• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 16
  • 6
  • 5
  • 4
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 42
  • 18
  • 15
  • 13
  • 10
  • 8
  • 8
  • 7
  • 6
  • 6
  • 6
  • 6
  • 5
  • 5
  • 5
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Increasing the Dynamic Range of Audio THD Measurements Using a Novel Noise and Distortion Canceling Methodology

Dunipace, Richard Alan 05 1900 (has links)
The objective of this study was to determine how a new experimental methodology for measuring Total-Harmonic-Distortion (THD) of operational amplifiers functioned when compared with two standard methodologies, and whether the new methodology offers any improvement in noise floor and dynamic range along with distortion canceling of the sine-wave source used in the testing. The new methodology (THD) is being tested against two standard methodologies: Spectral Analysis using a tuned receiver type Spectrum Analyzer with Notch Filter pre-processing, and a digitized Fast Fourier Transform (FFT) using Notch Filter pre-processing. The THD results appear to agree across all methodologies, and across all items of the sample within all methodologies, to within a percent or less. The distortion and noise canceling feature of the new methodology appeared to function as expected and in accordance with theory. The sample tested in the study consisted of thirty-five NE5534 operational amplifiers produced by Texas Instruments, Inc. and purchased from a local store. The NE5534 is a low-noise, low-distortion, operational amplifier that is widely used in industry and is representative of today's best audio amplifiers.

Measurement of Delta-Sigma Converter

Liu, Xiyang January 2011 (has links)
With today’s technology, digital signal processing plays a major role. It is used widely in many applications. Many applications require high resolution in measured data to achieve a perfect digital processing technology. The key to achieve high resolution in digital processing systems is analog-to-digital converters. In the market, there are many types ADC for different systems. Delta-sigma converters has high resolution and expected speed because it’s special structure. The signal-to-noise-and-distortion (SINAD) and total harmonic distortion (THD) are two important parameters for delta-sigma converters. The paper will describe the theory of parameters and test method.


Sweeney, Paul 10 1900 (has links)
International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The advent of a new generation of analog to digital converters (ADC’s) provides the aerospace signal-conditioning engineer with many design advantages, trade-offs and challenges for their next generation of signal conditioning systems. These advantages include increased range, resolution, accuracy, channel-count and sampling rate. However, in order to capitalize on these advantages, it is important to understand the trade-offs involved and to specify these systems correctly. Trade-offs include: • Analog vs. Digital signal conditioning • Implementation issues such as 12-bits vs. 16-bits (or even 24-bits) • Topology issues such as multiplexers vs. multiple ADC’s • Filter-type selection • Sigma-Delta vs. Successive Approximation ADC’s. Specification challenges include: • Total DC error vs. gain and offset (and drift, excitation, DNL, crosstalk, etc.) • ENOB vs. SINAD (or THD, SNR or Noise) • Coherency issues such as filter phase distortion vs. delay This paper will discuss some of these aspects and attempts to produce a succinct specification for the next generation of airborne signal conditioning, while also outlining some of the lessons learned in developing the same.

A Low Total Harmonic Distortion Sinusoidal Oscillator Based on Digital Harmonic Cancellation Technique

Yan, Jun 2012 May 1900 (has links)
Sinusoidal oscillator is intensively used in many applications, such as built-in-self-testing and ADC characterization. An innovative medical application for skin cancer detection employed a technology named bio-impedance spectroscopy, which also requires highly linear sinusoidal-wave as the reference clock. Moreover, the generated sinusoidal signals should be tunable within the frequency range from 10kHz to 10MHz, and quadrature outputs are demanded for coherent demodulation within the system. A design methodology of sinusoidal oscillator named digital-harmonic-cancellation (DHC) technique is presented. DHC technique is realized by summing up a set of square-wave signals with different phase shifts and different summing coefficient to cancel unwanted harmonics. With a general survey of literature, some sinusoidal oscillators based on DHC technique are reviewed and categorized. Also, the mathematical algorithm behind the technique is explained, and non-ideality effect is analyzed based on mathematical calculation. The prototype is fabricated in OnSemi 0.5um CMOS technology. The experimental results of this work show that it can achieve HD2 is -59.74dB and HD3 is -60dB at 0.9MHz, and the frequency is tunable over 0.1MHz to 0.9MHz. The chip consumes area of 0.76mm2, and power consumption at 0.9MHz is 2.98mW. Another design in IBM 0.18um technology is still in the phase of design. The preliminary simulation results show that the 0.18um design can realize total harmonic distortion of -72dB at 10MHz with the power consumption of 0.4mW. The new design is very competitive with state-of-art, which will be finished with layout, submitted for fabrication and measured later.

