ES2599606A1 - Device based on optical fiber and diffraction gratings for the measurement of temperatures that reach the thermal limits of the optical fiber, and manufacturing process (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Device (10, 20, 30, 40) based on optical fiber (11, 21, 31, 41) for the measurement of temperatures that reach the thermal limits of the optical fiber (11, 21, 31, 41), using networks of diffraction (12, 22, 32) and subjected to an encapsulation process, comprising: - an optical transduction element consisting of an optical fiber (11, 21, 31, 41) in which a diffraction grating (12, 22, 32) is inscribed in an area thereof; - an interior coating (13, 23, 33) that lines the optical transduction element; - an outer protection block (14, 24, 34) inside which the transduction optical element covered by the inner cover (13, 23, 33) is placed; - as many inlet/outlet protections (15, 25, 35) as orifices presents the outer protection block (14, 24, 34), anchored to the outer protection block (14, 24, 34); - at least one support (16, 26, 36) attached to the outer protection block (14, 24,, 34); A manufacturing process of the device (10, 20, 30, 40) comprising the steps of: inscribing the diffraction grating (12, 22, 32) in the optical fiber (11, 21, 31, 41), applying the coating internal, apply the outer protection block (14, 24, 34), incorporate the entry/exit protections (15, 25, 35) and apply the support (16, 26, 36). (Machine-translation by Google Translate, not legally binding)

Description

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DESCRIPTION

Device based on optical fiber and diffraction networks for measuring temperatures that reach the thermal limits of the optical fiber, and manufacturing process.

Field of the Invention

The present invention belongs to the field of devices for measuring high temperatures (temperatures up to about 500 ° C), and, more specifically, to the field of optical fiber based devices for measuring very high temperatures (temperatures reaching the thermal limits of the optical fiber (typically 1200 ° C in standard optical fibers), using diffraction networks and subjected to an encapsulation process.

Background of the invention

At present there is a great variety of devices to measure the temperature, based on a multitude of technologies and oriented to countless different applications. However, as the working temperature increases, the different options decrease. The most widespread method for measuring at high temperatures (Tmax ~ 500 ° C) is known as thermocouple, in which the voltage variation caused by the temperature difference at the junction of two metals is measured. However, this technology has certain limitations such as its precision or its vulnerability to electromagnetic interference, which is why the use of new fiber optic techniques is encouraged.

The measurement of temperature with optical fiber is a discipline widely worked during the last years. Because of this, there are numerous techniques such as fiber interferometers, diffraction networks and even distributed systems capable of obtaining the temperature at each point of the fiber. However, taking into account the limitations of each technique, diffraction networks stand out for their versatility and reliability, and in particular short-term or Bragg diffraction networks (in English, Fiber Bragg Gratings FBGs) [Kashyap. R. (1999). Fiber bragg gratings. Academic press].

These short-period diffraction networks consist of a periodic variation of the refractive index of the fiber nucleus that causes the reflection of those wavelengths that meet Bragg resonance conditions. This resonance is proportional to the period of each PBG and is selected during manufacturing, so that several FBGs can be connected in series, each of them reflecting a different wavelength (wavelength multiplexing), obtaining a quasi-transducer distributed capable of measuring at several points, using a single optical fiber. These types of structures are widely used for the measurement of deformation and temperature for more than two decades, presenting very different configurations and performance. However, while it is true that FBGs are a very stable technique, unwanted effects may occur when they are subjected to temperatures above 500 ° C, depending on the method of inscription in the fiber.

The inscription using high intensity lasers, as for example techniques based on point-to-point inscription (without the need for the interference pattern) allows to obtain structures capable of withstanding very high temperatures (Tmax ~ 1200 ° C) without the need for a subsequent thermal treatment [ US7835605B1, US8272236B2]. However, while it is

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It is true that research related to the measurement of high temperature using optical fiber has focused on its optical properties, by subjecting the fiber to the most extreme treatments (with laser, high energy), it becomes extremely fragile, and can only be used in very controlled environments, since it degrades excessively the fiber mechanically. That is, this type of inscription only focuses on the optical aspect, neglecting the mechanical aspect.

