AU771803B2 - Compact optical probe and related measuring method - Google Patents

Description

Compact optical probe and related measuring method This invention relates to a compact optical probe for measuring the properties of a sample and to a method of measuring with such a probe. The invention applies notably to the analysis of milk.

To analyse the milk obtained by milking animals, it is known to collect.a sample in a sampling container 1 to homogenlise this sample and to analyse said sample in a laboratory. Such measurements do not enable chain analyses of the milk sampled for each animal, but call for separate treatment, which causes delays and complex operations to obtain results. Moreover, homogenisation of the sample is relatively costly and complex. The more so, the sample of homogenised milk cannot be poured at B later- stage in a tank since it might degrade the milk contained in the tank by lipolysis, and is therefore wasted.

In order to allow chain processing during milking, or just after, it has been suggested to lay out optical probes directly in the milking room, whereas the probes are associated respectively with milk counters. Each of the probes comprises an input optical fibre and an output optical fibre, and all the probes are linked with an analyser, intended for analysing the signals from the differentprobes. The analyser also receives a reference signal which enables to correct the measurements obtained for these probes, as for example in the documents US-A-4677298 or in EP-A-0768521. However, in that state of the art, the reference may also undergo fluctuations depending on the sample measured because of the multiple reflections taken into account for the creation of the reference signal.

The invention concerns a compact optical probe advantageously for a milk counter, enabling to obtain a low-cost measuring device with little space requirements.

The probe of the invention also enables to reduce the noise significantly, by a factor up to 5-6, as well as fluctuations, by a factor greater than In the case of milk, the probe of the invention also enables to collect the milk analysed, since said milk can be poured directly into the tank without any risks of lipolysis.

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

Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material formed part of the prior art base or the common general knowledge in the relevant art in Australia on or before the priority date of the claims herein.

The present invention provides a compact optical probe for measuring the properties of a sample, including: means emitting an incident light beam on the sample, a light diffusion detector, capable of detecting the light diffused by the sample illuminated by the incident beam, and a wall semitransparent to the incident beam, arranged to as to separate the sample from the emitting means and the light diffusion detector, whereas the 15 semitransparent wall has a first surface on the side of the emitting means and of the detectors and a second surface on the side of the sample, a light reflection detector, capable of detecting a beam directly reflected by .the semitransparent wall illuminated by the same incident beam, whereas the reflected beam serves as reference for the diffused beam, characterised in that the reflected beam detected by the reflection detector corresponds only to a reflection on the first surface of the semitransparent wall, a o focus lens on the one hand, and an insulation wall in the form of an insulation cone with a narrow side towards the semitransparent wall and a wide side towards the reflection detector, on the other hand, being arranged on the path of 25 the reflected beam in order to focus said beam onto the reflection detector and to l insulate said beam, whereas the reflection detector distinguishes only a single spot corresponding to said reflection of said light beam incident on the first surface of the semitransparent wall, and in that the sample is a heterogeneous liquid to be analysed, preferably milk, and the probe includes a tub capable of holding the liquid and of being illuminated by the incident beam.

Thus, unlike the existing devices, the semitransparent wall has a double function, separation and semi-reflection, which enables notably the same incident beam to serve simultaneously to the detection of the reflection and of the diffusion. Consequently, each probe generates itself its own reference instead of having a common reference used for all the probes.

The probe of the invention also substantially avoids the detection of diffused light arising from secondary reflection from lower surfaces.

Moreover, such a detector is cheap and enables to obtain a good noise signal ratio.

The whole device including a plurality of probes benefits thus from reduced complexity and considerable improvement of accuracy, thanks to the usage of a reference given by a probe instead of a single reference.

The semitransparent wall has advantageously for a 450 incidence a reflection ration ranging between 3 and 6% and preferably equal to Such a rate surprisingly offers good measuring quality, without it being necessary to produce a higher reflection rate. Such a wall can be obtained by using a simple ordinary glass.

