Extension of Swerlein´s algorithm for AC voltage measurement in the frequency domain

Two sampling algorithms that use a high-resolution voltmeter for accurately measuring the amplitudes and phase angles of the harmonics of a low-frequency, low-distortion, voltage waveform are presented. The technique is an extension to the frequency domain of a previously described approach. In the new approach, the harmonic parameters are evaluated by a least-squares, three-parameter, sine-fit algorithm. A faster algorithm that uses discrete Fourier transforms is also presented. The latter algorithm can estimate the parameters of m harmonics of a 100-Hz low distortion waveform in less than 4m seconds. The relative standard uncertainty associated with the RMS estimate depends on the waveform stability, harmonic content, and noise variance, and is 2.5×10^-6 for low-distortion, 100 Hz sinusoidal waveforms in the 10-V range. This uncertainty figure includes the noise variance contribution of the waveform generator used in the tests.