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Automatic fire alarm and fire linkage control system is a comprehensive monitoring system for building fire prevention, which consists of fire alarm system and fire linkage control system. In practical engineering applications, the composition of the system is varied, and the number and types of equipment will be very different. However, it is the realization of automatic fire alarm and fire linkage control that determines the characteristics of the system.

(A) the composition of the automatic fire alarm system

The automatic fire alarm system generally consists of three parts: detector, signal circuit and automatic alarm device.

1, fire detector and manual alarm button

The fire detector is the detection element of the whole alarm system. Its working stability, reliability and sensitivity directly affect the operation of the whole fire fighting system.

1) detector type

There are many kinds of fire detectors, roughly as follows:

(1) ion smoke detector.

(2) photoelectric smoke detector.

(3) Temperature detectors (including constant temperature type and differential temperature type).

(4) gas detector.

(5) Infrared detector.

(6) ultraviolet detector.

2) Basic principles of common fire detectors

(1) Smoke fire detector

The fire development process can be roughly divided into initial stage, development stage and attenuation and extinction stage. The function of smoke-sensing fire detector is to automatically send out fire alarm signals at the initial stage when smoke is generated by combustion, so as to put out the fire before it becomes a disaster. According to different structures, smoke detectors can be divided into ion smoke detectors and photoelectric smoke detectors.

① ion smoke detector

The ion smoke detector consists of two series chambers containing Am24 1 radioactive source, field effect transistor and switching circuit. The inner ionization chamber, that is, the compensation chamber, is sealed, so that smoke is not easy to enter; The outer ionization chamber, that is, the detection chamber, is open and smoke can enter smoothly. The two ends of the two series ionization chambers are directly connected with a 24V DC power supply. When a fire breaks out, smoke enters the detection ionization chamber, and the α ray generated by Am24 1 is blocked, which reduces its ionization ability, reduces ionization current and increases the equivalent impedance of the air in the detection ionization chamber, while the impedance of the compensation ionization chamber remains unchanged due to the smoke-free entry, thus causing the change of the partial pressure ratio applied to the two ionization chambers. When the voltage at both ends of the ionization chamber rises to a certain value, the switch circuit acts and gives an alarm.

② photoelectric smoke detector

The photoelectric smoke detector consists of light source, photoelectric element and electronic switch. Using the principle of light scattering to detect the smoke produced in the early stage of fire and send out alarm signals in time. According to different light sources, it can be divided into general photoelectric type, laser photoelectric type, ultraviolet photoelectric type and infrared photoelectric type.

General photoelectric smoke detectors can be divided into two types according to their structural characteristics: shading type and scattering type.

The light shielding photoelectric smoke detector consists of a light source (light bulb or light emitting diode) and photoelectric elements installed in a small darkroom. In the smokeless state, the light emitted by the light source is converged into a light beam through the lens, which irradiates the photoelectric element and is converted into an electrical signal, so that the whole circuit is kept in a normal state without giving an alarm. When there is a fire and smoke enters the detector, the propagation characteristics of light change, the light intensity is obviously weakened, the normal state of the circuit is destroyed and an alarm signal is sent out.

The positions of light-emitting diodes and photoelectric elements of scattering photoelectric smoke detector do not correspond. The photoelectric element is arranged in a porous darkroom. When there is no smoke, the light can't reach the photoelectric element, and the circuit remains normal. When a fire breaks out, smoke enters the detector, and the light reaches the photoelectric element through the reflection or scattering of smoke particles, and then the optical signal is converted into an electrical signal, which is amplified by an amplifier circuit and then drives the automatic alarm device to send out an alarm signal.

B, laser smoke detector. It consists of laser transmitter (including pulse power supply and laser generator) and laser receiver (including photoelectric receiver, pulse amplifier and alarm). It uses the characteristics of strong directivity, high brightness, monochromaticity and good coherence of laser. Under smokeless conditions, the pulsed laser beam hits the photoelectric receiver and is converted into an electrical signal, and the alarm does not give an alarm. Once the laser beam is weakened to a certain extent when it is blocked by smoke, the signal of photoelectric receiver is obviously weakened and the detector sends out an alarm signal. Among all kinds of laser light sources, semiconductor laser has attracted much attention because of its advantages of low excitation voltage, high efficiency, high pulse power, small device size, impact resistance, long life and low price.

Ultraviolet and infrared smoke detectors. They have the advantages of high sensitivity, stable performance, reliability and accurate detection orientation, so they have attracted more and more attention and become the important equipment and development direction of fire detectors at present.

