Beat Jeckelmann

Determination of the Planck constant with the METAS watt balance

The METAS watt balance project was initiated slightly more than a decade ago. Over this time, the apparatus has been through an uninterrupted series of upgrades that have improved its reliability to a point where continuous series of measurements can be taken fully automatically over periods of several months. A comprehensive analysis of possible systematic errors has now been completed and a large set of data has been analysed to calculate a value for the Planck constant h. This paper describes the watt balance in detail, explains the data acquisition and analysis thoroughly and presents the uncertainty budget. The value of the Planck constant determined with our apparatus is h = 6.626?069?1(20) ? 10?34?J?s with a relative standard uncertainty of 0.29 ? 10?6. This value differs from the 2006 CODATA adjustment by 0.024??W?W?1.

Tracing Planck's constant to the kilogram by electromechanical methods

Among the priority tasks in the further development of the International System of Units is the redefinition of the kilogram based on fundamental constants. One of the strategies pursued today is to relate mass to Plancks constant h using the equivalence between mechanical and electrical energies. In this paper, possible experimental approaches in this direction are described. The approach which promises to reach the required uncertainty at the earliest is the concept of the moving-coil watt balance. The status of the different watt balance experiments is reviewed in detail.

A proposal for a new moving-coil experiment

A new type of moving-coil watt balance is under construction at the Swiss Federal Office of Metrology (OFMET). The aim of the experiment is the monitoring of the kilogram by means of the electrical quantum standards with a relative uncertainty of /spl les/10/sup -8/. The paper presents the main features of the proposed instrument.

The quantum Hall effect as an electrical resistance standard

The quantum Hall effect (QHE) provides an invariant reference for resistance linked to natural constants. It is used worldwide to maintain and compare the unit of resistance. The reproducibility reached today is almost two orders of magnitude better than the uncertainty of the determination of the ohm in the International System of Units. This article is a summary of a recently published review article which focuses mainly on the aspects of the QHE relevant for its metrological application.

The quantized Hall resistance: towards a primary standard of impedance

In this paper, it is shown that a quantum Hall resistor (QHR) which exhibits a proportionality relationship between the deviation of the Hall resistance from RK/i and the ac dissipation in the system, represented by ρxx, can be used as a primary standard of ac resistance. As an example, a calculable quadrifilar resistor was calibrated against the QHR at kilohertz frequencies. The agreement between the calibration using the QHR and the calculated frequency dependence of the quadrifilar resistor is better than 4 parts in 10 8 at 1 kHz. This result is achieved despite the frequency and current dependence of the ac-QHR. The most important criterion to achieve accurate measurements using an ac-QHR standard is to extrapolate the value of the Hall resistance to zero dissipation.

Evaluation of the local value of the Earth gravity field in the context of the new definition of the kilogram

A method is presented that can be used for the evaluation of the value of the Earth gravity field at any defined position inside or outside an instrument used for physical or metrological experiments. After a brief presentation of the gravimeters used and the evaluation of their respective uncertainties, we describe in detail the procedure developed to determine the gravitational acceleration g at the point of interest. Finally, a realistic evaluation of the uncertainty budget shows that the method can be used in many metrological applications and especially in all experiments aiming at a new definition of the kilogram by virtual comparison of mechanical and electromagnetic power.In this paper, we denote with g the Earth gravity field or gravitational acceleration, which is the sum of all accelerations felt by a free falling body at the surface of the Earth.

Effects of metallic gates on AC measurements of the quantum Hall resistance

Using a sample with a split back gate, a linear frequency dependence of the AC quantum Hall resistance (QHR) was observed. The frequency coefficient, which is due to dielectric losses produced by leakage current between the two-dimensional electron gas (2DEG) and the back gates, can be turned from a positive to a negative value by increasing the back-gate voltage. More interestingly, by removing these back gates, the losses can be considerably reduced, leading to a residual frequency coefficient on the order of (0.03/spl plusmn/0.03)/spl times/10/sup -6//kHz. Moreover, at 1 kHz, an extremely flat plateau was observed over a magnetic field range of 1.4 T. These results clearly indicate that the audio frequency dependence of the QHR is to a large extent related to the measurement apparatus and does not originate from the physical transport properties of the 2DEG.

Investigating the use of multimeters to measure quantized hall resistance standards

A new generation of digital multimeters was used to compare the ratios of the resistances of wire-wound reference resistors and quantized Hall resistances (QHRs). Specifically, a digital multimeter was used to compare the DC voltage ratio of a QHR sample with that of a reference resistor connected in series with the sample. The accuracies are better than 0.1 p.p.m. for ratios as large as 4:1 if the multimeters are calibrated with a Josephson array. >

The European ACQHE project: modular system for the calibration of capacitance standards based on the quantum Hall effect

Starting in 1998 a project funded by the European Commission has been carried out in a co-operation of seven partners. The aim of this project was to establish a measurement system which allows the calibration of standard capacitors in terms of R/sub K-90/. The whole system comprises suitable quantum Hall samples, an automated bridge system and auxiliary devices to calibrate and characterize the whole set-up. The uncertainty for the calibration of a 10-pF capacitor is about 1 part in 10/sup 7/.

Status of the METAS watt balance experiment

The Swiss Federal Office of Metrology and Accreditation (METAS) has been continuing to work toward a 100-g watt balance apparatus with an uncertainty of 1 /spl times/10/sup -8/ W/W. Currently the experiment is producing preliminary measurements reproducible at the 1 /spl times/10/sup -6/ W/W level. Our progress, measurements, and plans for the future are presented.