Application Of Time Domain Reflectometry Research Articles

Examination of the Dry Density Importances in TDR Use and of the ASTM D6780 Standard Based on a New Calibration Procedure

Abstract The use of time domain reflectometry (TDR) to monitor soil water content at either field or laboratory scales is highly common. Regarding the soil dry density, ρd, effect on the TDR application, three main approaches are found in the literature: (1) Ignore the density issue and use calibration to evaluate the water content regardless of the density. This approach is basic, yet common. (2) Include soil density in the calibration equation and use calibration for the water content as a function of both the TDR output and soil density. In this approach, the soil density should be provided from an independent source. (3) Determined ρd from the TDR waveform. In this case both water content and ρd are set from the TDR analysis. In cases where the ρd is not available, in order to use TDR for water content measurement, a decision has to be made whether to address the density issue although it requires resources, or to neglect it. This article reviews this issue and validates the density effect using an efficient TDR calibration methodology. A calibration scheme that controls ρd of the specimen has been developed and applied. The methodology creates continuous calibration curves over a range of volumetric water content from a single test specimen. Based on the results, it has been demonstrated that the soil density has a major effect on the TDR output and it cannot be ignored. In addition, this article presents a unique examination of ASTM D6780, Standard Test Methods for Water Content and Density of Soil In Situ by Time Domain Reflectometry (TDR). The ASTM dry density estimation was found to provide reliable results; however, the gravimetric water contents estimation gives unsatisfactory results, especially for low densities.

Application of time domain reflectometry to triaxial shear tests on hydrate-bearing sediments

Various triaxial shearing apparatus are used to quantify mechanical properties of hydrate-bearing sediments which are basically required to the assessment of risks posed by dissociation of natural gas hydrates. However, the key factor, hydrate saturation, has not been well measured during triaxial shearing tests. This study aims to show how a time domain reflectometry (TDR) method nondestructively measures hydrate saturation for triaxial shear tests on hydrate-bearing sands. Hydrate saturation is determined based on the difference of volumetric water contents measured by using a flexible TDR probe with two rods after calibration. The results suggest that values of hydrate saturation acquired by the TDR method are accurate, and the flexible TDR probe can monitor the kinetic process of hydrate formation and avoid any reinforcement effects on triaxial shearing properties of test specimens.

Enhanced complex wire fault diagnosis via integration of time domain reflectometry and particle swarm optimization with least square support vector machine

AbstractUrban power systems rely on intricate wire networks, known as the power grid, which form the essential electric infrastructure in cities. While these networks transmit electricity from power plants to consumers, they are vulnerable to faults caused by manufacturing errors and improper installation, posing risks to system integrity. Thus, accurate identification and assessment of these faults are crucial to prevent damage and maintain system reliability. The objective of this research is to present an innovative and efficient methodology for diagnosing complex wire networks through the application of time domain reflectometry (TDR) combined with the particle swarm optimization (PSO) and least squares support vector machine (LSSVM) algorithm. This research addresses the imperative need to accurately locate and assess breakage faults within wire networks, emphasizing their role in both power transmission and communication infrastructure. To model the TDR answer of a specific complex wire network, a forward model is established utilizing resistance, inductance, capacitance and conductance (RLCG) parameters and the finite difference time domain (FDTD) method. Subsequently, the PSO‐LSSVM approach is used to solve the inverse problem of localizing faults in complex wire networks. The experimental results validate the practicality of this approach in real‐world systems.

A review of new TDR applications for measuring non-aqueous phase liquids (NAPLs) in soils

• NAPL monitoring in soils is performed by using invasive techniques. • Many studies demonstrated that TDR offers the possibility to detect NAPL in soils. • NAPL tests were conducted in different soils, under variable saturated conditions. The time domain reflectometry (TDR) technique is a geophysical method that allows, in a time-varying electric field, the determination of dielectric permittivity and electrical conductivity of a wide class of porous materials. Measurements of the volumetric water content (θ w ) in soils is the most frequent application of TDR in Soil Science and Soil Hydrology. In last four decades several studies have sought to explore potential applications of TDR. Such studies (except those conducted on θ w estimation) mainly focused on monitoring soil solute transport. In more recent times, innovative TDR approaches have also been implemented to extend current TDR fields of application to the problem of monitoring non-aqueous phase liquids (NAPLs) in variable saturated soils. NAPLs are organic compounds with low solubility in water and are characterised by a high mobility in the vadose zone. Due to their high toxicity, NAPLs constitute a severe geo-environmental problem, thus making detection and observation of such substances in soils an increasingly important issue. The present paper deals with these studies and aims to provide an up-to-date review of the main NAPL-TDR studies. To date, the literature has focused on TDR applications in three main fields: (i) NAPL monitoring in homogeneous, variable saturated soils, (ii) NAPL monitoring in layered variable saturated soils, and (iii) NAPL monitoring during soil decontamination processes. For an exhaustive and complete overview of TDR research in this field, we also recall the basic principles of TDR signal propagation, the functioning of a typical TDR device, and the dielectric mixing models that are widely used to interpret the dielectric response of NAPL-contaminated soils.

