Field

The invention relates to a method and an apparatus for determining a degree of breaking down of fiber particles into fines in pulp.

Background

Property of paper, paperboard or board produced as an end product may vary a lot depending on the properties of the paper pulp used. Refining is one of the processes where properties of pulp are affected, and a degree of breaking down of fiber particles into fines in pulp is of great importance for determining quality of pulp and the end product.

However, although there have been attempts to measure a degree of refining, the degree of breaking down of fiber particles into fines in pulp has not been measured in a satisfying manner. Hence, there is a need to improve the measurement.

Brief description

The present invention seeks to provide an improvement in the determination of the degree of breaking down of fiber particles into fines in pulp. According to an aspect of the present invention, there is provided a method of determining a degree of breaking down of fiber particles into fines in pulp as specified in claim 1.

According to another aspect of the present invention, there is provided an apparatus of determining a degree of breaking down of fiber particles into fines in pulp in claim 7.

The invention has advantages. The degree of breaking down of fiber particles into fines in pulp may be determined accurately which also enables a more effective control of a process related to treatment of pulp. List of drawings

Example embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which

Figure 1 illustrates an example an apparatus for measuring a degree of breaking down of fiber particles into fines in pulp;

Figure 2 illustrates an example of the detection of the polarization of the optical radiation;

Figure 3 illustrates an example of the detection of a property of microwave radiation propagated through the pulp;

Figure 4 illustrates an example of a blade transmitter;

Figure 5 illustrates an example of a rotating consistency transmitter;

Figure 6 illustrates an example of the apparatus where the secondary detection is performed by a camera;

Figure 7 illustrates an example of the secondary depolarization detection combined with the primary optical detection using the at least two separate optical bands;

Figure 8 illustrates an example of the processing unit with a processor and memory;

Figure 9 illustrates an example of a control of a refining process; and

Figure 10 illustrates an example of effect of breaking down of fibers in different types of types of pulps;

Figure 11 illustrates of an example of a flow chart of a method of determining a degree of breaking down of fiber particles into fines in pulp. Description of embodiments

The following embodiments are only examples. Although the specification may refer to "an" embodiment in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, words "comprising" and "including" should be understood as not limiting the described embodiments to consist of only those features that have been mentioned and such embodiments may contain also features/structures that have not been specifically mentioned.

It should be noted that while Figures illustrate various embodiments, they are simplified diagrams that only show some structures and/or functional entities. The connections shown in the Figures may refer to logical or physical connections. It is apparent to a person skilled in the art that the described apparatus may also comprise other functions and structures than those described in Figures and text. It should be appreciated that details of some functions, structures, and the signalling used for measurement and/or controlling are irrelevant to the actual invention. Therefore, they need not be discussed in more detail here.

Refining refers to a mechanical treatment, a chemical treatment or a combination of mechanical and chemical treatment of paper pulp. The fibers of pulp may become partially broken, fibrils, which are fully separate from the fiber or attached from one end to the fiber, may be formed, the fibers may become shortened, a diameter of the fibers may change because of swelling, and/or the fibers may become softer, for example. When fibers break down they may be divided into pieces or sub-component or parts may separate from them. The parts which are separated from the fibers may also break down in refining. Typically a surface area of the particles may grow in refining which has on effect on how the fibers bind together. In the measurements these changes may be observed such that refining increases a value of consistency, for example. Also a number of particles and particularly a number of smaller particles such as fines per unit volume may increase. The fines are parts detached from fibers. Fines are typically considered to have a dimension smaller than about 0.2 mm.

Figure 1 illustrates an example of an apparatus for measuring degree of breaking down or disintegration of fiber particles into fines in pulp. The apparatus comprises a first detection unit 100 which detects separately optical powers of at least two different optical bands 106 interacted with the pulp 104. The interaction may mean that the detected optical band transmitted to the pulp 104 and detected after it has passed through the pulp 104, reflected from the pulp 104 and/or scattered from the pulp 104. The pulp 104 may be in a chamber 115, the chamber 115 being at least partially transparent to the optical radiation and microwave radiation used in the measurements. The pulp 104 may flow through the chamber 115, or the chamber 115 is a container which is filled with the pulp 104 before a measurement and emptied after the measurement. The first detection unit 100 may comprise at least one optical radiation source 112, 114 which directs the at least two different optical bands 106 to the pulp 104. In Figure 1 there are two optical radiation sources 112, 114 but the at least two optical bands may also be output from only one optical radiation source. The first detection unit 100 may further comprise at least one detector 114, 116 which detects separately optical powers of the at least two different optical bands 106 interacted with the pulp 104. In an embodiment, the optical bands 106 may have no overlapping or common wavelengths. In an embodiment, the optical bands 106 may be partly overlapping but still they have wavelengths which are not common. The detection of the at least two separate optical bands by the at least one detector 114, 116 is made for obtaining information about an increase in surface area caused by refining while reducing wavelength dependence of the measurement.

