Frequency detector including noise rejection means

Claim 1

APPARATUS ENERGIZED FROM A D.C. VOLTAGE SOURCE FOR MEASURING THE FREQUENCY OF A PERIODIC SIGNAL COMPRISING A SOURCE OF A PERIODIC SIGNAL, AMPLIFIER MEANS COMNECTED TO SAID SIGNAL SOURCE FOR AMPLIFYING SAID PERIODIC SIGNAL, METER MEANS ADAPTED TO PRODUCE AN INDICATION DIRECTLY RELATED TO THE FREQUENCY OF SAID PERIODIC SIGNAL, AND THRESHOLD MEANS ENERGIZED BY SAID AMPLIFIED SIGNAL AND APPLYING SAID AMPLIFIED SIGNAL TO SAID METER MEANS, SAID THRESHOLD MEANS COMPRISING A TRANSFORMER HAVING A PRIMARY WINDING CONNECTED TO THE OUTPUT OF SAID AMPLIFIER MEANS, FIRST DIODE MEANS, A NETWORK INCLUDING A RESISTANCE IN PARALLEL WITH A CAPACITOR, SAID NETWORK HAVING A TIME CONSTANT WHICH IS LONG IN REALTION TO THE PERIOD OF SAID PERIODIC SIGNAL, THE SECONDARY WINDING OF SAID TRANSFORMER, SAID DIODE AND SAID NETWORK BEING CONNECTED SERIATIM ACROSS SAID VOLTAGE SOURCE, TRANSISTOR MEANS HAVING AT LEAST EMITTER BASE AND COLLECTOR, SAID EMITTER AND BASE TERMINALS BEING CONNECTED ACROSS A PORTION OF SAID SECONDARY WINDING TO PROVIDE A SIGNAL INPUT TO SAID TRANSISTOR, RESISTANCE MEANS CONNECTING SAID COLLECTOR TO THE TERMINAL OF SAID VOLTAGE SOURCE TO WHICH SAID NETWORK IS CONNECTED, A CAPACITANCE, AND SECOND DIODE MEANS, SAID CAPACITANCE AND SAID SECOND DIODE MEANS BEING CONNECTED SERIATIM BETWEEN SAID COLLECTOR AND THE CONNECTION BETWEEN SAID FIRST DIODE MEANS AND SAID NETWORK, SAID FIRST AND SECOND DIODE MEANS HAVING A COMMON POLARITY WITH RESPECT TO SAID VOLTAGE SOURCE, SAID METER MEANS BEING OPERATIVELY CONNECTED TO THE COMMON CONNECTION OF SAID CAPACITANCE AND SAID SECOND DIODE MEANS.