A method and installation for the measuring and extended monitoring of the stress state of a continuously welded rail (CWR)

Description

[0001] The present invention regards a method and an installation for measuring and monitoring the stress state of a rail of a railway track.

[0002] As is known, railway line tracks are composed of multiple pieces welded together, so to make the so-called continuously welded rail (CWR).

[0003] Although the use of CWR tracks has contributed to resolving many problems connected with the stresses that the tracks sustain with the train passage, it is not easy to monitor the stress state in such system. In other words, it is not easy to measure the thermal, tension or compression stresses on an entire track section, which can be due both to climate changes and to mechanical stresses sustained with the passage of the trains.

[0004] Usually, during installation, the tracks are pre-tensioned so to bring them to have a length equal to the length which they would have if the track was at a predetermined temperature (in Italy, such temperature being 30°C). This temperature is defined as the stress-free temperature (SFT).

[0005] Measuring the variations of the stress-free temperature allows evaluating the stress state of a rail, and thus of the track.

[0006] After installation, the seasonal outdoor temperature variations, the maintenance operations and the so-called curve breathing (i.e. the transverse movements or deformations of the track) can induce stress states that the continuously welded rail (CWR) cannot tolerate. Considering, then, that the track must support the passage of the trains and possible seismic motions, one comprehends how there is a high risk that it undergoes substantial transverse deformations or even breakage capable of causing derailment.

[0007] Periodic observations of the track condition are carried out along many train lines, or experimental signaling installations have been installed which use so-called strain gauge systems (deformation gauges), which are composed of casings containing both a measurement sensor and its respective electronic components, which are welded or bolted to each rail of a track. The sensors are electrically connected with a computer set to monitor the stress state of the line and to process the data detected from the various sensors in order to signal possible risk or danger. Up to now, sensors have only measured the deformations of the track, through which it was possible to carry out the monitoring of the state of the wheels of the passing trains. To such end, various systems were employed, such as the so-called "WILD" system which uses a plurality of strain gauge devices, which are positioned along the tracks and are intended to measure the deformations of the tracks with the passage of the trains. Due to this measurement type, it is possible to evaluate if the train has flat, eccentric, flattened or in any case defective wheels.

[0008] The United States patent application US-2008/0019701, for example, describes a system for monitoring the deformations of a track upon the passage of a train, which provides for the use of fiber Bragg grating sensors (fiber optic sensors with Bragg grating) on the track and an optical fiber intercepted by each sensor along a rail, the optical fiber being connected on one side with a source of light energy and on the other side with a signal analyzer device. Such system is used for evaluating several characteristics of a train which passes on the rails, such as the number of axles, the instantaneous speed of the train, the unbalance of the train wheels.

[0009] It is clear that from the standpoint of safety and maintenance methods, it is desirable to have a control system available that is also suitable for monitoring the stress state of the line and which can predict the zones of potential danger, so to detect possible damage of the track before it is irreparably damaged or before it can cause derailments or another type of accident.

[0010] Currently, there are no measurement systems capable of continuously monitoring the stress state so as to prevent or in any case predict substantial transverse deformations or breakage and damage such to place the track at risk of accident.

[0011] EP-1 582 430 teaches a system and a plant for monitoring the state of a railway, which comprises an optical fiber and a plurality of sensors, e. g. fiber Bragg grating sensors, which are rigidly fixed, e. g. by means of an epoxy glue or by welding to a rail track. The system further includes an optical signal emitter designed to emit an optical signal to the fiber and an optical signal interrogator. According to such a prior art document, the system continuously monitors the wavelength of the optical signals reflected by each sensor and more particularly it monitors whether a wavelength shift occurs.

[0012] The main object of the present invention is that of providing a method suitable for allowing the evaluation and monitoring of the stress state of a continuously welded rail CWR.

[0013] Another object of the present invention is that of providing an installation for carrying out a method according to the present invention suitable for evaluating and monitoring the stress state of a continuously welded rail.

[0014] According to a first aspect of the present invention, a method is provided according to claim 1.

[0015] According to another aspect of the present invention, an installation is provided according to claim 10.

