WO2001036942A1

WO2001036942A1 - Compact optical probe and related measuring method

Info

Publication number: WO2001036942A1
Application number: PCT/FR2000/003203
Authority: WO
Inventors: Philippe Chauvin; Philippe Younes
Original assignee: La Federation Francaise De Controle Laitier (F.C.L.)
Priority date: 1999-11-19
Filing date: 2000-11-17
Publication date: 2001-05-25
Also published as: FR2801383B1; EP1234168A1; AU1868201A; CA2392258A1; JP2003515125A; IL149727A0; FR2801383A1; AU771803B2

Abstract

The invention concerns a compact optical probe and a measuring method associated with said probe. The probe (1) comprises means emitting (20) an incident light beam on a sample, a light diffusion detector capable of detecting the light diffused by the sample and a wall semitransparent (51) to the incident beam arranged so as to separate the sample from the emitting means and the light diffusion means. The probe also comprises a light reflection detector (40), capable of detecting a beam directly reflected by the semitransparent wall illuminated by the same incident beam. The reflected beam serves as reference for the diffused beam.

Description

Compact optical probe and associated measurement method

The present invention relates to a compact optical probe for measuring the properties of a sample and to a measurement method with such a probe. The invention is particularly applicable to the analysis of milk. To analyze the milk obtained following milking of animals, it is known to collect a sample in a collection container, to homogenize this sample and to analyze it in the laboratory. Such measures do not allow chain analyzes of the milk sampled for each animal but require separate processing, which involves time and complex operations to obtain results. In addition, the homogenization of the sample is relatively expensive and complex. What is more, the homogenized milk sample cannot be subsequently discharged into a reservoir, on pain of causing degradation of the milk contained in the reservoir by lipolysis, and is thus lost.

In order to authorize a chain processing during milking or immediately after, it has been proposed to have optical probes directly in the milking parlor, the probes being associated respectively with milk counters. Each of the probes comprises an input optical fiber and an output optical fiber, and all the probes are connected to an analyzer, intended to analyze the signals coming from the different probes. The analyzer also receives a reference signal which makes it possible to correct the measurements obtained for these probes.

The invention relates to a compact optical probe advantageously for a milk counter, making it possible to obtain a measuring device having a reduced size and which can be economical. The probe of the invention also makes it possible to significantly reduce noise, by a factor of up to 5 to 6, as well as fluctuations, by a factor of up to 10.

In the case of milk, the probe of the invention also makes it possible to recover the milk analyzed, the latter being able to be discharged directly into the reservoir without risk of lipolysis. The compact optical probe of the invention applies more generally to the measurement of various liquid, semi-solid or solid materials, such as, for example, fodder.

The invention also relates to a method for measuring the properties of a sample with the probe of the invention.

To this end, the invention applies to a compact optical probe for measuring the properties of a sample, comprising:

Means for emitting an incident light beam on the sample, a scattering detector capable of detecting light scattered by the sample illuminated by the incident beam, and

• a semi-transparent wall to the incident beam, arranged so as to separate the sample from the emission means and from the diffusion detector.

According to the invention, the probe also comprises a reflection detector, capable of detecting a beam reflected directly by the semi-transparent wall illuminated by the same incident beam, the reflected beam serving as a reference for the scattered beam. Thus, unlike existing devices, the semi-transparent wall has a double separation and semi-reflection function, which in particular allows the same incident beam to serve simultaneously for the detection of the reflection and of the scattering. Therefore, each probe itself produces its own reference instead of a common reference being used for all the probes.

The assembly of the device comprising a plurality of probes thus benefits from a reduction in complexity and a considerable improvement in precision, thanks to the use of a reference by probe instead of a single reference.

The semi-transparent wall advantageously has, for an incidence of 45 °, a reflection rate of between 3 and 6%, and preferably equal to 5%.

Such a rate surprisingly offers a good quality of measurement, without it being necessary to produce a rate of higher reflection. Such a wall can be obtained by the use of a simple ordinary glass.

In an alternative embodiment, the semi-transparent wall is treated to obtain a higher percentage of reflection. Preferably, the semi-transparent wall having a first surface on the side of the emission means and the detectors and a second surface on the side of the sample, the reflection detector is small enough to distinguish substantially only a single corresponding spot. to a reflection on the first surface of the semi-transparent wall.

