WO2012007542A1

WO2012007542A1 - Optical measurement method and apparatus

Info

Publication number: WO2012007542A1
Application number: PCT/EP2011/062046
Authority: WO
Inventors: Matthew Rice; James Duncan Holloway
Original assignee: Matthew Rice; James Duncan Holloway
Priority date: 2010-07-16
Filing date: 2011-07-14
Publication date: 2012-01-19

Abstract

The present invention relates to a method and apparatus for determining at least the concentration or turbidity of a dispersed phase suspended in a- fluid, comprising the emission of a light beam (12) into a sample (18) of the fluid and the detection of scattered light (19) from the fluid sample (18). The present invention specifically teaches the selection of used wavelength for the light beam (12) so that at least one wavelength of the light beam is absorbed by the continuous phase, e.g. water, of the fluid sample (18), and the use of the absorption in the determination of the concentration or turbidity of a dispersed phase, e.g. fat.

Description

Opt ical Measurement Method and Apparatus

FIELD OF THE INVENTION

This invention relates to turbidity apparatus used for measurement of the concentration of a dispersed phase in a fluid. More specifically, this invention relates to a method and apparatus for accurately measuring very turbid samples, such as the fat concentration in dairy cream.

BACKGROUND TO THE INVENTION

The turbidity of a fluid is the cloudiness caused by individual particles (dispersed phase) that are suspended in a fluid (continuous phase) and is a measure of the light scattered by the particles that is characteristic of the number and size of particles present in the sample. Typical examples of turbid samples include emulsions (e.g. milk, cream, personal care products, home care products, deodorants), suspensions (e.g. waste water, deodorant), dispersions (inks, paints, coatings), foams (e.g. shaving cream, hair mousse, personal care products, home care products) and also biological fluids, bacteria, polymer emulsions etc. Turbidity is a commonly employed technique for measuring the

concentration of the dispersed phase.

Turbidity can be determined by either measuring the attenuation of a light passing directly through a fluid sample or by the measurement of scattered light. In accordance with international standards for the measurement of turbidity, ISO 7027:1999(E) & EPA Method 180.1, turbidity is measured by monitoring scattered light at 90 degrees using a light that is not absorbed by either the continuous or dispersed phase. ISO 7027 specifies 860 nm as the wavelength of the light as this wavelength is least influenced by dissolved light-absorbing substances present in natural occurring waters, while EPA 180.1 and patent publication US 5064590 specifies the light from a tungsten lamp with a peak wavelength of between 400 nm and 600 nm.

When measuring the concentration of a dispersed phase using the attenuation of light, such as measuring the fat content in milk, a wavelength can be chosen that will be absorbed by the dispersed phase. This technique requires that discrete wavelengths of tight are absorbed by the dispersed phase (fat), typically between 2,5 Mm and 10 um. However, a limitation with this technique is that even low concentration milk samples oft en have very high optical densities; typically a 3,5 % fat milk sample will require an optical path length of 37 um, as shown in patent publication US 4247773, in order to allow sufficient light to reach the optical detector. Patent publication US 3 161768 describes a similar technique and teaches that optical path lengths of 10-100 μm are required. Such path-lengths are generally not practical and the sample would therefore require dilution prior to analysis. Dilution introduces both operator error plus the fact that any dilution may physically influence the sample. For real-time turbidity measurement in industrial process streams, dilution of the sample is not possible. Dilution is therefore not a preferred procedure.

Patent publication US 6937332 describes an improved turbidity apparatus that can monitor turbid samples up to 10000 NTU using a backscatter detector mounted at 138 degrees from the incoming light path. With such an approach, the backscatter sensing system will extend the range of a conventional turbidity sensing systems when the fluid under evaluation is so turbid that light scattered from the incoming light cannot make it to the light detector. The reason for this is that the detector is placed at a distance from the light source and as a result of multiple scattering; the absorption path-length is sufficiently long that all the photons become absorbed by the media. However, publication US 6937 332 only extends the operating range to 10000 NTU where it is presumed above this turbidity that no light can make it to the detector.

