WO2003067198A1

WO2003067198A1 - Detection method and device

Info

Publication number: WO2003067198A1
Application number: PCT/FR2003/000342
Authority: WO
Inventors: Bernard Hodac
Original assignee: Osmos Sa
Priority date: 2002-02-04
Filing date: 2003-02-04
Publication date: 2003-08-14
Also published as: FR2835607A1; AU2003222881A1

Abstract

The invention relates to a device (1) which is used to detect a piece of information and, in particular, to detect if a threshold (S) has been exceeded by measuring a parameter. The invention is characterised in that it comprises locally, i.e. close to the measuring site: a loop (7) which is formed with an optical fibre (9); and means (4) of modifying a curve of the aforementioned loop when the information appears locally, such that, for a light emitted at an inlet of the fibre, a residual quantity of said light is varied, said residual quantity being collected at an outlet of the fibre.

Description

"Detection method and device"

The present invention relates to a detection method. It also relates to a device associated with the method. To acquire information on the state of a product or structure, parameters can be monitored, for example temperature, displacement or deformation, acidity or even nuclear or electromagnetic radiation. These parameters can, for example, be measured, punctually, regularly or continuously. Thus, it is important to know the state of health of a structure, in particular to ensure its maintenance, prevent its ruin or ensure the safety of its users. However, this information is generally superabundant, that is to say that in order to obtain sought-after information it is necessary to analyze and interpret a large amount of information. Sensors to measure these parameters return instant measurements. This information must be interpreted by a specialist, for example to identify an anomaly in the parameter, such as excessive deformation of a structure. In addition, these parameters can be measured by sensors placed in places which are difficult or inaccessible, for example in a hostile environment, for example nuclear. Transmission means of the electrical and electronic type are then used, but these are liable to be disturbed in particular by electromagnetic radiation.

Furthermore, the number of sensors and / or parameters can be high, which is added to the overabundance of information transmitted by each sensor. Thus, systematic monitoring of parameters can be particularly laborious or even impossible with traditional means. To simplify this monitoring, it is possible to use means for processing the information transmitted by the sensors, but these means, generally computer or electronic, are all the more important and expensive the more information there is and the processing complex. It is therefore not conceivable to equip as many structures and as completely as would be desirable.

The object of the invention is to propose a method and a device for monitoring a parameter, or several parameters, and in particular, detecting and collecting desired information relating to a measurement of this parameter, even from a distance, with reliable and inexpensive means. expensive.

According to the invention, such a method for detecting information relating to a measurement, is characterized in that it comprises the following steps:

- A signal is transmitted to an input of transmission means for this signal, and a residual signal is collected at an output of these transmission means;

- the information to be detected is locally determined; then,

- when the information appears locally, the signal transmission is altered so as to significantly modify said residual signal; - The residual signal at the output of said transmission means is detected.

In a preferred method according to the invention:

the signal is transmitted in the form of light to an input of an optical fiber, which serves as transmission means for this signal, and a residual quantity of this light is collected at an output of this optical fiber;

when the information appears locally, a curvature of an area, preferably formed in a loop, of the optical fiber is modified so as to significantly modify said residual quantity;

- the residual quantity at the output of the optical fiber is detected. In fact, a straight or slightly curved optical fiber produces practically no attenuation of the amount of light transported by the fiber. On the other hand, beyond a limit curvature, that is to say for a curvature of which a radius is locally less than that of the limit curvature, at least part of the quantity of light is absorbed by a material serving, for the place of the curvature, at the light guide in the fiber. This limit curvature is a function of the refractive index of the material and the wavelength of light, if its color is pure. So, beyond the curvature limit, all of the light can be absorbed if the color and pure, and another part backscattered. If the color has multiple wavelengths, each wavelength is gradually absorbed, at least partially, as the curvature increases beyond the limit curvature.

In particular, the information to be detected may be the crossing of a threshold by the monitored parameter, for example the crossing of a safety temperature by a product or the opening of a crack beyond a size. predetermined. These thresholds can be chosen to guarantee that below these thresholds there is no risk of ruin for the structure. It is then necessary to be informed of the crossing of these thresholds by the monitored parameters.

The inlet and outlet of the fiber can constitute the same first end of the fiber if a second end of this fiber is equipped to reflect the light inside the fiber towards the first end. On the contrary, the input and the output can each constitute a different end of the fiber.

In another method according to the invention, an electric current can be used as a signal passing through an electric cable serving as transmission means. This signal can be continuous or alternating. It may only be sent from time to time. To alter this signal, a switch can be provided so that the residual signal at the cable outlet and a zero electric current.

Rather than a switch, it is also possible to use means to increase the resistance of the cable and thus reduce the intensity of the current collected at the outlet of the cable.

