Time Domain Reflectometry Technology Research Articles

Practical procedures of faults and aging inspection to Photovoltaic system using time domain Reflectometry

Photovoltaic (PV) technology has emerged as a promising and significant renewable energy source in recent decades. However, the assessment of the on-site power generation performance of a PV system is often hindered by inline faults. Additionally, the degradation of the PV module's performance over time indirectly affects the operation of the power conditioner, leading to a decrease in the overall conversion efficiency of the power supply. Therefore, the accurate and efficient inspection of faults and aging status in series-connected PV modules is essential for ensuring reliable operation. This study proposes an improved Time Domain Reflectometry (TDR) technology as a standard inspection method. The TDR technology is initially employed to detect both open and shorted-circuits in series-connected PV panels with the suggested breakpoint simulation. Furthermore, the proposed TDR impedance log method enhanced the evaluation of the PV modules at different aging degrees using various monocrystalline silicon modules for practical verification. The study provides TDR as a comprehensive and effective technique for simultaneously identifying faults and inspecting the aging of PV systems.

Development of a Rapid and Non-Destructive Method for the Detection of Water Addition in Octopus Species (Octopus vulgaris and Eledone cirrhosa) Using Time Domain Reflectometry (TDR).

Consumer expectations regarding the quality of octopus are often frustrated and dissatisfaction is frequent, namely due to the excessive reduction in weight after cooking. Therefore, a rapid and non-destructive method based in time domain reflectometry (TDR) was developed for the control of water added to octopus (Octopus vulgaris and Eledone cirrhosa). O. vulgaris had significant higher values of moisture content, moisture/protein ratio, and cooking loss than E. cirrhosa. Immersion in freshwater increased the weight of O. vulgaris in ca. 32% after 32 h, and of E. cirrhosa in ca. 21% after 36 h, and cooking losses increased about 13.9% and 26.1%, respectively. The results reveal how consumers can be misled by abusive water addition. Changes in electrical conductivity and TDR curves were linked with the increasing incorporation of water and dilution effect of salts from octopus muscle. TDR technology and linear discriminant analysis were combined to detect added water in octopus. The classification model developed was cross-validated and 98.6% of samples were correctly classified. The method can be used to proof the authenticity of octopus (O. vulgaris and E. cirrhosa) or to detect fraudulent practices regarding added water.

Study on design of visual intelligent detection instrument for aviation cable fault

Aviation cable is used to transmit electric energy and signal, and its performance directly affects the safety of aircraft. It is difficult to locate cable faults on aircraft and there is a lack of suitable high-precision detection equipment. Based on the Time-Domain Reflectometry Technology (TDR), combining with the embedded systems such as Raspberry Pi and FPGA, an aviation cable fault detector is designed. Firstly, based on the frequency-doubling clock generated by the PLL, the detector emits a low-voltage pulse whose width is smaller than the cycle of the source clock. Then, based on the multiple ADC sampling method, the detector samples the reflected pulse. Finally, the detector uses the intelligent algorithm to automatically determine the fault type and fault location, and displays the sampling waveform and detection results on the LCD screen. Through experimental verification, the detector can basically meet the requirements of aviation cable fault detection.

Automatic TDR Monitoring System for Rock Mass Deformation in a Landslide Area

This study employs time domain reflectometry (TDR) technology for the automatic monitoring of a landslide area to explore rock deformation mechanism in comparison with rock cores and to estimate the location of a potential sliding surface and the amount of the sliding. Comparing to the data from the TDR monitoring and rock cores in Lushan landslide area in Taiwan, sliding surfaces of the landslide area occurred mainly at two locations of rock formations. One was located at an interface between colluvium and weathered rock; the other’s location was a buckling type of rock structures associated with slope creeping. Using a regression equation of the relation between TDR reflection coefficients and shear displacements, the magnitude of a TDR-cable deformation in the field can be determined. Resulting from field TDR monitoring, rock mass creep increased from 0 to 0.67 cm at 13.4-, 57.9- and 70.6-m depths of T3 borehole in the landslide area from September 2018 to May 2019. Overall, the TDR technology is practically used for a real-time and automatic slope monitoring system to detect the location and magnitude of sliding surfaces in the landslide area.

