| 摘要 |
When a light emission element emits no light, a detected signal from a photodetection element is captured as an intensity of external light. Then, a threshold value is offset by the intensity of the external light. The offset threshold is then compared to a detected signal from the photodetection element when the light emission element emits light, thereby determining the presence of a through hole between the light emission element and the photodetection element through which hole light passes without being influenced by external light.
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