Method and system for contactless measurement of the temperature of a portion of an object, by absorption of a phosphor material

Abstract

The present invention relates to a system and a method for contactless measurement of the temperature of a portion (3') of an object (3) coated with a layer of a phosphor material from the zinc oxide family, by means of a light source (1) emitting in a wavelength range at least partially covering a range between 360 and 480 nm, and means for measuring a light intensity as a function of wavelength (5), covering at least one portion of the range of the light source (1), wherein a light intensity of the radiation scattered by the portion of the object is measured as a function of wavelength. Next, on the basis of the measurement of the light intensity as a function of wavelength, a value of at least one parameter is determined, and the temperature of the portion (3') of the object (3) is determined from the value of the parameter and a predetermined correspondence table.

Description

[0001] METHOD AND SYSTEM FOR CONTACTLESS MEASUREMENT OF THE TEMPERATURE OF A PORTION OF AN OBJECT, BY ABSORPTION OF A LUMINOPHOR MATERIAL

[0002] Technical field

[0003] The present invention relates to the field of measuring the temperature of an object, without direct contact with this object, by means of luminophore materials. The present invention is particularly relevant in the case of a rotating object.

[0004] Many technical applications require non-contact temperature measurement. This is the case for moving parts (e.g. turbine blades), for which the ability to take the measurement at a precise point on the surface of interest is an additional requirement, or for traction elements (e.g. power electronics), where direct contact with the measuring point poses technical challenges. In the specific case of developing a permanent magnet electric motor, it is essential to know the temperature of the magnets in order to approach the performance limits without the risk of demagnetization, and this, to ensure continuous performance. Temperature monitoring near critical areas must then be carried out without any electromagnetic, thermal or mechanical interference on a rotor rotating at high speed.

[0005] Prior art

[0006] Phosphor thermometry is a widely used approach for non-contact temperature measurement in laboratories or under specific conditions. The principle is based on the excitation of certain specific materials, generally called "phosphors," and the correlation of the light re-emitted by the phosphors with the temperature. This allows for an accurate temperature estimate without direct contact. However, this approach relies on a light source that must be powerful (usually lasers) and normally in the deep UV range to obtain usable light emissions from the phosphor.

[0007] A different approach, called thermochromism, is also known, where the temperature of the target object is deduced from the light that is absorbed by a temperature-sensitive substance. This approach allows the use of lower intensity light sources. In particular, the utility model CN202307819U is known, which relates to an in situ temperature measurement device. This device comprises a broad-spectrum light source located under a substrate, a broad-spectrum signal obtaining unit and a broad-spectrum signal analysis unit. Thus, in this device, the temperature is deduced by the absorption of light, but in this configuration, the thermosensitive substance is located between the light source and the light sensor (i.e., the transmitted radiation is used), which can make the device bulky.Application DE102014218284A1 is also known, which relates to a monitoring device intended to automatically monitor the temperature of a machine component comprising a thermochromic coating. More specifically, for this application, the thermochromic coating is placed directly on the object for which it is sought to detect the exceeding of a threshold temperature. The spectrum of the scattered light is then observed, which is affected by the absorption properties. However, this document uses light sources with wide wavelength ranges, from X-rays to infrared. Furthermore, no specific thermochromic material is mentioned.

[0008] The present invention aims to overcome these drawbacks. Thus, the present invention relates to a system and a method for measuring, without contact, the temperature of a portion of an object, by absorption of a phosphor material. More specifically, the present invention uses a phosphor material from the zinc oxide family. This material, resistant to high temperatures (up to 900K), allows monitoring of the temperature of machines operated in difficult conditions. In addition, the phosphor material according to the invention allows the use of light sources and detectors in a restricted wavelength range, from 360 to 480 nm.This aspect is particularly important because it allows implementation with inexpensive components (e.g. LEDs and photodiodes), as well as temperature measurement through liquid films, which tend to be transparent in this range for most working / cooling fluids. Furthermore, the invention exploits the fact that when the phosphor material according to the invention is illuminated with a source whose wavelength is at least partially between 360 and 480, part of the light is scattered and part is absorbed, the absorbed light spectrum varying with temperature. It is then possible to exploit the thermosensitive aspect of the phosphor material by using low-power, low-cost, and compact light sources and sensors.Finally, the use of a material from the ZnO family makes it possible to obtain a light response on a nanosecond scale, which makes it possible to determine the temperature with good spatial resolution of a moving object.