Time-domain reflectometry–based real-time slope stability monitoring in opencast mines: A review

Time-domain reflectometry plays a crucial role in slope stability. Slope stability factors are an important parameter in the mining regions over opencast mine slope failure. Conventional methods are oldest as well as poorest risk assessments for monitoring and predication over slope failure conditions. Time-domain reflectometry application has been used among various fields of research at different areas of interest. But, it is implemented in mining area at opencast mines for phonographic review over slope failure conditions. This is a recent technology with low cost, which uses a wireless transmission system for high-risk assessment over slope stability measurement by received signal strength indicator. Moreover, this research is more suitable for monitoring of slope stability as well as less complex about time-domain reflectometry application of installation and real-time slope stability monitoring. The review case of time-domain reflectometry application is linked into the mining area. So, this result is best suitability of time-domain reflectometry and the Internet of things for real-time slope stability monitoring in opencast mines.

Application of time domain reflectometry to high suspended sediment concentration measurements: Laboratory validation and preliminary field observations in a steep mountain stream

The dielectric constant around a sensor was measured with a time domain reflectometry (TDR) system and used to calculate the volumetric sediment concentration (SC) of stream water and deposition on a streambed. The measurements of various SCs in laboratory experiments demonstrated that the TDR system proposed in this study had an accuracy of 0.01 m3 m−3 for practical uses, and that the measured concentrations were not sensitive to particle size. The vertical SC distributions were measured at heights of 17–37 cm in a steep mountain stream. The resulting SCs at the various heights increased by 0.01–0.07 m3 m−3 at the time of peak stream discharge during an extreme storm with a return period of approximately 12 years. After extreme precipitation, the SC of the lowest probe increased rapidly from approximately 0 to 0.4 m3 m−3. This was followed by rapid increases in the SCs at the other heights, indicating deposition around each probe. The TDR measurement system, with its straightforward calibration procedure, effectively measured deposition and a high-concentration layer above the deposited layer even during the storm event.

Experimental Determination of TDR Calibration Relationship for Pyroclastic Ashes of Campania (Italy).

Time domain reflectometry (TDR) is one of the most widely used techniques for indirect determination of soil volumetric water content (θ). TDR measures the relative dielectric constant (εr) which, in a three-phase system like the soil, depends on water, air, and solid matrix dielectric constants. Since dielectric constant of water is much larger than the other two, εr of bulk soil mainly depends on water content. In many cases, the application of TDR requires a specific calibration of the relationship θ(εr) to get quantitatively accurate estimates of soil water content. In fact, the relationship θ(εr) is influenced by various soil properties, such as clay content, organic matter content, bulk density, and aggregation. Numerous studies have shown that pyroclastic soils often exhibit a peculiar dielectric behavior. In Campania (Southern Italy) wide mountainous areas are covered by layered pyroclastic deposits of ashes (loamy sands) and pumices (sandy gravels), often involved in the triggering of landslides induced by rainwater infiltration. Reliable field measurements of water content of such soils are therefore important for the assessment of landslide risk. Hence, in this paper, the θ(εr) relationship has been experimentally determined on samples of typical pyroclastic soil of Campania, collected around Sarno, reconstituted with different porosities. The aim of the study is to identify specific calibration relationships for such soils based not only on empirical approaches. In this respect, a three-phase dielectric mixing model with a variable exponent is introduced, and the variable value of the exponent is related to the different dielectric properties of bond and free water within the soil pores.

