Fiber optic measuring system for temperature measurement and methods for temperature measurement using the fiber optic measuring system

Abstract

Fiber optic measuring system for temperature measurement comprising at least one temperature-sensitive element, at least one light-conducting optical fiber, a light source, and at least one optical detector, wherein the at least one temperature-sensitive element comprises a mixture of substances comprising at least one thermoresponsive polymer, at least one viscosity enhancer, and at least one solvent selected from the group consisting of water, methanol, ethanol, propanol, butanol, butyl acetate, chloroform, ionic liquids, and mixtures thereof, wherein the at least one viscosity enhancer is at least one polymer soluble in the at least one solvent having a mass-average molar mass M w includes a density of at least 200 kg / mol.

Description

[0001] The present invention relates to a fiber optic measuring system for temperature measurement comprising at least one temperature-sensitive element, at least one optical fiber, a light source, and at least one optical detector, wherein the at least one temperature-sensitive element comprises a mixture of materials. The mixture comprises at least one thermoresponsive polymer, at least one viscosity enhancer, and at least one solvent, wherein the at least one solvent is selected from the group consisting of water, methanol, ethanol, propanol, butanol, butyl acetate, chloroform, ionic liquids, and mixtures thereof. The at least one viscosity enhancer is at least one polymer soluble in the at least one solvent, having a mass-average molar mass M wThe present invention relates to a method for temperature measurement using the fiber optic measuring system.

[0002] JP 2020-164 838 A discloses a temperature-sensitive indicator element in which a filler obtained by mixing an aqueous solution of a temperature-sensitive polymer and a gelatinizing agent that maintains a gelatinous state of the aqueous solution is filled into a housing frame equipped with a pair of transparent glass plates. The temperature-sensitive polymer alters the permeability of the glass plate of the housing frame and responds to changes before and after a critical solution temperature, thus making temperature changes perceptible.

[0003] US patent 2022 / 0218878A1 also discloses a heat-transfer medium consisting of a carrier and a material that interacts with an exogenous source, wherein the material absorbs energy from the exogenous source and converts the absorbed energy into heat. The heat then migrates outside the medium within a controlled temperature range to trigger or accelerate physical, chemical, or biological activity, and wherein the medium passes a test for extractable cytotoxicity.

[0004] Thermoresponsive polymer solutions, such as those described in DE 10 2015 100 097 A1, are suitable as measuring media for fiber optic measurement systems or sensors for temperature measurement because they exhibit temperature-dependent turbidity within a temperature range dependent on polymer structure, polymer concentration, solvent, and several other parameters. This means that the optical transmission values ​​of the mixture and the temperature are proportional to each other. However, this temperature-dependent turbidity, on which the measurement principle is based, does not remain constant over extended periods. Over time, the separated polymer phase forms macroscopic aggregates that then precipitate out. This significantly limits their practical applicability.

[0005] Due to this limitation, other measurement principles for fiber optic temperature sensors have been preferred so far, but these have certain disadvantages, as described below. Phaser-Bragg-Grating:

[0006] One variant incorporates a fiber Bragg grating (FBG) as the sensor element. This FBG is permanently embedded in an optical fiber. Light is reflected by this grating within a narrow wavelength range, with the center wavelength being known as the Bragg wavelength, which represents the actual measurement quantity. The FBG, with a length of a few millimeters, can be considered a point sensor. The Bragg wavelength is temperature-dependent, thus the FBG can be used as a temperature sensor. Due to the manufacturing process, the sensitive element is relatively expensive. Since a spectral measurement is typically performed, the measuring instrument also represents a significant cost factor. With precise—but also expensive—measuring instruments, a high spectral resolution of up to 1 pm is achieved. Given a temperature sensitivity of approximately 10 pm / K for the FBG, a resolution of 0.1 K can therefore be achieved.The disadvantage – besides the cost – lies in the greater weight and larger size compared to simpler FBG measuring devices. More compact, lighter, and less expensive measuring devices are available, but these have significantly lower resolution. GaAs element:

[0007] Fiber optic temperature sensors are also used, employing a GaAs semiconductor as the temperature-sensitive element. This semiconductor element is attached to the end of an optical fiber and acts as a point sensor. The GaAs semiconductor has a temperature-dependent band edge (GaAs becomes transparent at approximately 850 nm). A temperature change causes a shift in this band edge, which is typically detected spectrally. The measurement uncertainty of semiconductor-based fiber optic temperature sensors is approximately ± 0.2 K, which is greater than that of sensors based on thermoresponsive polymer solutions. Another disadvantage is the high cost. The measuring device usually captures the optical spectrum, necessitating relatively expensive measurement technology. Furthermore, the use of an optical spectrometer results in a relatively large device form factor. Fluorescence:

[0008] In another variant, fluorescent material is applied to the end of an optical fiber. With this point sensor, the material is excited by light, and the decay time of the fluorescent material is measured. This decay time depends on the temperature, and the optical signal is captured with time resolution. Due to the simple measurement method, this measuring system equipped with a fluorescent sensor element offers a cost-effective measurement technique. However, a disadvantage is the relatively large measurement uncertainty of approximately ± 0.5 K. DTS:

[0009] In addition to the point-like sensors mentioned above, the fiber itself can also be used as a temperature-sensitive element. By utilizing Raman scattering in an optical fiber, temperature measurements can be performed along the entire fiber length. Raman spectroscopy captures the Raman scattering with spatial resolution, thus enabling distributed temperature measurements along the optical fiber. Currently available Raman measurement technology is expensive and requires very large and correspondingly heavy instruments. Furthermore, Raman sensors achieve a spatial resolution of approximately 1 m, which is unsuitable for targeted temperature measurements in many cases. Additionally, the measurement uncertainty is ± 0.5 K, which is also often insufficient.

[0010] Based on this, the object of the present invention was to provide a mixture of substances containing at least one thermoresponsive polymer and at least one solvent, which has improved stability.

[0011] This problem is solved with respect to a mixture of materials with the features of claim 1, with respect to a fiber-optic measuring system with the features of claim 10, and with respect to a method for measuring temperature with the features of claim 14. The respective dependent claims represent advantageous embodiments.

[0012] According to the invention, a mixture of materials for a fiber optic measuring system for temperature measurement (or for a fiber optic temperature sensor) is provided, comprising at least one thermoresponsive polymer, at least one viscosity enhancer, and at least one solvent. The at least one solvent is selected from the group consisting of water, methanol, ethanol, propanol, preferably n-propanol, butanol, preferably n-butanol, butyl acetate, preferably n-butyl acetate, chloroform (CHCl3), ionic liquids, and mixtures thereof. According to the invention, the at least one viscosity enhancer is at least one polymer soluble in the at least one solvent (and different from the at least one thermoresponsive polymer), having a mass-average molar mass M w has a molar mass of at least 200 kg / mol. The mass-mean molar mass M w This can be determined, for example, using gel permeation chromatography (GPC).

[0013] The mixture of substances according to the invention can also be referred to as a thermoresponsive mixture or as a thermoresponsive polymer solution.

[0014] Thermoresponsive polymers are polymers that change their physical properties, such as their solubility, with temperature. Due to the presence of at least one thermoresponsive polymer, the mixture exhibits a temperature-dependent turbidity and can therefore, in principle, be used for a fiber optic measurement system for temperature measurement.

[0015] Within the scope of the present invention, it was surprisingly found that certain solvent-containing thermoresponsive polymer solutions, i.e., mixtures comprising at least one thermoresponsive polymer and at least one specific solvent, can be stabilized by increasing the viscosity of the solution through the addition of at least one viscosity increaser in the form of at least one polymer with a mass-average molar mass Mw The viscosity is increased by at least 200 kg / mol. The at least one viscosity increaser prevents or at least significantly reduces further aggregate formation or even precipitation of the separated polymer phase. Consequently, the turbidity of the solution remains constant at a constant temperature over long periods, thus ensuring reliable measurement not only at short intervals but also over extended periods. Therefore, the mixture according to the invention exhibits improved stability. It is thus better suited for fiber-optic temperature measurement than previous mixtures without viscosity increasers. In particular, the mixture according to the invention enables precise and cost-effective fiber-optic temperature measurement with high reliability, even over long periods.

[0016] The at least one viscosity increaser is at least one polymer soluble in at least one solvent, having a mass-average molar mass M wThis polymer (acting as a viscosity increaser) can be considered soluble in the solvent if, at a temperature of 20 °C, preferably at any temperature in the range of 5 °C to 60 °C, and particularly preferably regardless of temperature (i.e., at any temperature at which the solvent is liquid), it dissolves substantially completely in the solvent at a concentration of (at least) 1 g / l (i.e., 1 g of the polymer in 1 liter of the solvent). "Substantially completely" means that at least 95 wt.%, preferably at least 97 wt.%, particularly preferably at least 99 wt.%, and most preferably at least 99.5 wt.% of the polymer (based on the total weight of the polymer) dissolves in the solvent.

