FI106890B - Measuring method - Google Patents

Description

106890

Measurement method - Mätförfarande This application is divided by FI application 920101.

The present invention relates to a method of the species disclosed in the preamble of claim 1.

The amount of material to be suspended in the various types of aqueous suspension is an important measurement parameter, not least for environmental maintenance and protection. Suspended material herein generally refers to materials such as those which can be mechanically separated by filtration and centrifugation. Particularly in the forest-10 industry, suspended material may consist of many different components such as fibers, fibrous parts and various fillers and coatings. These components can vary widely in size, from a few millimeters in width and from a few tens of microns wide (fibers) down to a particle diameter of about 1 micron or less (filler). The concentration of the suspension can vary within wide limits, from a few milligrams per liter to tens of grams per liter. Measuring the concentration of suspended material is important, but in many cases it is also important to indicate when the size distribution of the suspended material changes and the extent of this change. In this sense, one area of application is the detection of flocculation chemicals.

Most of the instruments currently on the market for continuous measurement of suspended materials are based on optical measurement principles, such as light absorption, light scattering, and polarized light effects. The most common method involves measuring the turbidity of the suspension, using light attenuation or screening as a measure of the concentration of the suspended material. However, the amount of light scattering depends not only on the concentration of the suspended material, but also on the particle size, shape, surface structure and refractive index of the material in question.

Thus, suspensions with significant particle size distribution can give misleading information about suspension concentration. This is illustrated in Figure 22, which shows the results of turbidity measurements of the attenuation of light transmitted through the suspension. The result (output signal of the measuring device) is plotted against the concentration of cellulosic fibers (large particles) and clay (small particles). As can be seen, such an instrument at the same concentration is much more sensitive to clay than to fibers.

US 2,106,890, U.S. Pat. No. 4,110,044, discloses an optical method which, in principle, permits the concentration of suspended material to be determined regardless of particle size. The measurement principle is based on recording the average transmitted light, as well as measuring the variations in the intensity of light, in the form of a signal containing the square of the actual effective value of the ac voltage component of the resulting measurement signal. This value behaves as a function of particle size, similar to an inverse mirror image, compared to a signal based on the DC component of a measurement signal. Similarly, the sum of the two signals produces a measure of the amount of material in the suspension, regardless of the particle size.

Furthermore, it is possible to obtain a relative measure of the particle size distribution of the suspended material by generating a quotient of the two signals.

This method is called the TP method and is quite efficient, especially at low concentrations, whereby good linearization can be obtained for both the DC signal and the square of the effective value.

However, in the case of suspensions whose particle size distribution is primarily large particles, large particles affect the square of the effective value more strongly than small particles. Another disadvantage, which is often serious in practice, is that calibration of the TP method is relatively difficult.

20, U.S. Patent 3,879,129 discloses another method for detecting the DC value of a measuring signal and the effective value of the ac voltage component of a measuring signal. This has the same drawbacks as the TP method.

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In order for the TP method and similar methods based on measuring the effective value of the measurement signal to produce good particle concentration accuracy and good resolution for particle size, the volume measured must necessarily (depending on the particle concentration and particle size) be small and the light beam narrow. In order for substantially each particle to produce a significant indication in the ac voltage component of the signal, the illuminating light beam should be narrow and preferably collimated or focused, and the reflected light should be detected within a narrow angular range. Fluctuations in AC voltage level off when the light beam has a wide path. It is often desirable to measure the concentrations of suspended material in suspensions with a relatively high proportion of suspended material. In order for the light passing through the suspension to be detected at all, the light source must be relatively close to the light detector. As a result, the measuring device is usually located in the tapered or neck-like portion of the measuring cell. This narrowed area of the measuring cell is easily clogged by large particles, suspended material clumps and the like. As a result, these narrowed areas of the measuring cells are provided with back flushing devices and the like, whereby said area can be cleaned if necessary.

An example of this type of rigidity is described in W. Ditter et al., LASER OPTICAL METHOD FOR DYNAMIC FLOCCULATION TESTING IN FLOWING DISPERSIONS, BASF Aktiengesellschaft, The Effect of Polymers on Dispersion Properties, Academic Press, London 1982, pp. 353-342. The Sus-10 pillar is passed through a tapered measuring neck with a probe assembly. The laser light is focused on the measuring cell and the light emitted from the measuring cell is directed to the photo detector. Another example of a similar sequencer having a short tapered or necked part is described in U.S. Pat. No. 3,879,159, Fig. 2B. This arrangement also includes a known probe having an open channel for immersing in a flowing suspension. This probe, based on the fiber-optic methods described in US 4,040,743, comprises a very deep measuring slot, or throat. An optic is located at the bottom of the slot, which acts by sending light to the suspension flowing through the slot and receiving light from the suspension. Because the slot is very deep, it basically acts as a tapered measuring cell with a neck and therefore also produces the aforementioned clogging problem.

The concentration probe disclosed in WO-86/02162 also has a very deep measuring gap. It is equipped with an optic, which produces a wide measuring beam • through the paper pulp.

Another probe is disclosed in US-A-3,892,485. It discloses a measuring channel in which the entire suspension flows past an optical measuring arrangement. The top of the duct is turned at its edge to hold the fluid flowing in the duct. This device is made to measure with oil, which is a fairly pure liquid.

