IN Russian Federation Every day there are about 700 fires, which kill more than 50 people. Therefore, the preservation of human life remains one of the most important tasks of all security systems. IN Lately The topic of early fire detection is being discussed more and more.
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 fire and explosion safety requirements.
Metal oxide sensors are designed to determine the concentration 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 anti- fire alarm both fixed 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 the measurement thermal effect(additional increase in temperature) from the oxidation reaction of combustible gases and vapors on the catalytically active sensor element and further conversion of 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 a control error. This error also exists for 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 imbalance 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 RD BT 39-0147171-003-88 apply to oil and gas industry. 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 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 the next generation devices, and therefore they still require domestic and foreign companies involved in fire fighting systems, new research studies on the development of the theory of gas release and distribution of gases in rooms of different purposes and operation, as well as conducting practical experiments to develop recommendations for the rational placement of such detectors.
UDC 614.842.4
MODERN SYSTEMS FOR EARLY FIRE DETECTION
M. V. Savin, V. L. Zdor
All-Russian Research Institute of Fire Defense EMERCOM of Russia
given a brief description of different types of fire detectors, their advantages and disadvantages. The device and advantages of aspiration fire detectors are considered in detail.
One of the most important elements of a fire alarm system are the fire-broadcasters. They are subdivided depending on the type of physical fire factor to which they react, and, accordingly, are classified into heat, smoke, gas, flame detectors, combined. In addition, depending on the configuration of the measuring zone, there are point, multipoint and linear fire detectors. The point fire detector reacts to the fire factor controlled near its compact sensing element. A multi-point fire detector characterizes a discrete arrangement of point sensitive elements in a measuring line. A linear fire detector is a detector whose geometric shape of the control zone has an extended section, that is, control environment carried out along a line. Each type of fire detector has its own advantages and disadvantages. The combination of these properties determines the scope of their application. But still, all these detectors have one common drawback - this is the so-called "passive" scanning of the protected area. After all, they actually wait until the factors accompanying the fire (smoke, fever), will themselves be in the detection field of the detector. In particular, a smoke detector will only give an alarm when smoke enters the detector chamber, which largely depends on the presence of air currents in the protected room.
At present, aspiration fire detectors have begun to be actively introduced in our market. They represent the detector itself, consisting of a sensitive element and a signal processing circuit, which can be located both inside and outside the protected premises, and a system of intake pipelines through which air samples are transported from outside.
protected room to the sensitive element of the aspiration fire detector.
Aspirating fire detectors have several major advantages over traditional smoke detection systems. First of all, ensuring the delivery of air samples to the sensitive element, regardless of the presence of forced and natural air flows in the protected room.
Aspirating fire detectors provide so-called cumulative detection. As smoke spreads and disperses throughout a room, its concentration decreases and it becomes increasingly difficult to detect it by traditional means. Cumulative detection refers to the ability to draw air from many points within a protected area into a single detector. Aspiration fire detectors continuously take small amounts of air samples throughout the protected area and transfer them to the sensing element of the aspiration fire detector.
One of the service functions of modern aspiration fire detectors is the ability to continuously monitor the general background of air dust content, predicting and adjusting their work in accordance with the realities of the protected object. This is another of the possible applications of this product - monitoring the purity of the air in the room. In addition, most detectors constantly analyze possible faults in their work (contamination in pipes, clogging of smoke suction openings, etc.).
In essence, aspiration fire detectors are intelligent fire microstations. They, like conventional fire alarm systems, include fixed and peripheral equipment. As peripheral equipment, there are both a system of intake pipelines with smoke-suction capillary tubes, and various
FIRE AND EXPLOSION SAFETY 6"2003
modules (Fig. 1) designed to perform such functions as providing a visual indication of the status of the aspiration detector in individual zones, setting, checking and service maintenance, as well as programming any individual detector and the entire network as a whole.
As a sensitive element of aspiration fire detectors, both conventional fire detectors (smoke or gas) (Fig. 2) and intelligent smoke detection systems using the method of scanning laser technology (Fig. 3) can be used.
Let us analyze the principle of operation of aspiration fire detectors using the example of the VESDA series detectors from Vision Fire & Security. Air from the protected room is continuously sucked into the detector using a high-performance fan (aspirator) through the system of intake pipes (Fig. 4). A sample of this air is passed through filters. Dust and contamination are first removed before the sample enters the optical smoke detection chamber. Then, at the second stage of purification (if any), an additional supply of a portion of pure
air to prevent contamination of optical surfaces and ensure calibration stability and long life of the aspirating detector. After the filter, the air sample enters the measuring chamber, where the presence of smoke is detected. The signal is then processed and displayed using a bar graph, alarm threshold indicators or a graphic display (depending on the detector version). Further, aspiration detectors through a relay or interface can transmit this information to the devices of the fire control panel, fire control, to the centralized monitoring console or others. external devices.