[0017] The at least one viscosity increaser can also be referred to as at least one thickening agent.

[0018] Preferably, the at least one solvent is selected from the group consisting of water, methanol, ethanol, propanol, preferably n-propanol, butanol, preferably n-butanol, butyl acetate, preferably n-butyl acetate, chloroform, ionic liquids, mixtures of chloroform and methanol, mixtures of (different) ionic liquids, and mixtures of water and methanol, wherein preferably the ionic liquids each comprise or consist of (or are constituted from) at least one cation and at least one anion. - wherein the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphoshonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or - that at least one anion is selected from the group consisting of bis(trifluoromethanesulfon)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof.

[0019] Particularly preferred is the at least one solvent water, at least one ionic liquid or a mixture of water and at least one ionic liquid, wherein preferably the at least one ionic liquid comprises or consists of (or is constituted from) at least one cation and at least one anion. - wherein the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphoshonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or - that at least one anion is selected from the group consisting of bis(trifluoromethanesulfon)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof.

[0020] The chemical composition of the mixture according to the invention can be determined, for example, by means of NMR spectroscopy and / or IR spectroscopy, optionally with the additional use of GPC (gel permeation chromatography) and HPLC (high-performance liquid chromatography), preferably coupled with MS (mass spectrometry).

[0021] A preferred embodiment of the material mixture according to the invention is characterized in that the mass-average molar mass M w of at least one polymer soluble in at least one solvent - at least 300 kg / mol, preferably at least 400 kg / mol, particularly preferably at least 500 kg / mol, most preferably at least 600 kg / mol, in particular at least 700 kg / mol, for example at least 800 kg / mol, and / or - at most 20000 kg / mol, preferably at most 6000 kg / mol, particularly preferably at most 3000 kg / mol, most preferably at most 2000 kg / mol, in particular at most 1500 kg / mol, for example at most 1000 kg / mol.

[0022] The mass-average molar mass M w This can be determined, for example, using gel permeation chromatography (GPC).

[0023] According to a further preferred embodiment of the material mixture according to the invention, the mass-average molar mass M w of at least one polymer soluble in at least one solvent in a range of 200 kg / mol to 20,000 kg / mol, preferably from 300 kg / mol to 6,000 kg / mol, particularly preferably from 500 kg / mol to 3,000 kg / mol, most preferably from 700 kg / mol to 2,200 kg / mol, in particular from 800 kg / mol to 1,800 kg / mol, for example from 900 kg / mol to 1,500 kg / mol. The mass-average molar mass M w This can be determined, for example, using gel permeation chromatography (GPC).

[0024] For the present invention, it is generally the case that the mass-average molar mass M wThe composition of at least one polymer (used as at least one viscosity increaser) that is soluble in at least one solvent (and differs from the at least one thermoresponsive polymer) can be determined, for example, by gel permeation chromatography (GPC). The eluent can be, for example, 0.1 mol·l. -1 NaNO3 in water + 10 ppm sodium azide (NaN3) or water (or ultrapure water) + 10 ppm sodium azide (NaN3) or 0.07 mol·l -1 Na₂HPO₄ in water + 10 ppm NaN₃, pH 7.4, can be used. The concentration (of at least one polymer soluble in at least one solvent) in the eluent can be, for example, 5 mg / ml. -1 The flow rate can be, for example, 1.0 ml / min. -1The column sizes can be as follows: For example, 2 x ShodexOHpak SB806 MHQ or PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm). Molar mass determination can be performed, for example, by static light scattering. Alternatively (i.e., if molar mass determination is not performed by static light scattering), calibration can be carried out, for example, using PEG standards or pullulan standards (MP 0.342 - 710 g / mol). -1 ) or via poly(diallyldime-thylammonium chloride) standards.

[0025] However, other conditions can also be used to determine the mass-average molar mass M. w GPC can be used. For example, in the case of mixtures based on non-aqueous solvents, it may also be necessary to determine the mass-average molar mass M. wNon-aqueous eluents, such as chloroform, can be used with GPC. In these cases, column combinations other than those mentioned previously can also be used. The exact conditions for GPC generally depend on the polymer under investigation, whose mass-average molar mass M w to be determined.

[0026] In principle, suitable conditions for determining the mass-average molar mass M are available to a person skilled in the art. w known through GPC within the scope of his expertise.

[0027] For example, gel permeation chromatography can be used to determine the mass-average molar mass M. w of the (used as at least one viscosity increaser) at least one polymer soluble in at least one solvent (and different from at least one thermoresponsive polymer) - be carried out in accordance with the following conditions: Eluent: 0.1 mol·l -1NaNO3 in water + sodium azide; concentration of the polymer (soluble in at least one solvent) in the eluent: 5 mg / ml -1 Flow rate: 1.0 ml / min -1 Columns: 2 x ShodexOHpak SB806 MHQ; molar mass determination via static light scattering; or - be carried out in accordance with the following conditions: Eluent: Ultrapure water + 10 ppm NaN3; Concentration of the polymer (soluble in at least one solvent) in the eluent: 5 mg / ml -1 Flow rate: 1.0 ml / min -1 ; Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm); Calibration: PEG standards; or - be carried out in accordance with the following conditions: Eluent: 0.1 mol·l -1 NaNO3 in water + 10 ppm sodium azide; concentration of FLOPAM FO 4650 in the eluent: 5 mg / ml -1 Flow rate: 1.0 ml / min -1Columns: 2 x ShodexOHpak SB806 MHQ; Calibration: Poly(dia-Ilyldimethylammonium chloride) standards; or - be carried out in accordance with the following conditions: Eluent: 0.07 mol·l -1 Na2HPO4 in water + 10 ppm NaN3, pH 7.4; concentration of sodium alginate in the eluent: 5 mg / ml -1 Flow rate: 1.0 ml / min -1 ; Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm); Calibration: Pullulan standards (MP 0.342 - 710 g mol -1 ).

[0028] Another preferred embodiment of the material mixture according to the invention is characterized in that the material mixture - containing at least 0.01 wt.%, preferably at least 0.1 wt.%, particularly preferably at least 1.0 wt.%, most preferably at least 1.5 wt.%, in particular at least 1.8 wt.%, for example at least 2.0 wt.%, of at least one viscosity increaser, based on the total weight of the mixture, and / or - containing at most 20 wt.%, preferably at most 15 wt.%, particularly preferably at most 10 wt.%, most preferably at most 5.0 wt.%, in particular at most 3.0 wt.%, of at least one viscosity increaser, based on the total weight of the mixture.

[0029] According to a further preferred embodiment of the material mixture according to the invention, the material mixture contains 0.01 wt.% to 20 wt.%, preferably 0.1 wt.% to 15 wt.%, particularly preferably 1.0 wt.% to 10 wt.%, most preferably 1.5 wt.% to 5.0 wt.%, in particular 1.8 wt.% to 3.0 wt.%, for example 2.0 wt.% to 3.0 wt.%, of the at least one viscosity increaser.

[0030] Another preferred embodiment of the material mixture according to the invention is characterized in that the at least one viscosity increaser (or the viscosity-increasing effect of the at least one viscosity increaser) is characterized in that a solution comprising 2.0 wt.% of the at least one viscosity increaser and 98.0 wt.% of the at least one solvent has a dynamic viscosity, measured at 23 °C and a shear rate (or shear velocity) of 53.8 Hz, which - at least 0.6 Pa · s, preferably at least 0.8 Pa · s, particularly preferably at least 1.0 Pa · s, and / or - at most 50.0 Pa · s, preferably at most 20.0 Pa · s, particularly preferably at most 10.0 Pa · s, and / or - in a range of 0.5 Pa · s to 50.0 Pa · s, preferably from 0.7 Pa · s to 10.0 Pa · s, particularly preferably from 0.9 Pa · s to 8.0 Pa · s, and / or - at least 0.5 Pa · s higher, preferably at least 0.7 Pa · s higher, particularly preferably at least 0.9 Pa · s higher, than the dynamic viscosity, measured at 23 °C and a shear rate (or shear velocity) of 53.8 Hz, of the at least one solvent, and / or - at least by a factor of 50, preferably at least by a factor of 70, particularly preferably at least by a factor of 90, is higher than the dynamic viscosity, measured at 23 °C and a shear rate (or shear velocity) of 53.8 Hz, of the at least one solvent.

[0031] The dynamic viscosity can be measured, for example, using the following additional parameters: Measurement geometry / method: SV DIN; moment of inertia: 0.000 kg m 2 Damping: 30.00; Coefficient of expansion: 1,100 µm / °C. Furthermore, the dynamic viscosity can be measured, for example, using the "Thermo Scientific Haake Viscotester 550" device; driver version: 44; firmware version 1: V1 2.7-11 / 98.

