Verfahren und Vorrichtung zur Bestimmung der Netzfrequenz sowie zur Erkennung von Lichtquellen verschiedener Frequenzen

摘要

The method involves determining the presence of a line frequency from a group of possible line frequencies, including a first line frequency having an associated first flicker frequency period and a second higher line frequency having an associated second flicker frequency period. The method involves sampling the ambient light to obtain a first analogue voltage sample representative of ambient light level for a first sample group and digitally converting it. The first sample group corresponds to the first line frequency and consecutive analogue voltage samples for the first sample group are taken at a first sample rate. The ambient light is then sampled to obtain a first analogue voltage sample for a second sample group after a predetermined time from the first sample, and A/D converts it, the second sample group corresp. to the second line frequency. The two sample rates are defined by the following: sample rate = 1/(ffX n), where ff = flicker frequency in Hertz, and n = number of samples per flicker frequency period. The preset time interval is at least equal to a time required for the conversion and less than a shortest time such that a future sample for the first sample group would coincide with a future sample for the second sample group. The sampling and converting of both sample groups are repeated until a predetermined number of samples are taken, and the converted samples in at least one group are compared to determine if a presence of the line frequency is indicated.