The main object of the present invention is to provide a particularly advantageous method for processing measurement data of a fluid suspension produced by a probe.

It is another object of the present invention to provide a probe in which the multiple scattering effect often caused by particles frequently suspended in the suspension to be measured is largely avoided.

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It is another object of the invention to provide a probe that illuminates a flowing suspension with a narrow beam of light and detects light transmitted or scattered by the suspension within a narrow angle range. The light beam may be collimated or focused.

It is an object of the present invention to provide a probe that functions to measure a flowable suspension in which the risk of solids clogging is minimized.

The main object of the invention is achieved by an inventive method for registering the state of a flowing suspension having the features set forth in claim 1. Other features of the invention and its further developments, as well as apparatus 10 for recording the state of a flowing suspension, are set forth in other claims.

The width of the measuring beam is adjusted to be equal to or less than the spaces between the larger particles in the suspension being measured. When the measurement is made and the purpose is to determine the distribution of the fine and coarse fraction of the suspended material, the beam width is adjusted to the desired boundary line between the coarse and fine particles. The width of the measuring gap is adjusted so that the effect of multiple scattering of the particles in the suspension is minimized. As a result, the width of the measuring slot is small when the concentration of suspended material is high and large when the concentration of suspended material is low. The gap width is naturally larger than the largest particles that can be expected in the suspension to be measured.

The structure of the measuring device can vary greatly, for example with the body of a measuring detector intended to be immersed in a duct or flow path, or to be inserted into the pipe walls through which the medium is to flow, etc. The measuring device may also be provided with a plurality of optical measuring channels. and non-polarized light, light of different wavelengths, rays of different diameters, etc. In this sense, suitable information about the detector signal can be obtained by appropriate signal processing and correlation measurement methods. Measuring devices with one or more optical measuring channels may also be provided with measuring detectors which function to measure scattered light and which can provide more information about the composition of the suspension. Simultaneous measurement of transmitted and scattered light can also be used to compensate for absorption effects in suspension or optical surface coatings, or to improve the identification of suspension composition. The reference detector can be used to compensate for variations in the intensity of the light source 35. Optical glass fibers may be used with or without a suspension to be measured, depending on the purpose and the site of measurement. The ends of the fiber may also be provided with polarizing filters, an lms / index lens, and protected by a quartz window or sapphire window, etc., without departing from the basic design of the measuring channel and measuring slot of the inventive measuring device. When the used measuring detector body 5 is intended to be submerged in a flowing medium, the body is preferably designed in such a way as to provide good flow conditions around the body, at least near the measuring slot or throat, such that the suspension actually passes through the slot. The area around the measuring gap is therefore provided with smooth surfaces and rounded edges.

The invention will now be explained in more detail with reference to the accompanying drawings, in which: Figure 1 is a front view of a probe suitable for use with the method of the invention; Figure 2 is a bottom view of the device shown in Figure 1; Figure 3 is a longitudinal sectional view taken along line III-III of Figure 4 in another embodiment of the probe; Figure 4 is the embodiment shown in Figure 3 below; Figure 5 is an alternative view from below of the embodiment shown in Figure 3; Fig. 6 is a sectional view of a first embodiment of a probe having mechanical cleaning; Figure 7 is a sectional view of a second embodiment of the probe having mechanical cleaning; Figure 8 is a top view of the measuring channel side of Figure 7; Figure 9 illustrates another embodiment of the probe; Figure 10 illustrates a fourth embodiment of the probe; Fig. 11 is a diagram illustrating a detector output signal according to an embodiment of a measuring device according to the invention and showing a plurality of parameters; Fig. 12 is a block diagram of an embodiment of a signal processing device according to the invention; Fig. 13 is a graph of a set of curves obtained when testing the invention; Fig. 14 is a graph showing a plurality of curves obtained by performing experiments with the invention by increasing successively the concentrations of suspended materials; and Fig. 15 illustrates the results of concentration of suspended material containing various particle sizes from measurements made with a known concentration meter.

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The invention is illustrated in Figures 11-14 and a detailed description of the invention is given in the description of the said figures. Other Figures 1-17 show probes suitable for use in the method of the invention.

The measuring device, i.e. the meter shown in Figures 1 and 2, has a body of a measuring detector 5 in the form of a four-sided plate 1 with bevelled edges. The plate 1 forms a probe to be immersed in the suspension flow, with the wide side of the plate 1 facing the flow direction. A groove 2 is provided on the bottom surface of the plate, which serves as a measuring channel. On the other wide side of the plate 1 are two rounded and relatively deep grooves which at one end are joined to the measuring channel on its respective side and extend parallel to the underside of the plate at the said junction. A fiber optic light guide 3, 4 is embedded in each groove. The inner end of the conductor 3 is connected to a light source 5, such as a light emitting diode or a small laser, which is also embedded in a plate. The inner end of the conductor 4 is connected to a light detector 6 which is adapted to the light emitted by the light source and also embedded in the plate 15 1. The electrical wires or cables leading to the light source 5 and extending from the light detector 6 are also embedded in the plate , which is twisted at the top of the disc. Because the fiber optic light conductors have to be drawn in a gentle arc, in order not to affect their performance, the channels containing 3 and 4 are given a gentle arc shape.