[0009] Summary of the invention

[0010] The present invention relates to a method for non-contact measurement of the temperature of a portion of an object, by means of at least one light source and means for measuring a light intensity as a function of the wavelength, said light source being capable of emitting radiation in a wavelength range at least partially covering a wavelength range between 360 and 480 nm and said means for measuring the light intensity being capable of measuring an intensity of radiation in at least part of said wavelength range of said light source, said portion of said object being coated with a layer of a luminophore material from the zinc oxide family, the method according to the invention comprising at least the following steps:

[0011] A) by means of said at least one light source, at least one radiation is emitted in said wavelength range of said at least one light source, and, by means of said means for measuring a light intensity as a function of the wavelength, at least one light intensity is measured as a function of the wavelength of a radiation diffused by said portion of said object coated with said layer of said luminophor material when said portion of said object coated with said layer of said luminophor material is illuminated by said at least one radiation emitted by said at least one light source;

[0012] B) from said at least one measurement of said light intensity as a function of the wavelength of said at least one scattered radiation, a value of at least one parameter is determined;

[0013] C) determining said temperature of said portion of said object coated with said phosphor coating from said value of said at least one determined parameter and from a predetermined correspondence table, said correspondence table allowing a correspondence between values ​​of said at least one parameter and values ​​of said temperature.

[0014] According to an implementation of the invention, said correspondence table can be constructed in the following manner: said temperature of said portion of said object is varied between a minimum temperature and a maximum temperature with a predefined temperature step, steps A) and B) are applied for each temperature step, and a value of said at least one parameter determined at the end of step B) is recorded as well as said temperature of the portion of the object for each of said temperature steps in said correspondence table.

[0015] According to one implementation of the invention, said parameter can be determined from at least a part of at least one intensity spectrum or at least one absorption spectrum, said intensity spectrum and absorption spectrum being determined from said at least one measurement of said light intensity as a function of the wavelength.

[0016] According to one implementation of the invention, said method can be implemented using a single light source and a spectrometer, and said parameter can be determined from an integral of said intensity spectrum or said absorption spectrum over at least a portion of said wavelength range of the light source.

[0017] According to one implementation of the invention, said method can be implemented by means of a single light source and a spectrometer, and said parameter can be determined by a ratio between, on the one hand, an integral of said intensity spectrum or said absorption spectrum over a first part of the wavelength range of the light source and, on the other hand, an integral of said intensity spectrum or said absorption spectrum over a second part of the wavelength range of the light source.

[0018] According to an implementation of the invention, said method can be implemented by means of a single light source and a first and a second photodiode, and said parameter can be determined by a ratio between, on the one hand, an integral of said intensity spectrum or said absorption spectrum over a range of wavelengths of said first photodiode and, on the other hand, an integral of said intensity spectrum or said absorption spectrum over a range of wavelengths of said second photodiode, or vice versa.

[0019] According to an implementation of the invention, said method can be implemented by means of a first and a second light source, and a photodiode, and said parameter can be determined by a ratio between, on the one hand, an integral of said intensity spectrum or said absorption spectrum over a range of wavelengths of said first light source, and, on the other hand, an integral of said intensity spectrum or said absorption spectrum over a range of wavelengths of said second light source, or vice versa.

[0020] According to one implementation of the invention, said method can be implemented by means of a light source having a bandwidth of between 5 and 15 nm and a photodiode, and said parameter can be determined by a value of the intensity at the central wavelength of said bandwidth, optionally related to a reference intensity measured on a surface of the object not coated with said phosphor material.The invention further relates to a system for contactless measurement of the temperature of at least a portion of an object, said system being configured for implementing the method as described above, said system comprising at least said light source capable of emitting radiation in a wavelength range at least partially covering a wavelength range between 360 and 480 nm and said means for measuring the light intensity capable of measuring an intensity of radiation in at least a part of said wavelength range of said light source.