Patent publications EP 0017007 and WO 8809494 describes a backscatter turbidity apparatus whereby the light source is placed in very close proximity to the detector, essentially at 180 degrees to the direction of the incoming light path, further reducing the absorption path-length, using two adjacent parallel optical fibers. By this approach, samples with turbidities above 10000 NTU can be monitored, such as emulsions tike milk and dairy cream, up to approximately 15 % fat content. Above IS % the output from the analyzer no longer changes and no further discrimination can be made. The reason for this is that for such concentrated samples with high optical density, multiple scattering results in the attenuation of the scattered light due to destructive interference between the inbound and exiting photons, a phenomenon known as dependent or coherent scattering. The detector has lost the ability to discriminate between the Individual small particles and only sees them as groups of particles. This phenomena occurs with samples with a large refractive index contrast (difference between the refractive index of the dispersed and continuous phase), and when the inter particle size is less than the wavelength of the light e.g. milk & dairy cream.

Patent publication CA 1199813 describes a method and apparatus for measuring the consistency of pulp slurry utilizing dual measurement. This publication teaches the utilization of a two-signal ratio comprising a water sensitive and non-water sensitive wavelength. The purpose of the ratio is to compensate for disturbing factors such as brightness, wood species or chemicals, it is described that the method and apparatus provides a measurement range of 0,05 to 15% in consistency is possible. SUMMARY OF THE INVENTION

The present invention aims to remedy the disadvantages and improve on prior art and to provide a method and an apparatus that will provide measurement at high turbidities and/or fat concentrations by reducing the destructive interference of photons entering and leaving the sample matrix. By this method, we artificially decrease the absorption path- length by selecting a wavelength that is absorbed by the continuous phase of the measurement media. The result is that fewer photons are being scattered back, and therefore the risk for destructive interference is reduced, resulting in an extended measurement range. The present technique has been shown to increase the upper measurement range in dairy cream from 15 % to well over 50 % fat content.

In accordance with the present invention there is provided an improved backscatter turbidity apparatus which is capable of measuring turbidities well in excess of 10000 NTU.

It is another objective of this invention to provide a measurement method and apparatus which overcomes ineffectiveness in current optical backscatter sensing systems for determining the concentration of a dispersed phase in a fluid, such as determination of the fat concentration in dairy cream, up to or exceeding 50 % dispersed fat.

It is another objective of this invention to provide a measurement method and apparatus which overcomes ineffectiveness in current optical backscatter sensing systems for determining changes in the particle size of the dispersed phase of a sample, such as the determination of fat thickening when whipping dairy cream.

It is another object of this invention to provide a backscatter turbidity apparatus using an optical fiber measurement probe. The method for determining the concentration or change in the size of the dispersed phase in a continuous phase, such as the fat content in dairy cream {essentially fat dispersed in water}, in accordance with one embodiment of this invention comprises the steps of transmitting a light beam into the sample at a wavelength that wiil be appreciably absorbed by the continuous phase, measuring the amount of backscattered light and correlating the measured signal to the concentration of dispersed phase. The backscattered light should be measured at a point that forms an acute angle at the midpoint of the transmitted light with respect to the light source. BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of tills invention will be better understood from the following detailed description taken in conjunction with the drawings wherein:

Fig. 1 is an axial sectional view of a sensor head according to the present invention, which includes a central illuminating optical fiber and a juxtaposed optical fiber for detection of light;

Fig.2 is an end sectional view of the optical fiber sensor head as shown in Fig. 1, whereby the illumination and detection optical fibers are at an angle to one another;

Fig.3 is an end view of the optical fiber sensor head as used in the device of Fig.1, whereby a plurality of juxtaposed optical fibers are utilized;

Fig.4a & Fig.4b diagrammaticairy shows an apparatus according to the present invention;

Fig.5a & Fig.5b is a schematic and simplified diagram showing the operation and components of the apparatus according to the present invention;

Fig.6a & Fig.6b are schematic and partial views of the backscatter of light on

particles in suspension (prior art) compared to absorption by the continuous phase (present invention);

Fig.7 is a graphical representation of the signals received on the basis of the fat concentration of a dairy cream sample; and

Fig. 8 is a graphical representation of the signal received during the whipping of a dairy cream sample. DETAILED DESCRIPTION OF THE INVENTION

In the accompanying Figs. 1-8, like reference numerals designate parts having analogous functions.

