AT521003A1 - Method and measuring device for measuring a suspension - Google Patents

Abstract

The invention relates to a method for measuring a suspension comprising wood fibers. The consistency of the suspension is changed in a consistency range (100). Optical radiation is directed to the suspension using a first optical wavelength and a second optical wavelength (102). A first intensity value of the optical radiation associated with the first optical wavelength and a second intensity value associated with the second optical wavelength are determined (104) at least for a given consistency value. The ratio of the first and second intensity values is determined (106). A kappa number of the suspension is determined (108). A raw value for hexenuronic acid, HexA, is obtained by applying predetermined factors to the ratio of the first and second intensity values (110). The proportion of hexA in the suspension is determined by multiplying the predetermined ratio by the kappa number (112).

Description

Technical field

The exemplary and non-limiting exemplary embodiments of the invention generally relate to a measurement of a wood fiber suspension.

State of the art

The following description of the prior art may include insights, discoveries, understandings, or disclosures, or associations, together with disclosures that were not known in the relevant prior art of the present invention, but are provided by the invention. Some of these contributions to the invention can be particularly highlighted below, while other such contributions to the invention are apparent from their context.

In paper and pulp production, the goal is to achieve an end product with a good and uniform quality. To ensure quality, measurements are carried out during the manufacturing process. For example, a lignin portion of the pulp is measured. The lignin content of a suspension, such as a pulp, is usually referred to by a kappa number. In the SCAN-C 1:77 standard, known in the pulp manufacturing art, the kappa number is defined as the amount of a potassium permanganate solution at a concentration of 20 mmol / l in milliliters, which is one gram of a

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ΆΤ84696 • ·· · · ······ ···· · ····· ····· · · · · · dry pulp consumed under the conditions defined in the standard.

Another substance, the proportion of which in the pulp has an effect on the process and the end product, is hexenuronic acid, which is often referred to as HexA.

The proportion of HexA in the pulp or pulp can be measured under known conditions using laboratory methods. However, laboratory measurements are problematic because they usually take a long time (between 30 minutes to hours) and results should be obtained quickly under various manufacturing process conditions to allow control of the manufacturing process based on the measurements. There is therefore a need for a solution that enables monitoring of a HexA portion during a manufacturing phase.

Summary

An object of the invention is to provide an improved method and an apparatus which implements the method for reducing or avoiding the problems mentioned above.

The objects of the invention are achieved by the method claimed in claim 1 and the device claimed in claim 10. Some embodiments of the invention are described in the dependent claims.

Brief description of the drawing

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AT84696

The invention is described in more detail below by means of preferred exemplary embodiments with reference to the accompanying drawing, in which:

Fig. 1 shows a flow chart that an example of a

Illustrated embodiment of the invention;

2 illustrates an example of a measuring arrangement according to an embodiment;

3 illustrates an example of a measurement arrangement;

Figures 4A, 4B and 4C illustrate examples of measurement arrangements;

Figures 5A and 5B illustrate examples of measurement results;

6 illustrates the calibration of the measuring device;

FIG. 7 illustrates an example of a device configured to act as a measurement control device, and

8 illustrates an example of a measuring arrangement according to an exemplary embodiment.

Detailed description of some embodiments

The solution according to the invention is particularly suitable for measuring a suspension containing wood fibers, but it is in no way limited to this.

/ 34 • · ·· · · · ·

In this application, optical radiation means electromagnetic radiation with a wavelength of approximately 40 nm to 1 mm, and ultraviolet radiation means electromagnetic radiation with a wavelength of approximately 40 nm to 400 nm.

In the proposed solution, a suspension containing wood fibers is exposed to optical radiation and an interaction of the radiation with the suspension is measured while the consistency of the suspension is changed during the measurement process.

Fig. 1 shows a flow chart illustrating an example of an embodiment of the invention in which a suspension containing wood fibers is measured.

In step 100, a consistency of the suspension is changed in a consistency area. In one embodiment, the range of consistency extends from an initial consistency to an end consistency.

In step 102, optical radiation is directed onto the suspension using a first optical wavelength λΐ and a second optical wavelength Ä2. In one embodiment, the first optical wavelength is 235 nm ± 50 nm and the second optical wavelength is 280 nm ± 50 nm.

