| 摘要 |
PURPOSE:To reduce the change with time, by irradiating only a direct light beam which does not include scattered light to a light receiving element, changing the area of the light receiving element, to which said light beam is irradiated, thereby transducing the displacement of a diaphragm into an electric value. CONSTITUTION:A long hole 1a is provided in a supporting plate 1. Light shielding treatment is applied to a black box 2, which is fixed to the supporting plate 1. A reflection preventing means comprising a black stain-finish surface or concave parts 2a is provided on the inner surface of the black box 2. Two fixed light shielding plates 3 partitions the inside of said black box 2 and blocks the passage of the reflected light in the black box 2. Windows 3a are provided in the plates 3. A light emitting element 4 is provided at one end of the black box 2 and the light receiving device 5 is fixed to the other end. In said light receiving device 5, a light receiving element 5b for detection and a light receiving element 5c for reference are arranged on a substrate 5a in close proximity. A movable shielding plate 7 is slidden in response to the displacement of the diaphragm 6, to which a pressure is applied. Light shielding treatment is performed on the plate 7. The plate 7 is inserted in the long hole 1a of the supporting plate 1 and arranged in front of the light receiving device 5. A window 7a faces the element 5c. The upper end of the window 7a is moved on the element 5b in response to the displacement of the diaphragm 6. |
