Qinghai Shi

A New Algorithm for Wire Fault Location Using Time-Domain Reflectometry

In time domain reflectometry (TDR) attenuation and dispersion of the reflected signal limit the reachable accuracy for wire faults location. Because time of flight is evaluated, the wire faults with small impedance changing are difficult to locate. In this paper, a novel method for the TDR-based wire fault detection is presented by transfer function analysis in the time domain. For the determination of the transfer function, a deconvolution should be carried out. Thereby, an inverse problem is to be solved by an adaptive filter approach. Adaptive filters are able to reduce spurious noise of the deconvolution and lead to an acceptable deconvolution estimate. Therefore, a high signal-to-noise-ratio can be reached. The filters stopband characteristics are optimized by optimization technique to reduce the noise components of the transfer function in the frequency domain. For that a nonlinear fitting procedure is proposed using the Riad-Parruck optimization criterion. The developed method can locate both hard faults (open and short circuits) and soft faults with small impedance changes, and identify the type of wire faults simultaneously in a controlled laboratory environment (without the impedance changes from mechanical vibration, movement, and moisture). The algorithm using adaptive filters and optimization techniques is proposed in this paper for the traditional TDR method, but it is general for most other reflectometry approaches. The estimated wirings are coaxial cables and twisted pair cables, which are used in electrical and power distribution systems.

Detection and localization of cable faults by time and frequency domain measurements

The localization of cable faults is very important for communication systems, power distribution systems and vehicles. Reflectometry methods are often used to detect and locate cable faults. A high-frequency signal is send down the cable. The reflected signal includes information about changes of cable impedance. With measurement of the time or phase delay the faults can be detected and located. These methods are used to detect open and short circuits. There are also techniques available for detecting frays, joints and other small anomalies. This paper describes and simulates different wire test methods that suitable for portable or in-situ test equipment and compares their advantages and disadvantages. The methods compared are the time domain reflectometry (TDR), time frequency domain reflectometry (TFDR) and frequency domain reflectometry (FDR).

Application of iterative deconvolution for wire fault location via reflectometry

The novelty of this paper is to propose an efficient method for the detection and location of wiring faults with transfer function analysis using time domain reflectometry (TDR) method, iterative deconvolution and optimization techniques. The paper shows how iterative deconvolution and optimization techniques are used to locate hard faults, small discontinuities and enhance the signal-to-noise ratio. The developed method can also be used to characterize the wire faults in the branches of the network. The adaptive filters are applied to reduce the deconvolution noise. The performance of three frequency domain deconvolution techniques, the short window function, the optimum compensation and the automated-regularization technique are applied to solve the ill-posed inverse problem for the transfer function between incident and reflected waves. The proposed approach was applied to locate faults on the shielded coaxial cables and twisted pair cables.

Wire Fault Location in Coaxial Cables by Impedance Spectroscopy

A new technique is proposed to detect and locate wire faults using the impedance spectroscopy and a model-based approach. A modeling approach for transmission lines is developed, in which every cable part having the same characteristic impedance is represented analytically by a frequency-dependent ABCD model. The model parameter extraction is resolved by global optimization techniques based on genetic algorithms leading to a robust convergence behavior and excellent accuracy. This novel method enables the location of hard and soft faults and the identification of types of wire faults. The bandwidth of the developed transmission line model fits to experimental results, so that influence effects such as losses, dispersion, and frequency-dependent signal propagation can be precisely modeled. The calculation time is not proportional to the wiring length or dependent on cable system complexity by numerical methods such as FDTD.

Analysis of the parameters of a lossy coaxial cable for cable fault location

This paper presents an estimation of the per-unit-length parameters of a lossy cable. A RLGC lumped element model for the lossy transmission line parameters of a coaxial cable including frequency dependent filtering effect is used in this study to evaluate reflectometry responses of the cable systems. The simulated results of this model are compared with the measured results of a coaxial cable using impedance spectroscopy to show the accuracy in frequency domain. This lossy transmission line model then is solved in the time domain to accurately locate the faults. The simulated results are compared with the measured results using time domain reflectometry. Finally this model is used to simulate branched cable networks.

