| 摘要 |
PURPOSE:To detect the phase rotation of a three-phase AC power source automatically by providing polarity deciding circuits which output a rectangular wave signal according to the polarities of interline voltages of the three-phase AC voltage and a logic circuit which decides the phase rotation direction of the three-phase AC voltage. CONSTITUTION:The phase voltages 1a-1c of a three-phase AC power source 1 are insulated and transformed by respective transformers 2a-2c and applied to polarity deciding circuits 3a and 3b. Then the circuits 3a and 3b output a logical value H when the input voltages are positive or a logical value L when the input voltages are negative. Then the output of the circuit 3a is applied to the data input D of a D-type FF 4 and the output of the circuit 3b is applied to the clock input CK. This FF 4 changes the logical value of the output Q into the logical value of the input D only when the input CK is inverted from the logical value L to the logical value H. Thus, the phase rotation of the three-phase AC voltage is detected and outputted automatically.
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