| 摘要 |
Provided is a smoke detector having a structure in which, at a time of performing smoke detection, an S/N ratio of a signal of a light receiving element is improved, to thereby accurately detect occurrence of fire. At both end portions of an inside of an optical case ( 21 ) having a substantially cylindrical shape, a light emitting element ( 11 ) and a stray light portion ( 22 ) are arranged. In the stray light portion ( 22 ), a light trap ( 23 ) is provided. Further, in the vicinity of the light emitting element ( 11 ), a condenser lens ( 24 ) is provided to allow light L to incident on a curved surface of the light trap ( 23 ). At the time of smoke detection, light scattered by smoke particles in a smoke detection portion ( 25 ) is received by a light receiving element ( 12 ). However, the light incident on the light trap ( 23 ) is reflected on the curved surface a plurality of times to be attenuated in each reflection, so the light is not received by the light receiving element ( 12 ). Accordingly, the S/N ratio of an output signal S obtained from the light receiving element ( 12 ) is improved, thereby making it possible to accurately perform the smoke detection at an early stage.
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