Use of a device for measuring air temperature

Abstract

The invention relates to a use of a measuring device (1) comprising at least one optical fiber (3) coated with an external coating (4), which is made of a material having an emissivity (ε) less than or equal to 0.1, which is bare, which is exposed to air over at least a major part of a length of the optical fiber (3) and which has an external diameter less than or equal to 200 µm, for measuring the air temperature at at least one measuring point (x) located on an external surface of the external coating (4). Figure for abstract: Figure. 4A

Description

Title of the invention: Use of a device for measuring air temperature

[0001] The invention relates to a device for measuring air temperature, as well as its use.

[0002] The field of the invention relates to measurements of the air temperature in premises, such as for example in nuclear power plants for producing electricity.

[0003] One of the problems with air temperature measuring devices is measurement bias caused by radiative effects.

[0004] Radiative effects correspond to the consequences in terms of thermal exchanges on a body, of the electromagnetic radiation emitted by another (radiating) body. This mode of heat transfer takes place without transport of matter depending on the temperature of the radiating body. The higher the temperature of the radiating body, the more intense the thermal radiation is at short wavelengths. An example illustrating this mode of transfer concerns the thermal radiation emitted by the sun, which is located mainly in the visible range.

[0005] Air is a medium that is almost transparent to thermal radiation. However, any air temperature measuring instrument evaluates the air temperature from its own temperature and, as a solid body, exchanges thermal radiation with its environment, which generally results in measurement biases that can be of the first order. In industrial premises with relatively hot surface pipes (above 100°C), it is for example possible to observe differences greater than 5°C between the air temperature and the temperature seen by the probe used to measure the air temperature. These systematic measurement errors or measurement biases are not directly correctable, because they depend on the orientations and temperatures of each radiating body.

[0006] Air temperature measurements are generally intended to ensure that the equipment associated with these environments or temperature measurement zones is or will be in suitable conditions for the intended activities.

[0007] For example, in premises with electrical equipment (such as computer data centers, electrical connection panels, motors), an increase in temperature could either promote premature wear or induce a failure that could partially or totally compromise certain functionalities allocated to this equipment. This may also concern work spaces where the maximum temperature is generally regulated.

[0008] The different fields where such measurements are carried out are relatively diverse. and can be in the field of meteorology where we generally seek to measure atmospheric temperature, in the biological and medical field where we wish to finely control the temperature and quality of the air to avoid, for example, the development of bacteria, fungi or mites, in the field of physical measurement where we wish to have controlled measurements to participate in the characterization of physical phenomena.

[0009] In particular, the field of the invention relates to instruments and methods for measuring air temperature in an environment presenting or capable of presenting significant exchanges by radiation. This concerns both industrial premises with equipment having hot surfaces and outdoor environments where there is significant sunlight. The professions concerned are those seeking to have metrologically controlled air temperature measurements, that is to say with confidence and a guarantee regarding the measurements resulting from the air temperature measurement processes.

[0010] In the context of physical measurements, this makes it possible, for example, to justify the sizing of a system, and to validate or not the reception of an installation.

[0011] Known solutions implemented are point measurements using a material as a temperature vector: the sensor measures the temperature of the probe.

[0012] When the environment in which the measurement is to be carried out is subject to significant radiative effects (this may come for example from hot pipes, electrical equipment cabinets, or even high levels of sunlight), the material of the sensitive probe is influenced by the heat input brought by the radiation, which induces an error in the measurement of the air temperature.

[0013] This measurement bias cannot be characterized a priori (because it itself depends on the temperatures of surrounding surfaces).

[0014] An objective of the invention is to obtain a use of a temperature measuring device, which solves the above-mentioned problem related to measurement biases and which makes it possible to reliably and locally measure the air temperature in the possible presence of external radiating elements.

[0015] To this end, a first object of the invention is a use of a measuring device comprising at least one optical fiber coated with an external coating, which is made of a material having an emissivity less than or equal to 0.1, which is bare, which is exposed to air over at least a major part of a length of the optical fiber and which has an external diameter less than or equal to 200 μm, for measuring the air temperature at at least one measuring point located on an external surface of the external coating.

[0016] Thanks to the invention, the optical fiber has a small external diameter, in order to promote convective effects, and has a low-emissivity coating over a large part of the spectrum (particularly in the visible and infrared), which limits radiative heat exchanges and ultimately makes the biases of radiative effects negligible. We recall that convective effects correspond to the consequences in terms of heat exchanges at the interface between a fluid and a solid or a liquid, generated by the internal movements animating the fluid.

[0017] Furthermore, the invention avoids having to have as many probes as sampled measurement points, which are restrictive in terms of implementation. The invention avoids in particular the following difficulties: as many measurement channels as sensors, as many calibrations as sensors, wired connections of the equipment, high costs, effects of disturbance of the air flow, low fineness of the mesh.

[0018] According to one embodiment of the invention, the material of the external coating is metallic.

[0019] According to one embodiment of the invention, the material of the external coating is aluminum.

[0020] According to one embodiment of the invention, the material of the external coating is gold.

[0021] According to one embodiment of the invention, the measuring device comprises a module for sampling several temperature measurements at several measuring points along the length of the optical fiber.

