DE102018106710A1 - temperature sensor - Google Patents

Abstract

Temperature sensor (100) is indicated. The temperature sensor (100) comprises an optical waveguide (10) made of an optical waveguide material having at least one integrated temperature sensor element (11); a cladding (20) of a non-metallic cladding material radially spaced from the optical waveguide (10) and surrounding the temperature sensor element (11) of the optical waveguide (10); and a capillary (30) of a non-metallic capillary material radially spaced from the sheath (20) and surrounding the sheath (20) at least in regions. The optical waveguide (10) is fixed to the sheath (20) at an entry end (E3) of the sheath (20). The optical waveguide (10) is fixed to the sheath (20) at an exit end (E4) of the sheath (20). The optical waveguide (10) is fixed to the capillary (30) at an inlet end (E1) of the capillary (30). The cladding material has a coefficient of thermal expansion which is greater than the thermal expansion coefficient of the optical waveguide material.

Description

TECHNICAL AREA

The disclosure relates to a temperature sensor comprising an optical waveguide made of an optical waveguide material having at least one integrated temperature sensor element.

STATE OF THE ART

Conventional optical waveguides with an integrated temperature sensor element are known. The temperature sensor element is usually an interferometric element, for example a fiber Bragg grating. In a reflectance measurement, a fiber Bragg grating applied to light reflects a particular wavelength of light at a Bragg reflection wavelength. The Bragg reflection wavelength depends on the strain or compression of the optical waveguide in the region of the fiber Bragg grating. When the fiber Bragg grating is used as the temperature sensor element, it is desirable that the strain or compression be caused only by thermal expansion of the optical fiber in the region of the fiber Bragg grating. By measuring the Bragg reflection wavelength, it is possible to draw conclusions about the temperature in the vicinity of the Bragg grating. Such temperature sensors use the photolastic effect. In order to obtain a useful sensor sensitivity, metallic materials - for example aluminum - are introduced as substrate in this type of temperature sensors, which reinforce an expansion or compression.

There are also metal-free temperature sensors, which exclusively use the thermo-optic effect for the measurement. Such temperature sensors have a comparatively poor sensitivity or a poor resolution.

SUMMARY OF THE REVELATION

There is therefore a need for a metal-free temperature sensor having a relatively high sensitivity or resolution.

The present disclosure provides a temperature sensor according to claim 1. Further developments emerge from the dependent claims.

According to one aspect, a temperature sensor comprises an optical waveguide made of an optical waveguide material. The optical waveguide comprises at least one integrated temperature sensor element. The temperature sensor further comprises a cladding of a non-metallic cladding material. The sheath is radially spaced from the optical waveguide and surrounds the temperature sensor element of the optical waveguide. The temperature sensor also includes a capillary made of a non-metallic capillary material. The capillary is radially spaced from the sheath and surrounds the sheath at least partially. The optical waveguide is fixed to an inlet end of the enclosure at this. The optical waveguide is also fixed to an outlet end of the enclosure at this. The optical waveguide is also fixed to an inlet end of the capillary at this. The cladding material has a coefficient of thermal expansion which is greater than the thermal expansion coefficient of the optical waveguide material s.

An optical waveguide material comprises, for example, a fiber material made of glass or plastic. The optical waveguide typically comprises a core and a cladding, wherein the optical waveguide material of the core and the optical waveguide material of the cladding have different optical properties. The integrated temperature sensor element typically includes, but is not limited to, a fiber Bragg grating. The integrated temperature sensor element can, for example, also have a backscatter element for a fiber optic backscatter measurement method.

Fixation, as used herein, generally refers to a compound between the constituents involved which is capable of transmitting forces to the other constituent on the one constituent. In particular, a fixing here comprises a fixed connection between the components involved for transmitting forces which act in the axial direction of the arrangement of the components of the temperature sensor.

An existing cladding of the optical waveguide that governs the waveguiding properties of the optical waveguide is not equivalent to the cladding of the temperature sensor, as used herein. The sheath is provided in addition to an existing sheath of the optical fiber. The cover is used to apply a strain on the integrated temperature sensor. The fixation of the optical waveguide at both the entrance end of the enclosure and at the exit end of the enclosure generally serves to apply to the integrated temperature sensor an amount of expansion or compression resulting from thermal expansion or compression. Typically, the cladding is substantially tubular in shape, and the optical waveguide passes approximately linearly through the cladding in its axial direction. The tubular formation of the envelope has in particular a cylindrical shape.

