No. 1

       Measurement of Physical Quantities

    Pages

Viktor Witkovský, Ivan Frollo: 

Measurement Science is the Science of Sciences - There is no Science without Measurement

Abstract: 

Omnia in mensura et numero et pondere disposuisti is a famous Latin phrase from the Solomon’s Book of Wisdom, dated to the mid first century BC, meaning that all things were ordered in measure, number, and weight. Naturally, the wisdom is appearing in its relation to man. The Solomon’s wisdom is understood as the perfection of knowledge of the righteous as a gift from God showing itself in action. Consequently, a natural and obvious conjecture is that measurement science is the science of sciences. In fact, it is a basis of all experimental and theoretical research activities. Each measuring process assumes an object of measurement. Some science disciplines, such as quantum physics, are still incomprehensible despite complex mathematical interpretations. No phenomenon is a real phenomenon unless it observable in space and time, that is, unless it is a subject to measurement. The science of measurement is an indispensable ingredient in all scientific fields. Mathematical foundations and interpretation of the measurement science were accepted and further developed in most of the scientific fields, including physics, cosmology, geology, environment, quantum mechanics, statistics and metrology. In this year, 2020, Measurement Science Review celebrates its 20th anniversary and we are using this special opportunity to highlight the importance of measurement science and to express our faith that the journal will continue to be the excellent place for exchanging bright ideas in the field of measurement science. As an illustration and motivation for usage and further development of mathematical methods in measurement science, we briefly present the simple least squares method, frequently used for measurement evaluation, and its possible modification. The modified least squares estimation method was applied and experimentally tested for magnetic field homogeneity adjustment.

On Robust Estimation of Error Variance in (Highly) Robust Regression

Abstract: 

The linear regression model requires robust estimation of parameters, if the measured data are contaminated by outlying measurements (outliers). While a number of robust estimators (i.e. resistant to outliers) have been proposed, this paper is focused on estimating the variance of the random regression errors. We particularly focus on the least weighted squares estimator, for which we review its properties and propose new weighting schemes together with corresponding estimates for the variance of disturbances. An illustrative example revealing the idea of the estimator to down-weight individual measurements is presented. Further, two numerical simulations presented here allow to compare various estimators. They verify the theoretical results for the least weighted squares to be meaningful. MM-estimators turn out to yield the best results in the simulations in terms of both accuracy and precision. The least weighted squares (with suitable weights) remain only slightly behind in terms of the mean square error and are able to outperform the much more popular least trimmed squares estimator, especially for smaller sample sizes.

Chen JH, Zhang JJ, Gao RJ, Jiang CH, Ma R, Qi ZM, Jin H, Zhang H, Wang XC:

Research on Modified Algorithms of Cylindrical External Thread Profile Based on Machine Vision

Abstract: 

In the non-contact detection of thread profile boundary correction, it remains challenging to ensure that the thread axis intersects the CCD camera axis perpendicularly. Here, we addressed this issue using modified algorithms. We established the Cartesian coordinate system according to the spatial geometric relationship of the thread. We used the center of the bottom of the thread as the origin, and the image of the extreme position image was replaced by the image of the approximate extreme position. In addition, we analyzed the relationship between the boundary of the theoretical thread image and the theoretical profile. We calculated the coordinate transformation of the point on the theoretical tooth profile and the coordinate function of the point on the boundary of the theoretical image. At the same time, the extreme value of the function was obtained, and the boundary equation of the theoretical thread image was deduced. The difference equation between the two functions was used to correct the boundary point of the actual thread image, and the fitting results were used to detect the key parameters of the external thread of the cylinder. Further experiment proves that the above algorithm effectively improves the detection accuracy of thread quality, and the detection error of main geometric parameters is reduced by more than 50 %.

