Teaching Magneto-Thermal Coupling Using Thomson\u27s Levitating Ring Experiment

The levitating ring experiment is presented as a method for teaching magneto-thermal interactions. The complete electromagnetic model of a problem is given, together with the insight in thermal analysis. The factors for determining the vertical displacements are explained, and an elegant method for indirect measurement of induced current in the ring is introduced. The whole apparatus is explained in detail so an accurate computer model can be made. Several simulation approaches are given, and all prove the applicability in teaching coupled problems using laboratory experiments and computer modeling

A Resistive Voltage Divider for Power Measurements

The paper presents a resistive voltage divider (RVD), developed for power measurements at much higher frequencies than the traditional 50 Hz. The design of the RVD and the methods of its evaluation are described. The RVD is intended to be used in a digital sampling wattmeter application based on National Instruments PXI-4461 Dynamic Signal Analyzer. The design of the divider includes individual copper guards for each resistor, driven by the auxiliary chain of resistors. To reduce the leakage currents, the PTFE terminals are applied between pins of the resistors and the printed circuit board

A CIRCULAR LOOP TIME CONSTANT STANDARD

A time constant standard, developed for the phase angle measurement of precision current shunts is developed and described, and its time constant has been determined. Based on a single circular loop placed in an air thermostat, its construction is very simple and it gives accurate results in the frequency band of interest, e.g. for frequencies between 50 Hz and 100 kHz. The influence of the shielding is calculated using numerical Finite Element Analysis (FEA). The thermostatic stability is analyzed, and the time-constant of the thermostat is determined using temperature measurement and Butterworth filtering. The power coefficient of the standard is determined, and limits of errors are discussed

A CIRCULAR LOOP TIME CONSTANT STANDARD

A time constant standard, developed for the phase angle measurement of precision current shunts is developed and described, and its time constant has been determined. Based on a single circular loop placed in an air thermostat, its construction is very simple and it gives accurate results in the frequency band of interest, e.g. for frequencies between 50 Hz and 100 kHz. The influence of the shielding is calculated using numerical Finite Element Analysis (FEA). The thermostatic stability is analyzed, and the time-constant of the thermostat is determined using temperature measurement and Butterworth filtering. The power coefficient of the standard is determined, and limits of errors are discussed

A Resistive Voltage Divider for Power Measurements

The paper presents a resistive voltage divider (RVD), developed for power measurements at much higher frequencies than the traditional 50 Hz. The design of the RVD and the methods of its evaluation are described. The RVD is intended to be used in a digital sampling wattmeter application based on National Instruments PXI-4461 Dynamic Signal Analyzer. The design of the divider includes individual copper guards for each resistor, driven by the auxiliary chain of resistors. To reduce the leakage currents, the PTFE terminals are applied between pins of the resistors and the printed circuit board

Ac-Dc Characterization of Coaxial Current Shunts and Application of the hunt in the Digital Sampling Wattmeter

The purpose of this paper is to give a review of ac-dc characterization of the current shunts and application of the current shunt (nominal current 1A) within the digital sampling wattmeter. It is described the ac-dc transfer difference measurement of six cage type ac shunts from 10 mA up to 10 A using step-up measurement procedure. Furthermore, the substantial part of the measurement setup is fast switching system which is also described in detail. For the purpose of measurement procedure, the application is developed in LabVIEW and whole process is fully automatized. Obtained results are analyzed and shown on graphs. This paper is extended version of two papers: [1] and [2] which are presented on 1st International Colloquium on Smart Grid Metrology. Thus, paper is extended with presented application of the shunt 1 A in the digital sampling wattmete

