| 摘要 |
PURPOSE: To measure the speed of a continuous substance to be measured, by a method wherein scattered light at the same position of irradiation on the substance is received in directions different from one another and output signals within the allowable limits out of ones of a plurality of light-receiving means are selected and outputted. CONSTITUTION: A beam LB of a laser light source 1 is divided in two, beams LB1 and LB2 , by a half mirror 2 and the same point on a substance 7 to be measured is irradiated by direct transmitted light and by reflected light via a mirror 3, a crossing angleθbeing formed by them. Scattered light 9 from the point is passed through lenses 4a-4e and detected by photosensors 5a-5e. Then, light reception levels of the sensors 5a-5e are compared with ones in the allowable limits by a light reception level discriminating circuit 6, and an error display is made when no level is present within the limits, while selection of the sensor is executed in conformity with a predetermined priority order by a selecting circuit 8 when any one of the levels is present therein. A Doppler signal is detected from an output of the sensor by an amplifier 10 and BPF 11 and converted into a speed.
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