[0016] With reference to the single attached Figure, there are illustrated: a track 1, comprising two rails 1 a, 1 b, a plurality of pairs (in the Figure, three pairs are illustrated but it will be understood that there could be additional pairs) of sensors 2a, 2b, an emitter means of at least one light energy beam 3, a control unit 4 for sensor interrogation, an optical fiber 5 and a processor (computer) 6 designed to receive and process data from the control unit. The interrogation control unit 4 advantageously comprises an optical spectrum analyzer, e. g. a monochromator and a signal-acquisition opto-electronic interface. The optical fiber 5 is designed to optically connect the emitter means 3 with the deformation sensors 2a, 2b and with the spectrum analyzer 4.

[0017] Advantageously, the optical fiber has an array or sequence of sensors. Each measurement point comprises two sensors, fixed on the neutral axis of a rail, a first sensor 2b designed to measure temperature variations of the rail itself, and a second sensor 2a integral in longitudinal sense with the track, arranged to measure the variation of the pair of quantities constituted by longitudinal deformations of the rail, and temperature.

[0018] Still more advantageously, both sensors are of fiber Bragg grating (FBG) type, and are prearranged on a metal surface which in turn can be directly secured to the track, by means of electrical micro-welding. For the installation of the sensors, the track will only be locally cleaned, so as to allow the fixing of the sensors directly on the rail.

[0019] As is known, FBG sensors are diffractive optical elements, present in pre-established zones of the fiber, which have the property of reflecting the incident light with a wavelength that is a linear function of the temperature and the deformations experienced by the optical fiber in the zone of interest.

[0020] A light energy beam will then be sent from the source into the fiber 5, and will intercept the Bragg grating sensors 2a, 2b, and will be at least partly reflected towards the spectrum analyzer 4, which will analyze the received signals and will send the data to the processor 6, which will process such data and measure the stress state of the rail, in particular the SFT or stress control temperature.

[0021] An installation according to the present invention preferably has a beam splitter 7 which is designed to intercept the beam transmitted along the optical fiber; the beam splitter 7 is arranged between the emitter means and the interrogation control unit, on one side, and the sensors on the other side.

[0022] In order to facilitate the installation of the sensors, fibers are used which are composed of multiple sections, each several hundred meters long. Such sections will be connected to each other through suitable joints, which assure an "insertion loss" of less than 0.3dB, as is known at the state of the art. It will then be possible to interrupt the installation if necessary, even at later times, since the stress state can be monitored even with an only partly-installed installation. Such solution moreover facilitates possible maintenance operations on the line.

[0023] Preferably, the fiber is monomodal, i.e. an optical fiber which allows only one mode of optical propagation, and is guided, in the non-sensitive part, i.e. that part not corresponding with the FBG sensors, into a duct/sheath of any suitable type. Such sheath will then be fixed to the rail by means of a suitable glue, i. g. a water-hardening, single-component epoxy resin glue, or simple silicon.

[0024] The distance interval between pairs of sensors can vary as required.

[0025] With the method according to the present invention, one can measure the stress state of a rail in a track by means of an indirect quantity, the stress-free temperature (SFT), which is obtained from two simultaneous measurements at the same point of the rail with regard to the deformation and the temperature, each measurement being carried out by means of a respective FBG sensor.

[0026] Assuming that the SFT of a material at a specific instant has been determined, since one would have ΔL/L = αΔT for an object that is not subjected to constraints, if after this instant a deformation ε = ΔL/L is measured, then the SFT variation will be given by ΔT₀ = ε/α.

[0027] For the evaluation of the SFT, it is therefore necessary to substantially simultaneously determine the longitudinal deformation of the track and its temperature.

[0028] A FBG sensor can be directly fixed to a material subjected to deformations due to temperature, and then the variation of the wavelength returned by a FBG sensor will be Δλ/λ = (α+β) ΔT, in which β is the thermo-optical coefficient of the fiber (equal to 6.9 * 10^-6 °C^-1), while α is the thermal expansion coefficient of the material to which the fiber is fixed.

[0029] Alternatively, the sensor can be fixed on a metal support, in turn fixed on the material subject to deformations, and in such case the rigidity of the fixing is not compromised since the thermal expansion coefficient of the sensor is much less than that of the metal (typical values are 5.5 * 10^-7 °C^-1 for the sensor, while for the metals they are on the order of 10^-5 °C^-1).

[0030] A method according to the present invention therefore provides for installing at least two sensors of the neutral axis of the track, at least one of which (2a) rigidly secured to a rail, thus designed to detect its deformation and temperature variation, and at least another secured to a metal support that is not rigidly fixed to the rail, so that such sensor (2b) only measures the temperature of the rail.

