Flame sensing

A system comprising:

• a combustion source in which a flame may be generated and in which the flame emits electromagnetic radiation;
• a sensor for detecting the presence of the flame in the combustion source, the flame sensor comprising:
• a body disposed proximate to the combustion system;
• a photodetector supported in the body, the photodetector configured to generate an electrical signal proportional to an intensity of electromagnetic radiation;
• a window supported in the body and located between the combustion system and the photodetector;
• and
• a source supported in the body, the source emitting electromagnetic radiation toward the window, wherein the source and photodetector being positioned adjacent each other such that at least some of the electromagnetic radiation emitted by the source reflects back from contamination present on the window toward the photodetector when contamination is present on the window;
• and
• a modulator to modulate the source by varying an emission intensity of the electromagnetic radiation emitted by the source to a predetermined pattern that is different than a flicker pattern emitted by the flame so the electromagnetic radiation sensed by the photodetector can be distinguished between the electromagnetic radiation emitted by the source and the electromagnetic radiation emitted by the flame.

A method of detecting contamination on a flame sensor window, the method comprising the steps of:

• providing a flame sensor for detecting the presence of a flame in a combustion system in which the flame emits electromagnetic radiation, the flame sensor including a body disposed proximate to the combustion system;
• supporting a photodetector in the body, the photodetector detecting the electromagnetic radiation emitted by the flame, the photodetector configured to generate an electrical signal proportional to an intensity of the electromagnetic radiation;
• supporting a window in the body and locating the window between the combustion system and the photodetector;
• supporting a source in the body at a position adjacent to the photodetector, the source emitting electromagnetic radiation toward the window;
• passing a first predetermined amount of the electromagnetic radiation emitted by the source through the window when there is no contamination on the window;
• reflecting, from contamination present on the window a second predetermined amount of the electromagnetic radiation emitted by the source in a direction towards the photodetector when there is contamination on the window;
• detecting with the photodetector the second predetermined amount of the electromagnetic radiation emitted by the source, and reflected from contamination present on the window, and communicating a signal indicative of contamination on the window;
• and
• modulating the source by varying an emission intensity of the electromagnetic radiation emitted by the source in a predetermined pattern that is different than a flicker pattern emitted by the flame so the electromagnetic radiation sensed by the photodetector can be distinguished between the electromagnetic radiation emitted by the source and the electromagnetic radiation emitted by the flame.