On the other hand, the most widespread method for the registration of FBGs is the exposure to an interference pattern centered in the ultraviolet that causes a change of refractive index in the fiber nucleus. This method of registration uses low intensity lasers which allows the optical fiber to have sufficient mechanical integrity at room temperature. However, when the change of refractive index is obtained by this method, increasing the temperature of the FBG causes a degradation of said modulation, reaching "erase" said modulation. This effect usually occurs in normal telecommunication fibers around 600 ° C and limits the use of these devices. To mitigate this limitation, two thermal treatments that stabilize the optical behavior of FBGs induced by ultraviolet exposure stand out.

The first is to make a thermal aging of the FBG (annealing) [Rodriguez- Cobo, L., & Lopez-Higuera. J M. (2016). SLM Fiber Laser Stabilized at High Temperature. IEEE Photonics Technology Letters. 28 {6), 693-696], in order to minimize its degradation with temperature [US7499605B1]. Through this aging, it is possible to increase the longevity of the FBG at high temperatures, although it can only be applied when the operating temperature of the FBG is below its erasure (eg 500 ° C).

The second method is based on a phenomenon known as "regeneration", consisting of applying a higher temperature to the FBG (above that of the erasure), removing the FBG and obtaining a similar response again centered on a similar wavelength [ Canning. J. Cook. K., Aslund, M., Stevenson, M., Biswas, P, & Bandyopadhyay, S. (2010). Regenerated fiber Bragg gratings. INTECH Open Access Publisher]. With this mechanism, the changes in the index of refraction of the material will be transformed into permanent changes in the material with the same period as the FBG seed, so that its optical properties are not erased by increasing the temperature above 500- 600 ° C A multitude of parameters influence the regeneration process, so there is no single process to regenerate, there are several variants, in which the stable temperature is generally maintained above the regeneration threshold (which depends on various factors such as the type of fiber , the presence of hydrogen ...) for several hours, causing the deletion and regeneration of the optical spectrum of the FBG [Lindner, E., Chojetzki, C., Bruckner, S., Becker. M., Rothhardt, M. & Bartelt. H. (2009). Thermal regeneration of fiber Bragg gratings in photosensitive fibers. Optics express. 17 (15), 1 2523-12531). [Lindner. E .. Canning. J., Chojetzki, C., Bruckner. S. Becker M., Rothhardt. M. & Barre / t. H (201 1). Thermal regenerated type IIa fiber Bragg gratings for ultra-high temperature operation. Optics Communications 284 (1). 183-185]. [WO2015181419A1). Although it is not the only method to obtain FBGs resistant to high temperatures, the regeneration is the one that demands less complexity during the registration of the FBG, so it is more easily scalable. However, this thermal treatment generally requires raising the temperature of the fiber above 800-1000 ° C so that it becomes

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extremely brittle, although its optical properties are stabilized for high temperatures.

That is to say, the inscription using high intensity lasers and the inscription by means of an interference pattern centered in the ultraviolet and subjected to a subsequent thermal treatment, are very aggressive for the optical fiber, neglecting in both cases the mechanical aspect.

In the case of existing devices for measuring temperatures up to approximately 300-400 ° C, an encapsulation of the optical fiber with thermo-moldable and / or sprayable materials is carried out in order to protect the fiber. For example, it is common to use polyimide to measure temperatures up to 300 ° C or aluminum for temperatures up to 400 ° C. However, the use of this type of encapsulation, in devices capable of measuring up to very high temperatures (registration using high intensity lasers and registration through an interference pattern focused on ultraviolet and subjected to a subsequent thermal treatment) to provide them with rigidity mechanics is not feasible, and its adaptation to this type of devices entails a series of inconveniences that currently have not been overcome.

First, the fiber protection materials have to withstand very high temperatures (eg several hours above 1000 ° C) limiting both the possible materials to be used and their geometry etc. On the other hand, materials capable of withstanding very high temperatures require that the optical fiber be adapted to the encapsulation, so that shear cuts and the need for mechanical insertion arise. Finally, the use of materials that withstand very high temperatures makes it difficult to isolate tensions and forces on the optical fiber

In US6923048B2, a method is proposed to monitor parts of an engine analyzing the deformation and / or temperature by means of FBGs. Without going into details of how to obtain a stable optical response up to 1200 ° C, it is proposed to embed the FBGs in metal being sensitive to changes in deformation and temperature, this metal acting as physical and thermal protection of the fiber. However, this document does not mention how the encapsulation has to be, nor its manufacturing process, nor does it comment on how to give stability to the optical fiber.

