| 摘要 |
PURPOSE:To prevent an accident due to early start by connecting a fixed resistance between a time limit setting variable resistance means of a timer and an earth, and operating it by a time limit which is set in advance, even if a variable resistance is deteriorated and time limit setting goes to abnormal. CONSTITUTION:A variable resistor 2 having a slider 3 and a fixed resistor 9 are connected in series to a DC power source 1 whose voltage is V0. A time limit deciding means B sets the voltage V0 as the maximum time limit, and decides a desired time limit by a divided voltage V1 generated by the slider 3. A targeted counting value determining means C determines a targeted counting value by an output of the time limit deciding means B. A counting and time limit signal generating means E outputs a signal G, when a clock from a counting signal generating means D is counted by a targeted counting value. The time limit deciding means B decides a ratio of the power supply voltage V0 and the divided voltage V1, and for instance, when V1/V0 goes to <=0.1, it is decided to be an abnormality caused by a contact failure, etc., and by the target discrete value determining means C, for instance, a counting value of 0.5 of the maximum counting value is outputted. In such a way, an abnormal early start is prevented.
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