| 摘要 |
PURPOSE:To automate complicated adjusting operation and to detect a pattern printed on paper, etc., the light transmission characteristics of a form itself, the stain of the form, etc., stably with high accuracy. CONSTITUTION:An operation mode setting part 19 sets a control circuit 17 in a reference initial value setting mode and a reference form is interposed between a light source and a photodetector 11. Then a 1st set value is set in the circuit 17 so that the output level of an AD converter 15 is a prescribed value or within a prescribed range. Then, the reference form is removed and the output level of the converter 15 when reduction is performed with the 1st set value and a prescribed reduction ratio is stored as a reference initial value in a nonvolatile storage part 18. Then, a normal operation mode is set by an operation mode setting part 19 and a 2nd set value is set in the circuit 17 so that the output level of the converter 15 is equalized or approximated to the reference initial value when there is nothing between the light source and photodetector 11. Further, a 3rd set value is set in the circuit 17 so that the output level of the converter 15 increases at a prescribed increase rate; and a series of reading operations is performed by supplying a signal from an amplifier 14 to the converter 15.
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