AU2008309338A1

AU2008309338A1 - Spectrometry device for fluid analysis

Info

Publication number: AU2008309338A1
Application number: AU2008309338A
Authority: AU
Inventors: Johan Fournel; Thierry Gergaud; Alain Lunati
Original assignee: SP3H SAS
Current assignee: SP3H SAS
Priority date: 2007-10-12
Filing date: 2008-09-30
Publication date: 2009-04-16
Anticipated expiration: 2028-09-30
Also published as: WO2009047607A3; RU2010119063A; CA2713310C; AU2008309338B2; EP2198276A2; FR2922306B1; EP2198276B1; CA2713310A1; FR2922306A1; BRPI0818064A2; RU2473058C2; WO2009047607A2

Description

INTERNATIONAL PCT APPLICATION O/Ref.: 100451 WO FILING NO: PCT/IB2008/002599 FILED: 30/09/2008 IN THE NAME OF: SP3H TITLE: SPECTROMETER FOR FLUID ANALYSIS INVENTORS: Johan FOURNEL Alain LUNATI Thierry GERGAUD SPECTROMETER FOR FLUID ANALYSIS The present invention relates to the analysis of fluids. The present invention relates more particularly to the qualitative analysis of fluids, and particularly of hydrocarbon- or biofuel-based fuels, ensuring the operation of a combustion engine such as those on motor vehicles. 5 Motor vehicles are more and more equipped with an electronic management system configured to optimize the operation of the engine according to different parameters measured by sensors. Such systems are generally configured to adjust the quantity of fuel injected into the engine, set the injection time, the ignition advance, the intake pressure and the recycling of exhaust gas, according, in particular, to the 10 engine speed, the temperature of oil and coolant, and external parameters such as the atmospheric pressure and ambient temperature. However, such optimization is limited by fluctuations in the quality of fuels. Indeed, although they are defined by standards, fuels are subject to significant variations in quality depending on the weather and the filling station. Fuels are 15 generally characterized by physico-chemical parameters such as octane ratings and the vapor pressure for spark ignition engines, the cetane rating, the flashpoint and resistance to low temperatures for diesel engines, as well as the distillation curve, the density and the oxygenated compound content. It is thus estimated that the physico chemical parameters of hydrocarbon-based fuels can vary by 15 to 40% or more, 20 around standardized average values specified in standards. Now, the operation of a combustion engine is optimized for standardized fuels. If the quality of the fuel taken at the pump is too different from the standardized fuel quality, such optimization is no longer done, and the engine will tend to consume more fuel and generate more polluting gas. 25 Therefore, it is desirable to determine the quality of fuel supplying the engine and to take the results obtained into account to manage the operation of the engine. For that purpose, near-infrared absorption spectrometry is suited to the qualitative assessment of a hydrocarbon or a hydrocarbon mix. A standard spectrometer generating a fluid absorption spectrum generally 30 comprises the following elements: - a light source covering at least one wavelength band in which the measurements must be taken, 2 - a device referred to as a "probe" in the following description, in which the light produced by the light source and the fluid to be analyzed interact, and - a spectrum analyzing sensor which analyses the light at the output of the probe. Such a spectrometer enables an absorption spectrum to be obtained in the 5 form of a curve of T = f(X) type, indicating the quantity T of light having passed through the fluid to be analyzed according to the wavelength X. A spectrometer is characterized mainly by its spectrum analysis range (width and position of the spectra generated), its precision of analysis or the number of measurement points constituting the spectra supplied, its accuracy of measurement 10 for the absorption value and its sensitivity, i.e. its capacity to measure low quantities of light. Present-day spectrometers are generally very complex and thus very expensive, and are relatively large in size. In particular, present-day spectrometers comprise many optical components (lenses, filters, prisms, mirrors, diffraction 15 gratings) separated by air spaces. The alignment of these components is critical for the spectrometer to function correctly. Therefore, present-day spectrometers, generally designed for laboratories, are not suited to the environment of a combustion engine or a motor vehicle. In particular, they are not designed to withstand the intense vibrations generated by the combustion engine or the motor 20 vehicle. Indeed, between the light source and the spectrum analyzing device, the light beam passes through a significant number of optical components separated by air spaces. Each interface between an optical component and the air is a potential source of misadjustment or deterioration. The light sources traditionally used in spectrometry (incandescent or metal 25 vapor lamps, halogens, etc.) are not compatible with the requirements of robustness, service life and size required in an application on board a combustion engine or in a vehicle. The use of lasers must also be ruled out because the same number of lasers as measurement points in the desired spectrum would be necessary. The use of lasers must also be ruled out for reasons of service life, stability and robustness in a hostile 30 environment. Furthermore, patent applications No. FR 2 798 582 and FR 2 789 294 considered using light-emitting diodes associated with standard optical components. It is therefore desirable to produce a fluid analyzing spectrometer capable of being installed on-board a combustion engine or in a motor vehicle.