[0022] According to one embodiment of the invention, the measuring device comprises at least one pair of supports spaced apart from each other,

[0023] the at least one optical fiber coated with the outer coating is attached to the supports and extends between the supports over the majority of the length of the optical fiber, the outer coating of which is bare and exposed to the air.

[0024] According to one embodiment of the invention, the supports comprise posts.

[0025] According to one embodiment of the invention, several sections of the length of the optical fiber coated with the outer coating, each extend in a first measurement direction between the supports of the at least one pair of supports and are spaced from each other at least in a second direction perpendicular to the first measurement direction.

[0026] According to one embodiment of the invention, the sections of the length of the optical fiber coated with the external coating are located in a measurement plane comprising the first measurement direction and the second direction.

[0027] According to an embodiment of the invention, a two-dimensional temperature map is calculated by a computer of the measuring device, by interpolation of the temperature measurements taken respectively at the measuring points along the length of the optical fiber, to calculate the temperature at points interpolation of the measurement plane, which are located between the sections of the optical fiber of the at least one pair of supports and / or which are located between the measurement points along the length of the optical fiber.

[0028] According to one embodiment of the invention, the measuring device comprises several optical fibers coated with the external coating and respectively several pairs of supports, spaced along a third direction, which is perpendicular to the first measurement direction and to the second direction,

[0029] the optical fibers coated with the outer coating being fixed respectively to the supports of the pairs and extending respectively between the supports of the pairs over the major part of the length of the optical fibers, the outer coating of which is bare and exposed to the air.

[0030] According to an embodiment of the invention, a three-dimensional temperature map is calculated by a computer of the measuring device, by interpolation of the temperature measurements taken respectively at the measuring points along the length of the optical fiber, to calculate the temperature at interpolation points in space, which are located between the sections of the optical fiber spaced apart along the third direction and / or which are located between the sections of the optical fiber along the second direction and / or which are located between the measuring points along the length of the optical fiber.

[0031] According to one embodiment of the invention, the measuring device comprises a screen for displaying the mapping.

[0032] According to an embodiment of the invention, the second direction is vertical, the sections of the length of the optical fiber have between them a spacing in the second direction, which is smaller at the top than at the bottom.

[0033] According to one embodiment of the invention, at least a first of the optical fibers and at least a second of the optical fibers are arranged at a distance from an object and on either side of the object in the third direction, for measuring the temperature on either side of the object in the third direction.

[0034] According to one embodiment of the invention, the measuring device comprises a calculation module, which is connected to at least one end of the optical fiber and which is configured to calculate the temperature of the air at at least one measurement point located on the external surface of the external coating, by reflectometry of first signals emitted in the optical fiber, to calculate the at least one measurement of the temperature at at least one measurement point on the external surface of the optical fiber.

[0035] According to one embodiment of the invention, the calculation module comprises at least one Raman type interrogator.

[0036] According to one embodiment of the invention, the Raman type interrogator comprises at least one transmitter for emitting first signals along the fiber optical, at least one receiver for receiving second signals, which are reflected by the optical fiber in response to the first signals, and a calculator configured to calculate the temperature from a ratio ( ) of power of two lines of PaitJ) different prescribed frequencies, which correspond to a Stokes peak and an anti-Stokes peak and which are present in the second signals.

[0037] According to one embodiment of the invention, the calculator is configured to calculate the temperature T(t. Z) according to the following equation:

[0038] n ( 7777) ) +£■ U ) 7 / la

[0039] where Ps is the power of the Stokes peak measured by the receiver, Pa<; is the power of the anti-Stockes peak measured by the receiver, t is the time, l is the abscissa of the measurement point along the first direction along the optical fiber from the Raman interrogator, Toffset is a prescribed coefficient of the Raman interrogator, Aa is a prescribed coefficient of differential attenuation between the Stockes peak and the anti-Stockes peak, y and C(t) are intrinsic parameters of the Raman interrogator.

[0040] According to one embodiment of the invention, a computer of the measuring device performs a spatial recalibration of the measurements of the air temperature along the length of the optical fiber, by identifying by the computer the temperature measured at at least one prescribed position along the length of the at least one optical fiber, on which a source of prescribed temperature gradient is imposed on the external coating.

[0041] According to one embodiment of the invention, the prescribed position of the temperature gradient source is located on at least one of the supports.

[0042] According to one embodiment of the invention, the prescribed temperature gradient source is arranged on the outer coating in several prescribed positions located respectively on several sections of the length of the optical fiber coated with the outer coating, spaced from each other at least in the second direction.

[0043] According to one embodiment of the invention, the prescribed temperature gradient source comprises a heating cable.

[0044] According to one embodiment of the invention, the same heating cable passes over the prescribed positions located on the same support.

[0045] According to one embodiment of the invention, the computer performs spatial oversampling of temperature maxima located at prescribed positions located on the same support, in order to perform spatial recalibration of the air temperature measurements along the length of the optical fiber.

[0046] According to another embodiment of the invention, the prescribed temperature gradient source comprises a cold air projection source.

[0047] The invention will be better understood on reading the description which follows, given solely by way of non-limiting example with reference to the figures below of the attached drawings.

