watt balance


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watt balance

[′wät ‚bal·əns]
(physics)
A device for making a highly accurate comparison of electrical and mechanical powers, in which the force on a current-carrying coil in a constant magnetic field is balanced by the gravitational force on an accurately measured mass, and then, with the current source removed, the coil is moved at constant speed in the same magnetic field and the induced potential difference is measured.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
2019.The quantized Hall resistance (Nobel Prize 1985) plays a crucial role for the realization of this new SI system since this quantum resistance can be used not only for high precision measurements of electrical standards, but also for a new realization of a kilogram by comparing electrical and mechanical forces with the Watt balance. The talk summarizes the application of the quantum Hall effect in metrology with the focus on the replacement of the kilogram with a fixed value for the Planck constant.
Mass, then, would be rooted in measurements made with a highly precise but rather esoteric device known as a watt balance. The Bureau International de Poid et Mesures (BIPM) intends to have the issue settled and the new definitions in place by 2018.
The watt balance and atom-counting techniques now give nearly identical values of Planck's constant, with an uncertainty of less than 20 parts in a billion, says metrologist Ian Robinson of the National Physical Laboratory in Teddington, England.
As this is a physical constant (e), the amp will be directly measurable without reference to the attraction between two wires carrying a current in a watt balance.
The other, called the watt balance, measures the constant by an indirect or "virtual" comparison of mechanical power to electromagnetic power.
The Bureau International des Poids et Mesures (International Bureau of Weights & Measures) proposed alternative kilogram definitions, such as the experimental measurement of force on the Watt balance or counting atoms on a silicon sphere.
Key words: absolute watt measurement; electronic kilogram; electronic watt determination; fundamental physical constants; Planck constant; SI power measurement; SI watt unit; watt balance.
The main rival relies on a watt balance, which measures the mass of a test cylinder by suspending it using a combination of electrical currents and magnetic fields.
This realization can be done using electromagnetic forces (e.g., the NIST Watt Balance Experiment [46]) or using electrostatic forces [47].
The first, called the moving coil watt balance method, relates electrical energy to mechanical power at the quantum level.
The NIST watt balance experiment is being completely rebuilt after its 1998 determination of the Planck constant.
A recent moving-coil watt balance experiment carried out at NIST, based on equating electric power and mechanical power, has determined the Josephson constant to be 483 597.892 GHz/V, with a relative standard uncertainty of 4.4 X [10.sup.-8] (82).