According to another aspect of the invention, a device for detecting information, particularly when a threshold is crossed by measuring a parameter, is characterized in that it comprises locally, that is to say in the vicinity from the place of measurement, means for recognizing the information and means for altering a signal passing through the device. In a preferred device according to the invention, the means for altering the signal comprise an area, preferably formed in a loop, of an optical fiber and means for modifying a curvature of said area when the information is recognized so that, for an amount of light transmitted to an inlet of the fiber, a residual amount of this light, collected and detected at an outlet of said fiber, varies considerably.

Such a device advantageously comprises triggering means sensitive to the recognition of information and, when the device comprises an optical loop, means controlled by said triggering means, for deforming the optical loop. When the loop is deformed, we say that the device is triggered, that is to say that it has detected the appearance of the information.

The triggering means can be sensitive to the crossing of a threshold by the measurement. The device can also comprise means for predetermining a sought information, for example a threshold, as well as means for modifying the sought information, for example means for adjusting this threshold. It advantageously comprises means for reading the measurement, directly, for example on a structure, or indirectly on a sensor for the measurement. The sensor can be included in the device.

A threshold will, for example, be favorably predetermined so that external disturbances (for example the passage of a railway convoy in the vicinity of the structure whose displacement is measured) do not cause an untimely triggering of the device. The device can be provided to detect several pieces of information. Thus, instead of a single threshold, the device can be provided to detect the crossing by a single measurement of several successive thresholds. These thresholds can for example be detected by successive deformations of the same loop, each of the successive deformations inducing an additional attenuation of the quantity of light collected at the output of the optical fiber. According to another arrangement, each threshold can correspond to the deformation of a different loop. The device can also include two thresholds defining an interval for the measurement, the device being designed to be triggered when the measurement leaves the interval by crossing one or the other of the limits.

Advantageously, the device can be resettable, that is to say that after being triggered, it can be brought back into a configuration for which it can again detect new information or the same information, for example crossing a threshold. .

According to another aspect, the invention relates to a detection line which comprises a device, or several detection devices mounted in series on the same signal transmission means, preferably between two ends of an optical fiber. Each device can be provided to monitor a single measured parameter. Advantageously, the optical fiber comprises a number of loops equal to the number of parameters monitored.

Thus, by monitoring only the variation of the light at the output of the optical fiber, one receives only the information necessary for monitoring many parameters, without overabundant information.

Optical fibers can transport light over practically infinite distances while being insensitive to most disturbances, especially electromagnetic, unlike electric cables. It is therefore possible, with the same detection line, to monitor a structure over a long distance, linearly or according to a large mesh.

When the line comprises several devices, it may be necessary to determine where the triggered device is located, that is to say having detected a threshold crossing. For this, it is possible to use a device of the type called "OTDR" (Optical Time Domain Reflectometer), known in the field of telecommunications, for measuring the time of backscattering of the light. Another way of determining the position of the triggered device is to provide warning means, for example visual means, in the device. For practical reasons of mounting the device or the detection line, the optical fiber can consist either of a single segment or of several segments connected together so that they can transport the light as if the fiber were made up of only one segment. Thus, an optical loop can be formed by a segment of optical fiber included in a device and this segment can comprise connection means to be connected to other segments of the optical fiber.

Commercial optical fibers can be used, the cost of which is very low. Preferably, a multi-modal fiber will be used, for which the attenuation effect during the deformation of a loop is most notable.

The low cost of a detection line according to the invention can make it possible to equip new buildings or engineering structures, during their construction, without significantly increasing the cost.

The information given by a device according to the invention is simple. It is indeed of binary type, for example "yes, a threshold has been crossed" or "no, a threshold has not been crossed". It does not require complex analysis and can be used directly. Thus, by monitoring only the variation of the light at the output of the optical fiber, we receive only the information necessary, even for the monitoring of many parameters, without overabundant information.

Other features and advantages of the invention will become apparent from the description. below, relating to nonlimiting examples. In the accompanying drawings:

- Figure 1 is a sectional representation of a detection device according to the invention, in the armed position;

- Figure 2 is a sectional representation of the device of Figure 1 in an intermediate position;

- Figure 3 is a sectional representation of the device of Figure 1 after a trip;

- Figure 4 is a representation of a detection line which comprises several detection devices connected in series; - Figure 5 is a sectional representation of another detection device operating according to the principle of the device of Figure 1; - Figures 6 to 8 are illustrations for deformation principles different from those used in the devices of Figures 1 to 5;

- Figure 9 is a sectional representation of a detection device according to the invention, different from that of Figure 1, in the armed position; and,

- Figure 1 0 is a sectional representation of a detection device according to the invention, different from those of Figures 1 and 9, in the armed position, but neutralized.

