| 摘要 |
A method of and apparatus for controlling the opening and/or closing of contacts 13 and 14 of an electro-mechanical switching device 10 in an alternating current circuit. Detection is made for the existence of a voltage having a level which is indicative of a back emf in a load circuit 11 immediately following opening of the contacts 13 and 14, and if such a voltage level is detected an incremental adjustment is made in the phase angle at which successive actuations of the contacts are effected. This procedure is repeated under the control of a microprocessor 17 until such time as the voltage which is indicative of back emf reduces to zero, this providing an indication that ccntact opening is occurring at a time corresponding to zero current crossing in the alternating current waveform. <IMAGE> |