Photoelectric smoke detectors have developed rapidly and there are more and more types. As far as its function is concerned, it can realize early fire alarm, especially suitable for places with high electrical fire risk, such as computer rooms, instrument rooms, cable trenches, tunnels and so on.

(2) Temperature-sensitive fire detector

According to the structural principle, there are three kinds of temperature detectors: bimetal type, capsule type and heat-sensitive electronic component type.

(1) bimetallic plate type adopts two kinds of metal plates with different expansion coefficients as sensitive elements, which are generally made into two forms: differential temperature and constant temperature. Constant temperature type is that when the ambient temperature rises to the set temperature, the constant temperature element acts immediately and sends out an alarm signal; Differential temperature type means that when the ambient temperature rises sharply and its heating rate (℃/min) reaches or exceeds the heating rate specified by the detector, the differential temperature element will act immediately and send out an alarm signal.

(2) The bellows detector is composed of corrugated plates, and the indoor air can only communicate with the atmosphere through the small holes of the air plug screws. Under normal circumstances (that is, the temperature rise rate of the environment is not more than 65438 0℃/min), when the air chamber is heated, the indoor expanded gas can leak into the atmosphere through the small hole of the air plug screw. When a fire breaks out, the temperature rise rate increases sharply, the air pressure in the air chamber increases, the corrugated plate bulges upward, the elastic contact piece is pushed, the electrical contact is connected, and an alarm signal is sent out.

③ The electronic temperature detector consists of two thermistors with the same resistance and temperature characteristics and an electronic switch circuit. One of the two thermistors can directly sense the change of ambient temperature, and the other is encapsulated in a sphere with a certain heat capacity. When the outside temperature changes slowly, the resistance values of the two thermistors are basically close with the temperature change, and the switch circuit does not act. In case of fire, the ambient temperature rises sharply, and the resistance changes of the two thermistors are different. The original stable state is destroyed, the switch circuit is opened and an alarm signal is sent out.

3) Selection of fire detectors

(1) Select the detector according to the characteristics of the fire.

(1) There is a smoldering stage at the beginning of the fire, which produces a lot of smoke and a little heat, with little or no flame radiation. Smoke detectors should be selected.

(2) The fire develops rapidly, producing a lot of heat, smoke and flame radiation. Smoke detector, temperature detector, flame detector or their combination can be selected.

(3) The fire develops rapidly, the flame radiation is strong, and there is a small amount of smoke and heat, so the flame detector should be selected.

(4) The characteristics of fire formation are unpredictable, so a simulation test can be conducted and the detector can be selected according to the test results.

(2) Select the detector according to the environmental characteristics of the installation site.

(1) In places where the relative humidity is more than 95% for a long time, the airflow speed is more than 5m/s, and a large amount of dust and water mist are trapped, which may generate corrosive gases. In general, ion smoke detectors are not suitable for places where smoke is captured and organic substances such as alcohols, ethers and ketones are produced.

② Temperature detectors are not suitable for places where smoldering may occur, or places where failure to give an alarm in time will cause great losses when a fire occurs; In the place where the temperature is lower than 0℃, it is not appropriate to choose a constant temperature detector; In general, it is not advisable to choose a differential temperature detector where the temperature changes greatly.

(3) In any of the following circumstances, the flame detector should not be selected:

A, flameless fire may occur;

B, there is smoke diffusion before the flame appears;

C, the lens of the detector is easy to be polluted;

D, the' line of sight' of the detector is easily blocked;

E, the detector is vulnerable to direct or indirect irradiation by sunlight or other light sources;

F, under normal circumstances, there are effects such as open flame operation, X-ray and arc light.

2. Automatic alarm device

Although the research, production and application of automatic fire alarm device in China started late, it developed rapidly. Especially in recent years, with the rapid development of China's four modernizations and the continuous strengthening of fire control work, great progress has been made in the production and application of automatic fire alarm devices, and the number of manufacturers, product types, output and application units has been increasing. At present, the automatic fire alarm device produced in China is an automatic complete set of devices including alarm display, fault display and control instruction. When receiving fire signals from fire detectors, manual alarm buttons or other trigger devices, it can send out sound and light alarm signals, record time, automatically print the time and place of fire, and output command signals to control other fire-fighting equipment to form an automatic fire extinguishing system. At present, the automatic alarm devices produced and used are mostly multi-wire systems, which are divided into regional alarm controllers, centralized alarm controllers and intelligent fire alarm controllers.