15 In an embodiment variation, the semitransparent wall is treated to obtain a higher reflection percentage.

Preferably, the probe includes at least an electronic processing board carrying the diffusion detection and/or the reflection detector.

Thus, the digital processing functions are distributed in the different probes instead of being concentrated in a central analyser, which amplifies the processing of the measurements considerably. Moreover, the compactness of each probe is not affected by the presence of these boards, which have not only a digital processing function, but also a supporting function for the detectors.

In a preferred embodiment, these boards consist of: 25 a diffusion processing board carrying the diffusion detection, and a reflection processing board carrying the reflection detector.

Thus the calculation and supporting functions are integrated at the same time for the information-carrying signals on the sample and for the reference signals.

The electronic processing boards are for example epoxy resin integrated circuit boards.

Moreover, the boards are advantageously fitted with a digital signal processing capacity (DSP) comprising a fast Fourier transformation module.

Preferably, the electronic processing boards have an adjustable positioning, which enables to adjust the position of the detectors. For example, the boards are hinged by means of 'O'-rings.

The insulation wall is preferably metallic.

Advantageously, as the emitting means exhibit an emitting end, the probe includes an integration sphere surrounding this end.

The positioning of the diffusion and reflection detectors involves 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. The point is to obtain sufficiently high ration 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 sees thus a significant solid angle of the light diffused by the sample.

Moreover, the diffusion detector is sufficiently remote from the reflection path of the incident beam by the semitransparent wall to prevent the diffusion 0 15 measurements from being penalised to much by the specular reflection. The reflection detector is for its own part arranged on the direct reflection path of the incident beam.

Such a probe can be used in a milking room, by being coupled with a milk counter wherein a sample is taken.

Preferably, the tub includes: :**the wall semitransparent to the incident beam, and o 00 a diffusing wall, opposite the emission means and the detectors with respect to the semitransparent wall.

Accordingly, the semitransparent and diffusing walls preferably delineate a oO0o 25 cavity intended for containing 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. It is therefore interesting that the diffusing wall covered by the reference liquid should have diffusion properties similar to those of the liquid sample to be measured. The use of ceramic for the diffusing wall is particularly advantageous to that end for measurements on milk, whereas the reference liquid is water.

In an advantageous embodiment of the probe for the analysis of liquid, this probe includes a circulation system of the liquid inside the tub and in front of the incident beam, in order to authorise the analysis of the heterogeneous liquid by weighing a plurality of measurements.

It is thus possible to skip any homogenisation of the liquid before taking the measurements. For milk, for instance, one need not dispose of sample after analysis any longer and one can pour it as such into the tub without any risk of lipolysis.

It is also advantageous that the probe should include a system for sampling and disposing of the liquid, the system including at least one inlet and at least one output.

Such a system can be connected to a milk counter for sample collections.

The combined use of the liquid circulation system and of the liquid S sampling and disposal system is particularly advantageous to perform on-line measurements on a non homogenised liquid, such as milk.

SO S•In a preferred realisation of such a probe: the liquid circulation system includes a bubble trap, and the liquid sampling and disposal system includes alternative reversal 0 means of the sampling direction.

Thus, during each sampling, reversing the inlet and the outlet of the 46 sampling and disposal system enables to evacuate bubbles contained in the 0 bubble trap.

Advantageously, the probe for liquid sample includes a liquid heating device including: 25 a wound electrically conducting tube, preferably made of stainless steel, intended for the circulation of the liquid, and means for applying a voltage at the terminals of the conducting tube.

The wound tube forms thus a thin coil, which may reach 2 m in length and have a resistance of a few ohms. With respect to conventional heat exchanger systems, this realisation offers quasi-instantaneous energy transfer with very rapid regulation and it is economical.

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

6 This realisation is particularly efficient for milk, and gives improved results with respect to measurements taken in medium-infrared on homogenised milk.

Such a preferred range of the wavelengths of the incident beam extends between 1000 and 2500 nm.

