| 摘要 |
In this device, the object is to achieve a reliable disconnection of the electrical device only when a phase fails totally and not when there is imbalance in the load. This is done by a resistor (W1, W2, W3), a diode (D1, D2, D3) and an optocoupler (O1, O2, O3) being connected in series between in each case two phases of the three-phase system, each optocoupler supplying an L signal during a positive halfwave of the alternating voltage and an O signal during a negative halfwave, the negated output signal of each optocoupler being supplied, on the one hand, directly to the first input and, on the other hand, after delay of the rise and fall to the second input of an EXCLUSIVE OR gate (E1, E2, E3), and the outputs of the EXCLUSIVE OR gates (E1, E2, E3) being connected to the inputs of an OR gate (1), which is followed by a retriggerable timing section (2) with a time set to approximately 90 DEG of the alternating current period. <IMAGE>
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