L.S. Chao

Determination of the Planck constant using a watt balance with a superconducting magnet system at the National Institute of Standards and Technology

For the past two years, measurements have been performed with a watt balance at the National Institute of Standards and Technology (NIST) to determine the Planck constant. A detailed analysis of these measurements and their uncertainties has led to the value h = 6.626 069 79(30) × 10−34 J s. The relative standard uncertainty is 45 × 10−9. This result is 141 × 10−9 fractionally higher than h90. Here h90 is the conventional value of the Planck constant given by , where KJ-90 and RK-90 denote the conventional values of the Josephson and von Klitzing constants, respectively.

Construction, Measurement, Shimming, and Performance of the NIST-4 Magnet System

The magnet system is one of the key elements of a watt balance. For the new watt balance currently under construction at the National Institute of Standards and Technology, a permanent magnet system was chosen. We describe the detailed construction of the magnet system, first measurements of the field profile, and shimming techniques that were used to achieve a flat field profile. The relative change of the radial magnetic flux density is <; 10-4 over a range of 5 cm. We further characterize the most important aspects of the magnet and give order of magnitude estimates for several systematic effects that originate from the magnet system.

A summary of the Planck constant measurements using a watt balance with a superconducting solenoid at NIST

Researchers at the National Institute of Standards and Technology have been using a watt balance, NIST-3, to measure the Planck constant

Coil motion effects in watt balances: a theoretical check

h

First Measurements of the Flux Integral With the NIST-4 Watt Balance

for over ten years. Two recently published values disagree by more than one standard uncertainty. The motivation for the present manuscript is twofold. First, we correct the latest published number to take into account a recently discovered systematic error in mass dissemination at the Bureau International des Poids et Mesures (BIPM). Second, we provide guidance on how to combine the two numbers into one final result. In order to adequately reflect the discrepancy, we added an additional systematic uncertainty to the published uncertainty budgets. The final value of

A Determination of the Local Acceleration of Gravity for the NIST-4 Watt Balance

h

Construction of a watt balance with the aim to realize the kilogram at the National Institute of Standards and Technology

measured with NIST-3 is

The design of the new NIST-4 watt balance

h = 6.626\,069\,36(37)\times 10^{-34}\,\mbox{J\,s}

First mass measurements with the NIST-4 watt balance

. This result is

The measurement of the local acceleration of gravity for the NIST-4 watt balance

77(57) \times 10^{-9}