The optical waveguide is also introduced into the capillary and fixed at its entrance end. Among other things, the capillary serves for the decoupling of external, non-thermal influences. The optical fiber generally does not exit the capillary at another end. Typically, the capillary is sealed on all sides, and the fixation of the optical waveguide at the inlet end of the capillary is a sealing fixation. For example, the capillary is substantially tubular. The tubular formation of the capillary has in particular a cylindrical shape. The optical waveguide is introduced into the capillary and fixed at the inlet end of the capillary, such that the region of the optical waveguide which has the at least one integrated temperature sensor element surrounded by the cladding is located completely inside the capillary and typically the only fixation area at the entrance end of the capillary - otherwise it is freely movable in the capillary.

The cladding material is selected such that its coefficient of thermal expansion is greater than the thermal expansion coefficient of the optical waveguide material such that the temperature sensitivity of the integrated temperature sensor element is measurably increased. For example, the cladding material may be selected such that the temperature sensitivity of the integrated temperature sensor element is increased by a factor greater than or equal to 2 over a comparable conventional temperature sensor element which exclusively utilizes the thermo-optic effect for temperature measurement.

A temperature sensor described herein may have a sensitivity or resolution at least as great as that of an electrically operating temperature sensor. At the same time, the temperature sensor described herein is metal-free and can be used in applications where the absence of metal is desirable or essential, for example, when incorporation of an electrically conductive material can adversely affect operation or measurement operations.

In embodiments, the envelope has a spring constant which is greater than the spring constant of the optical waveguide, at least in the region of the fixings between the envelope and the optical waveguide. The spring constant depends on the material-related modulus of elasticity and the wall thickness of the respective component. The spring constant of a component can be increased, for example, by selecting a material with a greater modulus of elasticity and / or increasing the wall thickness of the component. Such a ratio of spring constants can help to further improve sensitivity or resolution.

In embodiments, the wrapping material comprises a ceramic material containing zirconia (zirconia). Typically, the ceramic material consists essentially entirely of zirconia. Optionally, the wrapping material is substantially completely formed of the ceramic material. An envelope having the ceramic material may be very small, d. H. with a small extent and only a small radial distance from the temperature sensor element can be formed. In addition, a coating having the ceramic material is very stable and mechanically resistant and can be processed comparatively easily.

In further embodiments, the wrapping material comprises a plastic material containing polyimide. Typically, the plastic material is substantially entirely polyimide. Optionally, the wrapping material is substantially completely formed of the plastic material. Polyimide has a comparatively high coefficient of expansion and can greatly contribute to increasing the sensitivity or resolution of the temperature sensor. Polyimide is substantially free of plasticizers, which ensures good crosslinking with an epoxy material, for example in the region of the inlet end or the outlet end of the coating. This may result in an age-resistant and / or resilient connection. Polyimide can also help prevent drifting of the values.

In embodiments, the capillary material comprises a resinous material containing epoxide. Typically, the capillary material consists essentially entirely of epoxide. Optionally, the capillary material is substantially completely formed of the resin material.

In embodiments, the optical waveguide comprises a plurality of integrated temperature sensor elements. The individual temperature sensor elements are spaced from one another in the direction of an axis of the optical waveguide, for example, lined up along the axis in uniform or non-uniform distances to each other. Each of the temperature sensor elements has its own enclosure. The individual sheaths do not merge into one another, but are spaced from one another along the direction of the axis of the optical waveguide. Each temperature sensor element is housed in its associated enclosure, and the optical waveguide is accordingly respectively fixed at the entrance end of the enclosure and at the exit end of the enclosure such that the respective associated temperature sensor element detects a strain of expansion enhanced by the enclosure upon temperature change.

For example, the individual temperature sensor elements are spaced from each other by more than 3 cm or more than 5 cm or more than 10 cm. The distance between the individual temperature sensor elements, ie the spatial density of temperature sensor elements in the optical waveguide, need not be uniform. It can be provided, for example, to adapt the spatial density of the temperature sensor elements to an expected temperature distribution in a measurement object at or in which the temperature sensor is arranged or mounted.

