Fail-safe electric ignition systems

Claim 2

An electric ignition system for a fuel burner comprising input means adapted to be connected with a source of electricity, an electric igniter having a positive temperature coefficient of resistance and adapted to be disposed within igniting proximity of the burner, valve means adapted to control a flow of fuel to the burner, switch means connecting said electric igniter and said valve means with said input means, first control means connected with said electric igniter and said switch means and rEsponsive to the resistance of said electric igniter to control the operation of said switch means, and second control means connected with said input means and said electric igniter selectively placing said electric igniter in a fully energized condition in response to a demand for burner operation and in a partially energized standby condition when no such demand exists whereby thermal shock to said igniter is reduced.

Claim 3

The invention as recited in claim 1 wherein said second control means includes a dropping resistor connected in series with said electric igniter.

Claim 4

The invention as recited in claim 2 wherein said second control means includes a thermostat connected with said dropping resistor for selectively shunting said dropping resistor in response to a demand for burner operation.

Claim 5

The invention as recited in claim 1 wherein said second control means includes a dropping resistor.

Claim 6

The invention as recited in claim 4 wherein said dropping resistor is selectively connected in series with said electric igniter for placing said electric igniter in its partially energized standby condition.

Claim 7

The invention as recited in claim 4 wherein said second control means includes a thermostat connected with said dropping resistor whereby said dropping resistor is connected to said electric igniter by said thermostat during standby intervals and said dropping resistor is disconnected from said electric igniter by said thermostat in response to a demand for burner operation.

Claim 8

The invention as recited in claim 1 wherein said first control means includes a first sensing means responsive to the voltage across said electric igniter and a second sensing means responsive to the current through said electric igniter.

Claim 9

The invention as recited in claim 7 wherein said switch means includes a first switch controlled by said first sensing means and a second switch controlled by said second sensing means, said first switch and said second switch being connected in series between said input means and said valve means whereby said first switch and said second switch must be closed to open said valve means.

Claim 10

The invention as recited in claim 7 wherein said first sensing means is connected in parallel with said electric igniter.

Claim 11

The invention as recited in claim 9 wherein said first sensing means includes a holding coil.

Claim 12

The invention as recited in claim 7 wherein said second sensing means is connected in series with said electric igniter.

Claim 13

The invention as recited in claim 11 wherein said second sensing means includes a heat expansible wire having a low resistance.

Claim 14

The invention as recited in claim 12 wherein said second control means includes a dropping resistor and main switch means connected between said input means and said heat expansible wire to selectively place said heat expansible wire in parallel with said dropping resistor in response to a demand for burner operation whereby said dropping resistor is selectively bypassed.

Claim 15

The invention as recited in claim 13 wherein said main switching means includes a thermostat.

Claim 16

An electric ignition system for a fuel burner comprising input means adapted to be connected with a source of electricity, an electric igniter having a positive temperature coefficient of resistance and adapted to be disposed within igniting proximity of the burner, valve means adapted to control a flow of fuel to the burner, switch means connecting said electric igniter and said valve means with said input means, first control means connected with said electric igniter and said switch means and responsive to the resistance of said electric igniter to control the operation of said switch means, flame-proving means connected with said electric igniter and said valve means and responsive to actuation of said valve means to place said electric igniter in a flame-proving mode for closing said valve means upon burner flame outage and second control meanS connected with said input means and said electric igniter selectively placing said electric igniter in a fully energized condition in response to a demand for burner operation and in a partially energized standby condition when no such demand exists whereby thermal shock is reduced.

Claim 17

An electric ignition system for a fuel burner comprising input means adapted to be connected with a source of electricity, an electric igniter having a positive temperature coefficient of resistance and adapted to be disposed within igniting proximity of the burner, valve means adapted to control a flow of fuel to the burner, switch means connecting said electric igniter and said valve means with said input means, first control means connected with said electric igniter and said switch means and responsive to the resistance of said electric igniter to control the operation of said switch means, flame-proving means connected with said electric igniter and said valve means and responsive to actuation of said valve means to place said electric igniter in a flame-proving mode for closing said valve means upon burner flame outage and second control meanS connected with said input means and said electric igniter selectively placing said electric igniter in a fully energized condition in response to a demand for burner operation and in a partially energized standby condition when no such demand exists whereby thermal shock is reduced.

Claim 18

The invention as recited in claim 15 wherein said control means includes sensing means responsive to the voltage drop across said electric igniter.

Claim 19

The invention as recited in claim 16 wherein said switch means is controlled by said sensing means and has a closed position when the voltage drop across said sensing means is above a preselected value to provide an energizing current path to said valve means, and an open position when the voltage drop across said sensing means is below said preselected value to open said energizing current path to said valve means.

Claim 20

The invention as recited in claim 17 wherein said flame-proving means includes a resistor selectively coupled with said electric igniter in response to actuation of said valve means whereby the voltage drop across said sensing means is reduced below said preselected value upon burner flame outage.

Claim 21

The invention as recited in claim 18 wherein said flame-proving means includes time-delay switching means connected with said valve means and said resistor for selectively connecting said resistor with said electric igniter a predetermined time interval subsequent to actuation of said valve means whereby a burner flame is established prior to connecting said resistor with said electric igniter.

Claim 22

The invention as recited in claim 19 wherein said time-delay switching means includes a time-delay relay having a coil connected in parallel with said valve means and a set of normally open contacts connected between said electric igniter and said resistor.

Claim 23

The invention as recited in claim 19 wherein said time-delay switching means includes a bimetal operator, a heating coil connected in series with said valve means and disposed within heating proximity of said bimetal operator, and a double-pole double-throw switch controlled by said bimetal operator.

