Electric tachometer using biased pulse transformer

Claim 1

IN AN ELECTRICAL TACHOMETER OF THE TYPE IN WHICH AN ENGINE IGNITION SYSTEM BREAKER POINTS ARE CYCLICALLY OPENED AND CLOSED TO PRODUCE IGNITION PRIMARY PULSES AND IN WHICH AN ELECTRICAL METER IS ENERGIZED IN ACCORDANCE WITH THE PULSES TO INDICATE ENGINE SPEED, THE COMBINATION WITH THE METER OF A PULSE TRANSFORMER HAVING A PRIMARY WINDING ADAPTED FOR CONNECTION WITH THE BREAKER POINTS AND HAVING A SECONDARY WINDING CONNECTED TO THE METER, MEANS CONNECTED TO AT LEAST A PORTION OF SAID PRIMARY WINDING NORMALLY BIASING THE TRANSFORMER TO SATURATION IN ONE DIRECTION, PRIMARY IGNITION PULSES EFFECTIVE UPON CLOSURE OF THE BREAKER POINTS DRIVING THE TRANSFORMER TO SATURATION IN THE OPPOSITE DIRECTION TO PRODUCE OUTPUT PULSES IN THE SECONDARY WINDING SUBSTANTIALLY INDEPENDENT OF VARIANCES IN THE MAGNITUDE AND WAVE FORM OF THE IGNITION PULSES FOR ENERGIZING THE METER, AND A HALF-WAVE RECTIFIER IN SERIES CONNECTION WITH SAID METER AND SAID SECONDARY WINDING FOR PREVENTING APPLICATION OF PULSES TO THE METER INCIDENT TO OPENING OF THE BREAKER POINTS.