FIG. 1 represents a detection device 1 in the armed position. This device 1 includes:

- a housing 2,

- A piston 3 mounted to slide through a wall 21 of the housing 2, along an axis X substantially perpendicular to this wall, and, inside the housing: - trigger means 4 of the device under the action of the piston

3, and,

a segment 9 of an optical fiber, arranged to form a loop 7 able to deform elastically under the action of the triggering device 4. The piston 3 comprises a barrel 31 and a threaded rod 32 mounted screwed inside the was 31. The length of the piston, measured along the X axis between a base 35 of the barrel 31, inside the housing, and a feeler end 34 of the rod 32, projecting outside the barrel and the housing, can be adjusted by screwing the rod 32 more or less into the barrel 31, then stabilized by a lock nut 33, screwed onto the rod 32 with tightening against the annular end of the barrel 31.

The triggering means mainly comprise an elastic blade 5 of flat shape in the unstressed state, held between two pushers 6 mounted in translation in guides 11 formed in the housing 1 along a common axis Y perpendicular to X. Two edges opposite the blade 5 are each housed against the bottom, crossed by the axis Y, of a concave profile 62 in the form of a V on a corresponding side of a respective one of the pushers. On the side opposite the blade 5, each pusher 6 is biased towards the other plunger by a respective compression helical spring 61, so that the blade 5 is subjected to buckling (bending under the action of a longitudinal compression stress) elastic between the two plungers. Under the action of the springs 61, the blade takes one or the other of two positions 51, 52 of maximum buckling.

Each of the maximum buckling positions 51, 52 is defined by pressing one of the faces of the blade 5 against one of the faces of each V-shaped profile 62. In FIG. 1, the blade 5 is shown in a first position of maximum buckling 51. The same figure shows in dotted lines the second position of maximum buckling, called trigger position 52 as well as an unstable middle position 50, located along the Y axis in a plane perpendicular to the X axis. An arming position is a buckling position of the blade 5 lying between the middle position 50 and the first maximum buckling position 51. In the example of FIG. 1, the arming position is the maximum buckling position 51.

At each end of the segment 9 the optical fiber crosses the housing 2 by two crossings 70 to continue with other segments 91, 92 of the optical line. The crossings 70 correspond one to the entry of light from the optical line inside the segment 9 and the other to the exit of a residual light after its passage in the segment 9.

The segment 9 is substantially arranged in a plane which includes the axes X and Y. The loop 7 formed by the segment 9 is a closed loop, that is to say that the segment forms a crossing between the two crossings 70 on one side and loop 7 on the other side. In the armed position of the device, that is to say as shown in FIG. 1, the loop has a substantially circular deployed form 71, the minimum radius of which has the value R1. When the device is triggered, the loop takes an ovoid shape 72, shown in dotted lines, of which a minimum radius has the value R2, the value R2 being significantly less than the value R1. The loop 7 is arranged so that in its deployed position 71 it interferes with the trigger position 52 of the blade 5. The piston 3 further comprises, on the outer periphery of the barrel 31, for example on a flange, a shoulder 36, perpendicular to the axis X and oriented towards the blade 5. A stop 43 secured to the housing 2 is placed between the shoulder 36 and the blade 9. When the base 35 is on the axis Y there is between the shoulder 36 and the stop 43 a spacing T (FIG. 2) corresponding to a tare value specific to the device.

We will now describe the operation of the device 1 with reference to Figures 1 to 3. Figures 2 and 3 will only be described in that they differ from Figure 1.

The device 1 is provided for detecting the approximation along the axis X of an element 10 relative to a structure 20 of which the housing 2 is integral. More particularly, the device makes it possible to alert when this approximation is greater than a predefined threshold of value S. To define the threshold in the device 1, a wedge (not shown) is placed between the shoulder 36 and the stop 43 whose l 'thickness is equal to T + S where T is the aforementioned tare value.

The length of the piston 3 is then adjusted so as to pinch the shim between the stop 43 and the shoulder 36 while the feeler end 34 of the threaded rod 32 is in contact with the element 10. Finally, the shim is removed and it is ensured that the blade 5 is in an arming position, here the first maximum buckling position 51. The device is then in the position shown in FIG. 1. There is then a clearance J between the base 35 and the blade 5. But if the value S is less than or equal to the buckling arrow of the blade 5 in the first position of maximum buckling 51, the clearance J does not exist and the base 35 is in contact with the blade 5.

