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Page 749 of 977 Results 7481 - 7490 of 9762

Ivan Župunski, Vladimir Vujicic, Zoran Mitrovic, Slobodan Milovancev, Mile Pesaljevic
ON-LINE DETERMINATION OF THE MEASUREMENT UNCERTAINTY OF THE STOCHASTIC MEASUREMENT METHOD

The paper presents a stochastic sampling method applied to a measurement of the mean value of the product of two arbitrary signals. This method is especially convenient for measuring electric power, electric energy consumption, as well as root-mean-square of voltage and/or current. The method features a very simple hardware and the possibility of selecting the measurement accuracy by choosing a suitable measurement interval. When measuring electric energy, accuracy better than 0.01 % is achieved.
The measurement uncertainty of the stochastic sampling method is analysed and the influence of dominant factors is quantitatively derived. Special consideration is given to the influence of dispersion of A/D converter outputs and the waveforms of the two input signals as contributors to the measurement uncertainty. As the exact shapes of the waveforms are not known in advance, it is not possible to determine their influence on the measurement uncertainty. To overcome this issue, a novel additional hardware is designed, which provides the estimate of measurement uncertainty during the experiment - simultaneously with the measurement result, its measurement uncertainty is available on-line.

Abraham Mejía-Aguilar, Ramon Pallàs-Areny
ELECTRICAL IMPEDANCE MEASUREMENT USING VOLTAGE/CURRENT PULSE EXCITATION

Electrical impedance measurements based on pulse excitation are fast and simple to implement, which makes them attractive for low-power measurement systems such as remote water conductivity monitoring based on two-electrode cells. Pulse measurements also allow us to estimate electrode parameters but measurement errors increase when the electrode resistance is very different from that of the electrolyte. We propose a dual pulse excitation technique to minimize errors in estimating electrode parameters: a voltage pulse is followed by a current pulse whose amplitude is set according to the results for the first (voltage) pulse. Experimental results for impedance networks that emulate water resistivity from 100 Ω·cm to 10 kΩ·cm (corresponding to surface waters) measured with two stainless-steel electrodes, yield relative errors below 0,2 % even for (emulated) corroded electrodes. For actual electrodes, relative errors are below 2 % for the resistance and 4 % for the capacitance that model its impedance. Conductivity measurements for surface waters yield relative errors about 0,1 %, which is quite acceptable for low-cost autonomous sensors. Electrode impedance estimates differ from the first to the second pulse, presumably due to the different effective current density injected by each pulse. Nevertheless, experimental results can still be used to detect corrosion in stainless steel electrodes.

Lautaro Ramirez, Luis Omar Becerra, Luis Manuel Peña
COMPARISON AMONG METHODS EMPLOYED IN THE CALIBRATION OF HIGH ACCURACY MASS STANDARDS AND UNCERTAINTY VALIDATION BY NUMERICAL SIMULATION

The present work exposes the comparison among numerical methods used in the calibration of a set of high accuracy weights by subdivision method. This paper covers the comparison of the mean values, the uncertainties and correlations obtained with the Orthogonal, the Gauss Markov, the Ordinary Least Squares and the Weighted Least Squares (Lagrange Multiplier) methods. These methods are the most commonly used in the realization of the mass scale in the National Metrology Institutes (NMI). Also, the uncertainty evaluated by these methods was compared against the evaluation by a numerical simulation method (Monte Carlo’s method).

Maurizio Caciotta, Sabino Giarnetti, Fabio Leccese, Zbigniew Leonowicz
DETECTION OF SHORT TRANSIENTS AND INTERRUPTIONS USING THE HILBERT TRANSFORM

In electrical energy power networks, disturbances can cause problems in electronic devices so their monitoring is fundamental in Power Quality. In this paper we address the problem of disturbances estimation by using the Hilbert Transform (HT). It is employed as an effective technique for tracking the voltage waveforms in electrical distribution systems. The mathematical simplicity of the proposed technique, compared with the commonly used algorithms from the literature, renders them competitive candidate for the on-line tracking of disturbances. The accurate tracking of the HT facilitates its implementation for the control of disturbances mitigation devices. Simulation results are provided to verify the tracking capabilities of the algorithm and this has been tested under different conditions: voltage dip with phase jump, noise and frequency changes shows that the Hilbert Transform can be used as a valid methodology for this type of phenomena.