In summary, the following conclusions can be drawn from the revision of the state of the art related to the measurement of high temperatures (Tmax ~ 500 ° C) and very high temperatures (Tmax ~ 1200 ° C) by means of optical fiber.

• The systems described only focus on either the optical aspect or its mechanical protection, generally presenting incompatible requirements

• There are several techniques for measuring high temperatures with fiber optics, the most productive being the ultraviolet laser registration and the subsequent thermal treatment, which limits its possible embedding.

• The installation methods of very high temperature devices are not addressed, unless the fiber is embedded in some part of the structure, although it is not mentioned as.

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The following needs are also identified

• Design packages capable of supporting both the operation and the possible thermal treatments necessary to obtain stable optical devices (eg regeneration of FBGs)

• Define input (output) methods to (of) the device that avoid breakage of the optical fiber.

• Determine methods of anchoring and / or installation of the devices to the place to be monitored.

Summary of the invention

The present invention tries to solve the aforementioned inconveniences by means of a device based on optical fiber and diffraction networks for the measurement of temperatures that reach the l (thermal limits of the optical fiber, and its manufacturing process.

Specifically, in a first aspect of the invention a device based on optical fiber is provided for measuring temperatures that reach the thermal limits of the optical fiber, using diffraction networks and subjected to an encapsulation process, comprising:

- an optical transduction element consisting of an optical fiber in which a diffraction network is inscribed in an area thereof, being that area of the transduction optical element in which the diffraction network is registered, the transduction zone ;

- an inner covering that covers the optical transduction element at least in the transduction zone, configured to act as an intermediate layer that prevents any traction / pressure from being transmitted to the optical fiber, protecting the weak areas of the optical fiber and avoiding possible measurement failures caused by deformation;

- an outer protection block, which has at least one hole, inside which the optical transduction element coated by the inner coating is located, such that at least one end of the optical fiber is located outside the outer protection block said at least one hole passing through, the transduction zone remaining inside the outer protection block, such that the optical fiber can be arranged in different geometries, the outer protection block being configured for the mechanical fastening and protection of the whole assembly, that is, it has mechanical properties that do not degrade. and has a thickness whose range is between several millimeters and several centimeters:

- As many entry / exit protections as holes presents the outer protection block, with openings whose diameter is such that it allows the passage of the optical fiber inside, and that are anchored to the outer protection block, so that each input / output protection is positioned so that its opening is concentric with one of the holes of the outer protection block, such that the at least one end of the optical fiber that is outside the outer protection block, It is coated, in the part most in contact with said protection block

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outside, for an input / output protection. such that said input / output protections have a lower mechanical resistance than the outer protection block, which allows partial flexion when the optical fiber is deformed, avoiding shear cuts, and such that the input / output protections offer a rigidity Gradually as they move away from the outer protection block, the areas closest to the outermost protection block being more rigid, while the farthest ones bend more easily in order not to break the optical fiber:

- at least one support attached to the outer protection block, configured to anchor the device to the surface on which you want to measure;

the device being configured to be able to connect to an external interrogation equipment; and / or in series with other devices, using the optical fiber as a channel, and each centered on a different wavelength, allowing the measurement of several temperature points at the same time.

In a possible embodiment, the optical transduction element is a short period diffraction network inscribed in standard telecommunications optical fiber.

In a possible embodiment, the inner coating has a thickness of less than 0.5 mm and a roughness of less than 5 pm, so as not to cause irregularities in the transduction zone.

In a possible embodiment, the inner coating covers the entire optical transduction element.

In a possible embodiment, the inner coating is ceramic, and with a thickness between 20 and 500 micrometers. Alternatively, the inner lining is a 0.4 mm diameter stainless steel tube and is fixed to the optical fiber with ceramic glue. Alternatively, the inner coating is a ceramic layer, molded to the desired shape.

