Patent ID: 8625099

Claim:
A particle concentration measuring device characterized by comprising: a measurement region formation part which has a wall ( 10 ) of substantially ring-form defining an inner opening through which gas flows relatively orthogonally; a light curtain forming unit ( 12 A, 12 B) forming a planar light curtain (FL) in the opening inner part; a particle detecting unit ( 15 ) which uses a camera and receives scattered light from particles passing through the light curtain (FL) to detect the particles; and a calculating unit ( 22 ) calculating particle concentration based on a total number of the particles detected by the particle detecting unit ( 15 ) in a volume of an airflow passing through the light curtain in a unit time, by means of the expression c=n/(r×v×T) wherein c is particle concentration; n is number of particles; r is area of a measurement region; v is airflow velocity, but if a measurement region formation part move, v is movement speed of the measurement region formation part, and T is measurement time; where the device is provided at a place where an airflow flows uniformly through the inner opening; and where positions of the measurement region formation part, the light curtain forming unit ( 12 A, 12 B), and the particle detecting unit ( 15 ) are fixed.