[0048] [Fig. 1] represents a schematic view of an optical fiber coated for use in the air temperature measuring device according to the invention.

[0049] [Fig.2] represents a schematic view of the temperature measuring device of the air according to the invention.

[0050] [Fig.3] represents a schematic view of the temperature measuring device of the air according to one embodiment of the invention.

[0051] [Fig.4A] represents a schematic front view of the air temperature measuring device according to one embodiment of the invention.

[0052] [Fig.4B] represents a schematic top view of the air temperature measuring device according to one embodiment of the invention.

[0053] [Fig.4C] represents a schematic front view of a part of the air temperature measuring device according to an embodiment of the invention.

[0054] [Fig.5] represents an example of one-dimensional temperature mapping of the air, obtainable by the air temperature measuring device according to one embodiment of the invention.

[0055] [Fig.6] represents an example of two-dimensional mapping of the temperature of air, obtainable by the air temperature measuring device according to one embodiment of the invention.

[0056] [Fig.7] represents an example of three-dimensional mapping of the temperature of air, obtainable by the air temperature measuring device according to one embodiment of the invention.

[0057] Embodiments of the air temperature measuring device 1 according to the invention are described in more detail below with reference to FIGS. 1, 2, 3, 4A, 4B, 4C, 5, 6, 7, as well as a use of this air temperature measuring device 1 according to the invention.

[0058] In [Fig.l], the measuring device 1 comprises an optical fiber 3 coated with an external coating 4.

[0059] The optical fiber 3 may comprise a core 3a having a certain index for the propagation of signals in and along the optical fiber 3, which extends in a first measurement direction X. The signals are in a certain spectrum, visible or infrared, for example in the wavelength range from 0.3 pm to 100 pm. The optical fiber 3 may comprise an optical cladding 3b having an index lower than the index of the core 3a.

[0060] The external coating 4 is made of a material having an emissivity e less than or equal to 0.1. In a preferred embodiment, the emissivity e is less than or equal to 0.05. The outer coating 4 has a bare outer surface 40, which is exposed to the air over at least a major part of a length of the optical fiber 3, which extends along a first measurement direction X. The outer coating 4 has an outer diameter d, which is less than or equal to 200 μm. The measuring device 1 is configured to measure the air temperature at at least one measuring point x or at several measuring points x, which is (are) located on the outer surface 40 of the outer coating 4. Of course, several optical fibers 3 each coated with its outer coating 4 could be provided in the measuring device 1. The optical fiber 3 coated with the outer coating 4 forms a sensor of the local air temperature at the measuring point(s) x located on the outer surface 40 of the outer coating 4. The optical fiber 3 coated with the outer coating 4 can be rectilinear along the first measurement direction X.The first X direction of measurement can be horizontal, or other.

[0061] The Stefan-Boltzmann law defines the relationship between thermal radiation and the temperature T of an object, of emissivity e, considered as a black body, according to the following equation:

[0062] — gcrT4

[0063] where o is the Stefan-Boltzmann constant.

[0064] The external coating 4 with low emissivity e therefore acts as a radiative shield and makes it possible to limit the thermal radiation RTH captured by the material of the fiber 3. The small external diameter d of the external coating 4 makes it possible to increase the convection coefficient of the fiber 3 thus coated compared to the radiative coefficient thereof. This therefore favors taking into account the convective effects ECV near the external coating 4.

[0065] The low emissivity e of the external coating 4 of the optical fiber 3, associated with its external diameter d, makes it possible to reduce the measurement bias of the air temperature on the external surface 40 of the external coating 4 of the optical fiber 3. This measurement bias is in fact caused by the thermal radiation, which is emitted by surrounding objects or surfaces, towards this external coating 4.

[0066] This prevents the measurement of the air temperature on the external surface 40 of the external coating 4 from being distorted by surrounding thermal radiation.

[0067] The invention thus makes it possible to multiply the points x for measuring the air temperature along an optical fiber, without modifying the overall air flows, and makes it possible both to overcome the usual measurement biases caused by radiative effects and to allow, in addition, a spatial meshing of the temperature measurement in one, two or three dimensions and for example of a given volume of air. The invention makes it possible to measure by a single sensor 30, formed of the optical fiber 3 and its external covering 4 (in the case where a single aforementioned sensor 30 is provided) the air temperature at several measurement points x. Of course, several sensors 30 can be provided, as described below with reference to Figures 4B and 4C.

[0068] The material of the outer coating 4 having an emissivity e less than or equal to 0.1 may be metallic, for example gold or aluminum, or other. The surface condition of the outer coating 4 may be polished or ultra-polished. The emissivity e of the material of the outer coating 4 made of aluminum may be, for example, of the order of 0.05. The emissivity e of the material of the outer coating 4 made of gold may be, for example, of the order of 0.02.

[0069] The invention allows a measurement of the temperature T of the air subjected to a broad electromagnetic spectrum, visible and infrared, for example from 0.3 pm to 100 pm. The emissivity e is considered in this spectrum.

[0070] The optical fiber may be, for example, made of silica, or other. The optical fiber 3 may be single-mode, or preferably multi-mode.