Guangwei Xiang, Peng Mi, Guoqing Yi, Chao Wang, Wei Liu:

Automatic Strain Gauge Balance Design Optimization Approach and Implementation Based on Integration of Software

Abstract: 

The traditional wind tunnel strain balance design cycle is a manual iterative process. With the experience and intuition of the designer, one solution that meets the design requirements can be selected among a small number of design solutions. This paper introduces a novel software integration-based automatic balance design optimization system (ABDOS) and its implementation by integrating professional design knowledge and experience, stepwise optimization strategy, CAD-CAE software, self-developed scripts and tools. The proposed two-step optimization strategy includes the analytical design process (ADP) and the finite element method design process (FEDP). The built-in optimization algorithm drives the design variables change and searches for the optimal structure combination meeting the design objectives. The client-server based network architecture enables local lightweight design input, task management, and result output. The high-performance server combines all design resources to perform all the solution calculations. The development of more than 10 balances that have been completed and a case study show that this method and platform significantly reduce the time for design evaluation and design-analysis-redesign cycles, assisting designers to comprehensively evaluate and improve the performance of the balance.

Chingiz Hajiyev, Demet Cilden-Guler, Ulviye Hacizade:

Two-Stage Kalman Filter for Fault Tolerant Estimation of Wind Speed and UAV Flight Parameters

Abstract: 

In this study, an estimation algorithm based on a two-stage Kalman filter (TSKF) was developed for wind speed and Unmanned Aerial Vehicle (UAV) motion parameters. In the first stage, the wind speed estimation algorithm is used with the help of the Global Positioning System (GPS) and dynamic pressure measurements. Extended Kalman Filter (EKF) is applied to the system. The state vector is composed of the wind speed components and the pitot scale factor. In the second stage, in order to estimate the state parameters of the UAV, GPS, and Inertial Measurement Unit (IMU) measurements are considered in a Linear Kalman filter. The second stage filter uses the first stage EKF estimates of the wind speed values. Between these two stages, a sensor fault detection algorithm is placed. The sensor fault detection algorithm is based on the first stage EKF innovation process. After detecting the fault on the sensor measurements, the state parameters of the UAV are estimated via robust Kalman filter (RKF) against sensor faults. The robust Kalman filter algorithm, which brings the fault tolerance feature to the filter, secures accurate estimation results in case of a faulty measurement without affecting the remaining good estimation characteristics. In simulations, noise increment and bias type of sensor faults are considered.

Cheng-Yang Liu, Chung-Yi Wang: 

Investigation of Phase Pattern Modulation for Digital Fringe Projection Profilometry

Abstract: 

The fringe projection profilometry with sinusoidal patterns based on phase-shifting algorithms is commonly distorted by the nonlinear intensity response of commercial projector. In order to solve this issue, sinusoidal width modulation is presented to generate binary sinusoidal patterns for defocusing the projection. However, the residual errors in the phase maps are usually notable for highly accurate three-dimensional shape measurements. In this paper, we propose the fringe patterns of the sinusoidal, square, and triangular periodic waveforms with seven-step phase-shifting algorithm to further improve the accuracy of three-dimensional profile reconstruction. The absolute phase values are calculated by using quality guided path unwrapping. We learn that by properly selecting fringe patterns according to the target shape, the undesired harmonics of the measured surface have negligible effect on the phase values. The experiments are presented to verify the imaging performances of three fringe patterns for different testing targets. The triangular fringe patterns are suitable for the shape measurements of complex targets with curved surfaces. The results provide a great possibility for high-accuracy shape measurement technique with wider measuring depth range.

Top ↑

     Measurement of Physical Quantities

Andrej Krafcik, Peter Babinec, Melania Babincova, Ivan Frollo:

Importance of Basset History Force for the Description of Magnetically Driven Motion of Magnetic Particles in Air

Abstract: 

Lungs are used as an attractive possibility for administration of different therapeutic substances for a long time. An innovative method of such administration widely studied nowadays is the application of aerosolized magnetic particles as the carriers to the lungs in the external non-homogeneous magnetic field. For these reasons we have studied dynamics of such a system on a level of particle trajectory in air in the presence of magnetic force as a driving force exerted on micrometric magnetic particle. On two typical examples of magnetically driven systems—motion of magnetic particle in a gradient magnetic field and cyclotron-like motion of a charged particle in homogeneous magnetic field in microscale, where the external accelerating forces are very large and the relevant time scale is of the order from fraction of milliseconds to seconds, we have examined the importance of these forces. As has been shown, for particles with high initial acceleration, not only the commonly used Stokes force but also the Basset history force should be used for correct description of the motion.

