A Fiber Optical Sensor For Non-Contact Vibration Measurements

This paper describes an intensity based optical sensor for the evaluation of accelerations from non-contact displacement measurements. Plastic optical fibers are used to collect the reflected light from several points on the vibrating surface, allowing the reconstruction of the vibration distribution. Two compensation techniques to reduce systematic effects due to the target reflectivity are also described and compared: one is based on the spectral analysis of the received optical signal and the other takes advantage of a reference displacement sensor. Experimental results in real conditions during vibration tests have demonstrated the capability to measure sub-micrometer vibration amplitudes up to about 40 kH

Assessment of a Dual-Wavelength Compensation Technique for Displacement Sensors Using Plastic Optical Fibers

The paper analyzes the performance of a dual-wavelength technique devised to compensate power fluctuations in intensity-modulated plastic optical fiber sensors, which were specifically conceived for the measurement of displacements in industrial and civil applications. These sensors retrieve the displacement from the variation of the attenuation along the light path and use two signals at different wavelengths to compensate for the effects of parasitic quantities, such as temperature and strains along the fiber. The theoretical behavior of the compensation technique is presented, and the results of experiments carried out with different combinations of signal wavelengths and plastic fibers are reported. The experimental setup has proved that, by proper choice of the compensation signal wavelength, it is possible to monitor displacements in the range (0 to 10) mm, even for low received power and under severe perturbation conditions, thus significantly improving the long-term stability of the sensor

A Low-Cost Optical Sensor for Non contact Vibration Measurements

This paper presents a new noncontact method to measure vibrations by using a low-cost optical approach that is able to provide a submicrometer resolution. The transducer exploits a simple optical setup based on an intensity-detection scheme that is implemented with plastic optical fibers, whereas innovative non demanding spectral data processing allows compensation of the vibrating surface reflectivity and the gains of the measurement chain. The performance of the proposed system has been assessed, through comparison with other techniques, by performing several measurement tests that use targets vibrating at frequencies from a few hertz up to several tens of kilohertz and with different values of reflectivit

Displacement and acceleration measurements in vibration tests using a fiber optic sensor

This paper discusses the evaluation of displacements and accelerations from noncontact displacement measurements using a low-cost plastic fiber-optic sensor. Issues about sensor calibration in the presence of nonuniform targets, which is a situation occurring in many practical applications such as vibration tests of printed circuit board assemblies, are analyzed. Furthermore, a procedure to contemporaneously calibrate several optical sensors to allow mapping the vibration amplitude and acceleration distributions in a simple and low-cost way is also disclosed. The proposed calibration procedure is particularly effective since it requires just one reference accelerometer, which is actually already available in typical vibration test facilities. Experimental results obtained under real conditions during a sinusoidal vibration test are also provide

A precompliance EMC test-set based on a sampling oscilloscope

In this paper, a precompliance test-set for the measurement of conducted emissions based on a medium-level sampling oscilloscope and on a fast filtering algorithm (DFT) is presented. This system has been designed as a low-cost alternative to the typical precompliance test-sets that are based on spectrum analyzers equipped with EMC filters and peak detectors. Experimental examples of the results obtained using a sampling oscilloscope with 8 Kbytes of memory are given

Labor market performance in Argentina under Kirchner’s administration

El abandono del régimen de convertibilidad modificó los precios relativos, supuso una importante reducción en el nivel desalariosy puso enmarcha un acelerado proceso decrecimiento económico. Este proceso tuvo como uno desus principalesresultadosla generación decerca decinco millones de puestos de trabajo, lo que representa dos veces y media la cantidad de empleos creados en los veinticinco años previos. El proceso deexpansión delempleo, no obstante, no seregistró con igual intensidad en todos los sectores ni bajo las mismas condiciones. En este contexto, el propósito del presente trabajo es analizar la transformación que experimentó el mercado de trabajo durante la postconvertibilidad estudiando no solo los logros alcanzados sino también señalando las cuentas pendientes y desafíos futuros.The abandonment of the convertibility regime in Argentina changed relative prices, brought about a significant reduction in real wages and set up in motion a major process of economic growth. This process had as one of its main outcomes that have generated near five million jobs, which represents two and a half times the number of jobs created in the previous twenty-five years. However, the process of expanding employment was not homogeneous across sectors. In this context, the aim of this paper is to analyze the transformation experienced by the labor market during the Postconvertibility regime studying not only the achievements but also trying to point out the pending accounts and future challenges.Fil: Santarcangelo, Juan Eduardo. Universidad Nacional de General Sarmiento. Instituto de Industria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Perrone, Guido Agustín. Universidad Nacional de General Sarmiento. Instituto de Industria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

The Non Uniform Adaptive Angular Spectrum Method and its Application to Neural Network Assisted Coherent Beam Combining

Increasing the number of laser beams that can be coherently combined requires accurate and fast algorithms for compensating phase and alignment errors. The paper proposes to use a Fully Connected Artificial Neural Network (FCANN) to correct the beam positioning perturbations by evaluating the beam shifts and tilts from two images taken at slightly different locations. Then, since it is practically impossible to have a large enough experimental dataset to train the neural network, this approach required developing an accurate and fast simulation method to evaluate the beam propagation in arbitrary directions, overcoming the limitations occurring when the computation must be repeated a large number of times. The numerical approach is a variant of the Angular Spectrum (AS) method, called Non Uniform ADaptive Angular Spectrum (NUADAS) method, which relies on the combination of non-uniform and adaptive Fourier transform algorithms to allow the computation of an arbitrary field distribution in a plane that is shifted and tilted with respect to the source. The parallel implementation of the NUADAS method is discussed and the numerical and experimental validations are presented. Then, an FCANN is trained using the synthetic dataset generated with the NUADAS method and the results are discussed, demonstrating the viability of the proposed approach not only for coherent beam combing, but also in other beam alignment applications

Performance analysis of a noncontact plastic fiber optical fiber displacement sensor with compensation of target reflectivity

peer-reviewedAn inexpensive fiber-based noncontact distance sensor specific for monitoring short-range displacements in micromachining applications is presented. To keep the overall costs low, the sensor uses plastic optical fibers and an intensiometric approach based on the received light intensity after the reflection from the target whose displacement has to be measured. A suitable target reflectivity compensation technique is implemented to mitigate the effects due to target surface nonuniformity or ageing.The performances of the sensor are first evaluated for different fiber configurations and target reflectivity profiles and positions using a numerical method based on Monte Carlo simulations. Then, experimental validations on a configuration designed to work up to 1.5mm have been conducted. The results have confirmed the validity of the proposed sensor architecture, which demonstrated excellent compensation capabilities, with errors below 0.04mm in the (0-1)mm range regardless the color and misalignment of the target