[0071] In one embodiment, as illustrated in Figures 2 and 3, the measuring device 1 comprises a module 6 for sampling several measurements of the temperature T at respectively several measurement points x along the length of the optical fiber 3. This sampling module 6 can be provided in the calculation module 2 described below or in the Raman type interrogator 20 described below.

[0072] In one embodiment, as illustrated in Figures 2 and 3, the measuring device 1 comprises a calculation module 2, by reflectometry of first signals emitted in the optical fiber 3, to calculate several measurements of the temperature T at respectively several measurement points x on the external surface 40 of the optical fiber 3, distributed along the first measurement direction X. The calculation module 2 is connected to at least one end 32 of the optical fiber 3 and is configured to calculate the temperature T of the air at the measurement points x located on the external surface 40 of the external coating 4.The measurements of the temperature T are calculated on the principle of the OTDR (in English: Optical Time-Domain Reflectometer, or optical time-domain reflectometry) from first signals SI, which are emitted by one (or more) transmitters 21 (for example one or more laser sources 21) of the module 2 and which propagate along the optical fiber 3, and from second signals S2, which are reflected by defects in the optical fiber 3 in response to the first signals S1 and which are received by one (or more) receivers 22 (for example one (or more) photodiodes 22) of the module 2. The transmitter(s) 21 is (are) connected to the end 32 of the optical fiber 3 via a multiplexer 23 of the module 2. The receiver(s) 22 is (are) connected to the end 32 of the optical fiber 3 via the multiplexer 23. The transmitter(s) 21 and the receiver(s) 22 are connected to a control unit 24 configured to control these as well as . the multiplexer 23. This control unit 24 includes the calculation means or calculators described below.

[0073] The control unit 24 comprises the module 6 for sampling several measurements of the temperature T at respectively several measurement points x along the length of the optical fiber 3. The measurement points x can be distributed in a regular manner according to a fixed pitch PX along the optical fiber 3 in the first direction X. There is at or near each measurement point x a aforementioned defect in the optical fiber 3, which will reflect the second signals S2. The fixed pitch PX is greater than the distance between the aforementioned defects in the optical fiber 3 in the first direction X. There are therefore in each fixed pitch PX several aforementioned defects in the optical fiber 3. May be greater than or equal to 1 cm and less than or equal to 30 cm. The fixed pitch PX may for example be of the order of 15 cm.

[0074] Thus illustrated in Figure 3, the calculation module 2 may be or comprise at least one Raman type interrogator 20 or Raman type spectrometer. The Raman effect is a physical phenomenon of inelastic scattering of a photon of the first signals emitted along the optical fiber 3. The inelasticity of the scattering of the first signals SI along the optical fiber 3 causes an exchange of energy between the photon and the fiber 3, which causes a modification of the wavelength of the second reflected signals S2. In the case of measurement by optical fiber by Raman effect, the temperature for different lengths of optical fiber 3 is calculated by the calculator 24 from the power ratio (or the inverse) between two lines S2a, S2b of frequencies of PM different prescribed peaks (called Stokes peak S2a and anti-Stokes peak S2b) reflected in the second signals S2 at defects along the optical fiber 3, these defects being unprescribed and random along the optical fiber 3. For this purpose, the receiver 22 may comprise a first receiver 22a making it possible to detect and measure in the second signals S2 the power Ps of the Stokes peak S2a, and a second receiver 22b making it possible to detect and measure in the second signals S2 the power P^ of the anti-Stokes peak S2b. At the same measurement point x, a modification of the temperature T on the external surface 40 of the external coating 4 modifies this ratio and therefore the measurement of the temperature T, carried out by the module 2.

[0075] For example, the Raman type interrogator 20 emits as first signals SI a monochromatic laser pulse (for example, for a silica optical fiber 3, at 1064 nm and 1550 nm) and measures by the receivers 22a and 22b the powers Ps and Pas backscattered within the fiber 3 at the two prescribed frequencies S2a, S2b of the Stokes and anti-Stokes peaks. The instant of return of the pulse in the second reflected signals S2 relative to the instant of emission of the first emitted signals SI makes it possible to calculate t. At any instant t and at any measurement point x having the abscissa l along the fiber optical 3 from the Raman type interrogator 20, the ratio between the power of these two peaks S2a, S2b is linked to the temperature T = T ( 1, l) of the fiber 3 by the following formula:

[0076] r(u) = r,, / to + r ln[l^)+cpp!

[0077] Where is the power of the Stokes peak S2a, Pas is the optical power of the anti-Stockes peak S2b, measured by the photodiodes of the interrogator 20, T^ff^ is the coefficient of the interrogator 20 to correct for a constant bias, is the differential attenuation coefficient (aaS - a^) between the Stockes peaks S2a and anti-Stockes peaks S2b, P and C(t) are prescribed intrinsic parameters of the interrogator 20. The quantity , , f1 / \ , where a(x) is the differential attenuation between the Stockes peak and the lAa-]Qa(x)dx v 7 anti-Stockes peak at the abscissa point x.

[0078] The parameter C = C(t) can either have been calibrated or have been calculated in advance using a portion of fiber 3 internal to the interrogator 20 and a conventional temperature measurement, that is to say at the abscissa 1 between 0 and L, where L is the length of the fiber 3 between its two ends 32 and 33.

