Flame detector: When a substance burns, it produces visible or invisible light radiation while producing smoke and releasing heat. Flame detectors, also known as photosensitive fire detectors, are used to respond to the light characteristics of a fire. That is, a fire detector that diffuses the light intensity of flame burning and the flickering frequency of flame. According to the optical characteristics of the flame, there are two types of flame detectors currently in use: one is an ultraviolet detector that is sensitive to light radiation with a shorter wavelength, and the other is an infrared detector that is sensitive to light radiation with a longer wavelength.
The ultraviolet flame detector is a detector that is sensitive to the ultraviolet spectrum emitted by high-intensity flames. It uses a solid substance as a sensitive element, such as silicon carbide or aluminum nitrate, and can also use a gas-filled tube as a sensitive element.
Infrared light detectors basically include a filter device and lens system to filter out unwanted wavelengths and concentrate the incoming light energy on a photocell or photoresistor that is sensitive to infrared light.
Flame detectors should be installed in places where there is an instant explosion. Such as petroleum, explosives and other chemical manufacturing production and storage places.
Basic principles of flame detection
Flame radiation is gas radiation with discrete spectrum and solid radiation with continuous spectrum. Its wavelength is in the range of 0.1-10 μm or wider. In order to avoid the interference of other signals, ultraviolet rays with a wavelength of <300nm are often used, or unique in flames. The CO2 radiation spectrum with a wavelength around 4.4 μm is used as the detection signal. The ultraviolet sensor only responds to the ultraviolet in the narrow range of 185~260nm, and is not sensitive to the light in other spectral ranges. It can be used to detect the ultraviolet in the flame. The sunlight that reaches the ground under the atmosphere and the non-purple-transparent material used as the electric light source of the glass bulb emit light with a wavelength greater than 300nm, so the 220m-280nm mid-ultraviolet band of the flame detection belongs to the blind zone of the solar spectrum (solar blind zone). Ultraviolet flame detection technology enables the system to avoid the complex background caused by the most powerful natural light source, the sun, and greatly reduces the burden of information processing in the system. Therefore, the reliability is high. In addition, it is a photon detection method, so the signal-to-noise ratio is high, and it has the ability to detect extremely weak signals. In addition, it also has the characteristics of extremely fast response time. Compared with infrared detectors, ultraviolet detectors are more reliable, and have the characteristics of high sensitivity, high output, high response speed and simple application circuit. Therefore, gas-filled ultraviolet photoelectric cells are increasingly widely used in combustion monitoring, fire self-alarm, discharge detection, ultraviolet detection, and ultraviolet photoelectric control devices.
However, due to the limitation of structural design and manufacturing process, the noise and sensitivity of traditional ultraviolet photodiode devices are contradictory parameters. Generally speaking, it is necessary to control the sensitivity at an appropriate level. Excessively high sensitivity is very difficult for the low noise index of the device, because both the sensitivity and the noise signal are sent by the photosensitive tube, and the traditional detector will combine the two signals Zoom in at the same time. Therefore, its sensitivity is relatively poor, the detection distance is small, and it cannot resist the interference of lightning, and there is a certain false alarm rate. Therefore, it is necessary to intersect with other disciplines and technologies based on existing or newly developed detection principles and methods, and improve system performance by improving signal acquisition and processing methods.
Current status of flame detection and alarm technology
The national standard stipulates that the response time of point-type ultraviolet flame detectors is 30s, but due to the advancement of science and technology, the response time of flame detection and alarm products on the market can meet this time range, but for practical applications and security requirements This is a must, and the metrics and performance requirements are getting higher and higher. The response time of most of the domestic alarm systems is at the S level. The response speed of the top foreign companies such as Hamamatsu in Japan and MSA in the United States can reach the ms level the fastest. More long-distance flame detection is in progress. The flame detectors on the market mainly include smoke sensors, infrared sensors and ultraviolet photosensitive tubes. Even for flame detection systems that use multi-information fusion technology, the information sources for detection are mainly from these three aspects. Traditional flame detection sensors have the following deficiencies:
a. Smoke sensor, which is an indirect flame detector, when the flame is generated, the smoke is also generated. When the smoke reaches a certain concentration, an alarm signal is issued. There are great disadvantages in detecting flames in this way. There are many substances that do not produce smoke when they burn (such as natural gas, ethanol, methanol, etc.), and the detection distance is short. The sensor must be at the place where the smoke is the thickest. Thick smoke, then call the police, in some cases it may be too late.