Both the light source 5 and the light detector 6 are heat-sensitive components. As a result, a temperature sensor 8 is embedded in the plate 1, and an electric cable or fiber bundle extending from the sensor 8 is also passed through a tube 7 and coupled to a signal processing circuit (not shown) for temperature compensation by calculating the measurement result from the light detector 6. 25 as described. Preferably, the surfaces of the sheet 1 are smooth and repellent to avoid as much as possible adhering material flowing through the sheet. Of course, the material from which the sheet is made should be inert with respect to the medium in which the material is suspended and also with respect to the suspended material. The plate 1 is preferably made of plastic or the like, although it may also be made of stainless steel.

The essential properties of the probe are in the structure of the measuring channel and in the optics used in connection therewith. The width of the measurement gap between the side walls depends on the medium being measured. For example, if measurements are to be made on a fibrous suspension of wastewater from the papermaking industry, a width of about 3 mm may be appropriate. Preferably, the edges of the slot are shallow and, for manufacturing reasons, the fiber optic light conductors are positioned as close as possible to the outer edge of the slot. The underside of the plate holding the fiber optic light guide 106890 is preferably bevelled in the region of the measurement channel 2, while the ends of the optical fibers are preferably cut off perpendicular to the propagation direction and the cut end polished. The invention is primarily intended to detect light passing directly through the suspension, and thus the fiber-optic light conductors are placed at opposite ends. However, it is also possible to express light scattered within a defined angle, as will be apparent later in the description referring to Figure 16. As mentioned above, the optics, i.e. the ends 3, 4 of the fiber optic light conductors of the embodiment shown, must be positioned near the outer edge of the measuring slot. As shown in Fig. 2, the inlet and outlet of the channel are also 10 slightly rounded in the flow direction, as well as a small portion of the outer edge of the channel located outside the optic. Preferably, the fiber optic has a predetermined depth below the channel so that the effect of the friction between the flowing suspension and the bottom of the channel has no appreciable effect on the suspension flowing past the fiber optic. Sharp edges on the bottom of the duct should be avoided. All these measures contribute to the formation of a probe where the risk of channel clogging is minimized.

Preferably, the portion of the measuring device located in the medium or suspension, at least in the vicinity of the measuring channel, is given a somewhat streamlined shape to avoid the risk of deformation of the suspension through the measuring slot relative to the actual or actual composition of the suspension. In Figures 3 and 4, the measuring body has a rotationally symmetrical shape. Figure 3 is a section along line III-III of Figure 4, and Figure 4 is a view from below of Figure 3. These figures also illustrate an embodiment in which the fiber optic optical wires 10 and 11 are guided entirely through the body 9 and through the tube 12 which is wound to the upper 25 end of the body 9, although it is of course conceivable to integrate the light source, light detector and temperature detector. The body 9 is preferably pear-shaped so that the fiber-optic optical wires 10 and 11 can be guided as gently curves from the measurement channel 13 to and through the tube 12. Figure 4 illustrates a suitable embodiment of the channel 13 having wide flow inlet and outlet portions and a narrowed or neck-like portion of the measuring slot in the region of the openings terminating in the channel of the fiber optic optical wires 10 and 11.

The body 9 is preferably made in two parts which are glued together along the interface 14. One of said parts, the lower part of Figure 4, has molded or milled grooves to form a space for the fiber optic optical wires 10, 11.

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The body 9 of Figure 5 has an elongated shape in the downstream direction. The intersection between the fiber optic light conductors in this case is the same as in Figure 3. A more streamlined shape is conceivable.

In the embodiment of Figure 3, the light source 15 for the fiber optic light guide 10 and the light emitter 5 maize 16 for the fiber optic light guide 11 is disposed in a portion located at the end of the tube 12 outside the suspension medium. If this location is temperature stable, then the temperature sensor need not be tracked for temperature compensation. The light source 15 is supplied from a voltage source 17. An electrical output signal of the detector 16 is supplied to the estimation and calculation unit 18. Suitable calculations 10 will be explained below in connection with the description of Figures 11-15.

The results of the calculations are passed to the presentation unit 19, which may be in the form of a display screen or a graph for continuous use. The device is primarily intended to provide quick information about the suspension's tendency or tendency to change so that control personnel can immediately detect something happening and change the concentration of the medium being monitored and monitor the effects of the remedies.

The aforementioned measurement units may be intended to be immersed in a flowing suspension, e.g., a suspension flowing in an open channel or flow path.

Figure 6 shows a modification of the probe shown in Figure 3 which includes mechanical cleaning of the head 20. The fiber-optic light conductors 22 and 23, shown in the figure merely as solid lines and drawn up to the measurement channel 21, are located relatively close to the periphery of the measurement body 20.

The cleaning arrangement is disposed in a central cavity or cavity in the body 20. The cavity has a first cylindrical part 24 having a diameter 25 substantially corresponding to the measurement gap of the measuring passage 21, e.g. a width of about 3 mm, a second cylindrical part 25 having a slightly larger diameter, e.g. 5 mm, and a third cylinder shaped part 26 having an even larger diameter, e.g. 12 mm. The shaft 28 of the cylindrical brush 27 having substantially the same shape as the tooth brushes used for cleaning the tooth spaces is embedded in a third cylindrical portion 26 with a movable piston having substantially the same diameter as said portion. The brush is toward the outlet of the first cylindrical portion 24. The second cylindrical portion 25 serves as a brush guide to prevent the brush from bending outwardly through the opening at 24. The brush may also be rotated during the cleaning operation.