[0032] According to a further preferred embodiment of the material mixture according to the invention, the material mixture exhibits in a temperature range above an initial temperature T A and below a final temperature TE a monotonic progression of their optical transparency as a function of temperature, where the temperature range (T A are E preferably - extends over at least 3 K, preferably over at least 5 K, and / or - in the range of 5 °C to 300 °C, preferably from 10 °C to 95 °C, particularly preferably from 35 °C to 40 °C, most preferably from 36.5 °C to 40 °C, and / or extends over this range (i.e. a range of 5 °C to 300 °C, preferably from 10 °C to 95 °C, particularly preferably from 35 °C to 40 °C, most preferably from 36.5 °C to 40 °C).

[0033] It is still preferred that the monotone course of the optical transparency over a temperature range from the initial temperature T A up to the final temperature T E sufficient, whereby T E - T A ≥ 3 K, especially T E - T A ≥ 5 K.

[0034] Another preferred embodiment of the material mixture according to the invention is characterized in that the material mixture is adapted so that it functions at a temperature T above an initial temperature T A and below a final temperature T E exhibits a monotonic course of optical transparency as a function of temperature T, such that a measurement of the optical transparency of the material composition allows an optical determination of the temperature T, where T E > T > T A , wherein preferably the monotone profile of the optical transparency over a temperature range from the initial temperature T A up to the final temperature T E sufficient, whereby T E - T A ≥ 3 K, especially T E - T A ≥ 5 K.

[0035] Another preferred embodiment of the material mixture according to the invention is characterized in that adjacent upper critical mixing temperatures or adjacent lower critical mixing temperatures of the thermoresponsive polymers are within the temperature range between T A and T E have an essentially equal distance between them.

[0036] Another preferred embodiment of the material mixture according to the invention is characterized in that the concentration of the thermoresponsive polymers is selected such that a single one of n thermoresponsive polymers of the material composition reduces the optical transparency of the material composition by a maximum of 100 / n %.

[0037] According to a further preferred embodiment, the at least one thermoresponsive polymer comprises several (different) thermoresponsive polymers, for example at least two or at least three (different) thermoresponsive polymers.

[0038] Another preferred embodiment of the material mixture according to the invention is characterized in that the at least one thermoresponsive polymer - contains at least one acrylamide, methacrylamide, acrylate and / or methacrylate unit, and / or - (exclusively) has hydrogen bond acceptors, and / or - has no hydrogen bond donors, and / or - each has a lower critical mixing temperature or an upper critical mixing temperature, and / or - comprising at least two thermoresponsive polymers, which preferably have different lower critical mixing temperatures or different upper critical mixing temperatures.

[0039] Another preferred embodiment of the material mixture according to the invention is characterized in that the at least one thermoresponsive polymer - selected from the group consisting of • alkyl-substituted poly[(meth)acrylamide]enes, particularly preferably poly(dialkylacrylamide)enes, e.g., poly(diethylacrylamide); poly[oligo(ethylene glycol methacrylate)]enes, particularly preferably poly[2-(2-methoxyethoxy)ethyl methacrylate)] and copolymers thereof, as well as poly(2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) and copolymers thereof; poly[oligo(ethylene glycol acrylate)]enes; poly(N-vinylamide)enes, particularly preferably poly(N-vinyllactam)enes; polymethyl vinyl ethers; poly(oxazoline)enes; and mixtures thereof, • (at the terminal end of the repeating unit) cationic group-bearing polyvinyl ethers, and mixtures thereof, • Poly(butadiene), Poly(styrene), Poly(dimethylacrylamide), Poly(isopropylacrylamide), Poly(tert-butylacrylamide), Poly(methyl methacrylate), Poly(n-butyl methacrylate), Poly(benzyl methacrylate), Poly(3-fluorobenzyl methacrylate), Poly(3-methylbenzyl methacrylate), Poly(3-methoxybenzyl methacrylate), Poly(2-phenylethyl methacrylate), poly(4-phenylbutyl methacrylate), poly(4-(phenylazo)phenyl methacrylate), poly(N-(4-vinylbenzyl)carba-zene), poly(glycidyl(2-ethoxyethyl) ether), poly(glycidyl methyl ether), poly(glycidyl ethyl ether), poly(ethylene glycol), poly(propylene glycol), and mixtures thereof, • Poly(vinylbenzyldialkyldamine)ene, preferably poly(dialkyl-(4-vinylbenzyl)amine), and mixtures thereof • Poly(2-chloroethyl vinyl ether-alt-maleic anhydride), • Poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide), • as well as mixtures thereof, and / or - is contained in the mixture in a concentration in the range of 0.01 g / l to 100 g / l, preferably from 0.1 g / l to 10 g / l, particularly preferably from 1.0 g / l to 5.0 g / l.

[0040] The polyvinyl ethers bearing cationic groups at the terminal end of the repeating unit are preferably polyvinyl ethers according to one of the following two structural formulas: where A is selected as Cl, Br, PF6, BF4, N(CF3SO2)2(NTf2), where R is selected from CH3 (Me), n-C4H9 (Bu), n-C5H 11 (Pe), and n-C8H 17 (Oc), and where x is an integer in the range of 3 to 50000.

[0041] Another preferred embodiment of the compound according to the invention is characterized in that the at least one polymer soluble in the at least one solvent is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethyl celluloses, hydroxyethyl celluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl groups from C1 to C3; poly(styrene); poly(methyl methacrylate); poly(2-hydroxyethyl methacrylate); poly(acrylamide-co-choline acrylate); hydroxypropyl cellulose; and mixtures thereof.

[0042] Another preferred embodiment of the material mixture according to the invention is characterized in that - the ionic liquids each comprise or consist of (or are constituted by) at least one cation and at least one anion, wherein • that at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphoshonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or • that at least one anion is selected from the group consisting of bis(trifluoromethanesulfon)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof, and / or - the mixture additionally contains at least one surfactant (or detergent), preferably if the at least one solvent is or contains at least one ionic liquid, wherein the at least one surfactant is preferably sodium dodecyl sulfate.

[0043] In the event that the mixture additionally contains at least one surfactant (or detergent), preferably sodium dodecyl sulfate, it is preferred that the at least one solvent is water, at least one ionic liquid, or a mixture of water and at least one ionic liquid. The at least one surfactant serves, on the one hand, to prevent phase separation between the thermoresponsive polymer and the ionic liquid. In aqueous systems, the at least one surfactant shifts the phase transition temperature to higher temperatures, so that the phase transition temperature, and thus the measuring range, can be adjusted if necessary.

[0044] In the event that the at least one solvent is or contains at least one ionic liquid, the mixture additionally contains at least one surfactant (or detergent), wherein the at least one surfactant is preferably sodium dodecyl sulfate.

