- Détails du magazine
- Format
- Magazine
- eISSN
- 1335-8871
- Première publication
- 07 Mar 2008
- Période de publication
- 6 fois par an
- Langues
- Anglais

#### Chercher

- Accès libre

Application of conditional averaging to time delay estimation of random signals

Pages: 130 - 137

#### Résumé

The article presents the possibilities of using the function of conditional average value of a delayed signal (CAV) and the function of conditional average value of a delayed signal absolute value (CAAV) to determine the time delay estimation (TDE) of random signals. For discrete CAV and CAAV estimators, the standard uncertainties of the estimation of function values at extreme points and the standard uncertainties of the TDE were given and compared with the corresponding uncertainties for the direct discrete cross-correlation function (CCF) estimator. It was found that the standard uncertainty of TDE for CAV is lower than for CCF independent of signal-to-noise ratio (SNR) for parameter values of α ≥ 2 and M/N ≥ 0.25 (where: α - relative threshold value, M/N - quotient of number of averaging and number of samples). The standard uncertainty of TDE for CAAV will be lower than for CCF for SNR values greater than 0.35 (for N/M = 1).

#### Mots clés

- Time delay estimation
- random signals
- conditional averaging
- cross-correlation

- Accès libre

A Fast-Multi-Channel Sub-Millikelvin Precision Resistance Thermometer Readout Based on the Round-Robin Structure

Pages: 138 - 146

#### Résumé

The fast response multipoint high-precision temperature measurement is often necessary in many dynamical measurement fields and industrial applications. However, limited by the existing electric circuit architecture, either the AC or DC bridges have the shortcoming that the rates or precisions degenerate markedly in the multi-channel scanning mode. To overcome this disadvantage, a round-robin structural low-cost ratiometric resistance thermometer readout based on several commercial 32-bit sigma-delta analogue-to-digital converters (Σ-Δ ADCs) was presented in this article. The experimental results show that the precision of this readout corresponds to 0.1 mK at 1 Hz when sampling four channel resistors simultaneously, while the precision and rate are not degenerating with the channel number increasing. In addition, the uncertainty of the readout is investigated in this article. It shows that the presented readout can achieve an uncertainty as low as 2.1 mK at 1 Hz (K = 2).

#### Mots clés

- Temperature metrology
- resistance thermometry
- round-robin structure
- multi-channel scanning

#### Résumé

The algebraic structure underlying the quantity calculus is defined axiomatically as an algebraic fiber bundle, that is, a base structure which is a free Abelian group together with fibers which are one dimensional vector spaces, all of them bound by algebraic restrictions. Subspaces, tensor product, and quotient spaces are considered, as well as homomorphisms to end with a classification theorem of these structures. The new structure provides an axiomatic foundation of quantity calculus which is centered on the concept of dimension, rather than on the concept of unit, which is regarded as secondary, and uses only integer exponents of the dimensions.

#### Mots clés

- Quantity calculus
- algebraic structure
- group of dimensions

- Accès libre

A new line-shape asymmetry model for wavelength modulation spectroscopy in gaseous flows

Pages: 158 - 161

#### Résumé

This communication reports technical notes on the development and application of an automated line-shape fitting procedure for wavelength modulation spectroscopy (WMS). Near-infrared transitions of carbon dioxide (CO_{2}) around 1573 nm were measured in vertical cold (nonreacting) flow of CO_{2} at atmospheric pressure using WMS with demodulation at second harmonic frequency. Semi-empirical model based on the set of so-called Gabor functions was developed and parameters of Lorentzian line-shape profile and its asymmetry resulting from simultaneous frequency and amplitude response of the current-modulated semiconductor laser were determined. Nonlinear least-square fitting procedure employing differential evolution algorithm was successfully utilized for performing this task. Line-shape fitting procedure enabling efficient signal de-noising and background subtraction of wavelength modulation spectra was implemented into an open-source code.

#### Mots clés

- gas sensing
- spectroscopy
- modulation
- model
- line-shape asymmetry

- Accès libre

Frequency and time fault diagnosis methods of power transformers

Pages: 162 - 167

#### Résumé

The authors describe experimental and theoretical analyses of faults of power transformer winding. Faults were caused by mechanical effect of short-circuit currents. Measurements of transformer were carried out in high-voltage laboratory. Frequency and time diagnostic methods (method SFRA - Sweep Frequency Response Analysis, impact test) were used for the analyses. Coils of transformer windings were diagnosed by means of the SFRA method and the time impact test. The analyzed methods had a significant sensitivity to a relatively small deformation of coil. In the analysis a new technique for analyzing the effects of short-circuit currents is introduced. This technique is developed for high-voltage transformers (different types of power). The proposed analyses show that it is necessary to analyze the value of short-circuit current. Short-circuit current represents a danger for the operation of the power transformer. The proposed approach can be used for other types of transformers. Moreover, the presented techniques have a potential application for fault diagnosis of electrical equipment such as: transformers and electrical machines.

#### Mots clés

- Fault
- short-circuit
- transformer
- diagnostics
- frequency

- Accès libre

Measuring and evaluating the differences of compared images for a correct car silhouette categorization using integral transforms

Pages: 168 - 174

#### Résumé

The present paper focuses on the analysis of the possibilities of using integral transforms for measuring and evaluating the differences of compared images (car silhouettes) with the purpose of a correct car body categorization. Approaches such as the light intensities frequency change, the application of discrete integral transforms without the use of further supplementary information enabling automated data processing using the Fourier-Mellin transforms are used within this work. The calculation of the several metrics was verified through different combinations that implied using and not using the Hamming window and a low-pass filter. The paper introduced a method for measuring and evaluating the differences in the compared images (car silhouettes). The proposed method relies on the fact that the integral transforms have their own transformants in the case of translation, scaling and rotation, in the frequency area. Besides, the Fourier-Mellin transform was to offer image transformation that is resistant to the translation, rotation and scale.

#### Mots clés

- Automatic measurement system
- Fourier-Mellin transform
- image analysis
- Body in White (BIW)
- car silhouettes