b. The heat release infrared flame detector directly detects the infrared spectrum with a wavelength of 4.35±0.15μm in the flame. The detection target is relatively clear. It consists of a heat release probe and an amplifier. The disadvantage is that this type of sensor has piezoelectric It is very sensitive to sound electromagnetic waves and vibrations, so the place of use is subject to certain restrictions, and its detection distance is less than 80m.
c. The conventional ultraviolet flame detector directly detects the ultraviolet spectrum of 180-260nm in the flame, the detection target is also very clear, and the response speed is relatively fast. It consists of a UV photosensitive probe and an amplifier. The disadvantages are: poor sensitivity, the detection distance is less than 15m, it cannot resist the interference of lightning, and there is a certain false alarm rate, so it can only be used in a closed environment with a short distance, such as a heating furnace. , industrial boilers and other places.
According to the characteristics and limitations of different types of flame detectors, how to integrate the real-time and accuracy required by fire detection and alarm, the high-speed response of flame detection, long-distance detection (for different places), and accurate and false alarms have become flame detection technology. Problems that must be solved. In view of the advantages of the ultraviolet flame detection itself, the ease of implementation of the detection system, and the expansion of the detection distance, the intelligent flame detection module is added to the ultraviolet photosensitive tube, and the current market is improved by using the amplification circuit, signal processing and digital filtering technology. There are deficiencies in the fire alarm system.
Flame detector: When a substance burns, it produces visible or invisible light radiation while producing smoke and releasing heat. Flame detectors, also known as photosensitive fire detectors, are used to respond to the light characteristics of a fire. That is, a fire detector that diffuses the light intensity of flame burning and the flickering frequency of flame. According to the optical characteristics of the flame, there are two types of flame detectors currently in use: one is an ultraviolet detector that is sensitive to light radiation with a shorter wavelength, and the other is an infrared detector that is sensitive to light radiation with a longer wavelength.
The ultraviolet flame detector is a detector that is sensitive to the ultraviolet spectrum emitted by high-intensity flames. It uses a solid substance as a sensitive element, such as silicon carbide or aluminum nitrate, and can also use a gas-filled tube as a sensitive element.
Infrared light detectors basically include a filter device and lens system to filter out unwanted wavelengths and concentrate the incoming light energy on a photocell or photoresistor that is sensitive to infrared light.
Flame detectors should be installed in places where there is an instant explosion. Such as petroleum, explosives and other chemical manufacturing production and storage places.
Basic principles of flame detection
Flame radiation is gas radiation with discrete spectrum and solid radiation with continuous spectrum. Its wavelength is in the range of 0.1-10 μm or wider. In order to avoid the interference of other signals, ultraviolet rays with a wavelength of <300nm are often used, or unique in flames. The CO2 radiation spectrum with a wavelength around 4.4 μm is used as the detection signal. The ultraviolet sensor only responds to the ultraviolet in the narrow range of 185~260nm, and is not sensitive to the light in other spectral ranges. It can be used to detect the ultraviolet in the flame. The sunlight that reaches the ground under the atmosphere and the non-purple-transparent material used as the electric light source of the glass bulb emit light with a wavelength greater than 300nm, so the 220m-280nm mid-ultraviolet band of the flame detection belongs to the blind zone of the solar spectrum (solar blind zone). Ultraviolet flame detection technology enables the system to avoid the complex background caused by the most powerful natural light source, the sun, and greatly reduces the burden of information processing in the system. Therefore, the reliability is high. In addition, it is a photon detection method, so the signal-to-noise ratio is high, and it has the ability to detect extremely weak signals. In addition, it also has the characteristics of extremely fast response time. Compared with infrared detectors, ultraviolet detectors are more reliable, and have the characteristics of high sensitivity, high output, high response speed and simple application circuit. Therefore, gas-filled ultraviolet photoelectric cells are increasingly widely used in combustion monitoring, fire self-alarm, discharge detection, ultraviolet detection, and ultraviolet photoelectric control devices.
