FR2964232A1 - INTRUSION DETECTION SYSTEM AND METHOD OF MOUNTING SUCH A SYSTEM - Google Patents

Abstract

This intrusion detection system includes a barrier (102), an optical fiber cable (108), fasteners (110) by which the optical fiber cable (108) is attached to the barrier (102), each pair successive fasteners delimiting a portion (111) of the optical fiber cable (108) having two ends (111A, 1B) attached to the barrier (102) by the two fasteners (110), and a detection device of intrusion (120) configured to: emit a light signal into the optical fiber cable (108), and receive and analyze the light signal having traveled the optical fiber cable (108) to detect an intrusion. In addition, the fasteners (110) are designed to prevent longitudinal movement of the ends (111 A, 1 B) of each cable portion (111) relative to the barrier (102), the system includes, for each cable portion (111), mechanical coupling means of this cable portion (111) to the barrier (102), and the detection device (120) is further adapted to detect deformation of one of the cable portions (111). ) and identify this portion of cable (111), from the analysis of the light signal having traveled through the optical fiber cable (108).

Description

The present invention relates to an intrusion detection system and a method of mounting such a system. One type of known intrusion detection system comprises a barrier, a shock cable (electric wire or fiber optic cable), fasteners by means of which the impact cable is held against the barrier, and a detection device intrusion designed to measure the vibrations of the impact cable. This type of intrusion detection system is used to detect a basic threat (non-specialist intruder) or for low security installations (airport hangar, car park, etc.). It has the advantage of being inexpensive and discreet. However, it has the disadvantage of triggering a significant rate of false alarms, for example because of harsh weather conditions (hail, wind, ...) leading to nuisance alarms, usually over several kilometers. For the same reasons, it can not be installed along a route. In addition, this type of system is not sensitive to slow movements, usually caused by 'specialist' intruders. Finally, in practice, the removal of doubt about the intrusion requires another complementary technology, such as CCTV cameras. Another type of known intrusion detection system uses the detection of a cut of a barrier element (either a bar equipped with an electric or fiber optic cable, or the entire panel of the barrier turned detector) . As before, this type of intrusion detection system is used to detect a basic threat (non-specialist intruder) or for low security installations, and it has the advantage of being inexpensive and discreet. . On the other hand, it does not make it possible to detect an intrusion by climbing and thus, to prevent this type of intrusion, it must be coupled to `bavolets' in the high part of the barrier which can be inclined between 30 ° and 90 °, or even at concertinas. In an attempt to remedy these problems by proposing another technology, a new type of detection system takes advantage of the sensitivity to deformations, and in particular to elongation, of optical fibers.

Thus, the company Smartec offers a fiber optic cable sensitive to elongation with a BOTDR instrumentation (for "Brillouin Optical Time Domain Reflectometer") brand DiTest (trademark) Omnisens company. The company Novadetec also offers, on demand, to replace the (electric) impact cables usually used by optical fiber.

The present invention therefore relates more specifically to an intrusion detection system of the type comprising a barrier, an optical fiber cable, fasteners by means of which the optical fiber cable is attached to the barrier, each pair of successive fasteners delimiting a portion of the optical fiber cable having two ends attached to the barrier by the two fasteners, and an intrusion detection device adapted to: emit a light signal into the optical fiber cable and receive and analyze the light signal having traveled the fiber optic cable to detect an intrusion. Elno Technologies offers such a system in the form of a product called Sabrefonic II (registered trademark). In this intrusion detection system, the optical fiber cable runs along the barrier, so as to deform in the same way as the barrier. Its positioning is more precisely maintained by interlacing the cable in the mesh of the barrier and by the use of fasteners regularly arranged along the barrier (for example 30 cm from each other). Thus, in case of intrusion, the deformation of the barrier due to this intrusion causes a similar deformation of the optical fiber cable. The intrusion detection device, based on the detection of "speckles", detects the intrusion but does not locate it. It may thus be desired to provide an intrusion detection system which makes it possible to overcome at least part of the aforementioned problems. The subject of the invention is therefore an intrusion detection system of the aforementioned type, in which the fasteners are designed to prevent any longitudinal movement of the ends of each portion of cable with respect to the barrier, which furthermore comprises, for each portion of cable, mechanical coupling means of this portion of cable to the barrier other than the fasteners, and wherein the detection device is furthermore designed to detect a deformation of one of the cable portions and to identify this portion of cable, from the analysis of the light signal having traveled the fiber optic cable. Thanks to the invention, the deformation of the optical fiber cable is confined to one of the cable portions. Thus, it is possible to locate the position of the intrusion, with a precision corresponding to the length of the cable portions. Optionally, the deformation detected is an elongation variation of one of the cable portions, and the mechanical coupling means of each cable portion comprise a spacer connecting a point of the barrier, called the origin point, to a point the cable portion, called spaced point, which is remote from the line connecting the two ends of the cable portion. Thus, the portion of cable disturbed by the intrusion has an increased elongation when its spaced point moves a certain distance, compared to the elongation that would be observed if the separated point was, before this displacement, aligned with the two ends of the cable portion. Optionally also, the spaced apart point is farther from the straight line connecting the two ends of the cable portion than the origin point. Thus, the portion of cable disturbed by the intrusion has an increased elongation when its spaced apart point moves a certain distance, relative to the elongation that would be observed if the optical fiber cable was attached directly to the origin point of the barrier and that origin point moved the same distance. Optionally also, the spacer extends perpendicularly, ten degrees, to the barrier.

