1,721,028 research outputs found
Study of a New GPS-Carriers Based Time Reference with High Instantaneous Accuracy
No full textA possibility to obtain a new time reference
constantly locked to the Caesium-derived GPS satellites
carriers was investigated by means of a new GPS receiver
architecture able to lock the two GPS carriers and mix them
to obtain a reference frequency with an accuracy close to the
GPS one. This is very important in Perceived Power Quality
distributed measurements systems where the exact
knowledge of the events on the geographic compass is
strongly joined to the capability to associate them an
accurate time.
A simulation of the carrier tracking loop has been performed.
It shows how choosing appropriately the frequency of the
low-pass filter of Costas loop, a modified PLL typically used
in GPS system, it is possible to recover carriers in presence
of high noise to signal ratio too. The front-end of the system
able to select GPS frequencies, which is the first block of the
entire system, was also realized
Un Metodo Combinato per Migliorare l’Accuratezza nelle Misure di Costante Dielettrica in Materiali Granulari
No full textDielectric spectroscopy of liquids through a combined approach: evaluation of the metrological performance and feasibility study on vegetable oils
No full textIn this work, a time domain-based approach for the
estimation of the dielectric parameters of liquids is presented. The
proposed approach combines traditional time-domain reflectometry
measurements with a specific data processing and modeling
that leads to the evaluation of the Cole-Cole parameters. The pivotal
step of the procedure is the implementation of an accurate
transmission line model of the used measurement cell. In this way,
the error contributions due to undesired parasitic effects are minimized;
hence, the overall accuracy is significantly enhanced. The
proposed approach is tested through repeated measurements on
well-referenced materials; this also allowed performing the related
metrological analysis. Successively, the proposed procedure is applied
for the evaluation of the Cole-Cole parameters of vegetable
oils. In fact, at the state-of-the-art, only limited data are available
for the dielectric characteristics of vegetable oils. In particular, ten
different types of vegetable oils are considered. Results show that
the proposed approach has strong potential also for possible practical
applications in the area of anti-adulteration and quality control
Improvement and Metrological Validation of TDR-Methods for the Estimation of Static Electrical Conductivity
No full textAccurate measurement of the static electrical conductivity provides a great insight into the characteristics and quality status of various materials. To overcome some limitations of the traditional measurement methods, there has been a growing interest toward the investigation of enhanced techniques for measuring electrical conductivity. In this regard, time-domain reflectometry (TDR) has attracted considerable attention, also due to the possibility of simultaneously monitoring different physical parameters. Although initially introduced for monitoring soil properties, the application of the TDR-based technique might be an interesting and cost-effective means in many other fields. However, the accuracy of traditional TDR-based electrical conductivity measurements is strongly influenced by the preliminary calibration technique. On such basis, in this paper, two innovative approaches for a more straightforward and accurate evaluation of the electrical conductivity are presented. The first method relies on the combination of the TDR measurement with transmission-line modeling (TLM); the second method simply relies on a couple of independent capacitance measurements (ICMs) performed through an LCR meter. As a further goal, the metrological performance of this last method is compared with that of the traditional method, thus validating its applicability. Experimental results and related uncertainty analysis on various samples demonstrate that the proposed alternative method is definitely suitable for a simpler and accurate estimation of the static electrical conductivity, also when dealing with moistened soils
Classification and adulteration control of vegetable oils based on microwave reflectometry analysis
No full textOlive oil production represents a big part of the Mediterranean economy, and as such it must be protected
from frauds. For this reason, it is necessary to develop alternative low-cost techniques, applicable on large
scale, for checking the quality of the product and for detecting adulteration. On such bases, the present
work deals with the possibility of adopting microwave reflectometry for obtaining a ‘spectral signature’
of vegetable oils. For this purpose, time domain reflectometry (TDR) measurements, in combination with
specific data processing, are first used for the dielectric characterization of several oil types. Successively,
the acquired data are processed through the principal component analysis (for identifying clusters of oil
types that exhibit common features) and through the partial least square analysis (for identifying a predictive
model for detecting oil adulteration). Results confirm that the proposed procedure holds considerable
potential for quality and anti-adulteration control purposes, especially in view of practical
applications
MONITORAGGIO DEL LIVELLO DI LIQUIDI IN SERBATOI ATTRAVERSO SONDE RIFLETTOMETRICHE FLESSIBILI
No full textÈ stato presentato un sistema per la misura di livelli in serbatoi basato sulla tecnica TDR. Il sistema proposto può essere impiegato per il monitoraggio di serbatoi fatti in qualunque materiale, di forme particolari e alti anche decine di metri. Inoltre, il fatto che il sistema fornisce misure in tempo reale e che può essere controllato da remoto, lo rende particolarmente attraente per applicazioni industriali
Reflectometric Systems for in-Situ Diagnosis on Carbon Fibre-Reinforced Composite Structures
No full textIn this work, the feasibility of the adoption of microwave reflectometry (MWR) for diagnosing the
status of structures made of composite materials is investigated. In particular, two different “sensing structures”,
based on microstrip and coplanar configurations, are considered.
