Electrical control circuit including indirectly heated theremistor providing abrupt change in resistance with temperature

Claim 1

A CONTROL DEVICE RESPONSIVE TO CONTROL POWER APPLIED THERETO TO ALTER THE CURRENT FLOWING IN A CONTROLLED CIRCUIT INCLUDING IN COMBINATION, A FIRST SELF-HEATING POSITIVE TEMPERATURE COEFFICIENT THERMISTOR, A FIRST CONTROL CIRCUIT CONNECTED TO SAID FIRST THERMISTOR TO APPLY CONTROL CURRENT THERETO FOR HEATING THE SAME, A SECOND THERMISTOR PROVIDING AN ABRUPT CHANGE IN RESISTANCE WITHIN A GIVEN TEMPERATURE RANGE RELATIVE TO ITS CHANGE IN RESISTANCE OUTSIDE THE GIVEN RANGE, HEAT CONDUCTIVE MEANS THERMALLY COUPLING SAID FIRST AND SECOND THERMISTORS TO CAUSE SAID SECOND THERMISTOR TO BE HEATED BY SAID FIRST THERMISTOR TO A TEMPERATURE IN THE GIVEN RANGE UPON APPLICATION OF CONTROL POWER OF PREDETERMINED VALUE TO SAID FIRST THERMISTOR, A SECOND CONTROLLED CIRCUIT ELECTRICALLY ISOLATED FROM SAID FIRST CONTROL CIRCUIT, AND MEANS CONNECTING SAID SECOND THERMISTOR IN SAID CONTROLLED CIRCUIT TO CONTROL THE FLOW OF CURRENT THEREIN ACCORDING TO THE RESISTANCE OF SAID SECOND THERMISTOR, WHEREBY CONTROL POWER OF PREDETERMINED VALUE APPLIED TO SAID FIRST THERMISTOR BY SAID FIRST CIRCUIT WILL CAUSE SAID SECOND THERMISTOR TO ABRUPTLY CHANGE ITS RESISTANCE TO ALTER THE FLOW OF CURRENT IN SAID CONTROLLED CIRCUIT.