Inter-laboratory nanoamp current comparison with sub-part-per-million uncertainty

TL;DR

This paper demonstrates a highly precise inter-laboratory comparison of ultra-stable low-noise current amplifiers, achieving sub-part-per-million uncertainty, and establishes a new benchmark for small current transfer accuracy.

Contribution

It introduces a detailed methodology for calibrating and comparing ultra-stable low-noise current amplifiers with unprecedented precision across laboratories.

Findings

Relative change in trans-resistance gain < 2×10⁻⁷ across transfers

Calibration of ULCA using cryogenic current comparator

Measurement of 1 GΩ resistors with 10⁻⁷ level uncertainty

Abstract

An ultrastable low-noise current amplifier (ULCA) has been transferred between two laboratories, NPL and PTB, four times, with three of the transfers yielding a relative change in the trans-resistance gain of less than $2 \times 10^{-7}$. This is a new bench-mark for inter-laboratory transfer of small current. We describe in detail the use of a cryogenic current comparator to calibrate the ULCA at NPL, and the use of the ULCA to measure $1$ G$\Omega$ resistors with relative uncertainties at the $10^{-7}$ level.