Error estimation in sampling digital wattmeters

The problem of estimating the error due to time discretisation in sampling digital wattmeters is dealt with in the paper; in particular, those instruments based on the simultaneous sampling of the voltage and current waveforms at equally spaced time instants in one or more periods are considered. As the discretisation error is a periodic function with zero mean value of the initial sampling instant, its RMS value can be adopted as a useful parameter for evaluating its magnitude. An algorithm for the average power computation is proposed, which also allows for the estimation of the RMS value of the error component. Some examples of application in the area of power electronics systems are discussed. The proposed method can also be used in all those problems (e.g. FFT techniques) where the integral of a periodic function is approximated by an average of equally spaced samples.