A helical spring 34 is disposed between the piston 24 and the shoulder formed at the junction of the second and third cylindrical parts 25, 26 The ring 29 is provided with a ring-shaped seal 30 on the periphery of the piston 29. The piston can be operated pneumatically or hydraulically. through a closed passage 35 provided on the shaft of the measuring body 20. A nipple 31 is threaded around the neck of the body 20 near the third cylindrical portion 26. A nozzle coupled to a pressure medium arrangement 36 is provided on the nipple to supply pressure medium to the backside of the piston 29 to extend the brush 27 out of the opening 24.

The shaft of the brush 28 extends beyond the piston 24 for a defined distance. The nipple 31 and hose are removed when the shark 27 is cleaned or replaced with the piston. The end of the brush arm is gripped by a suitable tool, for example, a pointed tip 15 or the like, and the brush and piston are pulled out of the cavity thus formed.

The probing process is carried out with a flowable suspension. Despite the special shape of the measuring slot, which has slightly rounded edges, it forms a cover and accordingly the measuring slot needs to be cleaned, preferably me-20. The frequency at which the gap is to be cleaned depends on the composition of the suspension. The pressure medium arrangement 36, which operates to supply and remove the pressure medium for actuating the piston 34, is controlled by a control circuit 35 which may be program controlled, time controlled, manually controlled or a combination of these types of controls. The spring 34 is strong enough to move the brush into the retracted position even though some of the suspended material is adhered to the brush bristles. The bristles may adhere to very large suspended particles so as to prevent the brush from being completely drawn into the measuring slot, or so that the fiber portion is ul-machineed from said slot. This results in a significant indication of the measurement signal detected by the estimation and calculation unit (not shown in Figure 6), and this unit 30 then supplies the control signal to the control circuit 35, which then causes the pressure medium arrangement 36 to start a new brushing cycle. Unless one or more additional brush cycles produce the desired result, the evaluation and calculation unit may be designed to generate an alarm signal that indicates that the brush needs to be cleaned or replaced.

«10 106890

Figures 7 and 8 show a measuring frame 37, which is currently considered advantageous because this frame can be manufactured and maintained in a simple manner. The measuring body 37 of this embodiment is in the form of a flat plate having an outline of irregular shape. The fiber optic optical wires 33 and 40 5 of the measuring body 37 are drawn into the measuring slot 38, whereby these wires are schematically shown in the form of solid lines when the fibers are in the same plane as the cut shown and dashed when said fibers are in a different plane. The fiber conductors are housed in slightly rounded channels and routed through a nipple 41 which is threaded to the body and supports the other end of the hose 32 from which the conductors are routed to the estimation and calculation unit (not shown in Figure 7). The hose extends into a tube 33 which is threaded to the top of the body 37.

In this case, the measurement gap is disposed on a surface 43 which is inclined with respect to the surface along which the supply lines are routed to the control and evaluation circuits. Fig. 8 is a view of a surface 43 including a measuring slot channel and a measuring slot 38, and an inlet 15 into a channel 42 provided with a shark. The brush pass-through passageway 42 has substantially the same structure as the passageway shown in Fig. 6, but is inclined obliquely with respect to said passageway because the passageway of the embodiment of Fig. 8 extends perpendicularly to the surface 43. This provides an easily accessible opening on a side parallel to the surface 43 and through which the brush arrangement can be maintained opposite the inclined surface. This opening is provided with internal screw threads and can be closed by a screw cap or cover 44.

The pressure medium channel 45, optionally in the form of a tube shaped into the body, is disposed between the channel 42 and the nipple 46 threaded into the body, to which a hose 47 extending into the pressure medium arrangement (not shown) is attached.

This probe includes a second passage 48 extending between the nipple 49 threaded into the body and the passage 42 near the metering slot 38. The cleaning agent is fed through a hose connected to the nipple 49 immediately prior to and optionally 30 to facilitate removal of material adhered to the metering slot. This also avoids the excessive brushing of suspended material. The channel 48 can also be flushed clean between different brushing periods. The cleaning agent may be either a gas, such as air, or a liquid, such as water, optionally mixed with chemicals.

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Fig. 9 illustrates a third embodiment of a measuring device for insertion into a measuring cell or tube through which a suspension flows. The measuring device has the shape of a tube 50 having the same diameter as the main diameter of the measuring cell / tube. Inside the tube, a thicker portion 5 is provided with a measurement channel 51. The tube wall is provided with two fiber optic light conductors 52 and 53, each of which is connected to the corresponding side of the measurement channel 51 and each of which is connected to units of light source 54 and light detector 55. . Since units 54 and 55 are disposed so as to be affected by the temperature of the medium being measured, a temperature indicator 56 is disposed near said units. A voltage source 57 is coupled to a light source 54.

