CONTROLLING AND MONITORING COMBUSTIBLE GASES
First Claim
1. Apparatus for monitoring and controlling the flow of a combustible gas comprising, an alternating current supply, a gas valve operated by a solenoid for controlling the flow of gas to a burner, a semiconductor thyristor switch having a control electrode, means connecting the switch in series circuit with the solenoid and the AC supply so that the switch controls the flow of current from the AC supply to the solenoid, means for monitoring the ionization current that flows through the burner gas flame when the gas is ignited, circuit means coupling said monitoring means to said control electrode and responsive thereto so as to trigger the switch into conduction when the gas is ignited and to inhibit the triggering thereof in the absence of a flame whereby the solenoid is operated to close the gas valve and cut off the gas flow to the burner, and said circuit means includes a phase advance circuit connecting said control electrode to the AC supply thereby to trigger said thyristor switch from said AC supply.
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Accused Products
Abstract
Apparatus for monitoring and controlling the flow of a combustible gas includes a solenoid operated gas valve to control the gas flow. The solenoid is energized from an AC supply via a thyristor switch. When the gas is ignited an ionization current flows through the flame and is monitored to control the trigger electrode of the thyristor. When the flame is out the thyristor is not triggered so that it remains cut-off and deenergizes the solenoid. This closes the gas valve to cut off the gas flow. Triggering may take place through a phase advance circuit. Ignition sparks may be provided by means of a capacitor and a step-up transformer arrangement in which the capacitor is periodically discharged through the thyristor to produce spark pulses via the transformer.
17 Citations
19 Claims
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1. Apparatus for monitoring and controlling the flow of a combustible gas comprising, an alternating current supply, a gas valve operated by a solenoid for controlling the flow of gas to a burner, a semiconductor thyristor switch having a control electrode, means connecting the switch in series circuit with the solenoid and the AC supply so that the switch controls the flow of current from the AC supply to the solenoid, means for monitoring the ionization current that flows through the burner gas flame when the gas is ignited, circuit means coupling said monitoring means to said control electrode and responsive thereto so as to trigger the switch into conduction when the gas is ignited and to inhibit the triggering thereof in the absence of a flame whereby the solenoid is operated to close the gas valve and cut off the gas flow to the burner, and said circuit means includes a phase advance circuit connecting said control electrode to the AC supply thereby to trigger said thyristor switch from said AC supply.
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2. Apparatus as claimed in claim 1 wherein said circuit means further comprises a first transistor coupled to the control electrode of said thyristor switch to inhibit the triggering thereof when said first transistor is conductive, means for applying to the base of said first transistor a bias voltage derived from said AC supply and of a polarity to produce conduction in the transistor, means for applying the flame ionisation current to the base of said first transistor with a phase retardation relative to the AC supply so as to render that transistor non-conducting during at least a portion of each cycle of said alternating supply, at least a part of said portion coinciding with the beginning of each positive half cycle of the AC supply thereby allowing said switch to be triggered.
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3. Apparatus as claimed in claim 2 in which, in the absence of said flame ionisation current, said first transistor is rendered conductive by the bias voltage applied to its base thereby to inhibit the triggering of said thyristor switch.
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4. Apparatus as claimed in claim 2 wherein said circuit means further comprises second and third transistors, means operatively connecting said first transistor in cascade with said second and third transistors so that said third transistor is rendered conductive when said first transistor is conductive, and means connecting said third transistor to the thyristor control electrode.
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5. Apparatus as claimed in claim 4 wherein said circuit means further comprises a resistor capacitor circuit connected between one side of said alternating supply and the collector of said third transistor so that, with the flame ionization current present, the thyristor switch is triggered via said RC circuit, the collector of said third transistor also being connected to the trigger electrode of said switch.
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6. Apparatus as claimed in claim 5 in which said third transistor is connected between the cathode and the trigger electrode of said thyristor switch so that, in the absence of said flame ionisation current, said third transistor is rendered conductive bypassing the triggering current away from the trigger electrode of said switch.
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7. Apparatus for monitoring and controlling the flow of a combustible gas comprising, an alternating current supply, a gas valve Operated by a solenoid for controlling the flow of gas to a burner, a semiconductor switch having a control electrode, means connecting the switch in series circuit with the solenoid and the AC supply so that the switch controls the flow of current from the AC supply to the solenoid, means for monitoring the ionization current that flows through the burner gas flame when the gas is ignited, circuit means coupling said monitoring means to said control electrode and and responsive thereto so as to trigger the switch into conduction when the gas is ignited and to inhibit the triggering thereof in the absence of a flame whereby the solenoid is operated to close the gas valve and cut off the gas flow to the burner, a diode and a capacitor serially connected with the primary winding of a transformer across said AC supply, and means connecting the series circuit comprising said capacitor and primary winding in parallel with said switch so that said capacitor is charged from said alternating supply from the commencement of each cycle of said AC supply for a period until said switch is triggered and then is discharged via said switch through the primary of said transformer to produce a train of sparks across a spark gap located at said burner and connected across the secondary winding of said transformer.
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8. Apparatus as claimed in claim 1 further comprising a capacitor connected in series circuit with the primary winding of an ignition transformer across said AC supply so as to charge the capacitor at the start of each cycle of said AC supply until the switch is triggered into conduction, means connecting said series circuit in parallel with said switch so that the switch provides a discharge path for the capacitor through said primary winding, and wherein said circuit means includes electric delay means which, during a burner ignition period, delays the triggering of said switch to a period between 30* and 90* subsequent to the start of each cycle of said AC supply, and means connecting the secondary winding of said transformer to an ignition electrode of the burner.
