WO2007012903A1

WO2007012903A1 - Procedure and equipment for determining grain characteristics by optical measurements

Info

Publication number: WO2007012903A1
Application number: PCT/HU2006/000055
Authority: WO
Inventors: Gábor TAKÁCS; Tibor Pokorny; Áron TAKÁCS
Original assignee: Takacs Gabor; Tibor Pokorny; Takacs Aron
Priority date: 2005-07-27
Filing date: 2006-07-06
Publication date: 2007-02-01
Also published as: HU226833B1; HU0500723D0; HUP0500723A2

Abstract

The invention relates to a procedure for determining quantitativecharacteristics by measuring light intensity, in the course of which the sample to be examined is illuminated with measuring light, and the intensity of the light reflected from it or passing through it is measured, and in the interest of accurate measurement a sample reference of stable characteristics is also illuminated with measuring light via the same trace as the trace used in the case of the sample to be examined. The procedure is characterized that in the course of performing measurement(s) the measuring light is rotated in the circular space around the axis (t) of the circular space as an axis of rotation, or the circular space is rotated around as compared to the measuring light at a favourably speed. The invention also relates to equipment for determining quantitative characteristics by measuring light intensity.

Description

Procedure and equipment for determining quantitative characteristics by measuring light intensity

The invention relates to a procedure and equipment for determining quantitative characteristics by measuring light intensity. The solution can be used especially favourably for determining the quality characteristics of grains such as cereals.

Optical instruments measuring certain characteristics or constituents of materials on the basis of the spectrum of materials operate by lighting the sample with a light source and measuring the intensity of the light reflected from it or passing through it with a light detecting sensor at different wavelengths. On the basis of the connection revealed in the course of the calibration of the instrument between this data and the characteristics to be measured the numerical value of the given characteristic or constituent is determined. In the case of instruments used for quantitative measurement, in order to reach appropriate accuracy both the wavelength and the intensity of the measuring light on the one part and the characteristics of the sensor(s) on the other part need to be kept at a stable value. Light of different wavelengths is produced by known monochromators whose wavelength stability is checked or corrected periodically in most cases in practice. The appropriate stability of the measuring light and its sensing can be attained either by using components of a very good quality placed in a stabilised environment, or in the case of less stable construction elements of lower quality, faults can be corrected or compensated with the simultaneous measurement of a known stable sample reference. This known solution is characterised by that two traces of the same length containing the same elements are used for measuring the sample and the sample reference. The light proceeds towards the sensor along the two traces alternately in time. Appropriate compensation is conditioned on that the two traces, that is their optical elements, do not change in time. This known solution eliminates the changes of both the light source and the sensor in time, but it cannot eliminate the changes of the two traces and their optical elements.

Practically, the cross-section of the light channels should be determined in a way that the unhomogeneity of the sample to be examined can be neglected. In cases when it is not possible, because it results in too large sizes or too expensive constructions, the light channel and the sample are moved with respect to each other in the course of measuring in order to compensate unhomogeneity by performing measurement on different points of the surface, scanning the surface of the sample.

This function is solved mostly by moving the sample, because in this way it is easier to ensure permanent optical conditions, that is stability.

Patent specification No. US 4082464 describes an optical construction in the case of which the sample surface is lit at right angles to the surface, and the light diffusely reflected from the surface is sensed by detector(s) placed at an angle of 45° with respect to the plane of the sample surface. Patent specification No. US 4236076 describes a solution in which the light reflected from the lit sample surface is collected onto the detector by an integrating sphere. Patent specification No. HU212355 describes an optical construction consisting of a light source, optical elements transforming the light emitted by the light source into monochromatic measuring light beams of different wavelengths and into reference light beams, a detector connected to an electronic measuring and processing unit and light deflecting elements.

Patent specification No. US 4795256 describes a spectrophotometer system with two monochromators in which system a rotary mirror optical chopper projects or transmits the light emerging from light source cyclically toward the two light cantiel - monochromators. Unifying the two light beams with different wavelengths this is projected to the surface of the sample, and the light reflected from the sample is measured. The stability of the wavelength and intensity are guaranteed in such a manner that a part from the unified measuring light is measured back by a light divider, and on the basis of these results the measured spectrum is corrected by computer.

