A resistive ratio standard for measuring direct voltages to 10 kV

A highly accurate guarded voltage-ratio standard has been developed for measuring direct voltages from the range of a standard cell to 10 kV. The ratio standard has a resolution capability of 0.1 ppm for ratios of 1:1 to 10 000:1 with an estimated uncertainty of 0.2 ppm. It is designed for operation at a rating of 2 kΩ/V and consists of an adjustable reference section in series with three resistance groups each containing nine nominally equal sections. The resistance ratios are determined by a self-calibration technique using a 1:1 bridge. A series-parallel mode of calibration provides an additional check on the accuracies of the ratios. The standard is housed in a temperature-controlled oil bath whose oil is filtered to remove moisture and contaminants.