A Class D Power Amplifier with Passive RC Feedback

Chuang, Yao-Jen 22 August 2005 (has links)
The primary advantage of Class D amplifier is high power efficiency (typically >90%). However, there are two problems in open-loop Class D design: Total Harmonic Distortion (THD) and output dc static current (the power efficiency will be degraded). The THD is rising from non-ideal sample carrier in Pulse Width Modulation circuit, and output dc static current is due to the non-match transfer characteristic in output stage. For designer to have such problems will be a large load. To improve these two problems, we proposed a Class D power amplifier with passive feedback design. Simulation and Measurement results show that the power efficiency is higher than 90% at 250Hz ~ 4KHz. Furthermore, the THD is less than 0.24% at 4 KHz in both simulation and experimental results.

Evaluaton of sound-, current, and vibrations measurements in the Electric Arc Furnace

Ljungqvist, Pär January 2013 (has links)
The aim of this report was to investigate new methods for measuring the condition of the scrap in the electric arc furnace. This was done by evaluating three different methods theoretically and chooses two of them for test in the electric arc furnace in Avesta. Due to lack of time and equipment only Total harmonic distortion (THD) measurements was used. The results show that THD reaches low values during refining. This suggests that all the scrap is melted and the arcs are stable.

Utredning och åtgärder angående övertoner vid pappersindustri / Investigation and measures concerning harmonics in the paper industry

