| 摘要 |
<p>PURPOSE:To prevent erroneous measurement caused by diffused external light by converting a received light quantity into an electrical signal, fetching only an AC signal component, holding the maximum signal level of the AC signal component and judging whether or not the value of the signal exists in a sampling period. CONSTITUTION:As to the light receiving signal of 1st and 2nd sensors 11 and 12, DC noise component is removed by AC coupling circuits 13 or 14 respectively, amplified by amplifiers 21 and 22 and inputted in peak hold circuits 31 and 32. The maximum value of output signals from the circuits 13 and 14 is held in the circuits 31 and 32. When reset signals from reset circuits 41 and 42 are inputted, the maximum value which is held hithereto is reset and the maximum value of the output signal is started to be held attain. Next, the output signals from the circuits 31 and 32 are stored in a RAM 55 through an A/D conversion circuit 51 and a CPU 53. The CPU 53 judges whether the output signals from the circuits 31 and 32 stored in a RAM 55 are '1' or '0'. In the case that the judged result string is other than '0, 1, 0', the signal value is judged to be a noise caused by diffused external light and it is not adopted in succeeding signal processing.</p> |
