Fail safe electronic-control system

Claim 3

A system in accordance with claim 1 wherein said switch control means includes a unidirectional current switch coupled between a source of electrical power and the control terminal of said first switch means, said unidirectional current switch having a control element coupled to said means for producing the high-voltage electrical signal to permit said unidirectional switch means to be rendered conductive at a predetermined time subsequent to the production of the high-voltage signal.

Claim 4

A system in accordance with claim 2 wherein said second selectively energizable switch means includes in control element for controlling the conduction thereof coupled to said first sensor, said second selectively energizable switch means being connected in shunt with said unidirectional switch means for maintaining said unidirectional switch means for maintaining said unidirectional switch means nonconductive by shunting electrical power therefrom upon energization of said second selectively energizable switch means in response to variations in the electrical property of said first sensor.

Claim 5

A system in accordance with claim 3 wherein said first and second second sensor are in thermal communication with each other, said second sensor comprises a resistor adapted to produce heat in response to the flow of electrical current therethrough, and said first sensor comprises a resistor the resistance of which increases in response to an increase in sensed temperature.

Claim 6

A system in accordance with claim 4 wherein said means for producing a high-voltage signal includes a transformer having a primary winding and a high-turns ratio secondary winding, a pulse-producing network connected across said primary winding and coupled to said second sensor, and a spark gap coupled to saId secondary winding for producing high-voltage sparks in response to pulsing of said primary winding, said spark gap being coupled to said pulse-producing network for effecting deenergization thereof and a halt in the production of the high-voltage sparks in response to a reduction in the resistance across said spark gap as an indication of the occurrence of the predetermined condition, said spark gap also being coupled to said control element of said unidirectional switch means for effecting conduction thereof in response to the production of the high-voltage sparks.

Claim 7

A system in accordance with claim 5 wherein said second sensor is adapted to self-heat in response to current flow therethrough as a result of continued pulsing of said primary winding to effect an increase in the resistance of said first sensor sufficient to effect energization of said second selectively energizable switch means, thereby causing the shunting of electrical power from said unidirectional switch means and rendering said first switch means nonconductive, whereby the control device is maintained deenergized.

Claim 8

A system in accordance with claim 6 wherein said first switch means comprises a triac having its anodes serially connected with the control device, said unidirectional switch means comprises a silicon-controlled rectifier having its gate coupled to said spark gap, and said second switch means comprises a transistor having its base coupled to said first sensor, and having its collector-emitter circuit connected in shunt with the anode-cathode circuit of said silicon-controlled rectifier.

Claim 11

A system in accordance with claim 8 where in said second switch means includes a control element connected to said ignition network for receiving trigger signals therefrom at a predetermined time interval subsequent to the production of the high-energy electrical signals.

Claim 12

A system in a accordance with claim 9 wherein said switch control network includes a third selectively energizable switch means coupled to said selectively actuatable sensing means and arranged to shunt operating power from said second switch means to maintain said second switch means nonconductive in response to actuation of said selectively actuatable sensing means, thereby maintaining said firs switch means nonconductive in the absence of ignition.

Claim 13

A system in accordance with claim 10 wherein said ignition network includes an activating element in communication with said selectively actuatable sensing means, said activating element being adapted to effect actuation of said sensing means in response to continued production of the high-energy electrical signals.

Claim 14

A system in accordance with claim 11 wherein said activating element comprises a thermistor adapted to self-heat and generate heat in response to continued current flow therethrough, said selectively actuatable sensing means comprises a thermistor having a resistance which increases in response to sensed heat, and said activating element and said selectively actuatable sensing means are in thermal communication.

Claim 15

A system in accordance with claim 12 wherein said ignition network includes a forth switch means connected with said activating element, said forth switch means having a control element, a selectively energizable spark-producing means coupled to said activating element and to said fourth switch means, said spark-producing means including a spark gap adapted to produce the high-energy electrical signals subsequent to conduction of said fourth switch means, and means for coupling said spark-producing means to said control element for rendering said fourth switch means nonconductive subsequent to ignition across said spark gap so as to preclude further current flow through said actuating element.

Claim 16

A system in accordance with claim 13 wherein a voltage-responsive means is coupled between said control element of said fourth switch means and said selectively actuatable sensing means, said voltage responsive means being adapted to be rendered conductive in response to a predetermined increase in the resistance of said sensing means so as to increase the level of conduction of said fourth switch means and the current flow through said activating element, thereby increasing the resistance of said sensing means to render said third switch means conductive for shunting operatiNg power from said second switch means.

Claim 17

A system in accordance with claim 14 wherein said spark-producing means includes a charge storage network and a transformer, said transformer having a primary winding coupled to said charge storage network for receiving periodic pulses and having a secondary winding coupled to said spark gap.

Claim 18

A system in accordance with claim 15 wherein said spark gap is coupled to said second switch means for supplying trigger signals thereto in response to conduction across said spark gap. 17 A system for controlling the operation of a control device adapted to control the flow of a combustible fluid for maintaining the control device energized in response to ignition of the fluid and maintaining the control device deenergized in response to the nonignition of the fluid comprising a first semiconductor switch having a gate and having a pair of main terminals serially connected to the control device for supplying operating power to the control device in response to conduction of said first semiconductor switch and for preventing the supply of operating power to the control device in response to nonconduction of said first semiconductor switch, a second semiconductor switch having a gate and having a pair of main terminals serially connected to said gate of said first semiconductor switch, a third semiconductor switch having a control element and having a pair of main terminals connected in shunt with said main terminals of said second semiconductor switch for shunting operating power from said second semiconductor switch in response to conduction of said third semiconductor switch, a heat sensor coupled to the control element of said third semiconductor switch having a resistance which increases in response to heat so as to control the conduction of said third semiconductor switch, and an ignition network including a spark gap across which high-voltage sparks are developed, a fourth semiconductor switch having a gate terminal and a pair of main terminals, means for rendering said fourth semiconductor switch conductive, means for rendering said fourth semiconductor switch nonconductive, means for coupling a portion of the voltage developed, said spark gap to said gate of said first semiconductor switch for initially rendering said first semiconductor switch conductive in response to sparking, and heat-generating means coupled to said main terminals of said fourth semiconductor device and in thermal communication with said heat sensor for heating said heat sensor in response to continued current flow through said heat-generating means accompanying continued conduction of said fourth semiconductor switch.

Claim 19

S system in accordance with claim 17 wherein said heat-generating means said heat sensor each comprise a thermistor having a positive temperature coefficient of resistance and said first semiconductor switch comprises a triac.

Claim 20

A system in accordance with claim 18 wherein said second semiconductor switch and said fourth semiconductor switch each comprises a silicon-controlled rectifier and said third semiconductor switch comprises a transistor having its base coupled to said heat sensor and having its collector-emitter circuit connected in shunt with the anode-cathode circuit of said second silicon-controlled rectifier.