Josep Jordana

Electrical resistance tomography to detect leaks from buried pipes

This paper describes a non-invasive method for detecting leaks in buried pipes, which uses a surface linear electrode array perpendicular to the axis of the pipe. Two electrodes inject current and the remaining electrodes detect the drop in voltage on the ground surface using both the dipole-dipole array and a modified Schlumberger array. A single-step reconstruction algorithm based on the sensitivity theorem yields two-dimensional images of the cross section. A personal computer controls current injection, electrode switching and voltage detection, which allows us to easily test various arrays of electrodes and speed up the process of measurement. The system was first tested in the laboratory using a stainless steel tube immersed in water and covered by a rubber sleeve to simulate a non-conductive leak. By taking reference measurements with the immersed bare pipe, it is possible to reconstruct images showing the simulated leak using only 16 electrodes and even as few as eight electrodes, albeit with reduced resolution. Field measurements have involved simulated leaks of water from a plastic tube 1 m long and 8 cm in radius buried at a depth of about 24 cm in a farm field. The hardware system injected 1 kHz, 20 V peak-to-valley square waveforms, thus avoiding electrode polarization effects. The simulated leak was unmistakably distinguished.

Program-dependent uncertainty in period-to-code converters based on counters embedded in microcontrollers

Microcontrollers with embedded timers/counters offer a simple, compact, and low-cost interface to convert from time period to digital code. This makes them suitable to interface quasi-digital sensors that yield a signal whose period is modulated by the measurand. The accuracy, however, is limited by the uncertainty of the counting process, which depends on trigger uncertainty and other factors. This paper analyzes the effect that the counting program running in a PIC16F873 microcontroller has on the uncertainty of the measured time periods. Because different instructions imply different power consumption, when the microcontroller program involves a loop, the power supply rails display periodic transients corresponding to the more power-demanding instructions. These transients increase the internal noise at trigger inputs, and if they are spaced /spl tau/ /spl mu/s, the measured period when the input signal does not have a fast slew rate is also quantified to /spl plusmn/ /spl tau/ /spl mu/s.

Optimal two-point static calibration of measurement systems with quadratic response

Measurement devices and instruments must be calibrated after manufacture to correct for component and assembly tolerances, and periodically to correct for drift and aging effects. The number of reference inputs needed for calibration depends on the actual transfer characteristic and the desired accuracy. Often, a linear characteristic is assumed for simplicity, either for the overall input range (global linearization) or for successive input subranges (piecewise linearization). Thus, only two reference inputs are needed for each straight line. This two-point static calibration can be easily implemented in any system having some basic computation capability and allows for the correction of zero and gain errors, and of their drifts if the system is periodically calibrated. Often, the reference inputs for that calibration are the end values of the measurement range (or subrange). However, this is not always the optimal selection because the calibration error is minimal for those reference inputs only, which ...

Uncertainty in resistance measurements based on microcontrollers with embedded time counters

Microcontrollers with embedded time counters can measure resistance by determining the time needed to charge or discharge a given capacitor C. This paper analyzes the uncertainty and error in resistance measurements based on measuring the discharging interval depending on the value of C. Using the internal Timer1 of the PIC16F874, two calibration resistors, and averaging 1000 measurements, the relative error for resistors from 825 /spl Omega/ to 1540 /spl Omega/ and C = 220 nF, 1.5 /spl mu/F, and 4.7 /spl mu/F is below 0.2%, and the standard deviation for C = 1.5 /spl mu/F, and 4.7 /spl mu/F is below 0.3 /spl Omega/. Power supply noise greatly influences the uncertainty, which makes it essential to use power supply decoupling capacitors.

Automated electrical impedance measuring systems to detect leaks from buried pipes

This paper describes two automated electrical impedance-rneasuring systems intended for detecting leaks from buried pipes. Each system includes current injection and voltage detection, a switching system based on reed relays and a personal computer (PC). Both systems allow the implementation of any desired electrode configuration under PC control. AC current injection overcomes electrode polarisation and reduces electrode impedance. The injector and detector of the first system designed are commercially available instruments connected by GPIB, and permit the injection of sine and square waves from 10 Hz to 100 kHz. The PC obtains the real and imaginary parts of the soil impedance by digital coherent demodulation. The signals detected are contaminated by common mode voltage and electromagnetic interference between current-injecting wires and detecting wires. The second system designed uses a custorn-built detector that reduces interference by synchronously sampling square waveforms. Using an additional electrode eliminates the common mode voltage at the detector input. This second system yields only the real part of the soil impedance but is very cost-effective. Both systems have been successfully applied to the detection of simulated leaks from buried pipes in laboratory phantoms.

Evaluación Continua Aplicada a la Asignatura Componentes y Circuitos en su Adecuación al Espacio Europeo de Educación Superior (EEES)

This paper describes the continuous evaluation applied to the course Components and Circuits in the Telecommunications Engineering degree of the Castelldefels School of Technology in the autumn semester of 2006. The paper explores the relationship between the academic performance achieved by students, their previous studies and the results of the university entrance evaluation. This work demonstrates that there is a clear correlation between overall academic performance and the mark obtained to enter the university. This continuous evaluation study along with the application of active learning methodologies has allowed about 50% of students has passed the course.

Uncertainty in Resistance-to-Code Converters Based on Microcontrollers Measuring Time Intervals

Abstract This paper analyses the effect of trigger noise and quantization on the uncertainty of time intervals measured with Timerl of the PIC16F874 microcontroller. The time intervals result from charging and discharging a capacitor through a resistive sensor and two reference resistors. The uncertainty is described by the standard deviation and frequency distribution of the time counts. The uncertainty comes from quantization and trigger noise due to both the input channel noise and signal noise, which depends on the slew rate of the signal, and can be reduced by multiple time-interval averaging. Because of that uncertainty, a large capacitor does not necessarily yield a small relative uncertainty.

Analysis of the Optimum Gain of a High-Pass L-Matching Network for Rectennas

Rectennas, which mainly consist of an antenna, matching network, and rectifier, are used to harvest radiofrequency energy in order to power tiny sensor nodes, e.g., the nodes of the Internet of Things. This paper demonstrates for the first time, the existence of an optimum voltage gain for high-pass L-matching networks used in rectennas by deriving an analytical expression. The optimum gain is that which leads to maximum power efficiency of the rectenna. Here, apart from the L-matching network, a Schottky single-diode rectifier was used for the rectenna, which was optimized at 868 MHz for a power range from −30 dBm to −10 dBm. As the theoretical expression depends on parameters not very well-known a priori, an accurate search of the optimum gain for each power level was performed via simulations. Experimental results show remarkable power efficiencies ranging from 16% at −30 dBm to 55% at −10 dBm, which are for almost all the tested power levels the highest published in the literature for similar designs.