Aktivni sustavi za zaštitu od buke u cijevima

After reviewing the development of active noise control principles, we analyzed the elements of the active noise control system in ducts. On the basis of this analysis, we created a model of these elements. Especially, we brought a model of the loudspeaker in the z-domain, suitable for description of systems containing analog and digital parts. Such model enabled us to analyze work and convergence of the adaptive signal processing algorithms applied to active noise control. As an example, we analyzed performance of FXLMS algorithm on simplified model of active noise control system in ventilation duct, and have shown a strong influence of the loudspeaker\u27s transfer function on the power spectrum of the error signal.Uz dani prikaz razvoja aktivne zaštite od buke, analizirani su elementi sustava aktivne zaštite od buke u cijevima, a na temelju te analize napravljen je model elemenata. Posebno je provedena analiza zvučnika te je napravljen model zvučnika u z-domeni, prikladan za analizu sustava koji imaju analogne i digitalne dijelove. Primjenom takvog modela možemo u vremenskoj domeni analizirati rad i konvergenciju pojedinih adaptivnih algoritama obrade signala. Kao primjer provedena je analiza rada sustava aktivne zaštite na pojednostavljenom modelu ventilacijskog kanala primjenom FXLMS algoritma, te je pokazan jak utjecaj prijenosne karakteristike zvučnika na spektar snage zvučnog signala preostale buke

Calculating Lumbar Puncture Depth in Children

Lumbar puncture was performed in 195 children and the depth of needle was recorded. Our results show that the depth of lumbar puncture necessary to obtain uncontaminated cerebrospinal fluid correlates best with the child’s weight. The simple formula: mean depth of insertion (cm) = 1.3 + 0.07 x body weight (kg), can be used to estimate the depth of lumbar puncture of children older than 3 months. The depths of lumbar puncture of children younger than 3 months are mostly 1.0–1.5 cm

Algorithms for active control of noise and vibration

Tema ove disertacije su aktivni sustavi za zaštitu od buke i vibracija. Upotrebom pasivnih metoda zaštite od buke često nije moguće postići zadovoljavajuće rješenje, a koji put, ako je i moguće, nije financijski isplativo. Razvojem elektronike i audiotehnike, kao rješenje se sve više nameće upotreba aktivnih sustava za zaštitu od buke i vibracija, gdje se neželjeni zvučni signal buke nastoji poništiti protufaznim signalom, koji proizvodi elektronički sustav. Realizaciju učinkovitih aktivnih sustava zaštite omogućava u prvom redu upotreba suvremenih metoda adaptivne obrade signala. U ovoj radnji obrađeni su algoritmi adaptivne obrade signala koji se koriste u aktivnoj zaštiti. Tu se prije svega koristi LMS algoritam i njegove izvedenice. Kao neželjeni efekt u aktivnim sustavima zaštite koji koriste akustički senzor referentnog signala javlja se neželjena akustička povratna veza od sekundarnog izvora do senzora referentnog signala. Iako postoje akustičke mjere poput usmjerenih izvora i senzora, njihova je učinkovitost ovisna o nepromjenjivosti uvjeta prostora u kojemu se vrši zaštita. Upotrebom rekurzivnih adaptivnih filtara ovaj se problem može riješiti, i u tu svrhu se koristi u prvom redu Erikssonov FURLMS algoritam. Međutim rekurzivni adaptivni filtri nisu bezuvjetno stabilni, a i za navedeni se algoritam postavljalo pitanje konvergencije. U ovoj je radnji u slučaju akustičke povratne veze između sekundarnog izvora i senzora referentnog signala predložena upotreba filtrirano-x adaptivnog rekurzivnog filtra zasnovanog na Legendreovim funkcijama. Predložena filtarska struktura je stabilna i bez lokalnih minimuma, a usporedbom sa FURLMS algoritmom simulacijski je pokazana bolja konvergencija za realnu akustičku konfiguraciju kratke cijevi uz isti broj koeficijenata. Usporedbom dvaju algoritama uz uvjet istog broja multiplikacija po iteraciji postiže se jednaka razina preostale buke za dva algoritma.This thesis is dealing with active noise and vibration control systems. Passive methods in noise control often cannot give satisfying result, and in many cases it is too costly even if it is actually possible. Recent development in electronics and audiotechnics allowed application of active noise and vibration control instead. In active control unwanted noise signal is acoustically summed with an antiphase signal, produced by the electronic system. Application of effective active noise and vibration control systems became possible with modern adaptive signal processing methods. In this thesis algorithms of adaptive signal processing used in active control are presented. Most used algorithms are those based on LMS algorithm. As an unwanted effect, when using active noise control with an acoustical reference sensor, there is a acoustical feedback between secondary source and reference signal sensor. There are acoustical countermeasures, such as directed sources and sensors, they all depend on invariable conditions of space where the control is performed. Application of infinite impulse response (IIR) adaptive filters can solve this problem, and there is first of all used Eriksson's FURLMS algorithm. IIR adaptive filters are not unconditionally stable, and the mentioned one was particularly discussed about its convergence. In this thesis was proposed a filtered-x adaptive IIR filter based on Legendre functions for use when such a feedback exists. The proposed filter is stable and has got unimodal performance surface. Compared with FURLMS algorithm, it is shown by simulation better convergence for the real acoustical configuration of a short duct, using the same number of coefficients. Comparing two algorithms on the basis of same number of multiplications per iteration, it is achieved the same level of residual noise