3 This object is achieved by providing a spectrometer comprising a lighting device configured to generate a light beam covering a wavelength band, a probe configured so that the light beam coming from the lighting device interacts with a fluid to be analyzed, and a spectrum analyzing device configured to receive the light 5 beam after it has interacted with the fluid to be analyzed, and to provide light intensity measurements for various ranges of wavelengths. According to one embodiment, the probe comprises a retro-reflective type reflector to the light source, arranged to receive the light beam coming from the lighting device through the fluid to be analyzed and to reflect it substantially in an 10 opposite direction while widening it slightly, to a collecting light guide associated with the reflector and the spectrum analyzing device so as to collect at least partially the light beam having passed through the fluid to be analyzed and to send it to the spectrum analyzing device. According to one embodiment, the reflector is of Scotchlite@ type or safety 15 reflector type with retro-reflecting prisms. According to one embodiment, the device comprises an illuminating light guide coupled to the reflector to send the light beam coming from the lighting device to the fluid to be analyzed. According to one embodiment, the reflector has the shape of a spherical shell 20 centered substantially on the center of an output face of the illuminating light guide. According to one embodiment, the probe comprises a converging lens arranged between the output of the illuminating light guide and the fluid to be analyzed. According to one embodiment, the collecting light guide comprises several 25 collecting optical fibers spread around the illuminating light guide, the reflector being arranged to send back the light beam after it has passed through the fluid to be analyzed to the collecting optical fibers through the fluid to be analyzed. According to one embodiment, the probe comprises a Y optical coupler to send the light beam at the output of the illuminating light guide to the fluid to be 30 analyzed, and to send the light beam coming from the fluid to be analyzed to the collecting light guide. According to one embodiment, the lighting device comprises a light-emitting diode emitting light covering the wavelength band, coupled to the illuminating light guide.

