What is the overview of air filter detection methods?
Air filter detection system is divided into high efficiency air filter system and general ventilation air filter two categories.
Hepa filters shall be tested in accordance with GB6165-85 and its revision GB12554-92. This standard specifies the efficiency test methods as sodium flame and oil mist. The detection of air filters for general ventilation shall be carried out according to GB12218-89 and its revised GB14295-93. This standard stipulates that the efficiency detection method is the grouping counting method of atmospheric dust particle size.
Filter testing standards are developed as follows: In 1956, the United States Military Commission developed the high efficiency air filter testing standard USMIL-STD282, efficiency detection using DOP method. In 1965, the UK developed the British standard BS3928, efficiency test with sodium flame method. In 1973, the European Ventilation Association formulated the Eurovent4/4 standard, using the sodium flame detection method. Later, the American Society of Environmental Sciences developed a series of similar standards for recommended testing methods, all of which used the DOP diameter counting method to measure filter efficiency. In 1999, Europe developed the BSEN1822 standard, using the most permeable particle size (MPPS) to detect filtration efficiency. Our testing standard adopts sodium flame method, which is based on the principle that sodium atoms are excited by hydrogen flame and emit characteristic light with wavelength of 589nm, and the intensity of light is proportional to the aerosol mass concentration. Filtration efficiency is calculated by detecting the ratio of light intensity before and after the tested filter.
In 1938, the United States national standard developed a colorimetric efficiency detection method for medium-effect air filters, which was divided into two kinds according to the dust source: artificial dust colorimetric efficiency method and atmospheric dust colorimetric efficiency method. In 1952, the American Filter Institute developed the AFI artificial dust meter weight method, mainly used in coarse filter. ASHRAE52-76 has the greatest influence. In the 1980s, the air dust diameter counting method was proposed in China as a general filter detection method for ventilation.
Artificial dust meter weight method takes artificial dust as the dust source and determines the filter efficiency by detecting the change of artificial dust quality before and after the filter. Colorimetric efficiency method is based on the change of light flux or chroma of filter paper due to dust accumulation before and after sampling, using colorimeter to identify the difference, so as to obtain the efficiency of the filter; The diameter counting method is to measure the cumulative particle number of each particle size before and after the measured filter through the particle counter of the incandescent light source or laser light source to determine the cumulative counting efficiency of each particle size. This method gives a filter efficiency curve with the change of particle size, which can reflect the filter performance more comprehensively. With the development of the electronic industry, the requirement of cleanliness level is higher and higher, especially the emergence of level 1 clean room. Accordingly, higher requirements are put forward for testing technology and testing instruments. In order to meet this requirement, a laser particle counter measuring 0.1μm particle has been developed and started to be produced abroad, and recently a smaller particle counter measuring 0.01μm particle has been successfully developed. The appearance of new measuring instruments such as laser particle counter and condensed nuclear particle counter and the development of aerosol technology provide necessary methods and means for measuring diameter efficiency.
Air filter counting efficiency detection method will unify the test method of the filter and the detection method of the clean room, so the filter can be correctly selected according to the cleanliness requirements, this is a fast, simple and convenient filter detection method. In view of this, some people put forward a filter performance detection system which combines the high efficiency air filter detection system and the general ventilation air filter detection system into one. The efficiency detection uses the diameter counting method, and the test efficiency and test results are in line with the filter test requirements. There are also new tests for general ventilation air filters that use the counting efficiency method to detect the filter.