Stefan Marković , Milivoj Dopsaj, Veljko Veljković:

Reliability of Sports Medical Solutions Handgrip and Jamar Handgrip Dynamometer

Abstract: 

The aim of this paper is to determine inter-reliability, concurrent validity, and interchangeability of the SMS HG dynamometric system and a Jamar digital dynamometer for hand grip strength measurements performed in two relevant positions of the elbow joint, i.e. 90 ^o flexion and 180 ^o (full) extension. The sample in this research consisted of 61 participants and included 27 women and 34 men. Statistically significant differences in the results found between two positions in the elbow joint indicate that the results must be evaluated separately. However, regarding both testing positions, i.e. 90 ^o flexion and 180 ^o extension in the elbow joint, it was determined that SMS HG and Jamar instruments have a very high level of inter-reliability (ICC 0.948 to 0.980), but lack concurrent validity. The established mean difference of the results was higher for the 90 ^o than for the 180 ^o position but in both cases was considered to have a practical significance, thus not supporting the interchangeability of the instruments.

Jinfei Wang, Krzysztof Przystupa, Volodymyr Maksymovych, Roman Stakhiv, Orest Kochan:

Computer Modelling of Two-level Digital Frequency Synthesizer with Poisson Probability Distribution of Output Pulses

Abstract: 

The article presents the modified structure of the two-level digital frequency synthesizer (TLDFS), which combines the properties of classical digital frequency synthesizers (DFS) and Poisson pulse sequence generators (PPSG). The analysis of the statistical characteristics of synthesizer output signal, obtained in computer modelling with the use of appropriate software, has been carried out, which allowed determining the effective range of values of its control codes. The proposed generators can be effectively used to simulate various natural and technical processes, in particular, to simulate the output signals of dosimetric detectors during the design, adjustment and testing of dosimetric devices.

Rudolf Palenčár, Stanislav Ďuriš, Jakub Palenčár, Martin Halaj, Ľubomír Šooš:

Matrix Presentation of Uncertainties Propagation in the Realization of ITS-90 Temperature Scale using Standard Platinum Resistance Thermometers

Abstract: 

The paper presents a matrix approach to the propagation of uncertainties in the realization of the ITS-90 using Standard Platinum Resistance Thermometers (SPRT) calibrated at Defining Fixed Points (DFPs). The procedure allows correlations to be included between SPRT resistances measured during the calibration at the DFPs (i.e., the realization of the ITS-90) and the resistances measured during the subsequent use of the SPRT to measure temperature T90. The example also shows the possible contribution of these correlations to the overall temperature uncertainty measured by a calibrated SPRT.

Li-Guo Tan, Cheng Xu, Yu-Fei Wang, Hao-Nan Wei, Kai Zhao, Shen-Min Song:

Gaussian Recursive Filter for Nonlinear Systems with Finite-step Correlated Noises and Packet Dropout Compensations

Abstract: 

This paper is focused on the nonlinear state estimation problem with finite-step correlated noises and packet loss. Firstly, by using the projection theorem repeatedly, the mean and covariance of process noise and measurement noise in the condition of measurements before the current epoch are calculated. Then, based on the Gaussian approximation recursive filter (GASF) and the prediction compensation mechanism, one-step predictor and filter with packet dropouts are derived, respectively. Based on these, a nonlinear Gaussian recursive filter is proposed. Subsequently, the numerical implementation is derived based on the cubature Kalman filter (CKF), which is suitable for general nonlinear system and with higher accuracy compared to the algorithm expanded from linear system to nonlinear system through Taylor series expansion. Finally, the strong nonlinearity model is used to show the superiority of the proposed algorithm.

Lianfu Han, Haixia Wang, Yao Cong, Xingbin Liu, Jian Han, Changfeng Fu:

Oil Phase Velocity Measurement of Oil-Water Two-Phase Flow with Low Velocity and High Water Cut Using the Improved ORB and RANSAC Algorithm

Abstract: 

