| 摘要 |
PROBLEM TO BE SOLVED: To accurately detect the dirt/damage of a flame sensor. SOLUTION: A light emitting element is arranged in a glove projected from a body and the glove is a cylindrical body forming a smooth curved surface for an air current on the light receiving glass side. Through the smooth curved surface of the light receiving glass, the light emitted from a test light emitting element in dirt/damage detection operation is used to accurately detect the degree of dirt of the light receiving glass on the basis of the light receiving quantity of a light receiving element.
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