| 摘要 |
<p>PROBLEM TO BE SOLVED: To prevent the erroneous operation due to the noise of continuous high frequency in a reflection light modulating type detector. SOLUTION: A light-emitting element projects the light modulated according to the pulse signal generated from an oscillation circuit 21. If an object 29 exist there, reflected light is incident on a light receiving element 24 and light receiving output is selected by a BPF 34 and amplified by an AC amplifier 25, to be compared with a reference level by a comparator before inputted to a signal detection circuit 31 and a noise detection circuit 32. The light- receiving output is sampled with a timing shifted from the light-emitting timing of the light-emitting element 23 in the noise detection circuit 32. The matter 29 is detected, on the basis of the detection signal from the signal detection circuit 31, and the absence of the matter 29 is decided on the basis of the noise signal from the noise detection circuit 32.</p> |
