Tachometer responsive to ignition pulses utilizing a zener diode-inductor filter

Claim 1

A TACHOMETER ADAPTED TO BE CONNECTED ACROSS A SOURCE OF REPETITIVE VOLTAGE PULSES WHICH INCLUDE FUNDAMENTAL AND HIGH FREQUENCY COMPONENTS, THE TACHOMETER COMPRISING A ZENER DIODE CONNECTED ACROSS THE SOURCE IN A SERIES CIRCUIT WHICH INCLUDES INDUCTANCE AND RESISTANCE HAVING A TIME CONSTANT LARGE ENOUGH TO EFFECTIVELY SUPPRESS THE HIGH FREQUENCY COMPONENTS, THE ZENER DIODE BEING CONNECTED SO THE VOLTAGE PULSES ARE APPLIED THERETO IN THE REVERSE DIRECTION AND HAVING A REVERSE BREAKDOWN VOLTAGE LOWER THAN THE AMPLITUDE OF SAID PULSES SO THAT THE SERIES CIRCUIT EXHIBITS A SMALL TIME CONSTANT UNTIL THE ZENER DIODE BREAKS DOWN AND A LARGE TIME CONSTANT AFTER THE ZENER DIODE BREAKS DOWN WHEREBY EACH OF THE VOLTAGE PULSES ACROSS THE ZENER DIODE HAS A LEADING EDGE CORRESPONDING TO THAT OF THE PULSES FROM SAID SOURCE AND HAS A CONSTANT PULSE AMPLITUDE, A CAPACITOR, A PARALLEL CIRCUIT INCLUDING A UNIDIIRECTIONALLY CONDUCTIVE DEVICE IN ONE BRANCH AND AN IMPEDANCE ELEMENT IN ANOTHER BRANCH FOR PROVIDING SEPARATE CHARGING AND DISCHARGING PATHS FOR THE CAPACITOR, INDICATING MEANS CONNECTED IN ONE OF SAID BRANCHES AND BEING RESPONSIVE TO AVERAGE CURRENT, SAID PARALLEL CIRCUIT BEING CONNECTED ACROSS THE ZENER DIODE THROUGH SAID CAPACITOR, SAID RESISTANCE AND THE TIME CONSTANT OF SAID INDUCTANCE AND RESISTANCE BEING SMALL ENOUGH IN RELATION TO THE VALUE OF SAID CAPACITOR SO THAT THE CAPACITOR IS FULLY CHARGED DURING EACH PULSE AND IS FULLY DISCHARGED BETWEEN PULSES WHEREBY THE CURRENT FLOW THROUGH THE INDICATING MEANS HAS AN AVERAGE VALUE CORRESPONDING TO THE REPETITION RATE OF SAID PULSES.