[0031] In order to evaluate the calculation precision, an error can be considered in determining the wavelength returned by the sensor equal to 3 pm, therefore the error committed in calculating the deformation is (considering that kλ = 1.2 * 106 pm and α is equal to about 5 µε, there is an error in the calculation of the SFT variation of (5/11.8)°C = 0.4 °C.

[0032] Regarding instead the temperature, the error is instead (with αacc + β )λ = 29 pm/°C)) equal to about (3/29)°C = 0.1°C.

[0033] Starting from the variation of the SFT and the temperature, other quantities can also be easily obtained which are useful for establishing the correct functioning of the rail.

[0034] For example, it is possible to evaluate the stress on the rail (or better yet, also in this case, the stress variation) given by σ = E(αΔT-ε) = Eα(ΔT-ΔT₀), in which E is the elasticity modulus of the steel equal to about 200 GPa, and thus we have an accuracy of about 1 MPa.

[0035] Starting from the stress, we can obtain the compression force which acts on the rail, given simply by F = σA, in which A is the area of the rail section.

[0036] In order to measure the SFT with the systems proposed up to now, it is necessary to evaluate the characteristics of the track itself when it is not subjected to stress. In order to conduct such operation, it is necessary to cut the track and remove its constraints, or alternatively lift up the track and carry out static measurements.

[0037] With a method according to the present invention, it is thus possible to continuously monitor and record the local temperature and longitudinal stress of a railway section or an entire railway line, and hence to continuously evaluate the SFT variation in real time.

[0038] Since it is possible to have the data in real time, one can immediately verify possible irregular stress states on the rails, which can compromise train safety.

[0039] With a different processing of the available data, the present system can also be used for monitoring the position, the speed, the state of the trucks (e. g. the number of axles) and the wheels (e. g. eccentricity and flattening) of the trains, by simply changing the data ptocessing software and positioning the sensors in a suitable manner.

[0040] With a method according to the present invention, there is a series of advantages with respect to the methods known up to now, i.e.:

• complete immunity from external electromagnetic interferences and total absence of electrical signals generated by the on-site system, since the FBG sensors are not electrically-powered;
• continuous monitoring and nearly immediate accessibility to the data (SFT and other data);
• non-invasive fixing of the sensors to the track, which is easy to carry out;
• updating of the software directly on the control unit without, therefore, having to substitute the sensors;
• the number of sensors can be increased, and thus the measurement points, with lower costs with respect to conventional systems since the system does not have a defined number of sensors per measurement control unit.

[0041] The method described above is susceptible to numerous modifications and variations within the protection scope as defined by the claims.

[0042] Thus, the control unit could be located in opposite direction with respect to the emitter means, and in such case it will evaluate the stress state of the system on the basis of the light energy beam portion absorbed by the Bragg gratings.

Claims

1. A method of measuring the stress-free temperature (SFT) variations of at least one rail of a continuously welded rail to prevent or in any case predict substantial transverse deformations or breakage of the rail, comprising the steps of:

prearranging:

- one pair or a plurality of pairs of sensors: each pair including a first sensor (2b) not rigidly fixed to said rail, thereby being designed to operate in response to temperature variations only and a second sensor (2a) rigidly fixed to said rail, thereby being suitable for operating in response to temperature variations and longitudinal deformation in a rail section;

- at least one emitter means (3) of at least one light energy beam arranged far from said one pair or plurality of pairs of sensors (2a, 2b);

- at least one interrogation control unit (4) designed to receive said light energy beam that has passed through/been reflected by said one pair or plurality of pairs of sensors;

- at least one unit (6) for processing the data collected by the control unit (4); and

- at least one optical fiber (5): designed to optically connect at least one emitter means (3) with each sensor (2a, 2b) and with said interrogation control unit (4);

energizing said at least one emitter means (3) in order to supply at least one light energy beam to one pair or to a plurality of pairs of sensors (2a, 2b); and

processing the stress state of the rail by the at least one processing unit (6), on the basis of the signals received by the interrogation control unit (4).

2. A method according to claim 1, characterized in that at least one of said one or more plurality of pairs of sensors comprises a fiber Bragg grating (FBG) (2a, 2b).