However, due to the limitation of structural design and manufacturing process, the noise and sensitivity of traditional ultraviolet photodiode devices are contradictory parameters. Generally speaking, it is necessary to control the sensitivity at an appropriate level. Excessively high sensitivity is very difficult for the low noise index of the device, because both the sensitivity and the noise signal are sent by the photosensitive tube, and the traditional detector will combine the two signals Zoom in at the same time. Therefore, its sensitivity is relatively poor, the detection distance is small, and it cannot resist the interference of lightning, and there is a certain false alarm rate. Therefore, it is necessary to intersect with other disciplines and technologies based on existing or newly developed detection principles and methods, and improve system performance by improving signal acquisition and processing methods.
Current status of flame detection and alarm technology
The national standard stipulates that the response time of point-type ultraviolet flame detectors is 30s, but due to the advancement of science and technology, the response time of flame detection and alarm products on the market can meet this time range, but for practical applications and security requirements This is a must, and the metrics and performance requirements are getting higher and higher. The response time of most of the domestic alarm systems is at the S level. The response speed of the top foreign companies such as Hamamatsu in Japan and MSA in the United States can reach the ms level the fastest. More long-distance flame detection is in progress. The flame detectors on the market mainly include smoke sensors, infrared sensors and ultraviolet photosensitive tubes. Even for flame detection systems that use multi-information fusion technology, the information sources for detection are mainly from these three aspects. Traditional flame detection sensors have the following deficiencies:
a. Smoke sensor, which is an indirect flame detector, when the flame is generated, the smoke is also generated. When the smoke reaches a certain concentration, an alarm signal is issued. There are great disadvantages in detecting flames in this way. There are many substances that do not produce smoke when they burn (such as natural gas, ethanol, methanol, etc.), and the detection distance is short. The sensor must be at the place where the smoke is the thickest. Thick smoke, then call the police, in some cases it may be too late.
b. The heat release infrared flame detector directly detects the infrared spectrum with a wavelength of 4.35±0.15μm in the flame. The detection target is relatively clear. It consists of a heat release probe and an amplifier. The disadvantage is that this type of sensor has piezoelectric It is very sensitive to sound electromagnetic waves and vibrations, so the place of use is subject to certain restrictions, and its detection distance is less than 80m.
c. The conventional ultraviolet flame detector directly detects the ultraviolet spectrum of 180-260nm in the flame, the detection target is also very clear, and the response speed is relatively fast. It consists of a UV photosensitive probe and an amplifier. The disadvantages are: poor sensitivity, the detection distance is less than 15m, it cannot resist the interference of lightning, and there is a certain false alarm rate, so it can only be used in a closed environment with a short distance, such as a heating furnace. , industrial boilers and other places.
According to the characteristics and limitations of different types of flame detectors, how to integrate the real-time and accuracy required by fire detection and alarm, the high-speed response of flame detection, long-distance detection (for different places), and accurate and false alarms have become flame detection technology. Problems that must be solved. In view of the advantages of the ultraviolet flame detection itself, the ease of implementation of the detection system, and the expansion of the detection distance, the intelligent flame detection module is added to the ultraviolet photosensitive tube, and the current market is improved by using the amplification circuit, signal processing and digital filtering technology. There are deficiencies in the fire alarm system.