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Alexandre Cabral, Manuel Abreu, José M. Rebordão
ABSOLUTE DISTANCE METROLOGY FOR LONG DISTANCES WITH DUAL FREQUENCY SWEEPING INTERFEROMETRY

Coherent absolute distance interferometry is one of the most interesting techniques for length metrology. In frequency sweeping interferometry (FSI), measurements are made without ambiguity, by using a synthetic wavelengths resulting from a frequency sweep. Accuracy is mainly dependent on the capability to measure the synthetic wavelength, using a Fabry-Perot interferometer (FP) to count resonances as frequency sweeps, and therefore the number of detected synthetic fringes. For large ranges, the number of fringes dominates performance, leading to a linear decrease of the accuracy with range. By increasing the size of the interferometer reference arm, and measuring both the distance and the reference arm independently, it is possible to maintain small distance high accuracy measurements, even for much larger range.
In the context of the ESA-PROBA3 mission (coronagraph and demonstration of metrology for free-flying formation), we implemented a FSI sensor composed of a mode-hop free frequency sweep external cavity diode laser, a high finesse FP (to measure accurately the frequency sweep range) and a dual measurement system to enable the measurements at 150 m with an accuracy at the tens of micrometer level.
In this paper we describe the implementation of the prototype and present the first results obtained for a long range measurement.

João Carlos Giacomin, Flávio Henrique Vasconcelos, Elson José da Silva
RADIOMETRIC MEASUREMENT OF CORN CANOPY WATER CONTENT WITH A 916 MHz WIRELESS SENSOR NETWORK

A wireless sensor network is used as a distributed system for measuring plant water content in crop fields. The WSN works as a radiometric sensor which gets the information about vegetation water content from the RF communication signals. No specific sensor is needed. The equations of the measurement process are developed based on the two ray propagation model. Experimental results obtained in a corn field demonstrate a linear relation between gravimetric moisture of plants and the attenuation of the WSN RF signals.

Alex Pablo Ferreira Barbosa, C. R. da Costa Rodrigues, D. M. do Espírito Santo Filho, José Renato Real Siqueira, Roberto Guimarães Pereira, Luiz Henrique Paraguassú de Oliveira
METROLOGICAL APPROACH IN THE CHARACTERIZATION OF VISCOSITY OF CORN BIODIESEL RELATIVE TO TEMPERATURE, USING CAPILLARY VISCOMETERS

In this article we study the behavior of biodiesel viscosity from corn biodiesel, transesterified with methanol, in relation to temperature. These quantities were measured with capillary viscometers, from 20 ºC to 40 ºC. Measurement uncertainty was calculated. The behavior of viscosity with temperature is analyzed considering the estimated uncertainty.

Suzana Jakovljevic, Sanja Šolic, Tamara Aleksandrov, Željko Alar
APPLICATION OF THE SCANNIG ELECTRON MYCROSCOPE FOR THE ANALYSIS OF THE REFERENCE HARDNESS BLOCK SURFACE QUALITY

One of the most significant problems in realising hardness traceability are reference hardness blocks failures. The work included testing on one standard block prepared in compliance with the requirements defined in EN ISO 6507-3 standard. It was calibrated on the reference hardness testing machine. For the analysis of the hardness block surface and the indentation, a scanning electron microscope TESCAN, type: VEGA TSS136LS with EDS sensor was applied. Failures caused by the reference hardness blocks finishing and failures due to the material inhomogeneity were noted. Microanalysis of the chemical composition on typical spots was carried out with EDS sensor.

Aldo Baccigalupi, Mauro D'Arco, Annalisa Liccardo, Michele Vadursi
IMPLEMENTATION OF HIGH RESOLUTION DAC TEST STATION: A CONTRIBUTION TO DRAFT STANDARD IEEE P1658

The paper deals with the implementation of a measurement station for the test of high resolution of Digital-to-Analog Converters (DACs). The basic idea relies on the employment of a differential amplifier that provides a signal related to the difference between the voltage generated by the DAC under test and a reference signal. To solve problems associated to synchronization, the reference signal is gained by treating the DAC output voltage through a narrow band filter. Thanks to the differential amplifier, the difference signal, which holds information about DAC non linearity, is hugely expanded and, thus, can be acquired by means of an Analog-to-Digital converter whose resolution is lower than that of the DAC under test.

