| 摘要 |
PURPOSE:To know the presence of an object desired to be inspected, by a method wherein the output of a sensor when there exists no object to be inspected is digitized to obtain output before the present point of time and this output is analogized to be converted to a judge reference value which is, in turn, compared with the output of the sensor at the present point of time. CONSTITUTION:The outputs of light receiving elements 1a-1n when there exists no object to be inspected are successively scanned by a multichannel multiplexer 2 to be amplified by an amplifying circuit 3 and temporarily held by a sample holding circuit 4 and subsequently converted by an analog/digital converter circuit 5 to be inputted to a control circuit (CPU)6. CPU6 emits a synchronous pulse not only to control the sample temporarily holding circuit 4 and a digital/analog converter circuit 9 but also to inform the element read presently to a demultiplexer 10 and the latch circuit 11. By this constitution, CPU6 forms a judge reference signal on the basis of the past output temporarily held by the sample holding circuit 4. The reference signal is converted to an analogue signal by the D/A converter circuit 9 to be compared with the output of the light receiving element at the present time by a voltage comparing circuit 8 to be successively applied to the latch circuit 11 through a demultiplexer 10 and, for example, the crowded state of the object to be inspected such as paper can be detected on a terminal 12 and detection capacity of a digital level is obtained from a terminal 7 to display the cleaning period of a sensor. By this constitution, the change with time of the sensor or erroneous judgment due to the adhesion of dust is prevented.
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