DC voltage divider calibration system at NMIJ

A system to self-calibrate a DC voltage divider with increment taps up to 1 kV has been developed. During selfcalibration, the divider is grounded and is powered at the same level as it is when in normal use. A reference divider self-calibrated by this method is used as a standard to calibrate other dividers at NMIJ. Typical relative uncertainty is 3*10^-7 for 1000 V/10 V and 2*10^-7 for 100 V/10 V (k=2, confidence level of 95%).