A common disadvantage of these known solutions is that the sample - reference shift, needed to compensate the instability of the measuring light and the sensor, is realised on two traces, and as a result of this in the course of measurements they cannot eliminate the changes of non-identical optical elements used on the traces. A further problem is the scanning of the sample to be examined, for which complicated operating structures are required. The invention according to the No. P9902811 published Hungarian application eliminates the abovementioned disadvantages in that way that it employs a single common light route rotating around axis for scanning of the optical reference. It doesn't calculate, however, with the inhomogeneity of the light source nor in transmission, neither in reflection mode. The light cut emitted by halogen bulbs used typically is not axially symmetrical because the filaments are not punctual and axially symmetrical, respectively. The result of this situation is that the going-round measuring light alters slightly depending on the angular status. The present invention gives a solution to this problem, too, in such a manner that the light source is put out from the rotation axis. In this manner the measuring light rotates together with its light source, and there is not necessary for light-route modifying optical elements.

This invention doesn't take into consideration that in the case of predispersive spectrometers it is not absolutely important that the sensor should be in the rotation axis; it can rotate together with the measuring light beam in a fixed status. In this case there are not necessary light-route modifying optical elements, either, that the sensing light channel should be led back into the rotation axis.

According to this invention the putting-out of the rotating light cut from the axis is realized by the help of prisms or mirrors; this invention doesn't calculate with the application of other, just in the consequence of invention applicable, simple means, e.g. fibre optics or light guide.

The abovementioned invention according to the No. P9902811 published Hungarian application doesn't mention that possibility that not only the light cut can be rotated for the scanning of the sample(s) and standard(s) but the sample(s) and standard(s) can be rotated, too, as compared to the standing light cut.

The lecture delivered on 11^th International NIR (Near Infrared Reflectance) Conference (Cordoba, 2003) represents the technical level, too, in which lecture the inventors reviewed a rotating light cut optical arrangement realised by prisms, as a conceptual optical scheme of an instrument developed by them. The invention set as an aim to eliminate the deficiencies of known solutions and to create such procedure and equipment by the help of which the determination of quantitative characteristics should be realizable by the measurement of light intensity, by the application of a single optical route, by the increase of the accuracy of measurement, by simply adjustable conventional optical elements, by light sources of low efficiency, by a favourably portable equipment with simple construction and smaller size, and b)' cheaper production.

At the working-out of the solution according to the invention we realised that a significant part of measuring faults can be eliminated, if the different traces used so far in the course of the known measurements are combined, and both the sample to be examined and the sample reference are measured on this common path. We realised that if the sample to be examined and the sample reference are placed in a circular space, and in the course of performing measurements the measuring light is rotated in the circular space around the axis of the circular space as an axis of rotation, or the circular space is rotated around as compared to the measuring light, then the sample to be examined and the sample reference can be measured via one single common trace.

We also realised that on the place available in the circular space not only one, but several samples and sample references can be placed.

On the basis of our recognition in our solution only one single trace is used, but the elements used on this trace are time-dependent in a known way. We realised that if the measuring light is rotated in the circular space or the circular space is rotated with respect to the measuring light at an appropriate speed, then the time constant of change of the optical elements used on the trace can be neglected. Consequently by choosing the right speed of simple rotational motion the accuracy of measurement can be definitely improved, because the measuring of the sample and the reference measurement needed for the compensation of faults are performed in rapid succession, practically simultaneously. As compared to this time difference even the rate of change of the used elements changing relatively rapidly in time — that is elements of poor quality — can be neglected, even such elements of poor quality prove to be stable in the course of measurement. In the case of the solution according to the invention both the sample - reference shift and the generation of the rotational motion realising the scanning of the sample result in a cheap technical solution.

Consequently, the invention relates to a procedure for determining the quantitative characteristics by measuring light intensity, in the course of which the sample to be examined is illuminated with measuring light, and the intensity of the light reflected from it or passing through it is measured, and in the interest of the accuracy of the measurement a sample reference of stable characteristics is also illuminated with measuring light via the same trace used in the case of the sample to be examined, and the intensity of the light reflected from it or passing through it is also measured for the purpose of compensation, further the sample(s) to be examined and the sample reference(s) are placed in a circular space. It is characteristic to the procedure that in the course of performing measurement(s) the measuring light is rotated in the circular space around the axis of the circular space as an axis of rotation, or the circular space is rotated around as compared to the measuring light at a favourable speed, and in this manner the sample(s) to be examined and the sample reference(s) are measured on a single common optical route.

In the case of a favourable realisation of the procedure the measuring light is emitted from a light source in a position offset from the axis of rotation, but a solution may also be favourable, in the case of which the measuring light is produced by a trace modifying optical system, as light with an optical axis shifted from the axis of rotation.