[0021] According to one implementation of the invention, said system may further comprise a paint of said phosphor, or a white sticker and said paint of said phosphor intended to be applied to said white sticker, or a sticker comprising said phosphor on its non-adhesive surface. The invention further relates to a system for non-contact measurement of the temperature of at least one portion of an object, said portion of said object being coated with a layer of a phosphor material from the zinc oxide family, said system comprising: at least one light source capable of emitting radiation in a wavelength range at least partially covering a wavelength range between 360 and 480 nm; means for measuring a light intensity as a function of the wavelength capable of measuring an intensity of radiation in at least part of said wavelength range of said at least one source;means for analyzing said light intensity as a function of the wavelength, said analysis means being configured to determine at least one parameter from said light intensity measured as a function of the wavelength, as well as said temperature of said portion of said object coated with said layer of said phosphor coating from said at least one parameter and a predetermined correspondence table, said correspondence table allowing a correspondence between values ​​of said at least one parameter and values ​​of said temperature.;

[0022] According to one implementation of the invention, said system may further comprise a paint of said luminophore, or a white sticker and said paint of said luminophore to be applied to the non-adhesive part of said sticker, or a sticker comprising said luminophore on its non-adhesive surface.

[0023] According to one implementation of the invention, said system may comprise a support in which said at least one light source and said means for measuring a light intensity as a function of the wavelength are integrated.

[0024] According to one implementation of the invention, said analysis means may comprise computer means such as a computer, a processor or a calculator.

[0025] Other characteristics and advantages of the system and method according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the figures appended and described below.

[0026] List of figures

[0027] Figure 1 schematically illustrates an example of implementation of the system according to the invention.

[0028] Figure 2 shows examples of intensity spectra recorded by a spectrometer for different temperatures of the portion of an object.

[0029] Figure 3 illustrates an intensity spectrum of two LED lamps suitable for implementing the second variant of the invention.

[0030] Figure 4 illustrates an example of the evolution as a function of the temperature of the parameter defined for the third variant according to the invention. Figure 5 illustrates an example of the design of the system according to the invention, comprising a central LED integrated on a circular support and two photodiodes having distinct bandwidths distributed around the central LED.

[0031] Figure 6 illustrates another exemplary design of the system according to the invention, comprising a circular-shaped support, a central LED, and nine photodiodes having three distinct bandwidths distributed around the central LED.

[0032] Description of the embodiments

[0033] According to a first aspect, the invention relates to a method for non-contact measurement of the temperature of at least one portion of an object, by means of at least one light source and means for measuring a light intensity as a function of the wavelength.

[0034] According to a second aspect, the invention relates to a system for contactless measurement of the temperature of at least one portion of an object, for implementing the method according to the invention.

[0035] According to a third aspect, the invention relates to a system for contactless measurement of the temperature of at least a portion of an object.

[0036] "Non-contact temperature measurement of a portion of an object" means the measurement of the temperature of the portion of an object without directly applying a temperature measuring instrument to the portion of the object in question.

[0037] According to the invention, the portion of the object is coated with a layer of a luminophoric material (also called "phosphorescent") from the zinc oxide (ZnO) family. Phosphors from the ZnO family are characterized by an absorption spectrum that starts in the deep UV (100 to 200 nm) up to the visible. After numerous tests carried out in the laboratory, the Applicant was able to observe that the intensity spectrum of ZnO is strongly dependent on temperature in a range between 360 and 480 nm (also called the characteristic wavelength range of the luminophoric material according to the invention hereinafter), and is even more sensitive to temperature in the 380-420 nm range.Consequently, compared to other phosphor materials, the use of a phosphor material from the ZnO family allows the system and method according to the invention to be implemented using light sources and means for measuring light intensity in the visible range, as will be described below. It is clear that the layer of phosphor material according to the invention is in thermal connection with the portion of the object whose temperature is to be measured, which implies that the layer of phosphor material is (substantially) at the same temperature as the portion of the object whose temperature is to be measured. By "portion of the object coated with a layer of phosphor material", it is meant that the layer of phosphor material is in direct contact with the portion of the object or that the layer of phosphor material is in contact with the portion of the object via an intermediate material (for example glue).According to one implementation of the invention, the phosphor material may be attached to the portion of the object by glue, or any mechanical or adhesive means. Furthermore, the phosphor material may include, in addition to the phosphor components, components allowing the coherence of the layer.

[0038] According to one implementation of the invention, the layer of phosphor material according to the invention has a thickness of between 5 μm and 100 μm. Indeed, such a thickness is sufficient to allow diffusion of light radiation emitted by a source according to the invention, without having a thermal impact on the object. The layer of phosphor material according to the invention may have been previously applied to the portion of the object studied, or be applied in a prior step of the method according to the invention.

