the characteristics of the system. Let's study the most characteristic features of address-analogue systems.

Number of detectors in the loop

It usually ranges from 99 to 128 and is limited by the power supply capabilities of the detectors. In early models, the detectors were addressed using mechanical switches, in later models there are no switches, and the address is stored in the non-volatile memory of the sensor.

Alarm loop

In principle, most analog addressable devices are capable of operating with a stub. but there is a possibility of "losing" a large number of detectors due to a broken loop. Therefore, the ring loop is a means of increasing the survivability of the system. When it breaks, the device generates a corresponding notification, but ensures operation with each half ring, thereby maintaining the performance of all detectors.

Short circuit locating devices

This is also a means of increasing the "survivability" of the system. Typically, these devices are installed through 20-30 detectors. In the event of a short circuit in the loop, the current in it increases, which is detected by two localization devices, and the faulty section is turned off. only the loop segment with two short circuit localization devices fails, and the rest of it remains operational due to the ring organization of the connection.

In modern systems, each detector or module is equipped with a built-in short circuit localization device. At the same time, due to a significant reduction in prices for electronic components, the cost of sensors did not actually increase. Such systems practically do not suffer from short circuits of loops.

Standard set of detectors

It includes smoke optoelectronic, thermal maximum temperature, thermal maximum-differential, combined (smoke plus thermal) and manual call points. These detectors are usually sufficient to protect the main types of rooms in a building. Some manufacturers additionally offer quite exotic types of sensors, for example, an analog addressable linear detector, an optical smoke detector for rooms with a high level of pollution, an optical smoke detector for explosive rooms, etc. All this expands the scope of analog addressable systems.

Non-address sub-loop control modules

They allow the use of conventional detectors. This reduces the cost of the system, but, of course, the properties inherent in addressable analog equipment are lost. In some cases, such modules can be successfully used to connect conventional linear smoke detectors or create explosion-proof loops.

Command and control modules

They are connected directly to the alarm loops. Usually the number of modules corresponds to the number of detectors in the loop, and their address field is additional and does not overlap with detector addresses. In some systems, the address field of detectors and modules is shared.

The total number of connected modules can be several hundred. It is this property that allows, on the basis of the SPS addressable analog fire alarm system, to integrate the automatic fire protection systems of the building (Fig. 2).

During integration, executive devices are controlled and their operation is monitored. The number of control and management points is just a few hundred.

Branched logic for generating control signals

This is an indispensable attribute of analogue addressable control panels. It is the powerful logical functions that ensure the construction of a unified system of automatic fire protection of the building. Among these functions are the logic of generating a "Fire" signal (for example, by two triggered detectors in a group), and the logic of turning on the control module (for example, with each "Fire" signal in the system or with a "Fire" signal in this group), and the principle . the ability to set time parameters (for example, when the signal "Fire" turn on the control module M after time T1 for time T2). All this makes it possible to effectively build even powerful gas fire extinguishing systems on the basis of standard elements.

And not only early detection

The very principle of building addressable analog systems allows, in addition to early detection of a fire, to obtain a number of unique qualities, for example, an increase in the noise immunity of the system. Let's explain this with an example.

On fig. 3 shows several successive polling cycles (n) by the thermal addressable analog detector. For ease of understanding, along the ordinate axis, we will postpone not the duration of the signal from the detector, but immediately the temperature value corresponding to it. Let a false signal from the detector or a distortion of the duration of the detector's response under the influence of electromagnetic interference pass on the polling cycle 4, so that the value perceived by the device corresponds to a temperature of 80 °C. according to the received false signal, the device should generate a "Fire" signal, i.e. equipment will malfunction.

In addressable analog systems, this can be avoided by introducing an averaging algorithm. For example, we introduce averaging over three successive readings. the parameter value for "making a decision" about the fire will be the sum of the values ​​for the three cycles, divided by 3:

• for cycles 1, 2, 3 Т=60:3=20 °С – below the threshold;
• for cycles 2, 3, 4 Т=120:3=40 °С – below the threshold;
• for cycles 3, 4, 5 Т=120:3=40 °С – below the threshold.

