Evaluation of scattered-light signals in an optical hazard alarm and output both of a weighted smoke density signal and also of a weighted dust/steam density signal

A method for evaluating two scattered light signals in a hazard alarm operating in accordance with a scattered light principle, the method comprising:

• irradiating particles to be detected with a first light in a first wavelength range and with a second light in a second wavelength range;
• converting light scattered by the particles into first and second non-normalized signals;
• normalizing the first and second non-normalized signals to one another and producing two normalized scattered light signals having amplitude curves that approximately coincide for dust- and steam-sized particles;
• transforming the two normalized scattered light signals into a polar angle and a polar distance as polar coordinates of a polar coordinate system;
• forming a weighted smoke density signal and a weighted dust/steam density signal by weighting the polar distance depending on the polar angle, the polar distance being weighted oppositely in forming the weighted smoke density signal and the weighted dust/steam density signal;
• and
• outputting the weighted smoke density signal and the weighted dust/steam density signal for further evaluation.

An optical hazard alarm operating in accordance with a scattered light principle, comprising:

• a detection device comprising:
• at least one light source to irradiate particles to be detected with a first light in a first wavelength range and with a second light in a second wavelength range;
• and
• an optical receiver to convert light scattered by the particles into first and second non-normalized signals;
• and
• an electronic evaluation unit comprising:
• a normalization unit to normalize the first and second non-normalized signals to one another and produce two normalized scattered light signals having amplitude curves that approximately coincide for dust- and steam-sized particles;
• a processor to transform the two normalized scattered light signals into a polar angle and a polar distance as polar coordinates of a polar coordinate system;
• and
• a signal formation unit to form a weighted smoke density signal and a weighted dust/steam density signal by weighting the polar distance depending on the polar angle, the polar distance being weighted oppositely in forming the weighted smoke density signal and the weighted dust/steam density signal, the weighted smoke density signal and the weighted dust/steam density signal being output for further evaluation.