95 research outputs found
An uncertainty budget for the precursor Watt balance for South Africa
The 26th General Conference on Weights and Measures (CGPM) held on the 16th November 2018 has adopted the revision of the International system of units (SI) to be based on the fundamental physical constants
Measuring inertial mass with Kibble balance
A Kibble balance measures the mass (weight) of a test mass
with extreme precision by balancing the gravitational pull on the test mass
against the electromagnetic lift force. The uncertainty in such mass
measurement is currently ~. We show how the same Kibble
balance can be used to measure the mass of a test mass, that too
with potentially 50% better measurement uncertainty, i.e., ~.
For measuring the inertial mass, the weight of the test mass and the assembly
holding it is precisely balanced by a counterweight. The application of the
known electromagnetic force accelerates the test mass. Measuring the velocity
after a controlled elapsed time provides the acceleration and consequently the
inertial mass of the accelerated assembly comprising the Kibble balance coil
and the mass holding pan. Repeating the measurement with the test mass added to
the assembly and taking the difference between the two measurements yields the
inertial mass of the test mass. Thus, the extreme precision inertial and
gravitational mass measurement of a test mass with a Kibble balance could
provide a test of the equivalence principle. We discuss how the two masses are
related to the Planck constant and other coupling constants and how the Kibble
balance could be used to test the dynamic constants theories in Dirac
cosmology.Comment: 6 pages, 1 figure. Corrections and additions. Prepared for readers'
comments before submitting to a journa
Journey of Kilogram from Physical Constant to Universal Physical Constant (h) via Artefact: A Brief Review
The redefinition of mass adopted in November 2018 and implemented from 20 May 2019, i.e. World Metrology Day, eliminated the artefact-based approach dependent upon the International Prototype of the Kilogram (IPK), in favour of realizing the kilogram in terms of the Planck constanthby fixing its value as 6.62607015 x 10(-34) J s. In this paper, the authors present a general outline of the circumstances and related developments that paved the way for the new definition that replaced the IPK after a period of 130 years since it was formally sanctioned to define the kilogram in 1889. The new definition opens up fascinating developments in mass metrology which include different realization techniques, realizing the unit at values other than 1 kg, numerous sources for traceability can be envisaged etc
Contributions of precision engineering to the revision of the SI
All measurements performed in science and industry are based on the International System of Units, the SI. It has been proposed to revise the SI following an approach which was implemented for the redefinition of the unit of length, the metre, namely to define the SI units by fixing the numerical values of so-called defining constants, including c, h, e, k and NA. We will discuss the reasoning behind the revision, which will likely be put into force in 2018. Precision engineering was crucial to achieve the required small measurement uncertainties and agreement of measurement results for the defining constants
Fundamental Physical Constants: Looking from Different Angles
We consider fundamental physical constants which are among a few of the most
important pieces of information we have learned about Nature after its
intensive centuries-long studies. We discuss their multifunctional role in
modern physics including problems related to the art of measurement, natural
and practical units, origin of the constants, their possible calculability and
variability etc
Single-electron current sources: towards a refined definition of ampere
Controlling electrons at the level of elementary charge has been
demonstrated experimentally already in the 1980's. Ever since, producing an
electrical current , or its integer multiple, at a drive frequency has
been in a focus of research for metrological purposes. In this review we first
discuss the generic physical phenomena and technical constraints that influence
charge transport. We then present the broad variety of proposed realizations.
Some of them have already proven experimentally to nearly fulfill the demanding
needs, in terms of transfer errors and transfer rate, of quantum metrology of
electrical quantities, whereas some others are currently "just" wild ideas,
still often potentially competitive if technical constraints can be lifted. We
also discuss the important issues of read-out of single-electron events and
potential error correction schemes based on them. Finally, we give an account
of the status of single-electron current sources in the bigger framework of
electric quantum standards and of the future international SI system of units,
and briefly discuss the applications and uses of single-electron devices
outside the metrological context.Comment: 55 pages, 38 figures; (v2) fixed typos and misformatted references,
reworded the section on AC pump
Resolution of the paradox of the diamagnetic effect on the Kibble Coil
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 of the Kibble balance, in both determining fundamental constants (h, NA, e) and realizing a quasi-quantum mass in the 2019 newly revised International System of Units, relies on the perfection of Maxwell’s equations and the symmetry they describe between Lorentz’s force and Faraday’s induction, a principle and a symmetry stunningly demonstrated in the weighing and velocity modes of Kibble balances to within 1×10−8, with nothing but imperfect wires and magnets. However, recent advances in the understanding of the current effect in Kibble balances reveal a troubling paradox. A diamagnetic effect, a force that does not cancel between mass-on and mass-off measurement, is challenging balance maker’s assumptions of symmetry at levels that are almost two orders of magnitude larger than the reported uncertainties. The diamagnetic effect, if it exists, shows up in weighing mode without a readily apparent reciprocal effect in the velocity mode, begging questions about systematic errors at the very foundation of the new measurement system. The hypothetical force is caused by the coil current changing the magnetic field, producing an unaccounted force that is systematically modulated with the weighing current. Here we show that this diamagnetic force exists, but the additional force does not change the equivalence between weighing and velocity measurements. We reveal the unexpected way that symmetry is preserved and show that for typical materials and geometries the total relative effect on the measurement is ≈1×10−9
- …