Time Domain Reflectometry Technique Research Articles

Distributed Reflectometry for Soft Fault Identification in Wired Networks Using Neural Network and Genetic Algorithm

Based on the Multi-Carrier Time Domain Reflectometry (MCTDR) technique, new methods which could detect, locate and characterize multiple soft faults in complex wired networks are proposed in this paper. The first method combines the MCTDR with the Multi-Layer Perceptron Neural Network (MLP-NN), the second one combines the MCTDR with the well-known genetic algorithm (GA). Furthermore, in order to allow effective monitoring without ambiguity, a branched network is diagnosed by several reflectometers (sensors) at the different extremities. The main novelty here lies in the fact that the NN and GA methods are used for data fusion from several distributed reflectometers. The needed datasets for training and testing the NN are generated by simulation using MCTDR responses. These are obtained using a numerical direct model which describes the signal propagation in the branched network. The GA is used to reduce the differences between the measured responses and the simulated responses given by the direct model. The numerical and experimental results provided at the end of the paper confirm the performance of both approaches (MCTDR-NN & MCTDR-GA) in merging data between reflectometers and in eliminating diagnosis ambiguities.

Cooperative dynamics in dipropylene glycol–ethanol mixtures using dielectric spectroscopy

ABSTRACT The dielectric relaxation study of dipropylene glycol (DPG)–ethanol binary mixtures over complete composition have been carried out using time domain reflectometry (TDR) technique upto 50 GHz. From the measured complex permittivity spectra, the static dielectric permittivity (ε0), dielectric relaxation time (τ) and asymmetric relaxation distribution parameter (β) were obtained by least square fit method. The cooperative dynamics in the pure and binary mixtures have been discussed using the cooperative domains (CDs) of like and unlike molecules. Kirkwood correlation factor and thermodynamic properties were also determined to confirm the CDs heterogeneous interactions through hydrogen bonding.

Using time domain reflectometry to estimate water content of three soil orders under savanna in Brazil

Water is a limiting factor in agricultural lands on tropical Savannas. Due to low rainfall and long periods of drought, irrigation becomes a critical factor for increasing productivity. In this scenario, improving irrigation management techniques is crucial for increasing water use efficiency. Soil water content sensors are important tools not only for soil-based irrigation scheduling, but also to calibrate weather-based irrigation scheduling. Time domain reflectometry (TDR) type sensors are an important tool for water content monitoring due to its potential accuracy, automation and real-time measurement capability. The objective of this study was to evaluate the TDR technique for the estimation of water content in five soils of the Brazilian savanna (two Oxisols, two Entisols and one Histosol) using polynomial, square root and logarithmic calibration equations. The influence of soil bulk density, organic matter and clay content, and presence of magnetic materials were also examined. Magnetic permeability was estimated from magnetic hysteresis curves for each soil. The equations were calibrated and validated on an independent data set. Validation was evaluated using the Coefficient of Determination (R2), Root Mean Squared Error (RMSE), Nash-Sutcliffe Efficiency and the RMSE to the standard deviation of observed data ratio. There was no benefit of including bulk density, clay content or organic matter on the calibration equations. The relative magnetic permeability was very close to one in all soils and thus did not influence the calibration. For the soils evaluated in this study a single logarithmic calibration equation calibrated for all samples was the best predictor of volumetric water content.

Dielectric relaxation study of aqueous ethylene glycol mono-methyl ether (EGME) with water using time domain reflectometry technique in the frequency range 10MHz to 50GHz

The Complex permittivity spectra of glycol ether (GE) compounds such as ethylene glycol mono-methyl ether (EGME) with water mixture over entire concentration range and in temperature range of 10–25∘C have been determined using Time Domain Reflectometry (TDR) technique in the frequency range 10[Formula: see text]MHz to 50[Formula: see text]GHz. The complex permittivity spectra for EGME-water were fitted in the Cole–Davidson model. The Static dielectric constant ([Formula: see text], Relaxation time ([Formula: see text], effective Kirkwood correlation factor ([Formula: see text], excess permittivity ([Formula: see text], thermodynamic parameters (activation enthalpy and activation entropy) and Bruggeman factor ([Formula: see text] have been calculated by the nonlinear least square fit method. The intermolecular interactions between EGME-water binary mixtures suggest the nonlinear behavior of dielectric parameters. The contribution of hydrogen bonding interactions among the solute–solvent mixtures is confirmed by Excess properties and Bruggeman factor.

