| 摘要 |
PURPOSE:To enable highly accurate measurement of distance, by making the frequency of a clock higher enough than the beat frequency to allow the measurement of the number of waves below the decimal point precisely under one cycle. CONSTITUTION:A clock generator 23 for measuring the number of waves below the dicimal point is provided to generate a clock with the frequency by far higher than the frequency of a beat wave to be counted with a clock counter 24. A integral wave counter 22 outputs a reset signal 25 to a clock counter 24 each time counting the number of integral ones of beat waves to reset the clock counter 24, when a computation circuit 26 receives and memorizes counts corresponding to one cycle of the beat waves. A time setter 27 has a specified time set to obtain a predetermined frequency shift delta by modulating a laser beam. Under such a condition, the clock counter 24 counts the counts corresponding to the number of waves below the dicimal point, that is, under one cycle.
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