Apparatus for varying an alternating current flowing in a load to control the value of a parameter such as the temperature of a furnace

Claim 1

AN A.C. CONTROL CIRCUIT FOR CONTROLLING THE VALUE OF A PARAMETER BY VARYING THE MEAN CURRENT FLOW IN A LOAD, COMPRISING IN COMBINATION AN A.C. SUPPLY, SWITCH MEANS CONNECTED IN SERIES WITH SAID LOAD ACROSS SAID A.C. SUPPLY, SAID SWITCH MEANS BEING REVERSE BIASED BY SAID A.C. SUPPLY AT THE TERMINATION OF EACH CYCLE THEREOF AND THEREBY TURNED OFF, A PULSE GENERATOR, MEANS VARYING THE FREQUENCY OF SAID PULSE GENERATOR IN ACCORDANCE WITH THE VALUE OF SAID PARAMETER, SAID PULSE GENERATOR HAVING A FREQUENCY WHICH IS GREATER THAN THE FREQUENCY OF THE A.C. SUPPLY WHEN THE VALUE OF THE PARAMTER IS BELOW A PREDETERMINED VALUE, BUT WHICH DECREASES AS THE VALUE OF THE PARAMETER INCREASES, A BISTABLE CIRCUIT COUPLED TO SAID A.C. SUPPLY AND TO SAID PULSE GENERATOR, SAID BISTABLE CIRCUIT HAVING FIRST AND SECOND STABLE STATES AND BEING DRIVEN TO SAID FIRST STATE BY PULSES RECEIVED FROM SAID PULSE GENERATOR, SAID A.C. CIRCUIT DRIVING THE BISTABLE CIRCUIT TO ITS SECURED STATE AT THE COMMENCEMENT OF EACH CYCLE OF THE A.C. SUPPLY UNLESS THE BISTABLE CIRCUIT IS ALREADY IN ITS SECOND STATE, AND MEANS OPERABLE BY THE BISTABLE CIRCUIT WHEN DRIVEN TO ITS SECOND STATE FOR TURNING SAID SWITCH MEANS ON.