Electrothermal furnace control

Claim 2

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit for supplying power to said switching device and the fuel valve when the thermostat demands heat; a thermistor connected in a series circuit with the fuel valve for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature; means for heating said thermistor comprising a further thermistor thermally coupled to the first said thermistor, connected in series with said ignition means for concomitant energization therewith and being energized to cause heating of said thermistor when said ignition means generates sparking, said further thermistor being deenergized when said ignition means ceases to generate sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and the resistance of said further thermistor is increased by energization thereof for said predetermined time interval whereby energization of said ignition means is reduced for causing sparking to be generated at a reduced rate.

Claim 3

Furnace control apparatus as set forth in claim 1 wherein each of said thermistors has a positive temperature coefficient and a transition temperature above which the resistance thereof increases relatively abruptly, said further thermistor having a higher transition temperature than that of the first said thermistor, said thermistors together constituting an electrothermal timer.

Claim 4

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by tHe furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature, said thermistor being connected in the triggering circuit of said second switching device for preventing triggering thereof when heated above said predetermined threshold temperature; means for heating said thermistor interconnected with said ignition means and being energized to cause heating of said thermistor when said ignition means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and said power circuit also supplies power to said ignition means and further comprising means, interconnected with said thermistor, for supplying triggering current to said second switching device at a first voltage for initial triggering thereof and at a higher voltage for continued triggering thereof whereby if said thermistor is heated above said predetermined threshold temperature within said predetermined heating interval thereby preventing triggering of said second switching device, said means for heating said thermistor is deenergized and said thermistor cools for a cooling time interval substantially greater than said heating interval, thereby permitting retriggering of said second switching device.

Claim 5

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by tHe furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature, said thermistor being connected in the triggering circuit of said second switching device for preventing triggering thereof when heated above said predetermined threshold temperature; means for heating said thermistor interconnected with said ignition means and being energized to cause heating of said thermistor when said ignition means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and said power circuit also supplies power to said ignition means and further comprising means, interconnected with said thermistor, for supplying triggering current to said second switching device at a first voltage for initial triggering thereof and at a higher voltage for continued triggering thereof whereby if said thermistor is heated above said predetermined threshold temperature within said predetermined heating interval thereby preventing triggering of said second switching device, said means for heating said thermistor is deenergized and said thermistor cools for a cooling time interval substantially greater than said heating interval, thereby permitting retriggering of said second switching device.

Claim 6

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected in a series circuit with the fuel valve for causing interruption of tHe supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature; means for heating said thermistor interconnected with said ignition means and being energized to cause heating of said thermistor when said ignition means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and said power circuit includes a magnetic contactor having a winding and respective pairs of contacts connected, when closed, for energizing the first said switching device and the gas valve and for energizing the ignition means, said winding being connected with said second switching device and being energized by triggering thereof for causing said contacts to close.

Claim 7

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected in a series circuit with the fuel valve for causing interruption of tHe supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature; means for heating said thermistor interconnected with said ignition means and being energized to cause heating of said thermistor when said ignition means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and said power circuit includes a magnetic contactor having a winding and respective pairs of contacts connected, when closed, for energizing the first said switching device and the gas valve and for energizing the ignition means, said winding being connected with said second switching device and being energized by triggering thereof for causing said contacts to close.

Claim 8

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supply triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected in a series circuit with the fuel valve for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature; means for heating said thermistor interconnected with said ignition means and being energized to cause heating of said thermistor when said ignition means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and a second thermistor mounted for sensing the temperature in a plenum of the furnace and connected in the triggering circuit of said second switching device for preventing further triggering thereof, thereby preventing further energization of the fuel valve, when heated above a predetermined threshold temperature corresponding to a predetermined maximum permissible temperature in said plenum.

Claim 9

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supply triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected in a series circuit with the fuel valve for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature; means for heating said thermistor interconnected with said ignition means and being energized to cause heating of said thermistor when said ignition means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and a second thermistor mounted for sensing the temperature in a plenum of the furnace and connected in the triggering circuit of said second switching device for preventing further triggering thereof, thereby preventing further energization of the fuel valve, when heated above a predetermined threshold temperature corresponding to a predetermined maximum permissible temperature in said plenum.

Claim 10

Furnace control apparatus as set forth in claim 5 wherein said second thermistor has a positive temperature coefficient of resistivity and a transition temperature above which the resistance thereof increases relatively abruptly.

Claim 11

Furnace control apparatus as set forth in claim 5 for controlling the operation of a furnace normally having a forced-air draft supplying the burner, wherein said second switching device includes a triggering terminal and further comprising: an additional thermistor mounted for being cooled by the forced draft and connected in a series circuit with said second thermistor and said triggering terminal for preventing triGgering of said second switching device when said additional thermistor is heated above a predetermined threshold temperature; and means for heating said additional thermistor, said means normally supplying insufficient heat to cause said fourth thermistor to be heated above said threshold temperature as long as there is sufficient forced draft, but causing heating of said additional thermistor above said threshold temperatures thereby preventing energization of the fuel valve if there is insufficient forced draft.

Claim 12

Furnace control apparatus as set forth in claim 7 wherein said additional thermistor has a positive temperature coefficient of resistivity and a transition temperature above which the resistance thereof increases relatively abruptly, and said means for heating said additional thermistor comprises another thermistor having a positive temperature coefficient of resistivity and a transition temperature higher than that of said additional thermistor and above which the resistance thereof increases relatively abruptly.