Vesterberg, Henrik January 2018 (has links)
Detta arbete behandlar ämnet elkvalité vid en industri i Sverige. Arbetet utfördes vid Vattenfall Eldistribution och elkvalitégruppen. Elkvalité är ett begrepp som innefattar flera egenskaper hos spänningen i vårt elnät. För Vattenfalls del pratar man om ”God elkvalité” Enligt företaget skall det alltid finnas marginal mellan god elkvalité och gällande standarder och föreskrifter. Svensk Standard EN50160 med tillägget A1 är den gällande standarden inom elkvalité och där detta arbete har som utgångspunkt att leva upp till de nivåer som är beskrivna i standarden. Det är med tonvikt på spänningsdistorsionen detta arbete undersöker, mäter, analyserar, simulerar och beräknar spänningsdistorsionen. Denna industri dras periodvis med en stor variation på spänningsdistorsionen och målet med arbetet går ut på följande: • Att utifrån befintliga mätningar, nätets egenskaper och anslutna laster utreda orsaken till variationerna. • Beskriva fenomenet matematiskt och i tekniska termer. • Föreslå åtgärder som minskar övertonsnivån. Spänningsdistorsionen undersöktes med hänsyn för flera olika driftfall i överliggande elnät samt med industrins egna produktion, den uppmättes under flera månader där man tydligt kan se att den förändras vid olika tidpunkter. Spänningsdistorsionen mäts i procent relativt spänningens grundton och anger hur mycket övertonsinnehåll som finns i en spänning. Det framgick tidigt att strömmen för femte övertonen blev förstärkt när spänningsdistorsionen blev hög, detta undersöktes och beräknades med resultatet att en parallellresonanskrets uppfylls i detta fall. Den faskompenserade kondensatorbanken får samma storlek på reaktans men med motsatt tecken som överliggande nät vid frekvensen 250 Hz. Resonanskretsen förstärkte strömövertonerna och det medförde en ökad spänningsdistorsion. Elnätet och industrins egna produktion undersöktes ifråga om impedanser samt laster.  Kortslutningsströmmar erhölls och beräkning av impedanser för flera olika driftfall genomfördes. Beräkningar visade att det fanns två driftfall i detta elnät som var intressanta för var resonansfrekvensen hamnar, det normala driftfallet och när det maskade 130 kV-nätet går till radiellt nät. Vid radiellt överliggande nät reduceras kortslutningseffekten och det skapar en stor förändring i resonansfrekvensen. Kondensatorbankens storlek är i grundutförandet 27 MVAr men beräknas om till 12 MVAr och där flera nya simuleringar genomförs med programmet PSCAD.  Simuleringar i PSCAD visar att resonansfrekvensen ändras när kondensatorbankens storlek förändras. Fler simuleringar genomfördes med en mindre kondensatorbank med resultatet att spänningsdistorsionen fortfarande blir hög. Ett högpassfilter skapas med hjälp av den modifierade kondensatorbanken på 12 MVAr samt med en spole och kondensator. Filtret dämpade impedansen för femte och sjunde strömövertonen. Resultatet med filtret blev att de beräknade spänningsövertonerna fick ett något lägre värde än de som återfinns i SS-EN50160A1, därmed uppfylldes samtliga mål för detta arbete. / This work deals with the subject of power quality at an industry in Sweden. The work was carried out at Vattenfall Eldistribution within the power quality group. Good power quality is a concept that includes several characteristics of the voltage in our power grid. For Vattenfall's part, talking about "Good power quality" according to the company, there must always be a margin between good power quality and existing standards and regulations. The Swedish Standard EN50160 with Appendix A1 is the existing standard in power quality and where this work has as its starting point to live up to the levels described in the standard. It is with emphasis on voltage distortion this work investigates, measures, analyzes, simulates and calculates voltage distorsion.   This industry has had during a long time a wide variety of voltage distorsion and the objective of the work is based on the following:   • To investigate the cause of the variations based on existing measurements, power grid properties and connected loads.   • Describe the phenomenon mathematically and in technical terms.   • Suggest measures that reduce the overall level of harmonics.   The voltage distorsion was investigated considering several different operating modes in overlying power grids as well as industry's own production, it was measured for several months where it can clearly be seen that it changes at different times. Voltage distorsion is measured as a percentage with respect to the fundamental voltage and indicates how much harmonic content is present in a voltage. It appeared early that the fifth harmonic current was amplified when the voltage distorsion became high, this was investigated and calculated with the result that a parallel resonance circuit was met in this case. The capacitor bank has the same magnitude of capacitive reactance as the inductive reactance of the feeding transmission system at fifth harmonic. The resonant circuit amplifies the harmonic currents which results in increased voltage distorsion.   The power system and industry's own production was investigated in terms of impedances and loads. With short-circuit currents, the impedance could be calculated for several different operating modes. Calculations showed that there were two interesting modes in this power system, which are the normal mode and when the 130 kV-mesh power system go to the radial power system type. This reduces short-circuit power and creates a big change in resonant frequency. The size of the capacitor bank is 27 MVAr but is later changed to 12 MVAr and several new simulations are performed with the PSCAD software. Resonance frequency changes when the size of the capacitor bank changes. More simulations were carried out with a smaller capacitor bank with the result that the voltage distortion remains high. A high pass filter is created using the modified capacitor bank of 12 MVAr as well as a coil and capacitor. With this filter, the impedance of the harmonic five and seven was attenuated. The result of the filter was that the calculated voltage harmonics got a slightly lower value than the limits found in SS-EN50160A1. With these results, all goals were met for this work.