[0039] According to one implementation of the invention, the layer of luminophore material according to the invention can be of any shape but advantageously its surface can at least cover a disc with a surface area of ​​10 mm. 2 . Indeed, such a dimension is sufficient to allow diffusion of light radiation emitted by a source according to the invention.

[0040] The method and system may be implemented for a static or moving object. According to one implementation of the invention, the object may be a component of a rotating machine, such as a turbine blade, or the rotor of an electrical machine. In the case of a moving object, the measurement may be either averaged over the entire surface of the portion of the object coated with the phosphor material and illuminated by the light source, or limited to a certain region. According to one implementation of the invention, a synchronization system may make it possible to link the acquisition to the position of the target surface.

[0041] According to one implementation of the invention, the object may be a component of a static machine such as the inner surface of the cylinder of a reciprocating combustion engine.

[0042] The system according to the invention comprises at least: a light source capable of emitting radiation in a wavelength range at least partially covering a wavelength range between 360 and 480 nm; means for measuring a light intensity as a function of the wavelength capable of measuring an intensity of radiation in at least part of said wavelength range of said light source.

[0043] It is clear that the light source according to the invention can cover a narrower range or a wider range than the wavelength range characteristic of the phosphor material according to the invention. Similarly, it is clear that the means for measuring a light intensity as a function of the wavelength of the system according to the invention can cover a narrower range than the wavelength range of the light source according to the invention.

[0044] The method according to the invention can advantageously be implemented by means of the system according to the invention. However, the method according to the invention can be implemented by means of any light source capable of emitting radiation in a wavelength range covering at least partially the characteristic wavelength range of the phosphor material according to the invention (i.e. in a wavelength range between 360 and 480 nm) and means for measuring a light intensity as a function of the wavelength capable of measuring an intensity of radiation in at least part of the wavelength range of the light source according to the invention. Preferably, the width at half-maximum of the spectrum of the light source is at least 5 nm, preferably 10 nm.

[0045] Advantageously, the light source according to the invention may be capable of emitting radiation in a wavelength range of at most between 360 and 480 nm. A light source in this range is in fact sufficient for implementing the method according to the invention.

[0046] According to one implementation of the invention, the light source may be an LED (Light Emissive Diode) or a Xenon lamp emitting at least in a part of the wavelength range characteristic of the phosphor material according to the invention. The advantage of using an LED lamp is that lamps of this type consume little energy, and can be targeted on a range of particular wavelengths, in this case a part of the wavelength range characteristic of the phosphor material according to the invention. The advantage of using a Xenon lamp is that its light radiation has a wide range, requiring no particular adaptation (in particular a filter), and is more intense than that emitted by LED lamps.

[0047] According to one embodiment of the invention, the means for measuring a light intensity as a function of the wavelength may correspond to a spectrometer. It is clear that a spectrometer covers a range of wavelengths including by default at least part of the wavelength range of the light source according to the invention.

[0048] Alternatively, the means for measuring a light intensity as a function of the wavelength according to the invention may be formed by a photodiode covering at least part of the wavelength range of the light source according to the invention. Photodiodes are space-saving and inexpensive means for measuring a light intensity as a function of the wavelength.

[0049] Preferably, the means for measuring a light intensity as a function of the wavelength according to the invention may be formed by at least two photodiodes, each of the photodiodes covering at least part of the wavelength range of the light source according to the invention, preferably without overlap.

[0050] According to one implementation of the invention, the phosphor material according to the invention is a zinc oxide doped with Galium, or Zinc. Indeed, the Applicant has observed that these particular zinc oxides have a thermochromic response in the visible range, allow good measurement precision, are robust and relatively inexpensive.

[0051] The method and system according to the invention exploit the temperature-changing optical properties of a particular phosphorescent material. For this purpose, the surface of interest, which has been previously covered with the phosphorescent material according to the invention, is illuminated by a light source whose spectral characteristics correspond to those of the phosphor, i.e. the light source emits in the wavelength range in which the phosphor absorbs. Since the phosphor absorbs a fraction of the light in a manner that depends on the temperature of the phosphor, the intensity of the remaining scattered light is measured and from its spectral characteristics, the surface temperature can be determined, using a look-up table.According to one implementation of the invention, the system according to the invention may comprise means for analyzing the light intensity as a function of the wavelength, the analysis means being configured to determine at least one parameter from a light intensity as a function of the wavelength, as well as the temperature of the portion of the object coated with the phosphor coating, from the parameter and a predetermined correspondence table, the correspondence table allowing a correspondence between values ​​of the parameter and values ​​of the temperature. The analysis means may comprise computer means such as a computer, a processor or a calculator.

