| 摘要 |
PURPOSE:To enable the easy detection of the direction of rotation of a voltage vector of a three-phase alternating current, by a method wherein a voltage of each phase is made to be a pulse and a reference pulse train corresponding to one phase is compared on a time basis with two pulse trains corresponding to the two remaining phases. CONSTITUTION:After divided by resistances 11-16, a voltage of each phase of a commercial three-phase alternating current 1 is inputted to a differentiating circuit through buffers 20-22 and positive pulse trains (r), (s) and (t) corresponding on a one-to-one basis to the respective phase voltages of lines R0, S0 and T0. At the point of time when the pulse train (r) arrives, Q and Q' of both outputs of R.S flip-flop FFS 29 and 30 turn to be 0 and 1 respectively. Accordingly, an output of either an AND element 31 or 32 turns to be 1 first in response to a pulse of the pulse train (s) or (t) which arrives subsequently earlier in time than the one of the other. When the pulse train (s) arrives first, for instance, Q and Q' of the output FF 29 turn to be 1 and 0 respectively, an output of an off-delay element 33 turns to be 1, and thereby an output element 35 is operated.
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