Velocity is an important parameter for fluid flow characteristics in profile logging. Particle tracking velocimetry (PTV) technology is often used to study the flow characteristics of oil wells with low flow velocity and high water cut, and the key to PTV technology is particle matching. The existing particle matching algorithms of PTV technology do not meet the matching demands of oil drops in the oil phase velocity measurement of oil-water two-phase flow with low velocity and high water cut. To raise the particle matching precision, we improved the particle matching algorithm from the oriented FAST and the rotated BRIEF (ORB) feature description and the random sample consensus (RANSAC) algorithm. The simulation and experiment were carried out. Simulation results show that the improved algorithm not only increases the number of matching points but also reduces the computation. The experiment shows that the improved algorithm in this paper not only reduces the computation of the feature description process, reaching half of the computation amount of the original algorithm, but also increases the number of matching results, thus improving the measurement accuracy of oil phase velocity. Compared with the SIFT algorithm and the ORB algorithm, the improved algorithm has the largest number of matching point pairs. And the variation coefficient of this algorithm is 0.039, which indicates that the algorithm is stable. The mean error of oil phase velocity measurement of the improved algorithm is 1.20 %, and the maximum error is 6.16 %, which is much lower than the maximum error of PTV, which is 25.89 %. The improved algorithm overcomes the high computation cost of the SIFT algorithm and achieves the precision of the SIFT algorithm. Therefore, this study contributes to the improvement of the measurement accuracy of oil phase velocity and provides reliable production logging data for oilfield.

Top ↑

Measurement of Physical Quantities

Dominik Šedivý, Simona Fialová, Roman Klas, Michal Kotek:

FSI Computation and Experimental Verification of Fluid Flow in Flexible Tubes

Abstract: 

Presented paper is focused on the experimental and computational study of fluid flow in pipes with flexible walls. One possible real example of this phenomenon is the blood flow in arteries or their substitutes in the human body. The artery material itself should be understood as anisotropic and heterogeneous. Therefore, the experiment was carried out on the deforming tube, made of silicone (polydimethylsiloxane - PDMS). Obtained results and observed events were verified by numerical FSI simulations. Due to the large deformations occurring during loading of the tube, it was necessary to work with a dynamic mesh in the CFD part. Based on experimental testing of the tube material, a non-Hookean and Mooney-Rivlin material model were considered. Blood flowing in vessels is a heterogeneous liquid and exhibits non-Newtonian properties. In the real experimental stand has been somewhat simplified. Water, chosen as the liquid, belongs to the Newtonian liquids. The results show mainly comparisons of unsteady velocity profiles between the experiment and the numerical model.

Chao Tan, Ruijie Fu, Chenguang Wu, Xinglin Li:

A Linearized Model of FID Signal for Increasing Proton Magnetometer Precision

Abstract: 

A linearized model of frequency measurement for the Free Induction Decay (FID) signal is proposed to increase the Proton Magnetometer (PM) precision. First, the nonlinear model of frequency measurement is set up according to the characteristic of the FID signal. Then, according to the error analysis of the MCFM method, the model is linearized on the condition of precision requirement. Furthermore, to reduce the nonlinear error caused by approximate treatment and the trigger time error caused by the random noise, the Least Squares (LS) method is adopted to estimate the slope of the linearized model, and the frequency to be measured is the inverse of the slope. Finally, a PM Prototype is made to verify the effectiveness of the proposed method. Experimental results show that the precision of frequency measurement is obviously increased if the proposed method is adopted for the noised sine signal. Moreover, the RMSD and the NPSD of magnetic-field measurement are about 0.13 nT and 80 pT/Hz^1/2, respectively if the proposed method is adopted by PM, which is better than the comparison method.

Zuzana Rošt’áková, Roman Rosipal, Saman Seifpour, Leonardo Jose Trejo:

A Comparison of Non-negative Tucker Decomposition and Parallel Factor Analysis for Identification and Measurement of Human EEG Rhythms

Abstract: 

Analysis of changes in the brain neural electrical activity measured by the electroencephalogram (EEG) plays a crucial role in the area of brain disorder diagnostics. The elementary latent sources of the brain neural activity can be extracted by a tensor decomposition of continuously recorded multichannel EEG. Parallel factor analysis (PARAFAC) is a powerful approach for this purpose. However, the assumption of the same number of factors in each dimension of the PARAFAC model may be restrictive when applied to EEG data. In this article we discuss the potential benefits of an alternative tensor decomposition method – the Tucker model. We analyze situations, where in comparison to the PARAFAC solution, the Tucker model provides a more parsimonious representation of the EEG data decomposition. We show that this more parsimonious representation of EEG is achieved without reducing the ability to explain variance. We analyze EEG records of two patients after ischemic stroke and we focus on the extraction of specific sensorimotor oscillatory sources associated with motor imagery during neurorehabilitation training. Both models provided consistent results. The advantage of the Tucker model was a compact structure with only two spatial signatures reflecting the expected lateralized activation of the detected subject-specific sensorimotor rhythms.

