Abstract: The method according to the invention of monitoring a flame uses the known principle that a direct current signal (IF) of different magnitude is produced in dependence on the presence or intensity of the flame from an ac voltage signal. That purpose is served for example by ionization electrodes (3) or ultraviolet sensors (4, 4a) which in dependence on the intensity of the flame produce a corresponding direct current signal. When the flame is extinguished no direct current signal is produced. The direct current signal (IF) is detected by an evaluation circuit (6) and converted into a first output signal (A), wherein conversion is effected by various further circuit elements (7, 9, 10) in such a way that differently changing output signals (A1, A2) are obtained depending on the respective flame intensity.

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 (U1) and a flame signal amplifier (40) which converts the flame signal (U1) into an output signal (U5). A frequency-selective arrangement (6, 17, 18, 19) detects the presence of mains frequency-harmonic signals in the flame signal (U1) and activates the flame signal amplifier (40) when there are no mains frequency-harmonic signals in the flame signal (U1) and deactivates the flame signal amplifier (40) when there is a flame signal (U1) with periodic signals or no flames signal (U1) 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 (U1) and appropriately activates or deactivates the flame signal amplifier (40) by way of switching means (6, 17, 18, 19).