Practical Application of Latest Optimal Hollow Active Auxiliary Electrode in Vertical Calculable Cross-Capacitor at NIM

After continuous investigation on the electrical compensation method for the end effect error in the new vertical calculable cross-capacitor (VCCC), the latest optimal hollow active auxiliary electrode (OHAAE) has been developed and successfully substituted for the current geometrical nosepiece at one end of the movable guard electrode at the National Institute of Metrology, China (NIM). The critical electrical characteristics of the latest OHAAE are investigated by the model tests and eventually implemented with the least mechanical modifications to the new VCCC at NIM. The standard uncertainty of the reproduction of 1 pF capacitance unit from the new VCCC by adopting the latest OHAAE is decreased to 10.5 × 10
^-9
in comparison with that of 20.0 × 10
^-9
by the geometrical nosepiece.