The ampere and electrical standards

Abstract

This paper describes some of the major contributions to metrology and physics made by the NIST Electricity Division, which has existed since 1901. It was one of the six original divisions of the National Bureau of Standards. The Electricity Division provides dc and low-frequency calibrations for industrial, scientific, and research organizations, and conducts research on topics related to electrical metrology and fundamental constants. The early work of the Electricity Division staff included the development of precision standards, such as Rosa and Thomas standard resistors and the ac-dc thermal converter. Research contributions helped define the early international system of measurement units and bring about the transition to absolute units based on fundamental principles and physical and dimensional measurements. NIST research has helped to develop and refine electrical standards using the quantum Hall effect and the Josephson effect, which are both based on quantum physics. Four projects covering a number of voltage and impedance measurements are described in detail. Several other areas of current research at NIST are described, including the use of the Internet for international compatibility in metrology, determination of the fine-structure and Planck constants, and construction of the electronic kilogram.

The kilogram and measurements of mass and force

“…The mechanical electrical measurement approach, which uses what has become known as a “moving-coil watt balance,” is described in detail in this issue by Elmquist et al [ 26 ]. The main concept is to compare a power measured mechanically in terms of the kilogram, meter, and second to the same power measured electrically using the Josephson and quantum Hall effects.…”

Single‐Electron Pumps and Quantum Current Metrology in the Revised SI

“…[]). However, current‐balance setups delivered results limited to an accuracy level of few parts in a million and, thus, are not pursued anymore . Despite its practical flaw of hardly enabling a direct realization of the unit, the ampere definition is meaningful since it defines the exact value for the magnetic constant (vacuum permeability) µ 0 = 4π ⋅ 10 −7 H m −1 .…”

A LEGO Watt balance: An apparatus to determine a mass based on the new SI

“…At NIST, the quantum Hall effect is the starting point of resistance dissemination. 10 Scaling with a cryogenic current comparator allows researchers to measure a 100 Ω precision resistor with a relative uncertainty of a few parts in 10 9 . On the outside, a quantum Hall system looks similar to a Josephson voltage system: a bundle of cables leading into a liquid helium dewar.…”