Leon Chao
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View article: Leveraging the revised International System of Units: torque from the fundamental constants
Leveraging the revised International System of Units: torque from the fundamental constants Open
Calibration of tools designed to apply known torques, such as torque wrenches and torque screwdrivers, requires a chain of traceable standards to the definition of the kilogram and meter derived from the revised International System of Uni…
View article: Thoughts on the Kibble–Robinson theory
Thoughts on the Kibble–Robinson theory Open
We revisit the Kibble–Robinson theory, first proposed in 2014 by Kibble and Robinson. This theory significantly simplifies the construction and operation of Kibble balances. We conducted a theoretical investigation of the theory’s assumpti…
View article: The Design and Performance of an Electronic Torque Standard Directly Traceable to the Revised SI
The Design and Performance of an Electronic Torque Standard Directly Traceable to the Revised SI Open
The United States National Institute of Standards and Technology (NIST) has been developing a new device for primary standard realization of torque utilizing established traceability to quantum-electrical standards following the 2019 revis…
View article: Calculation of magnetic forces and torques on the Kibble coil
Calculation of magnetic forces and torques on the Kibble coil Open
Analytically the force acting on a current-carrying coil in a magnetic field can be calculated in two ways. First, a line integral can be conducted along the coil’s wire, summing up the differential force contributions. Each contribution r…
View article: Calculation of magnetic forces and torques on the Kibble coil
Calculation of magnetic forces and torques on the Kibble coil Open
Analytically the forces and torques on a coil in a field of magnetic flux density can be calculated one of two ways. The line integral can be conducted along the coil's wire, summing up the differential force contribution. For each differe…
View article: Design of electrostatic feedback for an experiment to measure $G$
Design of electrostatic feedback for an experiment to measure $G$ Open
The torsion pendulum at the heart of the apparatus to measure the gravitational constant, $G$ at the Bureau International des Poids et Mesures (BIPM) is used to measure the gravitational torque between source and test-mass assemblies with …
View article: The crane operator's trick and other shenanigans with a pendulum
The crane operator's trick and other shenanigans with a pendulum Open
The dynamics of a swinging payload suspended from a stationary crane, an unwanted phenomenon on a construction site, can be described as a simple pendulum. However, an experienced crane operator can deliver a swinging payload and have it s…
View article: Design of Electrostatic Feedback for an Experiment to Measure <i>G</i>
Design of Electrostatic Feedback for an Experiment to Measure <i>G</i> Open
The torsion pendulum at the heart of the apparatus to measure the gravitational constant, at the Bureau International des Poids et Mesures (BIPM) is used to measure the gravitational torque between source and test-mass assemblies with two…
View article: Resolution of the paradox of the diamagnetic effect on the Kibble coil
Resolution of the paradox of the diamagnetic effect on the Kibble coil Open
Employing very simple electro-mechanical principles known from classical physics, the Kibble balance establishes a very precise and absolute link between quantum electrical standards and macroscopic mass or force measurements. The success …
View article: Resolution of the paradox of the diamagnetic effect on the Kibble coil
Resolution of the paradox of the diamagnetic effect on the Kibble coil Open
Employing very simple electro-mechanical principles known from classical physics, the Kibble balance establishes a very precise and absolute link between quantum electrical standards and macroscopic mass or force measurements. The success …
View article: Measurement of the Planck constant at the National Institute of Standards and Technology from 2015 to 2017
Measurement of the Planck constant at the National Institute of Standards and Technology from 2015 to 2017 Open
Researchers at the National Institute of Standards and Technology(NIST) have measured the value of the Planck constant to be $h =6.626\,069\,934(89)\times 10^{-34}\,$J$\,$s (relative standard uncertainty $13\times 10^{-9}$). The result is …
View article: Bridging classical and quantum mechanics
Bridging classical and quantum mechanics Open
Using a watt balance and a frequency comb, a mass-energy equivalence is derived. The watt balance compares mechanical power measured in terms of the meter, the second, and the kilogram to electrical power measured in terms of the volt and …
View article: Monitoring gravity for the NIST-4 watt balance
Monitoring gravity for the NIST-4 watt balance Open
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View article: Invited Article: A precise instrument to determine the Planck constant, and the future kilogram
Invited Article: A precise instrument to determine the Planck constant, and the future kilogram Open
A precise instrument, called a watt balance, compares mechanical power measured in terms of the meter, the second, and the kilogram to electrical power measured in terms of the volt and the ohm. A direct link between mechanical action and …
View article: Coil motion effects in watt balances: a theoretical check
Coil motion effects in watt balances: a theoretical check Open
A watt balance is a precision apparatus for the measurement of the Planck constant that has been proposed as a primary method for realizing the unit of mass in a revised International System of Units. In contrast to an ampere balance, whic…
View article: A LEGO Watt balance: An apparatus to determine a mass based on the new SI
A LEGO Watt balance: An apparatus to determine a mass based on the new SI Open
A global effort to redefine our International System of Units (SI) is underway, and the change to the new system is expected to occur in 2018. Within the newly redefined SI, the present base units will still exist but be derived from fixed…
View article: A Determination of the Local Acceleration of Gravity for the NIST-4 Watt Balance
A Determination of the Local Acceleration of Gravity for the NIST-4 Watt Balance Open
A new watt balance is being constructed at the National Institute of\nStandards and Technology (NIST) in preparation for the redefinition of the\nInternational System of Units and the realization of mass through an exact\nvalue of the Plan…