Leak detection of high efficiency filters typically uses a PAO generator. A photometer is used to detect the aerosol concentration upstream and downstream of the filter to determine if the filter is leaking. If only the particle counter is used to detect without dusting, it is difficult to find a leak, and it is necessary to supplement the dust to make the leak obvious and easy. Atmospheric dust is sometimes large and sometimes low due to changes in its concentration with location and time, and is generally not used for leak detection. The FDA stated that the aerosols selected for leak detection should meet certain physical and chemical requirements. Aerosols that cause microbial contamination and cause microbial growth should not be used. PAO generators can be divided into heat generation and cold generation. The heat generator uses the principle of evaporative condensation. The atomized aerosol particles are evaporated by a heater and condensed into minute droplets under specific conditions. After removing too large and too small droplets, a fog-like DOP of about 0.3 um is left into the air passage, and the particle size distribution is 0.1 to 0.3 u. The cold generator refers to a polydisperse DOP aerosol which is made by using compressed air to bubble bubbles in a liquid and splashing through a laskin nozzle. The maximum distribution particle size is about 0.65 um.
Cold DOP is often used when scanning leaks on filters. There are two types of detectors, one is an aerosol photometer and the other is a particle counter. The commonly used detection instrument for high-efficiency filter leak detection is an aerosol photometer (hereinafter referred to as a photometer), which is a front-scattering linear photometer. It consists of a vacuum pump, a light scattering chamber, a photomultiplier tube, a signal processing converter, and a microprocessor.