Emerging fires usually go through four stages: smoldering, visible smoke, flame and fire. On fig. 5 shows how the development of sunbathing proceeds in time. Note that the length of the first stage, smoldering, allows more time to detect a potential fire and therefore control its spread before it causes significant damage and destruction. Traditional smoke detectors often detect smoke when a fire has already started, resulting in
t-th stage: 2nd stage:
Smoldering Fire Visible
1 Traditional
3rd Stage Flame
4th stage! Fire I
VESDA Fire 2 (Extinguishing system activated)
significant material damage. A number of aspiration fire detectors, due to their features, make it possible to detect a fire at the smoldering stage and recognize the process of its spread.
The scope of aspiration fire detectors is quite wide:
In warehouses;
In generalist department stores that hold a variety of inventories ranging from raw materials and bulk merchandise to retail commodities and finished goods;
In electronic data processing sites, such as Internet data centers, network management and similar systems, which present a significant fire hazard due to their high power requirements and density of electronic circuits;
In areas with clean industrial premises such as semiconductor fabrication plants, research and development organizations, pharmaceutical production capacity representing a significant fire hazard due to a constant supply of flammable materials;
In the energy industry, which uses various types of fuel to generate electricity.
Aspiration fire detectors with an air filtration system have a low probability of
the ability to generate false alarms, which makes it possible to reduce significant material damage that could occur during false start-up of fire extinguishing systems, shutdown of the technological process, etc.
At the same time, aspirating fire detectors can be used in buildings and premises with high requirements for aesthetics - these are modern offices, visual, rehearsal, lecture, reading and conference rooms, meeting rooms, backstage, foyers, halls, corridors, dressing rooms, as well as historical buildings, cathedrals, museums, exhibitions, art galleries, book depositories, archives.
Aspiration fire detectors can be used:
IN extreme conditions: at low temperatures, mechanical overloads and harsh operating conditions, since the intake pipeline system and the direct sensing element of the detector can be installed in different rooms;
They can work both independently as individual means, and as part of automatic systems collecting and processing information about the situation and transmitting signals to external devices in a different way(by wire, radio channel, etc.);
As an effective means of generating a start signal for starting fire extinguishing systems due to the presence of several levels of alarms and an adjustable sensitivity range. At the same time, for the implementation of the algorithm for starting fire extinguishing means, it is assumed that there are two separate detection points that are necessary for the system to operate, that is, the presence of two separate aspiration fire detectors. Therefore, smoke detectors
aspiration type are a serious addition to the complex of measures to ensure the safety of premises along with traditional fire detectors, in no way diminishing the significance and capabilities of the latter.
FIRE FLASH SAFETY 6"2003
Manufacturing company "Vision Fire & Security" "Securiton-Hekatron" "ESSER"
Characteristic Name of aspiration fire detector
VESDA Laser VESDA Laser PLUS SCANNER VESDA Laser COMPACT RAS ASD 515-1 RAS ASD XL ARS 70 LRS-S 700
Power, V 18...30 18.30 18.30 20.28 18.38 24.30 18.30
Operating temperature, °С -20...+60 -20...+60 -20...+60 0...+60 0...+52 0...+50 -10.+60
Sensitivity, % 0.005.20 0.005.20 0.005.20 Determined by fire detector 0.005.1 Determined by fire detector 0.005.20
Smoke detection technology Laser Laser Laser Optical smoke detector Laser Optical smoke detector Laser
Maximum pipe length in a beam, m 200 200 50 60 60 80 200
Pipe diameter, mm 25 25 25 25/40 25/40 25 25
Hole diameter, mm 2.6 2.6 2.6 3.4 3.4 2.6 2.6
Maximum protected area, m2 2000 2000 500 800 800 1200 1600
Number of filters, pcs. 2 2 2 No No 1 2
Number of fire danger levels, pcs. 4 4 2 1 4 1 4
Dimensions, mm 350 x 225 x 125 350 x 225 x 125 225 x 225 x 85 285 x 360 x 126 317 x 225 x 105 285 x 360 x 126 225 x 225 x 95
Weight, kg 4.0 4.0 1.9 2.7 3.4 2.7 3.5
Networking VESDANet (99 devices) VESDANet (99 devices) VESDANet (99 devices) No LaserNet (127 devices) No VESDANet (99 devices)
Auto compensation mode AutoLearnm programmable AutoLearnmm programmable AutoLearnmm programmable No Yes No Programmable
The aspiration fire detectors of the following leading Western companies are currently certified on the Russian market:
"Vision Fire & Security" (Australia) - fire smoke aspiration detectors of the VESDA Laser PLUS series (Fig. 6), VESDA Laser SCANNER (Fig. 7), VESDA Laser COMPACT (Fig. 8);
"Schrack Seconet AG" (Austria) - smoke and aspiration fire detectors RAS ASD
515-1 (FG030140), manufactured by Securiton-Hekatron, Germany (Fig. 9);
"Fittich AG" (Switzerland) - RAS ASD 515-1 smoke aspiration fire detectors, manufactured by "Securiton-Hekatron", Germany;
"MINIMAX GmbH" (Germany) - aspiration fire detectors AMX 4002.
