ES2599606B2 - Fiber optic based device and diffraction networks for measuring temperatures that reach the thermal limits of the optical fiber, and manufacturing process - Google Patents

Abstract

Device (10, 20, 30, 40) based on optical fiber (11, 21, 31, 41) for measuring 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 in an area thereof it is a diffraction net (12, 22, 32) is inscribed; # - an inner covering (13, 23, 33) covering the optical transduction element; # - an outer protection block (14, 24, 34) inside which the optical transduction element coated by the inner lining (13, 23, 33) is located; # - as many input / output protections (15, 25, 35) as holes the outer protection block (14, 24, 34) has , 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 On the device (10, 20, 30, 40) comprising the steps of: inscribing the diffraction network (12, 22, 32) in the optical fiber (11, 21, 31, 41), applying the inner coating, applying the outer protection block (14, 24, 34), incorporate the input / output protections (15, 25, 35) and apply the support (16, 26, 36).

Description

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

Field of the Invention

The present invention belongs to the field of devices for measuring high temperatures (temperatures up to about 5000C), and, more specifically, to the field of devices based on fiber optics for measuring very high temperatures (temperatures that reach the limits thermal fiber optic (typically 12000C in standard optical fibers), using diffraction networks and subjected to an encapsulation process.

15 Background of the invention

At present there is a wide variety of devices for measuring 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 (T max 5000 e) 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 accuracy or its vulnerability to electromagnetic interference, which is why the use of new ones is encouraged

25 fiber optic techniques.

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 nets and even distributed sistB'Tlas 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].

35 These short-period diffraction networks consist of a periodic variation of the refractive index of the fiber core 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 several FBGs can be connected in series, each of them reflecting a different wavelength (wavelength multiplexing), obtaining a quasi-distributed transducer capable to measure 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,

45 Undesirable effects may occur when subjected to temperatures above 5000c, depending on the method of fiber inscription.

The inscription using lasers of high intensity, as for example techniques based on point-to-point inscription (without the need of the interference pattern) allows to obtain structures capable of withstanding very high temperatures (T max-120QoC) without the need for a subsequent heat treatment [US7835605BI , US8272236B2]. However, while it is

true that investigations related to high temperature measurement by

fiber optics have focused on their optical properties, by subjecting the fiber to

more extreme treatments (with laser, high energy), it becomes extremely

fragile, being able to be used only in very controlled environments, since it degrades in

S

excess fiber mechanically. That is, this type of inscription only focuses on the

optical appearance, neglecting the mechanical aspect.

On the other hand, the most widespread method for the registration of FBGs, is the eXfX> location to a

ultraviolet-centered interference pattern that causes a change in the rate of

10

refraction in the fiber core. This registration method uses low lasers

intensity which allows the optical fiber to have sufficient mechanical integrity to

room temperature. However, when the refractive index change is obtained

by this method, increasing the temperature of the FBG produces a

degradation of said modulation, reaching "erase" said modulation. This effect,

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usually occurs in normal telecommunication fibers around 600 ° C and limits the use

of these devices. To mitigate this limitation, there are mainly two

thermal treatments that stabilize the optical behavior of FBGs

induced by ultraviolet exposure.

twenty

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 Photonies Teehnology Letiers. 28 (6), 693-696], in order to minimize their

degradation with temperature (US7499605B1).

manages to increase the longevity of the FBG at high temperatures, although it can only be

25

applied when the operating temperature of the FBG is below its erasure (e.g.

500 "C).

The second method is based on a phenomenon known as "regeneration," consistent

in applying a higher temperature to the FBG (ercima of the erase), do

30

disappear the FBG and get again a similar response centered on a length

similar wave (Canning. J. Cook. K., Aslund, M., Stevenson, M., BislM3s, P., &

Bandyopadhyay, S. (2010). Regenerated ffbre Bragg gratings. INTECH Open Aeeess

Publisher]. With this mechanism, the refractive index rates of the material are

they transform into permanent changes in the material with the same period as the FBG

35

seed, so that its optical properties are not erased by increasing again the

temperature above 500-6000C. In the regeneration process influence crowd

of parameters 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

40

presence of hydrogen ...) for several hours, causing erasure and regeneration

of the optical spectrum of the FBG [Undner, E., Chojetzki, C., Bruekner, S., Beeker. M.,