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

Advantageously, the probe is used fro spectral measurements on a sample. Thus, in a preferred embodiment, the emitting means of the probe are coupled to a monochromator. It is then interesting to use a wavelength modulation-demodulation technique.

The invention also concerns methods for 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 sampling and disposal system, the sample is milk and the probe is used in the following way: milk is sampled in the probe from a milk counter, the milk sampled using the probe is then analysed, and the milk once analysed is then poured into a tank.

.In another such preferred embodiment, before carrying out a series of 20 analyses, the probe is calibrated with water.

Thus, the specific contribution of the analysed liquid sample can be .g* derived. The calibration is advantageously carried out periodically, for example every day in normal milking conditions.

"Comprises/comprising" when used in this specification is taken to specify 25 the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof." The invention will be illustrated and understood better by means of particular embodiments and applications, with reference to the appended •*go drawings, whereon: Figure 1 represents a longitudinal section of a compact optical probe according to the invention; Figure 2 shows along a longitudinal section opposite that of Figure 1, a portion of the elements of the probe of Figure 1 comprising the elements for detecting the light diffused by a sample; Figure 3 shows along the section of Figure 1, a portion of the elements of the probe of Figures 1 and 2, comprising the elements for detecting the light reflected directly by a wall of the probe; Figure 4 is a principle scheme representing in the form of functional blocks, the probe of Figures 1 to 3 and the related device, and Figure 5 illustrates schematically the use of the tub of the probe of Figures 1 to4.

The content of the appended figures must be considered as an integral part of the description.

A compact optical probe 1 (Figures 1 and 4) comprises an optical fibre receiving a light emitted from a source 2 by means for a wavelength modulation system 3. This modulation system 3 comprises preferably a monochromator foreseen to operate in the near-infrared. Moreover, it is advantageously fitted with a chopper. The fibre 20 comprises an emitting end 24 through which a light going through that fibre 20 is intended to be sent to a sample. It is carried via a console 22 forming a square fixed on a base 54 (Figures 1 and The fibre 20 is S 20 surrounded with a brass sleeve 21.

The probe 1 has a structure including (Figure 1) the base 54 forming the bottom of a tub 50, itself covered with a lid 60 inside which are arranged the S various light emitting and detecting elements. The tub 50 comprise a wall 51 semitransparent to the incident beam, i.e. in this case substantially transparent to 25 the near-infrared, made for instance of a glass plate. This semitransparent wall 51 separates the tub 50 from the optical elements arranged under the lid The probe 1 is fitted 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 elements foreseen to detect the light reflected directly by the semitransparent wall 51.

The probe 1 comprises therefore a diffusion detector 30 (Figure 2) arranged close to the end 24 of the optical fibre 20. This detector 30 is carried by a integrated circuit board 31, formed for example of epoxy resin and positioned on three supporting columns 71-73 by means of respectively three positioning holes 74-76 (Figures 1 to 3).

The probe 1 also comprises a reflection detector 40 (Figures 1 and 3), capable of detecting a beam reflected directly by the wall 51 illuminated by the optical fibre 20. This detector 40 is carried by an integrated circuit board 41 and is arranged with respect to the orientation of the fibre 20 according to the conventional laws of the specular reflection with respect to the sample. A metal cone 43 is arranged between the detector 40 and the sample, in order to surround and to insulate, up to the detector 40, the beam reflected by the semitransparent wall 51. This cone 43 comprises a wide side 48 directed towards the detector 40 and a narrow side 49 directed towards the semitransparent wall 51. Moreover, it carries a focusing lens 4.

The probe is also fitted with an integration sphere 45 surrounding the end 24 of the fibre The boards 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 demodulation components of the boards 31 and 41 are synchronised by a clock 5 by means of a stepping motor 6 (Figure For example, the clock 5 emits 12-MHz pulses and the motor runs 500 steps per revolution and produces therefore 1000 pulses per revolution (using semi-steps).

