Time Domain Reflectometry Test Research Articles

Species-specific prediction model of wood moisture content based on electromagnetic wave propagation time

Laboratory and field experiments were performed to examine the feasibility of using Time Domain Reflectometry (TDR) to monitor moisture content (MC) of wood and standing trees. The TDR was used to detect the electromagnetic wave propagation time of four tree species (Betula platyphylla, Tilia tuan, Picea asperata, and Fraxinus mandshurica) at different MCs. During the TDR test, effects of probe insertion depths on MC predictive accuracy were considered. The best results were obtained at an insertion depth of 8 cm. At the selective 8 cm insertion depth, a species-specific MC prediction model (0.94 ≤ R2 ≤ 0.98), a generalized model for the four species (R2 = 0.65), and a hybrid model for the species with similar densities (0.80 ≤ R2 ≤ 0.96) were constructed, respectively. Overall, the species-specific MC prediction model showed good predictive ability for both tree and wood disc samples, including that TDR can be used to detect wood and standing tree MC. If possible, the hybrid model can be used for species with similar density.

Estimation of bulk electrical conductivity in saline medium with contaminated lead solution through TDR coupled with machine learning

Time-domain reflectometry (TDR) has been used for the characterization of media; however, the results of TDR tests significantly differ according to the types of solutions. The objective of this study is to suggest a new relationship between TDR output values and bulk electrical conductivity based on a machine learning algorithm for enhancing the reliability of TDR measurement. Various salinities (0%, 1%, 2%, and 3%) and lead concentrations (0, 0.5, 1, 2, 5, and 10 mg/L) are applied along with silica sand, classified as SP in USCS, to create media. A laboratory test is performed to measure the TDR waveform at the bottom of the cylindrical cell, and a resistance probe is also installed to obtain the true bulk electrical conductivity in the cell. A deep neural network machine learning algorithm is applied to establish the relationship between the TDR output value and the bulk electrical conductivity at each frequency of 0.1, 0.12, 1, 10, and 100 kHz. The highly important variables are also defined through random forest. This study demonstrates that the TDR can be reliably converted into bulk electrical conductivity when two different solutions are mixed.

Influence of Temperature on Wave Propagation in Low-Voltage Distribution Cables

Wave propagation in power cables depends on temperature. This paper explores its modeling for low-voltage cables, both main and service cables. Numerical thermal modeling combined with modal analysis, based on known and measured material properties, is employed to simulate waveforms expected in time-domain reflectometry tests. Comparison with laboratory measurements on a main cable shows that the main characteristics and their temperature dependency agree. The effect on wave propagation of rapid temperature rise in the conductor of a service cable during a fault is investigated. The predicted change in propagation velocity is confirmed by a field test. The perspectives of employing temperature dependent material characteristics, in particular the dielectric permittivity, on wave propagation for diagnostic techniques are briefly discussed. By accounting for the presence of different modes, the accuracy of locating the fault by means of time-domain reflectometry can be increased.

A new measurement algorithm for TDR-based localization of large dielectric permittivity variations in long-distance cable systems

One of the most common applications of time-domain reflectometry (TDR) is the localization of dielectric permittivity variations (DPVs) along cable systems. However, signal attenuation and dispersion phenomena limit the usability of TDR when used on long cable systems. Some TDR measuring instruments offer the possibility of modifying the amplitude and the width of the TDR test pulse signal, along with the gain of the input stage amplifier. Increasing these parameters generally allows to investigate longer distances; nevertheless, increasing the gain may saturate the instrument analog to digital converter (ADC) and increasing the pulse width leads to worse spatial resolution. For this reason, it is customary for the operator to repeat TDR measurements several times, with different settings, and proceed by focusing each time on a different TDR reflectogram; however, this procedure is time-consuming and, eventually, it does not guarantee optimal performance.Starting from these considerations, in this work, a new measurement algorithm for facilitating and making more effective the TDR-based localization of large DPVs on long cable systems is proposed. The algorithm automatically acquires several TDR reflectograms obtained by setting different values of the gain of the input stage amplifier and the values of the pulse width of the test signal. The reflectograms are then automatically processed, in an effort to balance the short-distance resolution and long-distance gain in a single composite reflectogram (CR), which can be conveniently used also by non-skilled operators. The developed algorithm was implemented and validated through experiments on a practical case study to localize DPVs on a 300 m-long cable system.