Validation of S-parameter Power Cable Joint Model on Two Cable Defect Sections

<p>Electricity disruption due to power cable failure is a major challenge to power utility companies worldwide. A technique which provides quick response with accurate result is needed to detect defects along the cable to reduce the disruption time. This paper discusses the application of time domain reflectometry (TDR) technique to identify and locate the defect along a cable. A cable system is modelled in MATLAB/Simulink to replicate the cable configuration with two joints using the scattering parameter (S-parameter). This research studies the fault identification for two degraded sections in a cable by analyzing the reflected signal from the TDR technique. The characteristics of the reflected signal which indicates the defect cable section are discussed in detail in this paper. Results from MATLAB/Simulink simulations are also compared to the experimental results of the same cable configuration. This study shows that the signal reflection characteristics from MATLAB/Simulink simulations are similar to the experimental results. This indicates that the cable model system built using MATLAB/Simulink replicates the actual cable system accurately which can be used for further analysis of cable fault localization.</p>

Power Cable with Two Joints Experimental Analysis for Defect Assessments

<span>Time domain reflectometry (TDR) is an easy technique that provides quick response which is ideal for power utility companies to conduct cable diagnostics on-site. Electricity disruption due to power cable failure is a major challenge for power utility companies due to the long length of cable installed with joints. The long time taken to diagnose the defect along the cable before electricity can be restored has not only jeopardized the reputation of power utility companies but also brings losses to the economy. Hence, this study conducts experimental analysis on cable with two joints with the application of TDR technique to reduce the electricity disruption time. This research is divided into two stages where stage 1 conducts experiments on cable with one degraded section while stage 2 looks into cable with two degraded sections. The TDR reflection characteristics are studied from stage 1 experiments and applied to stage 2 experiments to verify the consistency of the TDR reflection characteristics. The cable conditions of stage 2 experiments are predicted using the reflection characteristics from stage 1 observations and are then validated by comparing these predictions with the actual cable configuration. Results obtained from these experiments have proven that the TDR reflection characteristics are consistent and accurate which can be used to sectionalize the degraded cable section. Detail findings of all experiments conducted with the TDR application are discussed in part three of this paper.</span>

Verification of MATLAB/Simulink Power Cable Modelling with Experimental Analysis

Cross-linked polyethylene (XLPE) power cable is commonly used as the medium for transmitting power supply in the power system network. However, frequent exposure of XLPE cable to the high voltage causes its insulation to degrade over time leading to electricity outages. Degradation of cable can be prevented if regular maintenance is performed using the accurate assessment method. This study models and simulates a cable system comprising of three cable sections connected by two un-degraded cable joints. This model aims to assess defect along the tested cable with the application of time domain reflectometry (TDR) technique. A series of simulations are conducted by varying the cable insulation condition to study its influence on the cable joint reflection. These simulation results from MATLAB/Simulink are validated against the actual TDR experimental results. The identical results shown between the simulation and experimental results indicate that the cable model is valid and can be used to assess the condition of a cable.

Laboratory based continuous bedload monitoring in a model retention basin: Application of time domain reflectometry

AbstractIn this study, we applied time domain reflectometry (TDR) to determine the deposition height and porosity of sediment at a fine spatiotemporal resolution, and developed a continuous bedload monitoring method that can be applied to pools in steep mountain rivers. The TDR monitoring system consisted of sensor probes, a cable tester, multiplexers and coaxial cables. When the embedded probes penetrated both water and sediment, the boundaries of the sediment and water were consistent with the transition points in the observed waveforms of each TDR measurement. A semi‐automatic analysis of the recorded TDR waveforms, which did not require calibration or parameter fitting, was conducted to establish continuous monitoring. In addition, a flume experiment was performed to test the monitoring system in a model retention basin connected to a flume, with sand of uniform grain size (1.4 mm diameter) supplied for 30 min. The sediment volume in the container representing the model basin was monitored using a load cell underlying the container and eight sensor probes, with a length of almost 0.27 m. The sediment thickness determined by the TDR indicated a gradual deposition, and was consistent with manual measurements. Despite a marginal overestimation of 13% for a sand feed of 30 kg, the sediment volume in the model retention basin and the bedload transport rate were successfully estimated. A combination of our monitoring system and other indirect methods, such as geophones, can potentially serve as useful tools for better understanding bedload transport processes in steep mountain streams. Copyright © 2018 John Wiley & Sons, Ltd.