Rothhardt, M. & Bartell. H. (2009). Thermal regeneration of ffber Bragg gratings in

photosensitive ffbers. Opties express. 17 (15), 1 2523-12531). [Undner. E.. Canning. J.,

Chojetzki, C., Bruekner. S. Beeker. M., Rothhardt. M. & Barre / t. H (201 1). Thermal

Four. Five

regenerated type lIa fiber Bragg gratings for ultra-high temperature operation. Optics

Communieations 284 (1). 183-185]. IW02015181419AI). Although it is not the only method

to obtain high temperature resistant FBGs, the regeneration is what demands

less complexity during the registration of the FBG, so it is more easy

scalable However, this heat treatment generally requires raising the

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fiber temperature above 800-1000ee so it becomes

extremely brittle, although its optical properties are stabilized for high

temperatures

That is to say, the inscription using lasers of high intensity and the inscription by means of a

S

interference pattern focused on ultraviolet and subjected to heat treatment

later, they are very aggressive for the optical fiber, neglecting in both cases the appearance

mechanic.

In the case of existing devices for measuring temperatures up to

10

approximately 300-400OC, an encapsulation of the optical fiber is carried out with

thermo-moldable and / or sprayable materials in order to protect the fiber. By

For example, it is common to use polyimide to measure temperatures of

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

fifteen

temperatures (registration using high intensity lasers and registration through a

interference pattern focused on ultraviolet and subjected to heat treatment

later) to provide them with mechanical rig idez is not viable, and their adaptation to this type of

devices entails a series of inconveniences that currently have not been possible

overcome.

twenty

First, fiber protection materials have to resist very high

temperatures (eg several hours above 10000C) limiting both possible

materials to use as its geometry etc. On the other hand, materials capable of

resist very high temperatures require that the optical fiber adapts to the encapsulation, so

25

that shear cuts arise and the need for mechanical insertion. 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 by analyzing

30

deformation and / or temperature by means of FBGs. Without going into details of how to get

a stable optical response up to 1200 ° C, it is proposed to embed the FBGs in metal

being sensitive to canbs 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 how to give

35

fiber optic stability

In reslfTlen, of the review of the state of the art related to the measurement of discharges

temperatures (T max -500 ° C) And very high temperatures (T max -1200 ° C) using fiber

optics the following conclusions can be drawn.

40

The systems described only focus on the optical aspect or its protection

mechanical, generally presenting incompatible requirements

There are various techniques for measuring high temperatures with fiber optics,

Four. Five

the most productive being the ultraviolet laser inscription and the subsequent treatment

thermal, which limits its possible embedding.

Installation methods of very high devices are not addressed

temperature, unless the fiber is embedded in some part of the structure,

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although not mentioned how.

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 prevent fiber breakage

optics.

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 drawbacks by means of a device based on optical fiber and diffraction networks for the measurement of temperatures that reach the thermal limits of the optical fiber, and its manufacturing process.

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

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

-

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 failures to the extent caused by deformation;

35 - 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 protection block said outer crossing at least one hole, 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 mechanical fastening and protection of the entire assembly , that is, it has mechanical properties that do not degrade. and has a thickness whose range is between several millimeters and several centimeters:

45 -so 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 through its interior, and which 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 in the outer protection block, such that the at least one end of the optical fiber that is outside the outer protection block , is coated, in the part most in contact with said protection block

S

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

10

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

fifteen

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

twenty

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

25

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

30

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.

35

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 I block of outer protection and the ends of the fiber optic outside.

40

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

Four. Five

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 one possible embodiment, the support is based on mechanical clamping.

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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

Stages: enroll the diffraction network in the optical fiber, apply the internal coating, apply the outer protection block, incorporate the input / output protections and apply the support.

s

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 heat 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

fifteen

In order to help a better understanding of the features of the invention, in accordance with a preferred example of practical realization thereof, and to complement this description, ion, is used 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.

25

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

35

In this text, the term "comdends" 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 those that you end up accompanying, since due to calculation or measurement errors, it is impossible to achieve those values with total accuracy.

Four. Five

Furthermore, in the context of the present invention high temperature is understood to be that temperature range whose maximum temperature is 5000C. In addition, it is understood by very high temperature that range of temperatures whose maximum temperature is 120Qoc.

