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Working Principle of DOP Leak Detection Method for HEPA Filter
Working Principle of DOP Leak Detection Method for HEPA FilterLeak testing of HEPA filters usually uses a PAO generator to generate dust upstream of the filter, and a photometer to detect the aerosol concentration upstream and downstream of the filter to determine whether the filter is leaking. For some time, the artificial aerosol DOP has been suspected of carcinogenic effects on people, now often to D0s (Dioctylsebaeate dioctylate) also known as DEHSId2-ethvexysebaate and Apolvaphadlehn poly aene via) and so on instead of the experimental method is still called "DOP method". The method is still called the "DOP method".PAO generators can be divided into hot and cold generation two kinds, the hot generator uses the principle of condensation of the base hair, the aerosol particles are to be evaporated by the heater, and condensed into tiny droplets under specific conditions, removed too large and too small droplets to leave about 0.3 um to be DOP into the duct, the particle by the distribution of the 010.3 um. Cold generator refers to the use of compressed air bubbles in the liquid drum, through the laskin nozzle fly test generation. laskin nozzle fly test to produce the material state of the polydisperse phase DOP aerosol, the maximum distribution of particle size in 0.65um or so. Cold DOP is often used when scanning filters for leak detection. There are two kinds of high-efficiency filter testing instruments, the aerosol photometer, and the other is the particle counter, The high-efficiency filter leakage testing instrument commonly used in the aerosol photometer (hereinafter referred to as the photometer), is a kind of front-scattering linear photometer, which consists of vacuum pumps, light-scattering chambers, photomultiplier tubes, signal processor converter and microprocessor and other components. Its working principle is. When the airflow is pumped to the light-scattering chamber by the vacuum pump, the particulate matter in it scatters the light to the photomultiplier tube. In the photoelectric signal amplifier, the light is converted into an electrical signal, which is amplified digitized, and analyzed by a microprocessor to determine the intensity of the scattered light. By comparison with the signal generated by the reference substance, the mass concentration of the particulate matter in the gas can be measured directly, which makes it very versatile. The particle counter, its test value reflects the concentration of the number of particles in the gas stream particle "S and specifies the particle size range, its higher sensitivity, applicable to all dust sources aerosol, the choice of a larger margin, but in the high-efficiency oscilloscope leakage detection is less commonly used, the two instruments test results are difficult to quantitatively compare. Atmospheric dust in the dry concentration with the location and time and other changes, sometimes larger, sometimes lower, a ship is not used as a leak detection. The purpose of the dust is due to the high-efficiency filter traveling dust particles concentration is low, only with the pull counter in the absence of dust detection, it is more difficult to find leakage, need to supplement the dust only since the part of the obvious, easy to find the leakage. Pointed out that in leakage detection, washing with the aerosol should be in line with certain physical and chemical requirements, and should not be used to cause simple biological contamination, resulting in microbial growth of the aerosol. |