That is, when a false count came, the "Fire" signal was not generated. At the same time, I would like to pay special attention to the fact that since the "decision" is made by the control panel, no resets and re-requests of the detectors are needed.

Note that if the incoming signal is not false, then on cycles 4 and 5 the parameter value corresponds to 80 °C, then with this averaging the signal will be generated, since T=180:3=60 °C, which means it corresponds to the signal generation threshold "Fire ".

What is the result?

So, we have seen that, due to their unique properties, analog-address systems are an effective means of ensuring the fire safety of objects. The number of detectors in such systems can be several tens of thousands, which is enough for the most ambitious projects.

The market of address-analog systems abroad over the past few years has a steady upward trend. The share of analog addressable systems in the total production volume confidently exceeded 60%. The mass production of analog addressable detectors led to a decrease in their cost, which was an additional incentive to expand the market.

Unfortunately, according to various estimates, the share of addressable analog systems in our country is from 5 to 10%. The lack of an insurance system and current regulations do not contribute to the introduction of high-quality equipment and the cheapest equipment is often used. Nevertheless, certain shifts have already been outlined, and it seems that we are on the verge of a fundamental change in the market. Only in recent years, the cost of an optical smoke addressable analog detector in Russia has decreased by about 2 times, which makes them more affordable. Without address-analog systems, it is unthinkable to ensure the safety of high-rise buildings, multifunctional complexes and a number of other categories of objects.

In the Russian Federation, about 700 fires occur every day, in which more than 50 people die. Therefore, the preservation of human life remains one of the most important tasks of all security systems. Recently, the topic of early fire detection has been increasingly discussed.

Developers of modern fire fighting equipment compete in increasing the sensitivity of fire detectors to the main signs of a fire: heat, optical radiation from the flame and smoke concentration. A lot of work is being done in this direction, but all fire detectors are triggered when at least a small fire has already started. And few people discuss the topic of detecting possible signs of a fire. However, devices that can register not a fire, but only the threat or probability of a fire, have already been developed. These are gas fire detectors.

Comparative analysis

It is known that a fire can occur both from a sudden emergency (explosion, short circuit), and with the gradual accumulation of dangerous factors: the accumulation of combustible gases, vapors, overheating of a substance above the flash point, smoldering insulation of electrical cable wires from overload, rotting and heating of grain and etc.

On fig. Figure 1 is a graph of a typical gas fire detector response to a fire starting with a burning cigarette dropped on a mattress. The graph shows that the gas detector reacts to carbon monoxide after 60 minutes. after a burning cigarette hits the mattress, in the same case, the photoelectric smoke detector reacts after 190 minutes, the ionization smoke detector - after 210 minutes, which significantly increases the time for making a decision to evacuate people and eliminate the fire.

If you fix a set of parameters that can lead to the start of a fire, then you can (without waiting for the appearance of a flame, smoke) change the situation and avoid a fire (accident). If a signal from a gas fire detector is received early, the maintenance personnel will have time to take measures to mitigate or eliminate the threat factor. For example, it can be ventilation of the room from combustible vapors and gases, in case of insulation overheating, turning off the cable power and switching to the use of a backup line, in case of a short circuit on the electronic board of computers and controlled machines, extinguishing a local fire and removing the faulty unit. Thus, it is the person who makes the final decision: call the fire brigade or eliminate the accident on their own.

Types of gas detectors

All gas fire detectors differ in the type of sensor:
- metal oxide,
- thermochemical,
- semiconductor.

Metal oxide sensors

Metal oxide sensors are manufactured on the basis of thick-film microelectronic technology. Polycrystalline alumina is used as a substrate, on which a heater and a metal oxide gas sensitive layer are deposited on both sides (Fig. 2). The sensing element is placed in a housing protected by a gas-permeable sheath that meets all explosion and fire safety requirements.

