P.M. Ramos

PQ Monitoring System for Real-Time Detection and Classification of Disturbances in a Single-Phase Power System

This paper presents a system for detection and classification of power quality (PQ) voltage disturbances. The proposed system applies the following methods to detect and classify PQ disturbances: digital filtering and mathematical morphology are used to detect and classify transients and waveform distortions, whereas for short- and long-duration disturbances (such as sags, swells, and interruptions), the analysis of the root-mean-square (RMS) value of the voltage is employed. The proposed combined approach identifies the type of disturbance and its parameters such as time localization, duration, and magnitude. The proposed system is suitable for real-time monitoring of the power system and implementation on a digital signal processor (DSP).

On the effects of stresses in ferroelectric (Pb,Ca)Tio3 thin films

Abstract Grazing angle X-ray diffraction, profilemetry, permittivity vs. temperature and Raman spectrometry measurements have been carried out on Ca-substituted lead titanate thin films prepared by sol–gel and deposited on Pt/TiO 2 /SiO 2 /(100)Si substrates. Films with thicknesses of 150 and 350 nm were obtained. The crystalline (Pb,Ca)TiO 3 films were randomly oriented with a and c parameters slightly different from those of bulk ceramics. Profilemetry measurements indicated that the films were under tensile stresses, developed during the drying of the deposited wet layer and during the thermal treatment of crystallization of the amorphous film. These stresses were confirmed by the shift obtained in the Raman frequencies of these films. As a consequence of these stresses, a positive shift of the maximum of the permittivity vs. temperature is measured.

Effect of compositions and annealing conditions on the properties of sol-gel prepared calcium-modified lead titanate thin films

Sol-gel processing has been used for the preparation of calcium-modified lead titanate thin films with perovskite structure. The properties of the polycrystalline films have been studied as a function of the solution composition and the heating rate of the thermal crystallization treatment. The stoichiometry, crystallinity and microstructure of the films have been evaluated by Rutherford backscattering spectroscopy, grazing incidence X-ray diffraction analysis and scanning electron microscopy, respectively. The ferroelectric response of the films was determined by measurement of their hysteresis loops, in an attempt to relate electrical properties to processing conditions.

DSP Based Portable Impedance Measurement Instrument Using Sine-Fitting Algorithms

The development and implementation of a digital signal processor (DSP) based portable impedance measurement instrument is described in this paper. The circuit sinewave stimulus is generated by the device using a direct digital synthesizer at the desired measurement frequency. The sine is applied to a reference impedance in series with the unknown impedance. Two analog to digital converters (ADCs) acquire multiple samples of the two sine voltages which are transmitted to the DSP. Sine-fitting algorithms determine the sine amplitudes, phases, DC components and frequency. From these values and the reference impedance values, the impedance amplitude and phase are determined. Included in the device, amplifiers extend the ADCs input range while a digital potentiometer enables the adjustment of the reference impedance to improve accuracy

Uncertainty Analysis of Impedance Measurements Using DSP Implemented Ellipse Fitting Algorithms

Impedance measurements are extremely important in many fields of science and accurate impedance measuring devices are therefore required. Besides accuracy, low-cost and portability are also sought after characteristics in some applications. A DSP based prototype has been developed to accurately measure impedances. An ellipse fitting algorithm is implemented in this device introducing many advantages in terms of speed and memory requirements, when compared to other signal processing algorithms commonly used, such as sine-fitting. In this paper, the developed prototype is used to measure an RLC series impedance in a range of frequencies and the experimental measurement uncertainty is analyzed.

Fast ADC testing by spectral and histogram analysis

The integral nonlinearity (INL) of analog to digital converters (ADCs) can be described by a behavioral error model expressed as one dimensional image in the code domain. This image consists of low and high code frequency components which allow describing the ADC performance with a small number of parameters. This paper presents new methods for low code frequency and high code frequency testing. The identification of the low code frequency components is performed by multi-harmonic sine fitting in the time domain. The high code frequency components are estimated in the statistical domain by a narrow band histogram test using a triangular stimulus signal. The performance of the proposed method is assessed for various ADC devices.