Validation of the ultrastable low-noise current amplifier as travelling standard for small direct currents

TL;DR

This study validates the ultrastable low-noise current amplifier (ULCA) as a reliable travelling standard for small direct current measurements, demonstrating high accuracy and consistency across laboratories with potential for further precision improvements.

Contribution

The paper provides an interlaboratory validation of the ULCA as a travelling standard for small currents, showing its high accuracy and robustness under shipping conditions.

Findings

Consistency within 1 ppm across labs

Transfer accuracy limited to ±0.4 ppm after shipment

Potential for 0.1 ppm uncertainty with on-site calibration

Abstract

An interlaboratory comparison of small-current generation and measurement capability is presented with the ultrastable low-noise current amplifier (ULCA) acting as travelling standard. Various measurements at direct currents between 0.16 nA and 13 nA were performed to verify the degree of agreement between the three national metrology institutes involved in the study. Consistency well within one part per million (ppm) was found. Due to harsh environmental conditions during shipment, the ULCA's transfer accuracy had been limited to about +/-0.4 ppm. Supplemental measurements performed at PTB indicate that further improvements in accuracy are possible. Relative uncertainties of 0.1 ppm are achieved by applying on-site calibration of the ULCA with a suitable cryogenic current comparator.