Importance

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Abstract

A method of and apparatus for controlling the opening and/or closing of contacts of an electro-mechanical switching device 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 immediately following opening of the contacts, 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 until such time as the voltage which is indicative of back emf reduces to zero, this providing an indication that contact opening is occurring at a time corresponding to zero current crossing in the alternating current waveform.

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First Claim