When the element 10 approaches the structure 20, therefore of the housing 2, the piston slides towards the interior of the housing 2, under the action exerted by the element 10 against the feeler end 34. The possible initial clearance J between the base 35 and the blade 5 is gradually filled, then the blade 5 is pushed back to its middle position 50, the pushers 6 being pushed against the springs 61. The device 1 is then as shown in the Figure 2. The distance between the stop 43 and the flange 36 is at this instant equal to the tare T, that is to say that the approximation of the element 10 relative to the device has reached the threshold S. At this stage, the blade 5 is still spaced from loop 7. The middle position 50 is an unstable position for blade 5, that is to say that it tends to buckle towards one or other of its positions of maximum buckling 51, 52 under the combined action of the pushers 6. The blade 5, in abutment against the base 35 of the piston 3, therefore flares up to its release position 52 as soon as the approach of the element 10 reaches and crosses the threshold S. Thus , the device is triggered.

When triggered, the blade 5 radially compresses the loop 7 against an anvil 8 secured to the housing 2. When the blade 5 reaches its trigger position 52, the loop 7 is in its deformed position 72, and the device is as shown in FIG. 3. The value R1 of the minimum radius of the loop in its deployed position 71 has been chosen large enough for the light to travel through the loop without attenuation. The value R2 of the minimum radius of the loop in its deformed position 72 has been chosen sufficiently small so that the attenuation of the light is clearly perceptible at the end of the loop. Thus, the attenuation of light for an observer is the sign of crossing the threshold S.

To reset the device, simply bring the blade 5 into an arming position, for example after reducing the length of the piston 3 and / or having moved the housing 2 relative to the structure 20. FIG. 4 represents an optical line 90 for the detection of crossing thresholds during relative movements of successive slabs 20,200,201, 202 of a bridge deck. Line 90 includes three detection devices 1, 1 10,1 1 1 connected in series. The line further comprises an input optical segment 91 for bringing light to a first detector, two connecting optical segments 92 for bringing residual light from the output of a detector 1, 1 1 0 to the input of a detector immediately following 1 10.1 1 1, and an optical output segment 93 to collect residual light at the exit of a third and last detector 1 1 1.

Each detector 10,1 10,1 1 1 is respectively secured to a slab 20,200,201 and measures its displacement relative to an element 10,100,101 respectively secured to a slab immediately following 200,201, 202.

Thus, an observer of the light intensities entering and leaving the line can know whether one or more of the devices is triggered. For example, if the triggering of a device causes an attenuation of approximately 30%, the triggering of two devices causes an attenuation of approximately 50%, and the triggering of the three devices an attenuation of approximately 65%.

Figure 5, which will only be described in that it differs from Figure 1, illustrates a device 1 12 in the armed position. This device is intended to detect the crossing, during a relative displacement of the element 10 and of the structure 20, of one or the other among two thresholds delimiting an interval for this displacement.

Thus, the device 1 12 can detect, like the device 1 of the previous figures, the relative approximation along the axis X of the element 10 and the structure 20 beyond a first threshold. But in addition, the device 1 12 also detects the relative distance along an axis X2, of the element and of the structure beyond a second threshold.

For this, the device 1 12 comprises a second piston 30, movable in translation in the housing 2 along an axis X2 parallel to the axis X. The piston 30 is adjustable in length by means similar to those described for the piston 3. A feeler end 340 of the adjustment rod is kept in contact with the element 10 by means of a spring 370 compressed between the housing 2 and a base 350 of the second piston 30. The second piston further comprises, near its base 350, a lateral groove 360 defined for example between two twin flanges slightly spaced from each other and perpendicular to the axis X2. The device also comprises a balance 80 mounted in rotation, in the plane formed by the two axes X, X2, around a pivot 83 secured to the housing 2 and perpendicular to this plane. The balance comprises on either side of the pivot 83, a branch 81 engaged in the groove 360 and a branch 82 supported on a second shoulder 336 of the first piston 3. The shoulder 336 is for example formed on the rear face of the flange defining the shoulder 36. The first 81 and second 82 branches are respectively provided with a circular bulge at their free end. A displacement of the second piston 30 along the axis X2 causes the balance 80 to rotate around the pivot 83.

We will now describe the operation of the device 1 1 2 of FIG. 5 in that it differs from that of the device 1 of FIG. 1.

The interval is defined by two thresholds S and S2 respectively representing a distance of approach and a distance of distance on either side of an initial relative position of the element.

10 and of structure 20. The state is described as initial when the thresholds are adjusted.