Optionally also, each cable portion has an elongated length, with respect to its length at rest, of an elongation, called initial elongation, for example between 1 and 5 millimeters per meter. Optionally also, the barrier comprises posts to be fixed to the ground and panels extending between the posts.

Optionally also, the fasteners attach the optical fiber cable to the posts and the coupling means couples each portion of cable to a panel. Also optionally, the clips attach the fiber optic cable to the panels and the coupling means couples each cable portion to a pole. Also optionally, the detection device comprises an optical reflectometer, for example an optical time domain reflectometer Brillouin, for detecting an elongation variation of one of the cable portions.

The invention also relates to a method for mounting an intrusion detection system according to the invention, comprising the following steps: the optical fiber cable is extended, without being lengthened, along the barrier, the optical fiber cable is attached by the fasteners to the barrier, so as to prevent any longitudinal movement with respect to the barrier of the ends of each cable portion delimited between two successive fasteners, each cable portion is further mechanically coupled to the barrier by means other than the two successive fasteners delimiting it.

The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings, in which: FIG. 1 schematically represents the general structure of a detection system of 2 shows diagrammatically an attachment of the system of FIG. 1, FIG. 3 diagrammatically represents a spacer of the system of FIG. 1, FIG. 4 illustrates the position of a portion. of the system of FIG. 1 in the absence of intrusion, FIGS. 5 and 6 illustrate two possible positions of the optical fiber cable portion of FIG. 4 in the event of an intrusion, FIG. a curve of the relative elongation of the optical fiber cable portion of FIG. 4 as a function of a deformation displacement at a point of this cable portion, FIG. 8 is an example of a curve of the elongation measured fiber optic cable according to the position along the optical fiber cable, during an intrusion, and FIG. 9 illustrates the successive steps of a method of mounting the system of FIG. an embodiment of the invention. With reference to FIG. 1, an intrusion detection system 100 according to one embodiment of the invention firstly comprises a barrier 102. In the example described, the barrier 102 comprises vertical posts 104 fixed to the ground and panels 106 extending between the posts 104. The panels 106 consist for example of a simple grid constituting a flexible panel or welded metal rods constituting a rigid or semi-rigid panel. The intrusion detection system 100 further comprises an optical fiber cable 108 and fasteners 110 by means of which the optical fiber cable 108 is attached to the barrier 102. Each pair of successive fasteners 110 defines a portion 111 of the cable optical fiber 108 having two ends 111A, 111B attached to the barrier 102 by the two successive fasteners 110. The clips 110 are designed to prevent longitudinal movement of the ends 111A, 111B of the cable portion 111 relative to the barrier 102. In the example described, the clips 110 are attached to the posts 104 to attach the fiber cable. optical 108 to each of these. The ends 111A, 111B of each cable portion 111 define a line A connecting them to one another. The intrusion detection system 100 further comprises, for at least a portion of cable 111, a spacer 112 connecting a point 114 of the barrier 102, called the origin point 114, to a point 116 of the cable portion 111, called In the example described, the origin point 114 is located on the panel 106 extending between the posts 104 of the pair of successive fasteners 110. Specifically, the origin point 114 is located in the middle of the panel 106. Still in the example described, the spacer 112 extends perpendicularly, to ten degrees, to the barrier 102, so that the separated point 116 is located on a straight line passing through the origin point 114 and perpendicular, to ten degrees, to the barrier 102 at this origin point 114. The spacer 112 is furthermore arranged so that the separated point 116 is further from the line A than the origin point 114. Moreover, each portion of cable 111 is elongated with respect to its length at rest, for example an elongation, called initial elongation, of between 1 and 5 millimeters per meter. The spacer 112 is adapted to transmit at least a portion of the movements of the origin point 114 to the spaced point 116, so that a movement of the origin point 114 causes a movement of the spaced point 116. Because the ends 111A, 111B of the cable portion 111 are fixed longitudinally by the pair of successive fasteners 110, this movement of the spaced apart point 116 causes a variation in the elongation of the cable portion 111 between the pair of successive fasteners 110, which, if it is large enough, can be detected. It will be noted that, in the example described, each cable portion 111 is in mechanical connection with the barrier 102 only by the fasteners 110 and the spacers 112. The intrusion detection system 100 further comprises a detection device intrusion 120, to which one end of the optical fiber cable 108 is connected. The intrusion detection device 120 is adapted to emit a light signal into the optical fiber cable 108, for example by means of a pulse laser, and to receive and analyze the light signal having traveled the fiber cable. optical 108 to detect an intrusion. More specifically, the detection device 120 is designed to detect and locate a variation in the elongation of one of the cable portions 111 and to identify this portion of the cable 111 among all the cable portions 111, to from an analysis of the light signal having traveled through the optical fiber cable 108. For this purpose, the intrusion detection device 120 is designed to calculate, at each instant or at regular intervals, the relative elongation of the fiber cable. optical 108 (i.e. its current elongation relative to its initial elongation) as a function of the position along the optical fiber cable 108. The intrusion detection device 120 is further designed to compare, at each instant or at a regular interval, the relative elongation along the optical fiber cable 108 with a reference elongation, and to locate the cable portion or portions 111 where the relative elongation exceeds the elongation t reference, this or these portions of localized cables 111 being called portions of cables at risk.