If only one detector 114 or 116 is used, different optical bands may be measured at different moments, i.e. using TDM-method (TDM = Time-Division- Multiplexing). If more than one detector 114 or 116 is used, each optical band 116 may be measured with one detector 114, 116.

In an embodiment, two different optical bands 106 may be used. In an embodiment, one of the two optical bands 106 may be in the visible region, about 400 nm to 700 nm, and another of the two optical bands 106 may be in the infrared region, about 700 nm to 500 μιτι, for example. In an embodiment, one of the two optical bands 106 may be in the visible region, and another of the two optical bands 106 may be in the ultraviolet region, about 10 nm to 400 nm, for example. In an embodiment, one of the two optical bands 106 may be in infrared region, and another of the two optical bands 106 may be in the ultraviolet region. The optical band, which has shorter wavelengths than those of the other optical band, is typically attenuated more strongly by the smaller particles, such as fines, in the pulp 104 than by the larger particles, such as fibers. In this manner, a processing unit 108 of the apparatus may use the two different optical wavelengths 106 in determining a first measurement result on the basis of the primary detection. The first measurement result may refer to the degree of refining, although its value is disturbed by fine particles in the pulp 104 and by consistency. If a third optical band between the two optical bands is used, the attenuation of the third optical band will depend on particles of certain sizes different from those of the two different optical bands. In this manner, it is possible to detect effects of changes in distribution of sizes of the particles in the pulp 104 as a consequence of refining which enables a measurement of the degree of refining which is, however, distorted.

The apparatus may comprise a second detection unit 102 which performs a secondary detection related to at least one of the following: polarization of optical radiation propagated through the pulp 104, a property of microwave radiation propagated through the pulp 104, a force caused by a movement between the pulp 104 and a material structure in the pulp 104, and particles in at least one image of the pulp 104. The processing unit 108 may then receive information about the at least one of them. The processing unit 108 may determine a change of the polarization of optical radiation propagated through the pulp 104 or a change of the property of microwave radiation propagated through the pulp 104, for example. In a similar manner, the processing unit 108 may determine a change in the force caused by the movement between the pulp 104 and the material structure in the pulp 104, or a change associated with the particles in the at least one image of the pulp 104. The processing unit 108 may form a second measurement result on the basis of the secondary detection.

Figure 2 illustrates an example of the detection of the polarization of the optical radiation. An optical source 200 may output an optical beam towards the pulp 104. In an embodiment, the optical beam may be in a band of the visible light, for example. In an embodiment, the optical beam may be in a band of the infrared light, for example. In an embodiment, the optical beam may be in a band of the ultraviolet light, for example. The optical beam may be linearly polarized by a pre-polarizer 202 before entering the pulp 104. In an embodiment, the optical source 200 may output a linearly polarized optical beam, and in such a case, a separate pre-polarizer 202 is not necessarily required. The linearly polarized optical beam passes through the pulp 104 and propagates through a post- polarizer 204, which also polarizes the optical beam linearly, to a depolarization detector 206. The polarization axis of the optical radiation and the polarization axis of the post-polarizer 204 are perpendicular with respect to each other, i.e. the axes differ by at least approximately 90°. The polarization is sensitive to consistency of the pulp 104 because the fibers, for example, typically depolarize a polarized beam of light in the pulp 104.

In an embodiment, which is illustrated in Figure 3, a property of microwave radiation propagated through the pulp 104 is detected. The detector 302 may detect attenuation, moment of arrival or phase of the received microwave radiation. The reference detector 304 may detect attenuation, moment of transmission or phase of the transmitted microwave radiation. The property may be attenuation of the microwave radiation or a propagation time of the microwave radiation. To measure the attenuation, a transmission power of the microwave radiation from a transmitter 300 is detected at the reference attenuation detector 304 or it is known, and a reception power of the microwave radiation transmitted through the pulp 104 is detected at the receiver 302. The attenuation, which may be determined in the processing unit 108, is a function of a ratio of the transmission power and the reception power of the microwave radiation.