4 According to one embodiment, the lighting device comprises several light emitting components emitting light in various ranges of wavelengths included in the wavelength band, the illuminating light guide being coupled to the light-emitting components to send the light emitted by the light-emitting components to the probe. 5 According to one embodiment, the lighting device comprises a mixing optical component to combine the light flows emitted by the light-emitting components into a resulting light beam covering the wavelength band, the mixing optical component being coupled to the illuminating light guide to guide the resulting light beam in the lighting guide. 10 According to one embodiment, the mixing optical component has an input face receiving the light coming from the light-emitting components, an output face coupled to the illuminating light guide, and a shape having a substantially optimized revolution to send as much light as possible from the light-emitting components to the lighting guide. 15 According to one embodiment, the mixing optical component covers a light emitting surface of each of the light-emitting components. According to one embodiment, the mixing optical component is coupled by one or more optical fibers to a light-emitting surface of each of the light-emitting components. 20 According to one embodiment, the light beam produced by the lighting device covers a wavelength band between 700 nm and 1,100 nm. According to one embodiment, the lighting device comprises several light emitting components emitting light substantially in the same range of wavelengths. According to one embodiment, the light-emitting components are light 25 emitting diodes. According to one embodiment, the spectrum analyzing device comprises a first light guide coupled to the probe and receiving the light beam after it has interacted with the fluid to be analyzed and diffusing it to a first set of light-sensitive cells through a first optical filtering device arranged to send each of the light 30 sensitive cells one part of the light beam covering a respective range of wavelengths included in the wavelength band. According to one embodiment, the first light guide has the shape of a plate made of a transparent material, receiving the light beam coming from the fluid to be analyzed by an edge of the plate and diffusing it by spreading it to an opposite edge 5 of the plate opposite which the first filtering device and the first set of light-sensitive cells are placed. According to one embodiment, the collecting light guide is coupled to the first light guide to send it the light beam. 5 According to one embodiment, the spectrum analyzing device comprises a strip of photodetectors comprising the first set of light-sensitive cells, which is fixed onto the edge of the plate through the first filtering device. According to one embodiment, the first filtering device comprises a filter of the spectrum transmission interference type linearly variable over its length. 10 According to one embodiment, the filtering device covers a wavelength band between 700 nm and 1,100 nm. According to one embodiment, the spectrum analyzing device comprises a second light guide taking a part of the light beam directly at the output of the lighting device and sending the part of the light beam to a second set of light-sensitive cells 15 through a second optical filtering device arranged to send each of the light-sensitive cells a part of the light beam covering a respective range of wavelengths included in the wavelength band. According to one embodiment, the second light guide has the shape of a plate made of a transparent material, receiving the part of the light beam coming from the 20 lighting device by an edge of the plate and diffusing it by spreading it to an opposite edge of the plate opposite which the second filtering device and the second set of light-sensitive cells are placed. According to one embodiment, the device comprises a light guide coupled to the second light guide to send the light beam coming from the lighting device to the 25 second light guide. According to one embodiment, the spectrum analyzing device comprises a strip of photodetectors comprising the first and the second sets of light-sensitive cells, which is fixed onto the edge of the plates of the first and second light guides through the first and second filtering devices. 30 According to one embodiment, the second filtering device comprises a filter of the spectrum transmission interference type linearly variable over its length. Some examples of embodiments of the present invention will be described below in relation with, but not limited to, the following figures, in which: 6 - Figure 1 represents in block form some functions of a spectrometer adapted to the environment of a combustion engine or a motor vehicle, - Figure 2A is a side view of a lighting device of the spectrometer, - Figure 2B is a front view of light sources of the lighting device, 5 - Figure 3 represents in the form of curves some examples of emission spectra of light sources of the lighting device, - Figure 4 is a side view of an alternative embodiment of the lighting device of the spectrometer, - Figure 5A is a side view of a transmission probe for transmitting a light beam 10 generated by the lighting device to the fluid to be analyzed, - Figure 5B is a cross-section of an arrangement of optical fibers in the probe, - Figure 6 is a side view of an alternative embodiment of the probe, - Figure 7 is a side view of another alternative embodiment of the probe, - Figure 8A is a top view of a spectrum analyzing device of the spectrometer, 15 - Figure 8B is a side view of the spectrum analyzing device, - Figure 9 represents in block form the arrangement of the spectrometer, - Figure 10 represents in block form an alternative arrangement of the spectrometer, - Figure 11 is a top view of the spectrum analyzing device of the spectrometer represented in Figure 10, 20 - Figure 12 represents an example of a fluid absorption curve obtained by the spectrum analyzing device, In the following description of the figures, the same elements have the same references. Figure 1 represents a spectrometer FAN to analyze a fluid. The device FAN 25 comprises: - a lighting device LSRC covering at least one wavelength band in which spectrometry measurements must be taken, - a probe PRB configured so that the light produced by the lighting device LSRC interacts with the fluid to be analyzed, 30 - a spectrum analyzing sensor SPAN which analyses the light at the output of the probe, and - optical elements 4, 12 configured to guide the light beam between the source and the probe and between the probe and the sensor. The fluid to be analyzed may be a gas or a liquid, and in particular a 35 hydrocarbon or a hydrocarbon mix, or even a mix of hydrocarbons and biofuels.