[0079] In one embodiment of the invention, Z Az can be calculated in the following manner.

[0080] A first measurement is carried out at the abscissa / by connecting the interrogator 20 to the first end 32 of the optical fiber 3, having the abscissa 0, that is to say in the direct direction, noted ' below, to obtain the optical power P~^stokes(.Q of the Stokes peak 32a of this first measurement and the optical power P^ ant[^.stokes(.^^a anti-Stockes peak S2b of this first measurement.

[0081] Then, a second measurement is carried out at the abscissa l by connecting the interrogator 20 to the second end 33 of the optical fiber 3 (the one far from the first end 32), having the abscissa L, that is to say in the indirect direction, noted below, to obtain the optical power P*~$tokeS (0 Pæ Stokes S2a of this second measurement and the optical power an^[—stokes^) of the Pæ and'Stockes S2b of this second measurement.

[0082] The quantity , , d , , , is calculated according to the following equation: l Aa-Joa(x)ax fl, a. 1 A / P f Stokes^) \ . / P' StokesO) \\ „ a{x)dx ~ - In —--——— - In I —------- - E Jq £ \ \* anti—StokesKU / anti—stûkÉsHJ / /

[0083] with i / , / \ , 2\ V \mti~Stokesfâ anti-StokesC

[0084] This quantity E = E(t) can be calculated by making third and fourth measurements corresponding to the first and second measurements for the abscissa 1 = 0.

[0085] Then the temperature T = T ( L l ) of the fiber 3 can be calculated by the following formula: 0 = : -----------------T------------- 1 / > / P stokes^> 0 \ St <ikeç(b \ । 7 A TC - + ln p*- f I t y + C(O + ^(0 yv anti-stokes x1! LJ / v anti-Stokes^r J

[0086] In one embodiment of the invention, illustrated in Figures 4A, 4B, 4C, the measuring device 1 comprises a pair of supports 5 spaced apart from each other, to which the optical fiber 3 coated with the outer coating 4 is fixed. The optical fiber 3 coated with the outer coating 4 extends between the supports 5 along the first measurement direction X over the majority of the length of the optical fiber 3, the outer coating 4 of which is bare and exposed to the air between the supports 5. Each support 5 may be formed by a post or the like, which may for example be vertical or the like. Several pairs of supports 5 may be provided in the measuring device 1.

[0087] In one embodiment of the invention, illustrated in Figures 4A, 4B, 4C, several sections 31, hereinafter called main sections 31, of the length of the same optical fiber 3 coated with the external coating 4, each extend in the first measurement direction X between the supports 5 of the pair of supports 5 and are spaced from each other at least in the second direction Z perpendicular to the first measurement direction X. For example, the first measurement direction X may be horizontal and the second direction Z may be vertical. The optical fiber 3 coated with the external coating 4 and for example back and forth between the supports 5 or posts 5. The main sections 31 may be rectilinear in the first measurement direction X. The main sections 31 may be connected one after the other by curved secondary sections 34 of the optical fiber 3 coated with the external coating 4.In Figure 4, the secondary sections 34 are symbolically represented by straight lines but are curved. The radius of curvature of the curved secondary sections 34 is greater than the minimum radius of curvature of the optical fiber 3 coated with the external coating 4 (minimum radius of curvature before breaking), and is for example greater than 1.5 times this minimum radius of curvature. This minimum radius of curvature may be of the order of 200 times the external diameter d of the external coating 4. Means 340 for fixing the secondary sections 34 to the supports 5 are provided. These fixing means may comprise adhesive tapes 340, or . any other mechanical fastener. Each post 5 may be made of an electrically insulating material, such as PVC or other.

[0088] In one embodiment of the invention, illustrated in Figures 4A, 4B, the sections 31 of the length of the optical fiber 3 coated with the external coating 4 are located in a measurement plane P comprising the first measurement direction X and the second direction Z. The measurement plane P may be vertical or other. This makes it possible to have a mesh of the temperature measurement in each measurement plane P (for example between the supports 5), without causing an obstruction effect on the air flow.

[0089] In one embodiment of the invention, illustrated in Figures 1, 2, 3, 4A, 4B, 4C, 5, 6, 7 and 8, the measuring device 1 comprises (for example in the measuring module 2 or in the Raman type interrogator 20 or in the control unit 24) a calculator 8 configured to calculate by interpolation the temperature at interpolation points which are located between the measuring points x along the length of the optical fiber 3. This interpolation can be for example linear. This makes it possible to improve the spatial meshing of the temperature measurement in one dimension along the optical fiber 3, without causing an obstruction effect on the air flow.

[0090] In one embodiment of the invention, illustrated in Figures 2, 3 and 5, the measuring device 1 comprises (for example in the measuring module 2 or in the Raman type interrogator 20 or in the control unit 24) a computer 8 configured to calculate a one-dimensional map 10 of the temperature, by interpolation of the measurements of the temperature T taken respectively at the measuring points x along the length of the optical fiber 3, to calculate the temperature at interpolation points A along the fiber 3 along the measurement direction X, the interpolation points A being located between the measuring points x along the length of the optical fiber 3 along the first measurement direction X. This interpolation can be, for example, linear.The measuring device may include a screen allowing the one-dimensional temperature map 10 to be viewed, with different gray or color levels depending on the temperature value at each point A and x, as shown by way of example in [Fig.5].

