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Abstract

The method according to the invention of monitoring a flame uses the known principle that a direct current signal (I.sub.F) 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 (I.sub.F) 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 (A.sub.1, A.sub.2) are obtained depending on the respective flame intensity. The evaluation circuit (6) also is acted upon by an ac voltage signal whose absence, upon failure of the evaluation circuit (6), deactivates a monitoring circuit (7), which results in a second output signal (A.sub.A). That second output signal (A.sub.A) is advantageously a static output signal so that it is possible to detect defective performance on the part of the evaluation circuit (6). The function of the monitoring circuit (7) itself can be periodically tested.

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