Distributed SOP tracking fault detection technique for MeerKAT radio telescope array sub-metre single mode fibre link health monitoring

Deployed short-run receptor fibre network (RFN) in the MeerKAT radio telescope array require frequent health assessment due to their harsh environmental exposures. The inherent launch and event dead-zone of optical time-domain reflectometry (OTDR) technique limits its application in the MeerKAT radio telescope RFN sub-metre fibre links. This work experimentally demonstrates the first distributed polarization-based precise fault detection technique based on state-of-polarization (SOP) change tracking, for health monitoring of sub-metre fibre links and passive/active optical/photonic components. A beat frequency signature due to interference of the local oscillator with Rayleigh backscattered and Fresnel reflected optical signal is exploited to monitor Birefringence evolution over a 0.35 m MeerKAT digitizer fibre loom. Utilizing the ultra-sensitive inherent SOP change functionality due to mode coupling between fast and slow eigenmodes, an SOP change tracking technique is developed offline with 0.050 SOP angle change detection precision at 125μm spatial resolution. Fault location performance of the developed SOP change tracking technique is then compared to classical optical frequency-domain reflectometry (OFDR) technique over a 0.28 m SMF fibre link. The developed SOP change tracking technique is adopted for precise fault location along a 0.35 m MeerKAT digitizer fibre loom due to its high sensitivity. This work offers a precisely accurate, stable and reproducible approach for location of propagation defect detection in sub-metre single mode optical fibre links.

Investigating Polymer Fibre Optics for Condition Monitoring of Synthetic Mooring Lines

Synthetic mooring lines are becoming a popular alternative to conventional chain mooring systems. For marine renewable energy devices, they have been considered as an enabling technology for this nascent sector, given their reduced costs and ease of deployment. However, the extreme operating environment has led to an increased interest in the ‘in-situ’ condition monitoring of these mooring lines. This paper considers the use of polymer fibre optic technology and the optical time domain reflectometry (OTDR) technique for the condition monitoring of synthetic mooring lines. To establish the operating envelope of the fibres, Polymethylmethacrylate (PMMA) polymer optical fibres are mechanically tested. Additionally, an OTDR is used to monitor fibres whilst under elongation using a tensile test machine, and the sensitivity of the system in monitoring strain is established. At the lowest strain rate, the average proportional limit and yield points of the fibres are found at 1.16% strain and 5.41% strain, respectively. Fatigue exposure of fibres up to 1.25% strain identifies no measurable effect on fibres’ proportional limit or yield point. The occurrence of significant creep is identified for fibres strained beyond 1.5%. The OTDR system is able to identify strains at and above 4%. The study identifies important criteria that should be considered in the integration of polymer optical fibres for mooring applications. Limitations are discussed and suggestions for progressing this technology are provided.

Microwave Dielectric Relaxation in Binary Mixtures of 1,3-Diaminopropane in Dimethylaminoethanol

The dielectric dispersion ε′ and dielectric loss ε″ of binary mixture of 1,3-diaminopropane-N,N-dimethylaminoethanol were measured by employing the time domain reflectometry technique over a frequency range 10 MHz to 20 GHz at 288 K, 298 K, 308 K, and 318 K. To evaluate various dielectric parameters, the frequency dependents complex permittivity (ε* (ω) = ε′ – jε″) data viz., dielectric constant (ε0), relaxation time (τ), and permittivity at high frequency (ε∞) were fitted by the nonlinear least-squares fit method to Debye expression. Temperature dependent ε0, τ, Kirkwood correlation factor (geff), and free energy of activation (ΔG) have been determined and discussed in terms of the effect of -NH2 and -CH3 side-group on molecular dynamics and intermolecular hydrogen bonds.

Microwave dielectric relaxation dynamics of aqueous Nicotinamide (vitamin B3): a dielectric and thermodynamic approach using time domain technique

ABSTRACT The aqueous solutions of Nicotinamide (NIA, vitamin B3), with various concentrations, are investigated at different temperatures applying Time Domain Reflectometry (TDR) technique. The complex dielectric spectra of NIA-water solutions are fitted with the Debye relaxation model and the dielectric relaxation parameters like static dielectric constant, relaxation time have been determined by non-linear least square fit method. The Excess dielectric parameters and Kirkwood correlation factors show a significant change in dipole orientation also indicates the formation of cluster structures within the mixture. The thermodynamic parameters, Arrhenius characteristics and viscosity effects are reported. The FTIR spectroscopy confirms the heteromolecular hydrogen bond formation, through functional group interaction in the mixture systems; moreover, the NIA-Water clusters are optimized and the hydrogen bond interactions are discussed. The resulting theoretical vibrational frequency of C = O and C-N bond of NIA is found to be consistent with experimental frequencies.