The principles of the present invention are disclosed by way of example by a probe 1 shown in Fig. 1. The probe 1 can be made of any non-corrosive materia! relative to the media in the process. However, preferably the probe 1 is made of stainless steel construction. The probe 1 illustrated in Fig. 1 shows a sanitary TriClamp* process connection which allows the probe to be inserted into a pipeline or the body or wail of a reactor. The probe 1 can incorporate any other type of process connection such as a sanitary thread, Ingold* fitting, pipe thread(BSP, NPT), flange (e.g. DIN, ANSI), Swageiok* fitting , or alternatively, the probe 1 may have no process connection and be inserted or "dipped" into the process media by way of an open vessel or container.

Within the probe 1, there are optical fibers 2 and 3 for the transmission and detection of light, in Fig.1, the optical fibers 2 and 3 are protected by means of a flexible metal conduit 4. it should be understood that the present invention is not limited to how the optical fibers 2 & 3, conduit 4 and probe 1 are mounted, and this can be done in different ways. These components can for example be mounted by different mechanical means or they can be fastened using suitable glue S that is compatible with the media and conditions of the process. Suitable glue 5 would be an epoxy resin.

The probe as Illustrated in Fig. 1 shows an embodiment of the present invention using two optical fibers, however, it should be understood that the invention can be implemented with one or several optical fibers, and also without optical fibers, as will be shown in other embodiments in the following description.

The optical fibers 2 and 3 illustrated in Fig. 1 are substantially parallel and are spaced at a very short distance 6 from one another at the tip of the probe 1 by means of two holes slightly greater than the diameters of the optical fibers made through the tip of probe 1, thus minimizing the amount of epoxy in direct contact with the process media. Fig.2 is an end sectional view of the probe 1 as used in the device of Fig. 1, depicts a further embodiment of the present invention whereby the optical fibers 2 and 3 are at an acute angle to one another and are touching at the tip 7 of the probe 1. Such a configuration as depicted in Fig.2 will maximize the amount of backscattered light by reducing the absorption path-length.

A further embodiment of the present invention is depicted in Fig.3, illustrating an end view of the probe 1 as depicted in Fig. 1 with a central illuminating optical fiber 9 surrounded by a plurality of juxtaposed detection optical fibers 8a, 8b, 8c ...8n. Such an arrangement would provide greater light throughput and a greater region of process media to be monitored for the same absorption path length.

Fig.4a diagrammaticai!y shows an apparatus according to the present invention whereby the light transmitted to and received from the process media occurs via a singular light guide 17 to the measurement probe 1. Such a light guide 17 may be any compatible material such as a quartz, silica or sapphire optical fiber or even a plastic light guide such as acrylic. A light source 10 providing the necessary measurement wavelength, is preferably a LED lamp or laser diode due to the low power requirements and narrow optical emission spectra of such devices, however other suitable devices include incandescent lamps such as halogen, tungsten, deuterium and mercury vapor, as weli as fluorescent lamps, in accordance with the present invention, the wavelength of the incoming light must be chosen that will be absorbed by the continuous phase of the process media. An optical filter 11 can be utilized to obtain the desired optical wavelength and emission characteristics and can be placed either in front of the light source 10 as depicted in Fig.4a, or alternatively in front of the detector 20 as depicted in Fig.4b. Preferably, the optical filter 11 is a band pass or narrow band pass type of filter; however other filters such as laser line, long pass, short pass and colored glass filters could also be utilized.

The optical emission 12 from the light source may vary with temperature and/or aging of the lamp, in which case a reference detector 15 can be utilized to compensate for such variations by splitting the light radiated from the source 12 using a beam splitter 13 that will direct a portion 14 of the primary light to the reference detector 15. The same beam splitter 13 is also utilized to direct light 19 returning from the sample 18 to the measurement detector 20. If narrow diameter optical fibers, typically between 0,1 micron and a few millimeters, are utilized as the light guide 17, it is preferable to use a collimating lens 16 to ensure a good efficiency of light entering and exiting the optical fiber 17.

Fig.4b is a simplified apparatus according to the present invention whereby optical fibers 2 and 3 and light guide 17 as depicted in Figs. l-4a are not present. Instead, the light source 10, optical filter 11 and optical detector 20 are placed in dose proximity to an optical window 21 and, when in use, also close to the sample 18. The light radiated from the source 12 passes directly through the optical window 21 into the sample 18 where it is both scattered and absorbed, the resulting light 19 passes back though the same optical window 21, through an optional optical filter 11 and then to the detector 20. The arrangement depicted in Fig.4b would be the preferred method for configurations whereby the measurement wavelength is not compatible for use with optical fibers, typically x-ray and mid to high infrared.