3. A method according to claim 2, characterized in that at least one of said one pair or plurality of pairs of sensors is installed at the neutral axis of a rail.

4. A method according to claim 3, characterized in that said first sensor (2b) is prearranged on a metal support which is in turn fixed on the rail.

5. A method according to claim 4, characterized in that said metal support is electrically micro-welded on the rail.

6. A method according to any one preceding claim, characterized in that said fiber (5) is composed of multiple pieces, each of several hundred meters length, said pieces being connected with each other by means of joints.

7. A method according to any preceding claim, characterized in that said optical fiber is monomodal and guided, at a non-sensitive part, into a protective duct/sheath.

8. A method according to claim 7, characterized in that said sheath is fixed to the rail by means of a suitable glue.

9. A method according to any preceding claim, characterized in that said data interrogation control unit (4) comprises an optical spectrum analyzer and a signal-acquisition opto-electronic interface.

10. An installation for continuously evaluating the stress state of a continuously welded rail to carry out the method according to any preceding claim.

11. An installation as claimed in claim 10, comprising:

- one pair or a plurality of pairs of sensors: each pair including a first sensor (2b) not rigidly fixed to said rail, thereby being suitable for operating in response to temperature variations only and a second sensor (2a) rigidly fixed to said rail, thereby being suitable for operating in response to temperature variations and longitudinal deformation in a rail section;

- at least one emitter means (3) of at least one light energy beam arranged far from said one pair or plurality of pairs of sensors (2a, 2b);

- at least one interrogation control unit (4) designed to receive said light energy beam that has passed through/been reflected by said one pair or plurality of pairs of sensors;

- at least one unit (6) for processing the data collected by the control unit (4); and

- at least one optical fiber (5) designed to optically connect at least one emitter means (3) with each sensor (2a, 2b) and with said interrogation control unit (4).

12. An installation according to claim 11, characterized in that at least one of said one pair or plurality of pairs of sensors comprises a fiber Bragg grating (FBG).

13. An installation according to claim 11 or 12, characterized in that at least one of said one pair or plurality of pairs of sensors is installed at the neutral axis of a rail.

14. An installation according to claim 11, 12 or 13, characterized in that said first sensor (2b) is prearranged on a metal support which is in turn fixed to the rail.

15. An installation according to claim 14, characterized in that said support is fixed through electrical micro-welding.

16. An installation according to any claim 11 to 15, characterized in that said fibers are composed of multiple pieces, each of several hundred meters length, said pieces being connected to each other by means of joints.

17. An installation according to any claim 11 to 16, characterized in that at least one of said pairs of optical fibers is guided, at the non-sensitive part, into a protective duct/sheath.

18. An installation according to claim 17, characterized in that said sheath is fixed to the rail by means of a suitable glue.

19. An installation according to any claim 11 to 18, characterized in that said data interrogation control unit (4) comprises an optical spectrum analyzer and a signal-acquisition opto-electronic interface.

20. An installation according to any claim 11 to 19, characterized in that it comprises a beam splitter (7) designed to intercept the beam transmitted along the optical fiber; the beam splitter (7) being arranged between the emitter means and the interrogation control unit, on one side, and the sensors on the other side.

Ansprüche

1. Verfahren zum Messen der Normaltemperatur- (SFT) Variationen zumindest einer Schiene einer kontinuierlich geschweißten Schiene, um im Wesentlichen schräg verlaufende Deformationen oder Brüche der Schiene zu verhindern oder jedenfalls vorherzusagen, aufweisend die Schritte zum:

Voranordnen:

- eines Paars oder einer Vielzahl an Paaren von Sensoren: jedes Paar aufweisend einen ersten Sensor (2b), der nicht starr an der Schiene befestig ist, dadurch ausgestaltet, nur in Erwiderung auf Temperaturschwankungen zu arbeiten, und einen zweiten Sensor (2a), der starr an der Schiene befestigt ist, dadurch geeignet, in Erwiderung auf Temperaturschwankungen und Längsdeformationen im Schienenabschnitt zu arbeiten;

- zumindest eines Emittermittels (3) zumindest eines Lichtenergiestrahls, das weit entfernt von dem einen Paar oder von der Vielzahl an Paaren von Sensoren (2a, 2b) ausgestaltet ist;

