HEPA filters are usually used in the filter upstream of the PAO generator dust, the use of photometers (photometer) detection of upstream and downstream aerosol concentration filter to determine whether there is leakage filter. The purpose of dust is due to high dust particles upstream dust concentration is low, only the particle counter in the case of dust is not detected, more difficult to find a leak, need to add dust to be obvious, easy to find leaks. Artificial aerosol DOP has been nearly 40 years of history, for some time, due to suspected carcinogenic effect on humans, now often DOS (Dioctylsebaeate sebacate dioctyl fat) but the experimental method is still called “DOP method. Atmospheric dust due to its concentration with location and time changes, sometimes larger, sometimes lower, generally not used as a leak detection. FDA pointed out that the aerosol used in the leak detection should meet certain physical and chemical requirements, should not be used to cause microbial contamination, resulting in microbial aerosol breeding. PAO generator can be divided into two kinds of heat generation and cold generation, the heat generator is the use of the principle of evaporation condensation, atomized aerosol particles with a heater to evaporate and condense under specific conditions into tiny droplets, remove the excessive and After the droplets left about 0.3um droplets of DOP into the duct, particle size distribution in 0.1 ~ 0.3u. Cold generator is the use of compressed air in the air bubble in the liquid, the laskin nozzle splash to produce the state of polydisperse DOP aerosols, the maximum distribution of particle size in 0.65um or so. Cold DOP is often used when the filter is scanned for leaks. There are two types of detectors: the aerosol photometer and the particle counter. The most commonly used detection instrument for high efficiency filter leak detection is aerosol photometric (Hereinafter referred to as photometer), is a pre-scattered linear photometer, which consists of vacuum pumps, light scattering chamber, photomultiplier tube, signal processing converters and microprocessors and other components. Its working principle is: When the air is vacuum pumped to the light scattering chamber, where the particulate matter scattered light to the photomultiplier tube. In a photomultiplier tube, the light is converted into an electrical signal, which is amplified and digitized by the microprocessor to determine the intensity of the scattered light. By comparison with the signal produced by the reference substance, it is possible to directly measure the mass concentration of the particulate matter in the gas, and thus its use is extensive. The particle counter, its test value reflects the number of particles in the air flow concentration of particles and provides a range of particle size, the sensitivity is high, for all dust aerosols for a larger choice, but in high efficiency Filter leak detection less used, the two instruments test results difficult to quantitatively contrast.
