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The National Institute of Standards and Technology (NIST) new watt balance (NIST-4) has been constructed for the realization of mass through an exact value of the Planck constant in the new International System of Units (SI). The total relative uncertainty goal for the instrument of a few parts in 108 requires the determination of the local acceleration of gravity, g, with parts in 109 accuracy at...
In the past four years, we have constructed a new watt balance at the National Institute of Standards and Technology (NIST), with the goal to realize the unit of mass after the redefinition of the International System of Units, expected to occur in 2018. The new watt balance has been operational since the fall of 2015 and we describe our first measurements with it.
A watt balance is a promising instrument to realize the unit of mass at the kilogram level. The magnet system is one of the key elements of such an instrument. 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 construction of the magnet system, first measurements of the field profile, and...
A new watt balance is being constructed at National Institute of Standards and Technology (NIST) in preparation for the redefinition of the International System of Units and the realization of mass through an exact value of the Planck constant. We describe the procedures used and give results for the measurements of the local acceleration of gravity in the new watt balance facility.
A redefinition of the International System of Units, the SI, is impending and could occur as early as 2017. After redefinition, a means to realize the unit of mass is required. A watt balance is a promising device to realize the unit of mass at the kilogram level. At the National Institute of Standards and Technology (NIST), construction of a new watt balance with the sole purpose to realize mass...
The design of the new permanent-magnet driven watt balance and novel mechanical features will demonstrate the high-precision capabilities of a new watt balance mass measurement system. This article will introduce the concept of replacing the counter mass with an auxiliary mass and precision alignment of the coil using a large flexure. The system is expected to have overall uncertainties on the order...
This paper gives a brief description of the laser interferometer system designed for the next generation watt balance experiment aimed to realize the unit of mass by direct link to the Planck constant at the National Institute of Standards and Technology. The light source is an iodine-stabilized frequency-doubled Nd:YAG laser at λ=532nm. Three heterodyne interferometers with subnanometer non-linearity...
In 2013, a new measurement of the Planck constant h was performed using a watt balance at the National Institute of Standards and Technology (NIST). The value is h = 6.626 069 79(30) × 10−34 Js. The relative standard uncertainty of this determination is 45 × 10−9.
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