To set the thresholds, first set the distance threshold S2. So that the adjustment of this threshold is not hampered by the contact of the feeler end 34 of the first piston 3 on the element 10, the length of the piston 3 is reduced beforehand and sufficiently. A second shim is then placed (not shown) ) of thickness T + S2 between the reference stop 43 and the shoulder 36 of the first piston 3, then the length of the second piston 30 is adjusted so that when the second wedge is pinched between the stop 43 and the shoulder 36 , the second branch 82 is in contact with the second shoulder 336 and the end 340 of the second piston 30 is in contact with the element 10. After removing the second wedge, the length of the first piston 3 is adjusted as described with reference to Figure 1. If T + S is smaller than T + S2 (example shown in FIG. 5), this results in play between the shoulder 336 and the second branch 82, as shown. If T + S = T + S2, this game disappears. If T + S is larger than T + S2, the T + S shim can only be installed if the shoulder 336 pushes the pendulum 80 counterclockwise. This urges the second piston 30 in the direction of compression of the spring 370 and a spacing between the feeler end 340 and the element 10. After removal of the wedge T + S, the spring 370 reapplies the feeler end 340 against the element 10 and, via the pendulum 80, reveals a clearance between the feeler end 34 and the element 10.

In the event of the element 10 moving closer together, the operation of the device 1 1 2 is identical to the operation previously described with reference to FIGS. 1 to 3, with the exception of a possible initial phase of taking up the above play between the end feeler 34 and element 10 when T + S> T + S2.

When the element 10 moves away from the structure 20 and therefore from the housing 2, along the axis X2, the feeler end 340 of the second piston 30 is kept in contact with the element 10 by the pressure of the spring 370, c 'is to say that the second piston 30 slides through the wall 21, and rotates the pendulum 80. After catching up with the possible (when T + S is smaller than T + S2) clearance between the second branch 82 and the second shoulder 336, the second branch 82 pushes the first piston 3 in the direction of the blade 5, as the element 10 moves away, and the first piston 3 pushes the blade 5 towards the middle position 50.

When the element 10 has carried out in the direction of the distance a displacement equal to the value S2 of the distance threshold, the blade 5 is in the middle position 50 and the device is triggered.

Figures 6 to 8 show other modes of deformation for loops 7 formed by optical segments 9. For each figure, the drawing on the left represents a loop before its deformation and the drawing on the right represents the same loop after its deformation .

The loop 7 of Figure 6 is substantially identical to that previously described. It is of the closed loop type. It is its mode of deformation which differs. Thus the triggering means 4 comprise means for symmetrically pinching the loop and increasing one curvature by reducing an initial radius R1, to a radius R2 causing attenuation of the light passing through the loop 7.

The loops 7 of FIGS. 7 and 8 are open loops, that is to say that the optical segment 9, located inside the housing 2, comprises on either side of the loop 7 regions 98.99 which do not cross. The segment 9 thus has a substantially U shape.

In FIG. 7, the segment 9 bypasses, in the vicinity of the loop 7, a mandrel 88 secured to the housing 2. The radius of the mandrel is R2. The segment 9 comprises on its regions 98.99, sleeves 89 located in the vicinity of the inlet and the outlet of the segment through a wall of the housing 2.

In an armed position, the sleeves are not or only slightly visible outside the housing 2. The triggering means 4 are designed to drive, at least partially, the regions 98.99 outside the housing so that the sleeves 89 appear. At the same time, the length of the segment 9 inside the housing being reduced, the loop is pressed against the mandrel 88 and is deformed there by taking the radius R2 of the mandrel.

The principle of deformation illustrated in FIG. 8 is substantially identical to that described with reference to FIG. 7. However, only one of the regions 99 99 of the optical segment 9 is equipped with a sleeve 89 intended to be driven by the trigger means 4 while the other region 98 is immobilized through the wall of the housing 2.

On a line comprising several boxes, the visibility of the sleeves outside the box allows the triggered box to be located without using an OTDR. To color the sleeves, it is preferable to choose a very visible color, for example fluorescent, in order to allow their rapid identification. Figure 9 is the representation of another detection device 501 according to the invention, which will be described in that it differs from the devices of Figures 1 to 3 and 5. The device 501 is shown armed.

The device 501 comprises a piston 503 slidably mounted in a housing 2. As in the preceding devices, the end 34 of the piston is held in abutment on the element 10. In the example of FIG. 9 it is a spring of compression 570 which allows the end 34 to be supported. The trigger means 4 comprise a jack 505 consisting of a plate 550, a cylindrical rod 561 linked to the plate 550 and extending perpendicularly to the latter in the direction and perpendicular to the axis X of the piston 503. The rod 561 is slidably mounted in a bearing 508 of the housing 2.

The trigger means 4 further comprise a trigger spring 560, mounted in compression between the plate 550 and the housing 2, so that it tends to drive the plate from an arming position 551, which is shown in solid lines. in Figure 9, to a trigger position 552, shown in dotted lines. In the release position, the plate 550 is closer to the piston than in the armed position.