In step 104, a first intensity value of the optical radiation belonging to the first optical wavelength and a second intensity value belonging to the second optical wavelength are within a consistency range for at least a given consistency value

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Measured AT84696.

In step 106 the ratio of the first and the second intensity value is determined. Thus the values Ιλί and IÄ2 are obtained.

Thus, in one embodiment, intensity values are measured using two different wavelengths at a given consistency value. A ratio of these intensities is determined.

In a further exemplary embodiment, a consistency of the suspension is changed such that the consistency continuously passes through all consistencies in the consistency area.

The intensity of the optical radiation that has interacted with the suspension is measured at different consistencies in the consistency area. The maximum intensities of the optical radiation associated with the first optical wavelength and the second optical wavelength are determined, and the ratio of the maximum intensity of the optical radiation associated with the first optical wavelength to the maximum intensity of the optical radiation associated with the second optical wavelength is determined. The values IÄlmax and IÄ2max are thus obtained.

Thus, with a change in the consistency of the suspension from the initial consistency to the final consistency, the measurement is repeated at given time intervals using both the first and the second wavelength. The time interval can be a measurement parameter. As a result, a value Ιλί for the intensity for the first opti

6/34 see wavelength λΐ and a value IA2 for the second optical wavelength Ä2.

In one embodiment, the optical radiation is directed onto the suspension using one or more optical power sources. There may be a power source for each wavelength, or the wavelength of the radiation emitted by the source may be changed, or the wavelength of the radiation may be selected using filters, for example.

The intensity of the optical radiation that has interacted with the suspension is measured with one or more optical measurement sensors that have a given surface and distance from the one or more optical power sources.

In one embodiment, the given surface and distance are selected based on the range of consistency and the amount of intensity required.

In one embodiment, the first optical wavelength and the second optical wavelength are within the wavelength range of the ultraviolet radiation.

In step 108, the kappa number of the suspension is determined.

There are different ways of determining the kappa number K. In one embodiment, the kappa number of the suspension is determined based on one or both of the determined maximum intensity values IÄlmax, IA2max. However, any known prior art method for determining the kappa number of Sus7 / 34 can also be used here

AT84696 • · · · · ······ • · · · · ···· «» · · · · · ····

Pension can be used.

In step 110, a raw value for a hexenuronic acid, HexARaw, is obtained by applying predetermined factors to the determined ratio Ιλ1 / Ιλ2 or IÄlmax / IÄ2max. The predetermined values calibrate the measurement results. An example of obtaining the predetermined values is explained below with reference to FIG. 6.

In step 112, the proportion of hexenuronic acid, HexA, in the suspension is determined by multiplying the raw value by the kappa number. So is

HexA = K * HexARaw or HexA = K * HexARaw.

A HexA portion in a pulp can have an effect in kappa measurements. HexA and lignin have different properties and have different effects on bleaching in the manufacturing process. Knowledge of the HexA content is therefore important. In the oxidation phase of the manufacturing process, a HexA portion is not reduced like the lignin portion. Using CIO2 in the manufacturing process reduces both HexA and lignin, however, because of the high cost of CIO2, it is not a good choice for HexA removal because there are cheaper substances for HexA removal.

An example of a measurement arrangement of an exemplary embodiment is described below with reference to FIG. 2, which shows an application of the invention in the pulp and paper industry.

2 shows a line 200 in which a wood fiber ent8 / 34

AT84696 holding suspension 202, i.e. a wood fiber pulp flows. A suspension sample is taken from line 200 with a sampler 204. The sampler 204 can be a solution known per se, for example based on a piston or a cylinder. The sample is conveyed to a measuring chamber 208 using a line 206 with a valve 210 closed.

The suspension in the measuring chamber can be processed before the measurement. For example, a liquid can be filtered using compressed air. A valve 212 can be opened and the air coming through the valve presses the sample against the screen 214 and the liquid flows through the valve 216. The sample can be washed using water and by opening the valves 212 and 218, whereby the waste water flows through the valve 216.

Once the sample is washed, a measurement process can begin by mixing the sample using compressed air through valve 220 and adding water through valve 222. Once the sample is mixed, the air valve 220 is closed. The water valve 222 is left open. Water coming through the valve changes the consistency of the sample and mixes the sample at the same time. The consistency of the suspension is changed in a consistency area. In one embodiment, the range of consistency ranges from an initial consistency to an end consistency.

