Reflectometry

The reflectometry is a method of Diagnostic based on the principle of the Radar. A signal of probe is sent in the system or the medium to be diagnosed, this signal is propagated according to the laws of propagation of the studied medium and when it meets a Discontinuité (of Impédance), part of its energy is returned towards the point of injection. The analysis of the considered signal makes it possible to deduce from information on the system or the medium considered. Reflectometry is thus a means of Non destructive testing.

Types of reflectometry

Reflectometry is used mainly in two fields: temporal reflectometry (TDR) and frequential (FDR).

Both are based on the method described above. The principal differences lie in the procedure of injection and the treatment of the signal. In the temporal field (TDR), the analysis of the considered signals gives information on the compositiondu medium; in the frequential field (FDR), it is the analysis of the standing wave which provides this information. Many methods were developed and sometimes implemented on existing systems to decrease times and the costs of maintenance. However, the data processing run of the signal is essential for the precision of the analysis, and a precise physical model is more to improve the performances of them.

Scopes of application

Temporal reflectometry (TDR - Time Domain Reflectometry) was developed following work on the radar towards the end of the second world war, but it was really usable only towards beginning of the year 60 with the arrival of the oscilloscopes. Today, reflectometry is used in many fields going of the measurement of moisture in the grounds, the characterization of the layers in the earth's crust, the measurement of the respiratory tracts, and the detection of defects in the cables and fiberoptics.

Diagnosis of cables

Reflectometry is a method usually used for the determination of the electric state of cables and lines. This method provides information for detection, the localization and the characterization of electric defects.

In thirty years, the length of the cables embarked on a Automobile more than multiplied by ten, passing of almost 200 with more than 4000 meters. In same time the number of connections passed from two hundreds to more two thousand: it is understood that the interconnected network is regarded today by the manufacturers as a weak link for the modern vehicles. Moreover, the arrival of technology " by wire" - i.e. the replacement of the principal machine elements and hydraulic by programmed electronic systems (direction, braking, suspension, etc) - and electric whole will give him a cardinal importance, because it will be the single bond between the driver, its actions, and conveys it. The Fiabilité of wiring will become dominating then.

These problems are also present in aviation, where the lengths of cables exceed several hundred kilometers on the modern aircraft (nearly 40 km for the Rafale and to 400 km for the Airbus A380), field where reliability is a vital stake.

Reflectometry is also used to know the state of the cables drowned in the concrete (Reinforced concrete).

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