- zumindest einer Abfragesteuerungseinheit (4), die ausgestaltet ist, den Lichtenergiestrahl zu empfangen, der durch das eine Paar oder die Vielzahl an Paaren von Sensoren passiert hat/reflektiert wurde;

- zumindest einer Einheit (6) zum Bearbeiten von Daten, die von der Steuerungseinheit (4) erhoben sind; und

- zumindest einer Lichtleitfaser (5), die ausgestaltet ist, zumindest ein Emittermittel (3) mit jedem Sensor (2a, 2b) und mit der Abfragesteuerungseinheit (4) optisch zu verbinden;

Zuführen der Energie dem zumindest einem Emittermittel (3), um zumindest einen Lichtenergiestrahl dem einem Paar oder der Vielzahl an Paaren von Sensoren (2a, 2b) zuzuführen; und

Bearbeiten des Spannungszustands der Schiene durch die zumindest eine Bearbeitungseinheit (6) basierend auf den durch die Abfragesteuerungseinheit (4) empfangenen Signalen.

2. Verfahren nach Anspruch 1, gekennzeichnet dadurch, dass zumindest eines des einen oder der Vielzahl an Paaren von Sensoren ein Faser-Bragg-Gitter (FBG) (2a, 2b) aufweist.

3. Verfahren nach Anspruch 2, gekennzeichnet dadurch, dass zumindest eines des einen Paars oder der Vielzahl an Paaren von Sensoren an der neutralen Achse einer Schiene installiert ist.

4. Verfahren nach Anspruch 3, gekennzeichnet dadurch, dass der erste Sensor (2b) auf einem Metallträger vorangeordnet ist, welcher wiederum auf der Schiene befestigt ist.

5. Verfahren nach Anspruch 4, gekennzeichnet dadurch, dass der Metallträger auf der Schiene elektrisch mikrogeschweißt ist.

6. Verfahren nach einem der vorstehenden Ansprüche, gekennzeichnet dadurch, dass die Faser (5) aus mehreren Teilen zusammengesetzt ist, von denen jeder einige hundert Meter lang ist, wobei die Teile durch Zusammenfügungsmittel miteinander verbunden sind.

7. Verfahren nach einem der vorstehenden Ansprüche, gekennzeichnet dadurch, dass die Lichtleitfaser monomod ist und an einem nicht-sensitiven Teil in ein Schutzrohr / in eine Umhüllung geführt ist.

8. Verfahren nach Anspruch 7, gekennzeichnet dadurch, dass die Umhüllung mittels eines geeigneten Klebstoffs an der Schiene befestigt ist.

9. Verfahren nach einem der vorstehenden Ansprüche, gekennzeichnet dadurch, dass die Datenabfragesteuerungseinheit (4) einen Analysator des optischen Spektrums und eine opto-elektronische Signalerfassungsschnittstelle aufweist.

10. Einrichtung zum kontinuierlichen Auswerten des Spannungszustands einer kontinuierlich geschweißten Schiene, um das Verfahren nach einem der vorstehenden Ansprüche auszuführen.

11. Einrichtung nach Anspruch 10, aufweisend:

- einen Paar oder eine Vielzahl an Paaren von Sensoren: jedes Paar aufweisend einen ersten Sensor (2b), der nicht starr an der Schiene befestig ist, dadurch geeignet, nur in Erwiderung auf Temperaturschwankungen zu arbeiten, und einen zweiten Sensor (2a), der starr an der Schiene befestigt ist, dadurch geeignet, in Erwiderung auf Temperaturschwankungen und Längsdeformationen in einem Schienenabschnitt zu arbeiten;

- zumindest ein Emittermittel (3) zumindest eines Lichtenergiestrahls, das weit entfernt von dem einen Paar oder von der Vielzahl an Paaren von Sensoren (2a, 2b) ausgestaltet ist;

- zumindest einer Abfragesteuerungseinheit (4), die ausgestaltet ist, den Lichtenergiestrahl zu empfangen, der durch das eine Paar oder die Vielzahl an Paaren von Sensoren passiert hat/reflektiert wurde;

- zumindest eine Einheit (6) zum Bearbeiten von Daten, die von der Steuerungseinheit (4) erhoben sind; und

- zumindest eine Lichtleitfaser (5), die ausgestaltet ist, zumindest ein Emittermittel (3) mit jedem Sensor (2a, 2b) und mit der Abfragesteuerungseinheit (4) optisch zu verbinden.