7 Figures 2A and 2B represent one embodiment of the lighting device LSRC. The lighting device LSRC comprises a light source I mounted onto a medium 2, and connected to a source of energy (not represented) by connecting pins 5. The light source 1 comprises for example a light-emitting component of light-emitting diode 5 (LED) type. The medium 2 may comprise a printed circuit wafer onto and to which the light-emitting component 1 is mounted and connected. An optical fiber 4 is coupled to the light-emitting surface of the component 1 to send the light generated towards the probe PRB. If the wavelength band to be covered to take the spectrometric measurements 10 cannot be covered by a single light-emitting component, several light-emitting components la-Ig in various ranges of wavelengths can be mounted onto the medium 2. Thus, current light-emitting diodes have an emission wavelength spectrum of several tens of nanometers in width. Several light-emitting diodes are therefore 15 needed if the spectrum to be covered extends over several hundred nanometers. For example, the lighting device can thus cover a spectrum of wavelengths ranging between 700 and 1,100 nm. The lighting device LSRC then comprises an optical component 3 configured to mix the light coming from each of the light-emitting components la-1g and to 20 guide the mixed light towards the optical fiber 4. The optical component 3 can be made of a transparent material in the spectrum of measurement wavelengths of the analyzer. The optical component 3 is for example of TIR-type (Total Internal Reflection), so as to send the light energy produced by the light-emitting components la-I g to the optical fiber 4 with optimum efficiency. The component 3 has an input 25 face covering all the light-emitting components la-1g and an output face having substantially the same shape and dimensions as the input face of the fiber 4. The revolution of the component 3 is substantially conical, and its generator is optimized to send the optical fiber 4 as much light as possible from the light-emitting components Ia-I g. The component 3 is fixed onto the components Ia-I g and onto 30 the medium 2 for example by means of a layer of transparent glue 3a fully covering the components Ia- 1 g. The optical fiber 4 can also be fixed onto the component 3 by means of transparent glue. Figure 3 represents six curves of lighting power according to the wavelength, corresponding to the emission spectra Cl -C5 of various light-emitting diodes, and to 35 the resulting spectrum CR obtained after the optical component 3 has combined the 8 spectra CI-C5. Each emission spectrum CI-C5 has substantially the shape of a Gauss curve. The spectra Cl-C5 have respective maximum values in the vicinity of 850 nm, 890 nm, 940 nm, 970 nm, and 1,050 nm. As these maximum values are not identical, the lighting device LSRC may comprise several light-emitting components having a 5 substantially identical emission spectrum so that the resulting spectrum CR is as flat as possible (constant power) in the wavelength band to be covered. Figure 4 represents another embodiment of the lighting device. In Figure 4, the lighting device LSRC1 comprises several light-emitting components la, lb, Ic, each component being mounted onto a medium 2a, 2b, 2c, and coupled directly to an 10 optical fiber 7a, 7b, 7c. The light-emitting surface of each component la, 1b, Ic is thus in contact with the input surface of the optical fiber 7a, 7b, 7c. The output surface of each optical fiber is coupled to an optical component such as the optical component 3 previously described. The optical fibers 7a, 7b, 7c can be fixed onto the components I a, I b, I c or onto the media 2a, 2b, 2c and onto the component 3 by 15 means of transparent glue. Here again, the mixing optical component 3 may be omitted. The optical fibers coming from the diodes are then grouped together into a bundle of optical fibers sending the light beam coming from the lighting device to the probe PRB. It shall be noted that in the embodiment in Figure 4, the diodes la-Ic can also 20 be mounted onto the same medium 2 as shown in Figures 2A, 2B. Figure 5A represents the probe PRB. The probe PRB comprises several optical fibers 4, 12 arranged in a bundle and a converging lens 19. Figure 5B represents an example of arrangement of the fibers in the bundle. On Figure 5b, the bundle comprises a central optical fiber, referred to as the lighting 25 optical fiber, corresponding to the fiber 4 coming from the lighting device LSRC, and lateral optical fibers 12, referred to as collecting optical fibers, arranged around the central fiber 4. The central optical fiber 4 may have a different diameter, for example greater than that of the lateral fibers 12. In the example in Figure 5B, the probe PRB comprises seven fibers 12. 30 The lens 19 is coupled to the fibers 4, 12 so that its optical axis 16 substantially coincides with that of the light beam at the output of the central fiber 4, the centre of the output face of the fiber 4 being located in the vicinity of the focal point of the lens. The diameter of the lens 19 is such that a light beam sent by the fiber 4 is entirely sent by the lens to infinity, given the angle of the light beam at the 9 output of the fiber 4. All the fibers 4, 12 and the entire lens 19 can be housed in a box 18. The fluid to be analyzed is arranged on the route of the light beam at the output of the lens 19. For this purpose, a pipe or a tank 10 containing the fluid to be 5 analyzed 20 comprises a transparent window I Ia and a flat reflector 13, arranged on the route of the light beam at the output of the lens 19. The reflector 13 is arranged perpendicular to the optical axis 16, so that the light beam passes through the fluid to be analyzed 20 and is reflected towards the fibers 4 and 12 through the lens 19. The light beam thus passes twice through the fluid to be analyzed between the window 10 11 a and the reflector 13. The reflector 13 is of retro-reflective type to the light source, i.e. reflecting each incident light ray in the opposite direction to that of the incident light ray with a slight deflection so that the reflected beam is focused by the lens 19 on a surface area larger than the fiber 4, covering in particular the input face of the fibers 12. 15 For example, the reflecting surfaces marketed under the brand name Scotchlite@ by the company 3M have this property: a light beam arriving on such a surface leaves it in an opposite direction with a slightly wider angle. This type of surface is used for example to manufacture retro-reflecting safety clothing. For this purpose, the reflecting surface comprises transparent microbeads stuck onto a 20 medium and half of the surface of which turned toward the medium is covered with a reflecting layer. Safety reflectors with retro-reflecting prisms also have the same property. This property offsets an alignment fault between an axis perpendicular to the reflector 13 and the optical axis 16 of the lens 19. 25 The pipe or tank 10 may comprise a second transparent window 11b positioned on the route of the light beam, onto which the reflector 13 is fixed. It will be understood that the transparent window 11 a may be combined with the lens 19. Figure 6 represents another embodiment of the probe. In this embodiment, the 30 probe PRB1 differs from the one represented in Figure 5A due to the absence of the lens 19. The tank or pipe 10' containing the fluid to be analyzed 20 comprises, as in Figure 5A, a transparent window 11 a letting the light beam coming from the fiber 4 to enter the fluid to be analyzed. Opposite the transparent window 1 a, a reflector 13' in the form of a spherical shell centered substantially on the centre of the output 10 face of the fiber 4 is provided. Thus, all the rays of the light beam at the output of the fiber 4 travel a route of substantially the same length in the fluid to be analyzed 20. The reflector 13' has a retro-reflecting surface such that it enlarges the reflected beam to cover the input faces of the fibers 12. 5 The entire beam coming from the fiber 4 thus enters the pipe or tank 10' via the transparent window 1 a and is reflected by the reflector 13 towards the fibers 4, 12. The reflector 13' is once again arranged either inside the pipe or tank, or on a transparent window in the form of a spherical shell provided in the pipe or the tank 10 10'. Provision can also be made to interlock the ends of the fibers 4, 12 with the reflector 13' and to sink them into the fluid to be analyzed 20. Figure 7 represents another embodiment of the probe. In this embodiment, the probe PRB2 differs from the one represented in Figure 5A due to the presence of a Y 15 coupler 25 and a single collecting fiber 12'. The probe PRB2 comprises a single fiber 26 sending the light beam to the fluid to be analyzed 20 and capturing the light beam coming from the latter. The coupler 25 is configured to separate the light beams according to their direction of propagation and thus to direct the beam coming from the lighting device LSRC or LSRCl towards the fiber 26 and the fluid to be 20 analyzed, and the light beam having passed through the fluid to be analyzed is sent by the fiber 26 towards the optical fiber 12' coupled to the input of the spectrum analyzing sensor SPAN. The optical fibers 4, 26 and 12' can be fixed onto the coupler 25 by means of transparent glue. It will be understood that, as described above with reference to Figure 6, the 25 lens 19 in the embodiment in Figure 7 may be removed. In this case, a reflector in the form of a spherical shell like the one presented in Figure 6 is used. Figures 8A, 8B represent one embodiment of the spectrum analyzing sensor SPAN. The sensor SPAN comprises a light guide 21, an optical filter 22 and a light sensitive sensor 24. The light guide 21 is made of a transparent material, for example 30 glass, and has the shape of a substantially parallelepipedal plate, of a low thickness substantially equal to or greater than the diameter of the optical fibers 12 coming from the probe PRB. Each collecting optical fiber 12 is fixed onto a lateral face or edge 210 of the plate, for example using transparent glue. The sensor 24 comprises a set of light-sensitive cells which can be arranged 35 as a strip, and covered by the filter 22. The strip of light-sensitive cells with the filter 11 22 covers the lateral face or edge 211 of the guide 21 opposite the lateral face or edge 210 onto which the collecting optical fibers 12 are fixed. The sensor 24 is for example of the CMOS-sensor type comprising a plurality of light-sensitive elements, for example 64 or 128 light-sensitive cells. The filter 22 comprises one filter element 5 per light-sensitive cell, configured to send light rays located in a respective range of wavelengths of the wavelength band to be analyzed, so that each light-sensitive cell supplies the value of a point on the curve of the spectrum to be generated. The output signal of each cell is a measurement of a quantity of light having passed through the fluid to be analyzed for the range of wavelengths sent to the cell by the filter 22. 10 The measurements thus taken by the cells are sent to a signal processing device RDP configured to generate a spectrum of the shape I = f(k) indicating the quantity of light I sent by the fluid to be analyzed according to the wavelength X. The signal processing device is also configured to deduce from the absorption spectrum thus generated certain characteristics SPCT of the fluid passed through by the light 15 beam coming from the lighting device LSRC. The material constituting the guide 21 has a refraction index such that all the light rays introduced by the edge 210 are reflected by the walls of the guide and only leave the latter via the opposite edge 211. The light beams at the output of the collecting optical fibers 12 are thus fully sent to the filter 22. The geometry thus 20 chosen for the guide 21 enables the light beams coming from the probe PRB to be spread in a substantially homogeneous manner over the entire surface of the filter 22. The guide 21 has for example a thickness of about 1 mm and a width of approximately 7 mm for seven collecting fibers 12, each with a diameter of 1 mm. The length of the guide 21 is for example determined according to the angle of the 25 light beam at the output of the fibers 12 in the guide 21, so that the beam 27 at the output of the collecting fiber fixed in the middle of the width of the guide 21 covers the entire filter 22. The filter 22 can be of the spectrum transmission interference type linearly variable over its length, letting through each wavelength component of the light 30 beam received in a position depending on its wavelength, along the width of the output face (edge) 211 of the guide 21. Therefore, each light-sensitive cell of the sensor 24 receives light rays located in a distinct wavelength band, and two adjacent cells of the sensor receive light rays located in two contiguous ranges of wavelengths.