In accordance with our solution the evaluation of the measurement may also be performed favourably in a way that the measuring of the intensity of the light reflected from or passing through the sample(s) to be examined and the sample reference(s) is performed offset from the axis of rotation, or in a way that with the help of a further trace modifying optical system the optical axis of the light reflected from or passing through the sample(s) to be examined and the sample reference(s) is deflected to lie on the axis of rotation again, where the intensity of the light is measured.

In the course of the procedure a prism, mirror pairs or optical fibres are used as a trace modifying optical system and as a further trace modifying optical system. Practically a monochromator producing light of a given wavelength is used in the course of producing the measuring light, or the intensity of the light is measured with a spectrometer detecting light of a given wavelength.

In accordance with our solution rotation is performed by rotating the circular space containing the sample(s) to be examined and the sample reference(s), or the trace modifying optical system and/or the further trace modifying optical system.

The invention also relates to an equipment for determining quantitative characteristics by measuring light intensity, and a sample to be examined is placed on the first trace situated in the path of the measuring light emitted by the light source of this equipment, and the second optical part of the same length as the first trace contains a sample reference, the remaining parts of the traces have a common light detecting sensor. The equipment is characterised by that the first and the second traces are realised as one single common trace, where the sample(s) to be examined and the sample reference(s) are situated at the same distance from a given axis, in a circular shape. In the course of performing measurement(s) the measuring light is rotated in the circular space around the axis of the circular space as an axis of rotation, or the circular space is rotated around as compared to the measuring light at a favourable speed.

Consequently the invention relates to equipment that realises the sample — sample reference shift needed for the compensation of the instability of the measuring light and the light detecting sensor and the necessary scanning of the sample to be examined in a completely novel way and jointly.

In the case of a favourable construction of the equipment the optical axis of the light source is the same as the axis of the circular space. In this case it is possible to insert a trace modifying optical system emitting measuring light the optical axis of which is offset from the axis between the light source and the circular shape containing the sample(s) to be examined and the sample reference(s). Measuring can be evaluated in a way that the optical axis of the light detecting sensor is the same as the axis of the circular shape, and a further trace modifying optical system deflecting the optical axis of the light reflected from or passing through the sample(s) to be examined and the sample reference(s) to lie on the axis again is inserted between the circular space containing the sample(s) to be examined and the sample reference(s) and the light detecting sensor.

In the case of a practical realisation of the equipment the optical axis of the light source is offset from the axis of the circular shape. Measuring can be performed either according to the above, or in a way that the optical axis of the light detecting sensor is offset from the axis of the circular space so that it lies on the optical axis of the light reflected from or passing through the sample(s) to be examined and the sample reference(s).

In the case of a fairly favourable construction of the equipment the light source also has a monochromator, or the light detecting sensor contains a spectrometer. In accordance with our invention the optical grating in the monochromator or spectrometer is situated at a large optical distance from the light source or from the sample(s) to be examined and the sample reference(s), favourably at a distance corresponding to 10-20 times of the focal length of the spherical mirror positioned after the optical grating.

In the case of another fairly practical solution of the equipment, in the monochromator or spectrometer a light path extending optical system is placed between the light source or the sample(s) to be examined and the sample reference(s) and the optical grating.

The example of a possible realisation of the equipment according to the invention is described in detail on the basis of the attached drawings, where

figure 1 shows a possible realisation of the equipment operating on the basis of the principle of transmission,

- figure 2 shows a favourable solution of the equipment operating on the basis of the principle of reflection,

- figure 3 shows another possible realisation of the equipment operating on the basis of the principle of transmission, - figure 4 shows another possible realisation of the equipment operating on the basis of the principle of reflection,

- figure 5 shows the schematic construction of a traditional double-slit spectrometer/monochromator,

figure 6 shows the scheme of a certain part of figure 5,

- figure 7 shows the schematic construction of the spectrometer/monochromator according to the invention,

figure 8 shows a possible realisation of optical light extension

In figure 1 the equipment according to the invention has a light source LS emitting measuring light ML in the way of which there is a first trace where the sample S to be examined is placed. The second trace of the equipment, which is of the same length as the first trace, contains a sample reference SR. In accordance with our invention the first trace and the second trace are realised as a single common trace, where the sample(s) S to be examined and the sample reference(s) SR are positioned in a circular shape at the same distance from a given t axis. In the course of performing measurements the measuring light ML is rotated in the circular space around the t axis of the circular space as an axis of rotation, or the circular space is rotated around at a favourable speed. At the end of the common trace the equipment has a light detecting sensor LDS.

