Thermal measurement of AC power in comparison with the electrodynamic method

A thermal instrument for measurement of low-frequency ac power with a resolution of 1 ppm of maximum input is described. Due to its simple construction and, consequently, low number of error sources, it is well suited to precision measurements. The instrument has been applied to an accurate experimental comparison with the electrodynamic method carried out for identification of errors that cannot be traced by self-checks of each of the systems. The experimental configuration for the comparison is discussed and results of the measurements are given.