12 It will be understood that, if the probe comprises a single collecting optical fiber like the fiber 12' in Figure 7, a single fiber is fixed onto the input face (edge) 210 of the light guide 21, preferably in the middle of this face. Figure 9 represents the arrangement of the different components previously 5 described in the spectrometer FAN. In Figure 9, the lighting device LSRC is linked to the probe PRB (or PRB1, PRB2) through the optical fiber 4. In the case of the probe PRB or PRB2, the lens 19 is placed opposite the transparent window 11 a and the reflector 13 on the pipe or tank 10 containing the fluid to be analyzed 20. The probe PRB (or PRB1, PRB2) is linked to the spectrum analyzing sensor SPAN 10 through the optical fibers 12 (or the optical fiber 12' in the case of probe PRB2). Figure 10 represents another embodiment of the spectrometer. In Figure 10, the spectrometer FANI differs from the spectrometer FAN in that it comprises a spectrum analyzing device SPAN1, and an optical fiber 4' linking the output of the lighting device LSRC to the device SPAN1. 15 On Figures 9 and 10, the lighting device can also be the device LSRC1. Figure 11 represents the spectrum analyzing sensor SPAN I of the spectrometer FAN 1. In Figure 11, the spectrum analyzing sensor SPAN I comprises two sensors such as the one SPAN represented on Figures 8A, 8B. Thus, the sensor SPANI comprises two light guides 21, 21' and two optical filters 22, 22' and two 20 light-sensitive sensors. The input face of the guide 21 is coupled to the optical fibers 12 and the input face of the guide 21' is coupled to the optical fiber 4'. The optical fiber 4' can be connected to the lighting device LSRC (or LSRCl) through an optical fiber coupler (not represented) known per se, capable of sending the light beam at the output of the mixing component 3 substantially without 25 any loss and in a balanced manner to the two optical fibers 4, 4'. In the example in Figure 11, the sensor SPANI comprises a single light sensitive sensor 24 comprising two times more light-sensitive cells, for example 128 or 256, to analyze the light beams sent by the two guides 21, 21', each associated with a filter 22, 22'. 30 The light sent directly from the lighting device LSRC by the fiber 4' is analyzed through the filter 22' and indicates for each wavelength X the quantity of light R(X) emitted by the lighting device. The light sent from the probe PRB by the collecting fibers 12 indicates for each wavelength X the quantity of light t(X) having passed through the fluid to be 35 analyzed.

