Flame sensing for oil burner

A controller for a fuel oil burner system that controls a fuel oil burner to perform intermittent ON cycles and OFF cycles, the controller comprising a processor configured to:

• receive a series of one or more light samples from the fuel oil burner, wherein values of the one or more light samples are indicative of a level of light in the fuel oil burner;
• determine whether the values of the one or more of the light samples exceed a flame threshold;
• determine whether the values of the one or more light samples meet a secondary criteria by:
• determining whether the values of the one or more light samples exceeds a secondary threshold;
• determining whether a deviation criteria that specifies a minimum amount of deviation between the values of at least two of the one or more light samples is met by the one or more light samples;
• determining that the secondary criteria is met when the values of the one or more light samples exceed the secondary threshold or the values of at least two of the one or more light samples meet the deviation criteria;
• and
• determining that the secondary criteria is not met when the values of the one or more light samples are below the secondary threshold and at least two of the one or more light samples do not meet the deviation criteria;
• and
• determine whether a flame is present based on whether the values of the one or more light samples exceed the flame threshold or meet the secondary criteria.

A method configured to control a fuel oil burner to perform intermittent ON cycles and OFF cycles, comprising:

• receiving a series of one or more light samples from the fuel oil burner, wherein values of the one or more light samples are indicative of a level of light in the fuel oil burner;
• determining whether the fuel oil burner is operating in a flame expected mode or a flame not expected mode;
• selecting a first threshold when the fuel oil burner is operating in the flame expected mode or selecting a second threshold when the fuel oil burner is operating in the flame not expected mode, wherein the first threshold is different from the second threshold;
• when the fuel oil burner is operating in the flame expected mode,
• determining whether the values of the one or more of the light samples exceed the first threshold;
• and
• determining whether the values of the one or more of the light samples meet secondary criteria;
• determining that a flame is present when the values of the one or more light samples exceed the first threshold and meet the secondary criteria;
• and
• determining that a flame is not present when the values of the one or more light samples are below the first threshold or do not meet the secondary criteria;
• and
• when the fuel oil burner is operating in the flame not expected mode:
• determining whether the values of the one or more of the light samples exceed the second threshold;
• and
• determining that a flame is present when the values of the one or more light samples exceed the second threshold.