Cheng-Yang Liu, Tzu-Ping Yen, Chien-Wen Chen:

High-resolution Three-dimensional Surface Imaging Microscope Based on Digital Fringe Projection Technique

Abstract: 

The three-dimensional (3-D) micro-scale surface imaging system based on the digital fringe projection technique for the assessments of microfiber and metric screw is presented in this paper. The proposed system comprises a digital light processing (DLP) projector, a set of optical lenses, a microscope, and a charge coupled device (CCD). The digital seven-step fringe patterns from the DLP projector pass through a set of optical lenses before being focused on the target surface. A set of optical lenses is designed for adjustment and size coupling of fringe patterns. A high-resolution CCD camera is employed to picture these distorted fringe patterns. The wrapped phase map is calculated by seven-step phase-shifting calculation from these distorted fringe patterns. The unwrapping calculation with quality guided path is introduced to compute the absolute phase values. The dimensional calibration methods are used to acquire the transformation between real 3-D shape and the absolute phase value. The capability of complex surface measurement for our system is demonstrated by using ISO standard screw M1.6. The experimental results for microfiber with 3 μm diameter indicate that the spatial and vertical resolutions can reach about 3 μm in our system. The proposed system provides a fast digital imaging system to examine the surface features with high-resolution for automatic optical inspection industry.

Jaromir Zavadil, Josef Strom Bartunek, David Fojtik:

Analysis of Periodicities in Surface Topography of Cold rolled sheets Using Data Captured by Camera System

Abstract: 

A method for surface analysis of cold rolled sheets is proposed in this paper. The approach is based on a low-cost specially built camera system followed by spectral analysis of the data captured from metal surfaces. The focus is on the changes in the surface topography caused by cold rolling with emphasis towards periodicities in the processed surface. Angular profile of the spectrum is calculated and used to display periodicities in surface topography and show their direction. The results obtained by using the proposed system were compared with results obtained from the optical profilometer MicroProf FRT. The experiments show that cold rolling creates marks on the surface of the material, which represent periodicities that can be effectively detected by the proposed method and camera system. Even though the camera system is not able to measure precise surface roughness, it is able to detect periodicities and the results of spectral analysis are comparable with the results from the optical profilometer.

René Harťanský, Martin Mierka, Mikuláš Bittera, Jozef Hallon, Ján Halgoš, Jaroslav Hricko, Robert Andok, Michal Rafaj:

Novel Method of Contactless Sensing of Mechanical Quantities

Abstract: 

This article addresses the method of sensing mechanical quantities, in particular force and pressure, without the electrical connection of the sensing element and the electronics. The information about the mechanical quantity is transmitted only by evaluating the changes in the electromagnetic field created around the sensor. The sensor is designed on the basis of a flexible micro-electro-mechanical element (MEMS), the resonance of which carries the information about the measured quantity.

Top ↑

Measurement of Physical Quantities

Adam Kowalczyk, Rafał Chorzępa:

Processing Accuracy of Instantaneous Values of a Stochastic Signal in an Inertial Measurement System

Abstract:  

The article presents an analysis of the dynamic error occurring when processing a stochastic signal in an inertial measurement system. The problem was illustrated using both a calculation and a laboratory example. The technique of conditional averaging of signals was used in the experiment. The possibility to minimize the root mean square value of the error as well as the need for a time correction of measurement values in an inertial measurement system was demonstrated.