As regards the processing of signals, the boards 31 and 41 are preferably fitted respectively with pre-amplifiers 36 and 46 and analogue-digital converters 37 and 47 (Figure For exemplification purposes, these converters are 20 bit converters, which offers very important dynamics and dispenses with managing the gains.

A digital signal processing (DSP) module 38, for example arranged on the diffusion processing board 31 receives information from both converters 37 and 47. The module 38 processes information relating to the diffused light and 9 the light reflected directly by the wall 51 and comprises notably fast Fourier transformation calculation and spectre storage capacities.

The tub 50 also comprises a diffusing wall 52, made for example of ceramic, which delineates with the transparent wall 51 a cavity 53 intended for containing a liquid such as milk. A liquid inlet 55 and output 56, with interchangeable functions, enable to inject the liquid into the cavity 53 and to extract said therefrom, using a liquid sampling and disposal device. A lid 63, opposite the semitransparent wall 51 of the tub 50, serves as a cache.

The cavity 53 is associated with a liquid circulation device inside the tub, in front of the incident beam emitted by the fibre 20 and defines therefore a circuit 57 inside the tub 50 (Figure A bubble trap 58 is arranged in the circuit 57 for degassing the liquid analysed.

Moreover, the cavity 53 is associated with means for heating the sampled liquid comprising for instance a coil made of a long and wound stainless steel tube and to which voltage is applied, wherein the liquid circulates.

In operation, a liquid such as milk is sampled through the inlet 55 in the cavity 53 and it is subject to a series of measurements. To do so, an incident beam is emitted by the fibre 20 towards a point P of the upper surface of the transparent wall 51 (Figures 1 to 3) and thus towards the sample, whereas the sample represents the liquid inside the cavity 53.

One operates the modulation system 3 in order to produce for example a signal having a wavelength ranging between 1000 and 3000 nm and strobe modulated at I kHz frequency.

The temperature of the assembly is for example maintained equal to 2% and more accurately for liquid, equal to 40C 1 One proceeds, using analogue-digital converters 37 and 47, to acquisition of data, for example at a frequency of 40 acquisitions per period, i.e.

kHz. For each wavelength of the modulation produced in the incident beam, one performs on each period fast Fourier transforms by means of the module 38, while carrying out slipping measurements by offsetting the measuring period from one point to another. One proceeds in such a way for 20 to 150 complete periods, while storing the results obtained for each of the complete periods.

One goes then to another wavelength of the modulation produced by the modulation system 3 and one proceeds in the same way as previously. One repeats these operations on approximately 300 wavelengths, spaced for instance by 3 nm, which enables to obtain finally a response spectrum of the sample with an amplitude of approximately 0.9 pm. For twenty complete periods of one ms, the 300 points of the spectrum require then approximately 0.6 second.

As the liquid is heterogeneous, for example milk, one causes said liquid to circulate as a short-circuit inside the cavity 53 in front of the measuring point P while realising multiples spectra, then one weighs the results obtained in order to provide an average spectrum. Thus, the heterogeneity of the liquid is then taken into account thanks to a sufficient number of spectra.

Once the liquid sampled from the tub 50 is considered as analysed sufficiently, either by the production of a given number of spectra or the realisation of a convergence criterion over the average of the spectra, one discharges the liquid through the output 56 and one carries out a new sampling through the inlet 55. In order to discharge the bubble trap 58, one causes then the liquid sampled in the cavity 53 to circulate in one direction 62 of the circuit 57 opposite the direction 61 of circulation adopted previously (Figure In case when the liquid is milk, said liquid can be discharged directly into the tank since it has kept its heterogeneous form.

Before each series of measurements on the liquid to be analysed, one proceeds to a calibration while sampling water in the cavity 53.

In an embodiment variation, one does not use any modulators and one performs continuous measurements.

