| 摘要 |
PURPOSE:To obtain an optimum mounting position of a diffraction grating easily with a simple operation by repeating the operation that the diffraction grating is turned and the grating is reversed when a display light goes off. CONSTITUTION:A tracking error signal 21 held in a peak hold circuit 30 is compared with a triangle wave 44 at a level discriminating circuit 42. Then when the hold value 41 is higher than the level of the triangle wave 44, the discrimination circuit 42 outputs a discrimination signal 42a to sets and FF 50 of a display circuit 48 thereby turning on a display lamp 52 and stopping the oscillation of an oscillator 38. Conversely, when the hold value 41 is lower than the level of the triangle wave 44, the circuit 42 outputs a discrimination signal 42b to reset an FF 50 of the circuit 48, thereby turning off the lamp 52 and oscillating the oscillator 38. Thus, the signal 21 is inputted to the adjusting circuit to turn the diffraction grating and when the display light goes off, the grating is reversed, the optimum mounting position is obtained by repeating the operation.
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