| 摘要 |
PROBLEM TO BE SOLVED: To provide a fire sensor capable of correctly measure the degree of stain of the light receiving window without affection from the variation in the performance of parts of a test light source, a light receiving window or the like. SOLUTION: The MPU 9 if it goes into confirmation test of degree of stain, puts on and off the test light source 4 with 2 Hz so as to flicker same as a flame. After keeping the state for a prescribed time, obtains the value of the infrared detection signal detected by the infrared sensor 3. Thereafter, it is determined whether the check sum stored in the EEPROM 8 is the same as the first threshold value or not. If the check sum is correct, the first threshold value is determined to be correct, and the larger one is selected between the first threshold value and second threshold value which is previously set. If the first threshold value is not normal, the second threshold value is selected. When the value of the infrared detection signal is larger than the first threshold value or the second threshold value, the degree of stain of the light receiving window 1 is determined as normal. COPYRIGHT: (C)2008,JPO&INPIT
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