Guan Xu, Hui Shen, Xiaotao Li:

Active Vision Reconstruction Based on Ratio Invariability of Triangle Areas Generated from Triangle Array in Affine Space

Abstract:

An active-vision process is presented by the affine invariability of the ratio of triangle areas to reconstruct the 3D object. Firstly, a plate with the triangle array is designed in the same plane of the planar laser. The image of the plate is rectified from the projection space to the affine space by the image of the line at infinity. Then the laser point and the centroids of the triangles constitute a new triangle that bridges the affine space and the original Euclidean space. The object coordinates are solved by the invariant of the triangle area ratio before and after the affine transformation. Finally, the reconstruction accuracy under various measurement conditions is verified by experiments. The influence analyses of the number of line pairs and the accuracy of the extracted point pixels are provided in the experimental results. The average reconstruction errors are 1.54, 1.79, 1.90, and 2.46 mm for the test distance of 550, 600, 650, and 700 mm, which demonstrates the application potential of the approach in the 3D measurement.

Peter Pavlásek, Jan Rybář, Stanislav Ďuriš, Branislav Hučko, Miroslav Chytil, Alena Furdová, Sylvia Lea Ferková, Juraj Sekáč, Vítězslav Suchý, Patrik Grosinger:

Developments and Progress in Non-contact Eye Tonometer Calibration

Abstract:

This paper focuses on the problematic of intraocular pressure (IOP) measurements, performed by non-invasive methods. More specifically, the devices that are connected with the presented finding are non-contact tonometers that use concentrated air stream and optical sensors to determine the IOP within a human’s eye. The paper analyzes various influential factors that have an effect on the determination of the IOP values originating from the patients themselves and from the non-contact tonometer devices. The paper furthermore elaborates on the lack of independent methods of calibration and control of these devices. In order to fill this gap a measurement standard device that is capable of calibrating and testing these devices with traceability to the basic SI unit is presented. A detailed characterization and the determination of the expected uncertainty of the device are provided. By introducing an independent and traceable calibration method and control of non-contact tonometers into the clinical practice, the reliability of the measured IOP that is the primary indicator of glaucoma can be improved.

Dongjie Yan, Ziang Zhang, Zhenyang Li, Ya Yu, Hao Gong, Xueming Huang:

3D-PIV Measurement for EHD Flow of Spiked Tubular Electrode Corona Discharge in Wide Electrostatic Precipitator

Abstract:

The electrohydrodynamic (EHD) flow induced by a corona discharge has an important influence on the movement and collection of fine particles in an electrostatic precipitator. In this paper, three-dimensional particle image velocimetry (3D-PIV) is used to investigate the impact of different primary flow velocities and applied voltage on diffusion and transport of the spiked tubular electrode corona discharge EHD flow in a wide type electrostatic precipitator. In order to measure the flow characteristics of different positions of a spiked tubular electrode, the PIV measurements are carried out in several cross-sectional planes along the ESP duct. From 2D flow streamlines, in plane 1 (where the tip of the spike is oriented in the direction of primary flow), the velocity of the counter-clockwise vortex caused by the EHD flow near the plate decreases as the primary flow velocity increases. However, in plane 3 (where the tip direction is opposite to the primary flow), two vortices rotate adversely, and the flow velocity of the clockwise vortex near the plate increases as the primary flow velocity increases. Flow velocity increasing near the plate makes the particles deposited on the plate more easily to be re-entrained. It can be found in the three-dimensional analysis of the flow field that there are mainly “ascending vortex” and downward tip jet in the three observation planes. There is a discrepancy (in terms of distribution region and the magnitude of velocity) between the three-dimensional characteristics of these vortices and tip jets in the different cross-sectional planes.

Oleg Chernoyarov, Tatiana Demina, Yuri Kabanov, Alexander Makarov:

Detecting an Unknown Abrupt Change in the Band Center of the Fast-Fluctuating Gaussian Random Process

Abstract:

The generalized maximum likelihood algorithm is introduced for detecting the abrupt change in the band center of a fast-fluctuating Gaussian random process with the uniform spectral density. This algorithm has a simpler structure than the ones obtained by means of common approaches and it can be effectively implemented on the base of both modern digital signal processors and field-programmable gate arrays. By applying the multiplicative and additive local Markov approximation of the decision statistics and its increments, the analytical expressions are calculated for the false alarm and missing probabilities. And with the help of statistical simulation it is confirmed that the proposed detector is operable, while the theoretical formulas describing its quality and efficiency approximate satisfactorily the corresponding experimental data in a wide range of parameters of the observable data realization.

