| 摘要 |
PURPOSE:To prevent the effect of the reflectivity of the surface of a material to be measured, by controlling the amount of light emitted from a semiconductor light emitting element, which modulates a light projecting period, based on the amount of received light on the light receiving side, which takes out the signal based on the period and holds the peak. CONSTITUTION:Light projected from a semiconductor laser diode 1 is modulated into a specified frequency by a light-projecting-period modulating circuit 11. The light is projected on a material to be measured (not shown). The reflected light is received by a light receiving part 5. Disturbance light is separated by a bandpass filter 13. The peak value is held by a peak holding circuit 14. The result is outputted to a received-light-amount detecting circuit 15 and a distance detecting circuit 9. The output of the circuit 15 is supplied to a microprocessor 17 through an A/D converter circuit 16. The output is compared with a specified reference value. The amount of emitted light is controlled through an emitted- light-amount control circuit 10 so that the amount of the received light of the element 5 becomes constant. An analog voltage, which is proportional to the detected distance is outputted by the circuit 9. |