12. Einrichtung nach Anspruch 11, gekennzeichnet dadurch, dass zumindest eines des einen oder der Vielzahl an Paaren von Sensoren ein Faser-Bragg-Gitter (FBG) aufweist.

13. Einrichtung nach Anspruch 11 oder 12, gekennzeichnet dadurch, dass zumindest eines des einen Paars oder der Vielzahl an Paaren von Sensoren an der neutralen Achse einer Schiene installiert ist.

14. Einrichtung nach Anspruch 11, 12 oder 13, gekennzeichnet dadurch, dass der erste Sensor (2b) auf einem Metallträger vorangeordnet ist, welcher wiederum auf der Schiene befestigt ist.

15. Einrichtung nach Anspruch 14, gekennzeichnet dadurch, dass der Metallträger durch elektrisches Mikroschweißen auf der Schiene befestigt ist.

16. Einrichtung nach einem der Ansprüche 11 bis 15, gekennzeichnet dadurch, dass die Fasern aus mehreren Teilen zusammengesetzt sind, von denen jeder einige hundert Meter lang ist, wobei die Teile durch Zusammenfügungsmittel miteinander verbunden sind.

17. Einrichtung nach einem der Ansprüche 11 bis 16, gekennzeichnet dadurch, dass zumindest eines der Paare der Lichtleitfaser an dem nicht-sensitiven Teil in ein Schutzrohr / in eine Umhüllung geführt ist.

18. Einrichtung nach Anspruch 17, gekennzeichnet dadurch, dass die Umhüllung mittels eines geeigneten Klebstoffs an die Schiene befestigt ist.

19. Einrichtung nach einem der Ansprüche 11 bis 18, gekennzeichnet dadurch, dass die Datenabfragesteuerungseinheit (4) einen Analysator des optischen Spektrums und eine opto-elektronische Signalerfassungsschnittstelle aufweist.

20. Einrichtung nach einem der Ansprüche 11 bis 19, gekennzeichnet dadurch, dass sie einen Strahlenteiler (7) aufweist, der ausgestaltet ist, den entlang der Lichtleitfaser übertragenen Strahl abzufangen; wobei der Strahlenteiler (7) zwischen dem Emittermittel und der Abfragesteuerungseinheit auf einer Seite und den Sensoren auf der anderen Seite ausgebildet ist.

Revendications

1. Un procédé de mesure des variations de la température d'absence de contraintes (SFT) d'au moins un rail d'un long rail soudé pour empêcher ou en tout état de cause prédire des déformations transversales substantielles ou une rupture du rail, comprenant les étapes suivantes :

agencement préalable :

- d'une paire ou d'une pluralité de paires de capteurs, chaque paire comprenant un premier capteur (2b) non rigidement fixé audit rail, de manière à être configuré pour fonctionner en réponse aux seules variations de température, et un second capteur (2a) fixé rigidement audit rail, convenant ainsi pour un fonctionnement en réponse à des variations de température et à une déformation longitudinale d'une section de rail ;

- d'au moins un moyen émetteur (3) d'au moins un faisceau d'énergie lumineuse disposé à distance de ladite une paire ou pluralité de paires de capteurs (2a, 2b) ;

- d'au moins une unité de contrôle par interrogation (4) configurée pour recevoir ledit faisceau d'énergie lumineuse qui a traversé/a été réfléchi par ladite une paire ou pluralité de paires de capteurs ;

- d'au moins une unité (6) de traitement des données recueillies par l'unité de contrôle (4) ; et

- d'au moins une fibre optique (5) configurée pour relier optiquement au moins un moyen émetteur (3) à chaque capteur (2a, 2b) et à ladite unité de contrôle par interrogation (4) ;

- activation dudit au moins un moyen émetteur (3) afin de délivrer au moins un faisceau d'énergie lumineuse à une paire ou une pluralité de paires de capteurs (2a, 2b) ; et

- traitement de l'état de contrainte du rail par la au moins une unité de traitement (6), sur la base des signaux reçus par l'unité de contrôle par interrogation (4).

2. Un procédé selon la revendication 1, caractérisé en ce qu'au moins l'une desdites une paire ou pluralité de paires de capteurs (2a, 2b) comprend un réticule de Bragg à fibre (FBG) (2a, 2b).

