| 摘要 |
PURPOSE:To make it possible to obtaidn a stable photoelectric conversion output independently of the light-source illuminance change in an AC manner by detecting the cycle of the light-source illuminance and inputting the data from the sheet surface in a photoelectric transducer at a period of an integer multiple of the detected cycle. CONSTITUTION:The light reflected from a sheet surface 1 is led through an optical system 3 to a reading photoelectric transducer 4, where an electrical signal is formed having a level corresponding to the amount of the led light. In this case, a detecting circuit 5 to detect the frequency of the power source is provided on the power source line to a light source 2, so that the frequency of the light source is measured to calculate the cycle beforehand. According to the calculated cycle, a sample period deciding circuit 6 sets a period of an integer multiple of the cycle and controls the sampling period for reading the amount of the incident light by the transducer 4 and forming a signal. Thereby, regardless of the point of the starting point of the sampling period in the pulsating current of the power source, the integrated value of the amount of the light emitted from the light source is made constant. |