[0052] Figure 1 schematically illustrates an example of implementation of the system according to the invention. More specifically, the system according to this implementation comprises a light source 1 (for example an LED). The radiation emitted 2 by the light source 1 illuminates at least a portion 3' of an object 3 coated with a phosphor material according to the invention. A spectrometer 5 is arranged on an optical path capable of measuring radiation emitted 2 by the light source 2 and which is diffused 4 by the portion 3' of the object 3.

[0053] The method according to the invention comprises at least the following steps:

[0054] 1) Emission of radiation and measurement of light intensity

[0055] 2) Determination of at least one parameter

[0056] 3) Determination of temperature

[0057] The steps of the method according to the invention are detailed below.

[0058] 1) Emission of radiation and measurement of light intensity

[0059] During this step, by means of said at least one light source, at least one radiation is emitted in said wavelength range of said at least one light source, and, by means of said means for measuring a light intensity as a function of the wavelength, at least one light intensity is measured as a function of the wavelength of a radiation diffused by said portion of said object coated with said layer of said luminophor material when said portion of said object coated with said layer of said luminophor material is illuminated by said at least one radiation emitted by said at least one light source.

[0060] In other words, during this step, at least one radiation is emitted by means of at least one light source which illuminates at least the portion of the object coated with the layer of luminophor material, and simultaneously, by means of the means for measuring a luminous intensity as a function of the wavelength, at least one luminous intensity is measured as a function of the wavelength of the at least one radiation diffused by the portion of the object coated with the layer of luminophor material.

[0061] According to one implementation of the invention, at least one light source and means for measuring the light intensity may be arranged so as to receive the radiation diffused by the portion of the object coated with the phosphor material when it is illuminated by the light source. In this so-called direct configuration, the light source and the means for measuring the light intensity may have substantially the same position (the emitted and diffused radiation are then parallel to each other and perpendicular to the surface of the portion of the object coated with the phosphor material) or be distant (there is then an angle between the emitted and diffused radiation at the surface of the portion 3' of the object 3 coated with the phosphor material).

[0062] Alternatively, optical elements may be interposed between the radiation emitted by at least one of the light sources and the radiation diffused by the portion of the object coated with the phosphor material when it is illuminated by the light source and measured by the light intensity measuring means, such as optical fibers, lenses, beam splitters or even mirrors.

[0063] According to a first variant, the method and / or the system are implemented by means of a single light source and a spectrometer as means for measuring a light intensity as a function of the wavelength. Such a configuration makes it possible to ensure the measurement of the intensity for the entire wavelength range of the light source.

[0064] According to a second variant, the method and / or the system are implemented using a single light source and two photodiodes, each of the photodiodes covering at least part of the wavelength range of the light source, preferably without overlap. Advantageously, this variant can be implemented using LED lamps, which are inexpensive. An LED can emit in various wavelength ranges, from narrow wavelength ranges (+ / -5 nm) to broader ranges (+ / - 40 nm) and having varied central wavelengths. Advantageously, an LED lamp is used whose wavelength range is consistent with the temperature range to be explored. For example, for a temperature range between 20 and 300°C, an LED having a central wavelength at 395 nm with a half-maximum spectral width of + / -10 nm can be used.If the method and / or system are implemented using a Xenon arc source or an LED source, both photodiodes can have a filter adapted to the targeted measurement range.

[0065] According to a third variant, the method and the system are implemented by means of two light sources, emitting in wavelength ranges without total overlap (an overlap of up to 60% is however possible), preferably LED lamps, and a photodiode. According to this variant, each of the lamps can be capable of emitting radiation in at least a part of the wavelength range characteristic of the phosphor material, and the photodiode can be capable of measuring a light intensity as a function of the wavelength in at least each of the wavelength ranges of the lamps. This variant is particularly advantageous, in particular compared to the second variant, because LED lamps are less expensive than photodiodes.When the method according to the invention is implemented by means of this variant of the system according to the invention, it may comprise a repetition of step A) of the method according to the invention, for each of the light sources. In other words, the two LED lamps are switched on one after the other, at two different times (in other words, the lamps flash alternately, for example every 100 to 200 ns), and the light intensity is measured as a function of the wavelength for each of the rays emitted by each of the LED lamps and diffused by the portion of the object coated with the layer of phosphor material.

