| 摘要 |
PURPOSE:To detect a light source becoming abnormal by a relatively simple circuit by providing a light-source abnormality detecting method consisting of a direct photodetector, etc., that photodetects light direct from a light emitting body. CONSTITUTION:An electric power source provided to electric power source change- over circuit 7 supplies electric power to (a) only for time T1 at intervals of T2. Then, direct light output amplifying circuit 2, scattering light output amplifying circuit 3, etc., start to operate and at the same time, the charging of charging capacitor C1 starts. Next, (b) is supplied with electric power time T3 after (a) is supplied with electric power and light emitting diode LED turns on. Then, direct-light detecting silicon photodiode SPD1 receives light and then outputs signal (e), discharging C1. In the above-mentioned constitution, if any normal output is not obtained due to the breaking of light-source LED, etc., the output of amplifying circuit 2 drops remarkably or becomes zero and the charging of charging capacitor C1 is continued; and then as the output rises above fixed voltage Vth, the abnormality of the light source can be detected through light-source abnormality display circuit 6. |
