A traceable mains-frequency power standard

A mains-frequency power standard traceable to voltage and impedance standards has been realised. Standard uncertainties are 26 /spl mu/W/W at unity power factor, and 18 /spl mu/W/W of apparent power at zero power factor. A power bridge balanced to 0.2% is augmented by FFT analysis of samples of the detector voltage, eliminating harmonics and drift in the test sources.