Metal oxide sensors are designed to determine the concentrations of combustible gases (methane, propane, butane, hydrogen, etc.) in the air in the concentration range from thousandths to units of percent and toxic gases (CO, arsine, phosphine, hydrogen sulfide, etc.) at the level of maximum permissible concentrations, as well as for the simultaneous and selective determination of the concentrations of oxygen and hydrogen in inert gases, for example, in rocket technology. In addition, they have a record low electric power required for heating (less than 150 mW) for their class, and can be used in gas leak detectors and fire alarm systems, both stationary and portable.

Thermochemical gas detectors

Among the methods used to determine the concentration of combustible gases or vapors of combustible liquids in the atmospheric air, the thermochemical method is used. Its essence lies in measuring the thermal effect (additional increase in temperature) from the oxidation reaction of combustible gases and vapors on the catalytically active sensor element and further converting the received signal. The alarm sensor, using this thermal effect, generates an electrical signal proportional to the concentration of combustible gases and vapors with different proportionality factors for different substances.

During the combustion of various gases and vapors, the thermochemical sensor generates signals of different magnitudes. Equal levels (in % LEL) of various gases and vapors in air mixtures correspond to unequal sensor output signals.

The thermochemical sensor is not selective. Its signal characterizes the level of explosiveness, determined by the total content of combustible gases and vapors in the air mixture.

In the case of control of a set of components, in which the content of individual, previously known combustible components ranges from zero to a certain concentration, it can lead to control errors. This error also exists under normal conditions. This factor must be taken into account to set the limits of the range of signal concentrations and the tolerance for their change - the limit of the permissible basic absolute error of operation. The measurement limits of the signaling device are the smallest and highest values ​​of the concentration of the determined component, within which the signaling device measures with an error not exceeding the specified one.

Description of the measuring circuit

The measuring circuit of the thermochemical converter is a bridge circuit (see Fig. 2). Sensitive B1 and compensating B2 elements located in the sensor are included in the bridge circuit. The second branch of the bridge - resistors R3-R5 are located in the signaling unit of the corresponding channel. The bridge is balanced by resistor R5.

During catalytic combustion of an air mixture of combustible gases and vapors on the sensing element B1, heat is released, the temperature rises and, consequently, the resistance of the sensing element increases. There is no combustion on the compensating element B2. The resistance of the compensating element changes with its aging, changes in the supply current, temperature, speed of the controlled mixture, etc. The same factors act on the sensitive element, which significantly reduces the unbalance of the bridge caused by them (zero drift) and the control error.

With stable bridge power, stable temperature, and controlled mixture speed, bridge unbalance results with a significant degree of accuracy from changes in the resistance of the sensing element.

In each channel, the power supply of the sensor bridge provides a constant optimum temperature of the elements by regulating the current. As a temperature sensor, as a rule, the very same sensitive element B1 is used. The bridge unbalance signal is taken from the bridge diagonal ab.

Semiconductor gas sensors

The principle of operation of semiconductor gas sensors is based on a change in the electrical conductivity of a semiconductor gas-sensitive layer during chemical adsorption of gases on its surface. This principle allows them to be effectively used in fire alarm devices as alternative devices to traditional optical, thermal and smoke signaling devices (detectors), including those containing radioactive plutonium. And the high sensitivity (for hydrogen from 0.00001% by volume), selectivity, speed and low cost of semiconductor gas sensors should be considered as their main advantage over other types of fire detectors. The physical and chemical principles of signal detection used in them are combined with modern microelectronic technologies, which leads to low cost of products in mass production and high technical characteristics.

Semiconductor gas sensitive sensors are high-tech elements with low power consumption (from 20 to 200 mW), high sensitivity and increased speed up to fractions of a second. Metal oxide and thermochemical sensors are too expensive for this use. The introduction into production of gas fire detectors based on semiconductor chemical sensors manufactured using group technology makes it possible to significantly reduce the cost of gas detectors, which is important for mass use.

Regulatory requirements

Regulatory documents for gas fire detectors have not yet been fully developed. The existing departmental requirements of RD BT 39-0147171-003-88 apply to oil and gas industry facilities. NPB 88-01 on the placement of gas fire detectors says that they should be installed indoors on the ceiling, walls and other building structures of buildings and structures in accordance with the operating instructions and recommendations of specialized organizations.

