| 摘要 |
PURPOSE:To perceive smoke with constant sensitivity irrespectively of distance, by increasing gains of an amplifying circuit amplifying a photodetecting signal from the light emitting time of a luminous element and making the gains zero before a reflected light from the surface of a wall is reached. CONSTITUTION:Light emitted from a luminous element 2 subjected to the pulse driving by a pulse oscillation circuit 1 is reflected by the particles of smoke 3 and its scattered light is made incident to a photodetector 4. An amplifying circuit 5 amplifying a photodetecting signal is connected to the side of output of the photodetector 4 and an amplifying circuit 6 constituted so as to vary gains periodically is connected to the side of its output. The gains start to rise by receiving the signal of the circuit 1 and is made zero before the light emitted from the element 2 is reflected from the side of a wall and is reached the element 4. The output of the circuit 6 is added to a threshold circuit 7 and moreover, is connected to an alarm circuit 8. The smoke can be perceived with constant sensitivity irrespectively of distance by varying the gains periodically in such a manner. |
