A method of determining presence of a flame in a furnace of a heating, ventilation, and air conditioning (HVAC) system. The method comprises determining, using a controller, whether a processor signal (G) is active, responsive to a determination that the processor signal (G) is active, determining, using the controller prior to assertion of a flame-test input control signal, an output state of a first comparator, responsive to a determination that the output state of the first comparator is high, determining, using the controller prior to assertion of the flame-test input control signal, an output state of a second comparator, and responsive to a determination that the output state of the second comparator is low, transmitting, using the controller, a notification that a flame is present.

A method for detecting a flame is provided. The method includes the step of providing alternating current to a flame rectification probe to produce a first voltage as an input for a sense circuit, wherein the flame rectification probe is placed in proximity to the flame. The method further includes the step of conditioning the first voltage using the sense circuit to produce a second voltage. Additionally, the method includes the steps of outputting the second voltage to a microcontroller, and determining with the microcontroller whether the flame is present based on a magnitude of the second voltage.

A radiant gas heater includes one or more gas inlets 105, for receiving gas from a gas supply and one or more air inlets 110. The heater includes gas burners 120A-120E, in which the gas is burned using oxygen admitted through the air inlets 110. One or more heat emitting elements 125A-125E are included, which emit infrared radiation using energy generated by the gas burners. One or more ionization probes 130A are provided proximal to two or more of the heat emitting elements for detecting the presence or absence of a flame. A housing 115 accommodates the gas burners, the heat emitting elements and the ionization probes. One or more control units are provided which are in electrical communication with the ionization probes and the gas inlets, the control units operable to shut off the gas supply if the ionization probes detect the absence of a flame.

The state of a flame in a gas turbine engine combustor is acoustically monitored using a dynamic pressure sensor within the combustor. A spectral pattern of a dynamic pressure sensor output signal from the sensor is compared with a characteristic frequency pattern that includes information about an acoustic pattern of the flame and information about acoustic signal canceling due to reflections within the combustor. The spectral pattern may also be compared with a characteristic frequency pattern including information about a flame-out condition in the combustor.

A safety system for gas-operated cooking appliances which include at least one burner which is connected to the mains gas network via a distributor, the gas flow of which is controlled by a manually operated gas tap, includes a position switch, a flame detection device, an electrically controlled control valve which is installed in the mains gas network, a manually actuated restoring switch in operable communication with the control valve, and a control circuit. The control circuit is configured to open the control valve after the latter was shut off by the flame detector of the burner only when the control circuit simultaneously receives a signal from the restoring switch and the position switch. The safety system serves as a child safety measure which prevents an inadvertent re-activation of a gas flow system that has been shut off.

The state of a flame in a subject combustor of a gas turbine engine is acoustically monitored using a dynamic pressure sensor within the subject combustor and one or more additional sensors in nearby combustors. Dynamic pressure sensor output signals from the sensors are cross correlated to identify acoustic oscillations generated by a flame in the subject combustor and received by the sensors. The cross correlation may be constrained by a maximum time delay between correlated components of the signals, based on physical characteristics.

Systems and methods for pre-ignition moisture removal in heating appliances are provided. The heating appliance may be configured, prior to initiating a combustion process using a combustion system of the heating appliance, to determine whether a flame sensing unit is producing false positive outputs. In some instances, such false positive outputs may be caused by moisture within the combustion cabinet of the heating appliance. To attempt to eliminate any false positive outputs, the heating appliance may perform ana action to expel the moisture from the combustion cabinet. For example, an inducer may be activated to expel the moisture using airflow. This ensures that the flame sensing unit is producing accurate data before the combustion process is initiated.