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

The following preferred embodiments are provided by way of illustration, and are not

It is intended to be limiting of the present invention. In addition, the present invention

covers all possible combinations of particular and preferred embodiments here

indicated. For experts in the field, other objects, advantages and characteristics of the

S

invention will come off in part from the description and in part from the practice of

invention.

The device of the invention is described below, and its manufacturing method :: ion,

based on fiber optics for measuring temperatures that reach thermal limits

10

of the optical fiber (typically 12000C in standard optical fibers), using networks of

diffraction and subjected to an encapsulation process, according to the scheme of

Same as Figure 1. This device meets both the optical requirements for the

measurement of high temperatures (T max -500 ° C) And very high temperatures (T max -1200OC)

as its mechanical implementation, enabling its subsequent installation in environments

fifteen

aggressive.

The device 10 comprises an optical transducing element in a fiber

optics 11 in which a diffraction network 12 is inscribed in an area thereof.

Preferably, the optical transduction element is a diffraction network 12 of

twenty

Short period (FBG) inscribed in fiber optic 11 telecommunications standard (G652 or

G657). In the context of the present invention, transduction zone to

that area of the optical transduction element in which the network is registered

diffraction 1 2.

25

In most cases, for the registration of a diffraction network (in particular

FBG) inscribed in optical fiber (in particular a cemercial silica optical fiber) the

coating (typically plastic) exposing about 5-30 mm of sOice of the

fiber. By removing this coating mechanically (using a tool for it,

similar to a pliers) mcroscopic damage can be introduced to the fiber surface

30

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

use chemical or temperature techniques to eliminate the plastic protection of the

fiber. In any case, any of these techniques is fully known and is

outside the scope of the present invention. Once the protection is removed, the

35

fiber to the FBG engraving process (of a typical length of 5-20mm), either by

exposure to ultraviolet light or by other means (e.g. point-to-point inscription

with a high intensity laser). Most current systems are recorded

transversely to the fiber, being the most viable option for this purpose, independently

of the type of laser and inscription mode (point to point, ultraviolet ...).

40

On the other hand, and as previously cemented, when the optical element of

used transduction is unstable at high temperatures (eg diffraction networks

recorded with ultraviolet light) a heat treatment is required, such as

regeneration, to ensure the optical stability of the transduction element.

Four. Five

A possible regeneration method is to introduce hydrogen into the optical fiber

(submerging the optical fiber at a high pressure of H2, eg 20 bar), apply a

low temperature heat pre-treatment (eg 1 hour at 2000C), increase the

temperature above the regeneration threshold during another interval (eg 4 h at

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1000DC) and return to the FBG at room temperature. In order to guarantee integrity

FBG mechanical, it is necessary that the fiber is mechanically protected before

perform aggressive technical treatments (eg above BOQoe) or mechanized with

high intensity lasers. In any case, an expert in the field will understand that the

Heat treatment employed is outside the scope of the present invention.

S

These post-enrollment technical treatments through a pattern of

ultraviolet-centered interference generally require raising the temperature of

fiber above 800-1 DOQae by Jo that this becomes extremely

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

On the other hand, registration using high intensity lasers is very aggressive for

10

optical fiber, so the fiber also becomes brittle when neglecting the appearance

mechanic.

To solve this problem, an encapsulation is performed in the present invention.

of the optical transduction element with different elements: inner lining 13,

fifteen

external protection block 14, input / output protections 15 and support 16. These

Elements are made of materials resistant to very high temperatures, as per

example some metals (tungsten or steel) and ceramic materials ;, with the aim of

protect the optical transduction element during its operation and withstand the

thermal conditions during the manufacture of the device 10. As mentioned

twenty

previously, this encapsulation is not trivial because it is necessary to overcome a series of

existing problems, eg for example: 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 in obtaining stress isolation

and forces on the optical fiber.

25

The optical transduction element is coated at least in the area of

transduction, preferably is completely coated, by a

inner lining 13 configured to provide the first mechanical protection to the

optical transduction element. Preferably, this inner coating 13

30

it has a thickness of less than 0.5 mm and a very low roughness (eg Ra <5 IJm) of such

so that it does not cause irregularities in the transduction zone and does not harm the

measure.

