Constant current flame ionization circuit
First Claim
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1. A flame ionization sensor comprising:
- means for sensing resistance of the flame ionization sensor; and
means for supplying increasing voltage to the sensor in response to an increase in the resistance.
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Abstract
In a flame ionization sensor type gas combustion control apparatus, the sensor is provided with a power supply which will increase the voltage as contamination build up occurs on the in-flame sensor electrode thereby keeping a constant sensor current and enabling the sensor to perform as intended even though insulative contaminant build up is present on the electrode.
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Citations
18 Claims
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1. A flame ionization sensor comprising:
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means for sensing resistance of the flame ionization sensor; and
means for supplying increasing voltage to the sensor in response to an increase in the resistance. - View Dependent Claims (2)
means for stepping up a line voltage.
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3. A flame ionization sensor comprising:
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a controllable switch for controlling power to the flame ionization sensor;
means for routing a line voltage to the controllable switch;
a resistance sensor in series with the flame ionization sensor; and
means for increasing a duty cycle of the controllable switch in response to increased resistance across the flame ionization sensor.
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4. A flame ionization sensor comprising:
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means for routing a line voltage to the flame ionization sensor;
means for stepping up a line voltage to the flame ionization sensor;
a controllable switch between the line voltage and the flame ionization sensor;
means for sensing resistance across the flame ionization sensor; and
means for supplying increased voltage to the flame ionization sensor in response to increased resistance across the flame ionization sensor. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
the means for stepping up a line voltage being a transformer.
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6. The flame ionization sensor of claim 5 further comprising:
the controllable switch being a semiconductor switch.
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7. The flame ionization sensor of claim 6 further comprising:
the controllable switch being a field effect transistor.
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8. The flame ionization sensor of claim 6 further comprising:
the means for sensing resistance further including a sensing resistor in series with t he flame ionization sensor.
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9. The flame ionization sensor of claim 8 further comprising:
the means for sensing resistance further including a large common mode amplifier in parallel with the sensing resistor.
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10. The flame ionization sensor of claim 9 further comprising:
the means for sensing resistance further including a low pass filter in series with an output of the large common mode amplifier.
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11. The flame ionization sensor of claim 10 further comprising:
the means for sensing resistance further including a linear amplifier with a constant current reference in series with an output of the low pass filter.
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12. The flame ionization sensor of claim 11 further comprising:
the means for supplying increased voltage further including a timing circuit.
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13. The flame ionization sensor of claim 12 further comprising:
the timing circuit including a zero crossing detector and a sawtooth wave generator attached to an output of the transformer.
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14. The flame ionization sensor of claim 12 further comprising:
a voltage-to-pulse width converter using an output of the timing circuit as a trigger input and using an output of the linear amplifier as a control signal and outputting a duty cycle signal to the controllable switch.
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15. The flame ionization sensor of claim 14 further comprising:
a switch driver in series between the voltage-to-pulse width converter and the controllable switch.
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16. The flame ionization sensor of claim 5 further comprising:
the transformer having an output for providing a DC power supply to the means for sensing and the means for supplying increased voltage.
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17. A method of operating an flame ionization sensor comprising:
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running the flame ionization sensor at a first voltage;
monitoring resistance across the flame ionization sensor; and
supplying the flame ionization sensor with a voltage above the first voltage in response to increased resistance across the flame ionization sensor. - View Dependent Claims (18)
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Specification