This avoids the detection of scattering light from secondary reflections on lower surfaces. In addition, such a detector is economical and makes it possible to obtain a good signal to noise ratio. Preferably, the probe comprises at least one electronic processing card carrying the diffusion detector and / or the reflection detector.

Thus, the digital processing functions are distributed among the different probes instead of being concentrated in a central analyzer, which considerably simplifies the processing of the measurements. In addition, the compactness of each probe is not affected by the presence of these cards, which not only have a digital processing function but also a support function for the detectors. In a preferred embodiment, these cards consist of:

A diffusion processing card carrying the diffusion detector, and

• a reflection processing card carrying the reflection detector. Thus, the integration of the calculation and support functions is carried out both for the signals carrying information on the sample and for the reference signals.

The electronic treatment cards are for example integrated circuit boards made of epoxy resin. In addition, the cards are advantageously provided with digital signal processing capacity (DSP or Dig ital Signal Processing) comprising a fast Fourier transformation module (FFT). Preferably, the electronic processing cards have an adjustable positioning, which makes it possible to adjust the position of the detectors. For example, the cards can be articulated by means of O-rings.

The probe preferably comprises an isolation partition provided for surrounding and isolating the beam reflected by the semi-transparent wall. This insulating partition advantageously has a cone shape having a narrow side towards the semi-transparent wall and a wide side towards the reflection detector. In addition, it is advantageous for the isolation partition to carry a focusing lens designed to focus the beam reflected directly by the semi-transparent wall on the reflection detector. The insulation partition is preferably metallic.

Advantageously, the emission means having an emission end, the probe comprises a sphere of integration surrounding this end.

The positioning of the diffusion and reflection detectors brings into play on the one hand their proximity with respect to the emission end and on the other hand their orientation with respect to the incident beam. It is a question of obtaining a sufficiently high ratio between the diffused light and the reflected light detected. Preferably, the diffusion detector is arranged as close as possible to the emission end. This detector thus sees an ang the important solid of the light diffused by the sample. In addition, the scattering detector is far enough away from the direct reflection path of the incident beam by the semi-transparent wall to prevent the scattering measurements from being penalized too much by the specular reflection. The reflection detector is q uant disposed on the direct reflection path of the incident beam. In a preferred embodiment, the probe is provided for analyzing a liquid, preferably milk, and comprises a tank capable of containing the liquid and of being illuminated by the incident beam. Such a probe can be used in a milking parlor, coupled with a milk meter from which a sample is taken.

Preferably, the tank comprises: • the semi-transparent wall to the incident beam, and • a diffusing wall, opposite the emission means and the detectors with respect to the semi-transparent wall. The semi-transparent and diffusing walls delimit a cavity intended to contain the liquid.

The diffusing wall is then advantageously made of ceramic, preferably alumina.

The diffusing wall is particularly useful when calibrating the probe with a reference liquid, for example water. I t is then interesting that the diffusing wall covered by the reference liquid has diffusion properties similar to those of the liquid sample to be measured. The use of ceramic for the diffusing wall is particularly advantageous for this purpose for measurements on milk, the reference liquid being water.

In an advantageous embodiment of the probe for liquid analysis, this probe comprises a system for circulating the liquid inside the tank and in front of the incident beam, so as to allow the analysis of a liquid heterogeneous by weighting on a plurality of measures.

It is thus possible to refrain from any homogenization of the liquid before the measurements. For milk, for example, this avoids having to throw away the analyzed sample and it can be poured as it is into the tank without risk of lipolysis.

It is also advantageous that the probe comprises a system for collecting and rejecting the liquid comprising at least one inlet and at least one outlet. Such a system can be connected to a milk meter for sampling.

The combined use of the liquid circulation system and the liquid withdrawal and rejection system is particularly advantageous for carrying out series measurements (on-line) on a non-homogenized liquid, such as milk.

In a preferred embodiment of such a probe:

• the liquid circulation system comprises a bubble trap, and • the liquid collection and discharge system comprises means for alternating reversing the direction of collection.

Thus, during each sampling, the inversion of the inlet and the outlet of the sampling and rejection system makes it possible to evacuate bubbles contained in the bubble trap.

Advantageously, the liquid sample probe comprises a device for heating the liquid comprising:

A coiled electrically conductive tube, preferably made of stainless steel, intended for the circulation of the liquid, and

• means for applying a voltage across the conductive tube.