In a possible embodiment, the outer protection block has two holes, such that the coated transduction element is located inside the outer protection block through both holes, so that the transduction zone remains inside the block of outer protection and the ends of the fiber optic outside.

In a possible embodiment, the input / output protections have a cylindrical shape.

In a possible embodiment, the input / output protections are two superimposed steel or tungsten metal tubes of different lengths that allow the outer part to be flexed more than the inner part. Alternatively, the input / output protections are a reinforcement in the form of a ceramic filament, such that the filament is thicker in the area closest to the outer protection block.

In a possible embodiment, the support is based on mechanical imprisonment.

In another aspect of the invention, a manufacturing process of the device according to any of the preceding claims is provided. The process includes the

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stages of: inscribing the diffraction network in the optical fiber, applying the internal coating, applying the outer protection block, incorporating the input / output protections and applying the support.

In the event that the registration is carried out by means of an interference pattern centered on the ultraviolet, the process also includes the stage of subjecting the device to a thermal treatment, this stage being subsequent to the incorporation of any protection - inner covering, protection block exterior, input / output protections and support-, as long as these are made of a material resistant to very high temperatures, or prior to the incorporation of any protection whose material is not resistant to very high temperatures.

Brief description of the figures

In order to help a better understanding of the features of the invention, according to a preferred example of practical realization thereof, and to complement this description, it is accompanied as an integral part thereof. a set of drawings, whose character is illustrative and not limiting. In these drawings:

Figure 1 shows a diagram of the device of the invention, according to a possible embodiment.

Figure 2 shows a diagram of the device of the invention, according to a possible embodiment.

Figure 3 shows a diagram of the device of the invention, according to a possible embodiment.

Figure 4 shows several devices of the invention connected in series. Detailed description of the invention

In this text, the term "comprises" and its variants should not be understood in an exclusive sense, that is, these terms are not intended to exclude other technical characteristics, additives, components or steps.

In addition, you end them "approximately", "substantially", "around", "ones", etc. they should be understood as indicating values close to which these endings accompany, since due to calculation or measurement errors, it is impossible to achieve those values with total accuracy.

Furthermore, in the context of the present invention high temperature is understood to be that temperature range whose maximum temperature is 500 ° C. In addition, it is understood by very high temperature that range of temperatures whose maximum temperature is 1200 ° C.

The characteristics of the device of the invention, as! As the advantages derived therefrom, they may be better understood with the following description, made with reference to the drawings listed above.

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The following preferred embodiments are provided by way of illustration, and are not intended to be limiting of the present invention. In addition, the present invention covers all possible combinations of particular and preferred embodiments indicated herein. For those skilled in the art, other objects, advantages and characteristics of the invention will be derived partly from the description and partly from the practice of the invention.

Next, the device of the invention is described, and its manufacturing method, based on optical fiber for measuring temperatures that reach the thermal limits of the optical fiber (typically 1200 ° C in standard optical fibers), using diffraction networks and undergoing an encapsulation process, according to the scheme of the same in Figure 1. This device meets both the requirements of opticians for the measurement of high temperatures (Tmax ~ 500 ° C) and very high temperatures (Tmax ~ 1200 ° C ) as its mechanical implementation, enabling its subsequent installation in aggressive environments.

The device 10 comprises an optical transduction element consisting of an optical fiber 11 in which a diffraction network is inscribed in an area thereof 12. Preferably, the optical transduction element is a short period diffraction network 12 (FBG ) inscribed in fiber optic standard 11 telecom communications (G652 or G657). In the context of the present invention, a transduction zone to that area of the optical transduction element in which the diffraction network 1 2 is inscribed is understood.