The inner lining 13 is necessary even though the fiber optic 11 with the network of

35

inscribed diffraction 12 present sufficient mechanical integrity at room temperature

(for example because diffraction network 12 has been registered with low intensity lasers,

typically in the ultraviolet), and has two purposes: a) protect the optical fiber 11

naked during the manufacturing process of the device 10; AND b) isolate the optical fiber 11

of possible tensions, making it easier to avoid the breakage of fiber 11 during the use of

40

device 10 (for example, when this fiber 11 is incorporated into some materials

ceramic, being subject to very high temperatures and applying a slight tension, can

cause a shear break with a cutting edge). That is, this coating

interior 13 acts as an intermediate layer that prevents any traction / pressure from being

transmitted to fiber optic 11, protecting weak areas of fiber optic 11 and

Four. Five

avoiding possible measurement failures caused by deformation.

In a preferred embodiment, this inner coating 13 is ceramic, and with a

thickness taken between 20 and 500 micrometers. In another possible embodiment, this

inner lining 13 is a 0.4 mm diameter tube, stainless steel and fixed to

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11 fiber optic with ceramic glue. In another possible embodiment, the coating

Inner 13 is a ceramic layer, molded to the desired shape.

The optical transduction element covered by the inner covering 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 through said at least one hole, the transduction zone S 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 fiber optic 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 are not

15 degrade neither during the heat treatment nor during the use of the device 10, and has a thickness whose range is 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.

20 Memás, 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 art it will be understood that the transduction element and its inner covering 23, 33 must be arranged inside the outer protection block 24, 34 in geometries that favor thermal transfer and / or isolate the area of

25 transduction 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

30 fiber 21, 31. For this, simple geometries (straight, smooth curves ...) are proposed to avoid these problems, while improving optical transmission.

Depending on the material of the outer protection block 14, 24, 34, the optical fiber 11, 21, 31 covered by the inner lining 13, 23, 33 is coupled to said block 14, 24,

35 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 fiber optic, as it is the inconvenience that has been explained above - (for example, ceramic, ceramic, stoneware glue ...), thus avoiding shear cuts, roughness problems, etc.

40 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, are anchored to the outer protection block 14, 24, 34, so that each

45 input / output protection 15, 25, 35 is positioned so that its opening is concentric with one of the holes in block 14, 24, 34. Thus, the at least one end of the optical fiber 11, 21, 31 which is located outside the outer protection block 14, 24, 34, is covered, in the part most in contact with said block 14, 24, 34, by an input / output protection 15, 25, 35, such that said

SO protections 15, 25, 35 have a lower mechanical resistance than the outer protection block 14, 24, 34, which allows partial flexion when the

fiber optic 11, 21, 31, avoiding shear cuts. Preferably, within

input / output protections 15, 25, 35, the inner lining 13, 23, 33 is maintained

of the fiber 11, 21, 31 in order to avoid possible tensions to the transduction zone.

s

In addition, for said input / output protections 15, 25, 35 must be used

materials and geometries that offer a lower resistance to deformation as

that 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:

areas closest to block 14, 24, 34 are more rigid, while the farthest

10

they bend more easily in order not to break the fiber 11, 21, 31. This effect can

achieved by gradually reducing the thickness of the protections 15, 25, 35.

In a possible embodiment. the input / output protections 15, 25, 35 are two tubes

Metallic steel or tungsten overlays of different lengths that allow flexing

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the outer part more than the inner part. In another possible embodiment, the protections of

inlet / outlet 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,

3. 4.

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Finally, the device 10, 20, 30 of the invention comprises at least one support 16,

26, 36 based preferably on mechanized imprisonment attached to the block of

external protection 14, 24, 34, configured to anchor the device 10, 20, 30 to the

surface on which you want to measure. A subject matter expert will understand that

the material of said supports 16, 26, 36 depends on the temperature range at

25

monitor, with realization possible with simple mechanical anchors, such as

nuts, thyme, jaws, etc. . of metal (for example, tungsten) or ceramic

resistant to very high temperatures (12000C).

Within a possible embodiment of the invention, it is used as an optical element of

30

transduction an FBG that, as described above, only reflects certain

wavelengths, so that several devices 10, 20, 30 can be connected in

series using fiber optic 11, 21, 31 telecommunications standard as a channel, and

each centered on a different wavelength. In this way, it is possible to

measurement of several temperature points at once. Within a possible realization of

35

the invention, and as seen in figure 4, length multiplexing occurs

wave of the FBGs, which allows to send the data of each device 40 encoded in

different wavelengths Several devices 40 of the invention are interconnected

by fiber optic cable 41 until it reaches an interrogation team 47 of FBGs

which throws light at the fiber optic 41 and analyzes the spectrum at the output, obtaining the measurement

40

of temperature of each sensor. The set of several devices 40 in series with

different wavelengths, can be interrogated by different techniques of

interrogation of FBGs that typically consist of a light source, a detector and a

coupler or circulator to connect both devices to the same optical fiber.