A high accuracy voltage controlled current source for handheld bioimpedance measurement

In bioimpedance measurements, Beta-dispersion is an important working frequency range, from low frequencies kHz up to 1 MHz, since it includes the pathological states_ Along this relevant frequency range, getting a stable and safe injected current below than 0.5 rnA with load impedance changing from 5 Ω to 10 kΩ remains a challenge for the design of Voltage Controlled Current Source (VCCS)_ In this study, we suggest the Enhanced Howland circuit in dual configuration with a negative feedback using the high bandwidth amplifier AD8041 to reach higher accuracy at higher frequencies up to 1 MHz. According to experiments, this circuit configuration is capable to maintain approximately constant current amplitude within an accuracy of 0.54% at 1 MHz.

Comparative study of voltage controlled current sources for biompedance measurements

For bioimpedance measurement, the design of a voltage controlled current source (VCCS) is important to have a good compromise between performance of final results and patient safety. VCCS should have simultaneously large output impedance and wide bandwidth. In this paper, we compare between the Tietze topology, with and without Negative Capacitance Circuit (NCC), and the Improved Howland Current pump ICSA topology. Best results were reached with a Tietze current source with NCC over a wideband frequency range from 10 KHz to 1 MHz. The experiments show that the Tietze VCCS is able to drive loads of 25 Ω to 10 KΩ with current amplitude below 0.5 mA within the accuracy of 0.57% in practice. This fulfills even the requirements for bioimpedance measurements especially at high frequency and high load impedance.

Automated wire fault location using impedance spectroscopy and genetic algorithm

A new technique is proposed to detect and locate wire fault using impedance spectroscopy (IS) and a model-based optimization technique. The propagation along the cables is modeled by frequency dependent ABCD parameters. Genetic algorithms (GA) are used to solve the inverse problem. The novel method allows locating hard (short and open circuit) and soft (frays and junctions) faults and measuring the impedance of wire fault and consequently the types of wire fault can be distinguished. Results are presented to validate and illustrate the performance of this proposed method.

Wire Fault Diagnosis in the Frequency Domain by Impedance Spectroscopy

The typical methods for the wire fault location are the time-domain reflectometry (TDR) and frequency-domain reflectometry (FDR). In TDR, attenuation and dispersion of the reflected signal limit the reachable accuracy for wire faults location. Because time of flight is evaluated, the wire faults with small impedance changes are difficult to locate. The FDR method has better accuracy than the TDR method, because power signals are used as incident signals and Fourier transform is applied to locate wire faults. However, it is difficult to identify the types of wire faults. A new technique is proposed to detect and locate the wire fault using impedance spectroscopy (IS). IS is applied to measure the input impedance of the wiring system. The load impedance of the wire fault can be abstracted from the input impedance in order to identify the type of wire faults. The input impedance is a period function of the frequency and the period of this function is linearly proportional to the distance to the fault. The fast Fourier transform of the input impedance can give a single spike to locate the wire fault. This novel method enables the location of hard (open and short circuits) and soft (wire faults with small impedance changes) faults. The input impedance of the wire faults in the defined low-frequency range can be applied to identify the types of wire faults. The capacitance and inductance of the cable system can be applied to detect the wire fault if it is open or short circuit. The measurement deviation of the wire fault location in this paper is maximal 40 cm and is independent of the distance to wire faults.

Detection and location of single cable fault by impedance spectroscopy

Time-Domain Reflectometry (TDR) and Frequency-Domain Reflectometry (FDR) are typical methods for cable fault location. Because the TDR method has the worse signal-to-noise ratio (SNR), it is difficult to detect soft cable faults (frays, chafes, and joints) which cause tiny impedance changes in the cable and small reflected signals. The FDR method has better SNR than the TDR method because of using a power signal as incident signals and signal processing for cable fault location. However it is difficult to identify the type of cable fault. A new method using impedance spectroscopy (IS) for cable fault location is described in this paper. With the new method not only cable fault can be located, but also the type of cable fault can be identified. The periods of cables impedance can locate hard (open and short circuits) and soft wire faults (frays, chafes and joints). The angle of the cables impedance in low frequency domain can identify the types of the faults. A signal processing algorithm is developed to accurately locate the cable fault and provide enhanced resolution and range. The details and test results with IS system on realistic twisted pair lines are described. Only one single fault is detected in this work.