We describe a cryogenic two-terminal high-resistance bridge and its application in precision resistance scaling from the quantized Hall resistance (QHR) at RH = RK/2 = 12 906.4035 Ω to decade resistance standards with values between 1 MΩ and 1 GΩ. The design minimizes lead resistance errors with multiterminal connections to the QHR device. A single variable voltage source and resistive ratio windings are utilized to achieve excellent dynamic stability, which is not readily obtained in low-current measurements with conventional cryogenic current comparators (CCCs). Prototypes of this bridge have been verified by a successful international comparison of high-resistance scaling using two-terminal CCCs in the national metrology institutes of Argentina, Mexico, and the United States.

A digital H∞ controller for a two-terminal cryogenic current comparator is designed. To this end, a set of mathematical models covering the actual system is proposed. Simulation results compare the open-and closed-loop systems based on the proposed controller and the traditional integral control. According to these results, the new controller can significantly reduce the noise in the superconducting quantum interference device sensor.

This work presents a supplementary comparison of high value resistance standards performed during 2012 and January 2013, following the guidelines presented in a document about measurement comparisons in the CIPM MRA. The purpose of this task was to compare the high resistance cryogenic current comparator scaling of the participating institutes: National Institute of Standards and Technology, USA (NIST), Centro Nacional de Metrología, Mexico (CENAM) and Instituto Nacional de Tecnología Industrial, Argentina (INTI), all of which are members of the Sistema Interamericano de Metrología (SIM) Regional Metrology Organization.All the measurements of this comparison were performed with two-terminal cryogenic current comparators (CCC). Degrees of equivalence of the participating institutes relative to the comparison reference values are given in the report for the measured resistance values.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by SIM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

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