Effect of threshold size and counting efficiency on the leak evaluation of particle counters

In the previous work, two types of installed filter leak tests described in ISO 14644-3; aerosol photometer method and light-scattering airborne particle counter (LSAPC) method, were examined by considering the difference in the characteristics of each measuring instrument. It was found that the same leak detection criterion (LDC) could be applied to filters above H14 grade in both test methods. Hence, the LDC of the aerosol photometer method could be applied in the LSAPC method for H14 or higher grade filters. However, LSAPCs have different optical, flow and electrical systems, resulting in different counting efficiency functions (CEFs). Furthermore, ISO 21501-4 allows LSAPCs to have a certain range of CEF. Therefore, it was necessary to ensure whether the same LDC could be applied in the installed filter leak test when applying different measuring instruments admitted by 21501-4. In this study, using theoretical calculation, the determination of threshold size, which makes the LDC unification possible between the two test methods, was further discussed, and penetrations detected by LSAPC with various CEFs were evaluated. It was concluded that 0.3 μm is the most suitable threshold size, and the same LDC studied in the previous work could be applied to the LSAPC with different CEFs.