In an embodiment, the propagation time of the microwave radiation through the pulp 104 may be measured directly as a time that it takes for the microwave radiation to travel from a transmitter 300 to a reception time detector 302 through the pulp 104. A transmission moment is measured by the reference time detector 304 and an arrival moment of the microwave radiation is measured by the reception time detector 302. A time-of-flight transmitted through the pulp 104 or scattered from the pulp 104, which may be determined in the processing unit 108, depends on the path between the transmitter 300 and the receiver 302. The path between the transmitter 300 and the receiver 302, in turn, depends on the distance between the transmitter 400 and the receiver 302 and the consistency of the pulp 104. Changes in the time-of-flight, in turn, refer to changes in consistency of the pulp 104.

In an embodiment, the propagation time of the microwave radiation through the pulp 104 may be measured by a phase shift between the transmitted microwave radiation and the received microwave radiation. A phase at the transmission is measured by the reference phase detector 304 and a phase at arrival is measured by the reception phase detector 302. The phase shift, which may be determined in the processing unit 108, depends on the distance between the transmitter and the receiver and the consistency of the pulp 104. Changes in the phase shift, in turn, refer to changes in consistency of the pulp 104.

In an embodiment which is illustrated in Figure 4, the force caused by a movement between the pulp slurry 104 and a material structure in the pulp 104, may be measured with a blade transmitter which may also be called a viscometer. The material structure may be a blade 400 which is in a flowing pulp 104. The blade transmitter may comprise a measuring arm 402. The measuring arm 402 may be made of metal such as steel, for example. The blade 400 may be directed parallel to the direction of the flow pulp 104. The forces of the flowing pulp slurry 104 may tilt the blade 400 and the arm 402. The tilt, which is related to the consistency of the pulp slurry, may then be detected by a force detector 404 associated with the arm 402. The force detector 404 may be a displacement sensor, a force sensor or the like. The processing unit 108 may then determine consistency on the basis of the tilt.

In an embodiment an example of which is illustrated in Figure 5, the force caused by a movement between the pulp slurry 104 and a material structure therein, may be measured with a rotating consistency transmitter. The measuring device comprises two shafts in such a manner that the inner shaft 502, also called a measuring shaft, is inside the outer shaft 500. There may be propeller-like material structures 504, 506 at the end of both the outer shaft 500 and the inner shaft 502 to mix the suspension in the chamber 115. A motor 510 may rotate the outer shaft 500, also called a drive shaft. Both shafts rotate in the same direction, and by means of a magnetic coupling provided by electromagnets 552, and the swivel of the shafts 500, 502 can be kept constant in relation to each other, even though the cutting and friction forces dependent on the consistency of the measured pulp 104 try to swivel the inner shaft 502 relative to the outer shaft 500. The swivel between the shafts 500, 502, which can also be called an offset, refers to the swivel of the shafts from a predefined initial position. Ordinarily, the shafts 500, 502 that are flexibly mounted with bearings to each other may swivel at most to a predefined degree, which may be a few degrees at most.

The swivel can be measured optically using an optical measuring device containing an optocoupler, for instance. The measuring device may comprise an optical source 512, an optical chopper detector 514, and a chopper structure 550. The chopper structure 550 may, in turn, comprise two similar wheels 516, 518 equipped with chopper teeth (not shown in Figure 5). The outer shaft 500 may rotate the first of these wheels 516 and the inner shaft 502 may rotate the second wheel 518. As the wheels 516, 518 rotate along with the shafts 500, 502, the chopper teeth rotating act as choppers of the signal between the optical transmitter 512 and optical chopper detector 514 and form a pulsed signal to the optical chopper detector 514. Instead of the optical source, it is also possible to use some other source 512 capable of transmitting electromagnetic radiation, particle radiation, ultrasound or the like as a signal 513. Instead of the optical chopper detector 514, the detector of the second detection unit 102 may, in turn, be a detector that is sensitive to the non-optical signal transmitted by the transmitter 512. When the shafts 500, 502 are irrotational, i.e. inphase, with respect to each other, the chopper teeth of the wheels may converge. However, when swivel forms between the shafts 500, 502, the chopper teeth of the wheels shift correspondingly relative to each other. This phase shift alters the pulse ratio of the optical signal. Thus, swivel is directly proportional to the pulse ratio with a detection of which the processing unit 108 may control the electric current supplied to the electromagnets, and determine force between the shafts 500, 502. In this example, the processing unit 108 receives the secondary detection(s) from the optical chopper detector or the non-optical detector 514.

