Roman Malarić

Mutual Inductance of a Precise Rogowski Coil in Dependence of the Position of Primary Conductor

The Rogowski coil is a well-known current-to-voltage transducer. To use it for the high-accuracy measurement of AC current (at power supply frequency), all influencing quantities and their contribution should be recognized and analyzed. Thus, the partial influence due to the deviation from the central position of the primary conductor for a real sensor, with the nonhomogeneous density of secondary turns, is given in this paper. The measured deviation of mutual inductance in this case showed very good agreement with the theoretical prediction, which is promising for the expected application of such a sensor.

Signal propagation modeling in power-line communication networks

In this paper, we present a propagation model for the power-line communication (PLC) networks, based on the frequency-domain analysis. First, we set a simple two-port model of the network. Then, we calculate a complex attenuation factor from z-parameters, expressed in terms of impedances, easily calculable/measurable from the network ports. We explain simultaneously calculation and measurement methods based on the same principle, and then compare the results with direct measurements performed in the network designed for this purpose. We provide all of the elements for a simple end efficient propagation model. They include propagation by crosstalk between different circuits in, for example, three-phase networks, as well as the influence of the loads connected to the ports of different circuits in such networks. We have concluded that the model is suitable for PLC channels simulations that give very accurate results and enable modeling of wide-band channel characteristics.

Determination of Load Angle for Salient-pole Synchronous Machine

Determination of Load Angle for Salient-pole Synchronous Machine This paper presents two methods for load angle determination for salient-pole synchronous generator. The first method uses optical encoder to detect the rotor position. In some cases the end of the rotor shaft is not free to be used and mounting of an encoder is impossible. Therefore, the second method proposes estimation of the load angle based on the measured electrical values that have been already used in excitation control system of the synchronous generator. Estimation method uses corresponding voltage-current vector diagram and parameters of the synchronous generator, transformer and transmission lines. Both methods were experimentally verified on the digital control system and synchronous generator connected to power system. The estimation and measured results were compared. The accuracy of load angle estimation method depends on voltage and current measurement accuracy as well as generator, transformer and transmission line parameter accuracy. The estimation method gives satisfactory accuracy for load angles less than 120° el. Thus, it can be applied in excitation control system to provide stable work of synchronous generator in under-excitation operating area.

Comparison of RMS Value Measurement Algorithms of Non-coherent Sampled Signals

Comparison of RMS Value Measurement Algorithms of Non-coherent Sampled Signals Uncertainty and bias of RMS measurement of digitally non-coherent sampled signal is dependent on the algorithm used. This paper presents the new Averaging two subsets method for RMS value bias correction of non-coherent sampled signal. Methods for estimating RMS values in the time domain are also compared.

Fall Detection of Patients Using 3-Axis Accelerometer System

Triaxial accelerometers are used as a low cost solution in wide areas of patient care. This paper describes the use of triaxial accelerometer together with ZigBee transceiver to detect fall of patients. The system, including calibration of accelerometers and measurement is explained in detail.

Analysis of the mutual inductance of a precise Rogowski coil

A Rogowski coil is well-known current-to-voltage transducer, and in order to use it for the high-accuracy measurement of AC current (at power supply frequency) all influencing quantities and their contribution should be recognized and analyzed. Therefore, in this paper the analysis of the partial influence due to the deviation from the central position of the primary conductor for a real sensor, with the nonhomogeneous density of secondary turns is analyzed. The measured deviation of the mutual inductance in this case showed very good agreement with the theoretical prediction, which is promising toward the expected application of such sensor.

DVM input and leakage resistance analysis in the DVM-based resistance measurement systems

The digit voltmeter (DVM) input and leakage resistances have been analyzed in the DVM-based resistance measurement system using one or two DVMs. The results are given both theoretically and experimentally. Shunting errors due to DVM-input and leakage resistances were substantially reduced by using a proper measurement method. The method is being further investigated for measuring high-ohm standard resistors.

Determination of High-Resolution Digital Voltmeter Input Parameters

High-resolution digital voltmeters (DVMs) can be widely used when precise measurements are needed, but input circuitry can contribute to the results of measurement. Therefore, to make uncertainty of measurement as small as possible for a particular measurement, it is necessary to characterize its input parameters. In this paper, the methods for the determination of input resistance, input capacitance, and input offset current of widely used precise DVMs HP 3458A with 8 1/2-digit resolution are presented. The method with voltage source and high-ohmic divider resistor has been developed for the determination of both input offset current IS and input resistance RV. The second method with the source of the linear voltage ramp and the picoampermeter is primarily used for the determination of input capacitance CV. It was shown that the input offset current of voltmeters is in the range of picoamperes with relative instability of approximately plusmn0.1, the input resistance is in the range of teraohms with the same relative instability of plusmn0.1, and the input capacitance was measured to be in the range of a few hundred picofarads with uncertainty of a few picofarads.

Measurement of GSM phone emission

GSM (Global System for Mobile Communications) phones are part of everyday life. Their emission level is an EMC (Electro-Magnetic Compatibility) issue. It is important to know the peak of signal levels of the mobile phones. They can cause interference with other electronic devices. The emission testing was performed in GTEM-cell (Giga-Hertz Transversal Electromagnetic mode). The measured peak powers in various regimes of the operation were 15.1 mW for conversation and 2 W for ringing and SMS (short message service) message. Use of GSM mobile phones should be used carefully in the vicinity of electronic devices and systems.

Electrical measurements student laboratory : replacing hands-on with remote and virtual experiments

This paper discusses the problem of transferring knowledge to students of an undergraduate electrical measurement course, and also describes the design of a Web-based measurement laboratory and experimental setup of Web-based experiments at the Faculty of Electrical Engineering and Computing (FER) in Zagreb, Croatia. The suggested design offers the possibility of teaching or presenting high-precision experiments using expensive or sensitive equipment that is unavailable in sufficient quantities to serve large numbers of students.