[0045] Another preferred embodiment of the substance mixture according to the invention is characterized in that the at least one solvent - Water is, wherein the at least one thermoresponsive polymer is selected from the group consisting of alkyl-substituted poly[(meth)acrylamide]enes, particularly preferably poly(dialkylacrylamide)enes, e.g., poly(diethylacrylamide); poly[oligo(ethylene glycol methacrylate)]enes, particularly preferably poly[2-(2-methoxyethoxy)ethyl methacrylate)] and copolymers thereof, as well as poly(2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) and copolymers thereof; poly[oligo(ethylene glycol acrylate)]enes; poly(N-vinylamide)enes, particularly preferably poly(N-vinyllactam)ene; polymethyl vinyl ethers; poly(oxazoline)enes; and mixtures thereof, and wherein the at least one solvent-soluble polymer is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethyl celluloses, hydroxyethyl celluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(acrylamide-co-choline acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(di-allyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alky-loxazoline) with alkyl groups from C1 to C3; and mixtures thereof. or - at least one ionic liquid is present, wherein the at least one thermoresponsive polymer is selected from the group consisting of poly(butadiene), poly(styrene), poly(dimethylacrylamide), poly(isopropylacrylamide), poly(tert-butylacrylamide), poly(methyl methacrylate), poly(n-butyl methacrylate), poly(benzyl methacrylate), poly(3-fluorobenzyl methacrylate), poly(3-methylbenzyl methacrylate), poly(3-methoxybenzyl methacrylate), poly(2-phenylethyl methacrylate), poly(4-phenylbutyl methacrylate), poly(4-(phenylazo)phenyl methacrylate), poly(N-(4-vinylbenzyl)carbazole), poly(glycidyl(2-ethoxyethyl) ether), poly(glycidyl methyl ether), poly(glycidyl ethyl ether), poly(ethylene glycol), poly(propylene glycol), and mixtures thereof, wherein the at least one solvent-soluble polymer is selected from the group consisting of polysaccharides, preferably starch and derivatives of which, for exampleCarboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethyl cellulose, hydroxyethyl cellulose, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(acrylamide-co-choline acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(di-allyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alky-loxazoline) with alkyl groups from C1 to C3; and mixtures thereof. preferably • comprising or consisting of (or being constituted by) at least one ionic liquid, wherein the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimidazolium; 1-butylpyridinium; triethylpentylphoshonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or the at least one anion is selected from the group consisting of bis(trifluoromethanesulfone)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof, and / or • the mixture additionally contains at least one surfactant, preferably sodium dodecyl sulfate, or - Chloroform or a mixture of chloroform and methanol, wherein the at least one thermoresponsive polymer is selected from the group consisting of (at the terminal end of the repeating unit) cationic group-bearing polyvinyl ethers, and mixtures thereof, and wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of poly(styrene), poly(methyl methacrylate), poly(2-hydroxyethyl methacrylate), and mixtures thereof, or - Methanol or a mixture of methanol and water is, wherein the at least one thermoresponsive polymer is selected from the group consisting of poly(vinylbenzyldialkylamines), preferably poly(dialkyl-(4-vinylbenzyl)amine), and mixtures thereof, and wherein the at least one solvent-soluble polymer is selected from the group consisting of hydroxypropylcellulose, poly(2-hydroxyethyl methacrylate), and mixtures thereof, or - Butyl acetate, preferably n-butyl acetate, is, wherein at least one thermoresponsive polymer is poly(2-chloroethyl vinyl ether alt-maleic anhydride), and wherein the at least one polymer soluble in at least one solvent is poly(methyl methacrylate), or - Ethanol, propanol, preferably n-propanol, or butanol, preferably n-butanol, or a mixture thereof, wherein the at least one thermoresponsive polymer is poly(2-methac-rylamido-caprolactam)-co-(N,N-dimethylacrylamide), and wherein the at least one solvent-soluble polymer is poly(2-hydroxyethyl methacrylate).

[0046] The polyvinyl ethers bearing cationic groups at the terminal end of the repeating unit are preferably polyvinyl ethers according to one of the following two structural formulas: where A is selected as Cl, Br, PF6, BF4, N(CF3SO2)2(NTf2), where R is selected from CH3 (Me), n-C4H9 (Bu), n-C5H 11 (Pe), and n-C8H 17 (Oc), and where x is an integer in the range of 3 to 50000.

[0047] Furthermore, the present invention relates to a fiber optic measuring system for temperature measurement comprising (at least) one temperature-sensitive element, at least one light-conducting optical fiber, a light source, and at least one optical detector, wherein the (at least one) temperature-sensitive element comprises a material mixture according to the invention.

[0048] A preferred embodiment of the fiber optic measuring system according to the invention is characterized in that - the (at least one) temperature-sensitive element comprises a container in which the mixture is arranged, the container preferably comprising a metallic material, and / or - the (at least one) temperature-sensitive element is connected to at least one optical fiber, wherein preferably the (at least one) temperature-sensitive element is connected to the at least one detector via at least one optical fiber and / or to the light source via at least one optical fiber, and / or - the at least one optical detector is configured in such a way that it can detect a change in the light power of light emanating from the light source and passing through the (at least one) temperature-sensitive element.

[0049] Another preferred embodiment of the fiber optic measuring system according to the invention is characterized in that the fiber optic measuring system additionally comprises at least one fiber optic coupling element, wherein the at least one fiber optic coupling element preferably - selected from the group consisting of fiber optic couplers, fiber optic multiplexers, fiber optic switches, and combinations thereof, and / or - is connected to the light source by at least one optical fiber, and / or - is connected to the thermosensitive element by at least one optical fiber, and / or - is connected to at least one detector by at least one optical fiber.

[0050] Another preferred embodiment of the fiber optic measuring system according to the invention is characterized in that the at least one fiber optic coupling element comprises at least one first fiber optic coupling element and at least one second fiber optic coupling element, wherein - the at least one first fiber optic coupling element is connected to the thermosensitive element and to the at least one detector via at least one optical fiber, and / or - that at least one second fiber optic coupling element is connected to the thermosensitive element and to the at least one detector via at least one optical fiber, and / or - that at least one first fiber optic coupling element is connected to at least one second fiber optic coupling element via at least one optical fiber.

[0051] According to another preferred embodiment of the fiber optic measuring system according to the invention, the light source is an LED, an OLED, a laser, an incandescent lamp, a fluorescent lamp or a gas discharge lamp.

[0052] The present invention also relates to a method for temperature measurement using a fiber optic measuring system according to the invention, in which a) Light from the light source is coupled into the thermosensitive element and into the at least one detector by means of the at least one optical fiber, wherein light traveling from the light source to the at least one detector passes at least partially through the thermosensitive element on its way to the at least one detector; b) the intensity of the light that has passed through the thermosensitive element is determined using the detector; c) a value for the temperature of the thermosensitive element is determined using the measured intensity (of the light).

[0053] A preferred variant of the method according to the invention is characterized by the fact that - after step c) the determined temperature value is transmitted to a control and monitoring unit, and / or - additionally, light emanating from the light source is directed to the detector without passing through the thermosensitive element and serves as a reference signal.

[0054] Potential applications of the inventive mixture and / or the inventive fiber optic measuring system and / or the inventive method include, for example, temperature measurement in bioreactors in the food, pharmaceutical, and cosmetics industries. Furthermore, the inventive mixture and / or the inventive fiber optic measuring system and / or the inventive method offer the possibility of monitoring the temperature of processes in high-frequency, microwave, and magnetic fields. For example, the inventive mixture and / or the inventive fiber optic measuring system and / or the inventive method can be used for temperature monitoring during the charging of battery cells in high-voltage environments, which is essential for electromobility. Specialized applications also include, for example...Temperature monitoring in transformers or patient monitoring in MRI scanners with strong electromagnetic fields.

[0055] The present invention will be explained in more detail with reference to the following figures and examples, without limiting it to the specific embodiments and parameters shown here. Synthesis and characterization of the thermoresponsive polymers used. Synthesis example 1: Synthesis of poly(diethylacrylamide) by radical polymerization and characterization of the reaction product.

[0056] In a 100 mL single-necked round-bottom flask, 5.0 g of diethylacrylamide (39.3 mmol) was placed and dissolved in 60 mL of ethanol. The initiator (azobisisobutyronitrile, 71 mg, 0.43 mmol) was weighed out and transferred to the flask. The flask was sealed with a septum. To remove oxygen, nitrogen was passed through the solution via a cannula while stirring for 1 h. The flask containing the clear, colorless solution was then heated in an oil bath at 68 °C for 24 h. After this time, a sample was taken to determine the reaction. 1The reaction was to be determined by 1H NMR spectroscopy. Within the limits of the method's accuracy, no residual monomer could be detected. Therefore, the reaction was stopped after this time by cooling and opening the reaction vessel. For purification, the ethanol was removed by rotary evaporation, the colorless solid was dissolved in water, and the solution was dialyzed against water for 60 h (details of dialysis tubing: Spectra / Por 7 dialysis membrane, pre-treated regenerated cellulose tubing, nominal cut-off: 1 kDa). The dialyzed product was characterized using 1 H-NMR spectroscopy and gel permeation chromatography (GPC).

[0057] GPC (Eluent DMF, calibration with poly(methyl methacrylate) standards): M w = 11000 g mol -1 , M n = 5300 g mol -1 1 H-NMR (500 MHz, D2O):3.6 - 2.9 ppm (broad): 4 H, H B 2.8 - 2.1 ppm (broad): 1 H, H C 1.9 - 0.7 ppm (broad): 8 H, H D + HA Synthesis example 2: Synthesis of poly(N-vinylcaprolactam) by radical polymerization and characterization of the reaction product

[0058] In a 100 mL single-necked round-bottom flask, 5.0 g of N-vinylcaprolactam (35.9 mmol) was placed and dissolved in 60 mL of ethanol. The initiator (azobisisobutyronitrile, 35 mg, 0.21 mmol) was weighed out and transferred to the flask. The flask was then sealed with a septum. To remove oxygen, nitrogen was passed through the solution via a cannula while stirring for 1 h. Subsequently, the flask containing the clear, colorless solution was heated in an oil bath at 65 °C for 24 h. After this time, a sample was taken to determine the reaction by means of 1The residual monomer content was determined by 1H NMR spectroscopy. It was approximately 4 mol%. Therefore, the reaction was stopped after this time by cooling and opening the reaction vessel. For purification, the ethanol was removed by rotary evaporation, the colorless solid was dissolved in water, and the solution was dialyzed against water for 60 h (dialysis tubing details: Spectra / Por 7 dialysis membrane, pre-treated regenerated cellulose tubing, nominal cut-off: 1 kDa). The dialyzed product was characterized using 1 H-NMR spectroscopy and gel permeation chromatography (GPC).