Measurement of temperature and strain simultaneously with high spatial resolution for a long sensing range

This study presents a Brillouin distributed sensor (BDS) with high spatial resolution for the monitoring of temperature and strain simultaneously. Fourier deconvolution (FD), Fourier regularised deconvolution (FRD), and Fourier regularised denoising deconvolution (FRDD) algorithms have been explored to measure the Brillouin backscattered power using the optical time-domain reflectometry technique. The improvement of temperature and strain resolutions along with the spatial resolution using the FRDD algorithm is observed for 50 km sensing range. The numerical simulation process of the proposed sensing system has been simultaneously incorporated to extract temperature and strain information. The simulation results show that the temperature and strain resolutions are observed as 5°K and 138 μe, respectively, using FRDD compared with the FD algorithm which shows temperature and strain resolutions as 54°K and 1588 μe, respectively, at a 50-km distance. A high spatial resolution of 9 m is observed of the proposed BDS over the sensing range of 50 km using the FRDD algorithm. In addition, the denoising capability of the proposed FRDD algorithm is validated using the experimentally obtained Rayleigh backscattered signal.

Dielectric Relaxation in Water-Ethanolamine Mixtures as a Function of Composition and Temperature

Dielectric relaxation measurements on water–ethanolamine solvent mixtures have been carried out across the entire concentration range using Time Domain Reflectometry technique at 288 K, 298 K, 308 K, and 318 K over the frequency range from 10 MHz to 20 GHz. The mixtures exhibit a principle dispersion of the Davidson-Cole relaxation type at microwave frequencies. Bilinear calibration method is used to obtain complex permittivity ε*(ω) from complex reflection coefficient ρ*(ω) over the frequency range 10 MHz to 10 GHz. The excess permittivity (εE), excess inverse relaxation time (1/τ)E, Kirkwood correlation factor (geff) and thermodynamic parameters are also calculated to study the Solute-Solvent interaction.

Dielectric Relaxation Study Of 1,2 Dichloroethane With n,n-Dimethylformamide

The time-domain reflectometry (TDR) technique has been used for the study of dielectric relaxation spectra of 1,2 dichloroethane (DE) and n,n-dimethylformamide (DMF) binary mixtures. The frequency range used for the study is 10 MHz to 30 GHz. The study is carried out at 10°C, 15°C, 20°C and 25°C temperature for 11 different concentrations. The dielectric parameters such as static permittivity (?0), dielectric constant at high frequency (??) and relaxation time (?) have been obtained. The Excess parameters, Kirkwood parameters, and thermodynamic parameters are determined.

Dielectric relaxation and hydrogen bonding interaction of polyethylene glycol dimethyl ether in water mixture

ABSTRACT The complex permittivity spectra of binary mixtures of polyethylene glycol dimethylether [PEGDME: Molecular Weight 250 g.mol−1 & 500 g.mol−1] with water over entire concentrations and at different temperatures (5ºC, 15ºC and 25ºC) have been measured using time domain reflectometry (TDR) technique in the frequency range of 10–30 GHz. The complex permittivity spectra were fitted in Cole–Davidson model using non-linear least square fit method. The dielectric parameters, such as static dielectric constant and relaxation time, have been determined for PEGDME250+ water and PEGDME500+ water mixtures. The hydrogen bonding interactions for the PEGDME250- water & PEGDME500- water mixtures have been discussed through the determination of excess permittivity, Bruggemann factor and thermodynamic parameters.

Experimental comparison of thermal and solute dispersion under one‐dimensional water flow in saturated soils

Thermal dispersion, which is similar to solute dispersion, results mainly from microscopic differences in pore‐scale water velocities in porous media. In this study, heat and Cl− were used as tracers to perform a systematic and quantitative comparison of the characteristics of coupled heat and solute dispersion through three types of saturated packed media (a sand, silt loam and sandy clay loam soil). An inverse model was used to calculate the thermal dispersion coefficient (Dh) and solute dispersion coefficient (Ds) by fitting a heat and solute transport model to the measured temperature and solute breakthrough curves obtained using the thermo–time domain reflectometry (thermo–TDR) technique under the same experimental conditions. Results showed that Ds and Dh were both described by a power function of water flux. Most importantly, heat and solute dispersivities had the same dimensions of length , the magnitudes of which were maintained almost unchanged with water flux densities and depended considerably on soil texture. Fine‐textured soil had a greater dispersivity than did coarse‐textured soil, and solute dispersivity was 220% greater than heat dispersivity in sandy clay loam, about 92% greater in silt loam soil and 36% greater in sand. We suggest that the magnitude and dimension of heat dispersion were essentially comparable to those of solute dispersion, which provides a better understanding of the relation between heat and solute dispersion. It has also been shown to be advantageous in practice for using heat dispersion to quantify easily solute dispersion approximately (or vice versa).Highlights Thermal and solute dispersion coefficients were power functions of water fluxes. Heat and solute dispersivities had the same length and order of magnitude. Thermal dispersion was experimentally comparable to solute dispersion. Solute dispersion may be predicted quantitatively by heat dispersion values (or vice versa).