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9. Apparatus as claimed in claim 8 wherein said circuit means further comprises a first transistor coupled to the control electrode of said semiconductor switch so as to inhibit the triggering thereof when said first transistor is fully conductive, and a bias capacitor coupled to the base of the second transistor and to said AC supply and arranged to bias said first transistor into full conduction in the absence of said flame ionization current.
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10. Apparatus as claimed in claim 9 wherein said circuit means includes means for coupling the flame ionization current, when present, from said monitoring means to the base of the first transistor so as cut-off said first transistor at the start of each cycle of said AC supply thereby to allow said semiconductor switch to be triggered into conduction at that time.
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11. Apparatus as claimed in claim 1 wherein said circuit means further comprises a phase delay circuit interposed between said monitoring means and said control electrode whereby the triggering of the switch is controlled jointly by the AC supply and the ionisation current at a time subsequent to ignition of the gas.
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12. Flow control apparatus for a combustible gas comprising, input terminals adapted for connection to a source of AC supply current, a solenoid operated gas valve for controlling the gas flow, a semiconductor controlled switch connected in series circuit with the input terminals and the solenoid so that the switch controls the flow of current from the input terminals to the solenoid, phase control means coupling an input terminal to a control electrode of said switch to supply a periodic trigger signal thereto in advance of the start of each cycle of the AC supply and independent of the state of the gas thereby to initiate conduction through said switch, means for monitoring the gas so as to derive an ionization current from the gas when the gAs is burning, a first current control element with its output coupled to the control electrode of the switch and its input coupled to said monitoring means so as to respond to said ionization current, when present, said control element being operative to apply a first control signal to said control electrode that will inhibit the triggering of the switch when said ionization current is absent at its input thereby to operate the solenoid to close off the gas valve and being operative when said ionization current is present at its input to apply a second control signal thereto at or near the start of each cycle of the AC supply that allows said trigger signal to then trigger the switch into conduction.
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13. Apparatus as claimed in claim 12 wherein the input circuit of said control element further comprises means coupled to the input terminals for varying the DC bias voltage applied to the control element during an initial ignition period for the apparatus such that, in the absence of the ionization current, said first control signal is varied as a function of the bias voltage in a manner such as to gradually vary the delay in the triggering of the switch relative to the start of each cycle of the AC supply.
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14. Apparatus as claimed in claim 12 further comprising a capacitor connected in series circuit with the primary winding of an ignition transformer, means connecting said series circuit in parallel with said switch so that the switch provides a path for selectively discharging the capacitor through said primary winding, a charge circuit coupling said series circuit to the input terminals so that the capacitor is charged from said AC supply when the switch is cut-off, and means connecting the secondary winding of the transformer to an ignition electrode whereby sparks are produced at said electrode in synchronism with the discharge of the capacitor.
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15. Apparatus as claimed in claim 14 further comprising a bias capacitor connected to the input of said first control element and to the input terminals via a DC charge circuit and operative when the charge thereon reaches a given level to apply a bias voltage to said control element which, in the absence of any ionization current, will cause said control element to derive said first inhibit control signal to prevent the triggering of the switch and hence prevent the generation of sparks.
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16. Apparatus as claimed in claim 15 further comprising means for retarding the phase of said AC ionization current relative to the AC supply so as to overide said bias voltage near the start of each cycle of the AC supply whereby said control element becomes operative to derive and apply said second control signal to the switch to trigger same near the start of each cycle of the AC supply and thereby prevent the first capacitor from charging to a level sufficient to generate sparks.
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17. Apparatus as claimed in claim 16 wherein said charge circuit includes a rectifier element, said switch comprises a thyristor, and said phase control means includes a capacitor for advancing the phase of the trigger signal relative to the AC supply.
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18. Flow control apparatus for a combustible gas comprising, input terminals adapted for connection to a source of AC supply current, a solenoid operated gas valve for controlling the gas flow, a semiconductor controlled switch connected in series circuit with the solenoid across the input terminals to control the current flow from said terminals to the solenoid, phase control means coupling an input terminal to a control electrode of said switch to supply a periodic trigger signal thereto in advance of the positive half cycle of the AC supply voltage applied to the anode of the switch, ignition means for igniting said gas and coupled to said switch, means for monitoring the gas so as to derive an electric signal therefrom when the gas is ignited, and circuit means responsive to said signal, when present, to apply a first control signal to said control electrode at or near the start of each positive half cycle of the AC supply which allows said trigger signal to trigger the switch into conduction and thereby inhibits the operation of said ignition means, said circuit means being operative to delay the triggering of said switch for a given ignition period when said signal is absent thereby to operate said ignition means via said switch and to subsequently apply a second control signal to said control electrode that will inhibit the triggering of the switch if the gas does not ignite during said ignition period.
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19. Apparatus as claimed in claim 18 wherein said ignition means comprises a capacitor and an ignition coil serially connected across the switch terminals and to the input terminals in a manner whereby said capacitor is allowed to charge up only when the switch is cut-off, and wherein said circuit means includes an amplifier with a control electrode coupled to said monitoring means and an output electrode coupled to the control electrode of the semiconductor switch.
Specification