| 摘要 |
A relay control circuit is connected between a power source supplying an alternate current and a load to which the alternate current is supplied. The relay control circuit includes contacts for conducting/cutting off the alternate current supplied from the power source to the load. A first zero-crossing detection circuit is connected to the power source and generating a first zero-crossing signal to a control unit having a memory unit storing a time delay parameter. The control unit issues a control signal to energize a coil for actuating the contacts at a time point that leads the zero crossing point of the alternate current a time period equal to the time delay parameter whereby the contacts are actually actuated at a time point corresponding to the zero-crossing point. A second zero-crossing detection circuit is coupled to the load and generates a second zero-crossing signal. In case of deterioration of the performance of the relay, a difference exists between the time of detection of the second zero-crossing signal and the time point of the time delay parameter after the control signal. The difference is used to correct the time delay parameter.
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