The analysis focused on carbon fibre-reinforced composite structures, which are extensively used in aircraft
industry. It goes without saying that, despite the widespread diffusion of this class of materials in the aircraft
industry, there are two crucial requirements for which effective diagnostic methods are far from being
adequately implemented. First, it is necessary to detect the possible presence of gaps between structural
components after they are assembled. Secondly, there is the need to periodically control (during the service life
of the aircraft) the amount of moisture that may have been absorbed by the composite structure. To this purpose,
the present work intends to pave the way for future practical implementation of MWR based systems for these
diagnostic requirements
An Innovative Method for TDR Measurement of Static Electrical Conductivity in Granular Materials
No full textTime domain reflectometry (TDR) is a robust approach for measuring static electrical conductivity of moistened granular materials. Although initially introduced for monitoring soil salinity, its application to granular materials might be an interesting and cost-effective means for monitoring the quality-status of various materials. However, the traditional approach requires tedious and time-consuming preliminary calibration measurements on reference liquids. In this paper, an innovative approach for the direct estimation of the electrical conductivity is presented. In fact, it is demonstrated that the suitable combination of the TDR measurement with a transmission-line modeling of the measurement setup, successfully leads to the avoidance of the preliminary calibration procedure. Investigations carried out on water and on moistened sand samples demonstrate that the performance of the proposed method in estimating the static conductivity is comparable with that achievable through the traditional approach
An improved reflectometric method for soil moisture measurement exploiting an innovative triple-short calibration
No full textTime-domain reflectometry (TDR) techniques have become increasingly attractive for soil moisture evaluation thanks to their adaptability, low cost, and measurement accuracy. Many different TDR-based approaches are currently available for deriving moisture content: empirical calibration curve, empirical dielectric models, frequency-dependent dielectric mixing models, etc. Generally, TDR soil moisture measurements resort to multiple-rod probes, which provide good adhesion to the soil and ease of insertion. However, the typical configuration of such probes does not allow performing a short-open-load (SOL) calibration procedure, which is definitely necessary for retrieving accurate dielectric characterization from TDR waveforms. To overcome the impracticability of the traditional SOL calibration, in this paper, an innovative triple-short calibration (TSC) procedure for commercially available three-rod probes is proposed. First, the robustness of the TSC procedure is validated on well-referenced liquids, demonstrating that its application to TDR measurements leads to a substantial enhancement of the final accuracy in the evaluation of the frequency-dependent reflection coefficient. Successively, the TSC procedure is applied to TDR measurements performed on moistened sand samples. In particular, it is demonstrated that the proposed TSC method, applied to traditional TDR measurements in combination with a dielectric mixing model, leads to an accurate and effective moisture evaluation procedure. This goal is reached through an efficient optimization algorithm that minimizes the difference between experimental and theoretical reflection coefficients. Results show that the proposed strategy is a suitable candidate for low-cost, highly accurate, and easy-to-perform moisture content estimation of soils
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