A Technique for Improving the Accuracy of RMS Measurement for the Low-Pass Filtration Method

The low-pass filtration method is one of the most popular RMS measurement methods. This method is characterized by flexibility of use and ease of finding of the final error rna the RMS measurement. The approach is suitable for measuring both polyharmonic and pure-sinusoidal impacts, which ensures its wide practical use. It is known that the main source for the appearance of a systematical error is due to the finite stopband rejection of the applied filter. This setting results in incomplete suppression of noise that occurs after squaring the input signal. This paper proposes an approach that can greatly reduce this error source. The approach is based on calculating a correction for an interference signal that is not completely suppressed by the used filter of low-pass type. The proposed technique is characterized by high efficiency for the case of an input polyharmonic-type with low harmonic coefficients or pure-sinusoidal type signal. To improve efficiency, it is recommended to perform an initial phase adjustment and an additional frequency evaluation. These tasks allow to effectively apply the cross-zero technique. Analytical formulas are proposed the use of which ensures one to calculate the final error value for the polyharmonic and case of both sinusoidal input signal impacts. The mathematical modeling was carried out in Matlab package.