In an embodiment an example of which is illustrated in Figure 6, at least one image may be captured by a camera 600 which may be considered an optical detector. A number of particles in the at least one image of the pulp 104 may be determined by the processing unit 108. Alternatively or additionally, the processing unit 108 may determine a distribution of sizes of particles in the at least one image. The camera 600 may capture still images or video. The detecting element of the camera 600 may comprise a matrix of pixels. The detecting element of the camera 600 may comprise a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) cell.

The processing unit 108 then determines the degree of breaking down of fiber particles into fines in pulp 104 on the basis of the primary detections of the optical powers of the at least two different optical bands 106 interacted with the pulp 104, and the at least one of the secondary detections.

Thus, optical radiation is transmitted through the pulp 104, and the degree of breaking down of fiber particles into fines in pulp 104 is determined in the processing unit 108 on the basis of optical powers of at least two different optical bands 106 interacted with the pulp 104, and at least one of the following detections: polarization of optical radiation propagated through the pulp 104, a property of microwave radiation propagated through the pulp 104, a force caused by a movement between the pulp 104 and a material structure in the pulp 104, and particles in at least one image of the pulp 104.

Figure 7 illustrates an example of an embodiment, where the secondary depolarization detection is combined with the primary optical detection using the at least two separate optical bands. In an embodiment, the components of the two systems may be integrated together in addition to the common operational parts by containing them inside a common housing. A first optical radiation source 112 may direct a polarized optical beam in an optical band to the pulp 104. The optical band output by the first optical radiation source 112 and passed through the pulp 104 may propagate to a beam splitter 700. The beam splitter 700 then reflects a part of the optical beam to the detector 116. The part of the optical beam which doesn't reflect from the beam splitter 700 propagates through the polarizer 204 to the depolarization detector 206. Another optical beam is transmitted by the optical radiation source 110 and the optical beam is detected by the detector 114 after the optical beam has interacted with the pulp 104. The processing unit 108 then determines the degree of breaking down of fiber particles into fines in pulp on the basis of the primary and secondary detections made by detectors 114, 116, 206.

In embodiments examples of which are illustrated in Figures 1 and 7, the pulp 104 may be diluted until the second result on the basis of the secondary detections by the detectors 206, 302, 404, 514, 600 (shown in Figures 2, 3, 4, 5 and 6) has reached a desired value. The second result may refer to consistency. That is, the processing unit 108 may control a valve 710 in the dilution line and the processing unit 108 may open the valve 710 for starting the dilution. The dilution may be performed by adding water to the pulp 104. The processing unit 108 may then measure the second value repeatedly or constantly on the basis of the secondary detections of the at least one detector 206, 302, 404, 514, 600 of the second detection unit 102, and when the processing unit 108 determines that the measured value of the second result is at least approximately the same as the desired value, the processing unit 108 may measure the first result on the basis of the primary detections of the detectors 114, 116 of the first detection unit 100. In an embodiment, when the processing unit 108 observes that the measured value of the second result is at least approximately the same as the desired value, the dilution may be stopped for the measurement of the first result in a stable conditions with respect to the second result. The processing unit 108 may close the valve 710 for stopping the dilution, for example.

In an embodiment, the processing unit 108 may correct the first result based on the primary detection of the detectors 114, 116 on the basis of the second result based on the at least one secondary detection of the detectors 206, 302, 404, 514, 600 for forming the degree of breaking down of fiber particles into fines in pulp 104. The correction may be performed in a predetermined manner which is based on a theory, simulation(s) or experience.

In an embodiment, the processing unit 108 may form the degree of breaking down of fiber particles into fines in pulp on the basis of the primary detection and a consistency. The processing unit 108 may determine the consistency on the basis of the secondary detection of the detectors 206, 302, 404, 514, 600.

In an embodiment, the processing unit 108 may form a tentative degree of refining on the basis of the optical powers of the two different optical bands 106 interacted with the pulp 104.

