| 摘要 |
PROBLEM TO BE SOLVED: To provide a photoelectric circuit which is independent of changes in environmental temperature. SOLUTION: Light hνis introduced into an optical sensor 8 from a light emitting diode LED to convert modulated light hν' to a photocurrent Ip with a photodiode PD. The photocurrent Ip is compared with a reference current Ip and the resulting comparison currentΔIp is converted to a voltage signalΔVp to be supplied to an integration circuit. A DC voltage component Vdc in a voltage signalΔVp' is fed back to a drive circuit 9 through a DC component extraction circuit 15, a voltage/current conversion circuit 16 and a current addition circuit 17. Moreover, a compensation current Iad from a current generation circuit 18 as made up for by a temperature compensation circuit 19 is supplied to the current addition circuit 17 to let the drive circuit 9 undergo a feed back by an added current If of the compensation current Iad and a current Idc. The compensation current Iad is so set that no DC voltage component is generated in the voltage signalΔVp'. This enables measurement using the optical sensor 8 without being affected by an environmental temperature.
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