13 Therefore, the device SPAN1 can constitute a corrected transmission spectrum taking into account any fluctuations in the light beam coming from the lighting device, of the shape T(X)= t(X)/R( ). Figure 12 represents an example of such an absorption spectrum T between 5 the wavelengths equal to 850 nm and 1,050 rim, T being substantially equal to 1 when the fluid is totally transparent at the corresponding wavelength ? and substantially equal to 0 when the fluid is totally impenetrable at the corresponding wavelength X. It will be understood that the optical fibers 4, 4', 12, 12' described above, 10 linking up the lighting device LSRC, LSRCI, the probe PRB, PRB1, PRB2 and the analyzing device SPAN, SPAN 1, can be replaced by bundles of fibers. The different optical elements of the spectrometer FAN, FANI are aligned during the assembly of these elements and their connection by optical fibers. The assembly can be done so as to form a single block without any air or vacuum 15 between the optical components by using optical fibers, which also renders the device insensitive to vibrations. Thus, all the components and optical fibers of the device can for example be sunk in a resin, for example of potting type, suited to withstand aggressive environments. In addition, the spectrometer FAN, FANI uses only low-cost components 20 with a long service life, and its composition makes it compatible with a mass production process. Therefore, the spectrometer proves to be perfectly suited to the environment of a combustion engine and a motor vehicle. It will be understood by those skilled in the art that various alternative embodiments and (various) applications of the present invention are possible. In 25 particular, the present invention is not limited to the use of optical fibers to connect the different elements (lighting device, probe and spectrum analyzing device) of the spectrometer. The present invention is not limited either to a device comprising a single optical fiber linking the lighting device to the probe and to the spectrum analyzing device, and to one or seven optical fibers linking the probe to the spectrum 30 analyzing device. Indeed, these connections can also be produced by light guides made up of a bundle of optical fibers. The present invention may also comprise a lighting device without any mixing optical component 3. Indeed, this component can be omitted if an optical fiber or a bundle of optical fibers having an input face covering all the light-emitting 35 diodes is used. The optical fiber or the bundle can then be fixed onto the diodes by 14 means of a layer of transparent glue into which the diodes are sunk. In the absence of the mixing optical component 3, the light beams located in various ranges of wavelengths generated by the light-emitting diodes la-I g are mixed in the fluid to be analyzed, then collected by the optical fibers 12 or the fiber 12' and the optical guide 5 21. In the embodiment in Figure 11, the light beams sent directly to the spectrum analyzing device SPANI are mixed in the fiber 4' and in the light guide 21'. The present invention is not limited either to a light guide 21, 21' in the form of a plate. Other shapes may also be suitable depending on the shape and the distribution of the light-sensitive cells. By providing such a light guide, a light beam 10 can be spread in a substantially homogeneous manner over all the cells of the light sensitive sensor.

