# METLAB - Metrology of electrical quantities

**CTU FEE, Department of Measurement, Technická 2, 166 27 Praha 6**

Phone: 224 352 191, Fax: 233 339 929

http://measure.feld.cvut.cz/vyzkum/metlab

Phone: 224 352 191, Fax: 233 339 929

http://measure.feld.cvut.cz/vyzkum/metlab

## Who are we?

Jaroslav Boháček

coordinates research activities aimed at employment of the quantum Hall effect in calibrations of impedance standards and precision wideband LCR meters at frequencies up to 1 MHz.

Radek Sedláček

is mainly engaged in designing electronic modular units of special facilities for impedance calibrations.

Jan Kučera

participates in development of four-terminal-pair bridges for calibrations of resistance and capacitance standards at frequencies up to 1 MHz.

Jan Kotek

ensures fabrication of prototypes and final versions of the designed devices.

## What research are we doing?

Since 1993, increased attention has been paid to investigating metrological applicability of the AC quantum Hall effect (QHE). After finding that the unit
of resistance can be reproduced by means of AlGaAs/GaAs heterostructure devices with an uncertainty of the order of 1 part in 10^{-7} over a frequency range from
DC to at least 5 kHz, a number of metrological laboratories started to use these devices as reference standards in AC calibrations of resistance and, later,
also capacitance standards.

In the Czech Republic, the problems of AC QHE-based impedance calibrations have been solved within the framework of three projects supported by the Grant Agency of the Czech Republic and coordinated by our department. In addition to standards and bridges for resistance and capacitance calibrations, facilities for calibrating standards of self- and mutual inductance have been developed. At present, main attention is paid to increasing the frequency range, in which the calibrations are made.

## What is the purpose of our research?

Our present research is mainly devoted to problems of precision measurements of electrical quantities. Standards, bridges and procedures for a newly formed system for AC QBE-based calibrations of impedance standards are being developed, attention being also paid to realization of facilities for calibrating precision wideband LCR meters.

## What are we specifically concerned with?

### Special standards:

*Calculable standards*Calculable standards of various designs (coaxial, quadrifilar and octofilar resistors) have been realized for precision measurements of frequency dependences of both conventional and quantum resistance standards.

*Transfer standards*10 × 100 Ω a 10 × 1000 Ω Hamon transfer standards for a frequency range up to 5 kHz have been realized to be used in precision measurements of resistance ratios and in calibrations of inductive voltage dividers.

### Special measuring devices and their modular units:

*Electronic modular units of special measuring devices*In case of need, such units (e.g. precision voltage followers or electronic compensators of unwanted voltage drops) can be used to improve metrological characteristics of measuring devices.

*Reference divider formed by permuted capacitors*This divider is intended for calibrations of inductively coupled ratio arms of bridges for 1:10 comparisons of resistance or capacitance standards.

*Ratio arms of high-frequency bridges*With an intention to find an optimum way of winding, several versions of 1:10 inductively coupled ratio arms have been prepared and calibrated by comparison with the above reference capacitance divider.

*Digitally controlled 6-bit inductive voltage dividers*

These units will serve as balance controls of high-frequency bridges.

## Who supports our research financially?

Our research is funded from the MSM6840770015 Programme of the Ministry of Education, Youth and Sports of the Czech Republic, and from the Metrology Development Programme of the Czech Office for Standards, Metrology and Testing.

## Who do we collaborate with?

- We fabricate special standards for foreign metrology institutes:
- We realized a 12906,4 Ω calculable resistance standard for the Physikalish-Technische Bundesanstalt in Braunschweig in the framework of research activity 5.2 of the European SMT project "Modular System for the Calibration of Capacitance Standards Based on the Quantum Hall Effect".
- We realized 100 Ω a 1000 Ω calculable resistance standards for Glówny Urziad Miar in Warsaw.
- We realized 100 Ω a 1000 Ω calculable resistance standards for Istituto Nazionale di Ricerca Metrologica in Turin.

