The flame radiation is gas radiation with a discrete spectrum and solid radiation with a continuous spectrum. Its wavelength is in the range of 0.1-10 μm or wider. In order to avoid interference from other signals, ultraviolet rays with a wavelength of <300 nm are often used, or unique in flames. The co2 radiation spectrum with a wavelength near 4.4μm is used as the detection signal. The ultraviolet sensor only responds to ultraviolet rays in the narrow range of 185~260nm, and is not sensitive to light in other spectrum ranges. It can be used to detect ultraviolet rays in the flame. The wavelength of light emitted by the electric light source of the glass bulb as the sunlight and the non-violet material reaching the ground below the atmosphere are both greater than 300nm, so the 220nm-280nm mid-ultraviolet band of flame detection belongs to the blind zone of the solar spectrum (solar blind zone). Ultraviolet flame detection technology makes the system avoid the powerful natural light source-the complex background caused by the sun, which greatly reduces the burden of information processing in the system. So the reliability is high, and it is a photon detection method, so the signal-to-noise ratio is high, and it has extremely weak signal detection ability. 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 lines. Therefore, the gas-filled ultraviolet photoelectric tube is widely used in combustion monitoring, fire self-alarm, discharge detection, ultraviolet detection, and ultraviolet photoelectric control devices.
But for traditional UV phototube devices, due to the limitation of structural design and manufacturing process, its noise and sensitivity are contradictory parameters. Generally speaking, the sensitivity needs to be controlled at an appropriate level. Too high sensitivity is very difficult for the low-noise index of the device, because the sensitivity and noise signal are both emitted by the photosensitive tube. The signal is amplified at the same time. Therefore, its sensitivity is relatively poor, the detection distance is small, it cannot resist the interference of lightning, and there is a certain false alarm rate. Therefore, it is necessary to improve the performance of the system based on the existing or newly developed detection principles and techniques, and to intersect with other disciplines and technologies, and improve the system performance by improving signal collection and processing methods.
Current status of flame detection alarm technology:
In the national standard, the response of point-type UV flame detectors is acceptable for 30s, but due to the advancement of 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 necessary, and the requirements for indicators and performance are getting higher and higher. The response time of most domestic fire alarm systems is in the s level, and the response speed of foreign countries such as Japan and the United States can reach the ms level. The detection range of foreign flame detectors that can be consulted is 500 meters, and it cannot be used for further flame detection. in. The flame detectors on the market mainly include smoke sensors, infrared sensors and ultraviolet light sensitive tubes. Even if the flame detection system adopts multi-information fusion technology, the detection information sources are mainly these three aspects. Traditional flame detection sensors have the following shortcomings:
a. Smoke sensor, which is an indirect flame detector, when the flame is generated, smoke is also generated. When the smoke reaches a certain concentration, an alarm signal is issued. Using this method to detect flames has great disadvantages. It has been reported that no smoke is produced when multiple substances are burned (such as natural gas, ethanol, methanol, etc.), and the detection distance is short, and the sensor must be in a location with dense smoke. It can be seen that when the flame occurs and the smoke is dense, then the alarm is reported. 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±0.15μπ in the flame. The detection target is relatively clear. It consists of a heat release probe and an amplifier. The disadvantage is: this type of sensor has piezoelectric It is very sensitive to sound electromagnetic waves and vibration, so the place of use is subject to certain restrictions. 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-sensitive probe and an amplifier. The disadvantages are: poor sensitivity, detection distance is less than 15m, can not resist the interference of lightning, and has a certain false alarm rate, so it is only used in a closed environment with a short distance, such as heating furnace, Industrial boilers and other places.
In view of the characteristics of different types of flame detectors, how to integrate the real-time and accuracy required for fire detection and alarm, the high-speed response of flame detection, long-distance detection (for different places), and accuracy and false alarms have become flame detection technology. Problems that must be solved. In view of the advantages of ultraviolet flame detection and the easy realization of the detection system and the scalability of the detection distance, the intelligent flame detection module is added to the ultraviolet photosensitive tube, and the existing on the market is improved by the use of amplification circuit, signal processing and digital filtering technology. Deficiencies in the fire alarm system.
Finally, the editor will introduce two UV detectors that can be used in flame detection and ultraviolet detection. The first is the UV photodetector-TOCON_ABC1 imported from Germany. This detector is a broadband UV photodetector based on silicon carbide. With integrated amplifier. TOCON is a 5V power supply UV photodetector, with an integrated amplifier that converts UV radiation into 0~5V voltage output. The output voltage pin of TOCON can be directly connected to the controller, voltmeter or other data analysis device with voltage input. Highly modern electronic components and a sealed metal housing with UV glass windows can eliminate noise or electromagnetic interference caused by parasitic resistance paths in the package.
Finally, this product is also an ultraviolet photodiode imported from Germany-SG01D-5LENS. SiC has unique characteristics, can withstand high-intensity radiation, is almost insensitive to visible light, produces low dark current, fast response speed and low noise. These characteristics make SiC a good material for semiconductor ultraviolet detectors in the visible blind area. SiC detectors can always operate at temperatures up to 170°C (338°F). The temperature coefficient of the signal (response rate) is also very low, <0,1%/K. Due to the low noise (fA-level dark current), extremely low ultraviolet radiation intensity can be effectively detected. Please note that this device needs to be equipped with a corresponding amplifier.