Application of TDR Test Probe for Determination of Moisture Changes of Railway Substructure Materials

Abstract The initial part of the paper characterizes a non-destructive TDR (time domain reflectometry) method for measuring moisture. This method is used to identify the moisture changes in the materials incorporated in the structural layers of the railway models built at a 1:1 scale (experimental stand DRETM). The subsequent part specifies the procedure for calibrating the TDR probe for selected building materials composing the measuring profiles of the experimental stand (Liapor fr. 1/8 mm, sand and crushed aggregate fr. 0/31.5 mm). The result of the TDR probe calibration is the calibration curves for the tested building materials, which can be used to identify the real moisture values in the railway line structure, in any season. The specified moisture values represent the necessary inputs for the numerical modeling of the non-traffic load (climatic factors) on the railway line using the SoilVision software.

Analyses of GPR signals for characterization of ground conditions in urban areas

Ground penetrating radar (GPR) is applied for the characterization of the ground conditions in urban areas. In addition, time domain reflectometry (TDR) and dynamic cone penetrometer (DCP) tests are conducted for the accurate analyses of the GPR images. The GPR images are acquired near a ground excavation site, where a ground subsidence occurred and was repaired. Moreover, the relative permittivity and dynamic cone penetration index (DCPI) are profiled through the TDR and DCP tests, respectively. As the ground in the urban area is kept under a low-moisture condition, the relative permittivity, which is inversely related to the electromagnetic impedance, is mainly affected by the dry density and is inversely proportional to the DCPI value. Because the first strong signal in the GPR image is shifted 180° from the emitted signal, the polarity of the electromagnetic wave reflected at the dense layer, where the reflection coefficient is negative, is identical to that of the first strong signal. The temporal-scaled GPR images can be accurately converted into the spatial-scaled GPR images using the relative permittivity determined by the TDR test. The distribution of the loose layer can be accurately estimated by using the spatial-scaled GPR images and reflection characteristics of the electromagnetic wave. Note that the loose layer distribution estimated in this study matches well with the DCPI profile and is visually verified from the endoscopic images. This study demonstrates that the GPR survey complemented by the TDR and DCP tests, may be an effective method for the characterization of ground conditions in an urban area.

Novel TDR Test Method for Diagnosis of Interconnect Failures Using Automatic Test Equipment

This paper suggests a novel efficient interconnect failure diagnosis method, which is dubbed as “time of propagation delay pass fail (TPDPF),” employing time domain reflectometry (TDR). The proposed TPDPF has been applied to diagnose the interconnect failures in a high parallelism probe card with the TDR function of automatic test equipment (ATE), which has been exclusively used in calibrating the channel length skews. It has been shown that the TPDPF method could be very efficient in the diagnosis of the interconnect failures with the help of a short-end fixture (a metal wafer), which is also proposed in this paper. To check the validity of the proposed TPDPF method, an automatic probe card diagnosis system was constructed, and it turned out to take only a few minutes to diagnose the whole interconnects in a high parallelism probe card. Furthermore, the implemented diagnosis system does not require skilled hands due to its automatic execution, and it enables about a $20\times $ enhancement of the efficiency of the probe card management and wafer testing.

A New Non-Destructive TDR System Combined with a Piezoelectric Stack for Measuring Properties of Geomaterials.