In an embodiment, the processing unit 108 may form a tentative degree of refining by comparing the optical powers between the two different optical bands 106, and correcting the tentative degree of refining by the at least one secondary detection of the detectors 206, 302, 404, 514, 600 for forming the degree of breaking down of the fiber particles into fines in pulp 104.

In an embodiment an example of which is shown in Figure 8, the processing unit 108 (see Figure 1, for example) may comprise one or more processors 800 and one or more memories 802 including computer program code. The one or more memories 802 and the computer program code with the one or more processors 800 may cause the processing unit 108 to perform the determination of the degree of breaking down of the fiber particles into fines in pulp.

Figure 9 illustrates an example of an embodiment where a pulp treatment process 900 may be controlled on the basis of the determination of the degree of breaking down of the fiber particles into fines in pulp in the processing unit 108. The pulp treatment process 900 may be a refining process, for example. A sample of the pulp 104 may be taken from the pulp treatment process 900 to the chamber 115 where detections of the sample are made by the first detection unit 100 and the second detection unit 102. The detections are processed in the processing unit 108 and the determined degree of breaking down of the fiber particles into fines in pulp may be fed to a controller 902 which may control the pulp treatment process 900. The controller 902 may keep the refining going on if a desired degree of breaking down of the fiber particles into fines in pulp is not reached.

In an embodiment, the controller 902 may stop the refining when the desired degree of breaking down of the fiber particles into fines in pulp is reached. The processing unit 108 may be a controller 902 of the apparatus, the controller 902 of the apparatus may include the processing unit 108 or the controller 902 of the apparatus and the processing unit 108 may be operationally connected together wirelessly or by wire. The one or more memories 802 and the computer program code with the one or more processors 800 may cause the controller 902 to control the apparatus to perform its actions.

Figure 10 illustrates an example of effect of breaking down of fibers in different types of pulps. The vertical axis (y-axis) denotes a ratio of attenuations of two different optical bands of the primary optical measurement, and the horizontal axis (x-axis) denotes a degree of depolarization of the secondary measurement. That is, when the degree of depolarization increases, also consistency, for example, increases and vice versa.

Examine now the curve 1000 of cellulose having 50 % soft wood bleached SWB and 50 % fine particles which are smaller than fibers of the pulp. The average particle size is smallest in this specific sample among the three examples. When consistency of this cellulose type is changed from 0.04 % to 1.55 %, the ratio of attenuations of two different optical bands of the primary optical measurement vary between about 2.1 to about 1.28. It can be seen that fine particles cause a strong deviation in the ratio of the two attenuations as a function of consistency. This is an unexpected variation according to the prior art.

Examine now ground wood GW curve 1002. The GW has middle sized particles. When consistency of the GW is changed from 0.05 % to 1.75 %, the ratio of attenuations of two different optical bands of the primary optical measurement vary between about 1.68 to about 1.27. Examine now the curve 1004 of the SWB. The SWB has the largest particles in this group such that the amount of fine particles and/or fines is the smallest among these three samples. When consistency of the SWB is changed from 0.06 % to 1.36 %, the ratio of attenuations of two different optical bands of the primary optical measurement vary between about 1.45 to about 1.29.

The curves 1000 to 1004 show that the ratio of attenuations of two different optical bands of the primary optical measurement depend on consistency and cannot be used alone to determine the degree of breaking down of the fiber particles into fines in pulp.

Examine now curves 1006 and 1008 which refer to two different batches which are treated. The disintegration of fibers increases in the direction of the arrow headed line beside the curves 1006, 1008. It can be seen that the pulp treatment increases the ratio of the attenuations of two different optical bands of the primary optical measurement, which depends on the degree of refining, but also the consistency increases. The effect of increasing consistency could be eliminated from the measurement of the degree of refining on the basis of this information for providing the degree of breaking down of the fiber particles into fines in pulp. Then the curves 1006 and 1008 would be more vertical, and in a perfect case straight lines in a totally vertical positions.

Examine now curve 1010 which refer to a third batch which is refined.