[0066] According to a fourth variant, the method and the system are implemented by means of an LED type light source and a photodiode, the LED and the photodiode comprising a bandpass filter whose wavelength range is a function of a target temperature. In other words, for this configuration, the wavelength range of the light source and the means for measuring the light intensity can be narrow, for example with a width at half-maximum of 10 nm (limit width of current LED lamps). This variant can be implemented in particular when seeking to detect whether the object studied has reached a limit temperature beyond which operating risks are increased.

[0067] 2) Determination of at least one parameter

[0068] During this step, from said at least one measurement of said light intensity as a function of the wavelength of said at least one scattered radiation, a value of at least one parameter is determined.

[0069] According to one implementation of the invention, the parameter can be determined from at least one part of the at least one measured intensity spectrum or from at least one part of at least one absorption spectrum which can be determined from the measurement of the light intensity as a function of the wavelength of the at least one scattered radiation.

[0070] The intensity spectrum corresponds to the evolution of intensity as a function of wavelength.

[0071] Conventionally, an absorption spectrum (evolution of absorbance as a function of wavelength) is determined from a measured light intensity and a reference light intensity according to the following formula: where A is the absorbance, λ is the wavelength, / S (Â) is the luminous intensity as a function of the wavelength of the radiation being measured, and / 0(Â) is the luminous intensity as a function of the wavelength of the radiation being measured for a reference. In this case, the reference luminous intensity can be measured on any surface not containing a phosphor material.

[0072] According to one implementation of the invention, the parameter may be an absolute parameter or a relative parameter, determined by taking into account a reference intensity measurement, carried out for example at the start of the implementation of the method according to the invention or periodically. A relative parameter may be advantageous for compensating for variations in the light source and / or fouling of the portion of the object considered. Thus, a reference intensity spectrum could be measured on a surface of the object considered (or any other object) not coated with the layer of phosphor material.

[0073] When the method and / or the system are implemented according to the first variant described above (a single light source and measurement of the light intensity by a spectrometer), the parameter can be determined from the integral of the intensity spectrum (or the absorption spectrum) over the entire wavelength range of the light source (since the means for measuring the light intensity in the form of a spectrometer necessarily cover the entire wavelength range of the light source). Alternatively, the parameter can be determined in the form of a ratio between the integral of the intensity spectrum (or the absorption spectrum) over a first part of the wavelength range of the light source and the integral of the intensity spectrum (or the absorption spectrum) over a second part of the wavelength range of the light source.In other words, in this latter design, a ratio is made in two different wavelength windows of the measured light intensity (or absorbance). Figure 2 shows examples of intensity spectrum (evolution of intensity I as a function of wavelength L) recorded by a spectrometer for different temperatures T of the portion of an object, the temperature increasing in the direction of the arrow (between 23°C and 304°C). It can be observed in this figure that the intensity varies very clearly as a function of the temperature of the portion of the object. This figure also shows two zones Z1, Z2 corresponding to two parts of the wavelength range of the light source (ranging from 350 to 480 nm), with a view to determining a parameter in the form of a ratio as described according to the alternative above.It is quite clear from this figure that the ratio thus defined has different values ​​depending on the temperature of the portion of the object.

[0074] When the method and / or the system are implemented according to the second variant described above (a single light source and two photodiodes), the parameter can be determined in the form of a ratio between the integral (of at least a part) of the intensity spectrum (or of the absorption spectrum) over the wavelength range of the first photodiode and the integral of the intensity spectrum (or of the absorption spectrum) over the wavelength range of the second photodiode (or vice versa in an equivalent manner).

[0075] When the method and / or the system are implemented according to the third variant described above, the parameter may correspond to a ratio between the integral of the intensity (or absorption) spectrum measured for the first LED source and the integral of the intensity (or absorption) spectrum measured for the second LED source (or vice versa in an equivalent manner).

