Impulse TDR and its application to measurement of antennas

The traditional stimulus signal used in a time-domain reflectometer (TDR) is a voltage step. We propose an alternative technique, whereby an impulse generator is employed in place of the step generator in a TDR. The advantage conferred by “impulse TDR” is that more energy is available at higher frequencies than with conventional step TDR, and so a higher bandwidth and signal-to-noise ratio (SNR) is achieved. The theoretical result is compared with measurement

Impulse TDR and its Application to Characterisation of Antennas

Passive microwave systems are traditionally characterised in the frequency-domain with a vector network analyser (VNA). The measurement of antennas typically takes place in an anechoic chamber where the interference from spurious reflections and outside noise is minimised. Despite the high level of accuracy achieved with this approach, such facilities have high costs associated with them. Recent publications have demonstrated the characterisation of antennas using a step-function time domain reflectometer (TDR) along with frequency-domain processing techniques. Localisation of the measurement in time prior to transformation allows for the dismissal of unwanted spurious reflections, eliminating the need for an anechoic chamber. An alternative technique is proposed whereby an impulse generator is employed in place of the step generator in a TDR. The advantage conferred by "impulse TDR" (ITDR) is that more energy is available at higher frequencies than with conventional step TDR, leading to a higher bandwidth and signal-to-noise ratio (SNR). The theoretical result is compared with measurement

Application of phase detection frequency domain reflectometry for locating faults in an F-18 flight control harness

Journal ArticleThe performance of a phase-detection frequency-domain reflectometer (PD-FDR) for locating open and short circuits (hard faults) in a Navy F-18 flight control harness has been tested, and the analytical expressions for accuracy verified. Nine different types of aircraft wires appear in this harness: twisted pair, shielded wires with 1-4 inner conductors, "filter wire," and bundles of individual wires. PD-FDRs in a variety of frequency ranges (12-25, 100-220, 150-300, and 180-400 MHz) are compared. Signal processing techniques are utilized to remove the reflections where the PD-FDR is connected to the wire harness, which is critical to obtaining accurate measurements, particularly for short lengths of wire. For this specific application, open and short circuits are located to within 2.5 cm (1 in) for PD-FDR200 and 11 cm (5.5 in) for PD-FDR25 for wires ranging from 9 cm to 9.15 m (6-360 in)

Reflectometry for structural health monitoring

ManuscriptAging wiring and structural cables in buildings, aircraft and transportation systems, consumer products, industrial machinery, etc. are among the most significant potential causes of catastrophic failure and maintenance cost in these structures. Smart wire health monitoring can therefore have a substantial impact on the overall health monitoring of the system. Reflectometry is commonly used for locating faults on wire and cables. It can also be used for location of faults on structural cables, if they are electrically isolated. This chapter describes and compares several reflectometry methods -- time domain reflectometry (TDR), frequency domain reflectometry (FDR), mixed signal reflectometry (MSR), sequence time domain reflectometry (STDR), and spread spectrum time domain reflectometry (SSTDR) -- in terms of their accuracy, convenience, cost, size, and ease of use. Advantages and limitations of each method are outlined and evaluated for several types of aircraft cables, and the general equations that govern their performance are given. The impact of the fault location and size is also discussed

Experimental validation of the inverse scattering method for distributed characteristic impedance estimation

International audience— Recently published theoretic results and numerical simulations have shown the ability of inverse scattering-based methods to diagnose soft faults in electric cables, in particular, faults implying smooth spatial variations of cable characteristic parameters. The purpose of the present paper is to report laboratory experiments confirming the ability of the inverse scattering method for retrieving spatially distributed characteristic impedance from reflectometry measurements. Various smooth or stepped spatial variations of characteristic impedance profiles are tested. The tested electric cables are CAN unshielded twisted pairs used in trucks and coaxial cables

Experimental Evaluation of the Inverse Scattering Method for Electrical Cable Fault Diagnosis

International audienceRecently published theoretic and experimental results have shown the ability of inverse scattering-based methods to detect and to locate soft faults in electric cables, in particular, faults implying smooth spatial variations of cable characteristic parameters. The purpose of the present paper is to further experimentally evaluate the inverse scattering method for retrieving spatially distributed characteristic impedance from reflectometry measurements. With high quality coaxial cables connected in parallel, composite cables of piecewise constant characteristic impedance profiles are built in order to evaluate the accuracy of the inverse scattering method and its robustness in the presence of impedance discontinuities

Frequency-domain reflectometery for on-board testing of aging aircraft wiring

Journal ArticleAging aircraft wiring poses a significant safety threat and has been implicated in losses of both military and commercial aircraft. This paper describes the conceptual design and function of a "smart wiring system" based on a low-cost frequency-domain reflectometer (FDR) that can be used to test the integrity of aircraft cables nondestructively on board. This system will enable the pilot or maintainer to test all critical wiring systems prior to flight at the push of a button. The details and test results from the FDR system on realistic aircraft wires are described. The system has a bandwidth of 0.8-1.2 GHz, a range of 4.5 m, and a resolution of 3 cm and can determine the length and terminating impedance of a cable harnesses from measurements at a single end. The system is now being miniaturized to be imbedded in a "connector saver" format for aftermarket installation on common existing platforms

Modeling and simulation of time domain reflectometry signals on a real network for use in fault classification and location

Today, the classification and location of faults in electrical networks remains a topic of great interest. Faults are a major issue, mainly due to the time spent to detect, locate, and repair the cause of the fault. To reduce time and associated costs, automatic fault classification and location is gaining great interest. State-of-the-art techniques to classify and locate faults are mainly based on line-impedance measurements or the detection of the traveling wave produced by the event caused by the fault itself. In contrast, this paper describes the methodology for creating a database and a model for a complex distribution network. Both objectives are covered under the paradigm of the time-domain pulse reflectometry (TDR) principle. By using this technique, large distances can be monitored on a line with a single device. Thus, in this way a database is shared and created from the results of simulations of a real and complex distribution network modeled in the PSCADTM software, which have been validated with measurements from an experimental test setup. Experimental validations have shown that the combination of the TDR technique with the modeling of a real network (including the real injector and the network coupling filter from the prototype) provides high-quality signals that are very similar and reliable to the real ones. In this sense, it is intended firstly that this model and its corresponding data will serve as a basis for further processing by any of the existing state-of-the-art techniques. And secondly, to become a valid alternative to the already well-known Test Feeders but adapted to work groups not used to the electrical world but to the environment of pure data processing