| 摘要 |
PURPOSE:To enable the stable maintenance of an amount of projection and an amount of reception in a prescribed range, by controlling a projector driving circuit on the basis of a difference between an output of a monitor circuit detecting the amount of projection and a standard value of the amount of projection and a difference between an output of a photodetecting circuit and a standard value of the amount of reception. CONSTITUTION:Most of a laser light of a laser element 2 strikes on a substance 1 to be measured, and it is reflected therefrom and reaches a position detecting element 3. On the other hand, a photodiode 4 is disposed as a monitor circuit in the vicinity of the element 2, and a differential amplifier 6 supplies a difference between an output of the diode 4 and a standard voltage VR1 of an amount of projection to a first input terminal of a load addition circuit 5. The element 3 has two output terminals, and the outputs thereof are subjected to addition in an addition circuit 11 through amplifiers 8 and 9 and supplied to a differential amplifier 12. The amplifier 12 forms a difference between an added-up voltage and a standard voltage VR2 of an amount of reception and supplies same to a second input terminal of the load addition circuit 5. Then the circuit 5 adds up the output of the amplifier 6 and that of the amplifier 12 in an appropriate ratio and gives an output thus obtained to a projector driving circuit 7, so as to drive the element 2. |
