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Doctoral Thesis Czech Technical University in Prague Faculty of Electrical Engineering Doctoral Thesis June, 2020 Michal Ulvr Czech Technical University in Prague Faculty of Electrical Engineering Department of Measurement AC MAGNETIC FLUX DENSITY STANDARDS AND THEIR USE IN METROLOGY Doctoral Thesis Michal Ulvr Prague, June 2020 Ph.D. Programme: P2612 - Electrical Engineering and Information Technology Branch of study: 2601V006 - Measurement and Instrumentation Supervisor: Doc. Ing. Petr Kašpar, CSc. Declaration I declare, that this doctoral thesis is based at all my own work and I have cited all sources I have used in the bibliography. In Prague, June 22nd, 2020 Prohlášení Prohlašuji, že jsem předloženou disertační práci vypracoval samostatně a že jsem uvedl veškerou použitou literaturu. V Praze, 22. 6. 2020 …………......………………….. Michal Ulvr Acknowledgements I would like to express my gratitude to my supervisor, associate professor Petr Kašpar, and to my colleague, Dr. Josef Kupec, for their scientific and university guidance, invaluable comments and patience with my studies. Also I would like to thank my family for their support and patience throughout the study period. Abstract: This dissertation describes the development of AC magnetic flux density standards and their use in metrology. The dissertation focuses mainly on the design and realization of new standards, which will extend the existing ways of calibrating AC magnetometers in the primary laboratory of the Department of Electromagnetic Quantities of the Czech Metrology Institute. Various coil systems and various types of solenoids are commonly used for calibrating magnetometers (teslameters with a Hall probe, or 3-axis coil probe analyzers) up to several mT. The maximum value of the AC magnetic flux density generated in the center of the standard, and its homogeneity, depend on the dimensions and the type of the coil standard and the winding parameters. The induction and parasitic capacity of the winding affects the value of the resonance frequency and thus the frequency range in which the standard can be used. An electromagnet has to be used when a higher magnetic flux density value needs to be generated for calibration up to hundreds of mT. Here, some standard sensor (Hall probe, search coil) with traceable calibration should be used for precise measurements of the AC magnetic flux density generated in the center of the air gap. In the first part of the dissertation, various types of coil standards (Helmholtz, Maxwell, Garrett, Barker, Braunbek, etc.) and available AC electromagnets are described and are compared in terms of their parameters and their uses in AC applications. The standards for AC calibrations available in the primary laboratory of the Department of Electromagnetic Quantities of the Czech Metrology Institute before starting this dissertation work are also presented here. The second part of the dissertation describes the design and realization of the Helmholtz-type single-layer coil standard for calibrating magnetometers in the frequency range up to 100 kHz. The standard was designed primarily for calibrating magnetic field analyzers with a 3-axis coil probe (EFA 300, ELT 400). An AC magnetic flux density value of 105 μT up to 40 kHz and an AC magnetic flux density value of 40 μT at a frequency of 100 kHz can be generated by means of the coil standard that is developed. The serial resonance effect was used in order to generate a magnetic flux density of 105 μT up to 100 kHz. For this purpose, a capacitive programmable array was designed and realized. This array is connected in series with the winding of the coil standard. To ensure the metrological traceability of the generated AC magnetic flux density, a calibration method was developed involving special search coils and an AC current shunt with calibrated AC/DC differences, by which the coil standards can be calibrated up to 100 kHz with expanded uncertainty of (0.12 to 0.25)%. This section of the dissertation also describes the possibilities of using coil standards in metrology. The last part of the dissertation is devoted to the design and realization of the system with an AC electromagnet, which can be used for calibrating teslameters with a Hall probe up to 1 T at low frequencies (mainly at a frequency of 50/60 Hz). An AC electromagnet with a UNICORE core has been developed from oriented electrotechnical steel with a cross-section of 36 cm2 and with a length of the air gap of 10 mm. A single-layer, a double-layer and a 10-layer special PCB search coil were designed and fabricated for precise measurements/adjustments of the AC magnetic flux density generated in the center of the air gap, ensuring the metrological traceability of the teslameter calibration using the system with an AC electromagnet. The serial resonance effect was used when