The piston 503 comprises two cylindrical orifices 532,533 passing through it diametrically, perpendicular to the axis X. The diameter of the orifices 532,533 is substantially equal to the diameter of the rod 561 of the jack 505. The piston is immobilized in rotation around the axis X of so that the holes are kept parallel to the rod 561. The positions of the orifices relative to the end 34 of the piston and their center distance E define the limits of an interval for the movement of the element 10 along the axis X. The housing 2 comprises an anvil 8, which extends in parallel to the plate 550 beyond its trigger position 552 relative to its armed position 551. In the position of FIG. 9, the loop 71 is formed to extend between the plate 550 and the anvil 8.

When the detection device is armed, a free end 562 of the rod 561 is in contact, under the action of the trigger spring 560, with the barrel 531 of the piston 503, between the orifices 532,533.

If the element 10 moves along the axis X, the piston 503 follows this movement, and the barrel 531 moves in front of the free end 562. When during this displacement one of the orifices is aligned with the rod 561 of the jack 505, that is to say that the element 10 has reached one of the predefined limits, the free end 362 is no longer retained by the barrel 531. Under the action of the trigger spring 560, the rod 561 of the jack then enters the orifice and the plate 550 moves from the arming position 551 to the trigger position 552. The loop 7 is then deformed between the plate and the anvil, and takes a shape 72 represented by dotted lines at Figure 9. When the device is triggered, the free end 562 crosses the barrel

531 through the orifice and beyond the barrel emerges from the housing 2 through a bearing 509. The end thus apparent of the rod, as in the case of FIGS. 7 and 8, makes it possible to visually locate the device 501 when triggered. When the device is triggered, security means can be provided to prevent the device from being destroyed during movement of the element 10 while the piston is blocked in movement by the rod 561 of the jack 505. For example provision may be made for the oblong orifices on the outside side at the center distance E. FIG. 10 is the representation of another detection device 601 according to the invention, which will be described in that it differs from the devices in FIGS. 3 and 5 and 9. The device 601 is shown armed but neutralized, that is to say as will be explained later, that it cannot be triggered.

The device 601 comprises, as means for reading the displacements of the element 10, parallel to a direction DX relative to the structure 20, a pendulum 632 and a shuttle 630. The shuttle is fixed on the element 1 0. It is disposed in a guide 602, integral with the housing 2, which allows it to move in translation in the direction DX. The shuttle 630 includes a spherical recess 631 for maintaining there fitted a first sphere-shaped end 633 of the pendulum. Thus, the shuttle 630 drives the balance according to the relative displacements of the element and the structure in the direction DX.

The pendulum 632 is mounted in a joint 641 serving as a pivot between the first spherical end 633 and a second end 634 of this pendulum, so that a displacement of the first end of causes a proportional displacement of the second end.

The articulation 641 is part of a carriage 640 including one face 642, parallel to the pendulum, is notched and the opposite face 643 is smooth. The carriage is positioned between a notched wall 644 and a smooth wall 645 of the housing 2, so that the smooth face 643 is in contact with the smooth wall 645 and that notches of the face 642 cooperate with notches on the wall 644 for position the carriage, therefore the joint 641, longitudinally along the balance. A coefficient of proportionality K is thus fixed for the displacement of the second end 634 of the pendulum relative to the center of the sphere forming its first end 633, such that K = D2 / D1, where D1 is the distance between the center of the end spherical 633 and the joint 641 and where D2 is the distance between this joint and the center. The second end is a stopper tab of thickness EP1 in the direction of movement of the second end when the first is driven in the direction DX.

The triggering means of the device of FIG. 10 mainly comprise an arm 650 and a spring 660. The arm is mounted movable in rotation relative to the housing 2 in a pivot 651. The pivot is at a root 652 of the arm. The spring is disposed between the housing 2 and the arm 650 so that the spring tends to cause the arm to rotate relative to the housing. One end 653 of the arm 650, opposite the root 652, comprises tongue 654 which extends in a tangent to a circle described by the end 653 of the arm during the rotation of the arm. Said tongue serves as a buffer for the arm. The buffer tab 654 has a thickness EP2 measured without the plane of rotation of the arm in a perpendicular direction.

The axes of rotation of the pendulum 630 and of the arm 650, respectively defined by the articulation 641 and the pivot 651 are parallel.

In the armed position shown in FIG. 10, the stopper tongue 634 of the balance 630 extends parallel to the buffer tongue of the arm and the two tongues are opposite and in end-to-end contact according to their respective thicknesses. The spring 660 tends to hold the buffer tongue 654 in abutment against the stopper tongue 634. Thus, the arm cannot be in rotation as long as the buffer tongue 654 is in abutment on the thickness of the stopper tongue 634. When the element 10 is displaced in the direction DX, the stop tab 634 moves perpendicular to the tangent along the thickness EP2 of the buffer tab 654 until it is no longer in contact with this thickness EP2, releasing the buffer tongue 654 and authorizing the rotation of the shaft 650.

