| 摘要 |
The coincidence circuit includes negative and positive signal processing means. The negative and positive signal processing means each includes level detector circuit means for developing separate level detector output signals for each one of a plurality of a-c input signals when each one of the plurality of a-c input signals is of a negative or positive value respectively greater than predetermined negative or positive threshold levels. The predetermined threshold levels are of different magnitude for at least some of the a-c input signals. AND circuit means is coupled to receive the level detector output signals of the negative and positive signal processing means for developing AND circuit output signals respectively representative of negative and positive phase coincidence of the a-c input signals with threshold level attainment. OR circuit means is coupled to receive the AND circuit output signals for developing an OR output signal continuously representative of the phase coincidence of the a-c input signals. The coincidence circuit operates directly from a-c input signals of relatively low signal strength. In a preferred embodiment, a plurality of comparators are employed to receive four a-c input signals for use in a ground distance protective relaying application. In this embodiment, the predetermined threshold levels are in the millivolt range. Other embodiments are disclosed.
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