However, in any case, in order to accurately calculate the number of gas detectors and correctly install them at the facility, you first need to know:
- parameter by which safety is controlled (type of gas that is released and indicates a hazard, eg CO, CH4, H2, etc.);
- the volume of the room;
- purpose of the premises;
- availability of ventilation systems, air overpressure, etc.

Summary

Gas fire detectors are next-generation devices, and therefore they still require new research studies from domestic and foreign companies involved in fire systems to develop a theory of gas emission and distribution of gases in rooms of different purposes and operation, as well as to conduct practical experiments to development of recommendations for the rational placement of such detectors.

This system is designed to detect the initial stage of a fire, transmit a notice about the place and time of its occurrence, and, if necessary, turn on automatic fire extinguishing and smoke removal systems.

An effective fire warning system is the use of alarm systems.

The fire alarm system must:

* - quickly identify the place of fire;

* - reliably transmit a fire signal to the receiving and control device;

* - convert the fire signal into a form convenient for perception by the personnel of the protected facility;

* - remain immune to the influence of external factors other than fire factors;

* - quickly detect and transmit notification of malfunctions that prevent the normal functioning of the system.

Industrial buildings of categories A, B and C, as well as objects of national importance, are equipped with fire-fighting automation.

The fire alarm system consists of fire detectors and converters that convert the fire initiation factors (heat, light, smoke) into an electrical signal; a control station that transmits a signal and turns on light and sound alarms; as well as automatic fire extinguishing and smoke removal installations.

Detecting fires at an early stage makes it easier to extinguish them, which largely depends on the sensitivity of the sensors.

Automatic fire extinguishing systems

Automatic fire extinguishing systems are designed to extinguish or localize a fire. At the same time, they must also perform the functions of an automatic fire alarm.

Automatic fire extinguishing installations must meet the following requirements:

* - the response time must be less than the maximum allowable time for the free development of a fire;

* - have the duration of action in the extinguishing mode necessary to eliminate the fire;

* - have the required intensity of supply (concentration) of fire extinguishing agents;

* - reliability of functioning.

In the premises of categories A, B, C, stationary fire extinguishing installations are used, which are divided into aerosol (halocarbon), liquid, water (sprinkler and deluge), steam, powder.

The most widespread at present are sprinkler installations for extinguishing fires with sprayed water. To do this, a network of branched pipelines is mounted under the ceiling, on which sprinklers are placed at the rate of irrigation with one sprinkler from 9 to 12 m 2 of the floor area. There must be at least 800 sprinklers in one section of the water system. The floor area protected by one CH-2 type sprinkler should be no more than 9 m 2 in rooms with increased fire hazard (if the amount of combustible materials is more than 200 kg per 1 m 2; in other cases - no more than 12 m 2. The outlet in the sprinkler head is closed with fusible lock (72 ° C, 93 ° C, 141 ° C, 182 ° C), when melted, water splashes, hitting the deflector. The irrigation intensity of the area is 0.1 l / s m 2

Sprinkler networks must be pressurized to deliver 10 l/s. If at least one sprinkler opens during a fire, an alarm is given. Control and signal valves are located in visible and accessible places, and no more than 800 sprinklers are connected to one control and signal valve.

In fire hazardous premises, it is recommended to supply water immediately over the entire area of ​​\u200b\u200bthe premises. In these cases, group action installations (drencher) are used. Drencher are sprinklers without fusible locks with open holes for water and other compounds. In normal times, the water outlet to the network is closed by a group action valve. The intensity of the water supply is 0.1 l / s m 2 and for rooms of increased fire danger (with the amount of combustible materials 200 kg per 1 m 2 or more) - 0.3 l / s m 2.

The distance between drenchers should not exceed 3 m, and between drenchers and walls or partitions - 1.5 m. The floor area protected by one drencher should be no more than 9m 2. During the first hour of extinguishing a fire, at least 30 l / s must be supplied

The units allow for automatic measurement of monitored parameters, recognition of signals in the presence of an explosive situation, conversion and amplification of these signals, and issuance of commands to turn on protection actuators.

