Signal level detection circuit having automatically changed impedance

Claim 1

IN AN ELECTRICAL SYSTEM FOR DETECTING A PULSATING VOLTAGE INPUT AT A FIRST AMPLITUDE THRESHOLD LEVEL AND AT A SECOND AMPLITUDE THRESHOLD LEVEL HIGHER THAN THE FIRST LEVEL, A RELAY HAVING A COIL, A MAKE-BREAK SWITCH AND A SWITCH WITH A COMMON TERMINAL CONNECTED TO A SOURCE OF ELECTRICAL ENERGY THROUGH THE RELAY COIL, AND SECOND AND THIRD OUTPUT TERMINALS, AN ON-OFF CIRCUIT CONNECTED TO THE SECOND OUTPUT TERMINAL OF THE THREE TERMINAL SWITCH INCLUDING A GATING DEVICE THAT FIRES INITIALLY AT THE FIRST AMPLITUDE THRESHOLD LEVEL AND FIRES SUBSEQUENTIALLY AT THE SECOND AMPLITUDE THRESHOLD LEVEL , A CIRCUIT CONNECTED TO THE THIRD OUTPUT TERMINAL OF THE THREE TERMINAL SWITCH HAVING A DETECTING DEVICE THEREIN, AN INPUT CIRCUIT HAVING AN AMPLITUDE SENSITIVE RECTIFIER FOR PASSING PULSATING INPUTS ABOVE THE FIRST THRESHOLD LEVEL, A CIRCUIT CONNECTING THE RECTIFIER AND GATING DEVICE HAVING PARALLEL BRANCHES RESPECTIVELY INCLUDING A RESISTOR AND THE MAKE-BREAK RELAY SWITCH IN SWITCH CHANGES FROM A MAKE CONDITION SHORTING THE RESITOR TO A BREAK CONDITION AT THE FIRST AMPLITUDE LEVEL WITH OPERATING OF THE RELAY, AND A HIGHER THRESHOLD LEVEL FIRING CIRCUIT FOR THE GATING DEVIVCE HAVING A RECTIFIER THEREIN CONNECTING THE DETECTING AND ONOFF CIRCUITS IN BYPASSING RELATION TO THE DETECTING DEVICE.