Figs. Sa and 5b are block diagrams showing the components included in the apparatus according to the present invention. To obtain a reading, an analyzing unit 36 adapted to make the determination based on signals from the detector is utilized, the analyzing unit 36 consisting of numerous electronic and software devices including, but not limited to, a microprocessor, A 0 converter, lamp regulator, keyboard and display unit.

Fig Sa depicts a mode of operation whereby the light source 10 is emitting a broad wavelength spectrum with the monitoring of more than one light wavelength in the spectrum for the fight beam 12. A beam splitter 13 is utilized to direct broad spectrum light 19 returning from the sample 18 to two separate measurement detectors 20a and 20b with individual bandpass filters 11a and lib for transmission and finally the detection of only the narrow wavelength spectrum.

Fig 5b depicts a mode of operation monitoring at more than one light wavelength by the use of more than one light source 10a and 10b, one light source for the emission of each respective light wavelength, in this mode of operation, each lamp is pulsed and measured alternatively; the procedure controlled and regulated using a microprocessor.

In all embodiments used in Figs. 1 to 5, the detector 15, 20 utilized may be a device capable of only one electronic output, such as a photodiode, or alternatively, a

spectrophotometer capable of simultaneously providing detailed absorption measurements at multiple wavelengths. More than one light source 10, 10a, 10b and optical filter 11, 11a, lib could also be arranged to obtain the required measurement wavelengths. It may be desirable to monitor at multiple wavelengths to simultaneously determine the

concentration of more than one compound, such as measuring both milk fat {dispersed phase) and the concentration of proteins dissolved in the continuous phase of a dairy cream sample. Another example would be to simultaneously determine the concentration of the dispersed phase and the color of the continuous phase of a highly turbid sample.

In all embodiments used in Figs. 1 to 5, the detector 15, 20 utilized should be compatible with the desired measurement wavelength corresponding with the light source. For UV-ViS (200-1000 nm) a silicon photodiode or photomultipiier may be used, for NIR applications (800-3000 nm) an InGaAs device can be used, for mid-IR wavelengths (3000- 5000 nm) an InSb, HgCdTe or PbSe detector can be used, for long wave infrared

wavelengths (>5000 nm) HgCdTe devices can be used and for an x-ray source (<200 nm) a photodiode with phosphor coating could be used.

in all embodiments used in Figs. 1 to 5, the light source 10 and/or detector 20 may either be incorporated as part of the optical probe 1, placed in dose proximity to the measurement point as depicted if Fig.4b, or alternatively placed in a separate housing whereby tight is transferred to the measurement point and back utilizing optical fibers 2, 3 and 17.

in all embodiments used in Figures 1 to 5, it may be desirable to measure the temperature of the sample 18 and use this measurement to compensate for any

temperature dependence of the continuous phase, particularly relevant when measuring in the NIR region.

In Figs.6a and 6b, the two optical fibers 2 and 3 are identical and contiguous to the way shown in Fig. 1. The sample 18 Is illustrated by drdes (not drawn to scale) 23 representing tiie dispersed phase and the background 22 representing the continuous phase. The light entering tiie sample is depicted by the arrow pointing towards 12 the sample via a first optical fiber 2, while tiie light exiting the sample is depicted by an arrow in a direction away from 19 the sample via a second optical fiber 3.

Prior art is illustrated in Fig.6a and is detailed in patent publication WO 8809494, whereby light 12 at a wavelength that is not absorbed by tiie continuous phase 22, enters the sample 18 from the first optical fiber 2, falls on the dispersed phase 23 and is scattered in all directions.

Publication WO 8809494 states that the wavelength of the light source is preferably 630 nm which has negligible absorbance for a continuous phase of water. Among the multiple scattered light beams 24, only a portion of the light from the first optical fiber 2 will propagate to the second optical fiber 3, and this portion of scattered fight can be correlated to the concentration of the dispersed phase 23 present in the sample 18. Figs.6a and 6b drastically simplifies the path of light by illustrating only one of multiple separate scattered light paths 24 that would occur between the first optical fiber 2 and the second optical fiber 3, however for illustrative purpose, it should be dear that for all possible paths of scattered light, the continuous phase 22 will have negligible influence on the intensity of the light.