Claims

1. A spectrometer comprising: a lighting device (LSRC, LSRCl) configured to generate a light beam covering a wavelength band, a probe (PRB, PRB1, PRB2) configured so that the light beam coming from the lighting device interacts with a fluid to be analyzed (20), and a spectrum analyzing device (SPAN, SPAN1) configured to receive the light beam after it has interacted with the fluid to be analyzed, and to provide light intensity measurements for various ranges of wavelengths, characterized in that the probe (PRIB, PRB1, PRB2) comprises a retro reflective type reflector (13, 13') to the light source, arranged to receive the light beam coming from the lighting device through the fluid to be analyzed (20) and to reflect it substantially in an opposite direction while widening it slightly, to a collecting light guide (12, 12') associated with the reflector and the spectrum analyzing device (SPAN, SPAN1) so as to collect at least partially the light beam having passed through the fluid to be analyzed and to send it to the spectrum analyzing device.

2. Device according to claim 1, wherein the reflector (13, 13') is of Scotchlite@ type or safety reflector type with retro-reflecting prisms.

3. Device according to claim I or 2, comprising an illuminating light guide (4) coupled to the reflector (13, 13') to send the light beam coming from the lighting device (LSRC, LSRCI) to the fluid to be analyzed (20).

4. Device according to claim 3, wherein the reflector (13') has the shape of a spherical shell centered substantially on the center of an output face of the illuminating light guide (4).

5. Device according to claim 3, wherein the probe comprises a converging lens (19) arranged between the output of the illuminating light guide (4) and the fluid to be analyzed (20).

6. Device according to one of claims 3 to 5, wherein the collecting light guide comprises several collecting optical fibers (12) spread around the illuminating light guide (4), the reflector (13, 13') being arranged to send back the light beam after it has passed through the fluid to be analyzed (20) to the collecting optical fibers through the fluid to be analyzed.

7. Device according to one of claims 3 to 5, wherein the probe (PRB2) comprises a Y optical coupler (25) to send the light beam at the output of the illuminating light guide (4) to the fluid to be analyzed (20), and to send the light beam coming from the fluid to be analyzed to the collecting light guide (12').

8. Device according to one of claims 3 to 7, wherein the lighting device comprises a light-emitting diode emitting light covering the wavelength band, coupled to the illuminating light guide (4).

