| 摘要 |
PURPOSE:To avoid malfunctions and let the abnormality of the device be displayed as well by providing a first photo detector on the optical axis of light emitting part and a second photo detector out of the optical axis, detecting the signals of both differentially to detect smoke and lighting a display lamp with the input to the first photo detector. CONSTITUTION:A first photo detector 2 is provided on the axis of a light emitting part 1 and a second light emitting element 3 is provided with a deviation by an angle theta from the optical axis and these are so disposed that only the element 2 receives light when there is no smoke and the element 3 receives the scattering light owing to smoke when the smoke has evolved. The output of the element 3 and the output of the element 2 having been amplified 8 are removed of the effect of interior lighting through filter parts 9, 9' respectively, after which these are applied to a differential amplifier 10 to obtain the input difference of both, which triggers an alarm device 5 when there is the input of more than specified scattering light. When an obstruction such as insect other than smoke has existed in the detector, the output from the element 2 is so small that the display lamp 4 does not go on, indicating the abnormal state of the detector. Here, the alarm device 5 does not actuate either. |