Dielectric spectroscopy and hydrogen bonding studies of 1-chloropropane–ethanol mixture using TDR technique

The time-domain reflectometry technique was exercised to assess the complex permittivities of 1-chloropropane and ethanol along with their binary mixture in the frequency range of 10[Formula: see text]MHz–50[Formula: see text]GHz and in the temperature range of 10–[Formula: see text]C. Dielectric parameters like static dielectric permittivity ([Formula: see text] and relaxation time ([Formula: see text] have been acquired by the least-square-fit method. The obtained assessments of static permittivity and relaxation time were used to compute various dielectric parameters like excess dielectric constant, excess relaxation time, Kirkwood correlation factor and thermodynamic parameters. The experimental outcome illustrates the nonlinear variations in dielectric permittivity, relaxation time and authenticates the structural formation due to intermolecular interaction between 1-chloropropane and ethanol. Molecular rotary motion and dipole reorientation movements of these complex systems are presented in agreement with the molar entropy and enthalpy.

Using a Parallel Helical Sensing Cable for the Distributed Measurement of Ground Deformation.

Surface and underground stretched deformation is one of the most important physical measurement quantities for geological-disaster monitoring. In this study, a parallel helical sensing cable (PHSC) based on the time–domain reflectometry (TDR) technique is proposed and used to monitor large ground stretched deformation. First, the PHSC structure and manufacturing process are introduced, and then, distributed capacitance, distributed inductance, and characteristic impedance were derived based on the proposed stretched-structure model. Next, the relationship between characteristic impedance and stretched deformation was found, and the principle of distributed deformation measurement based on the TDR technique and PHSC characteristic impedance was analyzed in detail. The function of the stretched deformation and characteristic impedance was obtained by curve fitting based on the theoretically calculated results. A laboratory calibration test was carried out by the designed tensile test platform. The results of multi-point positioning and the amount of stretched deformation are presented by the tensile test platform, multi-point positioning measurement absolute errors were less than 0.01 m, and the amount of stretched deformation measurement absolute errors were less than 3 mm, respectively. The measured results are in good agreement with the theoretically calculated results, which verify the correctness of theoretical derivation and show that a PHSC is very suitable for the distributed measurement of the ground stretched deformation.

Remote Monitoring of Joints Status on In-Service High-Voltage Overhead Lines

This work presents the feasibility study of an on-line monitoring technique aimed to discover unwanted variations of longitudinal impedance along the line (also named “impedance discontinuities”) and, possibly, incipient faults typically occurring on high voltage power transmission lines, like those generated by oxidated midspan joints or bolted joints usually present on such lines. In this paper, the focus is placed on the application and proper customization of a technique based on the time-domain reflectometry (TDR) technique when applied to an in-service high-voltage overhead line. An extensive set of numerical simulations are provided in order to highlight the critical points of this particular application scenario, especially those that concern the modeling of both the TDR signal injection strategy and the required high-voltage coupling devices, and to plan a measurement activity. The modeling and simulation approach followed for the study of either the overhead line or the on-line TDR system is fully detailed, discussing three main strategies. Furthermore, some measurement data that were used to characterize the specific coupling device selected for this application at high frequency—that is, a capacitive voltage transformer (CVT)—are presented and discussed too. This work sets the basic concepts underlying the implementation of an on-line remote monitoring system based on reflectometric principles for in-service lines, showing how much impact is introduced by the high-voltage coupling strategy on the amplitude of the detected reflected voltage waves (also named “voltage echoes”).

Signal Propagation Through Piecewise Transmission Lines for Interpretation of Reflectometry in Photovoltaic Systems

We present a framework for analyzing electromagnetic signal propagation through piecewise-defined transmission lines with arbitrary, series-connected impedances. While the formulation is general and scalable, we apply it here to propagation through a photovoltaic module with cables on either side acting, with a home run cable, as a section of an inhomogeneous transmission line. Understanding propagation through this unit of a series-connected string of photovoltaic modules is necessary to enable the use of time-domain reflectometry techniques for monitoring the status of individual components in series-connected strings within large photovoltaic arrays.