The coiled tube thus constitutes a fine coil, which can reach, for example, 2 m in length and have a resistance of a few ohms. Compared to conventional systems of temperature exchangers, this embodiment offers an almost instantaneous transfer of energy with very rapid regulation and it is economical.

Preferably, the liquid analysis probe is such that the means for emitting an incident beam emit in the near infrared.

This embodiment is particularly effective for milk, and gives improved results compared to measurements carried out by infrared medium on homogenized milk. A preferred wavelength range of the incident beam is between 1000 and 2500 nm.

In other embodiments, the probe is applicable to a solid sample, such as for example fodder. The semi-transparent wall to the incident beam is then intended to be applied directly against the sample.

Advantageously, the probe is used for spectral measurements on a sample. Thus, in a preferred embodiment, the emission means of the probe are coupled to a monochromator. I t is then interesting to use a wavelength modulation-demod ulation technique.

The invention also relates to methods of measuring the properties of a sample with the probe for liquid analysis according to the invention. In one of these preferred methods, involving the probe with the liquid collection and rejection system, the sample is milk and the probe is used as follows:

• milk is taken from the probe from a milk meter, • the milk sampled is analyzed by the probe, and

• the milk analyzed is rejected into a tank.

In another of these preferred methods, before performing a series of analyzes, the probe is calibrated with water. The specific contribution of the analyzed liquid sample is thus identified. The swimming standard is advantageously carried out periodically, for example each day under normal milking conditions.

The invention will be illustrated and better understood by means of specific examples of embodiment and implementation, with reference to the appended drawings, on which:

Fig ure 1 shows a long itud inal section of a compact optical probe according to the invention;

Figure 2 shows in a long itudinal section opposite to that of Fig ure 1, part of the elements of the probe of the Figure 1 comprising the elements for detecting the light scattered by a sample;

Fig ure 3 shows along the section of Figure 1, a part of the elements of the probe of Fig ures 1 and 2, comprising the elements for detecting the light reflected directly by a wall of the probe;

Fig ure 4 is a block diagram showing in the form of functional blocks the probe of Fig ures 1 to 3 and the associated device, and Fig ure 5 schematically illustrates the use of the tank of the probe of Figures 1 to 4.

The content of the attached figures should be considered as an integral part of the description.

A compact optical probe 1 (Figures 1 and 4) comprises an optical fiber 20 receiving light emitted from a source 2 by means of a wavelength modulation system 3. This mod ulation system 3 preferably comprises a monochromator intended to function at near infrared. In addition, it is advantageously provided with a chopper. The fiber 20 comprises an emission end 24 through which a light passing through this fiber 20 is intended to be sent to a sample. It is carried by a console 22 forming a bracket fixed on a base 54 (Figures 1 and 3). The fiber 20 is surrounded by a brass sleeve 21. Probe 1 has a structure essentially comprising

(Figure 1) the base 54 forming the base of a tank 50, itself covered with a cover 60 inside which are arranged all of the light emission and detection elements. The tank 50 comprises a wall 51 semi-transparent to the incident beam, that is to say in this case essentially transparent to the near infrared, consisting for example of a glass plate. This semi-transparent wall 51 separates the tank 50 from the optical elements arranged under the cover 60.

The probe 1 is provided with a set of detection components comprising on the one hand elements used for the detection of a light diffused by the sample and on the other hand of the elements intended to detect a light reflected directly by the semi-transparent wall 51.

The probe 1 thus comprises a diffusion detector 30 (FIG. 2) disposed near the end 24 of the optical fiber 20. This detector 30 is carried by an integrated circuit card 31, formed for example of epoxy resin and positioned on three support columns 71 -73 by means of three positioning holes 74-76 respectively (Figures 1 to 3). The probe 1 also includes a reflection detector

40 (Figures 1 and 3), capable of detecting a beam reflected directly from the wall 51 lit by means of the optic fiber 20. This detector 40 is carried by an integrated circuit card 41 and is arranged relative to the orientation of fiber 20 according to the classic laws of specular reflection with respect to the sample. A metal cone 43 is placed between the detector 40 and the sample, so as to surround and isolate the beam reflected by the semi-transparent wall 51 up to the detector 40. This cone 43 includes a wide side 48 d towards the detector 40 and a narrow side 49 directed towards the semi-transparent wall 51. In addition, it carries a focusing lens 44.

