Burner including an electrical permittivity or electrical capacitance flame sensor

A burner, comprising:

• a fuel source;
• an oxidant source;
• a plenum wall defining an air plenum, the air plenum configured to receive fuel and oxidant respectively from the fuel source and the oxidant source, the air plenum further configured to convey the fuel and oxidant to facilitate mixture of the fuel and oxidant into a fuel-oxidant mixture;
• an ignition source disposed at a distal portion of the air plenum and oriented to ignite the fuel-oxidant mixture to produce a flame in a flame region;
• at least a first electrode and a second electrode arranged adjacent to the flame region and configured to produce a time-varying electromagnetic field across the flame region substantially transverse to a flow direction of the fuel and oxidant;
• and
• a control circuit configured to generate an excitation signal and provide the excitation signal to the first electrode;
• wherein a change in electrical permittivity or electrical capacitance in the flame region is determined from the time-varying electromagnetic field,
• wherein at least the first electrode and the second electrode are disposed opposite each other across the flame region, the first electrode configured to broadcast the excitation signal to produce the time-varying electromagnetic field between the first and second electrodes, the second electrode being configured to receive a detection signal, the detection signal including the broadcast excitation signal as affected by the change in electrical permittivity between the first and second electrodes,
• wherein the control circuit is further configured to receive the detection signal from the second electrode and to determine a magnitude of the electrical permittivity of the flame region by measuring or calculating a signal characteristic from the detection signal,
• wherein the control circuit is further configured to identify a flame characteristic by comparing the determined magnitude of the electrical permittivity against an index of flame characteristics corresponding to respective electrical permittivity magnitudes,
• wherein the control circuit is further configured to drive the ignition source responsive to the identified flame characteristic, and
• wherein the identified flame characteristic is a presence or absence of the flame as determined by comparison of the magnitude of the electrical permittivity with a threshold electrical permittivity, and the control circuit drives the ignition source when the flame is indicated to be absent.