The essence of the explosion termination process is the inhibition of chemical reactions by supplying fire extinguishing compositions to the combustion zone. The possibility of stopping the explosion is due to the presence of a certain time interval from the moment the conditions of the explosion arise to its development. This period of time, conditionally called the induction period (f ind), depends on the physicochemical properties of the combustible mixture, as well as on the volume and configuration of the protected apparatus.

For most combustible hydrocarbon mixtures f ind is about 20% of the total explosion time.

In order for an automatic explosion protection system to fulfill its purpose, the following condition must be met:< ф инд, то есть, время срабатывания защиты должно опережать время индуктивного периода.

The conditions for the safe use of electrical equipment are regulated by the PUE. Electrical equipment is divided into explosion-proof, suitable for fire hazardous areas, and normal performance. In hazardous areas, it is allowed to use only explosion-proof electrical equipment, differentiated by levels and types of explosion protection, categories (characterized by a safe gap, that is, the maximum diameter of the hole through which the flame of a given combustible mixture is not able to pass), groups (which are characterized by T with a given combustible mixture).

In explosive rooms and areas of external installations, special electric lighting equipment is used, made in an anti-explosion version.

smoke hatches

Smoke hatches are designed to ensure that adjacent rooms are smoke-free and reduce the concentration of smoke in the lower zone of the room in which a fire has occurred. By opening smoke hatches, more favorable conditions are created for the evacuation of people from a burning building, and the work of fire departments in extinguishing a fire is facilitated.

To remove smoke in the event of a fire in the basement, the norms provide for the installation of windows with a size of at least 0.9 x 1.2 m for every 1000 m 2 of the basement area. The smoke hatch is usually closed with a valve.

(light, heat, smoke) are capable only of the message: “We are burning! It's time to put out the fire!" But it cannot be otherwise, since the operation of their sensors is based on such physical principles as the detection of light, heat or smoke. Get the message "Attention! A fire is possible here!” is possible only by establishing constant control over the gas-dynamic composition of the indoor air. Such control will make it possible to take adequate measures to prevent a fire and eliminate it in the bud. This is what makes the method of early fire detection developed by Gamma specialists using semiconductor chemical sensors, which was awarded diplomas and gold medals at the international exhibitions Brussels-Eureka 2000 and Geneva 2001.

Thus, a reliable way to prevent a fire at an early stage, preceding ignition, is to control the chemical composition of the air, which changes dramatically due to the thermal decomposition of overheated or smoldering combustible materials. At this stage, preventive measures are still effective. For example, in case of overheating of electrical appliances (iron or electric fireplace), they can be automatically turned off in time by a signal from a gas sensor.

The composition of gases released during combustion

A number of gases released at the initial stage of combustion (smoldering) are determined by the composition of precisely those materials that participate in this process. However, in most cases, the main characteristic gas components can also be identified with confidence. Similar studies were carried out at the Institute of Fire Safety (Balashikha, Moscow Region) using a standard chamber with a volume of 60 m 3 to simulate a fire. The composition of gases released during combustion was determined by chromatography. The experiments gave the following results.

Hydrogen (H 2) is the main component of the gases emitted at the smoldering stage as a result of the pyrolysis of materials used in construction, such as wood, textiles, and synthetic materials. At the initial stage of the fire, in the process of smoldering, the concentration of hydrogen is 0.001-0.002%. In the future, there is an increase in the content of aromatic hydrocarbons against the background of the presence of underoxidized carbon - carbon monoxide (CO) - 0.002-0.008%. When a flame appears, the concentration of carbon dioxide (CO 2) rises to a level of 0.1%, which corresponds to the combustion of 40-50 g of wood or paper in a closed room with a volume of 60 m 3 and is equivalent to 10 smoked cigarettes. This level of CO2 is also achieved as a result of the presence of two people in the room for 1 hour.

Experiments have shown that the detection threshold for an early fire warning system in atmospheric air under normal conditions should be at the level of 0.002% for most gases, including hydrogen and carbon monoxide. It is desirable that the system speed be no worse than 10 s. This conclusion can be considered as fundamental to the development of a number of warning fire gas detectors.