The probe 1 is also provided with an integration sphere 45 surrounding the end 24 of the fiber 20.

The cards 31 and 41 are connected to a processing unit 4, which is also connected to the modulation system 3 (Figure

4).

The modulation system 3 and the demod ulation components of the cards 31 and 41 are synchronized by means of a clock 5 via a stepping motor 6 (Fig ure 4). For example, the clock 5 emits pulses at 12 MHz and the motor passes through 500 steps per revolution, and therefore produces 1000 pulses per revolution (use of half-steps).

With regard to signal processing, the cards 31 and 41 are preferably provided with preamplifiers 36 and 46 respectively and with analog- Numeric 37 and 47 (Figure 4). By way of example, these converters are 20 bit converters, which offers a very significant dynamic and avoids having to manage gains.

A digital signal processing module (DSP) 38, for example arranged on the broadcast processing card 31, receives information from the two converters 37 and 47. The module 38 processes information relating to both diffused light and light directly reflected by the wall 51, and in particular includes capacities for calculating fast Fourier transformation and storing spectrum.

The tank 50 also comprises a diffusing wall 52, made for example of ceramic, which delimits with the transparent wall 51 a cavity 53 intended to contain a liquid such as milk. An inlet 55 and an outlet 56 for liquid, having interchangeable functions, make it possible to introduce the liquid into the cavity 53 and to extract it therefrom, using a device for withdrawing and rejecting liquid. A cover 63, opposite the semi-transparent wall 51 of the tank 50, acts as a cover.

The cavity 53 is associated with a device for circulating the liquid inside the tank, in front of the incident beam emitted by the fiber 20 and therefore defines a circuit 57 internal to the tank 50 (Figure 5). A bubble trap 58 is placed in the circuit 57 to degas the liquid being analyzed.

In addition, the cavity 53 is associated with means for heating a liquid taken up comprising for example a coil made up of a long tube of stainless steel wound and tensioned, in which the liquid circulates.

In operation, a liquid such as milk is taken through the inlet 55 into the cavity 53 and is subjected to a series of measurements. For this, an incident beam is emitted by the fiber 20 towards a point P of the upper surface of the transparent wall 51 (Fig ures 1 to 3), and thus towards the sample, the sample representing the liquid within of cavity 53.

The modulation system 3 is operated so as to produce for example a signal having a wavelength between 1000 and 3000 nm and modulated in a slot at a frequency of 1 kHz.

The temperature of the assembly is for example maintained equal to 40 ° C + 2% and more precisely for the liquid, equal to 40 ° C + 1%. _.

Data acquisitions are carried out by means of the analog digital converters 37 and 47, for example at a frequency of 40 acquisitions per period, ie at 40 kHz. For each wavelength of the modulation produced in the incident beam, rapid Fourier transformations are performed over each period by means of the module 38, by carrying out sliding measurements by shifting the measurement period from point to point. This is done for 20 to 150 full periods, storing the results obtained for each of these full periods.

We then pass to another wavelength of the mod ulation produced by the modulation system 3, and we proceed in the same manner as above. These operations are repeated over approximately 300 wavelengths, spaced apart for example by 3 nm, which allows finally obtaining a response spectrum of the sample having an amplitude of approximately 0.9 μm. For twenty full periods of one ms, the 300 points of the spectrum thus require approximately 0.6 seconds.

The liquid being heterogeneous, for example milk, it is circulated in a closed circuit inside the cavity 53 in front of the measurement point P while carrying out multiple spectra, then the results obtained are weighted so as to get an average spectrum. One thus takes into account the heterogeneity of the liquid thanks to a sufficient number of spectra. Once the liquid taken from the tank 50 is considered to have been analyzed in a sufficient manner, either by obtaining a given number of spectra, or by achieving a convergence criterion on the mean of the spectra , the liquid is discharged through the outlet 56 and a new sample is taken through the inlet 55. In order to discharge the bubble trap 58, it is imposed then the liquid taken from the cavity 53 to flow in a direction 62 of the circuit 57 opposite to the direction 61 of circulation adopted previously (Figure 5). In the case where the liquid is milk, it can be discharged directly into the reservoir since it has retained its heterogeneous form.