In this case, several or all enclosures of the plurality of integrated temperature sensor elements can be surrounded by the same capillary. In this case, the number of capillaries needed is reduced, which may be more cost effective.

list of figures

• 1 eine schematische Querschnitts-Seitenansicht eines Temperatursensors gemäß einer Ausführungsform;
• 2 eine schematische Querschnitts-Seitenansicht eines Temperatursensors gemäß einer weiteren Ausführungsform;
• 3 ein Diagramm, das einen schematischen Messaufbau zur Durchführung einer Temperaturmessung mit dem Temperatursensor gemäß einer Ausführungsform zeigt;

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. In the drawings show:

• 1 a schematic cross-sectional side view of a temperature sensor according to an embodiment;
• 2 a schematic cross-sectional side view of a temperature sensor according to another embodiment;
• 3 a diagram showing a schematic measurement structure for performing a temperature measurement with the temperature sensor according to an embodiment;

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be explained in more detail. The drawings are illustrative of one or more examples of embodiments. Unless otherwise noted, the same or equivalent elements have the same reference numerals.

Embodiments described herein relate, inter alia, to a temperature sensor, generally designated 100, and in one embodiment, in the cross-sectional side view of FIG 1 and in a further embodiment in the cross-sectional side view of 2 is shown. In the schematic measuring structure in 3 In the illustration, a temperature sensor similar to the one in 2 shown for use; this serves in 3 however, only for the sake of illustration and is not meant to be limiting.

The temperature sensor 100 includes an optical fiber 10 which is at an axial entry end E1 in a capillary 30 is introduced. The optical fiber 10 includes in the embodiment shown by way of example a temperature sensor element 11 , which is designed as a fiber Bragg grating. The fiber Bragg grating is for example by means of a laser in the optical waveguide 10 enrolled. The temperature sensor elements described herein are not limited to fiber Bragg gratings, although the following exemplary description of the embodiment assumes fiber Bragg gratings.

The capillary 30 is in the embodiment of a glass capillary, but it can also be made of other suitable metal-free materials such. B. plastic be formed. The optical fiber 10 is at the entrance end E1 with a fixing element 41 at the capillary 30 fixed. The fixing element 41 is formed, for example, of an adhesive or a resin and is so with the optical waveguide 10 connected, that at least in the direction of the axis A at the optical waveguide 10 acting forces (axial forces) from the capillary 30 at the entrance end E1 be recorded. The fixing element may also be the entrance end E1 caulk. In addition, at the axial end E2 the capillary 30 , the entry end E1 opposite, a closure element 42 provided that the axial end E2 seals. The closure element 42 Again, for example, is formed of an adhesive or a resin. The optical fiber 10 is not out of the axial end E2 the capillary 30 led out, leaving the area of the optical fiber 10 with the temperature sensor element 11 freely suspended in the capillary 30 is arranged. This area is characterized by the capillary 30 decoupled from non-thermal influences and by means of the capillary 30 protected.

The temperature sensor element 11 is from a serving 20 surround. In this case, the temperature sensor element 11 from that in the embodiment according to 1 cylindrical tubular casing 20 radially spaced. The optical fiber 10 occurs at an entry end E3 into the serving 20 on and at an exit end E4 from the wrapper. The entry end E3 the serving 20 is on the fiber optic cable 10 with a fixing element 21 fixed; as well is the exit end E4 the serving 20 on the optical fiber 10 with a fixing element 22 fixed. The fixing elements are in turn each formed, for example, from an adhesive or a resin.

The serving 20 is formed of a non-metal material whose coefficient of thermal expansion is greater than the thermal expansion coefficient of the material of the optical waveguide 10 , For example, the wrapper is 20 formed of a ceramic material containing zirconia or formed substantially entirely of zirconia. Alternatively, the envelope is 20 formed of a plastic material containing polyimide or formed substantially entirely of polyimide.

In addition, it may be provided that the spring constant of the envelope at least in the region of the inlet end E3 and exit end E4 is greater than the local spring constant of the optical waveguide 10 ,

The thermally induced expansion or compression effect on the temperature sensor element 11 is by the serving 20 amplified, so that the temperature sensor 100 shows a high sensitivity or resolution. The structure is also metal-free, resulting in a wide range of applications.

2 shows a schematic cross-sectional side view of a temperature sensor 100 according to a further embodiment. The above with reference to 1 Descriptions will not be repeated. In addition to that also in 1 shown temperature sensor element 11 is in 2 another temperature sensor element 11 provided along the axis A spaced from the temperature sensor element 11 is arranged and its own wrapping 20 having. Both temperature sensor elements 11 are in the same capillary 30 arranged.