[0091] In one embodiment of the invention, illustrated in Figures 2, 3, 4A, 4B, 4C and 6, the measuring device 1 comprises (for example in the measuring module 2 or in the Raman type interrogator 20 or in the control unit 24) a calculator 8 configured to calculate a two-dimensional map 10 of the temperature, by interpolation of the measurements of the temperature T taken respectively at the measuring points x along the length of the optical fiber 3, to calculate the temperature at interpolation points A of the measuring plane P, the interpolation points A of the measuring plane P being located between the sections 31 of the optical fiber 3 of the pair of supports 5 and / or being located between the measuring points x along the length of the optical fiber 3 following the first measurement direction X. This interpolation can be linear, for example. The measuring device can include a screen for viewing the two-dimensional temperature map, with different gray or color levels depending on the temperature value at each point, as shown as an example in [Fig.6].

[0092] In one embodiment of the invention, illustrated in Figures 2, 3, 4A, 4B, 4C and 7, the measuring device 1 comprises several optical fibers 3 coated with the outer coating 4 and respectively several pairs of supports 5, to each of which is fixed one of these optical fibers 3 coated with the outer coating 4. The pairs of supports 5 are spaced along the third direction Y, which is perpendicular to the first measurement direction X and to the second direction Z. The third direction Y may be horizontal or other. The optical fibers 3 coated with the outer coating 4 are fixed respectively to the pairs of supports 5 and extend respectively between the supports 5 of the pairs over the major part of the length of the optical fibers 3, the outer coating 4 of which is bare and exposed to the air. The main section(s) 31 described above may be provided for each optical fiber 3 and each pair of supports 5.The secondary section(s) 34 described above may be provided for each optical fiber 3 and each pair of supports 5. The main sections 31 of the optical fibers 3 may be located in several other PXY planes containing the first direction X and the third direction Y, these other PXY planes therefore being able to be horizontal. This makes it possible to have a spatial mesh of the temperature measurement of a given volume of air in 3 dimensions (for example the volume delimited by the supports 5), without causing an obstruction effect on the air flow.

[0093] In one embodiment of the invention, illustrated in figures 2, 3, 4A, 4B, 4C, 7, the measuring device 1 comprises (for example in the measuring module 2 or in the Raman type interrogator 20 or in the control unit 24) a calculator 8 configured to calculate a three-dimensional map 10 of the temperature, by interpolation of the measurements of the temperature T taken respectively at the measuring points x along the length of the optical fiber 3, to calculate the temperature at interpolation points A of the space.The interpolation points A are located between the sections 31 of the optical fiber 3 spaced along the third direction Y, that is to say between the measurement planes P (the main sections 31 of the optical fibers 3 adjacent to each other may be located in several other planes PXY containing the first direction X and the third direction Y) and / or are located between the sections 31 of the optical fiber 3 along the second direction Z (that is to say in each of the measurement planes P) and / or are located between the measurement points x along the length of the optical fiber 3 along the first measurement direction X. This interpolation may be, for example, linear and, for example, three-dimensional of the triangulation type. Delaunay. The measuring device may include a screen allowing the three-dimensional temperature map to be displayed, with different gray or color levels depending on the temperature value at each point, as shown as an example in [Fig.7].

[0094] In one embodiment of the invention, illustrated in Figures 2, 3, 4A, 4B, 4C, the sections 31 of the length of the optical fiber 3 have between them a spacing DZ along the second direction Z, which is smaller at the top than at the bottom, the second direction Z being vertical. This spacing DZ is located in each measurement plane P. The main sections 31 of the optical fibers 3 can be located in several other planes PXY containing the first direction X and the third direction Y, these other planes PXY can therefore be horizontal. This embodiment makes it possible to better measure the stratification of the air. Indeed, there is more heterogeneity in the temperature of the air layers at the top than at the bottom.

[0095] In one embodiment of the invention, illustrated in Figures 1, 2, 3, 4A, 4B, 4C, at least a first 301 of the optical fibers 3 and at least a second 302 of the optical fibers 3 are arranged at a distance from an object 200 and on either side of the object 200 in the third direction Y, for measuring the temperature on either side of the object 200 in the third direction Y. Thus, one, several or all of the sections 31 of the first optical fiber 301 and / or the measurement plane P of the first optical fiber 301 is located in front of the object 200 in the third direction Y. One, several or all of the sections 31 of the second optical fiber 302 and / or the measurement plane P of the second optical fiber 301 is located in front of the object 200 in the third direction Y. 3a is located in front of the object 200 along the third direction Y. This makes it possible to measure the air temperature at several points in the space around the object 200.This object 200 can be of any type, in particular an object releasing heat, for example an electrical cabinet, or other.