[0076] Figure 3 illustrates the evolution of the intensity I as a function of the wavelength L of two LED lamps suitable for implementing the second variant of the invention, one centered on a wavelength equal to 395 nm and the other centered on a wavelength equal to 415 nm. In this case, the spectra 11, I2 of the two LED lamps partially overlap. Figure 4 illustrates an example of evolution as a function of the temperature T of the parameter defined for the third variant according to the invention, in the form of a ratio R. It can be observed that the parameter defined for this variant is indeed discriminating with respect to the temperature T: a single value of the ratio R corresponds to a single value of temperature T (monotonic curve).

[0077] When the method and / or the system are implemented according to the fourth variant described above (narrow bandwidth light source), the parameter may correspond to an absolute value of the measured intensity (maximum value or average value over the width of the wavelength range of the LED for example) or to a relative value of the measured intensity (for example a ratio between the measured light intensity and a reference intensity, measured on a reference surface not comprising a phosphor material).

[0078] 3) Determination of the temperature from the parameter

[0079] During this step, said temperature of said portion of said object coated with said layer of said luminophore coating is determined from said value of said determined parameter and from a predetermined correspondence table between values ​​of said temperature as a function of said ratio, said correspondence table allowing a correspondence between values ​​of said parameter and values ​​of said temperature.

[0080] It is therefore a question, from the value of the parameter determined in the previous step, of determining to which temperature this parameter value corresponds in a predetermined correspondence table.

[0081] According to one implementation of the invention, in a step prior to step 3), the correspondence table between values ​​of the parameter and values ​​of the temperature can be determined. To do this, the following procedure can be used: the temperature of the object studied is varied between a minimum temperature and a maximum temperature with a predefined temperature step, steps 1) and 2) of the method according to the invention are applied for each temperature step, and the value of the parameter determined at the end of step 2) as well as the temperature of the object for each of the temperature steps are recorded in the correspondence table. According to one implementation of the invention, the temperature of the object can be varied by 10°C. According to one implementation of the invention, the temperature of the object can be monitored by means of a temperature sensor such as a thermocouple.

[0082] According to one design of the invention, the system comprises a support in which said at least one light source and said means for measuring a light intensity as a function of the wavelength are integrated. The support may for example be circular in shape. The support may for example be made of metal, such as stainless steel. Each photodetector and the light source may be equipped with a collimating lens (lens array) to increase the efficiency of light collection.

[0083] According to this design, in the case of a single light source, the light source can be in the center of the support and the photodiodes distributed around the light source.

[0084] Figure 5 illustrates an example of this design, comprising a support 10 of circular shape, a central LED 20, and two photodiodes 30, 31 having distinct bandwidths, distributed around the LED 20. This design example is particularly suitable for implementing the second variant described above.

[0085] Figure 6 illustrates another example of this design, comprising a support 10 of circular shape, a central LED 20, and nine photodiodes 30, 31, 33 having three distinct bandwidths, distributed around the LED 20. The presence of several photodiodes having the same bandwidth allows redundancy of the measurement and thus improves the uncertainties on the measurement and / or allows an alternative measurement in the event of failure of one of the components. Compared to the second variant described above, the addition of at least one photodiode having a bandwidth distinct from the others allows an alternative measurement in the event of failure of one of the components.

[0086] Example

[0087] The characteristics and advantages of the method and system according to the invention will appear more clearly on reading the application example below.

[0088] More specifically, the method according to the invention was implemented for a contactless temperature measurement of a permanent magnet of a rotor. A layer of the phosphor material according to the invention was applied to the permanent magnet. The method according to the invention is implemented by means of a sensor as described in Figure 5, comprising a central LED integrated on a circular support and two photodiodes having distinct bandwidths distributed around the central LED. By means of a synchronization system, the LED can emit a light flash simultaneously as it passes the measurement target (portion coated with the phosphor material). The scattered light emissions are collected simultaneously by the two photodiodes. From the ratio of the light intensities collected by the two photodiodes and a correspondence table, the temperature of the permanent magnet of the rotor is then determined.

[0089] Thus, the present invention based on the use of a phosphor material from the ZnO family allows monitoring of the temperature of objects that can reach temperatures of at least 300°C. In addition, the use of this particular phosphor material allows implementation with light sources and detectors in a restricted wavelength range, at low cost. Finally, the use of a material from the ZnO family makes it possible to obtain a light response very quickly (of the order of a nanosecond), and therefore real-time monitoring.