It will be noted that the position of the intrusion along the barrier will be easily related to that along the optical fiber cable by a conversion established at the time of installation of the system 100. Preferably, the intrusion detection device 120 includes a database in which typical intrusion curves are recorded. Each typical intrusion curve represents the relative elongation of the fiber optic cable along the portion of the fiber optic cable where the typical intrusion occurs. These curves are for example obtained by learning. The intrusion detection device 120 is then adapted to locally correlate the relative elongation as a function of the position along the optical fiber cable with a rectangular signal and to compare the at-risk cable portion (s) with the intrusion curves. types saved. In this way, the confidence rate of the system is high. Also preferably, the detection device 120 comprises an optical reflectometer, for example an optical time domain reflectometer Brillouin (or BOTDR for "Brillouin Optical Time Domain Reflectometer"). Also preferably, the reference aspect ratio is a sliding reference over time. Thus, the intrusion detection device 120 can discriminate between a slow variation (a few minutes) of the relative elongation resulting for example from a global or specific temperature change of the optical fiber cable 108, and a rapid variation (a few seconds) of the relative elongation resulting from a deformation generated by an intrusion. Also preferably, the intrusion detection device 120 is designed to detect and locate, typically to the nearest meter in the case of an OTDR (Optical Time Domain Reflectometer), a break in the optical fiber cable 108 and to trigger an alarm accordingly. With reference to FIG. 2, the fastener 110 is for example a clamping piece provided with a groove 202 dimensioned to the optical fiber cable 108, so as to receive the latter, and provided with clamping nuts 204 for gripping the fiber optic cable between the pole 104 and the groove 202. With reference to Figure 3, the spacer 112 is for example constituted by a rod extending from the origin point 114 of the barrier 102 to the separated point 116 of the optical fiber cable 108. With reference to FIG. 4, the successive fasteners 110 of each pair are separated by a distance L and the points 114 and 116 by a distance E, corresponding to the length of the spacer 112. Between the two successive fasteners 110, the portion 111 of the optical fiber cable 108 has a length L '. In the example described, the cable portion 111 at rest has a length Lrepos equal to the distance L between the posts. Thus, the cable portion 111 has an initial elongation AL / L, with AL = L'-L, which is equal to: L AL 2 LL 2 As the optical fiber cables have a lifetime that depends on the constraints to which they are subjected during their use, this initial elongation, and therefore the length of the spacers, will preferably be chosen less than a limit calculated taking into account the aging specifications provided by the manufacturer of the optical fiber cable. For a barrier having 2.5 m long panels (L = 2.5 m) and 10 cm spacers (E = 10 cm), the initial elongation LL / L is 3 159 pm / m. Knowing that an elongated optical fiber cable of 3,000 pm / ma, generally with a life expectancy of 25 years, this order of magnitude of separation (a few centimeters) is compatible with the operating life of the intrusion detection system. 100.

