Principles and theory of wattmeters operating on the basis of regularly spaced sample pairs

Abstract

The contribution to the errors of a regularly sampling wattmeter caused by using n distinct instantaneous samples of the input signals taken at equal intervals of time is evaluated and discussed. It is shown that although most of the possible harmonic products are handled correctly, a significant number of harmonic autoproducts and particularly of harmonic cross products are not, namely all the components of the nth, 2nth, 3nth, ... product harmonics. Sinusoidal waveforms are handled correctly, and the errors with near-sinusoidal waveforms are generally negligible. Two particular classes of non-sinusoidal waveforms are examined, those controlled by phase-angle switching and those associated with discharge lamps.