| 摘要 |
PURPOSE:To improve photodetection efficiency by focusing smoke-scattered light on a photodetector by a rotary reflective surface formed of a paraboloid of revolution or ellipsoid of revolution. CONSTITUTION:A circular cylinder is formed of a transparent body and cylindrical hole 11 is provided on its center axis. On it, light emission element 5 is arranged, concave part 12 is formed in the center of the top surface, and photodetector 6 is positioned in the center of concave part 12. In the bottom surface of the above- mentioned concave part 12, arc surface 13 that has the center of curvature in the center of the photodetection surface of photodetector 6 is formed and at the lower outer circumference of the circular cylinder, paraboloid 14 of revolution having its focal point in the center of the photodetection surface of photodetector 6 and obtained by being turned around the axis perpendicular to the main axis including the focal point is formed and mirror-finished. When smoke enters smoke sensitive area 10 formed under hole 11, primary light emitted from light emission element 5 is scattered light C1 scattered in the radius direction of cylindrical hole 11 strikes paraboloid 14 of revolution in parallel to the main axis, so that reflected light C2 will all be focused, namely, photodetected by photodetector 6. |