Figure 1 shows a possible construction of the equipment, where the optical axis of the light source LS lies on the t axis of the circular space. In the case of this construction a trace modifying optical system TMO emitting measuring light MS the optical axis of which is offset from the t axis is inserted between the light source LS and the circular shape containing the sample(s) S to be examined and the sample reference(s) SR. The trace modifying optical system TMO emits measuring light ML the optical axis of which is offset from the incoming light IL lying on the t axis. The equipment shown in figure 1 operates on the basis of the principle of transmission, that is the measuring light ML passes through the sample S to be examined and changes into transmitted light TL. The optical axis of the light detecting sensor LDS lies on the t axis of the circular space shown in the figure, so a further trace modifying optical system TMO deflecting the optical axis of the transmitted light TL passing through the sample(s) to be examined and the sample reference(s) to lie on the t axis again is inserted between the circular space and the light detecting sensor LDS.

Figure 2 shows a favourable solution of the equipment according to the invention operating on the basis of the principle of reflection. In this case too there is a light source LS lying on the t axis of the circular shape and a light detecting sensor

LDS. The optical role and position of the trace modifying optical system TMO and the further trace modifying optical system TMO are similar to those described in connection with figure 1. The only difference lies in the principle of measuring, as the measuring light ML with an optical axis offset from the t axis is reflected from the sample(s) S to be examined and the sample reference(s) SR, and the further trace modifying optical system deflects this reflected light RL to lie on the t axis again in the light detecting sensor LDS.

Figure 3 shows another possible realisation of the equipment operating on the basis of the principle of transmission, in the case of which the optical axes of the light source LDS and the light detecting sensor LDS are offset from the t axis of the circular space, and the light source LS and the light detecting sensor LDS themselves are also positioned offset from the t axis.

Figure 4 shows the schematic view of a different favourable construction of the solution according to the invention operating on the basis of the principle of reflection. In this case too the light source LS and the light detecting sensor LDS are position offset from the t axis of the circular space.

Generally, in practice it is a problem in the case of transmission measurements that often the intensity of the transmitted light TL is very low. In the wavelength range that can be used in practice the transmitted light has a very low value in the case of measuring cereal grains. The generally used so-called double-slot optical grating spectrometers/monochromators that ensure adequate light intensity and wavelength dispersion in the course of transmission measurements are rather expensive, and a complicated and high technological level is required for their manufacturing.

In figure 5 a traditional double-slit - crossed Czerny-Turner - spectrometer/monochromator is shown. The light coming from the sample S / light source LS is directed by a mapping optical system not shown separately in the figure to a slit Sl, from where the light is reflected from the first spherical mirror Ml onto the optical grating G. By moving the optical grating G light of different wavelengths arrives onto the second spherical mirror M2, from where it is reflected and leaves the spectrometer/monochromator through a slit S2. The necessary light intensity is determined by the size of the optical grating G, the focal length L of the spherical mirrors Ml, M2 and the α angle of the light beam following the slit Sl. The wavelength dispersion - in the case of a given grating - depends on the ratio between the d dimension of the slit Sl and the focal length L of the spherical mirror Ml.

In order to have an appropriately intensive signal an intensive light source LS or an adequate light beam arriving from the sample S is needed. Figure 6 shows a schematic diagram, in which — in the given case - a light beam of a given diameter deriving from the light source LS and the light arriving from the surface of the sample S are directed into the ingoing slit IS of the spectrometer/monochromator via the mapping optical system MO.

In the interest of realising the scheme shown in figure 6 in respect of the invention according to the invention, the light source LS is equipped with a special monochromator or the light detecting sensor LDS is equipped with a special spectrometer.

Figure 7 shows the schematic construction of the special spectrometer/monochromator. As compared to the known double-slit construction shown in figure 5 the spectrometer/monochromator does not have an ingoing slit Sl or a spherical mirror Ml on the ingoing side. As there is no ingoing slit Sl, there is no need for an mapping optical system MO either. In the case of the spectrometer/monochromator according to the invention the parallel nature of the light beam going in to the optical grating G is achieved by placing the optical grating G in the monochromator; or in the spectrometer from the light source LS; from the samples S and the sample reference(s) at a large optical distance, favourably at a distance corresponding to 10-20 times more of focal length L of the spherical mirror M positioned after the optical grating G. So in the present case the spectrometer/monochromator has one single outgoing slit OS.