The initial relative position of the two tongues 634,654, their thicknesses EP1, EP2 and the coefficient of proportionality K define the interval beyond which the device is triggered.

In the case represented in FIG. 10, the tongues are perfectly opposite, their thicknesses are identical with a value equal to 2.5 mm and the coefficient K = 0.3. Thus, the stopper tab must have traveled 2.5 mm on the buffer tab, in one direction or the other, to trigger the device, a corresponding displacement of 0.3 x 2.5 mm = 0.75 mm for the element 10 in the direction DX, in one direction or the other, relative to the structure 20. so an interval of 1.5 mm is defined for the movement of the element 10 relative to the structure 20 according to The direction

Dx from a median initial position in the interval. More generally, the interval is defined by the sum of the thicknesses of the tongues and the detected thresholds limiting the interval are defined by the initial position of one tongue relative to the other.

Thanks to the notched carriage, the coefficient K can vary from 0.1 to 0.1, corresponding to an interval between two notches of the notched wall 644, so that one can detect a relative displacement of the element 10 and the structure 20 to 0.25 mm. The housing 2 further comprises two cylindrical studs 608, perpendicular to the plane of rotation of the arm 650, and arranged on the same radius relative to the pivot 651, on the side where the arm 650 folds down when the device 601 is triggered. The arm comprises a hook 655 which extends up between the two studs 608 along a cylinder centered on the pivot 651 so that, when triggered, the hook 655 circulates at equal distance from the two studs. The length of the hook is chosen so that the loop 7, in a position 71 before tripping, forms between the two studs 608 a straight segment 671 passing through the hook 655 through an opening 656 of the hook 655.

When triggered, the hook drives the segment 671 between the studs 608. The initially straight segment deforms to form around the studs 608 and the hook 655, meanders 72 contributing to the attenuation of the light passing through the loop 7.

The device of Figure 10 is equipped with neutralization means. These neutralization means comprise a latch 670, sliding in the housing 2, and a cleat 639, integral with the balance 632, intended to cooperate with the latch. When an operator places the device, that is to say when the box 2 is fixed on the structure 20 and the shuttle 630 on the element 10, in order to detect a relative displacement, this device is maintained in initial position using the latch 670. In its neutralization position, as drawn in FIG. 10, the latch cooperates with the cleat 639 to maintain the balance in its initial position. When the device is placed in its initial position, the operator slides the latch to release the cleat

639, therefore the balance 630. The balance can then move under the action of the shuttle 630, driven by the element 10.

For a better reading of the figures, they are not to scale. The dimensions given below are by way of example. Thus, in the example of a commercially available multimodal optical fiber, it is possible to form a loop having a radius of 20 millimeters which does not exhibit any significant attenuation. This loop will advantageously be deformed so that its smallest radius of curvature is of the order of 3 millimeters. Under these conditions the attenuation for a loop is of the order of 0.3 decibels. For a light source of 40 or 50 decibels, the information remains legible even if 50 detectors capable of being triggered simultaneously are placed on the same line, causing a maximum attenuation of 1 5 decibels. A fortiori, the attenuation remains legible for detectors which are triggered successively, without the need to rearm those which have already been triggered. For monitoring the deformation of a structure of the building or bridge type (such as the example in FIG. 4), it is possible to choose to detect movements of the structure of the order of at least 300 microns or in steps of at least 300 microns, in order to avoid detecting natural vibrational movements or even non-detrimental deformations, which would cause an untimely triggering of the detector.

Of course, the invention is not limited to the examples which have just been described and numerous modifications can be made to these examples without departing from the scope of the invention. In particular, the invention is not limited to the measurement of displacements, it can be used to measure other parameters such as temperatures. The same line can also be used to detect crossing of thresholds for different parameters. Thus the same line can comprise in series several displacement sensors and several temperature sensors, or more generally several sensors sensitive to different parameters.

A device for detecting a temperature threshold may include a bimetal temperature sensor, a deformation of which is provided to cause the device to trip. As described above, the deformation means, that is to say the blade, are included in the triggering means. A device according to the invention can also comprise, between the triggering means and the loop, specific deformation means. For example, a hammer moved by an electromagnet can serve as deformation means and can be controlled by electronic triggering means.

For example, the invention can be applied to monitoring a cliff, a breakwater, a support device or a masonry. It can also be used to detect an intrusion. The aging of the fiber and its clouding having no effect on the detection of the variation in the amount of light collected, the invention can be used in radioactive media. It can still be used to check the crossing of positions by security elements, for example detecting, in the petroleum industry, the opening of petroleum degassing valves.

