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SF6安全保障专家
专注于SF6气体检测的专业化
How does the SF6 leak detector work?
发布时间：2020-07-15
来源：ydlcb 浏览次数：26次
The working principle of SF6 leak detector mainly depends on which kind of sensor is used for detection. The sensor types of SF6 leak detector are analyzed as follows:
Performance comparison of various SF6 sensors | ||||||||
Sensor type | Brand channel | Specification and model | How it works is described in detail | Gas type can be detected | advantage | shortcoming | Fit the occasion | remark |
High frequency ionization method | Tangshan instrument | TLD-300 | When the rarefied gas is ionized at high frequency, the electronegative gas molecules can adsorb electrons into massive ions, which are much slower than the electrons in the electromagnetic field, so the gas will exhibit different electrical properties. | Electronegative gases, mainly SF6 and halogenated hydrocarbons | Detection limit is low, less than 100 PPB SF6 concentration can be detected, no poisoning | The device is complex, the working stability is not good, the operation is not convenient, and it needs to be marked zero before each use, and it is also sensitive to a variety of other gases | A quantitative leak detector for detecting small leaks | High frequency ionization method is widely used |
Semiconductor method | FIGEO Japan | TGS832 | The properties of high-temperature semiconductors change after adsorption of polar molecules (molecules containing halogens tend to have strong polarity) | Alcohols, aldehydes, halogenated hydrocarbons, mainly for various refrigerants and solvents | Low price | It needs to be heated. Is not sensitive to SF6 totally (SF6 does not belong to halogenated hydrocarbon, nor polar molecules, adsorption) will not be | Not suitable for monitoring SF6 | Semiconductor method |
Laser photoacoustic method | DEVELOT, Heraeus, Germany | LLD-5000 | The measured gas is irradiated with a laser whose wavelength is equal to the absorption peak of SF6 gas. When the measured gas contains SF6, the laser energy is absorbed and thermal expansion occurs, resulting in sound waves. The SF6 content in the measured gas can be obtained by measuring the intensity of the sound wave. | SF6 | The detection limit is low, up to 1~10ppb, | The device is complex, the price is expensive, there is a certain probability of false positives, the detection sampling is too much, and the response speed is slow | A quantitative leak detector for detecting small leaks | Acousto-optic method |
Ultrasonic method | SF6 gas has a larger molecular weight. When the gas contains SF6, the average molecular weight increases, and the sound velocity decreases accordingly. The Sf6 content can be obtained by measuring the speed of sound in a gas | SF6 | The work is more stable, the device is simple, and the price is low | Low resolution, high detection limit (usually above hundreds of ppm), greatly affected by temperature and humidity, and greatly disturbed by other gases | It can be used to measure SF6 content in dual gases (such as SF6 and nitrogen gas mixture) | Ultrasonic method | ||
Laser spectroscopy | The SF6 concentration of the gas in the absorption cell was measured by the strong absorption of SF6 to 10.6 micron laser | SF6 | 0.01 parts per million | It's expensive and the work is unstable | It has been replaced by laser photoacoustic and infrared spectroscopy | Laser method | ||
Infrared spectroscopy | WINFOSS Switzerland Smartgas Germany | WFS-S1-S | Dual beam non-spectral infrared (NDIR) detection technology. A measurement channel and a reference channel are provided, and filters of different wavelengths are installed respectively to obtain infrared light of different wavelengths. The wavelength in the measurement channel is located on the absorption peak of SF6, while the reference channel is not within the absorption range of SF6. The infrared light passing through the two channels is detected and compared, and the ratio represents the SF6 concentration in the measured gas. | All kinds of gases with infrared absorption peaks are only effective for SF6 gases | The true SF6 concentration value can be obtained, the device is simple, the volume is small, the precision is high, the work is stable, the life is long, the drift is small, and the poisoning is not | The lower limit of detection is higher than ECD method, high frequency ionization method and laser photoacoustic method. The sensor needs to be calibrated annually, and the price is moderate | On-line monitoring and hand-held quantitative leak detector | Infrared spectroscopy has high precision and stable performance, and is widely used at present |
High voltage breakdown method | SF6 has strong arc extinguishing performance. With high-voltage breakdown gas, the arc current and duration vary when SF6 is present in the gas. By detecting this change, SF6 gas concentration can be detected. | All kinds of gases with arc extinguishing properties | The device is simple and compact, but also more sensitive | Short service life. It is not easy to do quantitative detection | Suitable for handheld qualitative testing instrument | |||
Electron capture (ECD) method | Land and land in England | Q200 | The carrier gas is ionized under the action of the radiation source, and the electronegative molecules such as SF6 capture electrons and become negative ions. The negative ions enter the electric field, because of the different mass, the velocity is different under the electric field, and the electronegative gas molecules with different mass produce different current peaks under the narrow pulse electric field. In this way, a variety of electronegative gases with different molecular weights can be distinguished | All kinds of electronegative gases | The detection limit of SF6 is very low, up to PPT level | The device is equipped with a radioactive source and a high-pressure carrier cylinder. It's expensive. The linear range is small, the SF6 concentration is slightly larger, that is, saturation, and there is a long-term tailing (similar to poisoning). | A quantitative leak detector for detecting small leaks | Sensor poisoning |
Negative ion trapping method | When the charged nozzle (electrode) is used to inhale, SF6 in the gas will be adsorbed and charged after passing through the nozzle due to its strong electronegativity, resulting in a current. The SF6 concentration can be obtained by measuring the current | All kinds of electronegative gases | The device is simple and easy to operate | The device usually needs to be equipped with an air pump, and the detection limit is at a few ppm level, which is far less than laser photoacoustic, electron capture and other methods, with short life and slow reaction | Quantitative leak detectors, used to detect small leaks, are being replaced by other methods | |||