Comparison of performance of inclinometer casing and TDR technique

TDR (Time Domain Reflectometry) and GPR (Ground Penetrating Radar) are two of the electromagnetic methods in applied geophysics, which using them for various applications are developing. The Time Domain Reflectometry is a remote sensing method that has been used for years to determine the nature of the materials and spatial location. The use of TDR system has led to innovative applications of it and comparing it with previous measuring techniques, since it has developed. In this study, not only a summary of the basics of TDR application for monitoring of ground deformation is offered, but also a comparison of this technology with other measurement techniques (inclinometer casing) is provided. Actually, this paper presents a case study in which the opportunity arose to compare these two technologies in detecting subsurface deformation in slopes. A TDR system includes a radar wave receiver & generator, a transmission line and a waveguide. The generated electro-magnetic pulse moves toward the waveguide within the conductor cable and enters the test environment. For this study, slopes overlooking the Darian dam bottom outlet, power house and spillway were instrumented with RG59/U coaxial cables for TDR monitoring and slope inclinometer. Coaxial cables - as a TDR sensor - and inclinometer casings were installed in a same bore hole where coaxial cable was attached to the inclinometer casing. Shear and tensile deformations of the cable, which is caused by ground movements, significantly impacts on cable reflection coefficient. In Darian dam boreholes, the cable points subject to the shear and stretch were correlated with deformation points of the inclinometer casings in incremental displacement graphs. This study shows that TDR technique is more sensitive than inclinometer casing for small movement in the slide planes. Because manual processing of TDR data is hard and need experienced personnel, the authors have designed an algorithm to compare the shape of the new TDR waveforms with the base reading waveform in order to monitor the subsurface deformations.

TDR（時間領域反射測定法）を利用した堆積土砂面位および空隙率測定

TDR（時間領域反射測定法）を利用した堆積土砂面位および空隙率測定

Level Dynamics Monitoring of a Once-Through Steam Generator: A New Method Using the Reflectometric Technique

We present here some theoretical and experimental results about the application of the time-domain reflectometry (TDR) technique to a once-through steam generator (OTSG) bayonet-type, which is considered here, from a new point of view, as a coaxial transmission line and used as a level monitoring device for its own dynamics. This original approach leads to the design of a new kind of sensor, employable as a general-level measuring system in harsh conditions as well. This sensor may offer some interesting features for the design of control systems for nuclear facilities as well as for oil and gas plants. In order to experimentally verify the theoretical part, a mockup has been designed and built, so as to be used as a level control for a dedicated hydraulic loop system both in static and dynamic conditions. The purpose of the hydraulic loop system is to implement a short-/medium-term transient-level dynamics requiring fast sensor response, online measurement, and some nonlinearity features that are crucial for its control. The obtained results show that the TDR application on the OTSG is feasible at standard ambient temperature and pressure (SATP) conditions, paving the way for tests at the operating pressure and temperature ranges of a real plant.

Echo Response of Faults in Transmission Lines: Models and Limitations to Fault Detection

This paper introduces models of the time-domain echoes generated by faults in transmission lines excited by test signals, e.g., as in applications of time-domain reflectometry (TDR). Faults considered here include local modifications of the propagation characteristics of a transmission line. It is shown that the responses of faults are strongly dispersive in nature, which implies that the peak of their echo is far from providing an accurate measure of the severity of the fault, as it heavily depends on the frequency content of the test signal as well as on the length of the fault. It is argued that fault detection in transmission lines is an ill-posed problem that requires a priori knowledge on the fault itself. These results are important for applications of TDR methods, particularly for early warning monitoring of potentially critical faults from their onset, since it is shown that echoes from faults tested at relatively low frequencies can lead to underestimate their actual severity.

Application of time domain reflectometry for determination of wate content in Xiangsha Yangwei pills

Xiangsha Yangwei pill was selected as a model drug in this research, and time domain reflectometry (TDR) was used to determine the water content in the pill. The effects of five factors including the number of pill layers, pill packing density, atmospheric moisture, ambient temperature and the ratio of pill formula were investigated on water content. The results showed that the number of pill layers and ambient temperature had significant effects on water content of pills, while the pill packing density, atmospheric moisture and pill formula ratio had little effect on the determination of water content in pills. The reflection value was stable when 6 layers of pills were used. Under the condition of 25 ℃ and 45% relative humidity, the water content of pills ranged from 4.01% to 22.38%, showing good linear relationship between water content and reflection value, and the model equation was as follows: Y=0.279X－21.670 (R²=0.997 0). Verification experiment was used to explain the feasibility of this prediction model. The precision of the method complied with the methodology standard. It is concluded that TDR can be used in determination of water content in Xiangsha Yangwei pills. Additionally, TDR, as a new way to quickly and efficiently determine the water content, has a prospect application in the processing of traditional Chinese medicine pharmacy, especially for concentrated pill.

