| 摘要 |
PURPOSE:To correct the output from a photodetector generated when a raindrop, etc. oscillate by providing a filter which removes the low-frequency component occurring in the oscillation of the liquid drop sticking to a fixed position from the output of the photodetector. CONSTITUTION:An oscillation circuit 21 makes oscillation operation at 100kHz and the output thereof is applied to a driving circuit 22, by which a light emitting element 1 is driven. The light from the element 1 is detected by the photodetector 2 and the quantity of the detected light changes when the raindrop passes through an optical path 3 therebetween. The output from the photodetector 2 is applied to a BPF23 by which the noise arising from the sunlight, etc. is removed. The output from the BPF23 is applied to an amplifier circuit 24 and a detection circuit 25, by which only the component of the output fluctuation of the photodetector 2 arising when the path 3 is interrupted by the raindrop is taken out. An HPF26 shuts off the signal of the output from the photodetector 2 generated when the raindrop sticking to the fixed position in the path 3 oscillates. |