In most cases, for the inscription of a diffraction network (in particular FBG) inscribed in optical fiber (in particular a commercial optical fiber of silica) the coating (typically plastic) is removed, revealing about 5-30 mm of silica fiber. By removing this coating mechanically (using a tool for this, similar to a pliers) microscopic damage can be introduced to the surface of the fiber that can be propagated by applying some tension, making a shear cut in the fiber. In order to minimize these problems, it is recommended for this technique to use chemical or temperature techniques to eliminate the plastic protection of the fiber. In any case, any of these techniques is widely known and is beyond the scope of the present invention. Once the protection is removed, the fiber is subjected to the FBG etching process (of a typical length of 5-20mm), either by exposure to ultraviolet light or by other means (for example, point-to-point registration with a laser High intensity). Most current systems are recorded transversely to the fiber, being the most viable option for this purpose, regardless of the type of laser and mode of registration (point to point, ultraviolet ...).

On the other hand, and as mentioned above, when the optical transduction element used is unstable at high temperatures (eg diffraction networks recorded with ultraviolet light) a thermal treatment, such as regeneration, is required to guarantee The optical stability of the transduction element.

One possible method of regeneration consists in introducing hydrogen into the optical fiber (submerging the optical fiber at a high pressure of H2, eg 20 bar), applying a thermal pre-treatment at low temperature (eg 1 hour at 2000C ), increase the temperature above the regeneration threshold during another interval (eg 4 h at 1000 ° C) and return to the FBG at room temperature. In order to guarantee the mechanical integrity of the FBG, it is necessary that the fiber be mechanically protected before

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Perform aggressive thermal treatments (eg above 800 ° C) or mechanized with high intensity lasers. In any case, a person skilled in the art will understand that the thermal treatment used is outside the scope of the present invention.

These thermal treatments after enrollment by means of an interference pattern centered in the ultraviolet generally require raising the temperature of the fiber above 800-1000 ° C, so that it becomes extremely brittle, although its optical properties are stabilized for high temperatures On the other hand, the inscription using high intensity lasers is very aggressive for the optical fiber, so the fiber also becomes brittle when neglecting the mechanical aspect.

To solve this problem, an encapsulation of the optical transduction element with different elements is carried out in the present invention: inner covering 13, outer protection block 14, input / output protections 15 and support 16. These elements are made of materials resistant to very high temperatures, such as some metals (tungsten or steel) and ceramic materials, in order to protect the optical transduction element during its operation and withstand the thermal conditions during the manufacture of the device 10. As mentioned above, this encapsulation is not trivial because it is necessary to overcome a series of existing disadvantages, such as: selection of the materials to be used and geometry, difficulty adapting the optical fiber to the encapsulation (shear cuts, need for mechanical insertion ...) or difficulty to achieve the isolation of tensions and forces on the optical fiber.

The optical transduction element is coated at least in the transduction zone, preferably it is completely covered by an inner coating 13 configured to provide the first mechanical protection to the optical transduction element. Preferably, this inner coating 13 has a thickness of less than 0.5 mm and a very low roughness (eg Ra <5 pm) such that it does not cause irregularities in the transduction zone and does not impair the measurement.

The inner coating 13 is necessary even if the optical fiber 11 with the inscribed diffraction network 12 has sufficient mechanical integrity at room temperature (for example because the diffraction network 12 has been inscribed with low intensity lasers, typically in the ultraviolet), and it has two purposes: a) to protect the naked fiber optic 11 during the manufacturing process of the device 10; and b) isolate the optical fiber 11 from possible tensions, it being easier to avoid the breakage of the fiber 11 during the use of the device 10 (for example, when this fiber 11 is incorporated in some ceramic materials, being subject to very high temperatures and Apply a slight tension, it can cause a shear break with a cutting edge). That is, this inner coating 13 acts as an intermediate layer that prevents any traction / pressure from being transmitted to the optical fiber 11, protecting the weak areas of the optical fiber 11 and avoiding possible measurement failures caused by deformation.

In a preferred embodiment, this inner coating 13 is ceramic, and with a thickness between 20 and 500 micrometers. In another possible embodiment, this inner coating 13 is a 0.4 mm diameter tube, made of stainless steel and fixed to the optical fiber 11 with ceramic glue. In another possible embodiment, the inner coating 13 is a ceramic layer, molded to the desired shape.