Fig.6b illustrates the underlying mechanism of the present invention, whereby the wavelength and bandwidth of the incoming light 12 is selected so that the incoming light will be at least partially absorbed by the continuous phase 22 of the measurement medium 18. As illustrated by one of multiple scattered light paths 24, the amount of light 19 propagating from the first optical fiber 2 to the second optical fiber 3 is reduced in Fig.6b due to the absorption of light by the continuous phase 22 of the sample 18.

It should be understood that the present invention is not limited to the use of light in tiie visible area. The term "light beam" is used for emitted electromagnetic radiation in any wavelength that could be used to achieve the absorption by the fluid sample. The wavelength spectrum of the light source could vary depending on the implementation of the present invention. For example, the wavelength of the light source can be between 100 and 10000 nm, between 1000 and 10000 nm (IR), or between 1000 and 2000 nm ( NIR).

More generally it can be said that the light source emits light at a near-infrared wavelength, in which case the wide spectrum can be used or a band pass filter can be used to achieve a narrower band spectrum of wavelengths.

EXPERIMENTAL SECTION

A prototype of the present invention was built and tested using a dairy cream sample. The probe was constructed identical and contiguous to the way shown in Fig. 1, using a 1" TriClamp* type process connection 1 and two 600 μm silica optical fibers 2, 3 separated by a distance 6 of 50 μm.

Fig.7 shows a graphical representation of the measurement results of three separate light wavelength configurations with the same dairy cream sample having an initial concentration of 50% fat which was then gradually diluted with water.

The following series of measurements were conducted:

1. An optical emission wavelength of 850 nm was used, represented by graph 25 in Fig.7, as this wavelength is not absorbed by either the continuous or dispersed phase of the dairy cream sample. This measurement represents prior art, also described in patent publication EP 0017007.

2. In accordance with the present invention, the probe was evaluated using a wavelength that would be substantially absorbed by the continuous phase of the dairy cream sample. The continuous phase of dairy cream is water which has a strong NIR absorption at 1440 nm. For this measurement a 1440 nm LED lamp was used in combination with a 1440 nm narrow band pass filter with a 10 nm bandwidth, represented by graph 26 in Fig.7.

3. in accordance with another embodiment of the present invention, the

probe was also evaluated using a wavelength that would be partially absorbed by the continuous phase of the dairy cream sample. For this measurement the narrow band pass filter was not used, providing an optical emission wavelength of 1440nm with a 100nm bandwidth, represented by graph 27 in Fig.7. The result of the first test 25 in Fig.7 was the same as the results disclosed in prior art (EP 0017007) whereby from the graph it is evident that the probe has a range up to about 15 % fat concentration, at which a maximum signal is reached the analyzer output no longer changes. The mechanism behind this phenomena is destructive interference between the inbound and exiting photons due to multiple scattering of the inbound photons, and is typical of samples with very high optical density with a large refractive index contrast (difference between the refractive index of the dispersed and continuous phase), and when the inter particle size is less than the wavelength of the light e.g. milk & dairy cream. The detector has lost the ability to discriminate between the individual small particles and only sees them as groups of particles.

in accordance with the present invention, the probe was evaluated using a wavelength that would be substantially absorbed by the continuous phase of the sample in order to overcome limitations with prior art. The result of the second test 26 in Fig.7 clearly demonstrate a substantial increase in the upper measurement range of the apparatus, whereby the upper range was extended from 15% fat to at least 50 % fat which was the maximum concentration of the fat in the sample under test From the results 26, it is conceivable that substantially higher fat concentrations could also be analyzed. The mechanism behind this phenomenon is the suppression of destructive interference of photons entering and leavingthesamplematrix. Bythis newand novel method, the absorption path-length isartificiallydecreased byselectingawavelength that isabsorbed by thecontinuous phaseofthe measurement media resultingin fewer photons beingscattered back, and thereforereducing theoccurrenceofdestructive interference, resulting in an extended measurement range.

In accordance with anotherembodimentofthe present invention awavelength was selected thatwould have partial absorption bythecontinuous phaseofthe dairycream sampleby increasingthe bandwidth oftheincominglight. From the results 27, a benefitof this modeofoperation isto extendthelowerrangeofthe apparatus at theexpenseof resolution fromthe upper rangeofthe apparatus. In this modeofoperation 27 itis possible to monitorfrom approximately0,1% fatto at least 50%fat, whitethrough theprevious modeofoperation 26 itwas possibletooperatefrom approximately 2 %to at least 50%fat concentration.

