New impedance bridge at LNE for the two terminal-pair AC resistor calibration up to 20 kHz

This paper presents the evolution of LNE's impedance bridge (Wheatstone bridge) used to calibrate AC resistors defined in the two terminal-pair configuration. A new automated Wheatstone bridge, based on four resistances, was developed to operate in the full complex plane for resistances ranging from 400 omega to 2 M omega and for frequencies up to 20 kHz. A commercial dual precision arbitrary waveform generator supplies the bridge and PXI modules achieve the balance. Phase and frequency synchronization solutions between the arbitrary waveform generator source and the PXI modules were used. The choice of these instruments allows the bridge to be easily automated and to benefit from recent progress in the development of digital-analog converters, in particular those with high frequency sampling rates and resolution. The bridge is mainly dedicated to realize the periodic calibration of LNE's standard resistors, used for routine customer calibrations. The traceability of LNE's standard resistors is ensured, firstly, by the calibration of a 1 k omega resistor by comparison to a calculable resistor up to 20 kHz. Then, this resistor is used as a reference element to ensure the traceability of all LNE's standard resistors using the new bridge. The validation was done by comparing the results obtained, for some resistors with very low drift, with those obtained during calibrations performed in 1983, 1995 and 2009. For resistors of 1 k omega in a 1:1 ratio, the expanded uncertainty of series resistance variation and argument are, respectively, less than 1.3 mu omega omega(-1) (k = 1) and 1.2 mu rad (k = 1), up to 20 kHz.