Algorithms for active control of noise and vibration

Tema ove disertacije su aktivni sustavi za zaštitu od buke i vibracija. Upotrebom pasivnih metoda zaštite od buke često nije moguće postići zadovoljavajuće rješenje, a koji put, ako je i moguće, nije financijski isplativo. Razvojem elektronike i audiotehnike, kao rješenje se sve više nameće upotreba aktivnih sustava za zaštitu od buke i vibracija, gdje se neželjeni zvučni signal buke nastoji poništiti protufaznim signalom, koji proizvodi elektronički sustav. Realizaciju učinkovitih aktivnih sustava zaštite omogućava u prvom redu upotreba suvremenih metoda adaptivne obrade signala. U ovoj radnji obrađeni su algoritmi adaptivne obrade signala koji se koriste u aktivnoj zaštiti. Tu se prije svega koristi LMS algoritam i njegove izvedenice. Kao neželjeni efekt u aktivnim sustavima zaštite koji koriste akustički senzor referentnog signala javlja se neželjena akustička povratna veza od sekundarnog izvora do senzora referentnog signala. Iako postoje akustičke mjere poput usmjerenih izvora i senzora, njihova je učinkovitost ovisna o nepromjenjivosti uvjeta prostora u kojemu se vrši zaštita. Upotrebom rekurzivnih adaptivnih filtara ovaj se problem može riješiti, i u tu svrhu se koristi u prvom redu Erikssonov FURLMS algoritam. Međutim rekurzivni adaptivni filtri nisu bezuvjetno stabilni, a i za navedeni se algoritam postavljalo pitanje konvergencije. U ovoj je radnji u slučaju akustičke povratne veze između sekundarnog izvora i senzora referentnog signala predložena upotreba filtrirano-x adaptivnog rekurzivnog filtra zasnovanog na Legendreovim funkcijama. Predložena filtarska struktura je stabilna i bez lokalnih minimuma, a usporedbom sa FURLMS algoritmom simulacijski je pokazana bolja konvergencija za realnu akustičku konfiguraciju kratke cijevi uz isti broj koeficijenata. Usporedbom dvaju algoritama uz uvjet istog broja multiplikacija po iteraciji postiže se jednaka razina preostale buke za dva algoritma.This thesis is dealing with active noise and vibration control systems. Passive methods in noise control often cannot give satisfying result, and in many cases it is too costly even if it is actually possible. Recent development in electronics and audiotechnics allowed application of active noise and vibration control instead. In active control unwanted noise signal is acoustically summed with an antiphase signal, produced by the electronic system. Application of effective active noise and vibration control systems became possible with modern adaptive signal processing methods. In this thesis algorithms of adaptive signal processing used in active control are presented. Most used algorithms are those based on LMS algorithm. As an unwanted effect, when using active noise control with an acoustical reference sensor, there is a acoustical feedback between secondary source and reference signal sensor. There are acoustical countermeasures, such as directed sources and sensors, they all depend on invariable conditions of space where the control is performed. Application of infinite impulse response (IIR) adaptive filters can solve this problem, and there is first of all used Eriksson's FURLMS algorithm. IIR adaptive filters are not unconditionally stable, and the mentioned one was particularly discussed about its convergence. In this thesis was proposed a filtered-x adaptive IIR filter based on Legendre functions for use when such a feedback exists. The proposed filter is stable and has got unimodal performance surface. Compared with FURLMS algorithm, it is shown by simulation better convergence for the real acoustical configuration of a short duct, using the same number of coefficients. Comparing two algorithms on the basis of same number of multiplications per iteration, it is achieved the same level of residual noise