During the change in the consistency of the sample, a measurement can be carried out using a measuring arrangement 224, 226, which is carried out by a measuring control device 9/34. · · · · · ······ ···· · ·····

AT84696 device 228 is controlled. In one embodiment, the measurement arrangement comprises a source and detector part 226, and an optical fiber and measurement head part 226.

FIGS. 3 and 4A to 4C illustrate examples of a measuring arrangement 224, 226. In one exemplary embodiment, the arrangement comprises one or more optical power sources 300. For the sake of simplicity, only one source is shown in FIG. 3. Measurements are usually made with ultraviolet light, due to which the optical power source usually emits at least ultraviolet light. The source 300 can be, for example, a xenon lamp or an LED (light-emitting diode). The optical power source can be set up to direct optical radiation onto the suspension. In one embodiment, the optical radiation is directed onto the suspension using a first optical fiber 306. The first optical fiber 306 can be configured to direct the optical radiation onto the suspension, the first end of the fiber being connected to the optical power source 300 and the second end of the fiber being located at the measuring head and being introduced into the measuring chamber 208 ,

In one embodiment, the arrangement may further include one or more detectors 302, 304 arranged to measure the intensity of the optical radiation interacting with the suspension. In one embodiment, each detector is connected to a group of optical fibers 308, 310 with the ends of the optical fibers positioned near the second end of the first optical fiber 302.

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AT84696

FIGS. 4A to 4C show examples of the fiber arrangement in the measuring head 312, which can be inserted into the measuring chamber 208.

4A shows an exemplary embodiment in which the measuring arrangement comprises the optical power source 300 connected to the first optical fiber 308 and the detector 302 connected to the optical fiber 308. In the measuring head, the optical fiber 306 and the optical fiber 308 are arranged side by side at a predetermined distance 400 from one another.

FIG. 4B shows a further exemplary embodiment in which the measuring arrangement comprises the optical power source 300 connected to the first optical fiber 308 and the detector 302 connected to a group of optical fibers 308. In the measuring head, the ends of the optical fibers 308 are positioned close to the end of the first optical fiber 306 at the same distance 402 from the first optical fiber.

40 shows a further exemplary embodiment in which the measuring arrangement comprises the optical power source 300 connected to the first optical fiber 308 and detectors 302, 304 connected to a group of optical fibers 308, 310. In the measuring head, the ends of the optical fibers 308 are positioned close to the end of the first optical fiber 306 at the same predetermined distance 404 from the first optical fiber, and the ends of the optical fibers 310 are close to the end of the first optical fiber 306 at the same Position 406 from the first optical fiber.

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AT84696

In one embodiment, measurement chamber 208 includes a window 230 in a wall of the measurement chamber. The optical power source 300 or the first optical fiber 306 connected to the source can be placed outside the measuring chamber behind the window in order to direct optical radiation onto the suspension.

In the same way, one or more detectors 302, 304 or optical fibers 308, 310 connected to the detectors can be placed outside the measuring chamber behind the window 230 in the measuring chamber wall.

The use of optical fibers described above is only an example. The measurement can also be carried out without optical fibers. In one embodiment, the optical radiation is directed to the measurement chamber using a radiation guide such as a lens, a waveguide or any suitable medium. For example, the optical source and detectors can be placed behind window 230 without the use of optical fibers.

FIGS. 5A and 5B illustrate examples of measurement results if the intensity of the optical radiation which has interacted with the suspension is measured at different consistencies using the measuring arrangement described above using a first optical wavelength and a second optical wavelength. In the non-limiting examples of FIGS. 5A and 5B, the first optical wavelength is 235 nm and the second optical wavelength is 280 nm. Depending on the exemplary embodiment, the wavelength can vary, for example, by ± 50 nm.

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AT84696

Figure 5A illustrates measurements made using the first optical wavelength 235 nm. In the illustration, a consistency is plotted on the x-axis 500 and a measured intensity on the y-axis 502. 5B illustrates measurements made using the second optical wavelength 280 nm. In the illustration, a consistency is plotted on the x-axis 504 and a measured intensity on the y-axis 506. The consistency of the suspension sample is changed as a function of the consistency. Usually the consistency of the suspension is high at the beginning, and the more water mixed with the sample, the lower the consistency of the suspension.