Claims

Claims 1. Method for non-contact measurement of the temperature of a portion (3') of an object (3), by means of at least one light source (1) and means for measuring a light intensity as a function of the wavelength (5), said light source (1) being capable of emitting radiation (2) in a wavelength range at least partially covering a wavelength range between 360 and 480 nm and said means for measuring the light intensity (5) being capable of measuring an intensity of radiation in at least part of said wavelength range of said light source (1), characterized in that said portion (3') of said object (3) is coated with a layer of a luminophore material of the zinc oxide family and in that it comprises at least the following steps: A) by means of said at least one light source (1), at least one radiation (2) is emitted in said wavelength range of said at least one light source (1), and, by means of said means for measuring a light intensity as a function of the wavelength (5), at least one light intensity is measured as a function of the wavelength of a radiation diffused (4) by said portion (3') of said object (3) coated with said layer of said luminophor material when said portion (3') of said object (3) coated with said layer of said luminophor material is illuminated by said at least one radiation (2) emitted by said at least one light source (1); B) from said at least one measurement of said light intensity as a function of the wavelength of said at least one scattered radiation (4), a value of at least one parameter is determined; C) determining said temperature of said portion (3') of said object (3) coated with said luminophore coating from said value of said at least one determined parameter and from a predetermined correspondence table, said correspondence table allowing a correspondence between values of said at least one parameter and values of said temperature.

2. Method according to claim 1, in which said correspondence table is constructed in the following manner: said temperature of said portion of said object is varied between a minimum temperature and a maximum temperature with a predefined temperature step, steps A) and B) are applied for each temperature step, and a value of said at least one parameter determined at the end of step B) is recorded as well as said temperature of the portion of the object for each of said temperature steps in said correspondence table.

3. Method according to one of the preceding claims, wherein said parameter is determined from at least a part of at least one intensity spectrum or at least one absorption spectrum, said intensity spectrum and absorption spectrum being determined from from said at least one measurement of said light intensity as a function of wavelength.

4. Method according to claim 3, wherein said method is carried out by means of a single light source (1) and a spectrometer, and wherein said parameter is determined from an integral of said intensity spectrum or said absorption spectrum over at least a part of said wavelength range of the light source (1).

5. Method according to claim 3, wherein said method is implemented by means of a single light source (1) and a spectrometer, and wherein said parameter is determined by a ratio between, on the one hand, an integral of said intensity spectrum or said absorption spectrum over a first part of the wavelength range of the light source (1) and, on the other hand, an integral of said intensity spectrum or said absorption spectrum over a second part of the wavelength range of the light source (1).

6. Method according to claim 3, wherein said method is implemented by means of a single light source (1) and a first and a second photodiode, and wherein said parameter is determined by a ratio between, on the one hand, an integral of said intensity spectrum or said absorption spectrum over a wavelength range of said first photodiode and, on the other hand, an integral of said intensity spectrum or said absorption spectrum over a wavelength range of said second photodiode, or vice versa.

7. Method according to claim 3, wherein said method is implemented by means of a first and a second light source (1), and a photodiode, and wherein said parameter is determined by a ratio between, on the one hand, an integral of said intensity spectrum or said absorption spectrum over a range of wavelengths of said first light source, and, on the other hand, an integral of said intensity spectrum or said absorption spectrum over a range of wavelengths of said second light source, or vice versa.

8. Method according to claim 3, wherein said method is implemented by means of a light source (1) having a bandwidth between 5 and 15 nm and a photodiode, and wherein said parameter is determined by a value of the intensity at the central wavelength of said bandwidth, optionally related to a reference intensity measured on a surface of the object (3) not coated with said phosphor material.

9. System for contactless measurement of the temperature of at least one portion (3') of an object (3), said system being configured for implementing the method according to one of the preceding claims, said system comprising at least said light source (1) capable of emitting radiation in a wavelength range at least partially covering a wavelength range between 360 and 480 nm and said light intensity measuring means (5) capable of measuring an intensity of radiation in at least a part of said wavelength range of said light source (1).

10. The system of claim 9, wherein said system further comprises a paint of said phosphor, or a white sticker and said paint of said phosphor for application to said white sticker, or sticker having said phosphor on its non-adhesive surface.

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