Evaluating Power Quality in the Microgrid on Arholma Island

Nilsson, Anna January 2024 (has links)
The purpose of this thesis is to evaluate a selection of power quality parameters (harmonic distortion and voltage variations) in the microgrid on Arholma Island in the Stockholm archipelago, Sweden. Measurements of harmonic distortion, total harmonic distortion, and voltage magnitudes is evaluated and compared prior to and after the installation of the microgrid. Furthermore, a comparison is made between grid-connected mode and island operation mode where also the frequency is analysed. The measured values are compared against regulatory limits.  The microgrid is owned and managed by the company Vattenfall, who provides the data used for the evaluation. The microgrid consists of two battery energy storage systems and a small photovoltaic system. The central energy management system has different use cases, for example peak shaving and voltage regulation. At the time when this thesis is conducted, the microgrid has been up and running continuously for approximately 8 months, from September, 2023 to April, 2024. A power quality meter has been collecting data at the point of common coupling (connection to the mainland) for a period of two years, i.e., from April, 2022, which is one year prior to the installation of the microgrid in mid-April, 2023. The microgrid is also operated in island operation mode for three short periods on April 18, 2024.  The data analysis is executed in Excel and Matlab. The results show that all measured harmonics (2nd to 25th), and total harmonic distortion stays well within regulatory limits throughout the whole measuring period. The microgrid does not seem to make the harmonic magnitude increase in general, although there is a slight increase during island operation mode for certain harmonics. Only on one occasion (with the exception of a planned maintenance outage) does the voltage drop below the levels of what is considered as good voltage quality during the two-year measurement period. Also, during island operation mode, the frequency show less variations than during grid-connected mode. / Syftet med detta examensarbete är att utvärdera ett urval av elkvalitetsparametrar (spänningsdistorsion/övertoner och spänningsvariationer) i mikronätet på ön Arholma i Stockholms skärgård, Sverige. Mätdata för övertoner, total övertonsdistorsion och spänningsamplitud utvärderas och jämförs före och efter installationen av mikronätet. Dessutom görs en jämförelse mellan nätanslutet läge och ö-driftläge, där även frekvensen analyseras. De uppmätta värdena jämförs med föreskrivna gränsvärden. Mikronätet ägs och förvaltas av företaget Vattenfall, och tillhandahåller den data som används för utvärderingen. Mikronätet består av två batterilagringssystem och ett litet solcellssystem. Det centrala kontrollsystemet har olika funktioner, till exempel ”peak shaving” och spänningsreglering. Vid t idpunkten då detta examensarbete genomförs har mikronätet varit i drift kontinuerligt i cirka 8 månader, från september 2023 till april 2024. En elkvalitetsmätare har samlat in data vid sammankopplingspunkten mot fastlandet under en period av två år, dvs. från april 2022, vilket är ett år före installationen av mikronätet i mitten av april 2023. Mikronätet körs i ö-drift under tre korta perioder den 18 april 2024. Dataanalysen utförs i Excel och Matlab. Resultaten visar att alla uppmätta övertoner (2:a till och med 25:e) och total övertonsdistorsion håller sig väl inom regulatoriska gränser genom hela mätperioden. Mikronätet verkar inte bidra till att övertonernas magnitud ökar i allmänhet, men en liten ökning för vissa övertoner kan ses i samband med att mikronätet körs i ö-drift. Endast vid ett tillfälle (med undantag för ett planerat underhållsavbrott) under den tvååriga mätperioden sjunker spänningen under nivåerna för vad som anses vara god spänningskvalitet. Resultaten visar även att frekvensen varierar mindre vid ö-drift än när mikronätet är sammankopplat med fastlandsnätet.

Conception d’alimentations de puissance d’actionneurs piézo-électriques, avec et sans contact électrique, pour la génération des vibrations mécaniques / Contact and contactless power supply design for piezoelectric actuators that generate mechanical vibrations