Dry density and water content are two important factors affecting the degree of soil compaction. Conventional methods such as the sand cone test and the plate load test are used to measure such properties for evaluating the degree of compaction and the stiffness of soil in the field. However, these tests are generally very time-consuming and are inherent with some errors depending on the operator (in particular for the sand cone test). Elastic modulus is an indicator to describe the stress-strain behavior of soil and in some cases is used as a design input parameter. Although a rod type TDR (Time Domain Reflectometry) system has been recently proposed to overcome some shortcomings of the conventional methods (particularly the sand cone test), it requires driving the probes into the ground, thus implying that it is still a time-consuming and destructive testing method. This study aims to develop a new non-destructive TDR system that can rapidly measure the dry density, water content, and elastic modulus of soil on the surface of compacted soil, without disturbing the ground. In this study, the Piezoelectric Stack, which is an instrument for measuring the elastic modulus of soil, has been added to the TDR system with a flat type probe, leading to a non-destructive TDR system that is capable of measuring the dry density, water content, and elastic modulus of soil. The new TDR system developed is light enough for an engineer to carry. Results of the standard compaction and TDR tests on sand showed that the dry densities and the moisture contents measured with the new TDR system were in good agreement with those measured with the standard compaction test, respectively. Consequently, it appears that the new TDR system developed will be very useful to advance the current practice of compaction quality control.

Calibration of TDR Test Probes for Measuring Moisture Changes in the Construction Layers of the Railway Line

In the introduction of the paper there is characterized a way of monitoring the moisture in the structure of the railway substructure and its subgrade in the Experimental stand DRETM II, which is a part of the experimental workplace of the Department of Railway Engineering and Track Management. The substantial part of the paper is devoted to the characteristics and calibration of TDR (Time domain reflectometry) test probes for selected rock materials, which are incorporated into the construction of Experimental stand DRETM II (crushed aggregate fr.0/31.5mm, crushed aggregate fr.0/63mm and clay blended with river gravel), as a basic prerequisite for determination of the actual moisture and its changes in the body of the railway substructure and subgrade during the year. Finally, this article outlines a comparison of individual TDR probes used in calibration and their suitability for monitoring moisture in various materials used in construction layers of the Experimental stand DRETM II.

Temperature Corrections for Time Domain Reflectometry Parameters

AbstractThe waveforms from time domain reflectometry (TDR) tests on soil depend on the temperature of the soil being tested. This study provides a discussion of, and the basis for, temperature corrections for the parameters measured in the TDR test for use in calculating water content and dry density of soil. This paper is a companion to one that provides the basis for an updated ASTM Standard, but does not cover temperature effects. A brief synopsis of the new methodology is provided herein to identify parameters that are sensitive to temperature of the soil being tested.

Measurement of electrical conductivity of pore water in saturated sandy soils using time domain reflectometry (TDR) measurements

Studying solute transport in soils is hampered by a lack of technology for continuously monitoring ionic concentration of contaminants. The electrical conductivity of pore water is a strong indicator of ionic concentration of contamination in soil. Using the bulk electrical conductivity of a soil measured by time domain reflectrometry (TDR) to predict the soil pore-water electrical conductivity appears to be a promising technique. This study presents a new method for estimating the pore-water electrical conductivity of saturated sandy soils using a single TDR test. The effects of pore-water electrical conductivity, temperature, porosity, and ionic types on the electrical conductivity of soil were studied. An average value of the exponent in the Archie’s Law was found to be 1.457 for the saturated sandy soils used in this study. A laboratory model infiltration test was also conducted with continuous monitoring of the electrical conductivity of the pore water by TDR. The results showed that TDR is able to provide a reasonably accurate estimation of the electrical conductivity of pore water. Consequently, it may be possible to monitor the in situ ionic contamination in saturated sandy soils using TDR technology.

Seamless Maintenance and Protection Scheme for Next-Generation Access Networks

We propose and demonstrate a seamless maintenance and protection scheme based on remotely reconfigurable remote node. Protection for fiber failures and a centralized optical time-domain reflectometry test for preventive maintenance can be achieved within 90 ms by using instantaneous optical powering at the central office, while maintaining the passive nature of the passive optical network.