The consistency of the suspension sample is changed during the measurement process. FIGS. 5A and 5B show consistencies on an x-axis, with a small consistency value on the left and a larger consistency value on the right. In the actual measurement process, the consistency is initially large and the consistency decreases with the addition of water.

If optical radiation is directed from the optical radiation source onto the suspension sample, some of the radiation is scattered from the wood fibers to the detector, some is scattered elsewhere, and some is absorbed in lignin. When the consistency changes, there is a maximum value 508, 510 for the measured intensity at a certain point. The measuring arrangement can be set up to detect the maximum value 508, 510 of the intensity detected by the detector.

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AT84696

The consistency at which the maximum intensity is reached depends on the absorption. The greater the absorption, the smaller the consistency at which the maximum intensity occurs.

In one embodiment, the initial consistency of the consistency range measurement depends on the properties of the suspension. The measurement continues until the maximum intensity has been detected and is ended if the measured intensity becomes smaller after the maximum value.

In one embodiment, the measurement arrangement is calibrated by performing calibration measurements to function correctly. These measurements can be carried out using a standardization reference plate placed in front of the measuring arrangement. In one embodiment, calibration is performed using a reference pulp. Calibration is necessary before the measuring arrangement is actually used and must be carried out from time to time, for example because the path of the optical radiation can change or the detector responses can change over time. The reference pulp is a wood fiber pulp, the properties of which have been measured in the laboratory and have been stabilized over time. There are commercially available reference pulps for the calibration of measuring devices, e.g. a Paprican standard reference pulp 5-96 from a Canadian manufacturer.

In one embodiment, the surfaces and numerical apertures of the optical source and detectors are selected based on the range of consistency of the suspension and the amount of light required (amount of intensity).

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AT84696

In one embodiment, the distances 400, 402, 404, 406 and the surface area of the cross sections and numerical apertures of optical fibers or groups of optical fibers 306, 308 and 310 are selected based on the range of consistency of the suspension and the amount of intensity required.

The distances 400, 402, 404, 406 and the surface of the cross sections of the optical fibers or groups of optical fibers 306, 308 are referred to below as the measurement geometry. A measurement geometry affects the consistency area. If measurements are carried out, the consistency of the suspension must be such that sample processing (washing the sample and changing the consistency) is possible. If the consistency of the suspension is too high, the sample processing cannot be successful. On the other hand, if the consistency is too low, a dynamic of the measurement can suffer. Likewise, an available light intensity of the optical light source has an effect on the measurements. If a kappa number is measured, the larger the kappa number, the more light the lignin absorbs in the sample.

In one embodiment, the aim is to detect the maximum intensity of the optical radiation interacting with the suspension within the range of consistency. The consistency at which the maximum intensity is reached can depend on the following things:

The distance 400, 402, 404, 406 between the optical power source and the measurement point, i.e. the distance between the end of the first optical fiber 306 and the ends of the other optical fibers 306, 308. Each

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AT84696 the greater the distance, the smaller the consistency at which the maximum intensity occurs.

The surfaces of the optical power source and the measuring points. The larger the surface, the smaller the consistency at which the maximum intensity occurs.

The kappa number of the sample. The larger the kappa number, the smaller the consistency at which the maximum intensity occurs.

A wavelength of the radiation emitted by the optical power source. An absorption of the radiation in the suspension depends on the wavelength. The greater the absorption, the smaller the consistency at which the maximum intensity occurs.

A particle size of the suspension sample. The smaller the particles, the smaller the consistency at which the maximum intensity occurs.

Thus, in one embodiment, measurement parameters can include the measurement geometry, the wavelength of the optical radiation and the consistency range used in the measurements.

Furthermore, the range of consistency can depend on the properties of the suspension. For example, if a pine suspension is measured, a consistency range can be 0.3-0.1%, and if a birch suspension is measured, a consistency range can be 0.4-0.2%. These numerical values are only non-limiting examples.

Typical values for optical fiber diameters are around a few

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AT84696 ·· · · ······ • 9 · · · * · · # • · · · · · · · φ • Φ »··· ···» · «·«

100 μm, but also other values can be used depending on the property to be measured.

Even if no optical fibers are used, but the optical source and the detectors are connected to the measuring chamber using another suitable medium, the above discussion is generally applicable.