Before each series of measurements on the liquid to be analyzed, a calibration is carried out by taking water from the cavity 53.

In an alternative embodiment, no modulator is used and the measurements are carried out continuously.

Claims

REVENDI CATIONS

1. Compact optical probe (1) for measuring sample properties, comprising:

Means of emission (20) of a mined read beam incident on the sample,

• a diffusion detector (30), capable of detecting light scattered by the sample illuminated by the incident beam, and

A semi-transparent wall (51) to the incident beam, arranged so as to separate the sample from the emission means (20) and from the diffusion detector (30),

• a reflection detector (40), capable of detecting a beam reflected directly by the semi-transparent wall (51) illuminated by said same incident beam, said reflected beam serving as a reference for the scattered beam, characterized in that the semi wall -transparent (51) having a first surface on the side of the emission means (20) and detectors (30, 40) and a second surface on the side of the sample, the reflection detector (40) is small enough to not substantially distinguish only a single spot corresponding to a reflection on the first surface of the semi-transparent wall (51), and in that the sample is a liquid to be analyzed preferentially milk, and the probe comprises a tank (50 ) capable of containing the liquid and of being illuminated by the incident beam.

2. Probe according to claim 1, characterized in that the semi-transparent wall (51) has an incidence of 45 ° a reflection rate between 3 and 6%, and preferably equal to 5%.

3. Probe according to any one of claims 1 or 2, characterized in that it comprises at least one electronic processing card (31, 41) carrying the diffusion detector (30) and / or the reflection detector (40 ).

4. Probe according to claim 3, characterized in that said cards consist of:

• a diffusion processing card (31) carrying the diffusion detector (30), and • a reflection processing card (41) carrying the reflection detector (40).

5. Probe according to any one of claims 1 to 4, characterized in that it comprises an isolation partition (43) provided to surround and isolate the beam reflected by the semi-transparent wall (51), advantageously having a cone shape having a narrow side towards the semi-transparent wall (51) and a wide side towards the reflection detector (40).

6. Probe according to claim 5, characterized in that the isolation partition (43) carries a focusing lens (44) intended to focus the beam reflected directly by the first surface of the semi-transparent wall (51) on the reflection detector (40).

7. Probe according to any one of claims 1 to 6, characterized in that the emission means (20) having an emission end (24), the probe (1) comprises an integration sphere (45) surrounding said end (24).

8. Probe according to any one of claims 1 to 7, characterized in that the tank (50) comprises: • said semi-transparent wall (51), and

• a diffusing wall (52), opposite the emission means (20) and the detectors (30, 40) relative to the semi-transparent wall (51), the semi-transparent (51) and diffusing (52) walls delimiting a cavity (53) intended to contain the liquid.

9. A probe according to claim 8, characterized in that the diffusing wall (52) is made of ceramic, preferably alumina.

10. Probe according to any one of claims 1 to 9, characterized in that it comprises a circulation system of the liquid (57) inside the tank (50) and in front of the incident beam, so as to allow the analysis of a heterogeneous liquid by weighting on a plurality of measurements.

1 1. Probe according to any one of claims 1 to 10, characterized in that it comprises a system for withdrawing and rejecting the liquid comprising at least one inlet (55) and at least one outlet (56).

12. Probe according to claims 10 and 1 1, characterized in that: • the circulation system (57) of the liquid comprises a bubble trap (58), and

• the liquid withdrawal and rejection system comprises means for alternating reversing the direction (61, 62) of withdrawal.

13. Probe according to any one of claims 1 to 12, characterized in that it comprises a device for heating the liquid comprising:

• means for applying a voltage across the conductive tube.

14. Probe according to any one of claims 1 to 13, characterized in that the emission means (20) of the incident beam emit in the near infrared.

15. A method of measuring the properties of a sample with the probe (1) according to claim 1 1 and to any one of claims 1 1 to 14, characterized in that the sample is milk and in that '' use probe (1) as follows:

• milk is drawn into the probe (1) from a milk meter,

• the milk sampled is analyzed using the probe

(1) and • the milk analyzed is rejected into a tank.

16. Method for measuring properties of a sample with the probe according to any one of claims 1 to 14, characterized in that before carrying out a series of analyzes, the probe (1) is calibrated with some water.