3. Un procédé selon la revendication 1, caractérisé en ce qu'au moins l'une desdites une paire ou pluralité de paires de capteurs est installée sur l'axe neutre d'un rail.

4. Un procédé selon la revendication 3, caractérisé en ce que ledit premier capteur (2b) est préalablement agencé sur un support métallique qui est quant à lui fixé sur le rail.

5. Un procédé selon la revendication 4, caractérisé en ce que ledit support métallique est électriquement microsoudé sur le rail.

6. Un procédé selon l'une des revendications précédentes, caractérisé en ce que ladite fibre (5) est composée de tronçons multiples, chacun de plusieurs centaines de mètres de long, lesdits tronçons étant reliés les uns aux autres par des épissures.

7. Un procédé selon l'une des revendications précédentes, caractérisé en ce que ladite fibre optique est monomode et guidée, dans une partie non sensible, à l'intérieur d'un conduit/gaine de protection.

8. Un procédé selon la revendication 7, caractérisé en ce que ladite gaine est fixée au rail au moyen d'une colle appropriée.

9. Un procédé selon l'une des revendications précédentes, caractérisé en ce que ladite unité de contrôle par interrogation de données (4) comprend un analyseur de spectre optique et une interface optoélectronique d'acquisition de signal.

10. Une installation pour l'évaluation en continu de l'état de contrainte d'un long rail soudé pour mettre en oeuvre le procédé selon l'une des revendications précédentes.

11. Une installation selon la revendication 10, comprenant :

- une paire ou une pluralité de paires de capteurs, chaque paire comprenant un premier capteur (2b) non rigidement fixé audit rail, de manière à être configuré pour fonctionner en réponse aux seules variations de température, et un second capteur (2a) fixé rigidement audit rail, convenant ainsi pour un fonctionnement en réponse à des variations de température et à une déformation longitudinale d'une section de rail ;

- au moins un moyen émetteur (3) d'au moins un faisceau d'énergie lumineuse disposé à distance de ladite une paire ou pluralité de paires de capteurs (2a, 2b) ;

- au moins une unité de contrôle par interrogation (4) configurée pour recevoir ledit faisceau d'énergie lumineuse qui a traversé/a été réfléchi par ladite une paire ou pluralité de paires de capteurs ;

- au moins une unité (6) de traitement des données recueillies par l'unité de contrôle (4) ; et

- au moins une fibre optique (5) configurée pour relier optiquement au moins un moyen émetteur (3) à chaque capteur (2a, 2b) et à ladite unité de contrôle par interrogation (4).

12. Une installation selon la revendication 11, caractérisée en ce qu'au moins l'une desdites une paire ou pluralité de paires de capteurs comprend un réticule de Bragg à fibre (FBG).

13. Une installation selon la revendication 11 ou 12, caractérisée en ce qu'au moins l'une desdites une paire ou pluralité de paires de capteurs est installée sur l'axe neutre d'un rail.

14. Une installation selon la revendication 11, 12 ou 13, caractérisée en ce que ledit premier capteur (2b) est préalablement agencé sur un support métallique qui est quant à lui fixé au rail.

15. Une installation selon la revendication 14, caractérisée en ce que ledit support est fixé par microsoudage électrique.

16. Une installation selon l'une des revendications 11 à 15, caractérisée en ce que lesdites fibres sont composées de tronçons multiples, chacun de plusieurs centaines de mètres de long, lesdits tronçons étant reliés les uns aux autres par des épissures.

17. Une installation selon l'une des revendications 11 à 16, caractérisée en ce qu'au moins l'une desdites paires de fibres optiques est guidée, dans la partie non sensible, à l'intérieur d'un conduit/gaine de protection.

18. Une installation selon la revendication 17, caractérisée en ce que ladite gaine est fixée au rail au moyen d'une colle appropriée.

19. Une installation selon l'une des revendications 11 à 18, caractérisé en ce que ladite unité de contrôle par interrogation de données (4) comprend un analyseur de spectre optique et une interface optoélectronique d'acquisition de signal.

20. Une installation selon l'une des revendications 11 à 19, caractérisée en ce qu'elle comprend un diviseur de faisceau (7) agencé pour intercepter le faisceau transmis le long de la fibre optique, le diviseur de faisceau (7) étant disposé entre le moyen émetteur et l'unité de contrôle par interrogation, d'un côté, et les capteurs, de l'autre côté.

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