powering the electromagnet. It was possible to use a conventional amplifier for power supply thanks to the HV capacitors connected in series with the electromagnet winding. A feedback was also implemented to improve the stability of the AC magnetic flux density generated inside the air gap. The value of the generated AC magnetic flux density can be measured/adjusted in the center of the air gap with expanded uncertainty of 0.2%. To extend the frequency range of the calibrations, an AC electromagnet made from amorphous MetGlass 2605HB1 material was also realized, enabling it to generate magnetic flux density of about 100 mT up to a frequency of 1 kHz. Keywords: AC magnetic flux density, calibration, coil standard, electromagnet, metrology. Abstrakt: Tato dizertační práce se zabývá etalony střídavé magnetické indukce a jejich využitím v metrologii. Práce je zaměřena především na návrh a realizaci nových etalonů, které by rozšířily stávající možnosti kalibrací střídavých rozsahů magnetometrů v primární laboratoři oddělení elektromagnetických veličin Českého metrologického institutu. Pro kalibrace magnetometrů (teslametrů s Hallovou sondou nebo analyzátorů elektromagnetického pole s 3-osou cívkovou sondou) do několika mT se běžně využívají různé cívkové systémy nebo různé typy solenoidů. Maximální hodnota generované střídavé magnetické indukce ve středu etalonu a její homogenita závisí na rozměrech a typu etalonu a na parametrech vinutí. Z parametrů vinutí etalonu je nejdůležitější indukčnost a parazitní kapacita, která ovlivňuje velikost rezonanční frekvence a tím i frekvenční rozsah, ve kterém lze etalon používat. Pro kalibrace do vyšších hodnot střídavé magnetické indukce (stovky mT) je nutné použít silnější zdroj pro generování magnetické indukce (střídavý elektromagnet) ve spojení s etalonem (etalonový senzor), kterým se nastavená hodnota magnetické indukce ve vzduchové mezeře elektromagnetu přesně měří. V první části dizertační práce jsou popsány a srovnány různé typy cívkových etalonů (Helmholtz, Maxwell, Garrett, Barker, Braunbek atd.) a dostupných střídavých elektromagnetů z hlediska jejich parametrů a využití ve střídavých aplikacích. Také jsou zde popsány etalony pro střídavé kalibrace dostupné před zahájením řešení této dizertační práce v primární laboratoři oddělení elektromagnetických veličin Českého metrologického institutu. Druhá část práce je věnována návrhu a realizaci jednovrstvého cívkového etalonu Helmholtzova typu pro kalibrace magnetometrů v rozsahu do 100 kHz. Tento etalon byl navržen primárně pro kalibrace analyzátorů magnetického pole s 3-osou cívkovou sondou (EFA 300, ELT 400). Tímto etalonem bylo možné generovat střídavou magnetickou indukci 105 μT do 40 kHz a 40 μT na frekvenci 100 kHz. Aby bylo možné generovat hodnoty magnetické indukce 105 μT až do 100 kHz, byla využita sériové rezonance. Pro tento účel byla navržena a realizována programovatelná kapacitní dekáda, která byla připojena do série s vinutím etalonu. Aby byla zajištěna metrologická návaznost generované střídavé magnetické indukce, byla vyvinuta kalibrační metoda zahrnující speciální měřicí cívky a AC/DC bočník s kalibrovanou AC/DC diferencí, kterou je možné kalibrovat cívkové etalony do 100 kHz s rozšířenou nejistotou 0,12 % až 0,25 %. V této části práce jsou popsány možnosti využití cívkových etalonů v metrologii. Poslední část práce je věnována návrhu a realizaci systému se střídavým elektromagnetem, kterým je možné kalibrovat teslametry s Hallovou sondou do 1 T na nízkých frekvencích (především na frekvenci 50/60 Hz). Byl vyvinut střídavý elektromagnet s UNICORE jádrem z orientované elektrotechnické oceli o průřezu 36 cm2 a s délkou vzduchové mezery 10 mm. Pro přesné měření/nastavení generované střídavé magnetické indukce ve vzduchové mezeře byla navržena a realizována jednovrstvá, dvouvrstvá a 10-vrstvá speciální PCB měřicí cívka, která zajišťuje metrologickou návaznost kalibrace teslametrů při použití systému se střídavým elektromagnetem. Při napájení elektromagnetu byla opět využita sériová rezonance. Díky vn kapacitorům zapojeným do série s vinutím elektromagnetu je možné použít pro napájení běžný zesilovač. Pro zlepšení stability generované střídavé magnetické indukce byla také použita zpětná vazba. Tímto systémem je možné měřit/nastavit hodnotu magnetické indukce ve vzduchové mezeře s rozšířenou nejistotou 0,2 %. Pro rozšíření frekvenčního rozsahu kalibrací byl také realizován střídavý elektromagnet z amorfního materiálu MetGlass 2605HB1, díky kterému je možné generovat magnetickou indukci kolem 100 mT do frekvence 1 kHz. Klíčová slova: cívkový etalon, elektromagnet, kalibrace, metrologie, střídavá magnetická indukce. Table of Contents Abbreviations........................................................................................................................3
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