A High-Performance, Reconfigurable, Fully Integrated Time-Domain Reflectometry Architecture Using Digital I/Os

Time-domain reflectometry (TDR) is an established means of measuring impedance inhomogeneity of a variety of waveguides, providing critical data necessary to characterize and optimize the performance of high-bandwidth computational and communication systems. However, TDR systems with both the high spatial resolution (sub-cm) and voltage resolution (sub-$\muV$) required to evaluate high-performance waveguides are physically large and often cost-prohibitive, severely limiting their utility as testing platforms and greatly limiting their use in characterizing and trouble-shooting fielded hardware. Consequently, there exists a growing technical need for an electronically simple, portable, and low-cost TDR technology. The receiver of a TDR system plays a key role in recording reflection waveforms; thus, such a receiver must have high analog bandwidth, high sampling rate, and high-voltage resolution. However, these requirements are difficult to meet using low-cost analog-to-digital converters (ADCs). This article describes a new TDR architecture, namely, jitter-based APC (JAPC), which obviates the need for external components based on an alternative concept, analog-to-probability conversion (APC) that was recently proposed. These results demonstrate that a fully reconfigurable and highly integrated TDR (iTDR) can be implemented on a field-programmable gate array (FPGA) chip without using any external circuit components. Empirical evaluation of the system was conducted using an HDMI cable as the device under test (DUT), and the resulting impedance inhomogeneity pattern (IIP) of the DUT was extracted with spatial and voltage resolutions of 5 cm and 80 $\muV$, respectively. These results demonstrate the feasibility of using the prototypical JAPC-based iTDR for real-world waveguide characterization applications

Research on the adaptability of an improved high-intelligence long-distance optical fiber pre-warning system

With the development of technology, the total extent of global pipeline transportation is also increased each year. Nevertheless, owing to the wide distribution of gas and oil pipelines and the complex laying environment, the traditional long-distance optical fiber pre-warning system (OFPS) has a high false alarm rate when recognizing events threatening the pipeline safety, and it is difficult to define the type of intrusion events. Therefore, an improved high-intelligence long-distance OFPS was proposed, and the generalized adaptability of the system in various environments was studied. Φ-optical time-domain reflectometry technology was used in the distributed sensing part of the system, and a neural network (NN) was used in the signal recognition part to identify and classify intrusion events. Three methods were used in this system including an improved NN, a wavelet packet decomposition-based artificial NN, and a five-layer deep NN. Finally, through experiments in these three methods, the adaptability of the system was explored. The results show that the system possesses an excellent classification effect in the recognition of intrusion events with an average recognition rate reaching over 95%. Thus, it has good adaptability under various real environmental circumstances.

Monitoring of the transmission line galloping with a novel distributed optical fibre sensor and its statistical data analysis

The wind-induced galloping of the overhead transmission line threatens safety and serviceability of the power systems. In this study, a novel distributed optical fibre sensor system based on the polarisation-sensitive optical time-domain reflectometry technology is proposed, which can monitor the long-distance transmission line of over dozens of kilometres online in full scale by measuring its accompanying overhead ground wire grounding wire. Also it has good ability for surviving in harsh environments and easy maintenance. To meet the needs of long-distance monitoring, an equalisation processing method is used to reduce the influence of signal attenuation with the fibre length extension. In the continuous time-space statistics, adaptive galloping signal detection and the galloping level division of wind-induced disturbances are realised through the boxplot method; and in the continuous frequency-space statistics, the galloping frequency distribution along the cable is analysed simultaneously. Through the time-space and the frequency-space statistics upon the big data, the abnormal galloping moments and locations can be determined automatically in real time.

