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Page 748 of 977 Results 7471 - 7480 of 9762

Mateusz Kotarski, Janusz Smulko
ASSESSMENT OF SYNCHRONIC DETECTION AT LOW FREQUENCIES THROUGH DSP-BASED BOARD AND PC SOUND CARD

The lock-in amplifier, working at acoustic frequency range, can be cheaply realized by applying a sound card or a board kit with a digital signal processor, together with a low noise amplifier. Such realization can automatically retune frequency and can perform fast measurements at various frequencies to establish frequency characteristic of the investigated, and often time-varying, object. Quality of these two economical solutions is presented in detail and the possible improvements to limit measurement errors are discussed as well.

Dalibor Kuhinek, Igor Zoric, Josip Butorac
INCREASE OF STRAIN GAGE OUTPUT VOLTAGE SIGNALS ACCURACY USING VIRTUAL INSTRUMENT WITH HARMONIC EXCITATION

This paper describes the principle of harmonic excitation of strain gages in bridge configuration. This system's properties are mathematically determined and measurements are conducted with commutated excitation, AC and harmonic excitation - with and without filtering. The possibility of increasing the accuracy of output bridge voltage measurement by using harmonic excitation is shown.

Dusan Agrez
PERIOD ESTIMATION OF THE MODULATED SIGNAL

In the paper, the two non-parametric algorithms for the period estimation are compared: the autocorrelation approach and the interpolated discrete Fourier transform (IDFT) approach both added with algorithm for searching of the lowest common frequency component or the largest period of the modulated signal. The direct approach by IDFT shows better results at two and more cycles of the investigated period in the measurement interval. Simulation results also show the robustness of the searching algorithm of the lowest common frequency component.

Wojciech Fraczek, Ewa Fraczek, Janusz Mroczka
PARALLEL GLASS PLATE TEST WITH THE USE OF THE PHASE SHIFT TECHNIQUE IN THE OPTICAL VORTEX INTERFEROMETER

The Optical Vortex Interferometer (OVI) is described in earlier paper as usefully tool to generate regular lattice of optical vortices (OVs) by interference of three plane wave. To practically use OVI in metrology method to localization of vortex points (VPs) is necessary. In this paper method with phase shift technique to VPs localisation is presented. Phase shift technique in this method is applied to additional fourth wave. Phase shift of the fourth wave doesn't change intensity in vortex points and increases intensity gradient in their vicinity. Result of localisation can be useful to analyse wave-front deformation caused by the object inserted in OVI setup.

Koo-Hyun Chung, Gordon Shaw, Jon R. Pratt
ACCURATE PICOSCALE FORCES FOR INSITU CALIBRATION OF AFM

The force sensitivity of an atomic force microscope is calibrated directly using an in situ realization of primary electrostatic forces ranging from 320 pN to 3.3 nN with accuracy of a few percent. The absolute accuracy of a common atomic force microscope (AFM) force calibration scheme, known as the thermal noise method is evaluated via comparison to the electrostatic calibration. It is demonstrated that the thermal noise method can be applied with great success to yield force measurements with relative standard uncertainties below 5 % after application of a geometric correction factor.

Daniel Belega, Dominique Dallet
FAST AND ACCURATE MEASUREMENT OF THE RMS VALUE OF A NONCOHERENT SAMPLED SINE WAVE

In this paper a new estimator for the measurement of the rms value of a noncoherent sampled sine-wave is proposed. The key feature of this estimator is that the sine-wave offset, a priori estimated, is removed from the sine-wave. A formula used to estimate the sine-wave offset is also given in the paper. It has been proved by means of computer simulations and experimental results that by the proposed estimator accurate rms measurements are obtained if the total harmonic distortion (THD) of the sine-wave is smaller than or equal to -30 dB.

Timo Salpavaara, Jarmo Verho, Jukka Lekkala, Jouko Halttunen
WIRELESS INSOLE SENSOR SYSTEM FOR PLANTAR FORCE MEASUREMENTS DURING SPORT EVENTS

We are developing a wireless system that measures online the forces between foot and insole with a low-cost laminated capacitive sensor matrix. This measurement system can be utilized to monitor the timing and movements of the legs of an athlete during throwing, jumping and running in various sports events. The measured data is intended to be used to improve coaching. We chose the javelin throw event as a case study for our sensor system. We measured the force signals under both feet during several throws. Analysis showed that the measured signals provide additional information for coaching.

M. Nieves Medina, José Ángel Robles, Javier Castro
VALIDITY OF POLYNOMIALS AS RESULTS FOR COMPARISONS

Guidelines provided by [1] have been used worldwide to evaluate key comparisons. The aim of this paper is to demonstrate the validity of these procedures when polynomials instead of fixed values are provided as comparison results.

David Herranz, Salustiano Ruiz, Mª. Nieves Medina
VOLUME RATIO DETERMINATION IN STATIC EXPANSION SYSTEMS BY MEANS OF TWO PRESSURE BALANCES

Static expansion systems are used to generate known pressures in the high and medium vacuum range. In these systems the volume ratios are the crucial parameters and have to be determined very accurately. For this task different methods can be used. We have used the gas accumulation method with a dead weight pressure balance, a force-balanced piston gauge (FPG) and a differential pressure transducer (CDG 133.32 Pa). The final uncertainty of the expansion ratios obtained with this method is similar to other institutes uncertainties.

Pablo Lecumberri, Marisol Gómez, Alfonso Carlosena
APPROXIMATE GCD OF INEXACT UNIVARIATE POLYNOMIALS

The problem of finding the greatest common divisor (GCD) of univariate polynomials appears in many engineering fields. Despite its formulation is well-known, it is an ill-posed problem that entails numerous difficulties when the coefficients of the polynomials are not known with total accuracy, as, for example, when they come from measurement data. In this work we propose a novel GCD estimation method designed to cope with such inaccuracies. An example of recovery of transient impulsive signals is provided to show the performance of the proposed method working on measurement data.

Page 748 of 977 Results 7471 - 7480 of 9762