- We participate in international EURAMET comparisons:
- Comparison No. 432 "Frequency Performance of 12906.4 Ω and 6453.2 Ω Reference Resistors for AC Quantum Hall Effect Experiments" (coordination)
- Comparison No. 607 "100 mH Inductance Intercomparison"

- . We established mutually beneficial liaisons with a number of foreign metrology institutions. Papers prepared jointly with the following institutions
have been published:

Physikalisch-Technische Bundesanstalt, Braunschweig, Germany

National Physical Laboratory, Teddington, United Kingdom

Bureau International des Poids et Mesures, Sèvres, France

Electrotechnical Laboratory, Tsukuba, Japan

National Research Council, Ottawa, Canada

Istituto Nazionale di Ricerca Metrologica, Turin, Italy

National Metrology Laboratory, Pretoria, South Africa

## Selected publications

- Hartland A. - Kibble B. P. - Rodgers P. J. - Boháček J.: AC Measurements of the Quantized Hall Resistance. IEEE Trans. Instr. Meas., 1995, sv. 44, č. 2, str. 245-248.
- Boháček J. - Svoboda P. - Vašek P.: AC QHE-Based Calibration of Resistance Standards. IEEE Trans. Instr. Meas., 1997, sv. 46, č. 2, str. 273-275.
- Boháček J.: AC QHE-Based Resistance and Capacitance Calibrations. IEE Proc.-Sci. Meas. Technol., 2000, sv. 147, č. 4, str. 190-192.
- Boháček J. - Wood B. M.: Octofilar Resistors with Calculable Frequency Dependence. Metrologia, 2001, sv. 38, č. 3, str. 241-247.
- Boháček J.: EUROMET Project 432: Frequency Performance of 12906 Ω and 6453 Ω Reference Resistors for AC Quantum Hall Effect Experiments. Metrologia, 2002, sv. 39, č. 2, str.231-237.
- Melcher J. - Schurr J. - Pierz K. - Williams J. M. - Giblin S. P. - Cabiati F. - Callegaro L. - Marullo-Reedtz G. - Cassiago C. - Jeckelmann B. - Jeanneret B. - Overnay F. - Boháček J. - Říha J. - Power O. - Murray J. - Nunes M. - Lobo M. - Godinho I.: The European ACQHE Project: Modular System for the Calibration of Capacitance Standards Based on the Quantum Hall Effect. IEEE Trans. Instr. Meas., 2003, sv. 52, č. 2, str. 563-568.
- Boháček J.: A QHE-Based System for Calibrating Impedance Standards. IEEE Trans. Instr. Meas., 2004, sv. 53, č. 4, str. 977-980.
- Callegaro L. - D´Elia V. - Boháček J.: Four-Terminal-Pair Inductance Comparison Between INRIM and CTU. IEEE Trans. Instr. Meas., 2009, sv. 58, č. 1, str. 87-93.
- Sedláček R. - Boháček J.: Bridges for Calibrating Four-Terminal-Pair Standards of Self-Inductance at Frequencies up to 10 kHz. Meas. Sci. Technol. 20 (2009) 025105, doi: 10.1088/0957-0233/20/2/025105.
- Kučera J. - Vollmer E. - Schurr J. - Boháček J.: Calculable Resistors of Coaxial Design. Meas. Sci. Technol. 20 (2009) 095104, doi: 10.1088/0957-0233/20/9/095104.
- Kučera J. - Sedláček R. - Boháček J.: A New Capacitance Device for Calibration of N:1 HF Inductive Voltage Dividers. 2010 Conference on Precision Electromagnetic Measurements Digest, pp. 390-391. IEEE, Daejeon 2010. ISBN 978-1-4244-5.
- Boháček J. - Horská J. - Sedláček R.: Comparison of Frequency Dependences of Resistance Standards Made from Surface Mount Resistors. 2010 Conference on Precision Electromagnetic Measurements Digest, pp. 647-648. IEEE, Daejeon 2010. ISBN 978-1-4244-5.