As mentioned above with reference to FIG. 1, in one embodiment the ratio IÄlmax / IÄ2max of the maximum intensity of the optical radiation associated with the first optical wavelength to the maximum intensity of the optical radiation associated with the second optical wavelength is determined.

8 illustrates an embodiment of a measuring arrangement. In this example, intensity values are measured in a measuring chamber. The measuring arrangement comprises a measuring chamber 800 which has a suspension with a given consistency. The arrangement includes one or more light sources 802, 804. In one embodiment, a light source can transmit light with many wavelengths, such as a xenon light source. In one embodiment, there may be one light source for each wavelength. An example of a light source of a single wavelength is an LED. The arrangement further includes one or more detectors 806, 808. In one embodiment, a detector may include a filter that only passes a given wavelength. The filter can be exchangeable. This is particularly suitable if the light source transmits many wavelengths. In one embodiment in which the

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If the light source only transmits one wavelength, no filter is necessary.

A kappa number of the suspension is also determined. In one embodiment, the kappa number of the suspension is determined based on one or both of the predetermined maximum intensity values IÄlmax, IÄ2max. However, any conventional prior art method for determining the kappa number of the suspension can also be used.

If the ratio of the first and second intensity values and the kappa number have been determined, a value for HexA can be determined. In order to calibrate the measurement results, predetermined factors are applied to the ratio and a so-called raw HexA value is obtained. The HexA value is obtained in umol / g units by multiplying the raw HexA value by the kappa number.

6 illustrates an example of determining the predetermined factors. When determining the factors, the consistency of the suspension is changed and the intensity is measured at two wavelengths, in this example 235 and 280 nm. The samples, in which the intensity values are measured, are also brought into laboratory rooms, where a kappa number and a hexA value are determined using laboratory methods. Thus, for each intensity value ratio there is a laboratory HexA value and a laboratory kappa value, which can be called HexALAB and KappaLAB.

Figure 6 illustrates the relationship of the HexALAB / KappaLAB ratio as a function of the ratio of the intensity values. As can be seen, the relationship follows

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AT84696 in this example of a power function.

In general, the power function can be formulated as y = ax ^b , where y is HexALAB / KappaLAB and x is Ιλ1 / Ιλ2, and where variables a and b are the predetermined factors.

In the concrete example according to FIG. 6, the power function y = 0.6561 x ' ¹ · ⁴⁰² .

If the relationship follows the aforementioned power function, the RawHexA value can be obtained from the measured ratio of the intensity values as follows.

RawHexA = a * (IÄl / IÄ2) ^b or RawHexA = a * (IÄlmax / IÄ2max) ^b .

The power function is used here only as an example. Depending on the situation, the relationship can also be a linear function or a polynomial function, or another function that maps the ratio of the intensity values to the ratio HexALAB / KappaLAB.

In general, the determination of the predetermined factors only has to be carried out once for each measuring device if the configuration of the device or the type of suspension does not change (for example from one tree type to another). In one embodiment, the correctness of the factors can occasionally be checked using measurements.

Fig. 7 shows an embodiment. The figure shows a simplified example of a device that is set up to act as a measurement control device 228.

The device shown here must be regarded as merely an example to illustrate some exemplary embodiments. It is obvious to a person skilled in the art that the device can also have other functions and / or structures, and not all of the functions and structures described are necessary. Although the device is shown as a unit, various modules and memories can be implemented in one or more physical or logical instances.

The device 228 of the example includes a control circuit 700 configured to control at least a portion of the operation of the device.

The device may include a memory 702 for storing data. Furthermore, the memory can store software 704 that can be executed by the control circuit 700.

The memory can be integrated in the control circuit.

The device may further include an interface circuit 706 configured to connect the device to other devices. The interface can provide a wired or wireless connection. The interface can connect the device to the measuring arrangement 224, 226. In one embodiment, the device may be connected to an automatic process control computer used in pulp manufacture.

The device may also include a user interface 708, such as a display, keyboard, and mouse

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* Include AT84696. In one embodiment, the device does not include a user interface, but is connected to other devices that provide access to the device.

In some embodiments, the device can be implemented with a mini or micro computer, a personal computer or a laptop, or any suitable data processing device.

In one embodiment, intensity measurements and kappa measurements can be performed in the same measurement chamber using different measurement geometries. For example, in the solution according to FIG. 4C, one detector can measure a kappa number and another one an intensity.