(1) area alarm controller

Area alarm is an automatic alarm and monitoring device composed of electronic circuits. It connects all fire detectors in an area and gives out automatic fire alarm accurately and timely. Therefore, a complete and independent automatic fire alarm device can be formed after the alarm in each area is correctly connected with the fire detector in the area under its jurisdiction.

The basic principle of area alarm is as follows:

(1) Receive the fire signal sent by the detector or manual alarm button, and give an alarm in the form of sound and light;

The electronic clock can remember the time of the first fire;

③ It can drive several pairs of relay contacts and endow them with appropriate external functions; can

(4) Configure standby DC power supply, which will be put into use automatically when the mains power is cut off;

⑤ It has self-checking function. When the contact between the area alarm and the detector is poor or disconnected, the alarm will send out an acousto-optic alarm signal of open circuit or short circuit fault, and automatically display the fault position;

⑥ With the function of "fire alarm priority", all kinds of alarm signals are sent to the regional alarm, and after being processed by the signal selection circuit, the fire, short circuit and open circuit are judged. The alarm first sends out a fire alarm signal to indicate the specific fire location, sends out a fire alarm sound, and remembers the fire alarm signal, open circuit and short circuit fault signals;

⑦ The three signals are sent to the centralized alarm controller through the communication interface circuit. The regional alarm controller combines the received detector fire alarm signals with or logic, and controls the relays to use linked external devices, such as smoke exhaust valves, air supply valves, fire doors, etc.

At present, the capacity of the regional alarm, that is, the monitoring part, produced by domestic manufacturers is somewhat different. Different types of regional alarms need to be connected with different types of detectors. Take JB-QB-2700/088A series area alarm produced by Xi 'an 262 Factory as an example. There are two kinds of wall-mounted and cabinet-mounted, with a maximum capacity of 256 channels, each channel is a part number, and a detector occupies a part number.

In engineering design, the capacity of the alarm controller in the selected area should be greater than the number of detectors in this area. If a building takes the first floor as an area with ***24 rooms, each with a detector and ***24 rooms, then it is necessary to choose a 30-way area alarm controller. If there are 48 rooms, the 50-ring area alarm controller should be selected.

(2) Centralized alarm controller

The basic principle of centralized alarm controller is as follows:

(1) connect multiple regional alarms to form a system for centralized management;

(2) Can patrol and detect whether the connected area alarm has fire signal or fault signal, and can indicate the fire area and fault area in time, and send out audible and visual alarm signals at the same time;

③ Other functions and principles are the same as those of the regional alarm controller.

In the system, only detectors and centralized alarms can't work. Because the patrol function, fire alarm function and self-check function of centralized alarm are only available after the system is formed with regional alarm. Therefore, the automatic fire alarm system can only be formed if the regional alarm and the centralized alarm are used together.

Centralized alarm system is suitable for large and complex projects. The maximum capacity of centralized alarm can be connected to 40 regional alarms.

(3) Intelligent fire alarm controller

The basic principle of intelligent fire alarm controller is as follows:

(1) The use of analog detectors can automatically compensate external non-fire factors, such as temperature, humidity, dust, etc., thus laying a technical foundation for solving disaster-free false alarm and accurate alarm under various use conditions;

② The alarm controller adopts full-bus computer communication technology to realize bus alarm and bus linkage control and reduce the long-distance pipeline between the control output and the actuator;

(3) Large-capacity control matrix and cross-search software package are adopted, and software programming replaces hardware combination, which improves the flexibility and modifiability of fire fighting linkage.

The NA 1000 series fire alarm controller produced by Factory 262 belongs to this type.

(4) Selection of automatic alarm device

In the automatic fire alarm system, the selected fire alarm device should have the following basic functions:

(1) can supply power for fire detectors;

(2) can receive fire detector or manual alarm button alarm signal;

(3) It can detect and send out the fault signal of the system itself;

(4) You can check the alarm function of fire alarm;

⑤ It has power conversion function.

The selection of fire alarm controller generally considers the following factors:

(1) fire detectors and fire alarms shall be equipped with products from the same manufacturer;

(2) The number of cycles required by the alarm system;

③ Whether the automatic fire fighting linkage control function is needed;

(4) Installation location and installation method, etc.

(B) the composition of the fire linkage control system

The range of fire-fighting linkage control is very wide, which varies according to the size and level of actual projects. Linkage control equipment includes fire hydrants, water fire extinguishing, gas fire extinguishing, fire doors, fire shutters, exhaust fans, air conditioning facilities, fire dampers, smoke exhaust valves, elevators, induction lamp, emergency lights, alarm bells, and cutting off working power supply.