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The optical transduction element coated by the inner lining 13 is partially located inside an outer protection block 14 having at least one hole, such that at least one end of the optical fiber 11 is located outside the block 14 crossing said at least one hole, the transduction zone remaining inside the block 14. In a possible embodiment, the outer protection block 14 has two holes, such that the coated transduction element is located inside the block 14 through both holes, so that the transduction zone remains inside the block 14 and the ends of the optical fiber 11 outside. One skilled in the art will understand that the device 10 of the invention is configured to join at least one of the ends of the optical fiber 11 to an interrogation equipment.

The outer protection block 14, is configured for mechanical fastening and protection of the entire assembly, that is, it has mechanical properties that do not degrade during the heat treatment or during the use of the device 10, and has a thickness whose range It is comprised between several millimeters and several centimeters. The double coating (interior and exterior) allows to maintain the mechanical integrity of the device 10 and its sensitivity at high temperatures.

In addition, and as seen in Figures 2 and 3, this block 24, 34 allows the placement of the optical fiber 21.31 in different geometries (for example, linear or "U" shape), so that an expert in the matter will understand that the transduction element and its inner lining 23, 33 must be arranged inside the outer protection block 24, 34 in geometries that favor thermal transfer and / or clear the transduction zone of possible external stresses, avoiding generating deformations in the transduction element. When coupling the optical transduction element with its inner coating 23, 33 in the outer protection block 24, 34, it is important to pay special interest to the input and output of the optical fiber 21, 31: any placement that can deform the assembly into excess, is likely to cause a break in the fiber 21, 31. For this, simple geometries (straight, smooth curves ...) are raised to avoid these problems, while improving the optical transmission.

Depending on the material of the outer protection block 14, 24, 34, the optical fiber 11, 21, 31 coated by the inner liner 13, 23, 33 is coupled to said block 14, 24, 34 (for example, a steel block with a machined groove for this purpose) or block 14, 24, 34 is coupled to the inner lining 13, 23, 33 of the optical fiber 11,21, 31 - not to the optical fiber, as it is the inconvenience that has been explained above - (for example, ceramic glue, ceramic, stoneware ...), thus avoiding shear cuts, roughness problems, etc.

So many input / output protections 15, 25, 35 as holes have the outer protection block 14, 24, 34, preferably cylindrical, and with openings whose diameter is such that it allows the passage of the optical fiber 11, 21, 31 inside, they are anchored to the outer protection block 14, 24, 34, so that each input / output protection 15, 25, 35 is positioned so that its opening is concentric with one of the holes in block 14 , 24, 34. In this way, the at least one end of the optical fiber 11, 21, 31 that is outside the outer protection block 14, 24, 34, is coated, in the part most in contact with said block 14, 24, 34, by an input / output protection 15, 25, 35, such that said protections 15, 25, 35 have a lower mechanical resistance than the outer protection block 14, 24, 34, which allows a partial flexion when the

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fiber optic 11, 21, 31, avoiding shear cuts. Preferably, within the input / output protections 15, 25, 35, the inner lining 13, 23, 33 of the fiber 11,21, 31 is maintained in order to avoid possible tensions to the transduction zone.

Furthermore, for said input / output protections 15, 25, 35, materials and geometries that offer a lower resistance to deformation should be used as they move away from the anchor point, that is, protections 15, 25, 35 offer a gradual stiffness as they move away from the outer protection block 14, 24, 34: the areas closest to block 14, 24, 34 are more rigid, while the furthest ones bend more easily in order not to break the fiber 11,21, 31. This effect can be achieved by gradually reducing the thickness of the protections 15, 25, 35.

In a possible realization. the input / output protections 15, 25, 35 are two superimposed steel or tungsten metal tubes of different lengths that allow the outer part to be flexed more than the inner part. In another possible embodiment, the input / output protections 15, 25, 35 are a reinforcement in the form of a ceramic filament, such that the filament is thicker in the area closest to the outer protection block 14, 24, 34.

Finally, the device 10, 20, 30 of the invention comprises at least one support 16, 26, 36 based preferably on mechanical clamping attached to the outer protection block 14, 24, 34, configured to anchor the device 10, 20, 30 to the surface on which you want to measure. One skilled in the art will understand that the material of said supports 16, 26, 36 depends on the range of temperatures to be monitored, being possible with simple mechanical anchors, such as nuts, thymes, jaws, etc ... of metal (for example, tungsten) or ceramic resistant to very high temperatures (1200 ° C).