With reference to FIG. 5, when a mechanical disturbance P is applied to any point of the panel 106, the point 114 of the panel 106 moves from a perturbation shift D in the direction defined by the origin points 114 and spaced apart 116. Thanks to the spacer 112, the spaced apart point 116 of the cable portion 111 moves with the same disturbance displacement D. Thus, the cable portion 111 reaches a length L ".The optical fiber cable 108 then has a relative elongation AL% L '(with M' = L "- L), that is to say an elongation with respect to the initial elongation AL / L, which is equal to: E) 2 'L`2 z' L`2 ~ D + E) + - (E) + AL '2 ~ 2 1! (E) 2 + '1.'2 2 In the example of FIG. 5, the disturbance displacement D is positive, that is to say that the separated point 116 of the optical fiber cable 108 moves away from the line A connecting the ends 111A, 111B of the cable portion 111. With reference to FIG. 6, when the point 116 of the cable portion 111 approaches the line A connecting these fixed ends 111A, 111B, the displacement of Disturbance D is then negative so that the relative elongation AL% L 'also becomes negative. In this case, thanks to the initial elongation of dL / L the cable remains nevertheless elongated, its elongation then being AU + AL% L '. FIG. 7 is a curve representing, on the ordinate, the relative elongation AL% L 'in μm per meter as a function of the perturbation displacement D in cm, in the case where E = 10 cm and L = 2.5 μm. It will be noted in particular that the relative elongation AL% L 'is zero for a zero disturbance displacement D and that, at this point, the slope of the curve is high. Thus, the slightest displacement of disturbance causes a significant relative elongation. In the absence of a spacer, if the fiber optic cable were directly connected to the origin point, the slope of the curve would be zero, so that a small disturbance displacement would only result in a very small extension of the cable. optical fiber, which would be very difficult to detect (see next paragraph). Note further that when the disturbance shift D is -10 cm, this disturbance shift D completely compensates for the distance E, so that the fiber optic cable 108 is then in a position simply extended, but not elongated. In addition, this position would correspond to the rest position of the optical fiber cable 108 if the spacer 112 was not used and if the optical fiber cable L 'was fixed directly on the panel 106. However, the slope at this point position (D = -10 cm) is zero, so that, as explained above, a small displacement of disturbance would result in a very small extension of the optical fiber cable, which would be very difficult to detect.

FIG. 8 is a curve provided by the intrusion detection device from the analysis of the light signal having traversed the optical fiber cable 108, this curve showing the relative elongation AL% L'as a function of the position along the optical fiber cable 108. The vertical lines indicate the position of the fasteners 110.

As a disturbance occurring between two successive fasteners 110 causes the same relative elongation over the entire cable portion between these fasteners, a rectangular signal should be observed between the two vertical lines corresponding to these two fasteners. However, the rounded appearance obtained is due to the BOTDR apparatus function which is equivalent to the convolution product of the rectangular signal of the relative elongation of the optical fiber cable by the pulse signal of the Gaussian time profile laser. height equivalent to one meter. Note also that, because the fasteners 110 prevent a longitudinal displacement of the optical fiber cable 108, the variation of the relative elongation remains localized on a portion of cable (that is to say between two successive fasteners ), which allows precise localization (to the length of the cable portion near) of the intrusion. With reference to FIG. 9, a mounting method 900 of the intrusion detection system 100 previously described comprises the following steps. During a step 902, the optical fiber cable 108 is extended, without being elongated, between the posts 104. During a step 904, the optical fiber cable 108 is fixed by the fasteners 110 to the posts 104. During a step 906, each cable portion 111 is elongated between the two successive fasteners 110 delimiting it, until the initial elongation, by spreading the spaced point 116. During a step 908, the spacers 112 are placed in order to maintain the elongate optical fiber cable 108 at its initial elongation between the posts 104, in order to obtain the configuration shown in FIG. 1. It is clear that an intrusion detection system such as the one previously described allows to precisely locate, along the optical fiber cable, an intrusion. In addition, it amplifies the movement of the barrier, which improves the detection. In addition, the intrusion detection system is simple since it can use only one fiber optic cable. Moreover, it can be used for barriers of several kilometers in length (up to 25 km).

