| 摘要 |
PROBLEM TO BE SOLVED: To provide an encoder having a function of detecting an abnormality of a light emitting means for decreasing a light emitting amount according to progress of the operating time or increase in temperature. SOLUTION: The encoder comprises: a driving circuit of a light emitting means for making the light emitting amount of the light emitting means substantially constant by varying the current value made to flow in the light emitting means according to variation in light emitting amount of the light emitting means (LED); a temperature detecting means for detecting the temperature of the light emitting means or its periphery; and an abnormality detecting circuit for determining that the light emitting means is abnormal when the current value exceeds a predetermined current value and the temperature detected by the temperature detecting means is a predetermined temperature or lower. COPYRIGHT: (C)2007,JPO&INPIT
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