Within a possible embodiment of the invention, an FBG is used as an optical transduction element that, as described above, only reflects certain wavelengths, whereby several devices 10, 20, 30 can be connected in series using fiber Optical 11, 21, 31 standard telecommunication as a channel, and each centered on a different wavelength. In this way, it is possible to measure several temperature points at once. Within a possible embodiment of the invention, and as seen in Figure 4, the wavelength multiplexing of the FBGs occurs, which allows the data of each device 40 encoded in different wavelengths to be sent. Several devices 40 of the invention are interconnected by means of fiber optic cable 41 until they reach an interrogation equipment 47 of FBGs that throw the light to the optical fiber 41 and analyze the spectrum at the output, obtaining the temperature measurement of each sensor . The set of several devices 40 in series with different wavelengths can be interrogated by means of the different interrogation techniques of FBGs that typically consist of a light source, a detector and a coupler or circulator to connect both devices to it. optical fiber.

The general steps for the manufacture of the device 10, 20, 30, 40 of the invention are: inscription of the diffraction network 12, 22, 32 in the optical fiber 11,21, 31, 41, application of the internal coating 13, 23 , 33, application of the external protection block 14, 24, 34, incorporation of the input / output protections 15, 25, 35 and application of the support 16, 26, 36. In the event that the registration is made through a pattern of interference centered in the ultraviolet and it is necessary to subject the device 10, 20, 30, 40 to a thermal treatment, it is advisable to perform the thermal treatment after

the incorporation of any protection (inner covering 13, 23, 33, outer protection block 14, 24, 34, input / output protections 15, 25, 35 and support 16, 26, 36), as long as these are of a material resistant to very high temperatures. In this way, the heat treatment serves to harden them. Otherwise, for example 5 when the material is not resistant to very high temperatures, the thermal treatment must be carried out beforehand, otherwise its mechanical properties will be degraded.

