Control circuit for operating circuit interrupter at a zero current point in system wave form

Claim 1

A CONTROL FOR SIGNALING A CIRCUIT INTERRUPTER DEVICE IN A SYSTEM HAVING A GENERALLY PERIODIC SYSTEM WAVE FORM TO BEGIN SWITCHING AT A POINT IN SAID SYSTEM WAVE FORM AHEAD OF A ZERO CURRENT POINT IN ORDER TO EFFECT SWITCHING AT SAID ZERO CURRENT POINT, COMPRISING: (A) COUPLING MEANS ADAPTED TO BE COUPLED TO SAID SYSTEM TO PROVIDE AN INPUT SIGNAL REPRESENTING AN ANALOG OF SAID SYSTEM WAVE FORM, (B) A PHASE SHIFTER CONNECTED TO RECEIVE SAID INPUT SIGNALS AND TO PRODUCE A WAVE FORM THAT IS SHIFTED AHEAD OF SAID SYSTEM WAVE FORM SO AS TO HAVE A ZERO CROSSING WHICH IS APPROXIMATELY COINCIDENT WITH SAID FIRST POINT, (C) A RECTIFIER CONNECTED TO RECEIVE SAID SHIFTED WAVES FORM AND TO PRODUCE A RECTIFIED WAVE FORM HAVING SLOPE DERIVATIVE DISCONTINUITIES COINCIDENT WITH SAID FIRST POINT, (D) A CLIPPING CIRCUIT CONNECTED TO RECEIVE SAID RECTIFIED WAVE FORM AND TO PRODUCE AN AMPLIFIED CLIPPED WAVE FORM HAVING ITS PEAK CLIPPED BUT ITS VALLEYS PRESERVED, (E) PULSE PRODUCING MEANS CONNECTED RECEIVE THE AMPLIFIED CLIPPED WAVE FORM AND TO PRODUCE A PULSED SIGNAL THAT HAS PULSES OF OPPOSITE POLARITY WITH THE LEADING EDGE OF ONE OF SAID PULSES BEING SUBSTANTIALLY COINCIDENT WITH THE RISING SLOPE IN THE VALLEY OF SAID RECTIFIED WAVE FORM,