1, Forward scattering Fire detector Principle: Forward scattering means scattering light with an angle of acute angle.
Forward scattering smoke detector features: Forward scattering photoinductor smoke detector is extremely sensitive to lighter gray smoke, and has a low response sensitivity to black smoke generated by open flames. Suitable for places where visible smoke and fire hazards are generated before the fire spreads.
2. Principle of backscatter fire detector: backscatter means scattered light with an angle of obtuse angle.
3. Principle of light reduction fire detection: use the scattering and absorption effects of smoke particles to attenuate the incident light, reduce the incident light signal received by the receiver, and determine the smoke concentration in the environment based on the amplitude of the signal reduction.
4. Performance characteristics of infrared beam smoke detector: Because the infrared beam propagates linearly, its protection range is a space with a certain horizontal expansion angle and a vertical expansion angle, which is suitable for large warehouses, factories and other places with no blocking space for infrared beams.
5. Principle of temperature sensing fire detection: Use temperature sensing elements to accept heat transmitted by the monitored environment or objects, and determine whether a fire occurs based on the results of measurement and analysis. Features of
The temperature sensing detector: The temperature sensing detector works relatively stable, is not disturbed by non-fire smoke, dust, etc., has a low false alarm rate and high reliability. Classification of
temperature sensing detector:
(1) It is divided into point type and line type according to the structure of the detector.
(2) Linear temperature sensing fire detectors can be divided into fixed temperature type, differential temperature type and differential temperature type according to their operating performance.
(3) Point-type temperature sensing fire detectors can be divided into eight types: A1, A2, B, C, D, E, F, and G. in addition. Each type also appends an S or R suffix based on its characteristics.
6. Principle of flame detection: flame detector is to induce the electromagnetic radiation emitted by fire combustion. By converting the energy of flame radiation into current or voltage signals, the purpose of fire detection is achieved. The fire parameters sensed by the flame detector include the intensity and frequency of the flame radiation. Classification of
flame detectors: According to the different response wavelengths of the flame detectors, flame detectors with a response wavelength below 400nm are called ultraviolet flame detectors, and flame detectors with a response wavelength greater than 700nm are called infrared flame detectors. Performance characteristics of
flame detector:
(1) The flame detector has the characteristics of fast response speed and wide detection range.
(2) Due to the short wavelength of ultraviolet light, it is not suitable for fire detection accompanied by smoke when fire occurs, and is more suitable for fire detection of active metals and metal oxides.
(3) Infrared flame detectors are more suitable for detection of carbon-containing liquid fires due to their long detection wavelength.
7, infrared image fire detection technology
system composition: infrared camera, system host, infrared image analysis software.
Working principle: On-site ambient temperature change trend.
8. Basic principles of ionic smoke detector
Basic principles: α source atoms 241 in the ion chamber ionization chamber ionization air in ionization chamber , making the ionization chamber have resistance characteristics in electronic circuits. When the smoke enters the ionization chamber, the ionization current changes, and the impedance of the ionization chamber changes. Determine whether a fire occurs based on the magnitude of the impedance change.
Responsiveness of ion smoke detector: Generally speaking, the response sensitivity of ion smoke detectors to various smoke particles is relatively consistent. Whether it is large-particle smoke in the low-temperature combustion stage or small-particle smoke in open fires, it has a high sensitivity, so it has a wide response range.
9. Basic principles of photoinductive smoke detector: Photoinductive smoke detector is a device that uses fire smoke to absorb and scatter light to detect fires. In order to detect the existence of smoke, the light beam emitted by the emitter is hit on the smoke to detect its concentration. The detection methods can be divided into light reduction detection method and scattering detection method.
Light reduction detection method: a method to determine the smoke concentration by measuring the attenuation caused by smoke on its optical path.
Scattering detection method: a method to determine the smoke concentration by measuring the light energy generated by the smoke scattering effect on light.
10, air sampling and sensing fire detector (hereinafter referred to as the detector) is a smoke sampling detection device based on advanced laser optical air monitoring technology and microprocessor control technology. The device uses mature and advanced laser optics technology and a variety of sensing processing technologies, and combines state-of-the-art digital microprocessing technology to have many characteristics that other smoke detection technologies do not have. The air-absorbing fire alarm detector is also called an air-sampled fire detector and an extremely early fire detector alarm system. This detector has very high sensitivity. Air sampling fire detectors can be divided into single-tube type, double-tube type, and four-tube type (multi-tube type). Different specifications of air sampling fire detectors are selected according to different environmental requirements. The aspirated fire detector has four working stages: warning, action, fire alarm 1, and fire alarm 2. It generally has the following characteristics: the most sensitive detection capability (can detect the existence of a fire within a few hours before smoke) The most advanced fire detection means are suitable for any environment (absorbent air sampling), the lowest maintenance cost (maintenance cost is almost negligible) and will never be affected by any environmental factors to cause false alarms.
11. Linear fiber temperature sensing fire detector is a specific application of distributed fiber temperature detection (DTS) technology in the field of fire alarm. It is mainly used for long-distance and large-scale fire detection such as cables, tunnels, oil tanks, and gas tanks. Given the inherent safety characteristics of optical fibers themselves, this product is more suitable for fire detection in hazardous areas such as flammable and explosive and industrial fire protection projects with strong electromagnetic interference, corrosion, high temperature and explosion-proof requirements.
The cable-type linear temperature sensing fire detector and distributed linear fiber temperature measuring detector are commonly used on the market. The difference in principle:
1. Cable linear temperature sensing fire detector
(1) Copper tube: A fire alarm system with copper tubes and membrane boxes as differential temperature detectors has great influence due to environmental factors, false alarms and missed alarms will occur. Generally used for temperature detection of mines and cable pipelines.
(2) Unrecoverable temperature sensing cable: The unrecoverable temperature sensing cable is in the form of twisted pair or coaxial cable, and its outer layers are surrounded by the thermally sensitive insulation material respectively. In normal monitoring state, the temperature between the two wires is in a high resistance state, and when the ambient temperature rises to or exceeds a predetermined value, the wire is short-circuited in a ground resistance state, thereby sending a fire alarm signal. This type of detector uses a switching signal, and is basically not affected by electromagnetic interference.
(3) Recoverable temperature sensing cable: Recoverable temperature sensing cable consists of four-core copper wires. Each current-carrying wire is covered with a layer of insulating material with negative temperature coefficient characteristics. The four wires are evenly twisted together. When forming the system, the ends are shorted in two to form two monitoring loops that compare with each other. The ambient temperature change is transmitted to the control interface module through the temperature sensing cable. When the temperature in the detection area reaches or exceeds the system alarm value, the system will send a fire alarm signal.
2. Linear fiber temperature measurement detector
The main basis for optical fiber to be used as a temperature sensor is the optical time domain reflection principle of optical fiber and the backward Raman scattering temperature effect of optical fiber. The fiber distributed temperature measurement system performs distributed temperature sensing measurement and tracking based on the principle of optical time domain reflection. When the laser light source injects light pulses along the optical fiber, most of the pulses can be transmitted to the end of the optical fiber and disappear, but a small part of the Raman scattered light will be reflected back along the optical fiber, and the back reflected light is collected and analyzed in the photoelectric device to obtain information about temperature; then the position of the scattered light can be determined based on the time required for the scattered light to return to the light incident point. This way, the temperature distribution status on the entire optical fiber can be measured, and the temperature status of each point on the optical fiber can be visually seen through the PC.
Fire detector classification
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