Claims (15)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 1. Device (10, 20, 30, 40) based on optical fiber (11, 21. 3 1, 41) for measuring temperatures that reach the thermal limits of the optical fiber (11, 21, 31, 41), using diffraction networks (12, 22, 32) and subjected to an encapsulation process, characterized in that it comprises: - an optical transduction element consisting of an optical fiber (11,21, 31, 41) in which a diffraction network (12, 22, 32) is inscribed in an area thereof, being that area of the optical element of transduction in which the diffraction network (12, 22, 32), the transduction zone is registered; - an inner covering (13, 23, 33) that covers the optical transduction element at least in the transduction zone, configured to act as an intermediate layer that prevents any traction / pressure from being transmitted to the optical fiber (11,21, 31,41), protecting the weak areas of the optical fiber (11,21, 31, 41) and avoiding possible measurement failures caused by deformation: - an outer protection block (14, 24, 34), which has at least one hole. inside which the optical transduction element coated by the inner lining (13, 23, 33) is located, such that at least one end of the optical fiber (11, 21, 31, 41) is located outside the block of outer protection (14, 24, 34) through said at least one hole. allowing the transduction zone inside the outer protection block (14, 24, 34), such that the optical fiber (11,21, 31, 41) can be arranged in different geometries, the outer protection block (14, 24. 34) configured for mechanical fastening and protection of the whole assembly, that is, it has mechanical properties that do not degrade, and has a thickness whose range is between several millimeters and several centimeters; - As many input / output protections (15, 25, 35) as holes has the outer protection block (14, 24, 34), with openings whose diameter is such that it allows the passage of the optical fiber (11, 21, 31 , 41) inside, and that are anchored to the outer protection block (14, 24. 34), so that each input / output protection (15, 25, 35) is positioned so that its opening is concentric with one of the holes of the outer protection block (14, 24, 34), such that the at least one end of the optical fiber (11, 21, 31, 41) that is outside the block of outer protection (14, 24. 34), is covered, in the part most in contact with said outer protection block (14, 24, 34), by an input / output protection (15, 25, 35), such that said input / output protections (15. 25. 35) have a lower mechanical resistance than the outer protection block (14, 24. 34), which allows partial flexion when forms the optical fiber (11, 21, 31, 41), avoiding shear cuts, and such that the input / output protections (15, 25, 35) offer a gradual stiffness as they move away from the outer protection block ( 14, 24, 34), being the areas closest to the outer protection block (14. 24, 34) more rigid, while the farthest ones bend more easily in order not to break the optical fiber (11,21, 31, 41); - at least one support (16, 26, 36) attached to the outer protection block (14, 24, 34), configured to anchor the device (10, 20, 30, 40) to the surface on which you want to measure ; 5 10 fifteen twenty 25 30 35 40 Four. Five fifty the device (10, 20, 30, 40) being configured to be able to connect to an external interrogation equipment (47); and / or in series with other devices (10, 20, 30, 40), using the optical fiber (11, 21, 3 1, 41) as a channel, and each centered on a different wavelength, allowing the measurement of several temperature points at once. 2. The device (10, 20, 30, 40) of claim 1, wherein the optical transduction element is a short-term diffraction network (12, 22, 32) inscribed in optical fiber (11,21, 31, 41) telecommunications standard. 3. The device of any of the preceding claims, wherein the inner lining (13, 23, 33) has a thickness of less than 0.5 mm and a roughness of less than 5 pm, such that it does not cause irregularities in the transduction zone. 4. The device (10, 20, 30, 40) of any of the preceding claims, wherein the inner lining (13, 23, 33) covers the entire optical transduction element. 5. The device (10, 20, 30, 40) of any of the preceding claims. where the inner covering (13, 23, 33) is ceramic, and with a thickness between 20 and 500 micrometers. 6. The device (10, 20, 30, 40) of any one of claims 1 to 4, wherein the inner lining (13, 23, 33) is a 0.4 mm diameter stainless steel tube and is fixed to the optical fiber (11,21, 31,41) with ceramic glue. 7. The device (10, 20, 30, 40) of any one of claims 1 to 4, wherein the Inner lining (13, 23, 33) is a ceramic layer, molded with the shape desired. 8. The device (10, 20, 30, 40) of any of the preceding claims, wherein the outer protection block (14, 24, 34) has two holes. such that the coated transduction element is located inside the outer protection block (14, 24, 34) through both holes. so that the transduction zone remains inside the outer protection block (14, 24, 34) and the ends of the optical fiber (11, 21, 31,41) on its outside. 9. The device (10, 20, 30, 40) of any of the preceding claims, wherein the input / output protections (15, 25, 35) have a cylindrical shape. 10. The device (10, 20, 30, 40) of any of the preceding claims. where the input / output protections (15, 25, 35) are two overlapping steel metal tubes of different lengths that allow the outer part to be flexed more than the inner part. 11. The device (10, 20, 30, 40) of any one of claims 1 to 9, wherein the inlet / outlet protections (15, 25, 35) are two overlapping tungsten metal tubes of different lengths that allow flexing the outer part more than the inner part. 12. The device (10, 20, 30, 40) of any one of claims 1 to 9, wherein the input / output protections (15, 25, 35) are a filament-shaped reinforcement ceramic, such that the filament is thicker in the area closest to the outer protection block (14, 24, 34). 13. The device (10, 20, 30, 40) of any of the preceding claims, wherein the support (16, 26, 36) is based on mechanical clamping. 14. Process of manufacturing the device (10, 20, 30, 40) according to any of the preceding claims, characterized in that it comprises the steps of: inscribing the diffraction network (12, 22, 32) in the optical fiber ( 11, 21, 31, 41), apply the coating 10 internal, apply the outer protection block (14, 24. 34), incorporate the input / output protections (15, 25, 35) and apply the support (16, 26, 36). 15. The manufacturing process of the previous claim where in the event that the registration is carried out by means of an interference pattern centered on the ultraviolet 15 also includes the stage of subjecting the device (10, 20, 30, 40) to a thermal treatment, this stage being after the incorporation of any protection - inner coating (13, 23, 33), outer protection block (14 , 24, 34), input / output protections (15, 25, 35) and support (16, 26, 36) - as long as they are made of a material resistant to very high temperatures, or prior to incorporation of any protection whose material is not resistant to very high temperatures.