In accordancewith anotherembodimentofthe present invention the rangeofthe equipmentcould be increased by measuringat morethan onewavelength which would be dependent upon theconcentration ofthesample. From the results depicted in Fig.7, low concentrations,e.g. lessthan 10% milkfat,could be measured usinga non absorbing wavelength 25, while high concentrations, e.g. above 10% milkfat,could be measured using an absorbingwavelength 26or27. Therangecould be manuallyswitched, or alternatively, a microcontrollercould automaticallyswitch between thedesired measurement wavelengths dependingupon theelectronic signals receivedfrom the detector.

Fig.8 shows a graphical representation ofa measurementcharacterizingchanges in the particlesizeand distribution for a 40%cream samplethatwaswhipped usingan electronic mixingapparatus. The prototype probewas placed in the40%cream at timet = -60s priorto mixing,duringthistime 28theoutputfromthe analyzer did not change. Att* 0 (29 in Fig.8)theelectronic mixingapparatus wasturned on causing airbubblesto become entrapped in thecream sample leadingto a rapid increaseinthe analyzeroutputto a point wherea foam was presenton thetop ofthecream 30. Thefoam graduallydisappeared which was alsonoted by a decreasein analyzeroutput 31, to a pointwhere thefoam was gone32 afterwhich timethecream started tothicken. Duringcontinued mixingovera period ofapproximately 2 minutes 33,theanalyzeroutputgraduallyincreasedto a point where is reached a constant value 34, shortly after which the cream became suddenly thick at the same time the analyzer output decreased 35.

These two experiments demonstrate that the analyzer output is a measure of the light scattered by the particles that is characteristic of both the number and size of particles present in the sample. In the first experiment (Fig.7) the size of the dispersed phase was constant allowing accurate determination of the fat concentration. In the second experiment (Fig.8) the fat concentration was constant, however the size of the particles was varied providing a means of characterizing sample changes, for example, to control an industrial process or to monitor changes in a product brought about by shear forces applied during pumping and/or handling of the product

Other possible applications for this apparatus include process optimization such as controlling CIP cycles, product identification and quality control.

It will be understood that the invention Is not restricted to the aforedescribed and illustrated exemplifying embodiments thereof and that modifications can be made within the scope of the inventive concept as illustrated in the accompanying Claims.

Claims

CLAIMS 1. A method for determining at least the concentration or turbidity of a dispersed phase suspended in a fluid, comprising the emission of a light beam into a sample of said fluid and the detection of scattered light from said fluid sample, characterized by, the selection of used wavelength for said light beam so that at least one wavelength of said light beam is absorbed by the continuous phase of said fluid sample, and the use of said absorption in the determination of said concentration or turbidity.

2. A method according to claim 1, characterized by, the use of a narrow wavelength spectrum for said light beam matched to the absorption of the continuous phase of said sample.

3. A method according to claim 2, characterized by, the use of a light source emitting a narrow wavelength spectrum, such as a LED or laser.

4. A method according to claim 2, characterized by, the use of a light source emitting a broad wavelength spectrum, such as a traditional lamp, which could be as halogen, tungsten, or mercury vapor lamp.

5. A method according to claim 4, characterized by, the use of a band pass filter for transmission and finally the detection of only the narrow wavelength spectrum.

6. A method according to any preceding claim, characterized by, the use of more than one light wavelength in the spectrum for said light beam.

7. A method according to claim 6, characterized by, by the use of more than one light source, one light source for the emission of respective light wavelength.

8. A method according to any one of claims 4 to7, characterized by, the separation of different wavelengths within said wavelength spectrum to different detectors.

9. A method according to any one of claims 4 to 8, characterized by, the use of a first wavelength that is absorbed by the continuous phase and light with a second wavelength that is not absorbed by the continuous phase.

10. A method according to any one of claims 4 to 9, characterized by, the use of a spectrophotometer for said detection.

11. A method according to any preceding claim, characterized by, measuring the temperature of the sample, and compensating for in the temperature of said sample in said determination.

12. A method according to any preceding claim, characterized by, splitting the emitted light beam into one reference beam and one primary beam, by emitting said primary beam into said fluid sample, and by measuring and compensating for any variations in the emission of said light beam through the detection of said reference beam.