It will be apparent to those skilled in the art that as technology advances, the inventive concept can be implemented in several ways. The invention and its exemplary embodiments are not limited to the examples described above, but can be modified within the scope of the patent claims.

The invention relates to a method for measuring a suspension comprising wood fibers. The consistency of the suspension is changed in a consistency area (100). Optical radiation is directed onto the suspension using a first optical wavelength and a second optical wavelength (102). A first intensity value of the optical radiation associated with the first optical wavelength and a second intensity value associated with the second optical wavelength are determined (104) at least for a given consistency value. The ratio of the first and second intensity values is

21/34 determined (106). A kappa number of the suspension is determined (108). A raw value for hexenuronic acid, HexA, is obtained by applying predetermined factors to the ratio of the first and second intensity values (110). The proportion of HexA in the suspension is determined by multiplying the predetermined ratio by the kappa number (112).

Claims (17)

claims 1. A method for measuring a suspension containing wood fibers, the method comprising: Changing (100) a consistency of the suspension in a consistency range; Directing (102) optical radiation onto the suspension using a first optical wavelength and a second optical wavelength; Measuring and determining (104) a first intensity value of the optical radiation associated with the first optical wavelength within the consistency range and a second intensity value associated with the second optical wavelength at at least one given consistency value; and Determining (106) the ratio of the first and second intensity values; Determining (108) a kappa number of the suspension; marked by Obtaining (110) a raw value of hexenuronic acid, HexA, by applying predetermined factors to the ratio of the first and second intensity values; and Determine (112) the proportion of hexenuronic acid, HexA, in the suspension by multiplying the raw value by the kappa number. 2. The method of claim 1, further comprising: Directing the optical radiation onto the suspension using an optical power source; and Measuring the intensity of the optical radiation that has interacted with the suspension with one or more optical measuring sensors with a given surface, nu23 / 34 • ·· · · ······ • · · · · ····· • · · · · · ···· 23 ....................... meric aperture and a given distance from the optical power source. 3. The method of claim 1 or 2, wherein the first optical wavelength and the second optical wavelength are within the ultraviolet wavelength range. 4. The method according to any one of claims 1 to 3, wherein the first optical wavelength is 235 nm ± 50 nm, and the second optical wavelength is 280 nm ± 50 nm. 5. The method according to claim 1, further comprising: changing the consistency of the suspension such that the consistency continuously passes through all consistencies in the consistency area, Measuring the intensity of the optical radiation that has interacted with the suspension at various consistencies in the consistency area; Determining the maximum intensity of the optical radiation associated with the first optical wavelength and the second optical wavelength; and Determining the ratio of the maximum intensity of the optical radiation associated with the first optical wavelength to the maximum intensity of the optical radiation associated with the second optical wavelength. 6. The method according to any one of claims 1 to 5, further comprising: Take a sample of the suspension to be measured in a measuring chamber without applying pressure. 7. The method according to any one of claims 1 to 6, further comprising: 24/34 • · · ·· ·· ·· ·· • · · · · ······ • · · · · ····· ····· · ···· ·· ·· · ··· ···· ·· ·· 24 AT84696 Directing the optical radiation onto the suspension using a first optical fiber with a given diameter and numerical aperture, and Measuring the intensity of the optical radiation that has interacted with the suspension with a detector connected to a group of optical fibers, each optical fiber having a given diameter, and the ends of the optical fibers close to the end of the first optical Fiber are positioned at the same distance from the first optical fiber. 8. The method according to any one of claims 1 to 7, further comprising: Directing the optical radiation onto the suspension using one or more light sources placed outside the measuring chamber behind a window in a measuring chamber wall, and Measuring the intensity of the optical radiation that has interacted with the suspension with a detector placed outside the measurement chamber behind a window in the measurement chamber wall, the detector having a predetermined diameter and at a given distance from the one or more light sources is located. 9. The method according to any one of claims 1 to 8, further comprising: Measuring the intensity of the optical radiation that has interacted with the suspension at different consistencies in the consistency range using the first optical wavelength and the second optical wavelength; Obtaining HexALAB and KappaLAB, which give the HexA value and the Kappa number of the suspension at the same consistency. 