From the calculable AC resistor to capacitor dissipation factor determination on the basis of time constants

This paper presents a new measuring method for comparing different impedances, which allows, for example, the capacitance and the dissipation factor of a capacitor to be determined from the resistance and the time constant of an AC resistor. This method combines elements of the classical bridge technique (Thomson balancing and Wagner earthing) with the digital synthesis of signals and their sampling using the discrete Fourier transform (DFT). A particularly interesting application, the derivation of the dissipation factor of a 1 μF capacitor at the measuring frequency 1 kHz from the calculable time constant of a 200 Ω AC measuring resistor of bifilar structure is dealt with in detail. The method enables the determination of the dissipation factor with an estimated standard uncertainty of measurement (k=1) of 2×10^-6