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

Abstract

A method evaluates two scattered-light signals in a hazard alarm operating in accordance with the scattered light principle. The particles to be detected are irradiated with light in a first wavelength range and with light in a second wavelength range. The light scattered by the particles is converted into a first and second non-normalized scattered light signal. The two scattered light signals are normalized in relation to one another such that their amplitude curve approximately coincides for larger particles such as dust and steam. The two normalized scattered light signals are transformed into a polar angle and a distance as polar coordinates of a polar coordinate system. Finally a respective smoke density signal and a respective dust/steam density signal is formed from a current distance value, wherein for this purpose the respective current distance values, depending on a current polar angle value, are weighted in opposition to one another.