In this case, consistency of a sample from the batch is measured on the basis of attenuation of an optical signal. The disintegration of fibers increases in the direction of the arrow headed line beside the curve 1010. Consistency of the sample from the batch is then tried to keep constant the basis of the measurement. But as can be seen, the determination of consistency on the basis of optical attenuation with no depolarization measurement fails to keep the consistency constant (curve 1010 would be a line in a vertical position if a constant consistency were achieved). Hence, consistency of the pulp 104 is useful to measure with depolarization, microwaves, a mechanical device and/or a camera, and use the information in conjunction with the ratio of the attenuations of different optical bands of the primary optical measurement. In an embodiment (see Figure 10), a degree of breaking down of the fiber particles into fines may be performed such that ratios of attenuations of two different optical bands of the primary optical measurements related to a batch (curves 1000, 1002, 1004) is measured at a certain depolarization i.e. consistency CO or within a known range of depolarization i.e. within a known range of consistency. The range may be CI to C2 where CI is the lowest consistency and C2 is the highest consistency in the range. The highest consistency C2 of the range may be smaller than the highest consistency of the whole measurement and the lowest consistency CI may be larger than the lowest consistency of the whole measurement. In an embodiment, the difference C2 - CI may be between 0.5 % and 1 %, for example. In an embodiment, the difference C2 - CI may be between 0.5 % and 0.1 %, for example. C2 may be between 0.2 % and 0.5 %, for example. CI may be between 0.05 % and 0.3 %, for example (CI is always smaller than C2). Then the degree of breaking down of the fiber particles into fines in the batch of curve 1000 may depend on the value Yl. The degree of breaking down of the fiber particles into fines in the batch of curve 1002 may, in turn, depend on the value Y2, and the degree of breaking down of the fiber particles into fines in the batch of curve 1004 may depend on the value Y3. In general, the degree of breaking down of the fiber particles into fines in any batch may depend on the value Y. That is, degree of breaking down of the fiber particles into fines may be a function of Y. The person skilled in the art may define the function easily on the basis of the batch measurements (which are similar to the examples of Figure 10).

In an embodiment, a degree of breaking down of the fiber particles into fines may be performed such that the curves 1000, 1002, 1004 of batches may be modelled using a function. In Figure 10, two measurement points PI and P2 have been used to form a linear model of the curve 1000. The linear mode i.e. the line may be expressed as Y = A1*C + Bl, where Y is the ratio of attenuations of two different optical bands, Al and Bl are constants, and C is consistency/depolarization value. Then the degree of breaking down of the fiber particles into fines may depend on the constants Al and Bl of the function in the batch of the curve 1000. In a similar manner, points PI' and P2' may be used to form a linear model of the curve 1002, the model being expressed as Y = A2*C + B2. The degree of breaking down of the fiber particles into fines may accordingly depend on the parameters A2 and B2 of the function in the batch of the curve 1002. Still in a similar manner, points PI" and P2" may be used to form a linear model of the curve 1004, the model being expressed as Y = A3*C + B3. The degree of breaking down of the fiber particles into fines may accordingly depend on the parameters A3 and B3 of the function in the batch of the curve 1004. The function that models the dependency between the consistency/depolarization and the ratio of attenuations of two different optical bands of the primary optical measurements may also be a non-linear. In general, the parameters of a modelling function may be related to the degree of breaking down of the fiber particles into fines in different batches. Also in these cases, the person skilled in the art may define the model function easily on the basis of the batch measurements (which are similar to the examples of Figure 10).

Figure 11 is a flow chart of the method of determining a degree of breaking down of the fiber particles into fines in pulp. In step 1100, optical radiation is transmitted to the pulp 104. In step 1102, the degree of breaking down of the fiber particles into fines in pulp 104 is determined on the basis of a primary detection of optical powers of at least two different optical bands 106 interacted with the pulp 104, and at least one of the following secondary detections: depolarization of optical radiation propagated through the pulp 104, a property of microwave radiation propagated through the pulp 104, a force caused by a movement between the pulp 104 and a material structure 400, 504, 506 in the pulp 104, and particles in at least one image of the pulp 104.

The method shown in Figure 11 may be implemented as a logic circuit solution or computer program. The computer program may be placed on a computer program distribution means for the distribution thereof. The computer program distribution means is readable by a data processing device, and it encodes the computer program commands, carries out the measurements and optionally controls the processes on the basis of the measurements. The computer program may be distributed using a distribution medium which may be any medium readable by the controller. The medium may be a program storage medium, a memory, a software distribution package, or a compressed software package. In some cases, the distribution may be performed using at least one of the following: a near field communication signal, a short distance signal, and a telecommunications signal.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the example embodiments described above but may vary within the scope of the claims.