Benjamin Sanchez, Ebrahim Louarroudi, Rik Pintelon, Ramon Bragos
Modeling the non-stationary behaviour of time-varying bioimpedance

The electrical bioimpedance (EBI) measurement of varying biological systems Z(&omega,t) (e.g. the heart, the lungs, …) by means of electrical impedance spectroscopy (EIS) remains an open challenge today. Briefly stated, the bioimpedance is widely assumed to be time-invariant when it is measured with the frequency sweep EIS approach. Hence, time-varying changes are thus ignored or treated as a noise source. In this work, we attempt to model the time-variant effects and obtain a simple (periodically) time-varying [(P)TV)] electrical circuit model with (P)TV parameters from experimental in vivo EBI data using the model proposed by Fricke- Morse. The aim is then to illustrate that a limited number of harmonic components of the electrical circuit parameters, which corresponds to an integer number of the bio-system periodicity, can be used to have a realistic evolution of the bioimpedance over time as well as in frequency.

Henryk Urzedniczok
A numerical method of correcting the influence of the additional quantities for nonselective sensors

At present the modern sensors, based on the microelectronic, optoelectronic and bio-electronic technologies, are widely applied in various measuring systems. However, these sensors have often one essential disadvantage - wrong properties in metrological sense, mainly due to the poor selectivity and high sensitivity to the impact of the additional physical quantities. To apply such sensors in measuring transducers, for example in gas concentration transducers, effective methods of correction of these quantities influence are required.
An effective numerical method based on model with variable coefficients is described in this paper. An example of using this method for the simultaneous correction of influences both temperature and humidity for a gas concentration measuring transducer with Figaro TGS2442 carbon monoxide sensor is given.
Dispersion of measurement results due to the influence of these quantities, changing in a fairly wide range, is reduced about 11 times, from 64% to 6 % of range.

Predrag Petrovic
A New Peak Detector Based on Usage of CCCIIs

The paper presents a completely new realization of peak detector/full-wave rectifier of input sinusoidal signals, employing four CCCIIs (controlled current conveyors), metal-oxide-semiconductor transistors and single grounded capacitor, without any external resistors and components matching requirements. The circuit gives a DC output voltage that is the peak input voltage over a wide frequency range, with a very low ripple voltage and low harmonic distortion. The proposed circuits use an all-pass filter as a 90° phase shifter of the square value of the processed input signal. The proposed circuit is very appropriate to further develop into integrated circuits. To verify the theoretical analysis, the circuit PSpice simulations has also been included, showing good agreement with the theory.

Luís Rosado, Pedro Ramos, Moisés Piedade
Time Domain Processing of Pulsed Differential Eddy Currents Testing Signals

The use of pulsed stimulus on Eddy Currents Testing is currently applied on multiple applications from conductivity measurements to defects detection on metallic parts. This type of stimulus is frequency rich since it is composed by multiple harmonics and this allows testing with different depth concentration of the eddy currents as they are subject to the skin effect. In this paper, pulsed stimuli are used while testing with a custom probe. The probe output signals are acquired and processed digitally in the time domain using a simple feature, its RMS value. Two-dimensional scans were performed allowing the imaging of a tested metallic part with different defects.

Aleksandar Nikolic, Blagoje Babic, Aleksandar Zigic, Nikola Miladinovic, Srdjan Milosavljevic
Multi-channel System for Remote Power Quality Monitoring of Electricity Supplied by Public Distribution Networks

Multi-channel system for remote power quality monitoring of distribution power stations in low and medium voltage supply networks is presented in the paper. The goal was to develop low-cost, space saving device that could simultaneously take measurements from all (usually eight or up to twelve) outgoing threephase feeders in distribution substation. In that case, we should perform at least 3 voltage measurements and 36 current measurements at the same time. In order to save space, but not to reduce the measurement accuracy, a data acquisition system is designed based on real-time multiprocessing with microcontroller and FPGA circuit. Voltage and current measurements and their corresponding high-order harmonics are calculated using fast FPGA circuit, while other calculations (power, power factor, voltage and current phase angles, etc.) are performed in microcontroller. Further savings are obtained using multichannel analog input modules with multiplexed inputs. Communication with supervising computer is done using GPRS modem or wireless network module depending of station location. Results obtained on the developed industrial prototype confirm proposed solution.