Slope deformation monitoring in the Jiufenershan landslide using time domain reflectometry technology

This paper assesses potential slope movement in a landslide area using a grouted cable of time domain reflectometry (TDR) technology compared with data from an inclinometer and bore logs. The paper quantifies the magnitude of a TDR coaxial cable by laboratory shear and extension tests. The maximum and average magnitudes of cable deformation by laboratory shear failure were 60 mm and 47 mm, respectively. Then, in the paper, the results of the laboratory testing were applied to a case study where there were two inclinometers and two TDR monitoring stations. Based on laboratory shear and extension testing, differences in TDR-reflected waveforms can be regarded as locations of cable deformations. Meanwhile, the magnitude of cable deformations can be measured by the regression equation of the relation between reflection coefficients and shear displacements. Finally, the working limit of the cable for potential slope movement can be determined at 210-mρ reflection coefficient in laboratory and field testing. When a grouted cable ruptured, the TDR technology can detect a reflection coefficient at 210 mρ corresponding to the potential shear displacement at approximately 47 mm, which means that a localized slope deformation significantly occurred at the location of the cable rupture.

Toward Prevention of Pipeline Integrity Threats Using a Smart Fiber-Optic Surveillance System

This paper presents the first available report in the literature of a system aimed at the detection and classification of threats in the vicinity of a long gas pipeline. The system is based on phase-sensitive optical time-domain reflectometry technology for signal acquisition and pattern recognition strategies for threat identification. The system operates in two different modes: 1) machine+activity identification, which outputs the activity being carried out by a certain machine; and 2) threat detection, aimed at detecting threats no matter what the real activity being conducted is. Different strategies dealing with position selection and normalization methods are presented and evaluated using a rigorous experimental procedure on realistic field data. Experiments are conducted with eight machine+activity pairs, which are further labeled as threat or nonthreat for the second mode of the system. The results obtained are promising given the complexity of the task and open the path to future improvements toward fully functional pipeline threat detection systems operating in real conditions.

Use of Brillouin optical time domain reflectometry to monitor soil-cave and sinkhole formation

With the economic development in China, sinkholes have become one of the main geological hazards during highway, railway and oil-pipe construction in the karst regions of southwestern China. This paper introduces an experimental study of monitoring the process of sinkhole collapse using Brillouin optical time domain reflectometry technology. In a series of tests of an experimental model, sinkholes are induced by pumping simulated karst water. Real time strains of optical fibers buried in sediments and soil damages are measured. One segment of soil along with buried optical fibers was excavated to verify the final positions of optical fibers and their relation to soil deformation. Results of the experimental study demonstrate that positions of peak strain in optical fibers correspond well to areas of maximum disturbance and soil void formation. Changes of optical fiber strains in different soil layers are good indicators of vertical disturbance in soil. Time series of optical fiber strain analysis exhibit the progress of horizontal disturbance in soil.

Calcium alginate hydrogel filtration membrane with excellent anti-fouling property and controlled separation performance

Calcium alginate (CaAlg) hydrogel filtration membrane was prepared using polyethylene glycol (PEG) as the pore-forming agent. Ultrasonic time-domain reflectometry technology was employed to analyze the membrane-forming process. The CaAlg filtration membrane was characterized by SEM, FTIR, TG and DTG. The mechanical behavior of the membrane was also evaluated. Concentrations of sodium alginate (NaAlg) and PEG on the pure water flux (PWF) and filtration properties of lysozyme (Lyz) solutions were investigated. Results showed that the PWF increased with an increase in the pressure initially, and then reached a stable value. The CaAlg filtration membrane prepared with lower NaAlg concentration and higher PEG concentration had higher flux. CaAlg filtration membranes exhibited good anti-fouling properties. The rejection of PEG reached above 90% when the molecular weight (Mw) of PEG in feed solution was larger than the pore-forming agent PEG for preparing the membranes. The CaAlg filtration membrane prepared using PEG400 as the pore-forming agent could reject almost 100% Brilliant Blue G250 (Mw=854.02Da), and 99.5% Congo Red (Mw=696.68Da).

