| 摘要 |
PURPOSE:To simplify the structure and to reduce the cost by providing a Fresnel lens type convergent cover to the opening part of an instrument main body, and stopping down heat rays to the specific sensitivity of a heat ray sensor. CONSTITUTION:The Fresnel lens type convergent cover 4a is fitted to the open ing part of the instrument main body 1 which incorporates the heat ray sensor to protect the optical system 2A against dust and water and also stop down a wide heat ray optical path b1 before the convergent cover 4a is fitted to a narrow heat ray optical path b2. Consequently, complex constitution for recovering the attenuation of heat rays due to the light absorption of the cover is not necessary and the practical sensitivity of the heat ray sensor 2 is switched automatically, so the operation is facilitated and the cost is reduced. |
