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Abstract

The invention concerns a flame monitoring system and a method of monitoring a flame with a flame sensor (1) which converts the radiation emanating from the flame into a flame signal (U.sub.1) and a flame signal amplifier (40) which converts the flame signal (U.sub.1) into an output signal (U.sub.5). A frequency-selective arrangement (6, 17, 18, 19) detects the presence of mains frequency-harmonic signals in the flame signal (U.sub.1) and activates the flame signal amplifier (40) when there are no mains frequency-harmonic signals in the flame signal (U.sub.1) and deactivates the flame signal amplifier (40) when there is a flame signal (U.sub.1) with periodic signals or no flames signal (U.sub.1) or a test signal (T). In that respect the frequency selective arrangement (6, 17, 18, 19) has a frequency detector (18) which detects the absence of mains frequency-harmonic flame signals (U.sub.1) and appropriately activates or deactivates the flame signal amplifier (40) by way of switching means (6, 17, 18, 19). The frequency detector (18) integrates the flame signal (U.sub.1) for example over defined periods or with respect to a reference value so that mains frequency-harmonic signals are detected by a defined value and the flame signal amplifier (40) is correspondingly controlled.

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First Claim