[0059] GPC (Eluent DMF, calibration with poly(vinylpyrrolidone) standards): M w = 31000 g·mol -1 , M n = 11000 g mol -1 1 H-NMR (500 MHz, D2O):4.6 - 4.0 ppm (broad): 1 H, H B 3.5 - 2.8 ppm (broad): 2 H, H C 2.7 - 2.1 ppm (broad): 2 H, H G 2.1 - 0.6 ppm (broad): 8 H, HA , H D , H E , H F Synthesis Example 3: Synthesis of poly(oligoethylene glycol methyl ether methacrylate-block-2-(2-methoxyethoxy)-ethyl methacrylate) by controlled radical polymerization (reversible addition fragmentation chain transfer, RAFT) and characterization of the reaction product. Step 1: Synthesis of poly(oligoethylene glycol methyl ether methacrylate)

[0060] In a 50 mL single-necked round-bottom flask, 55.8 mg of 4-cyano-4-(thiobenzo-ylthio)pentanoic acid (0.2 mmol), 3.3 mg of azobisisobutyronitrile (0.02 mmol), and 3575 mg of oligoethylene glycol methyl ether methacrylate (7.15 mmol) were weighed out and dissolved in 10 mL of ethanol. The flask was then sealed with a septum. To remove oxygen, nitrogen was passed through the solution via a cannula while stirring for 30 minutes. Subsequently, the flask containing the clear, red solution was heated in an oil bath at 70 °C for 8 hours. After this time, a sample was taken to determine the reaction by means of 1 The reaction was carried out by ¹H NMR spectroscopy. Since approximately 47% residual monomer was still present, another 1.65 mg of initiator was added, the oxygen was removed again, and the reaction was continued at 70 °C for 8 h. The conversion was again determined by 1The composition was determined by 1H NMR spectroscopy. Since the residual monomer content had decreased to approximately 9%, the reaction was terminated. To isolate the reaction product, the ethanol was removed by rotary evaporation, the remaining red-colored viscous mass was dissolved in water, and the solution was dialyzed against water for 60 h (dialysis tubing: Spectra / Por 7 dialysis membrane, pre-treated regenerated cellulose tubing, nominal cutoff: 1 kDa). Characterization of the dialyzed product was performed with 1 H-NMR spectroscopy and gel permeation chromatography (GPC).

[0061] GPC (Eluent DMF, calibration with poly(methyl methacrylate) standards): M w = 17000 g·mol -1 , M n = 14000 g mol -1 1 H NMR (500 MHz, D2O):8.0 ppm (broad): H G 7.8 ppm (broad): H H 7.6 ppm (broad): H F 4.4 - 4.0 ppm (broad): 2 H, H A 4.0 - 3.2 ppm (broad): 37H, HB 2.8 - 0.6 ppm (broad, aged): 5 H, H C , H D , also H I , H J , H K Stage 2: Synthesis of the block copolymer

[0062] In a 50 mL single-necked round-bottom flask, 1000 mg of poly(oligoethylene glycol methyl ether methacrylate) (0.067 mmol end groups), 1.1 mg of azobisisobutyronitrile (0.0067 mmol), and 1267 mg of 2-(2-methoxyethoxy)ethyl methacrylate (6.73 mmol) were weighed out and dissolved in 10 mL of ethanol. The flask was then sealed with a septum. To remove oxygen, nitrogen was passed through the solution via a cannula while stirring for 30 minutes. Subsequently, the flask containing the clear, red solution was heated in an oil bath at 70 °C for 50 h. After this time, a sample was taken to determine the conversion by 1The reaction was carried out using ¹H NMR spectroscopy. Since considerable amounts of residual monomer were still present, another 1.1 mg of initiator was added, the oxygen was removed again, and the reaction was continued at 70 °C for 70 h. As the conversion was still not very high, these steps were repeated once more. The reaction was then stopped at approximately 75% conversion. To isolate the reaction product, the ethanol was removed by rotary evaporation, the remaining red-colored viscous mass was dissolved in water, and the solution was dialyzed against water for 60 h (dialysis tubing: Spectra / Por 7 dialysis membrane, pre-treated regenerated cellulose tubing, nominal cut-off: 1 kDa). The dialyzed product was characterized using 1 H-NMR spectroscopy and gel permeation chromatography (GPC).

[0063] GPC (Eluent DMF, calibration with poly(methyl methacrylate) standards): M w = 28000 g·mol -1 , M n = 18000 g mol -1 1 H-NMR (500 MHz, D2O):4.4 - 4.0 ppm (broad): H A 4.0 - 3.2 ppm (broad): H B 2.8 - 0.6 ppm (broad, aged): H C , H D Signals of the end groups H F , H G , H H and H I , H J , H K are no longer recognizable Data on the polymers used as viscosity increasers

[0064] Since the molar masses specified by the manufacturers of the polymers used as viscosity enhancers were determined in very different and partly unknown ways, the molar masses of the polymers used were additionally determined by gel permeation chromatography (GPC).

[0065] The following are different types of molar mass. Here, M stands for Molar Mass. w for the mass-average molar mass, M n for the numerical molar mass and M vfor a viscosity-based molar mass. Hydroxyethylcellulose (HEC) Polymer samples used: Details HECs according to manufacturer HEC 776 kg·mol -1 HEC 155 kg·mol -1 2-Hydroxyethylcellulose 2-Hydroxyethylcellulose Sigma-Aldrich Sigma-Aldrich Lot# MKBD2868V Pcode: 1003429775 Pcode: 1000852844 Source: MKCQ6758 average M v = 1300000 Da average M v = 90000 Da (Manufacturer's information) (Manufacturer's information) GPC characterization: GPC characterization: M w = 776000 g·mol -1 M w = 155000 g·mol -1 M n = 499000 g·mol -1 M n = 69000 g·mol -1 Eluent: 0,1 mol·l -1 NaNO3 in Eluent: 0,1 mol·l -1 NaNO3 in Water + sodium azide Water + sodium azide Concentration of HEC in Concentration of HEC in Eluenten: 5 mg·ml -1 Eluenten: 5 mg·ml -1 Flussrate: 1,0 ml·min -1 Flussrate: 1,0 ml·min -1 Columns: Columns: 2 x ShodexOHpak SB806 MHQ 2 x ShodexOHpak SB806 MHQ Molar mass determination via Molar mass determination via static light scattering static light scattering PEG 100

[0066] Polyethylene glycol Sigma-Aldrich Lot# 01426CU-010 average M w = 100000 g·mol -1 (Manufacturer's information) GPC characterization:

[0067] M w = 135000 g·mol -1 M n = 11000 g mol -1 Eluent: ultrapure water + 10 ppm NaN3 Concentration of PEG 100 in the eluent: 5 mg / ml -1 Flow rate: 1.0 ml·min -1 Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm) Calibration: PSS PEG standards PEG 5000

[0068] Polyethylene glycol Sigma-Aldrich Lot# 97117-078 average M v = 5,000,000 g / mol -1(Manufacturer's information) GPC characterization:

[0069] M w = 675000 g·mol -1 M n = 109000 g mol -1 Eluent: ultrapure water + 10 ppm NaN3 Concentration of PEG 5000 in the eluent: 5 mg / ml -1 Flow rate: 1.0 ml·min -1 Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm) Calibration: PSS PEG standards FLOPAM FO 4650

[0070] FLOPAM FO 4650 SNF SA Lot# GE3948 average molar mass = 4500 - 7100 kg·mol -1 (Manufacturer's information) 45 mol% amide (x), 55 mol% cationic groups (y) poly(acrylamide-co-choline acrylate) GPC characterization:

[0071] M w = 890000 g·mol -1 M n = 150000 g·mol -1 Eluent: 0.1 mol·l -1 NaNO3 in water + 10 ppm sodium azide Concentration of FLOPAM FO 4650 in the eluent: 5 mg / ml -1 Flow rate: 1.0 ml·min -1 Columns: 2 X ShodexOHpak SB806 MHQ Calibration: Poly(diallyldimethylammonium chloride) standards sodium alginate

[0072] Alginic acid sodium salt Roth Batch 263193296 Viscosity (1% solution, 20 °C) 350-550 mPas (manufacturer's specification) GPC characterization:

[0073] M w = 551000 g·mol -1 M n = 246000 g·mol -1 Eluent: 0.07 mol·l -1 Na2HPO4 in water + 10 ppm NaN3, pH 7.4. Concentration of sodium alginate in the eluent: 5 mg / ml -1 Flow rate: 1.0 ml·min -1 Columns: PSS Suprema Guard (50 × 8 mm) + 3000 Å + 1000 Å + 100 Å (300 × 8 mm, 20 µm) Calibration: PSS pullulan standards (MP 0.342 - 710 g / mol) -1 ) Experiments with thermoresponsive mixtures. Comparison example 1: Aqueous solution of poly(diethylacrylamide) (prepared according to synthesis example 1) without additive.

