30 research outputs found

    Precision calculations of the characteristic impedance of complex coaxial waveguides used in wideband thermal converters of AC voltage and current

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    The article presents precision and numerically stable method of calculation of the characteristic impedance of cylindrical multilayer waveguides used in high-precision wideband measuring instruments and standards, especially calculable thermal converters of AC voltage and precision wideband current shunts. Most of currently existing algorithms of characteristic impedance calculation of such waveguides are based upon approximations. Unfortunately, application of such methods is limited to waveguides composed of a specific, usually low number of layers. The accuracy of approximation methods as well as the number of layers is sometimes not sufficient, especially when the coaxial waveguide is a part of precision measurement equipment. The article presents the numerically stable matrix analytical formula using exponentially scaled modified Bessel functions to compute characteristic impedance and its components of the cylindrical coaxial multilayer waveguides. Results obtained with the developed method were compared with results of simulations made using the Finite Element Method (FEM) software simulations. Very good agreement between results of those two methods were achieved

    CCE 92-05 intercomparison of ac-dc voltage transfer standards at high frequencies (1-50 MHz)

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    The method for extending the frequency range of the RF power sensor calibration

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    Teма дисертације је унапређен метод еталонирања радио-фреквенцијских (РФ) сензора снаге у фреквенцијском опсегу испод 10 МHz. Метод подразумева одређивање фактора еталонирања комерцијалних сензора средње снаге, као најбитније карактеристике која се проверава приликом њиховог еталонирања. Критичне тачке у реализацији метода су биле селекција одговарајућег еталона РФ снаге у опсегу ниских фреквенција и постизање прихватљиве мерне несигурности. С обзиром да је један од основних услова истраживања био да се развијени метод реализује применом мерне опреме којом располаже већина метролошких лабораторија из области РФ домена, што подразумева одсуство типичног еталона РФ снаге у поменутом опсегу, одабрани еталон је требало да задовољи различите услове по питању својих метролошких карактеристика. Међутим, изналажење одговарајућег еталона је био неопходан, али не и довољан услов за успешну реализацију метода. Формирање мерног ланца и успостављање таквог мерног поступка који ће обезбедити прихватљиву мерну несигурност, овом истраживању даје посебан значај. Дисертација обухвата анализу постојећих еталона РФ снаге и метода еталонирања сензора РФ снаге, развој новог метода, анализу мерне несигурности и постигнута побољшања метода са резултатима мерења. Побољшање метода се односи на вишеструко смањење мерне несигурности. Валидација метода еталонирања сензора је извршена у Техничком опитном центру Војске Србије, поређењем експерименталних резултата са познатим вредностима фактора еталонирања различитих типова сензора. Реализованим истраживањем успешно је потврђена дефинисана хипотеза дисертације да се може реализовати метод еталонирања сензора снаге у опсегу испод 10 MHz при одсуству одговарајућег еталона РФ снаге са прихватљивом мерном несигурношћу. Крајњи резултат истраживања јесте успостављена следивост РФ снаге у фреквенцијском опсегу испод 10 МHz, на основу које су проширене мерне могућности метролошке лабораторије Техничког опитног центра Војске Србије. Корисницима мерне опреме метод обезбеђује следивост РФ снаге у опсегу ниских фреквенција и смањење несигурности мерења РФ снаге сензорима и до седамдесет процената, корекцијом резултата мерења на основу добијених фактора еталонирања. Различите теоријске и практичне анализе, експериментални резултати и на основу њих донети закључци, спроведеном истраживању дају технички и научни значај за РФ метролологију у целини.Tema disertacije je unapređen metod etaloniranja radio-frekvencijskih (RF) senzora snage u frekvencijskom opsegu ispod 10 MHz. Metod podrazumeva određivanje faktora etaloniranja komercijalnih senzora srednje snage, kao najbitnije karakteristike koja se proverava prilikom njihovog etaloniranja. Kritične tačke u realizaciji metoda su bile selekcija odgovarajućeg etalona RF snage u opsegu niskih frekvencija i postizanje prihvatljive merne nesigurnosti. S obzirom da je jedan od osnovnih uslova istraživanja bio da se razvijeni