Evaluating scattered-light signals in an optical hazard detector and outputting a dust/steam warning or a fire alarm

摘要

The invention relates to a method for evaluating two scattered-light signals (IR, BL) of an optical hazard detector (1) operating according to the scattered-light principle. The particles to be detected are irradiated by light in a first wavelength range and by light in a second wavelength range. The light that is scattered by the particles is converted into a first and second scattered-light signal (IR', BL'). The two scattered-light signals (IR', BL') are normalized with respect to one another such that the amplitude profile thereof approximately corresponds for relatively large particles such as dust and steam. Furthermore, an amplitude ratio (R) is formed between the two scattered-light signals (IR, BL) and an amplitude comparison value (90%) is set, which corresponds to a predeterminable particle dimension in the cross-over region between smoke and dust/steam. The two scattered-light signals (IR, BL) are processed further in respect of fire characteristic variables, depending on the current comparison result (C). According to the invention it is at least mainly the first scattered-light signal (IR) that is evaluated if the amplitude ratio (R) exceeds the amplitude comparison value (90%) and a dust/steam-density signal (SD) is emitted. In the other case, it is at least mainly the second scattered-light signal (BL) that is evaluated and a smoke-density signal (RS) is emitted.