A Modified Technique for Calibration of Current-Comparator-Based Capacitance Bridge and Its Verification

A modified technique for calibrating both the capacitance-ratio and dissipation-factor (DF) dials of a current-comparator-based high-voltage capacitance bridge has been developed at the Korea Research Institute of Standards and Science (KRISS). The capacitance-ratio and DF dials are calibrated in the ratio range from 1/1 to 1000/1 and in the DF range from 10 × 10^-6 to 1 × 10^-1 for both positive and negative polarities. From the calculated and measured values of the corresponding dial balanced readings, the errors in the capacitance-ratio- and DF-dial readings are derived. The relative uncertainty of the modified calibration technique is also obtained to be not more than 10 × 10^-6 of unity for the ratio-dial calibration, whereas the relative uncertainty of the DF dials from 1 × 10^-3 to 1 × 10^-1 is not more than 0.4% of the dial indication except the dissipation lower than 1 × 10^-3 for which the corresponding absolute uncertainty is 5 × 10^-6. The comparison results of the calibration performed at KRISS and the National Research Council of Canada show a good consistency with the measurement uncertainty.