Claim 24

An ignition proving system for a fuel burner comprising input means adapted to be connected to a source of electricity, an electric igniter having a positive temperature coefficient of resistance and adapted to be disposed in igniting proximity to the burner, valve means adapted to control a flow of fuel to the burner, switch means connecting said electric igniter and said valve means with said input means, first control means connected in circuit with said electric igniter and said switch means and responsive to the voltage across said electric igniter to control the operation of said switch means, second control means connected in circuit with said electric igniter and said switch means and responsive to the current through said electric igniter to control the operation of said switch means, flame-proving means connected with said electric igniter and said valve means and responsive to actuation of said valve means to place said electric igniter in a flame-proving mode for closing said valve means upon burner flame outage, and third control means connected with said input means and said electric igniter to selectively place said electric igniter in a fully energized condition in response to a demand for burner operation and a partially energized standby condition when no such demand exists whereby thermal shock to said igniter is reduced.

Claim 25

An ignition proving system for a fuel burner comprising input means adapted to be connected to a source of electricity, an electric igniter having a positive temperature coefficient of resistance and adapted to be disposed in igniting proximity to the burner, valve means adapted to control a flow of fuel to the burner, switch means connecting said electric igniter and said valve means with said input means, first control means connected in circuit with said electric igniter and said switch means and responsive to the voltage across said electric igniter to control the operation of said switch means, second control means connected in circuit with said electric igniter and said switch means and responsive to the current through said electric igniter to control the operation of said switch means, flame-proving means connected with said electric igniter and said valve means and responsive to actuation of said valve means to place said electric igniter in a flame-proving mode for closing said valve means upon burner flame outage, and third control means connected with said input means and said electric igniter to selectively place said electric igniter in a fully energized condition in response to a demand for burner operation and a partially energized standby condition when no such demand exists whereby thermal shock to said igniter is reduced.

Claim 26

The invention as recited in claim 22 wherein said first control means includes a holding coil, and wherein said second control means includes a thermally expansible wire.

Claim 27

The invention as recited in claim 22 wherein said input means includes transformer means having a plurality of secondary winding terminals, and wherein said flame-proving means includes time-delay switching means connected with said valve means, said electric igniter, said transformer means anD said second control means for connecting said electric igniter and said second control means to different pairs of said plurality of secondary winding terminals when said valve means is deenergized whereby said igniter is placed in an ignition mode and for connecting said electric igniter in series with said second control means across a particular pair of said plurality of secondary winding terminals a predetermined time interval subsequent to energization of said valve means whereby said igniter is placed in a flame-proving mode.

Claim 28

The invention as recited in claim 24 wherein said switch means includes first and second switches connected between said input means and said valve means and controlled by said first control means.

Claim 29

The invention as recited in claim 25 wherein said first control means includes a calibration resistor and a holding coil connected in series across said electric igniter, and wherein said holding coil is responsive to at least a preselected voltage drop thereacross to maintain said first and second switches closed.

Claim 30

The invention as recited in claim 26 wherein said flame-proving means includes a second calibration resistor selectively connected in parallel with said first calibration resistor by said time-delay switching means in response to energization of said valve means whereby said first and second switches are thereafter released by said holding coil upon burner flame outage.

Claim 31

The invention as recited in claim 27 wherein said time-delay switching means includes a coil connected in series with said valve means.

Claim 32

The invention as recited in claim 22 wherein said switch means includes first and second switches controlled by said first control means and third and fourth switches controlled by said second control means, said first, second and third switches being connected in series between said input means and said valve means whereby said first, second and third switches must be closed to open said valve means.

Claim 33

The invention as recited in claim 29 wherein said second control means is electrically connected in series with said electric igniter between said electric igniter and a point between said first and third switches, and wherein said first control means is connected in parallel with said electric igniter.

Claim 34

The invention as recited in claim 29 wherein said third and fourth switches have a common contact arm and are alternately operated between open and closed positions, and wherein said first and second switches have a connecting link and are simultaneously operated between open and closed positions.

Claim 35

The invention as recited in claim 31 wherein said third and fourth switches cooperate to alternately connect said first switch with said second switch and said first switch with said first control means.

Claim 36

The invention as recited in claim 29 wherein said first control means includes a calibration resistor and a holding coil connected in series across said electric igniter, and wherein said holding coil is responsive to at least a preselected voltage drop across said electric igniter to maintain said first and second switches closed.

Claim 37

The invention as recited in claim 33 wherein said flame-proving means includes a second calibration resistor selectively connected in parallel with said first calibration resistor in response to energization of said valve means whereby the voltage drop across said electric igniter is reduced below the value of said preselected voltage drop upon burner flame outage.

Claim 38

The invention as recited in claim 34 wherein said flame-proving means includes time-delay switching means connected with said valve means, said second calibration resistor and said third control means for connecting said third control means to said electric igniter when said valve means is deenergized and for connecting said second calibration resistor in parallel with said first calibration resistor a predetermined time interval subsequent to energization of said valve means whereby said electric igniter is alternately maintained in a partially energized standby condition prior to energization of said fuel valve and a flame-proving condition subsequent to energization of said fuel valve.

Claim 39

The invention as recited in claim 35 wherein said time-delay switching means includes a time-delay relay having a coil connected in parallel with said valve means and a relay switch having pole connected to said electric igniter, a first contact connected to said third control means, and a second contact connected to said second calibration resistor.

Claim 40

The invention as recited in claim 36 wherein said third control means comprises a dropping resistor connected between said input means and said second contact of said relay switch.