[0096] In one embodiment of the invention, illustrated in Figures 1, 2, 3, 4A, 4B, 4C, 5, 6, 7, the computer 8 of the measuring device 1 performs a spatial recalibration of the measurements of the temperature T of the air along the length of the optical fiber 3. To do this, the measuring device 1 comprises a source 71 of prescribed temperature gradient. The source 71 of prescribed temperature gradient is placed against the external surface 40 of the external coating 4 of the optical fiber(s) 3 at one (or more) prescribed position (or point) 7, known, along the length of the optical fiber 3. The source 71 of prescribed temperature gradient has a prescribed temperature, known, different from the air temperature.Then, the calculator 8 identifies the temperature T measured by the measuring device at the measuring point x located in this prescribed position 7 at the prescribed temperature and known from the source 71 of the prescribed temperature gradient located in this prescribed position 7. Thus, the measuring point x. having the measured temperature T equal to the prescribed temperature and known from the source 71 of prescribed temperature gradient will be reset by the calculator 8 as being located at the prescribed position 7. This makes it possible to reset the three-dimensional coordinates of the measurement points x relative to a reference given by the prescribed position 7.

[0097] For each pair of supports 5, the prescribed position 7 of the source 71 of prescribed temperature gradient can be located on one of the supports 5 of the pair, or on several of the supports 5 of the pair.

[0098] In one embodiment of the invention, illustrated in figures 1, 2, 3, 4A, 4B, 4C, 5, 6, 7, the source 71 of prescribed temperature gradient is arranged on the outer coating 4 in several prescribed positions 7 located respectively on several sections 31 of the length of the optical fiber 3 coated with the outer coating 4, spaced from each other at least along the second direction Z.

[0099] Consequently, the source 71 of prescribed temperature gradient can therefore pass over several prescribed positions 7 located on the same support 5.

[0100] In one embodiment of the invention, illustrated in Figures 1, 2, 3, 4A, 4B, 4C, 5, 6, 7, the source 71 of prescribed temperature gradient comprises a heating cable 73 (for example electric) having the known prescribed temperature, greater than the air temperature. This known prescribed temperature can for example be equal to 50°C. The heating cable 73 can therefore pass over several prescribed positions 7 of the external coating 4 of the optical fiber 3, these prescribed positions 7 being located on the same support 5.

[0101] In another embodiment of the invention, illustrated in Figures 1, 2, 3, 4A, 4B, 4C, 5, 6, 7, the source 71 of prescribed temperature gradient comprises a source 72 of projection of cold air having a prescribed temperature, smaller than the temperature of the air, at the prescribed position(s) 7.

[0102] In one embodiment of the invention, illustrated in figures 11, 2, 3, 4A, 4B, 4C, 5, 6, 7, the computer 8 performs a spatial oversampling of temperature maxima T located at the prescribed positions 7 located on the same support 5, to perform the spatial resetting of the measurements of the temperature T of the air along the length of the optical fiber 3. The spatial oversampling allows a better definition of the temperature maxima with a better spatial resolution, lower than the fixed step PX, which can be of the order of 3 cm in the example above of the fixed step PX equal to 15 cm.

[0103] Alternatively, in the above embodiments (one-dimensional, two-dimensional in the measurement plane P or three-dimensional in several measurement planes P), the first measurement direction X of the optical fiber 3 and its external coating 4 could be vertical instead of horizontal, to measure the stratification of the air. Indeed, there is more heterogeneity in the temperature of the air layers at the top than at the bottom.

[0104] Of course, the embodiments, features, possibilities and examples described above can be combined with each other or selected independently of each other.

Claims

Claims

1. Use of a measuring device (1) comprising at least one optical fiber (3) coated with an external coating (4), which is made of a material having an emissivity (e) less than or equal to 0.1, which is bare, which is exposed to air over at least a major part of a length of the optical fiber (3) and which has an external diameter less than or equal to 200 μm, for measuring the air temperature at at least one measuring point (x) located on an external surface of the external coating (4), the measuring device (1) comprising at least one pair of supports (5) spaced apart from each other, the at least one optical fiber (3) coated with the external coating (4) is fixed to the supports (5) and extends between the supports (5) over the major part of the length of the optical fiber (3), the external coating (4) of which is bare and exposed to air, the supports (5) comprise posts (51),several sections (31) of the length of the optical fiber (3) coated with the outer coating (4), each extend in a first measurement direction (X) between the supports (5) of the at least one pair of supports (5) and are spaced from each other at least in a second direction (Z) perpendicular to the first measurement direction (X), the second direction (Z) is vertical, the sections (31) of the length of the optical fiber (3) have between them a spacing (DZ) in the second direction (Z), which is smaller at the top than at the bottom.,

2. Use according to claim 1, characterized in that the material of the external coating (4) is metallic.

3. Use according to claim 2, characterized in that the material of the external coating (4) is aluminum.

4. Use according to claim 2, characterized in that the material of the outer coating (4) is gold.

5. Use according to any one of the preceding claims, characterized in that the measuring device (1) comprises a module (6) for sampling several measurements of the temperature (T) at respectively several measurement points (x) along the length of the optical fiber (3).

6. Use according to any one of claims 1 to 5, characterized in that the sections (31) of the length of the optical fiber (3) coated with the external coating (4) are located in a measurement plane (P) comprising the first measurement direction (X) and the second direction (Z).

