An alternating current bridge for comparing four-terminal-pair impedances at ω = 104 rad/s

An AC bridge has been developed for comparing capacitances from 10 to 1000 pF and resistances from 1 to 100 kΩ with a relative uncertainty of about 6×10^-8 at ω=10⁴ rad/s using an inductive voltage divider (IVD) with a nominal ratio of 1:10. Apart from these two quantities the difference in the dissipation factor of the capacitances can be determined with an uncertainty of about 9×10^-8 and the difference in the time constants of the resistances with an uncertainty of about 2×10^-11 s. It is proved that the uncertainty, particularly in the measurement of capacitances and resistances, can be considerably reduced, because it mainly depends on the errors of the IVD. This bridge has been developed to derive the SI unit ohm from the SI unit farad at the Physikalisch-Technische Bundesanstalt (PTB).