25/34 • · ····· ····· · ···· ·· ·· ···· ···· ·· ·· 25 AT84696 denote zen determined in a laboratory; Determining a function that maps the ratio of the measured first and second intensity values to the relationship of HexALAB and KappaLAB; and Determine the predetermined factors based on the function. 10. Measuring device for measuring a suspension containing wood fibers, wherein the measuring device has one or more optical power sources (300) for aligning optical radiation onto the suspension, and at least one optical measuring sensor (302) for measuring optical radiation that has interacted with the suspension , where the measuring device is set up: Changing (100) a consistency of the suspension in a consistency range; Directing (102) optical radiation onto the suspension using a first optical wavelength and a second optical wavelength; Measuring and determining (104) a first intensity value of the optical radiation associated with the first optical wavelength and a second intensity value associated with the second optical wavelength within the consistency range for at least one given consistency value; Determining (106) the ratio of the first and second intensity values; Determining (108) a kappa number of the suspension; characterized in that the measuring device is also set up to: Obtaining (110) a raw value of hexenuronic acid, HexA, by applying predetermined factors to the ratio of the first and second intensity values; and 26/34 φ · • ·· · · ······ ···· · ·· «·· ····· · ···· ·· ·· ···· ···· ·· ·· 26 AT84696 Determine (112) the level of hexenuronic acid, HexA, in the suspension by multiplying the predetermined ratio by the kappa number. 11. The apparatus of claim 10, wherein: at least one measurement sensor has a given surface area, numerical aperture and a given distance from the one or more optical power sources, the given surface area and the given distance being selected on the basis of the range of consistency and the required degree of intensity. 12. The apparatus of claim 10 or 11, wherein the one or more optical power sources are configured to output the first optical wavelength and the second optical wavelength that are within the wavelength range of the ultraviolet radiation. 13. Apparatus according to one of claims 10 to 12, wherein the one or more power sources are set up to output the first wavelength with the value of 235 nm ± 20 nm and the second wavelength with the value of 280 nm ± 20 nm. 14. An apparatus according to any one of claims 10 to 13, further configured to: Changing the consistency of the suspension such that the consistency continuously passes through all consistencies in the consistency area, Measuring the intensity of the optical radiation that has interacted with the suspension at different consistencies in the consistency area; Determining the to the first optical wavelength and 27/34 • · ··· · ·· ·· • ·· · · ······ ···· · ····· ····· · ···· ·· ·· · ··· ···· ·· ·· AT84696 maximum intensities of the optical radiation associated with the second optical wavelength; and Determining the ratio of the maximum intensity of the optical radiation associated with the first optical wavelength to the maximum intensity of the optical radiation associated with the second optical wavelength. 15. Apparatus according to any one of claims 10 to 14, further comprising: a first optical fiber (306) configured to direct the optical radiation onto the suspension, the first end of the fiber connected to the optical light source (300) and the second end of the fiber located in the measurement chamber; and one or more detectors (302) for measuring the intensity of the optical radiation which has interacted with the suspension, each detector being connected to a group of optical fibers (308), each optical fiber having a predetermined diameter, and the ends of the optical fibers are positioned near the second end of the optical fiber at the same distance from the first optical fiber (306), the given diameter and distance being selected based on the range of consistency and the amount of intensity required. 16. Apparatus according to one of claims 10 to 14, further comprising a window (230) in a measuring chamber wall, the optical power source being placed outside the measuring chamber (208) behind the window in a wall for directing the optical radiation onto the suspension; and one or more detectors (302) for measuring the intensity of an optical radiation which has interacted with the suspension, the detectors outside the measuring chamber behind a window (230) in the measuring chamber wall 28/34 • · · · · ·· ··· ···· · · · ·· · ····· · · · · · ·· ·· ···· ···· ·· ·· 28 AT84696, each detector is given a given diameter, and placed at a given distance from the optical power source (300), the given diameter and distance being selected based on the range of consistency and the amount of intensity required. 17. The apparatus of any one of claims 10 to 16, further comprising measuring the intensity of the optical radiation that has interacted with the suspension at different consistencies in the range of consistency using the first optical wavelength and the second optical wavelength; Obtaining HexALAB and KappaLAB, which indicate the HexA value and a kappa number of the suspension at the same consistencies determined in a laboratory; Determining a function that maps the ratio of the measured first and second intensity values to the relationship between HexALAB and KappaLAB; and Determine the predetermined factors based on the function.