Measuring and monitoring of power quality of supplied electric energy are important links in electro-distribution chain. Modern systems used for this purpose are complex. Goal of this paper is to present a new approach to the measurements of power quality, which can achieve equal or better performances using less complicated hardware. In this paper, we have presented the method of measuring over an interval in measurements of relevant factors of power quality: grid voltage frequency, grid voltage RMS and grid voltage distortion factor. Also given is the analysis of performances from metrology point of view, which shows that the measurement uncertainty of proposed method is many times lower than required, regarding...