A determination of the Planck constant h using the LNE Kibble balance in air was carried out in the spring of 2017. Substantial improvements since 2014, chiefly related to the mass standard, mechanical alignments, voltage measurements and type A evaluation uncertainties, leads to a h value of 6.626 070 41(38) × 10 -34 J • s, with a relative standard uncertainty of 5.7 × 10 -8 .
After separate developments of the different elements with continuous characterizations and improvements, the LNE watt balance has been assembled. This paper describes the system in detail and gives its first measurements of the Planck's constant h. The value determined in air is h = 6.626 068 8(20) × 10 −34 Js which differs in relative terms by −0.05 × 10 −7 from the h 90 value and by −1.1 × 10 −7 from that of the 2010 CODATA adjustment of h. The relative standard uncertainty associated is 3.1 × 10 −7 .
This paper describes the result of work performed at the Laboratoire National de Métrologie et d'Essais (LNE) aiming at characterizing the metrological performance of analogue-to-digital converters of a commercial digital voltmeter in the 20 Hz to 400 Hz frequency range. In order to reach uncertainties at the 10−6 level, ac–dc thermal transfer techniques have been used to determine the most suitable sampling parameters for these digitizers with respect to the measured signal frequency. Under such conditions, the agreement between the sampling technique and thermal ac–dc transfer is of the order of 2 µV V−1.
This article presents a numerical modeling of a negative corona caused by an overvoltage pulse (∼250%), in a point-to-plane electrode system. The field value applied to the cathode is high, thus, the numerical simulation described in this article attempts to show that the field-effect emission can be responsible for the ignition of the corona and for its first stage of development, while the positive-ion bombardment is responsible for sustaining the discharge during the current decay phase. A time-dependent enhancement factor is introduced in the classical Fowler–Nordheim relationship in order to model the switch on of some emissive site at the cathode surface. Preliminary experiments were carried out in order to better understand the ignition and development of the corona. The role of the field-effect emission is underlined and the dimension of the corona is optically determined. The negative corona current pulse and its associated emitted UV light are computed and compared to experimental results.
This paper presents a numerical simulation of the first negative corona
in SF6 at atmospheric pressure, in a point-to-plane electrode
system. A few experiments are first carried out in order to acquire
a basic knowledge of the physical processes involved in the first
negative corona. Since it does not seem convincing that photoemission
would be the predominant secondary process at the cathode surface,
field effect emission will be introduced into the numerical modelling
of the ignition and development of the first negative corona. The
axial and radial development of the discharge is also optically measured.
Continuity equations of electron, positive- and negative-ion densities
are numerically solved on a non-uniform mesh with
a monotonic upwind scheme for conservation law (MUSCL) method. These equations
are coupled with Poisson's equation by using the classical method
of disks introduced by Davies. The novelty of this model bears upon
the choice of the boundary conditions which take field effect emission
into account. According to the numerical simulation, this secondary
effect could indeed explain the fast rise time of the typical negative
corona current pulse, and enables numerical simulation results to
be in agreement with the experimental ones.
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Alignments of watt balance experiments are necessary to achieve a relative uncertainty at a level of few parts in 10 8 . This paper briefly describes the LNE watt balance and concentrates on adjustments made to minimize the coil movements during weighing mode. The parasitic forces and torques involved in these movements are estimated by a mathematical model. Some of the calculated parasitic forces are compared with an evaluation done by studying the yaw movement of the beam.
Breakdown sequence in SF6 of an electrode arrangement which
represents the contacts of a circuit-breaker is investigated at pressures up
to 8 bar under positive impulse voltages. The Schlieren frames point out the
role played by the cathode as a source emitting electrons by field effect
emission. Photomultiplier records demonstrated, at Pd = 2 bar, that the
discharge's formative time strongly decreases: from 1 µs at pressure lower
than Pd, down to 150 ns at pressure higher than Pd. A change in the
discharge regime is associated with this transition. An experimental
investigation, using photomultipliers and Schlieren devices, allows us to
describe both breakdown sequences. At low pressures, there is a critical
volume at the anode. Nevertheless, it is a negative discharge which is
responsible for the breakdown although the geometrical electrical field at the
cathode boundary is about 60 kV cm-1. At high pressures, there is no
critical volume. However, a positive discharge develops across the gap.
Physical considerations taking into account the electron energy are proposed
to explain the mechanisms involved in both types of discharge.
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