[0074] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to synthesis example 1) is dissolved by shaking for 2 h at a concentration of 3 g·l -1 dissolved in H2O.

[0075] The turbidity measurement was carried out at a constant temperature of 41.4 °C over a period of 70 hours. The result of the turbidity measurement is in Fig. Figure 1 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l). -1) without a temperature-independent, water-soluble polymer additive. The transmission increases during the experiment from an initial value of slightly over 50% to a final value of almost 90%. Since the turbidity value does not remain constant over extended periods, the solution is unsuitable for fiber-optic temperature measurement over long periods. Comparative example 2: Aqueous solution of poly(diethylacrylamide) (prepared according to synthesis example 1) with 2 wt% HEC 155 kg·mol -1

[0076] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to synthesis example 1) is dissolved by shaking for 2 h at a concentration of 3 g·l -1 dissolved in H2O. Then so much HEC 155 kg·mol is added. -1 admittedly, its concentration reaches 2.0 wt.%.

[0077] The turbidity measurement was carried out at a constant temperature of 38.0 °C over a period of 70 hours. The result of the turbidity measurement is in Fig. Figure 2 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l-1) with 2.0 wt% HEC 155 kg·mol. -1 (M w = 155 kg·mol -1 ) as a temperature-independent, water-soluble polymer additive. Despite the addition of the additive, the transmission increases during the experiment from an initial value of approximately 40% to a final value of approximately 80%. At the concentration used, the additive does not have the desired stabilizing effect on the turbidity value. Example 1: Aqueous solution of poly(diethylacrylamide) (prepared according to synthesis example 1) with 2 wt% HEC 776 kg·mol -1

[0078] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to synthesis example 1) is dissolved by shaking for 2 h at a concentration of 3 g·l -1 Dissolved in H2O. Then, while stirring, add enough HEC (776 kg·mol) -1 admittedly, its concentration reaches 2.0 wt.%.

[0079] The turbidity measurement was carried out at a constant temperature of 39.5 °C over a period of 70 hours. The result of the turbidity measurement is in Fig. Figure 3 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l). -1 ) with 2.0% by weight HEC 776 kg mol -1 (M w = 776 kg·mol -1) as a temperature-independent, water-soluble polymer additive. The straight, continuous line represents a linear fit through all measurement points. In the case of high molecular weight HEC, the additive exhibits the desired effect. Within the limits of measurement accuracy, the turbidity values ​​remain constant over a period of 70 hours. This solution with a composition according to the invention is suitable for fiber-optic temperature measurement over extended periods. Example 2: Influence of viscosity: Aqueous solutions of poly(diethylacrylamide) (prepared according to synthesis example 1) with different weight fractions of HEC 776 kg·mol -1

[0080] Preparation of the additive polymer solutions for viscosity measurements: The polymer masses calculated for a given concentration were weighed out, and the required masses of H2O were added. The mixtures were then shaken on an automatic shaker until clear solutions were obtained.

[0081] Dynamic viscosities were determined for these solutions. The graph shows... Fig. 4 are the determined dynamic viscosities of aqueous solutions of HEC 776 kg·mol-1 (M w = 776 kg·mol -1 The dynamic viscosity is shown as a function of the polymer concentration. As can be seen, the dynamic viscosity increases with increasing polymer concentration.

[0082] Preparation of solutions for turbidity measurements: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to synthesis example 1) is prepared by shaking for 2 h at a concentration of 3 g·l -1 Dissolved in H2O. Then, while stirring, add enough HEC (776 kg·mol) -1 (M w = 776 kg·mol -1 ) admitted that its concentration reaches the desired weight percentage.

[0083] Turbidity measurements were carried out using these solutions over a period of 70 hours. The result of the turbidity measurements is in Fig.Figure 5 shows the time courses of the transmission through solutions of the thermoresponsive polymer (c = 3.0 g·l). -1 ) with different concentrations of HEC 776 kg·mol -1 as a temperature-independent, water-soluble polymer additive. The straight lines are fits through all points of each measurement. The drift of the transmission values ​​over time, illustrated by the linear fit to the respective measurement curve, correlates with the dynamic viscosity of the solution, as shown in Fig. 5 can be seen from the measurement curves. The measurement curves show that even concentrations lower than 2 wt% of HEC 776 kg·mol -1 and thus correspondingly lower viscosities already lead to an improvement in the stability of the solution compared to a solution without viscosity increasers. From a dynamic viscosity of approximately 1 Pa·s, which is 776 kg·mol for the HEC used. -1Corresponding to an additive concentration of approximately 2 wt%, the transmission values ​​then remain constant within the limits of measurement accuracy over the entire test period. Comparative example 3: Aqueous solution of poly(diethylacrylamide) (prepared according to synthesis example 1) with 2 wt% PEG 100 additives

[0084] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to synthesis example 1) is dissolved by shaking for 2 h at a concentration of 3 g·l -1 dissolved in H2O. Then so much PEG 100 (M w = 135 kg·mol -1 ) admitted that its concentration reaches 2.0 wt.%.

[0085] The turbidity measurement was carried out at a constant temperature of 34.6 °C over a period of 70 hours. The result of the turbidity measurement is in Fig.Figure 6 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l⁻¹) with 2.0 wt% PEG 100 as a temperature-independent, water-soluble polymer additive. Despite the addition of the additive, the transmission increases during the experiment from a starting value of approximately 48% to a final value of approximately 69%. At the concentration used, the additive does not have the desired stabilizing effect on the turbidity value. Example 3: Aqueous solution of poly(diethylacrylamide) (prepared according to synthesis example 1) with 2 wt% PEG 5000 added.

[0086] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to synthesis example 1) is dissolved by shaking for 2 h at a concentration of 3 g·l -1Dissolved in H₂O. Then, enough PEG 5000 is added to achieve a concentration of 2.0 wt%. Turbidity was measured at a constant temperature of 34.5 °C over a period of 70 hours. The result of the turbidity measurement is shown in Fig. Figure 7 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l). -1 ) with 2.0 wt.% PEG 5000 (M w = 675 kg·mol -1 ) as a temperature-independent, water-soluble polymer additive. The straight, continuous line represents a linear fit through all measurement points. In the case of the high-molecular-weight PEG, the additive exhibits the desired effect. An increase in turbidity values ​​is observed over a period of 70 hours; however, this increase is so slight that it remains within the limits of the instrument's measurement uncertainty. This solution with a composition according to the invention is suitable for fiber-optic temperature measurement over extended periods. Example 4: Aqueous solution of poly(diethylacrylamide) (prepared according to synthesis example 1) with 2 wt% FLOPAM FO 4650 added.

[0087] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to synthesis example 1) is dissolved by shaking for 2 h at a concentration of 3 g·l -1 dissolved in H2O. Then so much FLOPAM FO 4650 (M w = 4500 - 7100 kg·mol -1 ) admitted that its concentration reaches 2.0 wt.%.

[0088] Turbidity measurements were taken at a constant temperature of 31.5 °C over a period of 76 hours. The results of the turbidity measurement are shown in Fig. Figure 8 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l). -1) with 2.0 wt% FLOPAM FO 4650 as a temperature-independent, water-soluble polymer additive. The straight, continuous line is a linear fit through all measurement points. FLOPAM FO 4650, as an additive, exhibits the desired effect. A decrease in turbidity values ​​is observed over a period of 76 h; however, this decrease is so slight that it remains within the range of instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber-optic temperature measurement over extended periods. Example 5: Aqueous solution of poly(diethylacrylamide) (prepared according to synthesis example 1) with 2 wt% sodium alginate added.

[0089] Preparation of the solution: The thermoresponsive polymer poly(diethylacrylamide) (prepared according to synthesis example 1) is dissolved by shaking for 2 h at a concentration of 3 g·l -1 dissolved in H2O. Then so much sodium alginate (M w = 551000 g·mol-1 ) admitted that its concentration reaches 2.0 wt.-%.