Similarly to the probes described above, the signals of units 55 and 56 are fed to an estimation and calculation unit 58 which, in accordance with the invention, operates to calculate the desired data for suspension, i.e. concentration, particle size distribution, fiber content, etc. The calculations are performed continuously, correcting for the temperature indicated by the detector 56, and are led to the display unit 59. The display unit 59, for example, may be a graph plotter which continuously outputs curves representing one or more calculated properties of the suspension. Control personnel can be aware of the trend toward a change in suspension, by curve or curve changes, and can quickly detect the effects of measures to correct the composition of the suspension. The measures may include adding a flocculating chemical to the wastewater to precipitate solids. The tube 50 may include a plurality of measurement channels 51 for measuring different properties of the suspension. For example, the measurement channels may be arranged in series 25 in the flow direction, or they may be located at different locations on the periphery of the tube (not shown). For example, the particle size distribution of a suspension can be measured by two or more measurement channels with different path diameters of the transmitted beam.

Figure 10 illustrates another embodiment of a measuring device. This device is a variant of the device shown in Figure 9 for measuring cell / tube flow rate, although the principle can also be applied to variants of the other aforementioned measuring device. Fiber optic optical fiber light beam transmitted. Instead, in the embodiment of Fig. 17, there is a straight channel 90 extending to the measurement channel 88 in the thickened portion of the measuring cell / tube 89. A laser transmitting a narrow beam of light 35 through channel 90 is disposed at one end of the channel. On the opposite side of the measuring channel 88 there is a fiber optic light guide 92 which passes around the tube 89 12 106890 and leads to a light detector 93 whose electrical output signal is coupled to the calculation and display unit 94 as well as the temperature sensor output signal. An operating voltage source 96 is connected to the laser 91.

By using a narrow beam relative to the spaces between the large particles in the suspension, the alternating voltage component of the detection signal can produce detection of the material flowing past with good resolution.

The novel signal processing method of the invention has been found to be very suitable for use with the above-described probe, since said end can provide a clearly defined and narrow radius path and narrow measuring gap required for said signal processing method for measuring suspensions typical of the pulp and paper industry. The inventive method is based on the first assumption that the suspension essentially consists of two components, large and small particles. The large particles can then be regarded as a relatively transparent network in which many of the small particles are suspended-15. The smaller fraction volume of such a suspension is considered according to the principles of statistical distribution, the number of small particles is large and relatively constant. On the other hand, the number of large particles is very small and varies greatly.

For example, a suspension of fibers having a length of 1 mm and a width of 20 microns and a concentration of 100 mg / 1 20 contains approximately two particles per mm 2. If 100 mg / l of clay with a particle size of 1 micron in diameter are added to this suspension, the number of particles will increase to 7.5 * 10 4 / mm 3. Measuring the attenuation of light in a small volume of this suspension gives an average of the intensity of light transmitted. Deviations from this mean are mainly due to fluctuations in the fiber-25 material (fibers coming from time to time). In principle, the highest signal level is obtained when no fibers are present in the light beam, and the light beam is attenuated solely by the clay particles. This allows the proportion of large or small particles in the suspension to be determined by measuring the average value of transmitted light VdC and the maximum value of said light, i.e. the peak value Vp over a predetermined period of time. (In this context, light-absorbing solutes in suspension work in the same way as clay and can be determined by measuring the peak value VP.)

Lambert Beer's law is used to calculate the turbidity or concentration of a suspension, whereby this law gives the transmitted light intensity according to the following relation: 35, 106890 V = V0 * e-alN (1) where

Vo = intensity of transmitted light with clear water, i.e. water without any suspended particles; Average intensity of light attenuated in the presence of 5 V particles; a = scattering factor; 1 = path length of light beam through suspension; N = number of particles per unit volume.

10 Turbidity S is normally defined as: S = N * a = ln (VQ / V) / l (2)

From the above, it is seen that for the same particle type, turbidity is directly proportional to the concentration of the suspension.

The following relation applies to suspensions comprising a plurality of 15 different types of particles: ES = ENj * aj = (1/1) * Eln (Vo / V) (3) where i is an index for different types of suspensions, whereby summation is made over all types of particles. The concentration of the suspension in mg / l is thus: conc = (1/1) * EC! * ln (V0 / V) (4) 20 where Ci is a constant for converting turbidity to a concentration in mg / l for a given particle type.

If the suspension under consideration comprises a mixture of two completely different types of suspension, i.e. a suspension containing small particles, such as clay, and a suspension containing relatively large particles, such as fibers, then these particles have a different effect on transmitted light as mentioned above. Roughly speaking, the particle suspension particle contains the largest signal level deviation from the signal measured with clear water, while the particle particle suspension part results in a clear signal variation (change).

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Fig. 11 is a diagram showing an AC voltage signal obtained from an inventive probe. The figure shows the levels of the clear water signal V0 (whereby these levels have been measured previously when the instrument has been calibrated with clear water), the signal DC level Vp> c and the peak level Vp of the signal. Since, according to the theory 5 described above, small particles do not significantly influence the fluctuation of the resulting signal, but cause the peak of the signal to fall from clear water to peak Vp, ln (V () / Vp) is obtained for this part of the suspension ln (Vp / Vj), c).

10 Applying Lambert Beer's law thus, with a "model suspension" comprising two types of particles - large and small, the following result is obtained from the signals of Figure 10: cone = a * ln (V () / Vp) + b * ln (Vp / Vp) c) ( 5) where a and b are constants, a * ln (V () / Vp) is the concentration of small particles, and ln (Vp / V £) c) is the concentration of large particles.

The above equation (5) can be rewritten as follows: cone = (ln (V () / Vp) + cj * ln (Vp / Vp) c)) * C2 (6) where ci is the sensitivity coefficient of the measuring instrument and C2 is the standard measurement result. to mg / l. It will be appreciated that these constants can be readily obtained when the measuring device is calibrated.