13. A method according to any preceding claim, characterized by, said fluid sample comprising dairy cream.

14. An apparatus adapted to determine at least the concentration or turbidity of a dispersed phase suspended in a fluid, comprising a light source for the emission of a light beam, a detector adapted to detect any scattered light, a probe adapted to transmit said light beam into a sample of said fluid, and to receive and transmit any back scattered light from said fluid sample to said detector, and an analyzing unit adapted to make said determination based on signals from said detector, characterized in, that said light source is adapted to emit a light beam with a wavelength so that at least one wavelength of said light beam is absorbed by the continuous phase of said fluid sample, and that said analyzing unit is adapted to use said absorption in the determination of said concentration or turbidity.

15. An apparatus according to claim 14, characterized in, that a narrow wavelength spectrum is used for said light beam matched to the absorption of the continuous phase of said sample.

16. An apparatus according to claim 15, characterized in, that said tight source is adapted to emit a narrow wavelength spectrum, such as a LED or laser.

17. An apparatus according to claim 15, characterized in, that said light source is adapted to emit a broad wavelength spectrum, such as a traditional lamp, which could be as halogen, tungsten, or mercury vapor lamp.

18. An apparatus according to claim 17, characterized in, that said apparatus comprises a band pass filter for transmission and finally the detection of only the narrow wavelength spectrum.

19. An apparatus according to any one of claims 14 to 17, characterized in, that said apparatus is adapted to use more than one light wavelength in the spectrum for said light beam,

20. An apparatus according to claim 19, characterized in, that said apparatus comprises more than one light sources, one light source for the emission of respective light

wavelength.

21. An apparatus according to any one of claims 17 to 20, characterized in, that said apparatus comprises several detectors and means for separating different wavelengths within said wavelength spectrum to different detectors.

22. An apparatus according to any one of claims 17 to 21, characterized in, that said light source or light sources are adapted to emit light with a first a wavelength that is absorbed by the continuous phase and light with a second wavelength that is not absorbed by the continuous phase.

23. An apparatus according to any one of claims 17 to 22, characterized in, that said detector is a spectrophotometer.

24. An apparatus according to any one of claims 14 to 23, characterized in, that said apparatus comprises a sensor for measuring the temperature of the sample, and that said analyzing unit is adapted to compensate for in the temperature of said sample in said determination.

25. An apparatus according to any one of claims 14 to 24, characterized in, that said apparatus comprises a beam splitter and a reference detector, that said beam splitter is adapted to split the emitted light beam into one reference beam and one primary beam, that said probe is adapted to transmit and emit said primary beam into said fluid sample, that said reference detector is adapted to detect said reference beam and that said analyzing unit is adapted to measure and compensate for any variations in the emission of said light beam through the detection of said reference beam.

26. An apparatus according to any one of claims 14 to 25, characterized in, that said probe comprises at least one light guide such as an optical fiber adapted to allow light to enter to and from the sample.

27. An apparatus according to any one of claims 14 to 24, characterized in, that said probe comprises an illuminating optical fiber for the transmission of said emitted tight beam, and at least one detection optical fiber for the reception and transmission of said scattered light.

28. An apparatus according to claim 27, characterized in, that said illuminating optical fiber and detection optical fiber are separated by a small transverse distance.

29. An apparatus according to any one of claims 14 to 28, characterized in, that said probe is arranged so that the angle between light entering and leaving the sample is acute.

30. An apparatus according to claim 25, characterized in, that said probe comprises optical conveyance means for conveying said primary light beam from said beam splitter and for focusing or collimating said primary light beam to said sample, and for receiving light backscattered from said sample and returning the backscattered light to said beam splitter, and that said detector is positioned to receive said backscattered tight from said beam splitter.

31. An apparatus according to any one of claims 14 to 30, characterized in, that said probe comprises a return optical fiber having a first end positioned to receive light backscattered by the continuous phase of said sample, and a second end coupled to, or related to, said detector, and that said apparatus is physically divided into said probe and a controller, said probe comprising the optical system and said controller comprising said light source, said detector and said analyzing unit, thereby providing an intrinsically safe probe having no electrical components.

32. An apparatus according to any one of claims 14 to 25, characterized in, that said probe comprises an optical window, adapted to be positioned in said sample, that said light source and said detector are placed in close proximity to said optical window, that said light beam is adapted to pass directly through said optical window into said sample, and that said optical window is adapted to allow said back scattered light into said probe and to said detector.

33. An apparatus according to any one of claims 14 to 32, characterized in, that said apparatus is adapted to be used with a fluid sample comprising dairy cream.