Saulius Kausinis, Algimantas Barakauskas Barakauskas, Rimantas Barauskas, Aurimas Jakstas, Albinas Kasparaitis
REDUCING DYNAMICALLY-INDUCED DEVIATIONS FOR LINE SCALE CALIBRATION IN NON-IDEAL MEASUREMENT SITUATION

The paper treats the issue of embedding the traceable length metrology into technological process by performing precise dynamic measurements of line scale in its manufacture line. It addresses the error-related problems specific to line scale calibration in dynamic mode of operation that are caused primarily by dynamic loads. Introducing the dynamic regime of calibration leads to the dynamic calibration error originating due to vibration sources in the structure. This uncertainty contribution should be considered and implicated in the total uncertainty budget. A new 3D finite element model was developed in order to both investigate the influence of dynamical excitations of a long stroke comparator structure and evaluate possible influence of vibrations on geometrical dimensions of the line scale. Both the dynamically induced deviations and current capabilities to carry out line scale calibrations were examined experimentally. The experiments were conducted on the interferometer-controlled comparator setup with a moving microscope that was further developed to reduce the calibration repeatability error.

Jan Malinsky, Petr Kocourek
DEMONSTRATIONAL SYSTEM FOR TRAINING IN FLEXRAY COMMUNICATION

This work deals with an educational system for the teaching of standard FlexRay (FR). The FR is a new communication standard intended to be used in cars in the near future. It is primarily intended for communication among so-called x-by-wire systems. Many fundamental and advanced features of FR standard, as well as basic kinds of x-by-wire systems, can be demonstrated by this educational system. The largest benefit is in an illustrative presentation of the FR synchronization mechanism (SM) in operation, as well as of its robustness. The SM is probably the most important FR process, and provides synchronization among time bases in a FR network. The educational system allows the disturbance of the time bases by modification of clock frequency. External generators are used for this purpose. The changes in SM behaviour can be observed as a result of time base disturbing. The most interesting observation is to what degree the SM is able to cope with this clock frequency fluctuation. No similar FR educational systems have previously been equipped with a possibility like this.

Pablo Luna-Lozano, Ramon Pallàs-Areny
HEART RATE DETECTION FROM IMPEDANCE PLETHYSMOGRAPHY BASED ON CONCEALED CAPACITIVE ELECTRODES

Physiological monitoring outside clinical environments and medical offices can contribute to people's wellness, particularly if that monitoring does not disturb their daily activities, and can also help in life-style improvement. We propose a novel non-conscious method to monitor the heart rate which is based on detecting blood volume changes in the thigh through electrical impedance plethysmography while the subject is seated. Four conductive strip electrodes are concealed underneath seat's upholstery, hence working as capacitive electrodes. A 50 kHz current is injected trough two outer electrodes and the changes in the drop in voltage between the inner electrode pair are detected.
Tests performed with a system designed in our laboratory show that the recorded signal has peaks that unmistakably coincide with the heart rate. The waveform depends on the relative position of both pairs of electrodes, and the sensitivity to impedance changes depends on the position and area of the voltage-detecting electrodes with respect to those of the current injection electrodes. The amplitude and waveform of the recorded signal are good enough for the heart rate to be straightforwardly obtained by a slope-detection-based algorithm.

Ramon Casanella, Ramon Pallàs-Areny
ON THE DESIGN OF LOW-POWER SIGNAL CONDITIONERS FOR RESISTIVE SENSORS

This work analyzes power consumption in signal conditioning circuits for resistive sensors. We show that, for a given dynamic range for the measurand, simple conditioners based on voltage dividers or Wheatstone bridges directly connected to an analog-to-digital converter (ADC) do not usually have minimal power consumption. We develop analytical guidelines to achieve the optimal power design for signal conditioners and apply them to the actual design of the conditioner for an RTD sensor. We show that by adding a low-power amplifier plus a passive low-pass filter to a voltage divider sensor interface, the power consumption can be significantly reduced as compared to that of standard voltage dividers designed for maximal sensitivity.

Maria Teresa Todisco
GRADUALLY-VARIED FLOWS IN OPEN-CHANNEL NETWORKS

Reported here are some results obtained, from a calculus algorithm application that, based on known equation analytical solutions of water flow profiles, allows the study of steady-state, gradually varied flow in open channel networks. The procedure allows to calculate, in the case of slow water flow into gradually downward slope channels, in the direction of motion, the florates and water levels respectively, in all the nodes and sides of the network. The results have been compared with the solutions proposed by other authors.

Pedro M. Ramos, Fernando M. Janeiro, Tomáš Radil
PERFORMANCE COMPARISON OF THREE ALGORITHMS FOR TWO-CHANNEL SINEWAVE PARAMETER ESTIMATION: SEVEN PARAMETER SINE FIT, ELLIPSE FIT, SPECTRAL SINC FIT

The comparison of three different algorithms for the estimation of parameters of two sine signals with common frequency is presented. The algorithms are the ellipse fit, the seven parameter sine fit and the spectral sinc fit. The comparison includes signal to noise ratio analysis, amplitude analysis and phase difference analysis.

Page 749 of 977 Results 7481 - 7490 of 9762