Figure 8 shows a practical realisation of the spectrometer/monochromator according to the invention. In the spectrometer; or in the monochromator between the sample(s) S to be examined and the sample reference(s) SR; or between the light source LS and the optical grating G there is a light path extending optical system LE. The light path extending optical system LE ensures the large optical distance favourably with appropriately positioned mirrors, in a way that the trace is diffracted several times with the mirrors. In the case of using good quality mirrors this method of extending the trace results in a very high, 95% efficiency in practice, beside a significant reduction in dimension.

The use of the spectrometer/monochromator in the equipment according to the invention has several advantages. A light source LS of a lower efficiency is needed, it can be realised with conventional optical elements, in this way they can be adjusted in a simple way, and it from the aspect of economy it is cheaper to produce the equipment.

The simple construction of the equipment according to the invention results in simple and quick operation by generating rotational motion around the t axis. In the course of performing measurements the rotational motion of either the circular space containing the sample(s) S to be examined and the sample reference(s) SR or the measuring light ML needed for measuring can be generated. The measuring light ML can be moved as required in a simple way by rotating the trace modifying optical system TMO. The further trace modifying optical system TMO providing the necessary light beam can be moved in a similarly simple way for the light detecting sensor LDS. Optional combinations of the favourable solutions described both in connection with generating the measuring light ML and as an example of detection can be realised in the equipment according to the invention. The advantage of the solution according to the invention is that both the sample- reference shift needed for the compensation of the instability of the measuring light ML and the light detecting sensor LDS and the necessary scanning of the sample S to be examined is realised in a completely novel common way, using one single trace. Due to the fact that the optical elements used are common, perfect compensation can be realised. From the rotational motion the measuring of the sample S and the measuring of the sample reference SR are performed in rapid succession, practically simultaneously. As compared to this time difference even the rate of change of the parts - of poor quality - changing rapidly can be neglected, in the case of our solution they seem to be stable.

In the course of a concrete realization of the invention the instruments measure the internal content values and components of cereals (wheat, barley, maize) at the same time by a single measurement, e.g. in the case wheat the aleurone-, protein- and moisture content, the hardness of grain and Zeleny index. The measuring time is about 1 minute, the preparation of the sample is not necessary. The traditional chemical procedure requests live labour of several hours, and chemical reagents. The principle of the measurement is that transilluminating the sample the intensity of the transmitted light is measured on different near-infrared wavelengths, and the numerical value of each components is determined by a mathematical model, the input variables of which are the measured intensity values. For a particular grain, e.g. for wheat the mathematical model, necessary for the measurement of certain characteristics, and wavelengths or wavelength-ranges are determined in advance on a "master" instrument. To measure wheat aleurone % the model can be a linear equation with 12 variables the input variables of which are the measured intensities (or their logarithms, respectively), and the determination of the model consists of the determination of the coefficients. If the model is a linear equation, the determination of coefficients can occur with the measurement of numerous samples with known components by linear regression. On the basis of numerous variables as well as coefficients of often thousand order it can be judged what a considerable stability is necessary for the measurement of good quality. This invention guarantees this stability more simpler and cheaper compared to other optical arrangements with similar purpose. In a different previous procedure there is determined that in the case of a particular model the measurement should be accomplished on what wavelengths, that is where is a suitable correlation between the transmitted light intensity and the characteristics to be measured, e.g. aleurone content of wheat.

The structure of the equipment according to the invention makes it possible to realise a cheap construction, and the creation of the circular shape results in reducing the dimensions of the equipment. The use of the light path extending optical system makes it possible to reduce the dimensions even more. The characteristic features described above also provide a unique possibility for the realisation of a fairly favourable, practically portable construction of the quantitative measuring equipment according to the invention.

Claims

1. Procedure for determining quantitative characteristics by measuring light intensity, in the course of which the sample to be examined is illuminated with measuring light, and the intensity of the light reflected from it or passing through it is measured, and in the interest of the increase of the accuracy of the measurement a sample reference of stable characteristics is also illuminated with measuring light via the same trace as the trace used in the case of the sample to be examined, and the intensity of the light reflected from it or passing through it is also measured for the purpose of compensation, further the sample(s) to be examined and the sample reference(s) are placed in a circular space, characterized by that in the course of performing measurement(s) the measuring light is rotated in the circular space around the axis of the circular space as an axis of rotation, or the circular space is rotated around as compared to the measuring light at a favourable speed, and in this manner the sample(s) to be examined and the sample reference(s) are measured on a single common optical route.

