| CPC G01N 15/1434 (2013.01) [G01N 15/1404 (2013.01); G01N 2015/1486 (2013.01)] | 20 Claims |

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1. A method of determining a filtration efficiency of a filter comprised of a plurality of intersecting porous walls, the filter having a longitudinal axis extending from an inlet end to an outlet end, and an outer peripheral portion extending parallel to the longitudinal axis and surrounding the plurality of intersecting porous walls, the method comprising:
sealing the outer peripheral portion to prevent gas flow across an outermost surface of the outer peripheral portion;
forcing an inlet flow comprised of a gas into the inlet end of the filter at a set flow rate;
introducing particles into the inlet flow; and
optically counting the number of particles entering and exiting the filter during a sampling event.
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