Power Quality assessment is based on measuring and monitoring of specific parameters. Measure uncertainty level is important because parameters values are estimated based on this information and then compared with admissible limits. More, the decisions and solutions for electromagnetic pollution limitation is also based on that results. ISO/IEC 61000-4-30:2008 Standard contains uncertainty levels for each parameter evaluation depending of equipment class.
The paper addresses the issue of reducing of the informational entropy from the measurement process, in order to obtain adequate results for the PQ determinations. As a significant example, we present an experiment to determine the dipresidual voltage end maximum swell voltage magnitude in distribution at low voltage.