| 摘要 |
PURPOSE: To measure the speed of a continuous substance to be measured, by judging whether the light reception level of a light-receiving means is within the allowable limits or not and by controlling the quantity of light of a light source so as to make the level be within the limits when it is outside the limits. CONSTITUTION: A beam LB of a laser light source l 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 a lens 4 and detected by a photosensor 5. The photosensor 5 is connected with a light reception level discriminating circuit 6 discriminating light reception levels on the basis of an output of the sensor and with a conversion circuit 8 converting cycles of the light reception level and a reference value thereof into current values. When the light reception level of the sensor 5 is outside the allowable limits, the quantity of light of the light source l is controlled by the circuit 8 so that it be kept within the limits. The output of the sensor 5 is passed through an amplifier 10 and subjected to heterodyne detection by BPF 11, a Doppler signal is detected therefrom and the speed of the substance 7 is determined.
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