Note also that the invention is not limited to the embodiment described above. It will be apparent to those skilled in the art that various modifications can be made to the embodiment described above, in the light of the teaching that has just been disclosed. In particular, the fiber optic cable can be attached to any side of the barrier. Preferably, it is fixed inside (on the side of the zone protected by the barrier) for security reasons. In addition, the fasteners and the spacers are not necessarily positioned as described above. For example, the spacers could connect the fiber optic cable to the poles, while the clips would longitudinally attach the fiber optic cable to the panels. In addition, it is possible to use several spacers between two successive fasteners, taking into account the spatial resolution limit of the intrusion detection device (which is of the order of one meter when it comprises a BOTDR). In addition, the intrusion detection device could include, in place of the BOTDR, a stimulated Brillouin sensor (or BOTDA of the English "Brillouin Optical Time Domain Analysis"), a backscattering optical reflectometer (OBR or OBR). "Optical Backscatter Reflectometer"), a phase-sensitive Optical Time Domain Reflectometer (OOTDR), a bidirectional Mach Zehnder interferometer, or Bragg gratings. In the following claims, the terms used are not to be construed as limiting the claims to the embodiments set forth in this specification, but should be interpreted to include all the equivalents that the claims are intended to cover because of their formulation and whose prediction is within the reach of the person skilled in the art by applying his general knowledge to the implementation of the teaching which has just been disclosed to him.

Claims (10)

REVENDICATIONS1. An intrusion detection system comprising: a barrier (102), an optical fiber cable (108), fasteners (110) by which the optical fiber cable (108) is attached to the barrier (102), each pair of successive fasteners delimiting a portion (111) of the optical fiber cable (108) having two ends (111A, 111B) attached to the barrier (102) by the two fasteners (110), an intrusion detection device (120) ) designed to: - emit a light signal in the fiber optic cable (108), - receive and analyze the light signal having traveled through the fiber optic cable (108) to detect an intrusion, characterized in that: fasteners (110) are designed to prevent longitudinal movement of the ends (111A, 111B) of each cable portion (111) relative to the barrier (102), it further includes, for each cable portion (111), means (112) for mechanically coupling this portion of cable (111) to the barrier (102) other than the fasteners (110), and the detection device (120) is adapted to detect a deformation of one of the cable portions (111) and to identify that portion of cable (111), from the analysis of the light signal having traveled the fiber optic cable (108). An intrusion detection system according to claim 1, wherein the detected deformation is an elongation variation of one of the cable portions (111), and wherein the mechanical coupling means of each cable portion ( 111) comprises a spacer (112) connecting a point (114) of the barrier (102), called the origin point (114), to a point (116) of the cable portion (111), called the spaced point (116), which is remote from the straight line (A) connecting the two ends (111A, 111B) of the cable portion (111). An intrusion detection system according to claim 2, wherein the spaced apart point (116) is further away from the straight line (A) connecting the two ends (111A, 111B) of the cable portion (111) than the point origin (114). An intrusion detection system according to claim 2 or 3, wherein the spacer (112) extends perpendicularly, within ten degrees, to the barrier (102). An intrusion detection system according to any one of claims 2 to 4, wherein each cable portion (111) has an elongate length, relative to its rest length, of an elongation, termed initial elongation, for example between 1 and 5 millimeters per meter. An intrusion detection system according to any one of claims 1 to 5, wherein the barrier (102) includes posts (104) for attachment to the ground and panels (106) extending between the posts. (104). An intrusion detection system according to claim 6, wherein the fasteners (110) attach the optical fiber cable (108) to the posts (104) and the coupling means (112) couples each cable portion (111). to a panel (106). The intrusion detection system of claim 6, wherein the fasteners (110) attach the optical fiber cable (108) to the panels (106) and the coupling means (112) couples each cable portion (111). to a pole (104). An intrusion detection system according to any one of claims 1 to 8, wherein the detection device (120) comprises an optical reflectometer, for example an optical time domain reflectometer of Brillouin for the detection of an elongation variation of one of the cable portions (111). 10. A method of mounting an intrusion detection system according to any one of claims 1 to 9, comprising the following steps: the optical fiber cable (108) is extended, without being elongated, along the barrier (102), the optical fiber cable (108) is attached by the fasteners (110) to the barrier (102), so as to prevent longitudinal movement with respect to the barrier (102) of the ends (111A, 111B) of each cable portion (111) delimited between two successive fasteners (110), each cable portion (111) is further mechanically coupled to the barrier by means other than the two successive fasteners (110) delimiting it. 35