Claims (17)

1. A compact optical probe for measuring the properties of a sample, including: means emitting an incident light beam on the sample, a light diffusion detector, capable of detecting the light diffused by the sample illuminated by the incident beam, and a wall semitransparent to the incident beam, arranged to as to separate the sample from the emitting means and the light diffusion detector, whereas the semitransparent wall has a first surface on the side of the emitting means and of the detectors and a second surface on the side of the sample, a light reflection detector, capable of detecting a beam directly reflected by the semitransparent wall illuminated by the same incident beam, whereas the reflected beam serves as reference for the diffused beam, characterised in that the reflected beam detected by the reflection detector corresponds only to a reflection on the first surface of the semitransparent wall, a focus lens on the one hand, and an insulation wall in the form of an insulation cone with a narrow side towards the semitransparent wall and a wide side towards the reflection detector, on the other hand, being arranged on the path of 200"0 the reflected beam in order to focus said beam onto the reflection detector and to .o 20 insulate said beam, whereas the reflection detector distinguishes only a single :00 spot corresponding to said reflection of said light beam incident on the first .0 S" surface of the semitransparent wall, and in that the sample is a heterogeneous liquid to be analysed, preferably milk, and the probe includes a tub capable of holding the liquid and of being illuminated by the incident beam. 0 0 loll 25

2. A probe according to claim 1, characterised in that the semitransparent 0 .00. wall has for a 450 incidence a reflection ratio ranging between 3% and and preferably equal to

3. A probe according to any one of the claims 1 or 2, characterised in that it includes at least one electronic processing board carrying the diffusion detector and/or the reflection detector.

4. A probe according to claim 3, characterised in that said boards include: a diffusion processing board carrying the diffusion detector, and a reflection processing board carrying the reflection detector.

A probe according to any one of the claims 1 to 4, characterised in that the emitting means exhibit an emitting end of a light beam and the probe includes an integration sphere surrounding said end.

6. A probe according to any one of the claims 1 to 5, characterised in that the tub includes: said semitransparent wall, and a diffusing wall, opposite the emission means and the detectors with respect to the semitransparent wall, the semitransparent and diffusing walls delineating a cavity intended for containing the liquid.

7. A probe according to claim 6, characterised in that the diffusing wall is made of ceramic, preferably alumina. o•

8. A probe according to any one of the claims 1 to 7, characterised in that it o includes a circulation system of the liquid inside the tub and in front of the incident beam. ••loll

9. A probe according to any one of the claims 1 to 8, characterised in that it includes a system for sampling and disposing of the liquid, the system including at least one inlet and at least one output coupled to the tub.

10. A probe according to claim 8 or 9, characterised in that: ll the liquid circulation system includes a bubble trap, and the liquid sampling and disposal system includes alternative reversal *ooo means of the sampling direction.

11. A probe according to any one of the claims 1 to 10, characterised in that it includes a liquid heating device including: 13 a wound electrically conducting tube, preferably made of stainless steel, intended for the circulation of the liquid, and means for applying a voltage at the terminals of the conducting tube.

12. A probe according to any one of the claims 1 to 11, characterised in that the emitting means of the incident beam emit in the near-infrared.

13. A method of measuring the properties of a sample with the probe according to any one of the claims 9 to 12, characterised in that the sample is a heterogeneous liquid, preferably milk, and in that one uses the probe in the following way: the liquid is sampled in the probe from a counter; the liquid sampled using the probe is then analysed, and the liquid once analysed is then poured into a tank.

14. A method according to claim 13, characterised in that the analysis of the heterogeneous liquid involves weighing a plurality of measurements.

15 15. A method of measuring the properties of a sample with the probe according to any one of the claims 1 to 12, characterised in that, before carrying out a series of analyses, the probe is calibrated with water. o

16. A compound optical probe for measuring the properties of a sample substantially as herein described with reference to the accompanying drawings. o oooo o. oooo 0o 14

17. A method for measuring the properties of a sample substantially as herein described with reference to the accompanying drawings. DATED this 4th day of February 2004 LA FEDERATION FRANCAISE DE CONTROLE LAITIER WATERMARK PATENT TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA RLT/MAS/AXO *o