Jan Kucera

The quantum Hall impedance standard

Alternating current measurements of double-shielded quantum Hall devices have revealed a fascinating property of which only a quantum effect is capable: it can detect its own frequency dependence and convert it to a current dependence which can be used to eliminate both of them. According to an experimentally verified model, the residual frequency dependence is smaller than the measuring uncertainty of 1.3 ? 10?9?kHz?1. In this way, a highly precise quantum standard of impedance can be established, without having to correct for any calculated frequency dependence and without the need for any artefact with a calculated frequency dependence. Nothing else like that is known to us and we hope that our results encourage other national metrology institutes to also apply it to impedance metrology and further explore its beautiful properties.

Calculable resistors of coaxial design

1000 Ω and 1290.64 Ω coaxial resistors with calculable frequency dependence have been realized at PTB to be used in quantum Hall effect-based impedance measurements. In contradistinction to common designs of coaxial resistors, the design described in this paper makes it possible to remove the resistive element from the shield and to handle it without cutting the outer cylindrical shield of the resistor. Emphasis has been given to manufacturing technology and suppressing unwanted sources of frequency dependence. The adjustment accuracy is better than 10 µΩ Ω−1.

An HF coaxial bridge for measuring impedance ratios up to 1 MHz

A four-terminal pair coaxial ac bridge developed for calibrating both resistance and capacitance ratios and working in the frequency range from 100?kHz up to 1?MHz is described. A reference inductive voltage divider (IVD) makes it possible to calibrate ratios 1:1 and 10:1 with uncertainty of a few parts in 105. The IVD is calibrated by means of a series?parallel capacitance device (SPCD). Use of the same ac bridge with minimal changes for calibrating the SPCD, IVD and unknown impedances simplifies the whole calibration process. The bridge balance conditions are fulfilled with simple capacitance and resistance decades and by injecting voltage supplied from the auxiliary direct digital synthesizer. Bridge performance was checked on the basis of resistance ratio measurements and also capacitance ratio measurements.

A Novel Optical Method of Dimension Measurement of Objects with Circular Cross-section

Common optical methods for dimension measurement apply an imaging sensor with lens. The presence of the lens in the camera (and sometimes also in the employed illuminator) increases the total dimensions of the measuring set-up. The aberrations of the lens represent a source of uncertainty. In order to simplify the measuring set-up and to reduce its overall dimensions, the proposed method applies a measuring set-up that contains no lens (it employs an imaging sensor without lens and two point light source). In this paper, the application of this method for dimension measurement of objects with circular cross-section is described. Also, several issues related to its implementation are discussed and its performance is illustrated using experimental results

Using a Current Loop and Homogeneous Primary Winding for Calibrating a Current Transformer

This paper presents two methods for determining the ratio error and the phase displacement of a protective current transformer (PCT) with a transformation ratio of 10 kA/1 A and a measuring current transformer (MCT) with a transformation ratio of 20 kA/5 A. The primary conductor passed by a current (10 or 20 kA) placed in the center of the toroid is replaced by a current loop with ten turns placed in the center of the toroid. In the second case, the conductor is replaced by ten turns uniformly distributed along the circumference of the toroid. The primary current (2 or 1 kA) is measured in both cases using a toroidal current comparator, and the secondary current difference is evaluated by means of a current transformer (CT) error measurement system. The errors were also measured using a CT analyzer.

Dimension Measurement of Objects With Circular Cross Section Using Point Light Sources and an Image Sensor Without Lens

Common optical methods for dimension measurement apply an image sensor with a lens. The presence of the lens in the camera (and sometimes in the employed illuminator as well) increases the total dimensions of the measuring setup. Furthermore, the aberrations of the lens represent a source of uncertainty. In order to simplify the measuring setup and to reduce its overall dimensions, the method proposed in this paper applies a measuring setup that contains no lens - it employs an image sensor without a lens and two point light sources that illuminate the measured object. In this paper, the application of this method for dimension measurement of objects with a circular cross section is described. In addition, several issues related to the methods implementation are discussed, and its performance is illustrated using experimental results.

Self-compensating networks for four terminal-pair impedance definition in current comparator bridges

The four-terminal-pair (4TP) definition of impedance standards allows reaching ultimate accuracy in impedance metrology. In general, the 4TP definition requires dedicated circuitry to be included in the bridge network and the attainment of auxiliary bridge balances during the measurement. A careful choice of the network topology allows the bridge to be self-compensating: the 4TP definition is in large part achieved by the behavior of the network itself without any adjustment. The additional circuitry required for impedance definition can therefore be simpler, the balancing procedure becomes easier, and a more robust 4TP can be achieved. This paper analyzes a current comparator bridge network with a topology featuring self-compensation. A digitally assisted test bridge has been implemented; test measurements on ac resistance comparison in the 25-100-Ω range at kilohertz frequencies are reported.

Self-Compensating Networks for Four-Terminal-Pair Impedance Definition in Current Comparator Bridges

The four terminal-pair definition of standards allows to reach ultimate accuracy in impedance metrology. The four terminal-pair definition requires dedicated circuitry to be included in the bridge network, and the reach of auxiliary bridge balances during the measurement. A careful choice of the network topology allows the bridge to be self-compensating: the four terminal-pair definition is in large part achieved by the behaviour of the network itself, without any adjustment. The additional circuitry required for impedance definition can therefore be simpler, the balancing procedure becomes easier, and a more robust four terminal-pair definition is achieved. This paper analyses a current comparator bridge network with a topology featuring self-compensation. A digitally-assisted test implementation was realized; test measurements on ac resistance comparison in the 25Ω to 100Ω range, at kHz frequency, are reported.

Influence of humidity contained in building material on wedge diffraction

The aim of the paper is to show the influence of humidity contained in real building materials on diffraction part of the field in the vicinity of a wedge-shaped obstacle. Field measurement around both dry and wet wedge formed by real building material was performed to get an idea what the influence of water content of the building material is on wedge diffraction. The measured results are compared with theoretical prediction by Uniform Theory of Diffraction. The results can be used for improvement of propagation prediction models in urban areas.