Development and implementation of an automated four-terminal-pair Josephson impedance bridge

The four-terminal-pair impedance bridge using pulse-driven Josephson voltage standards at PTB has been fully automated. The same bridge configuration was employed to determine R:R and C:C ratios over the frequency range between 53 Hz to 50 kHz. Only minor changes are needed to cover this large frequency range: amplifiers to increase the sensitivity of the current detections for low frequencies and signal generators with higher resolution at high frequencies to reach 50 kHz. Furthermore, the bridge can be operated for quadrature R:(1/omega C) measurements. The combined standard uncertainties (k = 1) for the new bridge were evaluated for all operating frequencies. They reach 2 nF F-1 and 4 n omega omega-1 at 1233.15 Hz. At this frequency, the 10 nF:10 nF ratio matched the ratio of PTB's bridge employing inductive voltage dividers within 1 nF F-1 +/- 3 nF F-1 (k = 1). Over 45 days, the 10 nF:10 nF ratio deviated less than -2 nF F-1 +/- 3 nF F-1 (k = 1). The 12.9 k omega:10 k omega ratio at 53 Hz differed -2 n omega omega-1 +/- 5 n omega omega-1 (k = 1) from the DC ratio measured by the PTB's cryogenic current comparator bridge. Using a 12.9 k omega resistance standard and a graphene AC quantum Hall resistance, the 10 nF:10 nF ratios derived from quadrature measurements agreed with the PTB's inductive voltage divider bridge better than 9 nF F-1 +/- 13 nF F-1 (k = 1).