The table shows comparative characteristics some types of aspiration fire 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.
Efficient system Fire danger alert is the application 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 influence external factors, different from fire factors;
Quickly identify and report malfunctions that prevent the normal functioning of the system.
Equipped with fire-fighting equipment industrial buildings categories A, B and C, as well as objects of national importance.
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. circuit diagram 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 - connection diagram in electrical network
The cost of damage from a fire, even in a single room, can reach impressive amounts. For example, when there is equipment in the premises, the price of which significantly exceeds the cost of a fire protection device. Traditional fire extinguishing methods are unsuitable in this case, since their use threatens no less damage than the fire itself.
That is why there is a growing need for early fire detection systems that can detect signs of a fire in its infancy and take prompt measures to prevent it. Early fire detection equipment performs its functions due to ultra-sensitive sensors. These are temperature sensors, smoke sensors, as well as chemical, spectral (flame-responsive) and optical sensors. All of them are part of a single system aimed at early detection and super-efficient fire localization.
The most important role here is played by the property of early fire detection devices for continuous monitoring. chemical composition air. When burning plastic, plexiglass, polymeric materials, the composition of the air changes dramatically, which should be recorded by the electronics. For such purposes, semiconductor gas-sensitive sensors are widely used, the material of which is capable of changing the electrical resistance from chemical exposure.
Systems using semiconductors are improving all the time, the market for semiconductors is constantly growing, as evidenced by the performance of financial markets. Modern semiconductor sensors are able to capture the minimum concentrations of substances released during combustion. First of all, these are hydrogen, carbon monoxide and dioxide, aromatic hydrocarbons.
When the first signs of a fire are detected, the work of fire extinguishing systems is just beginning. The detection equipment operates accurately and quickly, replacing several people and excluding the human factor when extinguishing a fire. These devices are ideally connected to all engineering systems buildings that can speed up or slow down the spread of a fire. The early detection system, if necessary, will completely turn off the ventilation of the room, the required number of power supply elements, turn on the alarm, and ensure timely evacuation of people. And most importantly - launch a fire extinguishing complex.
In the earliest stages, extinguishing a fire is much easier than in later stages and may take only a few minutes. Fire extinguishing at the initial stages can be carried out using methods that exclude the physical destruction of objects located in the room. Such a method is, for example, extinguishing by replacing oxygen with a non-combustible gas. In this case, the liquefied gas, when it becomes volatile, lowers the temperature in the room or in a particular area, and also suppresses the combustion reaction.
Fire doors are an integral part of any system fire safety. This is a structural element that prevents the spread of fire to neighboring rooms for a certain time.
Early fire detection devices are indispensable in the first place to ensure the safety of people. Their necessity has been proved by numerous and bitter experience. Fire is one of the most unpredictable natural disasters, as the whole story speaks human civilization. In our time, this factor has not become less relevant. On the contrary, today even a local fire can cause catastrophic losses associated with the failure of expensive equipment and machinery. That is why it is profitable to invest in such an early detection system.
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 conventional and addressable systems, the "fire decision" is made directly by the detector itself and then transmitted to 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 and enough exotic species sensors, for example, addressable analog 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 value of the parameter 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, it means that on cycles 4 and 5 the parameter value corresponds to 80 °С, then with this averaging the signal will be generated, since Т=180:3=60 °С, 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 addressable systems are effective tool ensuring 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.
Smoke protection systems for buildings: design problemsWrite off too early
