| 摘要 |
PURPOSE:To provide a tester for surface defect which eliminates adjustment against a temperature change and a change with the passage of time, by self-adjusting it so that a sweep speed of transmitting light is normally held constant. CONSTITUTION:A time required for sweeping of collecting elements 19 and 20 by transmitted light is found by counting a clock sweep time counter 21 of a reference clock oscillator 13 during a time covering from collecting of transmitted light to the collecting element 19 to collection of it to the collection element 20. If a rotation angle of a galvanometer 4 reduces due to a factor such as deterioration in the sensitivity of the galvanometer 4, a sweep width of a transmitted light, swept by a mirror 5 operating in synchronism with the galvanometer, decreases, the sweeping speed of the transmitted light delays than a speed previously determined. This lengthens a time required for sweeping of the collecting elements 19 and 20 by the transmitted light, and the number of clocks counted by the counter 21 increases. If an analogue voltage of a D/A converter 22 increases, a gain of a voltage gain variable amplifier 23 increases, and a voltage amplitude of a sweeping signal applied to the galvanometer 4 increases. Thus, the rotation angle of the galvanometer 4 increases, which results in causing a device to function so that the speed of the transmitted light returns back to a speed previously set. |