Soil water sensing for water balance, ET and WUE

The soil water balance can be solved for evapotranspiration (ET) using soil water change in storage data from either weighing lysimetry or soil water sensing and measurement, along with data on the other components of the water balance. Weighing lysimeters are expensive and, although accurate, are difficult to manage and afford little replication. Direct soil water measurement by coring is accurate enough, but plagued by spatial variability that induces unwanted variability in the change in soil water storage between dates, and is destructive and time/labor consuming. Here we focus on soil water sensing using the neutron probe and various electromagnetic (EM) sensors (capacitance, time domain reflectometry (TDR) and quasi-TDR) with respect to the relative levels of uncertainty in profile water content, change in soil water storage, and estimates of deep flux; and their impact on estimated ET and water use efficiency (WUE). Studies consistently showed errors up to and >0.05 m3 m−3 for capacitance sensors used in access tubes, which implied errors in soil water flux estimation of up to 50 mm day−1, and calibrations that were so sensitive to soil bulk electrical conductivity (σdc) and temperature that water content and change in storage estimates were rendered unreliable. Also, larger spatial variability of water contents reported by capacitance sensors was tied to the EM field penetration in structured soils around access tubes being non-uniform and influenced by the random arrangement of soil micro-scale water content, σdc and bulk density distribution. Thus, we recommend that profiling sensor systems based on capacitance technology not be used for studies of water balance, ET and WUE, nor for irrigation scheduling. Recommended methods include the neutron probe, direct volumetric soil sampling and, in some cases, conventional time domain reflectometry with waveform capture and analysis. New sensor development efforts should focus on waveguide approaches using TDR technology.

A novel distributed optic fiber transduser for landslides monitoring

Unstable slopes have been monitored since the beginning of the last century. Current electro-optic detection technology can achieve automatic monitoring remotely with high safety and includes such methods as time domain reflectometry, optical time domain reflectometry and Brillouin optical time domain reflectometry. However, these technologies cannot simultaneously meet the requirements of distributed sensing, high initial measurement accuracy, large sliding distance and high dynamic range. Based on the space frame theory of reinforced concrete beams, this study presents an innovative design for a distributed optic fiber sensor: a novel transduser with a bowknot. Using the optic fiber microbending loss mechanism and optical time domain reflectometry technology, bending and shear tests based on the combined fiber sensor are conducted, and the vertical displacement of midspan, optical fiber sliding distance and loss data under three different spans are collected. Feasibility study and economic analysis of the transduser used for landslide monitoring are also presented. The results show that the maximum sliding distance of our transduser is 21.8, 26.5 and 30.6 mm with corresponding initial accuracies of 1.2, 2.3 and 3.3 mm, and the dynamic ranges are 0–20.6, 0–23.2 and 0–27.3 mm. The cost of the transduser is economical at $0.15/m, which demonstrates promising economic application, high monitoring effectiveness and stability in monitoring civil works, such as slope, dam and tunnel construction and measurement.

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.

Seismic damage identification for steel structures using distributed fiber optics

A distributed fiber optic monitoring methodology based on optic time domain reflectometry technology is developed for seismic damage identification of steel structures. Epoxy with a strength closely associated to a specified structure damage state is used for bonding zigzagged configured optic fibers on the surfaces of the structure. Sensing the local deformation of the structure, the epoxy modulates the signal change within the optic fiber in response to the damage state of the structure. A monotonic loading test is conducted on a steel specimen installed with the proposed sensing system using selected epoxy that will crack at the designated strain level, which indicates the damage of the steel structure. Then, using the selected epoxy, a varying degree of cyclic loading amplitudes, which is associated with different damage states, is applied on a second specimen. The test results show that the specimen's damage can be identified by the optic sensors, and its maximum local deformation can be recorded by the sensing system; moreover, the damage evolution can also be identified.

Time Domain Reflectometry Automatic Bridge Scour Measurement System: Principles and Potentials

Bridge scour is a major factor contributing to the failures of highway bridges constructed over waterways. During flood events, sediments can be washed away and bridge substructures (piers and abutments) are left inadequately supported. Field monitoring of bridge sour process is necessary to study the scour mechanism, to develop scour-resistant design of bridge piers and abutments, to implement effective scour countermeasures, and to deploy safety warning systems. The current instruments are not completely satisfactory in providing real-time monitoring data during critical flood events. This study introduces the development of an automatic scour monitoring system using time domain reflectometry (TDR) principle. It presents the principles and system design of the TDR sediment scour monitoring system. An analyses algorithm for scour signals has been developed. It was found to be robust and can be implemented to automate scour signal interpretation. Simulated experiments were conducted to validate the performance of the scour monitoring system prototype. The results showed that this TDR technology can accurately measure the scour depth. Besides, the properties of the sediments, such as the porosity and density can be estimated with reasonable accuracy. At the end of the paper, a few important issues associated with field deployments of TDR scour monitoring system are discussed.