Suitability of time domain reflectometry (TDR) for moisture content monitoring in historic building walls

Measuring moisture content in building materials is crucial for the correct diagnosis of buildings pathologies, for the adoption of appropriate intervention measures and for the efficiency evaluation of the treatment solutions applied. There are several different techniques available to measure and monitoring the moisture content in building materials. However, it still remains a great challenge to perform those studies in historical buildings, since minor-destructive techniques are required. Furthermore, if continuous moisture content readings in space are desired, in order to study the moisture transfer phenomenon along the wall thickness, the challenge is even greater. The TDR technique is a relatively new method for measurement of moisture content in building materials with a set of unexplored potentialities capable of satisfying the two mentioned requirements. In this paper, the suitability of the TDR technique to obtain continuous cross-section moisture content profiles has started to be tested on two limestone prototype walls. Each wall was equipped with four TDR probes, designed practically with the same length of the wall thickness and placed at different heights. All the necessary equipment, installation steps, and difficulties are here presented. The preliminary results suggest that the TDR technique is suitable for moisture content monitoring in consolidated porous building materials.

A Noninvasive TDR Sensor to Measure the Moisture Content of Rigid Porous Materials.

The article presents the potential application of the time domain reflectometry (TDR) technique to measure moisture transport in unsaturated porous materials. The research of the capillary uptake phenomenon in a sample of autoclaved aerated concrete (AAC) was conducted using a TDR sensor with the modified construction for non-invasive testing. In the paper the basic principles of the TDR method as a technique applied in metrology, and its potential for measurement of moisture in porous materials, including soils and porous building materials are presented. The second part of the article presents the experiment of capillary rise process in the AAC sample. Application of the custom sensor required its individual calibration, thus a unique model of regression between the readouts of apparent permittivity of the tested material and its moisture was developed. During the experiment moisture content was monitored in the sample exposed to water influence. Monitoring was conducted using the modified TDR sensor. The process was additionally measured using the standard frequency domain (FD) capacitive sensor in order to compare the readouts with traditional techniques of moisture detection. The uncertainty for testing AAC moisture, was expressed as RMSE (0.013 cm3/cm3) and expanded uncertainty (0.01–0.02 cm3/cm3 depending on moisture) was established along with calibration of the applied sensor. The obtained values are comparable to, or even better than, the features of the traditional invasive sensors utilizing universal calibration models. Both, the TDR and capacitive (FD) sensor enabled monitoring of capillary uptake phenomenon progress. It was noticed that at the end of the experiment the TDR readouts were 4.4% underestimated and the FD readouts were overestimated for 12.6% comparing to the reference gravimetric evaluation.

The value of satellite remote sensing soil moisture data and the DISPATCH algorithm in irrigation fields

Abstract. Soil moisture measurements are needed in a large number of applications such as hydro-climate approaches, watershed water balance management and irrigation scheduling. Nowadays, different kinds of methodologies exist for measuring soil moisture. Direct methods based on gravimetric sampling or time domain reflectometry (TDR) techniques measure soil moisture in a small volume of soil at few particular locations. This typically gives a poor description of the spatial distribution of soil moisture in relatively large agriculture fields. Remote sensing of soil moisture provides widespread coverage and can overcome this problem but suffers from other problems stemming from its low spatial resolution. In this context, the DISaggregation based on Physical And Theoretical scale CHange (DISPATCH) algorithm has been proposed in the literature to downscale soil moisture satellite data from 40 to 1 km resolution by combining the low-resolution Soil Moisture Ocean Salinity (SMOS) satellite soil moisture data with the high-resolution Normalized Difference Vegetation Index (NDVI) and land surface temperature (LST) datasets obtained from a Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. In this work, DISPATCH estimations are compared with soil moisture sensors and gravimetric measurements to validate the DISPATCH algorithm in an agricultural field during two different hydrologic scenarios: wet conditions driven by rainfall events and wet conditions driven by local sprinkler irrigation. Results show that the DISPATCH algorithm provides appropriate soil moisture estimates during general rainfall events but not when sprinkler irrigation generates occasional heterogeneity. In order to explain these differences, we have examined the spatial variability scales of NDVI and LST data, which are the input variables involved in the downscaling process. Sample variograms show that the spatial scales associated with the NDVI and LST properties are too large to represent the variations of the average soil moisture at the site, and this could be a reason why the DISPATCH algorithm does not work properly in this field site.