Vladimir Vujicic

Low frequency stochastic true RMS instrument

A stochastic instrument for true RMS measurement in the low-frequency range is presented. Variable accuracy is achieved by varying the measuring time of the instrument. Inaccuracy of 0.1% of full scale is demonstrated. A complete theory of operation of the instrument is developed and the explicit dependence of measurement error on the measured signal shape is given. Simulations and experimental results strongly confirm the described theory. Simple hardware structure allows easy implementation of parallel measurement.

Accuracy limit of high precision stochastic watt-hour meter

This paper deals with the practical application of the newly developed stochastic watt-hour meter. The limit of its precision is analyzed theoretically, via simulation, and experimentally. The precision of 0.0062 % is achieved in the laboratory experiment. Field experiments also confirm good application properties of the device.

Generalized low frequency stochastic true RMS instrument

The instrument, described in the paper, represents a generalization of the low frequency stochastic true RMS instrument given in (1999). The generalization consists of replacing the input two-bit A/D flash converters with m-bit flash A/D converters, and replacing the two-bit multiplier-accumulator with an m-bit multiplier-accumulator. In this generalized case the stochastic impact decreases, while the deterministics impact increases, causing the theory of operation to be more complicated then originally assumed. A complete theory of operation is also developed. Simulations strongly confirm this theory. It is shown that this generalization is equivalent, even in the case of a 5-bit instrument to acceleration of at least, 450 times over the instrument described in (1999).

Further Generalization of the Low-Frequency True-RMS instrument

This paper shows that the use of random uniform dither in harmonic measurement can significantly shorten both the word of the input A/D converter and the word of the applied base function (sine and/or cosine, prestored in memory), without accuracy loss. This simplifies the hardware for a precise instrument for harmonic measurement. Theoretical considerations demonstrate that the upper limit of the absolute measurement uncertainty is identical for every harmonic coefficient. It is shown theoretically, by simulation, and by experiment that a 6-bit dithered A/D converter word, an 8-bit dithered base function word, and a 6 × 8 (14-bit) multiplier word assure a measurement of 16 harmonics (16 sine and 16 cosine components) with 13-bit accuracy. The measurement of 1 × 16 harmonics is realized in a small programmable-logic-device (PLD) chip.

A Novel Method for Stochastic Measurement of Harmonics at Low Signal-to-Noise Ratio

This paper presents a digital stochastic instrument for the measurement of the harmonics of mains voltages and currents. The instrument operation is based on stochastic analog-to-digital (A/D) conversion and accumulation, with a novel hardware structure tailored for harmonic measurements. A theoretical approach in determining measurement uncertainty is first presented, and the accuracy trends with varying signal-to-noise ratios (SNRs) are then analyzed. Using this theoretical analysis, the relative standard uncertainty of measurement is found to be 0.32% at -10-dB SNR and less than 0.01% at 20-dB SNR. The method and the predicted uncertainty for 50 harmonics are first validated by simulation. The proposed technique is then implemented into a newly developed prototype instrument that was coupled with a coreless current measurement transformer. Calibration shows high linearity of the coreless transformer and, hence, of the whole instrument in a wide range of primary signals. Experimental results, which measure low-level and highly distorted currents, confirm both the theory and simulation.

Digital Stochastic Measurement of a Nonstationary Signal With an Example of EEG Signal Measurement

This paper presents a method of digital stochastic measurement (DSM) of nonstationary signals. The method is based on stochastic analog-to-digital (A/D) conversion and accumulation, with a hardware structure based on a field-programmable gate array and a low-resolution A/D converter. The characteristic of previous implementations of DSM was the measurement of stationary signal harmonics. This paper shows how DSM can be extended and also used when it is necessary to measure the time series of nonstationary signals. An electroencephalography signal is selected as an example of a real nonstationary signal, and its DSM is tested by simulations and experiments. Tests are done without adding noise and with adding a noise-varying signal-to-noise ratio (SNR) from 10 to -10 dB. The results of simulations and experiments are compared versus theory calculations, and the comparison confirms the theory. The presented method provides control of the measurement uncertainty even at low SNR values, by controlling the sample rate of the used A/D converter. This enables designers of measurement systems to choose fast A/D converters with low resolution to achieve higher measurement accuracy.

Integer Codes Correcting Burst Errors within a Byte

This paper presents a class of integer codes that can correct any burst of length \le l within a b-bit byte. Their main advantages lie in linear complexity of encoding and decoding procedures, as well as in the fact that a look-up table-based error control procedure requires relatively small memory resources.

Stochastic Measurement of Power Grid Frequency Using a Two-Bit A/D Converter

This paper presents a new method for measurement of power grid frequency based on the use of three complementary strategies: stochastic A/D conversion, finite impulse response filtering and signal frequency estimation using zero-crossing detection. Although such an amalgamated concept offered great flexibility in choice of system parameters, this paper presents the variant with the two-bit A/D converter, which requires the simplest hardware. It is shown that this solution is highly robust against signal distortions, even when harmonic distortion factors have a value of 100%.

Integer Codes Correcting Spotty Byte Asymmetric Errors

In short-range optical networks, channel errors occur due to energy losses. Upon transmission, they mostly manifest themselves as spotty byte asymmetric errors. In this letter, we present a class of codes that can correct these errors. The presented codes use integer and lookup table operations, which make them suitable for software implementation. In addition, if needed, the proposed codes can be interleaved without delay and without using any additional hardware.

Comparator offset error suppression in stochastic converters used in a watt-hour meter

The paper presents a method of suppressing offset induced error in comparators used in stochastic converters. A stochastic converter has two analog voltage inputs, and the output is proportional to the integral of input product. This converter is used to build a precision watt-hour meter prototype at University of Novi Sad. A stochastic method uses a high oversampling frequency and fast, off-the-shelf commercial comparators. These comparators have relatively large offset, but we show that it does not affect the quality of measurement. Mathematical theory, simulation and testing results are presented. The results show offset error reduction up to three orders of magnitude.