Realization of Inductance Scale Using Digital Bridges at Low Frequencies.

This paper describes a traceability chain for the inductance scale from the DC quantum Hall resistance using a multi-purpose digital impedance bridge. In this study, the digital bridge was employed in various inductance measurements against either AC resistance standards or other inductance standards in the wide range from 100 μH to 10 H. An inductance standard of 100 mH was calibrated at 1 kHz using the digital bridge in a fully digital mode by a direct comparison against the AC resistance standard of 1 kΩ. The measurement result was in a good agreement with the reference value on the level of 10 ^-6 at the best. From the calibrated 100 mH standard inductor, the inductance scale was realized by 10:1 comparison from 100 μH to 10 H using the bridge in a digitally assisted mode. In the similar manner, the 10 mH inductance was calibrated against the 1 kΩ resistance at a higher frequency of 10 kHz, then scaled down to 100 μH. During the extensive measurements, the digital bridge was studied for various ways to improve the inductance measurement accuracy, such as the phase correction of the bridge.