| 摘要 |
PURPOSE:To perform a stable standing detection by comparing a first memory means for storing a value in accordance with a period corresponding to a rotational speed in response to a pulse having said period and a second memory means for storing the value of the period when the period becomes several times longer with each other. CONSTITUTION:A function generating circuit 4 is operated in response to a pulse with a period in accordance with a rotational speed and, after sampled by a gate circuit 6, the output of the circuit 4 is stored in a first capacitor 7 and indicated by a tachometer. On the other hand, a voltage equal to that obtained when the period of the pulse becomes several times longer is established by a resistor 12 and the value sampled from the voltage is stored in a second capacitor 14. The value (capacitance) of the second capacitor 14 is compared with that of the first capacitor 7 by a comparator 16 and, when the latter value becomes larger than the former one, a switch circuit 17 is turned off. Therefore, by removing the deflection of the pointer of the tachometer when stopped, a stable standing detection can be performed.
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