Sensors are positioned to converge and the radiation magnitude received by the individual sensors is similar. A circuit means subtracts the output signals of the individual sensors of the pair, the steady and slowly varying components of flame radiation from the flame are effectively canceled leaving the rapidly varying difference signal for flame detection. The high frequency flame flickering is due to random pulses or burst of radiation from very localized sources in the flame, and there will always be a residual, varying component from the dual sensor system as long as the flame is present.