Wide-Bandwidth Coaxial PWB Transmission Line Probe

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The design, fabrication, and test of a wide-bandwidth (3-dB attenuation bandwidth <formula formulatype="inline"><tex>$\geq$</tex></formula> 30 GHz), 50 <formula formulatype="inline"><tex>$\Omega$</tex></formula>, passive coaxial probe for the electrical characterization of printed wiring board (PWB) transmission lines is described. The probe can make thousands of repeated contacts, using spring-loaded interconnects, without affecting probe performance. The probe contains an internal mechanism for dissipating static charge on the signal line of the PWB transmission line and is long enough (approximately 10 cm) to act as a transfer standard for characteristic impedance testing, as per the time-domain reflectometry test method described in IPC TM 2.5.5.7. </para>

Time domain reflectometry for water content and density of soils: study of soil-dependent calibration constants

The paper studies the soil-dependent calibration constants used for determining water content and density of soil using time domain reflectometry (TDR), specifically, to establish the typical soil calibration values and study the extent of the uncertainty in calibration factors on measurement accuracy. The TDR method described here makes use of a calibration equation normalized by soil dry density, which involves two soil-dependent constants, a and b. Both a and b have physical significance, with the value of a related to the apparent dielectric constant of the dry density – normalized dry soil solids and the value of b related to the apparent dielectric constant of the pore fluid. From theoretical predictions, typical values of a are around 1.0, and typical values of b are around 9. Practically, the constants a and b are obtained through calibration tests performed in conjunction with standard compaction tests. Experimental study shows that calibration constants fall within the ranges from theoretical predictions. Tests on five soil mixtures provided average values of a = 0.945 and b = 8.76, while 11 clean sands resulted in average values of a = 1.0 and b = 8.5. The study also shows that there are no significant effects of compaction energy on the measured values of a and b. Sensitivity analyses indicate that variations in a and b both cause variations in TDR-determined water content and density, but the variations are typically within acceptable limits for engineering application purpose. Results from TDR tests on simulated field experiments are consistent with the sensitivity analyses.Key words: time domain reflectometry, TDR, calibration constants, water content, dry density, sensitivity.

Soil Water Content and Dry Density by Time Domain Reflectometry

Soil water content and dry density are two important properties for compaction quality control. This paper presents a new method for determining soil water content and dry density using a single time domain reflectometry test, which is an improvement over that designated by ASTM D6780. This new method is based on simultaneous measurement of apparent dielectric constant and bulk electrical conductivity on the same soil sample. Calibration equations correlate these two parameters with soil gravimetric water content and dry density, which are simultaneously solved after adjusting field-measured conductivity to a standard conductivity. The method compensates for temperature effects. The test process takes about 3 min and all calculations are automated. Testing may be done in situ using a special probe that provides sufficient sampling volume or in a compaction mold adapted to form a probe. Laboratory and field tests results show this one-step method is a fast, accurate, and safe method for construction quality control.

Cryosampler interface

A package that permits the electrical coupling of a cryosampling system with a high temperature device has been constructed and tested. The Faris sampling system has demonstrated 5 ps time resolution and 10 μV sensitivity. The interface couples the sampler at 4.2 K to a higher temperature region, with minimal heat transfer, by means of low inductance contacts to a high quality 50 ohm thin-film transmission line. Initial time domain reflectometry tests using the sampler have been carried out over a range from liquid helium temperature to 210 K. Five reflections have been observed of a step initiated and detected by the sampler at the low temperature end and traversing a 14 cm path to the high temperature end and back, No more than 20 ps was added to the pulse risetime for one roundtrip and signals on the order of 100 μV were detected, We expect to improve this performance and to use the system for experiments on superconductors, gallium arsenide, and semiconductor devices.