A Current Comparator System to Establish the Unit of Electrical Energy at 60 Hz

A compensated current comparator system to establish the United States legal unit of electrical energy at the National Bureau of Standards at energy levels of approximately 30 and 60 kJ is described. Analysis of the system uncertainties and experimental data indicates that the registrations of three standard type watthour meters were determined with total estimated uncertainties of about 30 ppm at unity power factor (PF) and 40 ppm at 0.5 PF. Of these uncertainties, 18 ppm represents the three standard deviation bound for the effects of random errors, and the remainder the root sum of squares of bounds to possible calibration and systematic effects. These results indicate that it should now be possible to disseminate the energy unit with uncertainties less than the presently quoted 500 ppm.