Widely accepted filter test methods are required to rate and compare filters from different manufacturers. Acomplete evaluation of air filters for any application involves several laboratory tests including pressure drop, filterlife and efficiency. The increasing number of air filter applications, growing concern with air quality and limitationof current gravimetric test methods has prompted several technical organizations to develop test standardsdescribing a test procedure to evaluate filter fractional efficiency. The accurate determination of fractionalefficiency can only be achieved by understanding the influence different test parameters and instrumentation canhave on the results. A good test standard will minimize these sources of variability, be simple to operate and notdeter potential users.This paper highlights some of the sources of variability and common errors possible. The effect of sampling probelocation, aerosol concentration and neutralization are investigated and discussed. Also examined is the impact ofparticle shedding from dust loaded filters on the efficiency measurement.
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