2. Procedure as in claim 1, characteri s e d by that the measuring light is emitted from a light source in a position offset from the axis of rotation.

3. Procedure as in claim 1, characteri s e d by that the measuring light is produced by a trace modifying optical system, as light with an optical axis shifted from the axis of rotation.

4. Procedure as in claim 2 or 3, characteri s e d by that the measuring of the intensity of the light reflected from or passing through the sample(s) to be examined and the sample reference(s) is performed offset from the axis of rotation.

5. Procedure as in claim 2 or 3, characteri s ed by that the optical axis of the light reflected from or passing through the sample(s) to be examined and the sample reference(s) is deflected to lie on the axis of rotation again, where the intensity of the light is measured.

6. Procedure as in claim 3 or 5, characteri s e d b y that a prism, mirror pairs or optical fibres are used as a trace modifying optical system and as a further trace modifying optical system.

7. Procedure as in claims 1 - 6, characteri s e d by that a monochromator producing light of a given wavelength is used in the course of producing the measuring light.

8. Procedure as in claims 1 - 6, characteri s e d by that the intensity of the light is measured with a spectrometer detecting light of a given wavelength.

9. Procedure as in claims 2 - 8, characteri s e d by that the circular space containing the sample(s) to be examined and the sample reference(s) is rotated.

10. Procedure as in claim 3 or 5 or 6, characteri s e d by that the trace modifying optical system and/or the further trace modifying optical system is rotated.

11. Equipment for determining quantitative characteristics by measuring light intensity, in which a sample to be examined is placed on the first trace situated in the path of the measuring light emitted by the light source of the equipment, and the second trace of the same length as the first trace contains a sample reference, the remaining parts of the traces have a common light detecting sensor, characteri s ed by that the first and the second traces are realised as one single common trace, where the sample(s) (S) to be examined and the sample reference(s) (SR) are situated at the same distance from a given axis (t), in a circular shape, and in the course of performing measurement(s) the measuring light (ML) is rotated in the circular space around the axis (t) of the circular space as an axis of rotation, or the circular space is rotated around at a favourable speed.

12. Equipment as in claim 11, characteri s e d by that the optical axis of the light source (LS) is the same as the axis (t) of the circular space.

13. Equipment as in claim 11, characteri s e d by that the optical axis of the light source (LS) is offset from the axis (t) of the circular space.

14. Equipment as in claim 12, characteri s ed b y that a trace modifying optical system (TMO) emitting measuring light (ML) the optical axis of which is offset from the axis (t) is inserted between the light source (LS) and the circular shape containing the sample(s) (S) to be examined and the sample reference(s)

(SR).

15. Equipment as in either of claims 11 - 14, characteri s e d by that the light source (LS) also has a monochromator.

16. Equipment as in either of claims 11 - 14, characteri s ed by that the light detecting sensor (LDS) contains a spectrometer.

17. Equipment as in either of claims 13 - 16, characteri s e d by that the optical axis of the light detecting sensor (LDS) is the same as the axis (t) of the circular shape, and a further trace modifying optical system (TMO) deflecting the optical axis of the light reflected from or passing through the sample(s) (S) to be examined and the sample reference(s) (SR) to lie on the axis again is inserted between the circular space containing the sample(s) (S) to be examined and the sample reference(s) (SR) and the light detecting sensor (LDS).

18. Equipment as in either of claims 13 - 16, characteri s ed by that the optical axis of the light detecting sensor (LDS) is offset from the axis (t) of the circular shape so that it lies on the optical axis of the light reflected from or passing through the sample(s) (S) to be examined and the sample reference(s)

(SR).

19. Equipment as in claim 15 or 16, characteri s ed by that in the monochromator; or in the spectrometer the optical grating (G) is situated at a large optical distance from the light source (LS); from the sample(s) (S) to be examined and the sample reference(s) (SR), favourably at a distance corresponding to 10-20 times of the focal length (L) of the spherical mirror (M) positioned after the optical grating (G).

20. Equipment as in claim 19, characteri s e d by that in the monochromator; or in the spectrometer a light path extending optical system (LE) is placed between the light source (LS) or the sample(s) (S) to be examined and the sample reference(s) (SR) and the optical grating (G).