Patent ID: 7714290

Claim:
A flame detector comprising: a first band pass filter, having a pass band containing an infrared wavelength specific to flame, that receives first light and passes second light from within the first light; a second band pass filter, having a pass band that does not contain an infrared wavelength specific to flame, that receives the first light and passes third light from within the first light; a first infrared-ray receiving element that receives the second light passed by the first band pass filter and outputs a first signal that is indicative of the amount of received second light; a second infrared-ray receiving element that receives the third light passed by the second band pass filter and outputs a second signal that is indicative of the amount of received third light; an adjusting unit that adjusts the level of one or both of the first and second signals; and a comparator that receives the first and second signals after their respective adjustments, if any, and compares the received levels to detect flame, wherein: the second band pass filter passes less incident light having homogeneous energy in a transmissive wavelength band of both the first and second band pass filters than does the first band pass filter, and the adjusting unit adjusts the level of one or both of the first and second signals to an extent that would make the first and second signals equal if light having homogeneous energy in the transmissive wavelength band of both the first and second band pass filters is incident upon the first and second band pass filters.