These constants were readily obtained experimentally by measuring two suspensions having! at the same concentration, and containing the smallest particles on the one hand and the largest particles on the other: (ln (Vo / Vp)) s + ci * (ln (Vp / Vp) c)) s = ln (V () / Vp) i + ci * (ln (Vp / Vp) c)) l where s means small particles and 1 means large particles.

25 (ln (V0 / VP)) s - (ln (V0 / Vp)) l ci = - (ln (Vp / VDC)) l - (ln (VPA ^ DC)) s ♦

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106890 conc.lab c2 = - ln (V0 / Vp) + ci * (Vp / Voc) 5 where conc.lab is the concentration of suspension obtained in the laboratory for measurement by standard methods. Of course, many such measurement processes can be performed, preferably at different concentrations, to provide a statistically more reliable result.

The values ln (V0 / Vp) and ln (Vp / Vp) c) may be used in conjunction with the calculated conc value 10 to calculate the relative composition of the suspension for small and large particles, respectively, as will be explained in more detail below with reference to FIG. The quotient ln (Vp / V £> c) / ln (V0 / Vp) yields another relative measure of particle size distribution.

Fig. 12 shows an embodiment of the device for carrying out the inventive method. The light beam L from light source 101 illuminates the flowing suspension S. The light beam L has a small diameter compared to the spaces between the large particles in the suspension, but large compared to the spaces between the small particles. In practice, this often results in a quest for a narrow beam of light.

The transmitted light is detected by a photo detector 102. The sensor signal is amplified by the amplifier 103. A filter, or average generator 104, is coupled to the output of the amplifier 103, which outputs a dc component Vdc of the signal. To the amplifier output '·' ·. there is also connected a peak value detector 105 which registers the largest signal Vp over a given measurement period.

The measurement period is set by means of timer 106. At the end of the measurement period, the timer 106 transmits a first signal to the sampling and holding circuit 107 whose input is coupled to the peak detector 105 output for temporarily storing the peak detector 105 output signal, and after a small delay transmits a second signal to the peak detector 105 for the measurement period. Thus, the peak values Vp of the preceding period are always present at the output of the sampling and holding circuit 107. The light source 101 can also be pulsed controlled and measurements are made only during pulses. This control (not shown) is performed by unit 108 which controls circuits 105 and 107 accordingly.

1Ä 106890

Signals Vj) c and Vp are supplied to control and computing unit 108, suitably a microprocessor, e.g., an IBM compatible personal computer, which performs the aforementioned calculations and displays the results on at least one presentation unit 109, 110, e.g., monitor, printer or the like.

The measurement period of the timer 106 is adjusted such that the peak value is quite likely to occur during each measurement period, but is kept so short that changes in suspension are detected as soon as they occur and that the temporal variation of these changes can be continuously monitored. This allows the measurement periods to be kept short when the coarse fraction concentration is low, although these periods should be longer as the coarse fraction concentration increases. The duration of the measurement period can be made variable according to predetermined parameters, which may optionally depend on previously obtained measurement results.

It may also be appropriate to control the sampling and holding circuit 113 via the timer 106 in the same manner as the sampling and holding circuit 107 downstream of the filter 104. The sampling and holding circuits 107 and 113 are the kind that operate by transmitting their value in digital form to the digitally operating unit 108. It will be apparent to those skilled in the art that some of the circuits 104-107 and 113 or all of said circuits may be simulated by software 108, Naturally, the signal or signals are converted to the signal form in which unit 108 operates. Such conversion units are not relevant in the present context and are therefore not disclosed. For example, filter 104 may consist of a calculation routine or an arithmetic routine that calculates the average of the signal during each measurement period. The signal from the amplifier 103 may be sampled by units 104 and 105 and the calculation performed digitally in a manner well known to the skilled artisan.

As also shown in Fig. 12, the calculations may also be performed according to the aforementioned TP method or may be based solely on measurements of effective value. It may be advantageous to reciprocally calculate the same properties of the suspension according to two different methods and continuously compare the results, and to send an alarm signal to the alarm unit, e.g., an audio alarm or optical alarm, as soon as the calculations performed according to these two methods differ.

Comparisons to methods based on effective value measurements do not include significantly additional measurements since the same basic signal from probe 17 106890 101, 102, 103 may be used. Similarly, a filter 115 is shown to be connected to the output of amplifier 103. Filter 115 acts to filter the AC component out of the signal to a unit that operates to measure the true effective value of the signal from the filter 115 and supplies this value to the unit 108, optionally through a sampling and holding circuit 118 similar in type and operation to circuits 107 and 113. The signal paths are represented by dashed lines elements 115, 116 and 118 may be omitted. It will be appreciated that elements 115, 116 and 118 may also be simulated with program loops in unit 108.

Figure 12 shows only one probe 101, 102. In this case, the division is made only into two particle size ranges, large and small. However, expression in more than one size range can be achieved by using multiple probes having radial paths with different widths. Measuring devices with these characteristics are described in SE-A-7,806,922. The described signal processing method 15 according to the invention can be applied to signals at all ends. In this case, the control and calculation unit 109 receives a Vp) C1 signal and a Vp signal at each probe and is provided with a program that calculates a particle concentration-on for a number of particle size ranges.

