| 摘要 |
PURPOSE:To reduce errors in detection due to temperature characteristics, an environmental change, noise variation, element deterioration, etc., by using a current, etc., flowing to a photodetecting element when a light emitting element is not in operation as a comparison reference value for the position detection of a shield plate provided with a slit moving between the light emitting and photodetecting elements. CONSTITUTION:A distributor 10 is controlled through a control part 13, and the current, which responds to ambient light, noises, etc. of the photodetecting element 2 when a transistor (TR) 12 is off and the light emitting element 1 is not in operation, is stored in a storage part 14. This stored value is compared with the comparison reference value, and an arithmetic comparison part 15 processes the photodetection current of the element 2 through the shield plate provided with the slit moving between the elements 1 and 2 to detect the position of the shield plate. Therefore, the reference value is set properly at every time, and the influence of temperature characteristics, an environmental change, noise variation, deterioration of the elements, etc., is eliminated, so that detection errors caused by them are reduced. |