Claim 13

Furnace control apparatus as set forth in claim 7 wherein said second switching device comprises a silicon controlled rectifier.

Claim 14

Furnace control apparatus as set forth in claim 1 wherein said switching device comprises a triac.

Claim 15

Furnace control apparatus as set forth in claim 1 wherein said ignition means includes a further triggerable semiconductor current-switching device and generates sparking when said further switching device is triggered.

Claim 16

Furnace control apparatus as set forth in claim 11 wherein the first said switching device includes a pair of main terminals and a triggering terminal for controlling conduction between said main terminals, said main terminals being connected in a series circuit with the fuel valve, and said means for normally supplying triggering current comprises circuit means interconnecting said further switching device and said triggering terminal.

Claim 17

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature, said thermistor being connected in the triggering circuit of said second switching device for preventing triggering thereof when heated above said predetermined threshold temperature; means for heating said thermistor interconnected with said ignition means and being energized to cause heating of said thermistor when said means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from beinG further supplied to the burner; and said power circuit includes a magnetic contactor having a winding and respective pairs of contacts connected, when closed, for energizing the first said switching device and the gas valve and for energizing the ignition means, said winding being connected with said second switching device and being energized by triggering thereof for causing said contacts to close.

Claim 18

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature, said thermistor being connected in the triggering circuit of said second switching device for preventing triggering thereof when heated above said predetermined threshold temperature; means for heating said thermistor interconnected with said ignition means and being energized to cause heating of said thermistor when said means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from beinG further supplied to the burner; and said power circuit includes a magnetic contactor having a winding and respective pairs of contacts connected, when closed, for energizing the first said switching device and the gas valve and for energizing the ignition means, said winding being connected with said second switching device and being energized by triggering thereof for causing said contacts to close.

Claim 19

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature, said thermistor being connected in the triggering circuit of said second switching device for preventing triggering thereof when heated above said predetermined threshold temperature; means for heating said thermistor interrconnected with said ignition means and being energized to cause heating of said thermistor when said ignition means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and a second thermistor mounted for sensing the temperature in a plenum of the furnace and connected in the triggering circuit of said second switching device for preventing further triggering thereof, thereby preventing further energization of the fuel valve, when heated above a predetermined threshold temperature corresponding to a predetermined maximum permissible temperature in said plenum.

Claim 20

Apparatus for controlling the operation of a furnace in response to the demand of a thermostat sensing the temperature of a zone heated by the furnace, the furnace having a burner and an electrically energizable fuel valve which, when energized, supplies fuel to the burner, said apparatus comprising: ignition means which, upon energization, generates recurrent sparking for igniting the fuel, said ignition means being energized when the thermostat demands heat and ceasing to generate sparking after ignition of the fuel; a triggerable semiconductor current-switching device interconnected with the fuel valve and, when triggered, being conductive for initially energizing the fuel valve; means for normally supplying triggering current to cause triggering of said switching device when said ignition means generates sparking; means for maintaining energization of the fuel valve following initial energization thereof by said switching device; a power circuit including a second triggerable current-switching device which is conductive, when triggered, for causing power to be supplied to the first said switching device and the fuel valve, said second switching device normally being triggered when the thermostat demands heat; a thermistor connected for causing interruption of the supply of power from said power circuit thereby deenergizing the gas valve when said thermistor is heated above a predetermined threshold temperature, said thermistor being connected in the triggering circuit of said second switching device for preventing triggering thereof when heated above said predetermined threshold temperature; means for heating said thermistor interrconnected with said ignition means and being energized to cause heating of said thermistor when said ignition means generates sparking, said thermistor requiring a predetermined heating time interval to reach said threshold temperature, whereby if the fuel is not ignited within said predetermined interval, the supply of power to the fuel valve is interrupted to prevent fuel from being further supplied to the burner; and a second thermistor mounted for sensing the temperature in a plenum of the furnace and connected in the triggering circuit of said second switching device for preventing further triggering thereof, thereby preventing further energization of the fuel valve, when heated above a predetermined threshold temperature corresponding to a predetermined maximum permissible temperature in said plenum.

Claim 21

Furnace control apparatus as set forth in claim 14 for controlling the operation of a furnace normally having a forced-air draft supplying the burner, wherein said second switching device includes a triggering terminal and further comprising: an additional thermistor mounted for being cooled by the forced draft and connected in a series circuit with said second thermistor and said triggering terminal for preventing triggering of said second switching device when said additional thermistor is heated above a predetermined threshold temperature; means for heating said additional thermistor, said means normally supplying insufficient heat to cause said fourth thermistor to be heated above said threshold temperature as long as there is sufficient forced draft, but causing heating of said additional thermistor above said threshold temperatures thereby preventing energization of the fuel valve if there is insufficient forced draft.

Claim 22

Furnace control apparatus as set forth in claim 15 wherein said additional thermistor has a positive temperature coefficient of resistivity and a transitIon temperature above which the resistance thereof increases relatively abruptly, and said means for heating said additional thermistor comprises another thermistor having a positive temperature coefficient of resistivity and a transition temperature higher than that of said additional thermistor and above which the resistance thereof increases relatively abruptly.