metod realizuje primenom merne opreme kojom raspolaže većina metroloških laboratorija iz oblasti RF domena, što podrazumeva odsustvo tipičnog etalona RF snage u pomenutom opsegu, odabrani etalon je trebalo da zadovolji različite uslove po pitanju svojih metroloških karakteristika. Međutim, iznalaženje odgovarajućeg etalona je bio neophodan, ali ne i dovoljan uslov za uspešnu realizaciju metoda. Formiranje mernog lanca i uspostavljanje takvog mernog postupka koji će obezbediti prihvatljivu mernu nesigurnost, ovom istraživanju daje poseban značaj. Disertacija obuhvata analizu postojećih etalona RF snage i metoda etaloniranja senzora RF snage, razvoj novog metoda, analizu merne nesigurnosti i postignuta poboljšanja metoda sa rezultatima merenja. Poboljšanje metoda se odnosi na višestruko smanjenje merne nesigurnosti. Validacija metoda etaloniranja senzora je izvršena u Tehničkom opitnom centru Vojske Srbije, poređenjem eksperimentalnih rezultata sa poznatim vrednostima faktora etaloniranja različitih tipova senzora. Realizovanim istraživanjem uspešno je potvrđena definisana hipoteza disertacije da se može realizovati metod etaloniranja senzora snage u opsegu ispod 10 MHz pri odsustvu odgovarajućeg etalona RF snage sa prihvatljivom mernom nesigurnošću. Krajnji rezultat istraživanja jeste uspostavljena sledivost RF snage u frekvencijskom opsegu ispod 10 MHz, na osnovu koje su proširene merne mogućnosti metrološke laboratorije Tehničkog opitnog centra Vojske Srbije. Korisnicima merne opreme metod obezbeđuje sledivost RF snage u opsegu niskih frekvencija i smanjenje nesigurnosti merenja RF snage senzorima i do sedamdeset procenata, korekcijom rezultata merenja na osnovu dobijenih faktora etaloniranja. Različite teorijske i praktične analize, eksperimentalni rezultati i na osnovu njih doneti zaključci, sprovedenom istraživanju daju tehnički i naučni značaj za RF metrolologiju u celini.The topic of this dissertation is an improved method for radio-frequency (RF) power sensor calibration within the frequency range below 10 MHz. The method involves the calibration factor determination of commercial RF power sensors, as the most important characteristic, which measures during their calibration. The critical points in the method realization were the selection of the appropriate RF power standard in the low-frequency range and the achievement of acceptable measurement uncertainty. Given that one of the basic conditions of the research was that the developed method be realized with measuring equipment available to most metrology laboratories in the field of RF domain, which implies the absence of a typical RF power standard in the mentioned range, the selected standard had to satisfy various conditions terms of its metrological characteristics. However, the selection of an appropriate standard was a requirement but not a sufficient condition for the successful method implementation. The forming of the measuring chain and the establishment of such a measurement procedure that provided acceptable measurement uncertainty, gave this research a special importance. The dissertation includes the analysis of the existing RF power standards and methods for RF power sensor calibration, the development of a new method, the analysis of a measurement uncertainty, improvement of the achieved method and experimental measurement results. The method improvement refers to the multiple reduction of measurement uncertainty. Validation of the method for power sensor calibration was performed at the Technical Test Center of Serbian Armed Forces, by comparing experimental results with known calibration factor values of different types of sensors. The possibility to realize the method for power sensor calibration in the range below 10 MHz in the absence of an appropriate RF power standard with acceptable measurement uncertainty is the hypothesis of the dissertation, which is confirmed by the successful realization of this research. The final result of the research is the established traceability of RF power in the frequency range below 10 MHz, which lead to the Technical Test Center of Serbian Armed Forces measuring capabilities expansion. The method ensures users the traceability of RF power within the low-frequency range and the reduction of the uncertainty of RF power measurements by sensors up to seventy percent, by applying the correction of measurement results using the obtained calibration factor values. Various theoretical and practical analyses, experimental results and derived conclusions, give the conducted research the technical and scientific importance for RF metrology as a whole

