The national capacitance standard on basis of the new vertical calculable cross-capacitor at NIM

The national capacitance standard on basis of the new vertical calculable cross-capacitor (VCCC) of 0.4 pF with the standard uncertainty of 0.01 μF/F at NIM is authorized since March 2023 in China. In the meantime, a new type vacuum toroidal cross-capacitor (TCC) with a nominal value of 1 pF has been developed as a substitute to maintain the capacitance unit and a transfer standard capacitor to perform intercomparisons in future. The mean cross capacitance determined by comparison to the new VCCC, is confirmed to be better than 0.03 μF/F per year.