Instead of increasing the curvature of the loop, one can choose to decrease the curvature to cause, when the device is triggered, an increase in the amount of light passing through the device.

The modes of deformation of a loop are not limiting. For example, as a variant of FIG. 7 or of FIG. 8, the trigger could pull the mandrel 88 towards the interior of the housing by making one or more initially visible sleeves disappear in the housing. Moving the chuck could also cause a visible signal to appear outside the housing.

The deformation mode could consist in causing a sinuosity in an initially rectilinear zone of the fiber, or conversely in straightening an initially sinuous zone.

Claims

1. Method for detecting information relating to a measurement, in particular the crossing of a threshold (S, S2), characterized in that it comprises the following steps: - a signal is transmitted to an input of transmission means for this signal and a residual signal is collected at an output of these transmission means;

- the information (S, S2) to be detected is locally determined; then,

- when the information appears locally, the signal transmission is altered so as to significantly modify said residual signal;

- the residual signal at the output of the transmission means is detected.

2. Method according to claim 1, characterized in that:

- the signal is transmitted in the form of light to an input of an optical fiber, which serves as transmission means for this signal, and a residual quantity of this light is collected at an output of the optical fiber;

- when the information appears locally, a curvature (R1, R2) is modified in an area (7) of the optical fiber so as to modify said residual quantity notably; - the residual quantity at the fiber outlet is detected.

3. Method according to claim 2, characterized in that said zone is a loop (7) whose curvature is modified.

4. Method according to claim 2 or 3, characterized in that the curvature is modified by a mechanical triggering action on the optical fiber.

5. Device (1, 1 10.1 1 1, 1 1 2.501, 601) for detecting information, particularly the crossing of a threshold (S, S2) by a measurement, characterized in that it includes locally means for recognizing the information (3,4), means for altering a signal passing through the device when the information is recognized so that, for a signal transmitted to an input of transmission means for this signal, the residual signal collected and detected at an output of said transmission means, varies significantly.

6. Device according to claim 5, characterized in that the alteration means comprise a zone (7) of an optical fiber (9), and means for modifying a curvature (R1, R2) of said zone when the information is recognized so that, the signal being emitted in the form of light at an input of the fiber, a residual quantity of this light, collected and detected at an output of said fiber, varies significantly.

7. Device according to claim 6, characterized in that said zone is shaped as a loop (7).

8. Detection device according to claim 6 or 7, characterized in that the entry and exit of the fiber constitute the same first end of the fiber, a second end of said fiber being equipped to reflect light inside. of fiber towards the first end.

9. Detection device according to one of claims 6 to 7, characterized in that it further comprises triggering means (4) sensitive to the recognition of information, and means (5), controlled by said trigger means (4), for deforming said area (7).

10. Detection device according to claim 9, characterized in that the triggering means are sensitive to the crossing of a threshold (S, S2) by the measurement.

1 1. Detection device according to claim 1 0, characterized in that it comprises means for adjusting the threshold.

1 2. Detection device according to one of claims 6 to 1 1, characterized in that it further comprises means for predetermining (3,30,80,43) of a sought information.

13. Detection device according to one of claims 6 to 12, characterized in that it comprises means (34,340) for reading the measurement.

14. Detection device according to claim 13, characterized in that the measurement is read from a sensor for the measurement.

1 5 Detection device according to claim 14, characterized in that the sensor is included in the device.

1 6. Detection device according to one of claims 6 to 15, characterized in that it comprises means (3,30,80) for detecting several pieces of information, particularly the crossing of several thresholds (S, S2).

17. Detection device according to claim 16, characterized in that said thresholds comprise successive thresholds for the same measurement.

18. Detection device according to claim 13 or 14, characterized in that it comprises two thresholds (S, S2) between which the value of the measurement is considered to be normal.

19. Detection device according to one of claims 16 to 18, characterized in that it comprises at least two loops assigned to the detection of two respective pieces of information.

20. Detection device according to one of claims 17 to 19, characterized in that it comprises means for causing successive deformations of the same area when crossing successive thresholds, respectively.

21. Detection device according to one of claims 5 to 20, characterized in that it can be reset.

22. Detection device according to one of claims 6 to 21, characterized in that the otic loop is formed with a multi-modal optical fiber.

23. Detection device according to one of claims 5 to 22, characterized in that it comprises means for warning (89) when the device is triggered.

24. Detection line comprising a device or several devices according to one of claims 5 to 21, mounted in series on the same transmission means.

25. Detection line according to claim 24 comprising a device or several detection devices according to one of claims 6 to 23, mounted in series between two ends of an optical fiber.