Four. Five

The general steps for manufacturing the device 10, 20, 30, 40 of the invention are:

inscription of the diffraction network 12, 22, 32 in the fiber optic 11, 21, 31, 41, application

of the internal coating 13, 23, 33, application of the outer protection block 14, 24,

34, incorporation of input / output protections 15, 25, 35 and application of

support 16, 26, 36. In the event that registration is made through a pattern of

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ultraviolet-centered interference and it is necessary to subject the device 10, 20, 30,

40 to a heat treatment, it is advisable to perform the heat 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 they are made of a material resistant to very high temperatures. In this way, the heat treatment serves to harden them. Otherwise, for example

S when the material is not resistant to very high temperatures, the heat treatment must be carried out beforehand, otherwise its mechanical properties would be degraded.

Claims (15)

1. Device (10, 20, 30, 40) based on optical fiber (11, 21. 31, 41) for measuring temperatures that reach the thermal limits of the optical fiber (11, 21, 31, 41), S using diffraction networks (12, 22, 32) And subjected to an encapsulation process, characterized by the fact that it includes:

-

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, that area of the optical transduction element being 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 avoids

15 that no traction / pressure is transmitted to the optical fiber (1 1, 21, 31,41), protecting the weak areas of the optical fiber (11,21, 31, 41) and avoiding possible measurement failures caused by the 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 (1 1, 21, 31, 41) is located outside the block of outer protection (14, 24, 34) crossing 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

25 geometries, the outer protection block (14, 24. 34) being configured for mechanical fastening and protection of the entire assembly, that is, it has mechanical properties that do not degrade, and has a thickness whose range is between several millimeters and several centimeters;

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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 35 of the outer protection block (14, 24, 34), such that the at least one end of the optical fiber (1 1, 21, 31, 41) that is located outside the block of external protection (14, 24. 34), is covered, in the part most in contact with said external protection block (14, 24, 34), by an input / output protection (15, 25, 35), that said input / output protections (15. 25. 35) have a lower mechanical resistance than the outer protection block (14, 24. 34), which allows a flexion essential when the optical fiber is defronted (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 block of external protection (14, 24,34), being the areas closest to the external protection block (14. 24, 34) more rigid, while the far ones are more easily folded in order not to break the optical fiber (11, 21, 31, 41);

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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;

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 period diffraction network (12, 22, 32) inscribed in optical fiber (1 1, 21, 31, 41 ) standard of telecommunications.

3.

The device of any of the preceding claims, wherein the inner coating (13, 23, 33) has a thickness of less than 0.5 mm and a roughness of less than 51 Jm, such that it does not cause irregularities in the transduction zone.

Four.

The device (10,20,30, 40) of any of the preceding claims, wherein the inner coating (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 (1 1, 21, 31, 41) with ceramic glue.

7.

The device (10, 20, 30, 40) of any one of claims 1 to 4, wherein the inner coating (13, 23, 33) is a ceramic layer, molded to the desired shape.

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 (1 1, 21, 31, 41) 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.

eleven.

The device (10, 20, 30, 40) of any one of claims 1 to 9, wherein the input / output protections (15, 25, 35) are two overlapping tungsten metal tubes of different lengths that allow the outer part to flex more than

inside. 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 block of external protection (14, 24, 34). 13. The device (10, 20, 30, 40) of any of the preceding claims, wherein S the support (16, 26, 36) is based on mechanical clamping. 14. Device manufacturing process (10, 20, 30, 40) according to any of The preceding claims, characterized in that the steps of: inscribing the diffraction network (12, 22, 32) in the optical fiber (11, 21, 31,41) are applied, applying the coating 10 internal, apply the outer protection block (14, 24. 34), incorporate the protections input / output (15, 25, 35) And apply the support (16, 26, 36). 15. The manufacturing process of the preceding claim wherein in the event that the registration is carried out by an interference pattern centered on the ultraviolet 15 also comprises the stage of subjecting the device (10, 20, 30, 40) to a heat treatment, this stage being 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 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.