An international trilateral comparison among the newest generations of digital and Josephson impedance bridges

This work reports and thoroughly discusses the results of an onsite trilateral comparison between a dual Joseph-son impedance bridge developed by METAS and the electronic fully-digital impedance bridges developed by CMI and INRIM-POLITO. The target accuracies of the bridges are at the level of 10−9–10−8 for the former and at the level of parts in 107 for the latter. The bridges were tested with R : R and R : C standards, with nominal magnitudes of 12.9kΩ, and with a quantum Hall resistance standard, in conditions suitable for the primary direct realization of the impedance units ohm and farad from AC quantum Hall resistance standards or from AC/DC calculable transfer resistance standards calibrated against DC quantum Hall resistance standards. The results were fully compatible at the expected level of uncertainty for what concerns the magnitude ratio, but phase measurements with R : C standards showed some incompatibilities.