Existing environmental gas analysis tools (including those based on electrochemical, thermal catalytic and other sensors) are too expensive for such use. The introduction of fire detectors based on semiconductor chemical sensors manufactured using batch technology into production will dramatically reduce the cost of gas sensors.

Semiconductor gas sensors

The principle of operation of semiconductor gas sensors is based on a change in the electrical conductivity of a semiconductor gas-sensitive layer during chemical adsorption of gases on its surface. This circumstance makes it possible to effectively use them in fire alarm devices as alternative devices to traditional optical, thermal and smoke alarms, including those containing radioactive plutonium. And high sensitivity (for hydrogen - from 0.000001%!), Selectivity, speed and low cost of semiconductor gas sensors should be considered as their main advantages over other types of fire detectors. The physical and chemical principles of signal detection used in them are combined with modern microelectronic technologies, which determines the low cost of products in mass production and high technical and energy-saving characteristics.

In order for physical and chemical processes to proceed on the surface of the sensitive layer quickly enough, providing a speed of several seconds, the sensor is periodically heated to a temperature of 450-500°C, which activates its surface. Finely dispersed metal oxides (SnO 2 , ZnO, In 2 O 3 , etc.) with dopants Pl, Pd, etc. are usually used as sensitive semiconductor layers. Due to the structural porosity of the formed materials, achieved using certain technological methods, their specific surface area is about 30 m 2 /g. The heater is a resistive layer made of inert materials (Pl, RuO 2 , Au, etc.) and electrically isolated from the semiconductor layer.

With seeming simplicity, such formation methods have concentrated all the latest achievements in materials science and microelectronic technology. This led to the high competitiveness of the sensor, which can operate for several years, periodically being in a “stressed” state when heated to 500°C, while maintaining high performance characteristics, sensitivity, stability, selectivity, and consumes low power (a few tens of milliwatts on average). The industrial production of semiconductor sensors is widely developed all over the world, but the main share of the world market falls on Japanese companies. The recognized leader in this field is Figaro with an annual production of about 5 million sensors. and large-scale production of devices based on them, including the element base and circuit solutions with programmable devices.

However, a number of features in the production of semiconductor sensors make it difficult to be compatible with traditional silicon technology in a closed loop. This is explained by the fact that sensors are not as mass-produced as microcircuits, and have a larger spread of parameters due to the specifics of operating conditions (often in an aggressive environment). Their production requires very specific know-how in physical chemistry, materials science, etc. Therefore, success here accompanies large specialized firms (for example, Microchemical Instrument - the European subsidiary of Motorola), which are in no hurry to share their developments in the field of high technologies. Unfortunately, this industry has never been well developed in Russia and the CIS, despite a sufficient number of research groups - RRC "Kurchatov Institute", Moscow State University, Leningrad State University, Voronezh State University, IGIC RAS, N.I. Karpov, Saratov University, Novgorod University, etc.

Domestic developments of semiconductor sensors

The most developed technology for the production of semiconductor sensors is proposed at the RRC "Kurchatov Institute". It has developed small-sized semiconductor sensors for the analysis of the chemical composition of gases and liquids. They are manufactured using microelectronic technology and combine the advantages of microelectronic devices - low cost in mass production, miniaturization, low power consumption - with the ability to measure the concentration of gases and liquids over a wide range and with sufficiently high accuracy. The developed devices are divided into two groups: metal oxide and structural semiconductor sensors.

metal oxide sensors. Manufactured using thick film technology. Polycrystalline alumina is used as a substrate, on which a heater and a metal oxide gas sensitive layer are deposited on both sides. The sensitive element is placed in a gas-permeable housing that meets the requirements of explosion and fire safety.

Sensors are able to determine the concentration of combustible gases (methane, propane, butane, hydrogen, etc.) in the air in the range from 0.001% to a few percent, as well as toxic gases (carbon monoxide, arsine, phosphine, hydrogen sulfide, etc.) at the level of maximum permissible concentration (MAC). They can also be used for the simultaneous and selective determination of the concentration of oxygen and hydrogen in inert gases, for example, for rocket technology. For heating, these devices require a record low electric power for their class - less than 150 mW. Metal oxide sensors are designed for use in gas leak detectors and fire alarm systems (both stationary and pocket).