[0090] The turbidity measurement was carried out at a constant temperature of 32.1 °C over a period of 70 hours. The result of the turbidity measurement is in Fig. Figure 9 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l). -1 ) with 2.0 wt% sodium alginate as a temperature-independent, water-soluble polymer additive. The straight, continuous line is a linear fit through all measurement points. Sodium alginate, as an additive, exhibits the desired effect. An increase in turbidity values ​​is observed over a period of 70 h; however, this increase is so slight that it remains within the range of instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber-optic temperature measurement over extended periods. Example 6: Aqueous solution of poly(oligoethylene glycol methyl ether methacrylate-block-2-(2-methoxyethoxy)-ethyl methacrylate) (prepared according to synthesis example 3) with 2 wt% HEC 776 kg·mol -1

[0091] Preparation of the solution: The thermoresponsive polymer poly(oligoethylene glycol methyl ether methacrylate-block-2-(2-methoxyethoxy)-ethyl methacrylate) (prepared according to synthesis example 3) is prepared by shaking for 2 h at a concentration of 3 g·l -1 dissolved in H2O. Then so much HEC 776 kg·mol is dissolved. -1 (M w = 776 kg·mol -1 ) admitted that its concentration reaches 2.0 wt.%.

[0092] The turbidity measurement was carried out at a constant temperature of 29.8 °C over a period of 70 hours. The result of the turbidity measurement is in Fig. Figure 10 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l). -1) with 2.0% by weight HEC 776 kg mol -1 as a temperature-independent, water-soluble polymer additive. The straight, continuous line represents a linear fit through all measurement points. The thermoresponsive polymer poly(oligoethylene glycol methyl ether methacrylate-block-2-(2-methoxyethoxy)-ethyl methacrylate) also achieves a value of 776 kg·mol upon addition of the temperature-independent additive HEC. -1 Long-term stabilization of turbidity values ​​is achieved. Although a decrease in turbidity values ​​can be observed over a period of 70 hours, this decrease is so slight that it remains within the range of instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber-optic temperature measurement over extended periods. Example 7: Aqueous solution of poly(N-vinylcaprolactam) (prepared according to synthesis example 2) with 2 wt% HEC 776 kg·mol -1

[0093] Preparation of the solution: The thermoresponsive polymer poly(N-vinylcaprolactam) (prepared according to synthesis example 2) is prepared by shaking for 2 h at a concentration of 3 g·l -1 dissolved in H2O. Then so much HEC 776 kg·mol is dissolved. -1 (M w = 776 kg·mol -1 ) admitted that its concentration reaches 2.0 wt.-%.

[0094] The turbidity measurement was carried out at a constant temperature of 36.1 °C over a period of 70 hours. The result of the turbidity measurement is in Fig. Figure 11 shows the time course of the transmission through the solution of the thermoresponsive polymer (c = 3.0 g·l). -1 ) with 2.0% by weight HEC 776 kg mol -1 as a temperature-independent, water-soluble polymer additive. The straight, continuous line represents a linear fit through all measurement points. The thermoresponsive polymer poly(N-vinylcaprolactam) also exhibits a yield of 776 kg·mol upon addition of the temperature-independent additive HEC.-1 Long-term stabilization of turbidity values ​​is achieved. Although an increase in turbidity values ​​can be observed over a period of 70 hours, this increase is so slight that it remains within the range of instrument-related measurement uncertainty. This solution with a composition according to the invention is suitable for fiber-optic temperature measurement over extended periods. Example 8: Poly(propylene glycol) (PPG) in 1-butyl-3-methyl-imidazolium-bis-trifluoromethanesulfonylimide, additivated with 2 wt% poly(ethylene glycol) (PEG 5000)

[0095] PPG is dissolved in the ionic liquid 1-butyl-3-methylimidazolium-bis-trifluomethanesulfonylimide to create a mixture with a PPG content of 10 wt%. As soon as this solution is heated to the transition temperature range, a macroscopic phase separation occurs between the polymer and the ionic liquid, which persists even upon cooling without mechanical intervention. Only shaking or stirring at a lower temperature restores a clear solution. In this composition, the mixture is unsuitable for fiber optic temperature measurements for several reasons: it exhibits phase separation in the transition temperature range instead of showing temperature-dependent turbidity, and the phase separation is irreversible without mechanical intervention.

[0096] With the addition of 0.4 wt% sodium dodecyl sulfate and 2.0 wt% PEG 5000 (M w = 675 kg·mol -1The turbidity values ​​of this mixture are stabilized within the temperature range of the phase transition. The result of the turbidity measurement is shown in Fig. Figure 12 shows the time course of the transmission through the solution of PPG in 1-butyl-3-methylimidazolium bis-trifluoromethanesulfonylimide with 0.4 wt% sodium dodecyl sulfate and 2.0 wt% PEG 5000 as a temperature-independent soluble polymer additive. The transmission follows the temperature profile in all cycles; however, stabilization is not complete, as the transmission values ​​in later cycles at high temperature no longer reach the minimum transmission of the first cycles. Even though stabilization is not complete, there is a very significant improvement in stability compared to the unadditized sample.