To test the inventive method experimentally for particle sizes, experiments were initially performed on suspensions containing very small particles. Various flocculant chemicals were then added to these suspensions with continuous stirring or stirring to form large pellet deposits or flakes. The results of these measurements are shown in Figure 13.

· 'Curve A represents a measurement of turbidity corresponding to C3 * ln (V0 / Vp) c) where 25 C3 is constant.

Curve B shows the results obtained according to the invention for measuring the concentration of suspended material, i.e. cone = C2 * ln (V () / Vp) + cj * ln (Vp / V [) c). Curve C represents the large concentration of b * ln (Vp / Vj) c), i.e. the large particles in the suspension. It was found that ln (Vp / V] 3c) is essentially independent of variations in the light intensity of the light and of dirt and scratches on the optical surfaces. Curve D represents a high concentration of α * ln (V () / Vp), i.e. the concentration of small particles in the suspension. The curves are marked with different types of characters. Each mark, or mark, is placed at the time of measurement, which in turn is marked on the abscissa. There is a 15 second interval between each measurement time.

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Measurements were made in the laboratory with circulating water from a paper machine. The water was untreated at measurement time 1. Various flocculation chemicals were added to the water twice, immediately before measurement times 2 and 6. As shown in curves C and D, the first chemical added at measurement time 2 had a relatively low flocculation effect, while the second big effect. This is also represented by curve A obtained by the prior art encryption method, although less clearly. Curve C is virtually a mirror image of curve d. These curves show that the flocs decompose slowly after 10 heavy formation at flap measurement 6, i.e., curve D decreases and curve C rises. The determined tendency in this direction is also observed after measuring time 2. Curve B, which is the weighted summation of curves C and D, remains virtually at the same level that can be considered as an exceptionally good result, since this curve should indicate the total concentration held constant over the course of the laboratory measurement process.

The curves obtained by applying the inventive method show that clear information can be continuously obtained regarding, for example, the state of the filing suspension, and that when adding different chemicals, the results of the operations are quickly and reliably expressed. As shown in Curve D, it can be seen that the addition of the chemical is such that the addition of more chemicals does not have a greater effect on the flocculation of the small particles. When chemicals were added at time 6, the curve d dropped so low that it was relatively close to the x-axis. The user can try to lower the curve even more by adding more flocculation chemicals. However, if the curve does not lower. At this level, the addition of chemicals does not affect the flocculation of the remaining small particles, which is immediately detected. Other substances can then be tested, with the effect of these substances also visible on the curve immediately after their addition. Thus, the inventive method enables the dispensing of chemical flocculating additives, for example, in circulating water obtained from a paper mill and when the pulp purification has to be adjusted in a more optimal manner. 30 In addition, the effect of different chemicals can be seen quickly so that the most appropriate chemical can be used.

Figure 14 shows the results obtained by applying the inventive method to various mixtures of fiber and clay suspensions of known concentration. Similar to Fig. 13, curve A shows the results of turbidity measurements, curve B represents the results obtained when measuring the concentration of suspended matter, i.e. C2 * ln (V0 / Vp) + cj * ln (Vp / V]} c), 19 106890 curve C represents b * ln (Vp / V [) c), and curve D represents a * ln (V0 / Vp). Curves E and F illustrate the measured and calculated concentrations of large particles relative to total concentration, respectively. Known concentrations of clay, clay, clay, pine sulfate, pine sulfate, clay, birch sulfate, birch sulfate were successively added to the starting pine sulfate mass. When applying the method of the invention, the measured concentration, which was observed to increase almost linearly, correlated very well with the concentration determined in the laboratory (abscissa). The measured concentration of large particles (curve E) was also very well in agreement with the proportion of fiber material calculated by the blending method (curve 10F). As shown in curve A, for variations in the composition of the suspensions used here, where these variations are realistic in the forest industry, using turbidity as a measurement parameter would definitely be incorrect to obtain information on the events occurring in the suspension, considering both suspended material concentration and particle size distribution.

The inventive principle can also be applied to measurement according to the scattering principle. This may be the case, for example, when the suspension contains a very small amount of suspended material. In this measurement method, a small signal is measured relative to the background at the 0-level, instead of measuring a small signal relative to the high background level (clear water level), as is the case with the permeation measurement method. This may involve detecting the lowest value of the ac voltage signal Vg instead of the peak value of Figure 11 and comparing said lowest value to the zero level instead of the clear water level for that part of the suspension containing small particles. However, for the part of the suspension containing large particles, the lowest value Vg is related to the mean ν) χ \ These ratios, however, are more complex than simple logarithmic partial expressions for penetration measurements and depend inter alia on the geometry of the measuring device.

When measuring typical suspensions, such as circulating water generated by a paper mill, the inventive measuring method requires a relatively narrow measuring beam that is substantially collimated or focused. The suspensions are often relatively concentrated, which requires a small measurement gap in order to detect the light passing through the suspension and to provide a workable received signal. Known probes with these properties tend to clog and often need to be cleaned.

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It will be appreciated that many variations are possible within the scope of the invention. For example, the measurement channels can be designed for use with radiation other than light radiation, e.g., β radiation.

The embodiments shown in Figs. 9 and 10 may also be provided with arrangements of substantially the same type as those shown in Figs.

