| 摘要 |
PURPOSE:To detect overspeed of a motor, by judging the time of a drop of a period of a sinusoidal wave instructing signal from the prefixed value. CONSTITUTION:When a voltage VR1=VR2>0 is applied to + terminals of comparators 1, 2 and an input signal to (-) terminal, the output v1 of the comparator 1 is indicated as ''1'' while the width T1 is i>VR1 and the output v2 ''1'' while i>VR2 and by reversing by an inverter 5, for i>VR2 an output v5 of the inverter 5 becomes ''1'' with its width of T2 and then, monostable-multivibrators 3, 4 are triggered by the outputs v1, v5 and pulses v3, v4 provided with the same pulse width T are applied. When a period of input current (i) corresponding to the limit speed judging a motor speed as excessively high is assumed as T0, it is set as T=T0/2. Here, when a period TM of the current (i) becomes TM<T0= 2T, an output v6 of AND-gate becomes, during this time, as ''1'' and an output Q of FF7 is set at ''1'' and the motor is brought to a stand still.
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