Accurate high-current DC current ratio measurements

A setup has been developed for the accurate calibration of DC current ratios for DC currents up to 600 A. The setup is based on a DC current comparator and suitable for the calibration of DC current ratio measurement devices up to 100 A primary current. For higher primary currents, multiple turns of the primary conductor are made through the device under test. It has been verified that for well-designed devices this adds less than 1 part in 10⁶ to the measurement uncertainty. A preliminary evaluation indicates that the total uncertainty of the setup is better than 5 parts in 10⁶ in current ratio for primary currents up to 600 A.