Fail safe gas furnace optical flame sensor using a transconductance amplifier and low photodiode current
AssigneeGas Research Institute
InventorsJoseph DiTucci, Stephen K. Phelps, Martin F. Zabielski
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Abstract
A fail safe gas furnace optical flame sensor uses a transconductance amplifier with low photodiode current to sense the presence or absence of a gas flame within the burner of a gas furnace. The photodiode signal appears as the only negative voltage signal in the circuit, and the equivalent resistance feedback network is redundantly designed, thus ensuring that no false flame-on conditions will be detected due to the failure of a single resistive component. Because it does not reside within the flame, the sensor is immune to false flame-off conditions caused by material deposition and corrosion of the sensor.
Claims10
An optical flame sensor, comprising:
- a photodiode flame sensor operating in a photovoltaic short circuit mode designed to produce a low output current electrical signal when a flame is detected;
- a transconductance amplifier operating in said photovoltaic short circuit mode connected via a transistor to said flame sensor, said transconductance amplifier including a feedback network designed to conduct said low output current from said flame sensor causing said transconductance amplifier to output a voltage high signal;
- voltage comparator circuitry designed to compare said transconductance amplifier voltage high signal with a threshold voltage signal in order to develop a logic level output signal for input to a processor, and
- test circuitry designed to provide a test signal, said test signal designed to interrupt said low output current from said flame sensor in order to interrogate the functionality of said flame sensor during a test pulse.
A method for detecting the presence of a gas flame, comprising the steps of:
- operating a photodiode flame sensor in a photovoltaic short circuit mode in order to produce a low output current electrical signal when a flame is detected;
- operating a transconductance amplifier that is connected via a transistor to said flame sensor in said photovoltaic short circuit mode, said transconductance amplifier designed to output a voltage high signal when a flame is detected by said photodiode flame sensor;
- operating a voltage comparator circuit designed to compare said transconductance amplifier voltage high signal with a threshold voltage signal in order to develop a logic level output signal for input to a processor, and
- sending a test pulse, said test pulse designed to interrupt said low output current from said flame sensor in order to interrogate the functionality of said flame sensor during a test pulse.
Dependencies are inferred from the claim text.