Patent ID: 7755750

Claim:
A method of detecting a defect in a porous body, the method comprising: applying a planar light beam to fine particles discharged from the porous body, and detecting the light and shade of scattered light caused by the fine particles to specify the position of a defect, the light and shade of the scattered light being detected at a position facing the light beam, wherein, a light source that emits the light beam is defined as an origin, a position in a plane formed by the light beam corresponding to a center of an end face of the porous body through which the fine particles are discharged is defined as a center point, a straight line that extends from the origin toward the center point is defined as l 1 , a straight line that extends from the origin toward the detection position of the scattered light is defined as l 2 , and the angle formed by the straight line l 1 and the straight line l 2 in the plane formed by the light beam is defined as θ 1 , and the light and shade of the scattered light is detected at a detection position at which the angle θ 1 is 0 to 80° and, a straight line that extends from the center of the end face of the porous body to the detection position of the scattered light is defined as l 3 , and the angle formed on the side of the porous body opposite the light source by the straight line l 1 and straight line l 3 is less than 90°.