Criteria for Automated Estimation of Time of Flight in TDR Analysis

In this paper, a performance analysis, in terms of accuracy, linearity, and repeatability, of three criteria to estimate the time of flight in time-domain reflectometry (TDR) signals is carried out. In a first set of experiments, the three criteria [referred to as maximum derivative (MD), zero derivative, and tangent crossing (TC)] are applied to TDR signals propagating along a set of coaxial cables, with different known lengths and known electrical parameters. In a second set of experiments, the same criteria are applied to biwire cables in air, with different known lengths and unknown electrical parameters. Finally, in the last set of experiments, the criteria are applied in a more complex situation, i.e., on a biwire used as a sensing element for water-level measurement. The results show that, among the tested criteria, TC appears to provide a very good performance in terms of systematic errors and superior performance in terms of repeatability. The popular MD criterion appears to be more prone to random errors due to noise and TDR artifacts. The results of this paper are relevant to many practical applications of TDR, ranging from fault location in cables to media interface sensing.

Enhancing modelled water content by dielectric permittivity in stony soils

Applicability of time domain reflectometry (TDR) under naturally distributed stone fragments in soils has seldom been investigated. A multilayer profile of a 30-m-deep well was sampled and the natural distribution of stone fragments in the soils was replicated in the laboratory. Gravimetric soil water content (SWC) was measured simultaneously with TDR dielectric permittivity (Ka) readings and bulk densities in three subsamples as replications. Two connector and buriable probes and three reflection-time capture windows (10, 20 and 40 ns) were used for the measurements. These were repeated for sieved soil samples <2 mm with fixed, pre-measured bulk densities. Measurements of Ka and observed SWC were repeated for extension-cable lengths of 3–30 m. All measurements were taken in samples saturated from the bottom. A semi-empirical mixture model was applied for different fractions of stony samples in order to convert bulk Ka to bulk volumetric SWC (θv) by the mixture model (θvmx), to be compared with θv by the conventional Topp equation (θvTp). An improvement in model performance was observed with lower root-mean-square error (RMSE, 0.02–0.04 v. 0.07–0.1) and ratio of RMSE to observation standard deviation (0.32–0.87 v. 1.07–3.05) for θvmx compared with θvTp. This approach for converting the in-situ measured dielectric permittivity to the θv of the bulk soil can be applied based on the determined stoniness. The 15-cm, 2-rod (connector) probe type with capture windows 20 ns resulted in a better performance than the 20-cm, 3-rod (buriable) probe type with capture windows 10 and 40 ns. Development of regression equations for the stone-free samples resulted in calibrated equations for converting the measured Ka to θv with better results (RMSE ~0.002 m3 m–3) than those obtained using the Topp equation. In contrast to the traditional equation, new sets of coefficients for the Topp equation were also capable of estimating extremely low θv values of ≤0.02 m3 m–3 where the minimum calculated θv values were adequately similar to the observed ones. Noticeable effects of cable length on measured Ka were found for lengths exceeding 10 m. Accurate Ka values might be obtained in similar soil conditions if the suggested regression equations are employed, provided a correction is made for the extension cables.

Application of Time-Domain Reflectometry for Measurement of Moisture Profiles in a Drying Experiment

The time-domain reflectometry (TDR) method is used for the measurement of moisture profiles in calcium silicate during a drying experiment. The specimens are saturated at first by water, and their lateral sides and one of the face sides are water- and vapor-proof insulated to ensure one-dimensional (1-D) water transport. Then, the drying process is started in an environment with a relative humidity of 20%. Moisture profiles are measured at specified time intervals using the TDR method. The experiment is stopped when the moisture content along the whole length of the sample is lower than the maximum hygroscopic moisture content. The obtained results can be used for the determination of moisture diffusivity in the drying phase of moisture transport.

Study on Application of Time Domain Reflectometry to Highway Slope Monitoring

To apply Time Domain Reflectometry (TDR) in slope monitoring, on the base of brief summary of principle of TDR, and with types of indoor shear tests and situ construction of different cables, reflection waves of types of different cables are studied. Compared with the monitor results by TDR and oblique monitoring result by drilling hole, the following conclusions can be gained, i.e. TDR can be fast applied in determining the sliding plane, more economical, safety, and precisely. By the research results, to satisfy different monitoring goal, the application rules of types of TDR is put forward , and TDR is a very useful tool for slope survey.