    Characterisation of concentrating solar optics by Light Field Method

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    Abstract: This dissertation develops ideas and techniques for the measurement of the light field produced by the concentrating optics that are used in solar thermal power systems. The research focussed on developing a framework and the principles for the implementation of a scalable technology that is suitable, in principle, for cost effective industrial implementation in the field. Investigation from first principles and technological surveys resulted in formulation of a number of model techniques, from which one was developed. A key component of the proposed model was evaluated using a novel reformulation and application of electrical impedance tomography (EIT). This was to implement an information transform effecting a highly non-linear compressive sensing mechanism, offsetting manufacturing and material complexity in the measurement of high solar flux levels. The technique allows sensing of a wide range of phenomena over arbitrary manifolds in three-dimensional space by utilizing passive transducers. An inverse reconstruction method particular to the structure of the device was proposed, implemented, and tested in a full simulation of intended operation. The parameter space of internal configurations of the method were the subject of a uniform, statistical search, with results also indicating geometrical properties of the transform used. A variety of design guides were developed to better optimize the implementation of the techniques in a range of applications.M.Ing. (Mechanical Engineering Science

    The telecommunications and data acquisition report

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    Deep Space Network operations, engineering, and implementation are reported. Developments in Earth-based radiotechnology as applied to other research programs in the fields of Geodynamics, Astrophysics, and programs related to radio searchers (instrumentation and methods) in extraterrestrial areas in the microwave region of the electromagnetic spectrum are also presented

    A.C. losses in superconducting nobium

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    The thesis is introduced by a discussion of the technological importance of developing superconducting materials having low losses at power frequencies. The following two chapters are devoted to a presentation of the reversible magnetic properties of superconductors using the Ginzburg-Landau equations, and a discussion of the irreversible behaviour of real materials in terms of flux pinning and the critical state concept. Following this background discussion, previous work on a.c. losses is reviewed. Particular emphasis is given to the losses below Hc1 and it is shown that, while losses above Hcl can be interpreted using the critical state model, below Hc1 they are only partially understood. Modifications to an electronic wattmeter which enable accurate measurements to be made at 10- 4 WHz- 1 m-2 are discussed. An improved vibrating sample magnetometer, is described, together with the theory and design of an a.c , permeability apparatus used to obtain critical current values. The preparation of a range of niobium samples is described. The techniques employed include annealing, spark-machining, mechanical, chemical and electro-polishing, neutron irradiation and ion-implantation. The magnetization curves, surface profiles and other data for the treated specimens are presented. Measurements of the low frequency losses in these samples at 4.2 K are described. It is shown that in rough samples hysteretic losses arise below Hcl·from the penetration of surface asperities and that the results are in good agreement with an expression, similar to Buchhold’s (1963), which is derived, namely : L =4 μOHm2 f(Hm/HCL) KD where Hm is the peak field, HCL the lower critical field, HCl or HC, D the centre line average height of the surface profile and K a ‘hysteresis factor’. The losses in cold-worked and annealed niobium samples and lead, tin and indium specimens with values for D between 0.33 and 20 μm are found to fit (within a factor of two ) the expression : L = ½ μ0Hm2 (Hm/HCL)2D Different results are observed in smooth samples and explanations for these are suggested. The losses in samples previously penetrated by a large a.c. field are found to be increased by a factor of up to thirty. This is related to trapped flux and ppossible loss mechanisms arc discussed. The losses above Hcl are shown to be reduced in damaged samples. Neutron irradiation induces heavy bulk damage but has little effect on the surface. Mechanical treatment produces large surface currents and is most effective reducing the loss, the dissipation at 50 Hz being below 0.1 W m-2 at fields up to 85 kA(RMS)m- 1 (1500 0e - Peak) in a mechanically polished, annealed polycrystalline sample. Implantation of niobium ions to a depth of 10 nm does not alter the losses. Measurements of the critical currents and flux profiles in two annealed samples are presented and it is shown that a critical state exists within them. The losses above Hcl in both irreversible and annealed samples fit the Ullmaier (1966) expression L = ⅔ μO(Hm - ∆H/2)3/JC, but it is found that equating ∆H/2 with HCl gives critical currents an order of magnitude smaller than those obtained in other measurements. It is shown that ∆H/2 is not constant and that the shielding currents are negligible except near HC

    Particle Physics Reference Library

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    This third open access volume of the handbook series deals with accelerator physics, design, technology and operations, as well as with beam optics, dynamics and diagnostics. A joint CERN-Springer initiative, the “Particle Physics Reference Library” provides revised and updated contributions based on previously published material in the well-known Landolt-Boernstein series on particle physics, accelerators and detectors (volumes 21A,B1,B2,C), which took stock of the field approximately one decade ago. Central to this new initiative is publication under full open acces
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