Low contamination rate flame detection arrangement

1. A flame sensor system comprising:

a burner for a heating unit;

a flame sensor proximate to the burner; and

a controller connected to the burner and the flame sensor; and

wherein during operation of the system, the controller is configured to periodically and repeatedly activate and deactivate the flame sensor while the heating unit is in operation, whether the burner has a flame or not.

2. The system of claim 1 , wherein during operation of the system, the flame sensor is configured to be activated and deactivated periodically while the burner has no flame.

3. The system of claim 2 , further comprising:

a valve for controlling fuel to the burner; and

wherein during operation of the system:

shortly after the valve is opened the burner should have a flame;

shortly after the valve is closed the burner should not have a flame;

after the valve is closed, the burner may have a flame for a brief time to burn residual fuel; and

after the valve is closed, the burner may continue to have a flame due to a faulty valve.

4. The system of claim 3 , wherein during operation of the system, after the valve is closed, the controller is configured to activate the flame sensor for at least a short period of time.

5. The system of claim 4 , wherein after the flame sensor is activated for the short period of time:

while the valve remains closed and the heating unit is in operation, the flame sensor has an X percent duty cycle;

the X percent duty cycle means that the flame sensor is activated for X percent of a certain period and is deactivated for (100−X) percent of the certain period.

6. The system of claim 4 , wherein:

while the valve is open and the heating unit is in operation, the flame sensor has a Y percent duty cycle;

the Y percent duty cycle means that the flame sensor is activated for Y percent of a certain period and is deactivated for (100−Y) percent of the certain period.

7. A method for reducing a contamination rate of a flame sensor for detecting a flame of a burner, comprising:

controlling an activation of a flame sensor to a minimum amount of time needed for adequate flame sensing;

wherein said controlling includes periodically and repeatedly activating and deactivating said flame sensor during operation of the burner whether or not the burner has a flame, and

wherein a minimum amount of time of activation of the flame sensor may result in a minimum amount of contamination of the flame sensor.

8. The method of claim 7 , wherein the flame sensor is periodically activated and deactivated when the burner has no flame.

9. The method of claim 8 , wherein the flame sensor is activated for one period of time when not proximate to a flame and inactivated for another period of time when not proximate to a flame.

10. The method of claim 8 , wherein the flame sensor is activated for one period of time when proximate to a flame and inactivated for another period of time when proximate to a flame.

11. A flame sensor system comprising:

a burner;

a flame sensor proximate to the burner;

a controller connected to the flame sensor; and

wherein the controller activates the flame sensor for a first period of time and then deactivates the flame sensor for a second period of time, wherein the controller activates and deactivates the flame sensor regardless of whether the burner has a flame or does not have a flame, wherein the controller activates and deactivates the flame sensor repeatedly in sequence.

12. The system of claim 11 , wherein:

the flame sensor is activated for a minimum amount time needed for adequate sensing of a flame; and

wherein a minimum amount of activation of the flame sensor may result in a minimum amount of contamination of the flame sensor.

13. The system of claim 11 , wherein the flame sensor is activated for the first period of time when not proximate to a flame and deactivated for the second period of time when not proximate to a flame.

14. The system of claim 13 , wherein the first period of time and the second period of time occur in sequence in a repeated manner for a certain length of time.

15. The system of claim 14 , wherein:

the first period of time does not necessarily have the same duration when repeated in the sequence; and

the second period of time does not necessarily have the same duration when repeated in the sequence.

16. The system of claim 11 , wherein the flame sensor is activated for the first period of time when proximate to a flame and deactivated for the second period of time when proximate to a flame.

17. The system of claim 16 , wherein, for the flame sensor proximate to a flame, the first period of time and the second period of time occur in sequence in a repeated manner for a certain length of time.

18. The system of claim 17 , wherein:

the first period of time does not necessarily have the same duration when repeated in the sequence; and

the second period of time does not necessarily have the same duration when repeated in the sequence.

19. The system of claim 11 , wherein the controller determines the certain times according to model predictive control, proportional-integral-derivative control, fuzzy logic control, or neural network control.

20. The system of claim 11 , wherein:

if the flame sensor accumulates contamination at a first rate when activated and not proximate to a flame, and the flame sensor accumulates contamination at a second rate when inactivated and not proximate to a flame, then the first rate may be greater than the second rate; and

if the flame sensor accumulates contamination at a third rate when activated and proximate to a flame, and the flame sensor accumulates contamination at a fourth rate when inactivated and proximate to a flame, then the third rate may be greater than the fourth rate.

21. The system of claim 20 , wherein the controller adjusts the first and second time periods to achieve a smaller contamination rate, which may lead to a longer life of sensing by the flame sensor.