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Claims (15)

A method of recording the state of a moving suspension which may contain fractions having particles of very different sizes, wherein the suspension is illuminated with a bundle of light and detecting light emitted from the suspension to provide one against it. detected light intensity corresponding electrical signal, characterized in that the illumination of the suspension takes place with a narrow bundle of light particles relative to the spaces between the particles and light emitted from the suspension within a narrow angular range; that an extreme value (peak or bottom value) of the electrical signal is indicated within predetermined time intervals; and that within each time interval the extreme value forms the output value for calculating at least one preselected property of the suspension. Method according to claim 1, indicating light transmitted by the suspension, characterized in that the extreme value is the highest value of the signal, peak value (Vp), during the time interval, and that the fm action in the suspension is indicated by setting the peak value in relation to a voltage level (V0). , which was obtained when measuring on clear water. Method according to claim 1 or 2, indicating light transmitted by the suspension, characterized in that the extreme value is the highest value of the signal, peak value (VP), during the time interval, that the mean value (VDc) of the signal is indicated and that the coarse fraction in the suspension is indicated. by setting the peak value in relation to the mean of the signal. 4. A method according to claim 2, characterized in that the concentration of fine action: is indicated by forming the signal a * ln (Vo / VP), where a is a constant obtained by calibration against a suspension with a previously known fraction fraction concentration. 25 5. A method according to claim 3, characterized in that the concentration of coarse fraction is indicated by forming the signal b * ln (VP / VDC), where b is a constant obtained by calibration against a suspension with a predetermined coarse fraction concentration. 6. A method according to any one of claims 2 to 5, characterized in that the total concentration of suspended substances in the suspension is indicated by forming the signal cone = (ln (Vo / VP) + Ci * ln (VP / VDC)) * c2 ( 6) where the constant c1 is the sensitivity coefficient of the measuring arrangement and c2 is a constant for converting measured values to concentration in mg / l, the constants being obtained by calibration against suspensions with known fractions. Apparatus for detecting the state of a moving suspension which may contain fractions having particles of very different sizes, including a light source (1) illuminating the suspension with a ratio of large particles to the suspension. narrow light bundle and further comprising a light detector (2) which detects light emitting from the suspension within a narrow angular range and also emits an electrical signal corresponding to the detecting light intensity, characterized by a signal processing arrangement (104-108) predetermined time intervals indicate an extreme value (peak or bottom value) of the signal from the detector (102) and which also calculates at least one preselected property of the suspension using the extreme value. Apparatus according to claim 7, characterized in that the signal processing arrangement (104-108) additionally indicates the DC voltage level (Vdc) around which the detector signal varies, and calculates a value from an algorithm comprising the extreme value and the indicated DC voltage level and adapted for configuration. one of a measuring head comprising the light source (101) and the light detector (102). Apparatus according to claim 7 or 8, characterized in that the light source and the light detector are arranged in a measuring head, the measuring head comprising an open measuring channel (2, 13; 21, 38, 51, 88) having two mutually opposing channel sides. and there ·. the radiation from the radiation source is emitted from one channel side and received at the other channel side, the mechanical transitions between surfaces of mutually different stretching being softly rounded, a) the depth of the measuring channel being shorter than the distance between its channel sides; b) transmitting the measuring beam from the radiation source to one channel side and from the other channel side to said radiation indicator via a respective thin light channel, such as a fiber optic light guide (3, 4; 10, 11; 22, 23; 52, 53) or a a narrow straight channel (90) of a size providing a light beam which is narrow in relation to the distance between Large particles in the suspension transmitting a narrow beam; c) the light channels, close to the measuring channel, run practically parallel to the bottom of the measuring channel and in line with the optical beam passing through the measuring channel, and are positioned near the outer edge of the measuring channel; and d) the only type of optical components that may exist between the light channels and the channel sides are components of divergence reduction and / or light filtering and / or protective nature (Figs. 12, 13, 14, 15). Apparatus according to claim 9, characterized in that the width of the measuring channel between the side edges is between 1-5 mm. Apparatus according to claim 9 or 10, characterized in that located adjacent to the measuring channel is a cleaning arrangement (24-35; 42, 44, 45, 48) which is automatically controlled to provide mechanical cleaning of the measuring channel at intermittent time. said cleaning arrangement comprising a brush (27) which, when inoperative, the hallway is retracted in channel (25-26; 42) with an opening to the bottom of the measuring channel (21; 31) and as when operative during the intermittent cleaning of the channel caused by reciprocal movement through the opening (Figs. 6 and 7). Apparatus according to claim 11, characterized in that the cleaning arrangement comprises a channel (48) through which a flushing or rinsing medium can be fed through an opening to the bottom of the measuring channel (38) (Fig. 7). Apparatus according to any of claims 7-12, characterized in that, within the radiation-conducting elements mounted adjacent to the measuring channel, the measuring channel has a depth of such value that the effect of friction between the liquid suspension and the bottom of the channel has negligible effect on the suspension flowing past the elements. Apparatus according to any of claims 7-13, characterized in that the measuring channel: is in the form of a recess or depression in a measuring body (1; 9) intended for immersion in the suspension in which measurements are to be made. Apparatus according to any one of claims 7-11, characterized in that the measuring channel 25 is in the form of a recess or depression in a part of an inner wall of a pipe (50; 59) through which the suspension flows. «