Flame sensing for oil burner

1. 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 fuel oil burner is operating in a flame expected mode or a flame not expected mode;

select a first threshold when the fuel oil burner is operating in the flame expected mode or select 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; and

when the fuel oil burner is operating in the flame expected mode,

determine whether the values of the one or more of the light samples exceed the first threshold; and

determine whether the values of the one or more of the light samples meet secondary criteria;

determine 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

determine 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,

determine whether the values of the one or more light samples exceed the second threshold; and

determine that a flame is present when the values of the one or more light samples exceed the second threshold.

2. The controller of claim 1 , wherein the processor is configured to, when the fuel oil burner is operating in the flame not expected mode:

determine that a flame is not present when the values of the one or more light samples are below the second threshold.

3. The controller of claim 2 , wherein the first threshold is higher than the second threshold.

4. The controller of claim 1 , wherein the processor is configured to, when the controller is operating in the flame not expected mode:

determine whether the values of the one or more of the light samples meet the secondary criteria;

determine that a flame is present when the values of the one or more light samples meet the secondary criteria; and

determine that a flame is not present when the values of the one or more light samples do not meet the secondary criteria.

5. The controller of claim 1 , wherein the processor is configured to determine whether the values of the one or more light samples meet the secondary criteria by:

determining whether the values of the one or more light samples exceed, by a predetermined margin, a burner OFF light sample value taken when the fuel oil burner is in an OFF cycle;

determining that the secondary criteria is met when the values of the one or more light samples exceed the burner OFF light sample value by the predetermined margin; and

determining that the secondary criteria is not met when the values of the one or more light samples do not exceed the burner OFF light value by the predetermined margin.

6. The controller of claim 1 , wherein the processor is configured to determine whether the values of the one or more light samples meet the secondary criteria by:

determining whether the values of the one or more light samples exceed a predetermined portion of a previous representative value of one or more previous light samples;

determining that the secondary criteria is met when the values of the one or more light samples exceed the predetermined portion of the previous representative value; and

determining that the secondary criteria is not met when the values of the one or more light samples do not exceed the predetermined portion of the previous representative value.

7. The controller of claim 1 , wherein the processor is configured to determine whether the values of at least two of the one or more light samples meet the secondary criteria based on a deviation criteria that specifies a minimum amount of deviation between the values of the one or more light samples.

8. 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.

9. The controller of claim 8 , wherein the secondary threshold is higher than the flame threshold and a no flame threshold.

10. 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.

11. The method of claim 10 , further comprising,

when the fuel oil burner is operating in the flame not expected mode:

determining that a flame is not present when the values of the one or more light samples are below the second threshold.

12. The method of claim 11 , wherein the first threshold is lower than the second threshold.

13. The method of claim 10 , further comprising, 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 meet the secondary criteria;

determining that a flame is present when the values of the one or more light samples meet the secondary criteria; and

determining that a flame is not present when the values of the one or more light samples do not meet the secondary criteria.

14. The method of claim 10 , further comprising determining whether the values of the one or more light samples meet the secondary criteria by:

determining whether the values of the one or more light samples exceed, by a predetermined margin, a burner OFF light sample value taken when the fuel oil burner is in an OFF cycle;

determining that the secondary criteria is met when the values of the one or more light samples exceed the burner OFF light sample value by the predetermined margin; and

determining that the secondary criteria is not met when the values of the one or more light samples do not exceed the burner OFF light value by the predetermined margin.

15. The method of claim 10 , further comprising determining whether the values of the one or more light samples meet the secondary criteria by:

determining whether the values of the one or more light samples exceed a predetermined portion of a previous representative value of one or more previous light samples;

determining that the secondary criteria is met when the values of the one or more light samples exceed the predetermined portion of the previous representative value; and

determining that the secondary criteria is not met when the values of the one or more light samples do not exceed the predetermined portion of the previous representative value.

16. The method of claim 10 , further comprising determining whether the values of at least two of the one or more light samples meet the secondary criteria based on a deviation criteria that specifies a minimum amount of deviation between the values of the one or more light samples.

17. The method of claim 16 , further comprising determining whether the values of the one or more light samples meet the secondary criteria by:

determining whether the values of the one or more light samples exceeds a secondary threshold;

determining whether the deviation criteria is met by at least two of 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.

18. The method of claim 17 , wherein the secondary threshold is higher than the first threshold and the second threshold.