7. Use according to claim 6, taken in combination with claim 5, characterized in that a two-dimensional temperature map (10) is calculated by a computer (8) of the measuring device (1), by interpolation of the temperature measurements (T) taken respectively at the measuring points (x) along the length of the optical fiber (3), to calculate the temperature at interpolation points of the measuring plane (P), which are located between the sections (31) of the optical fiber (3) of the at least one pair of supports (5) and / or which are located between the measuring points (x) along the length of the optical fiber (3).

8. Use according to any one of claims 1 to 6, characterized in that the measuring device (1) comprises several optical fibers (3) coated with the outer coating (4) and respectively several pairs of the supports (5), spaced along a third direction (Y), which is perpendicular to the first measuring direction (X) and to the second direction (Z), the optical fibers (3) coated with the outer coating (4) being fixed respectively to the supports (5) of the pairs and extending respectively between the supports (5) of the pairs over the major part of the length of the optical fibers (3), the outer coating (4) of which is bare and exposed to 1 " Q If

9. 1 dll . Use according to claim 8, taken in combination with claim 5, characterized in that a three-dimensional temperature map (10) is calculated by a computer (8) of the measuring device (1), by interpolation of the temperature measurements (T) taken respectively at the measuring points (x) along the length of the optical fiber (3), to calculate the temperature at interpolation points in space, which are located between the sections (31) of the optical fiber (3) spaced apart along the third direction (Y) and / or which are located between the sections (31) of the optical fiber (3) along the second direction (Z) and / or which are located between the measuring points (x) along the length of the optical fiber (3).

10. Use according to claim 7 or 9, characterized in that the measuring device (1) comprises a screen for displaying the map (10).

11. Use according to any one of the preceding claims, taken in combination with claim 8, characterized in that at least a first of the optical fibers (3) and at least a second of the optical fibers (3) are arranged at a distance from an object (200) and on either side of the object (200) in the third direction (Y), for measuring the temperature on either side of the object (200) in the third direction (Y).

12. Use according to any one of the preceding claims, characterized in that the measuring device (1) comprises a calculation module (2), which is connected to at least one end (32) of the optical fiber (3) and which is configured to calculate the temperature (T) of the air at at least one measurement point (x) located on the external surface of the external coating (4), by reflectometry of first signals (SI) emitted in the optical fiber (3), to calculate the at least one measurement of the temperature (T) at at least one measurement point (x) on the external surface (40) of the optical fiber (3).

13. Use according to claim 12, characterized in that the calculation module (2) comprises at least one Raman type interrogator (20).

14. Use according to claim 13, characterized in that the Raman type interrogator (20) comprises at least one transmitter (21) for transmitting first signals (SI) along the optical fiber (3), at least one receiver (22) for receiving second signals (S2), which are reflected by the optical fiber (3) in response to the first signals (SI), and a calculator (24) configured to calculate the temperature (T) from a ratio ( ) of power of two p,M lines (S2a, S2b) of different prescribed frequencies, which correspond to a Stokes peak (S2a) and to an anti-Stokes peak (S2a) and which are present in the second signals (S2).

15. Use according to claim 14, characterized in that the calculator (24) is configured to calculate the temperature T(t, l) according to the following equation: 0 — ToffSet + , \ f( . where Ps is the power of the Stokes peak (S2a) measured by the receiver (22a), Pas is the power of the anti-Stockes peak (S2b) measured by the receiver (22b), t is the time, l is the abscissa of the measurement point (x) along the first direction (X) along the optical fiber (3) from the Raman type interrogator (20), T offset is a prescribed coefficient of the Raman type interrogator (20), is a prescribed coefficient of differential attenuation between the Stockes peak (S2a) and the anti-Stockes peak (S2b), y and C(f) are intrinsic parameters of the Raman type interrogator (20).

16. Use according to any one of the preceding claims, characterized in that a computer (8) of the measuring device (1) carries out a spatial recalibration of the measurements of the temperature (T) of the air along the length of the optical fiber (3), by identifying by the computer (8) the temperature measured in at least one prescribed position (7) along the length of the at least one optical fiber (3), on which a source (71) of prescribed temperature gradient is imposed on the external coating (4).

17. Use according to claim 16, characterized in that the prescribed position (7) of the temperature gradient source (71) is located on at least one of the supports (5).

18. Use according to claim 17, characterized in that the source (71) of prescribed temperature gradient is arranged on the outer coating (4) at several prescribed positions (7) located respectively on several sections (31) of the length of the optical fiber (3) coated with the outer coating (4), spaced from each other at least in the second direction (Z).

19. Use according to any one of claims 16 to 18, characterized in that the source (71) of prescribed temperature gradient comprises a heating cable (73).

20. Use according to claim 19 taken in combination with claim 18, characterized in that the same heating cable (73) passes over the prescribed positions (7) located on the same support (5).

21. Use according to claim 20, characterized in that the computer (8) performs a spatial oversampling of temperature maxima (T) located at the prescribed positions (7) located on the same support (5), to perform the spatial recalibration of the measurements of the temperature (T) of the air along the length of the optical fiber (3).

22. Use according to any one of claims 16 to 18, characterized in that the source (71) of prescribed temperature gradient comprises a source (72) of projection of cold air.

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