Several temperature sensor elements 11 in a single optical fiber 10 can allow a measurement of the respective temperature or temperature change at different spatial positions. When the temperature sensor 100 out 2 is arranged or mounted on or in a measurement object, the respective temperatures can be measured at different locations in or on the measurement object. With an associated measurement, several measurement signals can be determined. An assignment of the individual measurement signals to the locations in or on the measurement object takes place, for example, via the known and / or previously determined different characteristics of the temperature sensor elements 11 , In the case of the fiber Bragg gratings shown by way of example, the assignment takes place, for example, via the respective characteristic wavelength; Accordingly, the assignment takes place in backscatter elements for a fiber optic backscatter measurement method on the respective characteristic scatter pattern.

3 is a diagram showing a schematic measurement setup for performing a temperature measurement with the temperature sensor 100 out 1 or 2 shows. The temperature sensor 100 is on or in a test object 200 arranged, whose temperature or location-specific temperatures to be determined.

The one from the measurement object 200 led out optical fiber 100 is optically with a beam splitter 110 connected. Behind the beam splitter, the optical fiber 10 preferably with broadband measuring light from a measuring light source 120 be applied to the temperature sensor elements 11 of the optical waveguide is guided and is reflected there wavelength-dependent. Returning measuring light can after passing through the beam splitter 110 with a possibly wavelength-sensitive photosensor 130 be detected. A measurement control 140 controls the measuring light source 120 and the photosensor 130 accordingly and evaluates the signals from the photosensor 130 out.

When the temperature changes, the temperature sensor elements become 11 in the optical fiber 10 mechanically stretched or compressed. The thermo-optic effect also has an effect on the behavior of the temperature sensor elements 11 , The thermo-optic effect can have a stronger influence on the behavior of the temperature sensor elements 11 as an elongation or compression, for example a ten times stronger effect. A Bragg reflection wavelength of the temperature sensor elements formed as fiber Bragg gratings 11 is a measure of the temperature change ΔT: $$\frac{\Delta \lambda }{\lambda }=k\cdot \Delta T$$

The constant k depends on the material of the optical waveguide. The characteristic wavelengths of the temperature sensor elements formed in the embodiment as a fiber Bragg grating 11 differ from each other. This makes it possible, the measurement signals of the individual temperature sensor elements 11 to distinguish from each other.

Although the embodiments of the present invention have been described above by means of typical embodiments, it is not limited thereto, but modifiable in many ways. Also, the invention is not limited to the applications mentioned.

Claims (9)

A temperature sensor (100) comprising: an optical waveguide (10) of an optical waveguide material having at least one integrated temperature sensor element (11); a cladding (20) of a non-metallic cladding material radially spaced from the optical waveguide (10) and surrounding the temperature sensor element (11) of the optical waveguide (10); a capillary (30) of a non-metallic capillary material that is radially spaced from the sheath (20) and at least partially surrounding the sheath (20), wherein the optical waveguide (10) at an entrance end (E3) of the sheath (20) on the sheath ( 20) is fixed, wherein the optical waveguide (10) at an outlet end (E4) of the sheath (20) is fixed to the sheath (20), wherein the optical waveguide (10) at an inlet end (E1) of the capillary (30) on the Capillary (30) is fixed, wherein the cladding material has a thermal expansion coefficient which is greater than the thermal expansion coefficient of the optical waveguide material. Temperature sensor (100) after Claim 1 wherein the envelope has a spring constant which is greater, at least in the region of the fixations, than the spring constant of the optical waveguide. A temperature sensor (100) according to any one of the preceding claims, wherein the cladding material comprises a ceramic material containing zirconia, typically a ceramic material consisting essentially of zirconia. Temperature sensor (100) after Claim 1 or 2 wherein the wrapping material comprises a plastic material containing polyimide, typically a plastic material consisting essentially of polyimide. A temperature sensor (100) according to any one of the preceding claims, wherein the capillary material comprises a resinous material containing epoxide, typically a resinous material consisting essentially of epoxide. Temperature sensor (100) according to one of the preceding claims, wherein the sheath and / or the capillary are each formed cylindrical-tubular. Temperature sensor (100) according to one of the preceding claims, wherein the at least one integrated temperature sensor element (11) comprises a fiber Bragg grating and / or a backscatter element for a fiber optic Rückstreumessverfahren. Temperature sensor (100) according to one of the preceding claims, wherein the optical waveguide (10) comprises a plurality of integrated temperature sensor elements (11), typically two or three or more integrated temperature sensor elements (11), wherein the individual temperature sensor elements (11) from each other in the direction of Axis (A) of the optical waveguide are spaced, wherein each of the temperature sensor elements (11) has its own enclosure (20). Temperature sensor (100) after Claim 8 in which several or all sheaths (20) are surrounded by the same capillary (30).

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