Goenaga, Ekaitz 04 July 2013 (has links)
Les travaux de thèse présentés dans ce manuscrit portent sur l’alimentation d’actionneurs de type piézo-électrique qui seront placés sur la partie tournante d’une perceuse. Ces actionneurs possèdent un comportement capacitif et sont habituellement alimentés par des systèmes linéaires. Une étude de dimensionnement et de conception a été menée sur différents amplificateurs à découpage qui peuvent fournir, dans un repère fixe, un signal de puissance sinusoïdal à fréquence variable dans les meilleures conditions possibles (rendement et THD). Ensuite, un système pouvant transférer l’énergie sans contact à l’actionneur piézo-électrique placé sur un repère tournant a été analysé. Cela a été possible grâce à l’utilisation des systèmes à induction, c’est-à-dire, par couplage magnétique à travers un transformateur tournant présentant un entrefer. Trois types de systèmes de transfert d’énergie sans contact ont été étudiés : l’un qui travaille à la fréquence de l’actionneur [50-500 Hz] et deux autres basés sur des stratégies de résonance permettant ainsi de diminuer les dimensions du coupleur magnétique. Pour cela, la modélisation tant magnétique qu’électrique a été effectuée dans les trois systèmes.Un prototype d’onduleur en pont complet fournissant jusqu’à 680 VAR a été réalisé. Ce dernier est placé en amont d’un coupleur magnétique basse fréquence transférant 1,75 kVAR à l’actionneur piézo-électrique en rotation. Les résultats obtenus en pratique ont montré la pertinence du travail de dimensionnement et conception. / Placed on the rotating part of a drilling system. These actuators have a capacitive behavior and are usually supplied by linear systems. In this case, the design and the sizing of different switching amplifiers that provide, in a fixed frame, a sinusoidal power signal with modular frequency in the best possible conditions (efficiency and THD) have been made. Then, a contactless power system for piezoelectric actuators placed in a rotating frame was analyzed. This was possible thanks to the use of induction systems through a rotating transformer with an air gap. Three types of contactless systems were studied. The first one works at modular low frequencies [50-500 Hz] and the other two use resonant strategies in order to reduce transformer’s size. For this, both magnetic and electrical modeling was performed in the three cases.A full-bridge inverter prototype that can deliver up to 680 VAR and a low frequency contactless energy transfer system of 1.75 kVAR that supplies the piezoelectric actuator at rotating frame have been made. Experimental results showed satisfactory results and proved the system feasibility.

Refrigerant-lubricated gas foil bearings : A thermo-hydrodynamic study (application to rigid bearings) / Lubrification par gaz réfrigérant des paliers à feuilles : Une étude thermo-hydrodynamique (application aux paliers à feuilles rigides)

Garcia, Mathieu 11 December 2012 (has links)
Des études internes à Liebherr-Aerospace France, concernant la conception de nouveaux compresseurs lubrifiés par gaz réfrigérant, ont montré que dans des conditions de fonctionnement spécifiques, un mélange de vapeur et de liquide apparaît au sein du compresseur, au lieu d'une phase vapeur seule. De ce fait, le comportement des paliers à feuilles lubrifiés au gaz réfrigérant est étudié, y compris la possibilité d'un écoulement diphasique du lubrifiant. L'étude porte sur le comportement du lubrifiant uniquement, dans des conditions de fonctionnement qui sont celles des paliers à feuilles. L'approche Thermo-Hydrodynamique décrit les caractéristiques du lubrifiant telles que la pression, la densité, la viscosité et la température. Dans ce modèle, une équation de Reynolds généralisée pour écoulement turbulent, une équation d'état non-linéaire pour écoulement diphasique et une équation de l'énergie tridimensionnelle pour film-mince et écoulement turbulent sont utilisées. Les paramètres globaux du palier sont calculés en régime permanent. / Internal experiments at Liebherr-Aerospace FRANCE on new refrigerant-lubricated compressor designs have shown that under specific operating conditions, a mixture of vapor and liquid appears in the compressor, instead of a single-phase vapor flow. Therefore, refrigerant-lubricated foil bearings behavior is studied, including the likelihood of two-phase flow in the lubricant. We focus on the lubricant behavior only, in the operating conditions of foil bearings. The Thermo-Hydrodynamic approach describes lubricant characteristics such as pressure, density, viscosity, and temperature. It involves the use of a generalized Reynolds equation for turbulent flow, a nonlinear cubic equation of state for two-phase flow and a 3D turbulent thin-film energy equation. Journal bearing global parameters are calculated for steady-state conditions.

Page generated in 0.0458 seconds