Claims

[1] Fiber optic measuring system for temperature measurement comprising at least one temperature-sensitive element, at least one optical fiber, a light source, and at least one optical detector, wherein the at least one temperature-sensitive element comprises a mixture of substances comprising at least one thermoresponsive polymer, at least one viscosity enhancer, and at least one solvent selected from the group consisting of water, methanol, ethanol, propanol, butanol, butyl acetate, chloroform, ionic liquids, and mixtures thereof, wherein the at least one viscosity enhancer is at least one polymer soluble in the at least one solvent having a mass-average molar mass M w includes a density of at least 200 kg / mol. [2] Fiber optic measuring system according to the preceding claim, characterized by that the mass-average molar mass M w of at least one polymer soluble in at least one solvent - at least 300 kg / mol, preferably at least 400 kg / mol, particularly preferably at least 500 kg / mol, most preferably at least 600 kg / mol, in particular at least 700 kg / mol, for example at least 800 kg / mol, and / or - at most 20000 kg / mol, preferably at most 6000 kg / mol, particularly preferably at most 3000 kg / mol, most preferably at most 2000 kg / mol, in particular at most 1500 kg / mol, for example at most 1000 kg / mol. [3] Fiber optic measuring system according to one of the preceding claims, characterized by that the mixture of materials - at least 0.01 wt.%, preferably at least 0.1 wt.%, particularly preferably at least 1.0 wt.%, most preferably at least 1.5 wt.%, in particular at least 1.8 wt.%, for example at least 2.0 wt.%, of at least one viscosity increaser, based on the total weight of the mixture, and / or - containing at most 20 wt.%, preferably at most 15 wt.%, particularly preferably at most 10 wt.%, most preferably at most 5.0 wt.%, in particular at most 3.0 wt.%, of at least one viscosity increaser, based on the total weight of the mixture. [4] Fiber optic measuring system according to one of the preceding claims, characterized by , that the at least one viscosity increaser is characterized in that a solution comprising 2.0 wt. % of the at least one viscosity increaser and 98.0 wt. % of the at least one solvent has a dynamic viscosity, measured at 23 °C and a shear rate of 53.8 Hz, which - at least 0.6 Pa · s, preferably at least 0.8 Pa · s, particularly preferably at least 1.0 Pa · s, and / or - at least 0.5 Pa · s higher, preferably at least 0.7 Pa · s higher, particularly preferably at least 0.9 Pa · s higher, than the dynamic viscosity, measured at 23 °C and a shear rate of 53.8 Hz, of the at least one solvent, and / or - at least by a factor of 50 higher, preferably at least by a factor of 70 higher, particularly preferably at least by a factor of 90 higher, is than the dynamic viscosity, measured at 23 °C and a shear rate of 53.8 Hz, of the at least one solvent. [5] Fiber optic measuring system according to one of the preceding claims, characterized by that it is at least one thermoresponsive polymer - selected from the group consisting of • alkyl-substituted poly[(meth)acrylamide]enes, particularly preferably poly(dialkylacrylamide)enes, e.g., poly(diethylacrylamide); poly[oligo(ethylene glycol methacrylate)]enes, particularly preferably poly[2-(2-methoxyethoxy)ethyl methacrylate)] and copolymers thereof, as well as poly(2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) and copolymers thereof; poly[oligo(ethylene glycol acrylate)]enes; poly(N-vinylamide)enes, particularly preferably poly(N-vinyllactam)enes; polymethyl vinyl ethers; poly(oxazoline)enes; and mixtures thereof, • cationic group-bearing polyvinyl ethers at the terminal end of the repeating unit, as well as mixtures thereof, • Poly(butadiene), Poly(styrene), Poly(dimethylacrylamide), Poly(isopropylacrylamide), Poly(tert-butylacrylamide), Poly(methyl methacrylate), Poly(n-butyl methacrylate), Poly(benzyl methacrylate), Poly(3-fluorobenzyl methacrylate), Poly(3-methylbenzyl methacrylate), Poly(3-methoxybenzyl methacrylate), Poly(2-phenylethyl methacrylate), poly(4-phenyl-butyl methacrylate), poly(4-(phenylazo)phenyl methacrylate), poly(N-(4-vinylbenzyl)carbazole), poly(glycidyl(2-ethoxyethyl) ether), poly(glycidyl methyl ether), poly(glycidyl ethyl ether), poly(ethylene glycol), poly(propylene glycol), and mixtures thereof, • Poly(vinylbenzyldialkyldamine)ene, preferably poly(dialkyl-(4-vinylbenzyl)amine), and mixtures thereof • Poly(2-chloroethyl vinyl ether-alt-maleic anhydride), • Poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide), • and mixtures thereof, and / or - is contained in the mixture in a concentration in the range of 0.01 g / l to 100 g / l, preferably from 0.1 g / l to 10 g / l, particularly preferably from 1.0 g / l to 5.0 g / l. [6] Fiber optic measuring system according to one of the preceding claims, characterized by, that the at least one polymer soluble in the at least one solvent is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethyl celluloses, hydroxyethyl celluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alky-loxazoline) with alkyl groups from C1 to C3; poly(styrene); poly(methyl methacrylate); poly(2-hydroxyethyl methacrylate); poly(acrylamide-co-cholin-nacrylate); hydroxypropyl cellulose; and mixtures thereof. [7] Fiber optic measuring system according to one of the preceding claims, characterized by , that - the ionic liquids each comprise or consist of at least one cation and at least one anion, wherein • that at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-allylimida-zolium; 1-butylpyridinium; triethylpentylphoshonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or • that at least one anion is selected from the group consisting of bis(trifluoromethanesulfon)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof, and / or - the mixture additionally contains at least one surfactant, preferably sodium dodecyl sulfate, preferably if the at least one solvent is or contains at least one ionic liquid. [8] Fiber optic measuring system according to one of the preceding claims, characterized bythat at least one solvent - Water is, wherein the at least one thermoresponsive polymer is selected from the group consisting of alkyl-substituted poly[(meth)acrylamide]enes, particularly preferably poly(dialkylacrylamide)enes, e.g. poly(diethylacrylamide); poly[oligo(ethylene glycol methacrylate)]enes, particularly preferably poly[2-(2-methoxyethoxy)ethyl methacrylate)] and copolymers thereof, as well as poly(2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate) and copolymers thereof; poly[oligo(ethylene glycol acrylate)]enes; poly(N-vinylamide)enes, particularly preferably poly(N-vinyllactam)enes; polymethyl vinyl ethers; poly(oxazoline)enes; and mixtures thereof, and wherein the at least one solvent-soluble polymer is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as e.g.Carboxymethyl starch, oxidized and quaternized starches, alginate, carboxymethyl cellulose, hydroxyethyl cellulose, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(acrylamide-co-cholin-nacrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl groups from C1 to C3; and mixtures thereof. or - at least one ionic liquid is present, wherein at least one thermoresponsive polymer is selected from the group consisting of poly(butadiene), poly(styrene), poly(dimethylacrylamide), poly(isopropylacrylamide), poly(tert-butylacrylamide), poly(methyl methacrylate), poly(n-butyl methacrylate), poly(benzyl methacrylate), poly(3-fluorobenzyl methacrylate), poly(3-methylbenzyl methacrylate), poly(3-methoxybenzyl methacrylate), poly(2-phenylethyl methacrylate), poly(4-phenylbutyl methacrylate), poly(4-(phenylazo)phenyl methacrylate), poly(N-(4-vinylbenzyl)carbazole), poly(glycidyl(2-ethoxyethyl) ether), poly(glycidyl methyl ether), poly(glycidyl ethyl ether), poly(ethylene glycol), poly(propylene glycol), and mixtures thereof, wherein the at least one solvent-soluble polymer is selected from the group consisting of polysaccharides, preferably starch and derivatives thereof, such as carboxymethyl starch, oxidized starches and quaternized starches, alginate, carboxymethyl celluloses, hydroxyethyl celluloses, dextran, pullulan; poly(acrylic acid); poly(acrylate); poly(acrylamide-co-cholin-nacrylate); poly(styrenesulfonic acid); poly(acrylamide); poly(N,N-dimethylacrylamide); poly(diallyldimethylammonium chloride); poly(vinyl alcohol); derivatives of poly(isobutene-co-maleic anhydride), poly(ethylene glycol); poly(alkyloxazoline) with alkyl groups from C1 to C3; and mixtures thereof, and preferably • comprising or consisting of at least one ionic liquid comprising at least one cation and at least one anion, wherein the at least one cation is selected from the group consisting of 1-alkyl-3-methylimidazolium, preferably 1-ethyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium; 1-alkyl-2,3-dimethylimidazolium; 1-ethyl-3-al-Iylimidazolium; 1-butylpyridinium; triethylpentylphoshonium; 1-butyl-1-methylpyrrolidine; and mixtures thereof, and / or the at least one anion is selected from the group consisting of bis(trifluoromethanesulfone)imide, tetrafluoroborate, hexafluorophosphate, and mixtures thereof, and / or • the mixture additionally contains at least one surfactant, preferably sodium dodecyl sulfate, or - Chloroform or a mixture of chloroform and methanol, wherein the at least one thermoresponsive polymer is selected from the group consisting of polyvinyl ethers bearing cationic groups at the terminal end of the repeating unit, and mixtures thereof, and wherein the at least one polymer soluble in the at least one solvent is selected from the group consisting of poly(styrene), poly(methyl methacrylate), poly(2-hydroxyethyl methacrylate), and mixtures thereof, or - methanol or a mixture of methanol and water, wherein the at least one thermoresponsive polymer is selected from the group consisting of poly(vinylbenzyldialkylamines), preferably poly(dialkyl-(4-vinylbenzyl)amine), and mixtures thereof, and wherein the at least one solvent-soluble polymer is selected from the group consisting of hydroxypropyl cellulose, poly(2-hydroxyethyl methacrylate), and mixtures thereof, or - Butyl acetate, preferably n-butyl acetate, is, wherein at least one thermoresponsive polymer is poly(2-chloroethyl vinyl ether alt-maleic anhydride), and wherein the at least one polymer soluble in at least one solvent is poly(methyl methacrylate), or - Ethanol, propanol, preferably n-propanol, or butanol, preferably n-butanol, or a mixture thereof, wherein the at least one thermoresponsive polymer is poly(2-methacrylamido-caprolactam)-co-(N,N-dimethylacrylamide), and wherein the at least one polymer soluble in the at least one solvent is poly(2-hydroxyethyl methacrylate). [9] Fiber optic measuring system according to one of the preceding claims, characterized by, that - the temperature-sensitive element comprises a container in which the mixture is arranged, the container preferably comprising a metallic material, and / or - the temperature-sensitive element is connected to at least one optical fiber, wherein preferably the temperature-sensitive element is connected to the at least one detector via at least one optical fiber and / or to the light source via at least one optical fiber, and / or - the at least one optical detector is configured in such a way that it can detect a change in the light power of light emanating from the light source and passing through the temperature-sensitive element. [10] Fiber optic measuring system according to one of the preceding claims, characterized bythat the fiber optic measuring system additionally comprises at least one fiber optic coupling element, wherein the at least one fiber optic coupling element is preferably - selected from the group consisting of fiber optic couplers, fiber optic multiplexers, fiber optic switches, and combinations thereof, and / or - is connected to the light source by at least one optical fiber, and / or - is connected to the thermosensitive element by at least one optical fiber, and / or - is connected to at least one detector by at least one optical fiber. [11] Fiber optic measuring system according to claim 10, characterized by , that the at least one fiber optic coupling element comprises at least one first fiber optic coupling element and at least one second fiber optic coupling element, wherein - the at least one first fiber optic coupling element is connected to the thermosensitive element and to the at least one detector via at least one optical fiber, and / or - that at least one second fiber optic coupling element is connected to the thermosensitive element and to the at least one detector via at least one optical fiber, and / or - that at least one first fiber optic coupling element is connected to at least one second fiber optic coupling element via at least one optical fiber. [12] Method for temperature measurement using a fiber optic measuring system according to any one of claims 1 to 11, wherein a) Light from the light source is coupled into the thermosensitive element and into the at least one detector by means of the at least one optical fiber, wherein light traveling from the light source to the at least one detector passes at least partially through the thermosensitive element on its way to the at least one detector; b) the intensity of the light that has passed through the thermosensitive element is determined using the detector; c) a value for the temperature of the thermosensitive element is determined using the measured intensity. [13] Method according to claim 12, characterized by , that - after step c) the determined temperature value is transmitted to a control and monitoring unit, and / or - additionally, light emanating from the light source is directed to the detector without passing through the thermosensitive element and serves as a reference signal.

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