| 摘要 |
PURPOSE:To detect a count error by guiding light from a light emitting element to two photodetecting elements intermittently through a rotary disk, and counting it by a counter. CONSTITUTION:Photocurrents of the 1st photodetecting element 11 of a front photodetection side unit and the 2nd photodetecting element 12 of a rear photodetection side unit are amplified by amplifiers 13 and 14 and shaped into pulse trains of 0 and 1. Outputs (a) and (b) of the amplifiers 13 and 14 are inputted to two input terminals of an exclusive OR gate 15 and ORed exclusively to input an absolute differential value output (c) to the clock input of the counter 16. Then, the least significant digit LSB (0 in this case) and the pulse train (a) are ORed (e) exclusively by an exclusive OR gate 17 for count error detection. The exclusive OR output (e) is 0 when the outputs (a) and (d) are equal and 1 when not. When the LSB output (d) is an error pulse, the outputs (d) and (a) are different, so an error signal appears at the output (e).
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