Structural semiconductor sensors. These are sensors based on metal-dielectric-semiconductor (MIS) silicon structures, metal-solid electrolyte-semiconductor and Schottky diodes.

MIS structures with a palladium or platinum gate are used to determine the concentration of hydrogen in air or inert gases. The hydrogen detection threshold is about 0.00001%. Sensors have been successfully used to determine the concentration of hydrogen in the coolant of nuclear reactors in order to maintain their safety. Structures with a solid electrolyte (lanthanum trifluoride, conducting over fluorine ions) are designed to determine the concentration of fluorine and fluorides (primarily hydrogen fluoride) in the air. They work at room temperature, allow to determine the concentration of fluorine and hydrogen fluoride at the level of 0.000003%, which is approximately 0.1 MPC. Hydrogen fluoride leakage measurement is especially important for determining the environmental situation in regions with large production of aluminum, polymers, and nuclear fuel.

Similar structures made on the basis of silicon carbide and operating at a temperature of about 500 °C can be used to measure the concentration of freons.

Indicator of carbon monoxide and hydrogen CO-12

An internationally featured method for early fire detection provides simultaneous monitoring of the relative air concentrations of two or more gases, such as aromatic hydrocarbons, hydrogen, carbon monoxide and carbon dioxide. The obtained values ​​are compared with the set ones, and if they match, an alarm is generated. Control and comparison of relative concentrations of gas components are carried out with a given frequency. The possibility of false alarms of the measuring device with an increase in the concentration of one of the gases is excluded if there is no ignition.

As a measuring device, the CO-12 indicator is proposed, designed to detect gaseous carbon monoxide and hydrogen in the air atmosphere in the range of their concentrations from 0.001 to 0.01%. The device is a nine-level proportional indicator in the form of a line of LEDs of three colors - green (low concentration range), yellow (medium level) and red (high level). Three LEDs correspond to each range. When the red LEDs light up, an audible signal is activated to warn people of the danger of poisoning.

The principle of operation of the indicator is based on registering the change in resistance (R) of a semiconductor gas sensitive sensor, the temperature of which stabilizes at 120 °C during the measurement process.

In this case, the heating element is included in the feedback of the operational amplifier - temperature controller - and periodically, every 6 s, is annealed for 0.5 s at a temperature of 450 ° C. This is followed by isothermal relaxation of the resistance R upon interaction with carbon monoxide. R is measured before the next annealing (Fig. 3, point C, followed by annealing O). The process of measurement and output to the indicator of data is controlled by a programmable device.

Its main technical characteristics:

The indicator can be effectively used as a fire alarm device both in residential premises and industrial facilities. Country houses, cottages, baths, saunas, garages and boiler houses, enterprises with production based on the use of open fire and heat treatment, enterprises in the mining, metallurgical and oil and gas processing industries and, finally, road transport - this is not a complete list of objects where the CO indicator is 12 might be helpful.

Such early detection fire detectors, united in a single network and controlling gas release during smoldering of materials before they ignite, when placed at industrial facilities, make it possible to prevent emergencies not only at ground fire protection facilities, but also in underground structures, coal mines, where, as a result of overheating, equipment transporting coal, coal dust may ignite. Each sensor, which has light and sound warning signals, is able not only to inform about the degree of gas contamination of the territory, but also to warn personnel located in close proximity to the extreme place about the danger. Stationary fire detectors installed in residential premises can prevent household gas explosions, carbon monoxide poisoning and fires due to a malfunction of household appliances or a gross violation of their operating conditions by automatically disconnecting from the network.

Electronics №4, 2001

This system is designed to detect the initial stage of a fire, transmit a notice about the place and time of its occurrence, and, if necessary, turn on automatic fire extinguishing and smoke removal systems.

An effective fire warning system is the use of alarm systems.