Erik Steinmetz, Ragne Emardson, Per Jarlemark
IMPROVED VEHICLE PARAMETER ESTIMATION USING SENSOR FUSION BY KALMAN FILTERING

Within several applications concerning the improvement of vehicle safety, accurate systems for determination of position, velocity and acceleration are useful. We present a system for accurate determination of these parameters using a sensor fusion technique. The main focus is on how GPS carrier phase data and accelerometer data are modeled and integrated in a Kalman filter that provides both estimates and accompanying uncertainties.

Olivier Pellegrino, Carlos Pires, António Cruz
SPEED MEASUREMENT UNCERTAINTY IN METROGICAL VERIFICATIONS AT IPQ

The speed measurement results of metrological verification of speedometers in the Portuguese Institute for Quality are presented. The associated measurement uncertainties are then taken into account. The measurement methodology and the results of nearly one hundred measuring instruments, with the uncertainty values are displayed and compared with the national maximum permissible errors. The results seem to suggest that the speed maximum permissible errors, for the metrological verifications, have to be changed.

Francisco Augusto Arenhart, Gustavo Daniel Donatelli, Mauricio de Campos Porath
MINIMIZATION OF THE UNEVEN SAMPLING EFFECTS ON EVALUATING ROUNDNESS WITH COORDINATE MEASURING MACHINES

This paper deals with the treatment of the uneven sampled data characteristic of high sampling rate roundness measurements on scanning coordinate measuring machines. Simulations using the sampling pattern presented by these machines and structured profiles resembling a multi-wave standard were performed for testing the response of several interpolation methods. The Lomb-Scargle transform for unevenly sampled data was tested for the same situations. A comparison between the techniques is carried out based on space and frequency domain characteristics of the simulated profile. Real measurements on a multi-wave standard were also performed on different machines to evaluate the behaviour of the measurement softwares with respect to the uneven sampling and to verify applicability of the simulated methods. Results show the improvements obtained on evaluated parameters with the use of the discussed techniques.

Jan Hrabina, Josef Lazar, Petr Jedlicka, Ondrej Cíp
MEASUREMENT OF IODINE CELL PURITY AND ABSOLUTE FREQUENCY SHIFTS FOR LASER STABILIZATION

This contribution deals with the investigation of uncertainties achievable through stabilization of lasers using saturated absorption in iodine vapour. The main focus is on the iodine cell technology and evaluation.
We present results from two independent methods for the measurement of the purity of molecular iodine in absorption cells. The purity was tested by improved method based on measurement of induced fluorescence and evaluation by the Stern-Volmer formula. Original measurement setup was upgraded with a system for compensation of unwanted effects of back-reflected and scattered light and multimode regime of the pumping laser. The modified arrangement results in a significant improvement of reproducibility.
The evaluation of absolute frequency shifts caused by iodine cells was measured by direct frequency comparison of iodine-stabilized frequency doubled Nd:YAG lasers. The absolute frequency shift of a reference laser system was calibrated by frequency comparison with a stabilized optical comb locked to the radiofrequency etalon, the measuring system consists of a commercial laser and our stabilization system with 3f technique. Correct function of the stabilization setup was verified through the evaluation of the Allan standard deviations.
A series of measurements with a special refillable iodine cell was conducted on both experimental setups for three various levels of impurities. Results of both methods are in a very good correlation and show very high purity of iodine in measured cells. The results also help for definition of procedures for improving iodine cell manufacturing technology at the Institute of Scientific Instruments.

Henrike Stephani, Michael Herrmann, Karin Wiesauer, Stefan Katletz, Bettina Heise
ENHANCING THE INTERPRETABILITY OF TERAHERTZ DATA THROUGH UNSUPERVISED CLASSIFICATION

We present the applicability of hierarchical agglomerative cluster algorithms to terahertz (THz) spectroscopic analysis. We show the influence of different windowing and filtering methods in the spectral data pre-processing to enhance the clustering results. Two distance measures are compared. Classical Euclidean distance on the full frequency range and a distance working only on the minima of the spectra. We further show the adaptability of our clustering methods for THz hyper-spectral image classification and visualization.

Page 720 of 977 Results 7191 - 7200 of 9762