Nondestructive Analysis of Interconnection in Two-Die BGA Using TDR

Nondestructive analysis (NDA) is one of the most important tasks that is performed during the industrial characterization of integrated circuits (ICs) because even a tiny defect or failure in the IC packages could be disastrous from the standpoint of quality control. To detect an interconnection failure in IC packages, a time-domain reflectometry (TDR) analysis system was developed. An open-end fixture (OEF) was employed to detect the rapid rise of edge signals from the package and to monitor them under the two parameters of time interval and reflection voltage. We developed a simple and effective electrical NDA system based on the TDR technology that can evaluate the interconnection of ball grid array (BGA) packages. The TDR-measurement results can determine both the failure location and type based on the aforementioned parameters for a two-die BGA package.

Electrical approach to Nondestructive Analysis on WB-PBGA with TDR Technology

Time Domain Reflectometry (TDR) is a powerful measurement technique that uses the reflection of a pulse sent down a transmission line to characterize the impedance of that line. The voltage of a reflection will vary depending on the distance to the fault and on the amount of energy reflected. In this paper we develop a simple and effective electrical nondestructive analysis (NA) system for the evaluation of the interconnection of wire-bonded plastic ball grid array (WB-PBGA) package. An open-end fixture (OEF) was employed to connect fast rising edge signals to the package which was monitored for its time delay and reflection voltage parameters. This technology represents a valuable new method for the NA of WB-PBGA packages, and it has enabled the rapid and efficient detection and location of faults. Comparative TDR measurements accurately predicted the location of opens and short circuits in the copper traces of the substrate, bond wire, and solders balls. The TDR analysis was verified by using X-ray analysis. The paper establishes the use of a TDR system incorporating an open-end fixture for locating opens and shorts in WB-PBGA packages.

Density Compensation of TDR Calibration for Geotechnical Applications

Abstract Time Domain Reflectometry (TDR) technology has been widely used in areas such as agricultural science, soil science, and water resources for measuring soil volumetric water content and is beginning to be used in geotechnical engineering. Calibration relationships, which generally relate the soil volumetric water content to TDR measured dielectric constant, are critical for the accuracy of TDR measurements. For TDR technology to be useful for geotechnical engineering practice, the calibration relationship needs to be expressed in terms of gravimetric water content. Besides, geotechnical engineering deals with more compacted earth materials, where the effects of soil density on TDR calibration are significant. This paper introduces an improved TDR calibration relation that accounts for the density of soil skeleton while at the same time is simple in format. Application of this calibration relationship shows that it significantly reduces data scatter and achieves more accurate results than other existing calibration relationships.

Time Domain Reflectometry for Compaction Control of Stabilized Soils

Chemical stabilization is widely used in geotechnical engineering to improve the engineering properties of geomaterials. The interaction between the stabilizers and soil particles changes the physicochemical structure of these materials and increases their performance. Water content and density are the indicators used in field practice for construction quality control of the stabilized soils. The nuclear method is currently the preferred technology for field measurement of water content and dry density in geotechnical engineering. However, the nuclear method has been found to give inaccurate results when used on stabilized soils. Researchers at Purdue University developed a procedure to measure soil water content and dry density using time domain reflectometry (TDR). Tests performed on conventional soils indicate that this procedure is accurate and fast. The feasibility of this technology on the stabilized soils was investigated; the preliminary conclusion was that TDR achieves satisfactory accuracy. In addition, the electrical properties measured by TDR are strong indicators of the physicochemical reactions taking place in the stabilized soils, which show that TDR technology can be a useful tool for monitoring these reactions.