9. Device according to one of claims 3 to 8, wherein the lighting device (LSRC, LSRCI) comprises several light-emitting components (la-1g) emitting light in various ranges of wavelengths included in the wavelength band, the illuminating light guide (4) being coupled to the light-emitting components to send the light emitted by the light-emitting components to the probe (PRB, PRBI, PRB2).

10. Device according to claim 9, wherein the lighting device (LSRC, LSRC1) comprises a mixing optical component (3) to combine the light flows emitted by the light-emitting components (la-Ig) into a resulting light beam covering the wavelength band, the mixing optical component being coupled to the illuminating light guide (4) to guide the resulting light beam in the lighting guide.

11. Device according to claim 10, wherein the mixing optical component (3) has an input face receiving the light coming from the light-emitting components (Ia I g), an output face coupled to the illuminating light guide (4), and a shape having a substantially optimized revolution to send as much light as possible from the light emitting components to the lighting guide.

12. Device according to one of claims 10 and 11, wherein the mixing optical component (3) covers a light-emitting surface of each of the light-emitting components (l a-I g).

13. Device according to one of claims 10 to 12, wherein the mixing optical component (3) is coupled by one or more optical fibers (7a, 7b, 7c) to a light emitting surface of each of the light-emitting components (l a-Ic).

14. Device according to one of claims I to 13, wherein the light beam produced by the lighting device (LSRC, LSRC I) covers a wavelength band between 700 nm and 1,100 nm.

15. Device according to one of claims I to 14, wherein the lighting device (LSRC, LSRCI) comprises several light-emitting components emitting light substantially in the same range of wavelengths.

16. Device according to one of claims 9 to 15, wherein the light-emitting components (la-I g) are light-emitting diodes.

17. Device according to one of claims I to 16, wherein the spectrum analyzing device (SPAN, SPAN1) comprises a first light guide (21) coupled to the probe (PRB, PRB1, PRB2) and receiving the light beam after it has interacted with the fluid to be analyzed (20) and diffusing it to a first set of light-sensitive cells (24, 24') through a first optical filtering device (22) arranged to send each of the light sensitive cells one part of the light beam covering a respective range of wavelengths included in the wavelength band.

18. Device according to claim 17, wherein the first light guide (21) has the shape of a plate made of a transparent material, receiving the light beam coming from the fluid to be analyzed (20) by an edge (210) of the plate and diffusing it by spreading it to an opposite edge (211) of the plate opposite which the first filtering device (22) and the first set of light-sensitive cells (24, 24') are placed.

19. Device according to claim 18, wherein the collecting light guide (12, 12') is coupled to the first light guide (21) to send it the light beam.

20. Device according to claim 18 or 19, wherein the spectrum analyzing device (SPAN, SPANI) comprises a strip of photodetectors (24, 24') comprising the first set of light-sensitive cells, which is fixed onto the edge (211) of the plate (21) through the first filtering device (22).

21. Device according to one of claims 17 to 20, wherein the first filtering device (22) comprises a filter of the spectrum transmission interference type linearly variable over its length.

22. Device according to one of claims 1 to 21, wherein the filtering device (22) covers a wavelength band between 700 nm and 1,100 nm.

23. Device according to one of claims 17 to 22, wherein the spectrum analyzing device (SPANI) comprises a second light guide (21') taking a part of the light beam directly at the output of the lighting device (LSRC, LSRCI) and sending the part of the light beam to a second set of light-sensitive cells (24') through a second optical filtering device (22') arranged to send each of the light-sensitive cells a part of the light beam covering a respective range of wavelengths included in the wavelength band.

24. Device according to claim 23, wherein the second light guide (21') has the shape of a plate made of a transparent material, receiving the part of the light beam coming from the lighting device (LSRC, LSRC1) by an edge of the plate and diffusing it by spreading it to an opposite edge of the plate opposite which the second filtering device (22') and the second set of light-sensitive cells (24') are placed.

25. Device according to claim 24, comprising a light guide (4') coupled to the second light guide (21') to send the light beam coming from the lighting device (LSRC, LSRCI) to the second light guide (21').

26. Device according to one of claims 23 to 25, wherein the spectrum analyzing device (SPAN1) comprises a strip of photodetectors (24') comprising the first and the second sets of light-sensitive cells, which is fixed onto the edge of the plates of the first and second light guides (21, 21') through the first and second filtering devices (22, 22').

27. Device according to one of claims 23 to 26, wherein the second filtering device (22') comprises a filter of the spectrum transmission interference type linearly variable over its length.