The fire alarm system must:

Quickly identify the location of the fire;

Reliably transmit a fire signal to the receiving and control device;

Convert the fire signal into a form convenient for perception by the personnel of the protected facility;

Remain immune to the influence of external factors other than fire factors;

Quickly identify and report malfunctions that prevent the normal functioning of the system.

Industrial buildings of categories A, B and C, as well as objects of national importance, are equipped with fire-fighting automation.

The fire alarm system consists of fire detectors and converters that convert the fire initiation factors (heat, light, smoke) into an electrical signal; a control station that transmits a signal and turns on light and sound alarms; as well as automatic fire extinguishing and smoke removal installations.

Detecting fires at an early stage makes it easier to extinguish them, which largely depends on the sensitivity of the sensors.

Announcers, or sensors, can be of various types:

- thermal fire detector- an automatic detector that responds to a certain temperature value and (or) its rate of increase;

- smoke fire detector- an automatic fire detector that reacts to aerosol combustion products;

- radioisotope fire detector - a smoke fire detector that is triggered due to the influence of combustion products on the ionized flow of the detector's working chamber;

- optical fire detector- a smoke fire detector that is triggered due to the influence of combustion products on the absorption or propagation of the detector's electromagnetic radiation;

- flame fire detector- reacts to the electromagnetic radiation of the flame;

- combined fire detector- responds to two (or more) fire factors.

Heat detectors are divided into maximum, which are triggered when the temperature of the air or the protected object rises to the value to which they are adjusted, and differential, which are triggered at a certain rate of temperature increase. Differential thermal detectors can usually also operate in maximum mode.

Maximum thermal detectors are characterized by good stability, do not give false alarms and have a relatively low cost. However, they are insensitive and even when placed at a short distance from the places of possible fires, they work with a significant delay. Differential type heat detectors are more sensitive, but their cost is high. All heat detectors must be placed directly in the working areas, so they are subject to frequent mechanical damage.

Rice. 4.4.6. Schematic diagram of the detector PTIM-1: 1 - sensor; 2 - variable resistance; 3 - thyratron; 4 - additional resistance.

Optical detectors are divided into two groups : IR - direct vision indicators, which should "see" the fire, and photovoltaic flue. The sensing elements of direct vision indicators are of no practical importance, since they, like heat detectors, must be located in close proximity to potential sources of fire.

Photoelectric smoke detectors are triggered when the luminous flux in the illuminated photocell is weakened as a result of air smoke. Detectors of this type can be installed at a distance of several tens of meters from a possible source of fire. Dust particles suspended in the air can lead to false alarms. In addition, the sensitivity of the device decreases markedly as the finest dust settles, so the detectors must be regularly inspected and cleaned.

Ionization smoke detectors for reliable operation, it is necessary to thoroughly inspect and check at least once every two weeks, remove dust deposits in a timely manner and adjust the sensitivity. Gas detectors are triggered by the presence of gas or an increase in its concentration.

Smoke detectors designed to detect products of combustion in the air. The device has an ionization chamber. And when smoke from a fire enters it, the ionization current decreases, and the detector turns on. The response time of a smoke detector when smoke enters it does not exceed 5 seconds. Light detectors are arranged according to the principle of operation of ultraviolet radiation from a flame.

The choice of the type of automatic fire alarm detector and the installation location depends on the specifics of the technological process, the type of combustible materials, the methods of their storage, the area of ​​the room, etc.

Heat detectors can be used to control premises at the rate of one detector per 10-25 m2 of floor. A smoke detector with an ionization chamber is capable (depending on the installation location) of serving an area of ​​30 - 100m 2 . Light detectors can control an area of ​​about 400 - 600m 2 . Automatic detectors are mainly installed on the stream or suspended at a height of 6 - 10 m from the floor level. The development of the algorithm and functions of the fire alarm system is carried out taking into account the fire hazard of the facility and architectural and planning features. At present, the following fire alarm installations are used: TOL-10/100, APST-1, STPU-1, SDPU-1, SKPU-1, etc.

Rice. 4.5.7. Scheme of the automatic smoke detector ADI-1: 1.3 - resistance; 2 - electric lamp; 4 - ionization chamber; 5 - scheme for connecting to the electrical network