Kemal Arıkan, Emel Önal, Serhat Şeker:

Time-Frequency Analysis of Partial Discharge Current Pulses in Different Gases Environment under Lightning Impulse

Abstract:

This paper deals with a time-frequency analysis of the measured partial discharge (PD) currents in different insulation gases. These gas environments consist of a pure SF₆ (sulphur-hexafluoride) and sulphur-hexafluoride and nitrogen (1 % SF₆ + 99 % N₂) mixture, under both positive and negative lightning impulse (LI) voltage stresses. In this study, the short time Fourier transform was used to extract the time-frequency information of PDs for different gases at different pressures, and these results were compared to each other. Thus, the relationship between the time, amplitude, and frequency of PD currents was studied. Moreover, some statistical formulas, such as mean, standard deviation, kurtosis, and skewness were applied to the time-dependent PD current data. As a result, a correlation between obtained statistical results and PD frequencies was examined. In most cases, the frequency of partial discharge decreased when the pressure increased. The amplitude of the partial discharges for negative polarity was more than that for positive polarity gas insulations. The partial discharge amplitudes of the pressure of 2 bar were mostly high compared to other pressures. This case demonstrated that SF₆ had a maximum minimum character in terms of breakdown. The partial discharge frequency of a 1 % SF₆ mixture was higher than that of pure SF₆. It is thought that SF₆ suppresses the discharge frequency, and statistical evaluations support the experimental results.

Top ↑

Measurement of Physical Quantities

Xiang Zou, Kai Li, Bing Pan:

The Effect of Low-pass Pre-filtering on Subvoxel Registration Algorithms in Digital Volume Correlation: A revisited study

Abstract:

In digital volume correlation (DVC), random image noise in volumetric images leads to increased systematic error and random error in the displacements measured by subvoxel registration algorithms. Previous studies in DIC have shown that adopting low-pass pre-filtering to the images prior to the correlation analysis can effectively mitigate the systematic error associated with the classical forward additive Newton-Raphson (FA-NR) algorithm. However, the effect of low-pass pre-filtering on the state-of-the-art inverse compositional Gauss-Newton (IC-GN) algorithm has not been investigated so far. In this work, we focus on the effect of low-pass pre-filtering on two mainstream subvoxel registration algorithms (i.e., 3D FA-NR algorithm and 3D IC-GN algorithm) used in DVC. Basic principles and theoretical error analyses of the two algorithms are described first. Then, based on numerical experiments with precisely controlled subvoxel displacements and noise levels, the influences of image noise on the displacements measured by two subvoxel algorithms are examined. Further, the effects of low-pass pre-filtering on these two subvoxel algorithms are examined for simulated image sets with different noise levels and deformation modes. The results show that the low-pass pre-filtering can effectively suppress the systematic errors for the 3D FA-NR algorithm, which is consistent with the previously drawn conclusion in DIC. On the contrary, different form the 3D FA-NR algorithm, the 3D IC-GN algorithm itself can reduce the influence of image noise, and the effect of low-pass pre-filtering on it is not so obvious as on 3D FA-NR algorithm.

 Ján Buša, Miroslav Dovica, Mikhail Zhabitsky:

Using a Gauge Block for Derivation of Parameters of Four Laser Triangulation Sensors in a Local Coordinate System

Abstract:

The paper discusses the derivation of an accurate coordinate measuring system consisting of two, three, or four sensors based on the records of four fixed laser triangulation sensors done for a gauge block in movement. Three-dimensional case is considered. In the simulations, using a set of distances quadruplets, parameters of sensors in a local sensors coordinate system are determined through a least squares minimization process using the Differential Evolution approach. The influence of the measurement and rounding inaccuracy on the identification accuracy using numerical simulation methods are assessed.

Rupali Tiwari, Vlastimil Boháč, Peter Dieška, Gregor Götzl:

Thermophysical Parameters of Carbonate Rock estimated by Slab Model Developed for Pulse Transient Technique

Abstract:

The slab model has been used for parameter estimation from the measurement performed by the Pulse Transient Technique. The estimation of thermophysical parameters was done on carbonate rock sample. In addition to basic thermal parameter for example thermal diffusivity, thermal conductivity and specific heat capacity, the slab model takes into account the heat capacity of the heat source, as well as the heat transfer coefficient between the heat source and the sample. The thermophysical parameters were estimated for the case when thermal conductive paste as a heat contact agent was not used for the measurements. The paste contains silicone oil that penetrates into the porous stone material and thus causes irreversible changes of properties during the measurement so we decided not to use it. The experiment was done with dry contacts at the interfaces that causes the disturbances in the measurement that have been introduced and resolved using the slab model. Uncertainty analysis of the estimation of the parameters by the slab model was done for real measurements conducted on the carbonate rock. In this paper we analyzed the quality of the temperature response fit in dependency on the originally free fitted parameters of the heat transfer coefficient and the heat capacity of the heat source that was replaced by constant values in two steps. The heat capacity of the heat source was calculated from the material properties, e.g., the nickel and Kapton. The fit results obtained by the slab model were compared with the data obtained by the ideal and cuboid model. The analysis of the sensitivity coefficients and calculated uncertainties of estimated parameters with the slab model help to improve the accuracy of parameter estimation.

Zhongyuan Zhou, Peng Hu, Xiang Zhou, Mingjie Sheng, Peng Li, Qi Zhou:

Electromagnetic Shielding Performance Measurement for Braided-Shield Power Cables at Low Frequency Regimes

Abstract:

Although various measurement techniques have been applied to both qualitative and quantitative evaluation for the electromagnetic shielding performance of braided-shield power cables, the existing measurements cannot directly assess the low-frequency shielding performance (typically below 100 kHz) due to factors such as ground-loop effects and dynamic range problem in measurement. To solve these, an improved shield reduction factor method, based on gain (T/R) rather than scattering parameters, is proposed to evaluate the shielding performance of braided-shield power cables from 25 Hz to 1 MHz. In this work, we highlight the implementation of measurement setup to avoid the effects of ground-loop and stray electromagnetic field. Meanwhile, the test cell is simplified according to the definition of the shield reduction factor in order to obtain the gain (T/R) parameters, which can be used to calculate transfer impedance as well. From the measurements we present more intuitive evaluation of shielding behavior of braided-shield power cables at low frequency regimes, and showcase a detailed comparative discussion between transfer impedance and shield reduction factor. The proposed shield reduction factor method is expected to be a useful way for the evaluation of the low frequency shielding performance of braided-shield cables.

Ľuboš Kučera, Branislav Patin, Tomáš Gajdošík, Rudolf Palenčár, Jakub Palenčár, Miloš Ujlaky:

Application of Metrological Approaches in the Design of Calibration Equipment for Verification of Float Level Gauges

Abstract:

The paper deals with a scientific approach for an increase of accuracy of measurement and possibilities for automation of the standard equipment for calibration and verification of float level gauges. They are applied in high-capacity fuel storage tanks, and they are intended to measure the level of stored liquid hydrocarbons. In the submitted paper, we describe original approaches towards metrological control of float level gauges. Firstly, we present and describe the current ways of control by means of the standard equipment of the first generation with a precision caliper and manual measuring wire with the application of modern scientific and developing processes. A new system, whose design is based on research and development, represents a fully automated measuring system which utilizes the incremental optical encoder with a precision graduated ring and a rewind pulley. The paper deals with the issue of a design of the standard equipment and its measurement system from the standpoint of metrology and construction. Based on scientific procedures, we solve reasons of errors in measurement and their reduction on concrete components of the measurement system. The result is that, following the scientific approach and mathematical description of the determination of measurement uncertainties, constructors are able to design suitable tolerances for the production of components of measuring devices and related materials and technologies.

Peter Andris, Ivan Frollo:

Sensitivity Analysis of the Simply Noise-matched Receiving Coil for NMR Experiments

Abstract:

The article analyzes the sensitivity of unmatched receiving coil for the NMR scanner. Receiver of the scanner was investigated from the point of view of noise features. Theory of the noise figure has been modified to utilize the receiver for digitization of its own noise and the noise figure calculation. The resulting noise figure has been measured with different source impedances and the optimal value has been acquired. Influence of the noise figure on the resulting signal-to-noise ratio has been calculated for the sensitivity judgement. The output SNR has been investigated for constant input SNR as well as for constant input voltage. Many results are depicted in figures. Also examples of theoretical results are depicted graphically.

Top ↑

 No. 1    No. 2    No. 3   No. 4   No. 5

Journal is open for your papers

 Download and print the front cover  ->>