Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
  • G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
  • G01N29/4427—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison with stored values, e.g. threshold values
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/04—Analysing solids
  • G01N29/045—Analysing solids by imparting shocks to the workpiece and detecting the vibrations or the acoustic waves caused by the shocks
  • G01N29/046—Analysing solids by imparting shocks to the workpiece and detecting the vibrations or the acoustic waves caused by the shocks using the echo of particles imparting on a surface; using acoustic emission of particles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/22—Details, e.g. general constructional or apparatus details
  • G01N29/30—Arrangements for calibrating or comparing, e.g. with standard objects
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/01—Indexing codes associated with the measuring variable
  • G01N2291/014—Resonance or resonant frequency
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/02—Indexing codes associated with the analysed material
  • G01N2291/024—Mixtures
  • G01N2291/02416—Solids in liquids
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2291/00—Indexing codes associated with group G01N29/00
  • G01N2291/02—Indexing codes associated with the analysed material
  • G01N2291/028—Material parameters
  • G01N2291/02836—Flow rate, liquid level

Definitions

• the present invention relates to a method for process monitoring with vibration analysis of the type which is mentioned in the preamble of claim 1, and a device for performing the method.
• vibration measuring has in e main been performed in order to monitor bearings in machines of different types.
• the vibration measuring has been used in order to optimise the stability of constructions.
• Vibration measuring has also been used as a tool for identifying sources of noise in order to reduce noise.
• the sound sensor is placed preferably on a stator segment of the refiner's milling stator so that the refining beating characteristics can be monitored. This is a logical placement because the refining/Tjeating has a large influence on the pulp.
• the monitoring of the sound from the refiner gives information about the distance of the refiner discs from each other and their wear and tear and indirect information on the pulp characteristics.
• One object of die invention is to provide a method and a device which - with ranning measuring continuously or at short time intervals and automatically - can give information about me condition and contents of a flowing mixture (e.g. fibre pulp in fluid or gas) without any or with negligible influence on d e mixture.
• a flowing mixture e.g. fibre pulp in fluid or gas
• Another object of die invention is to provide a method and a device which at continuous measurements on a flowing mixture generates information regarding total mass flow and/or mass flow for at least one component in die existing mixture. Thereby, it is possible to check me pulp flow which is important to the stability and/or die quality of die paper made from the pulp.
• Still anodier object of the invention is to produce a method and a device which gives a measure of at least one special characteristic of d e components which are present in a flowing mixture or suspension, which measure gives an indication of suitable regulating for changing the measure to a desired value, and which is suitable for use in a servo control system.
• Yet another object of die invention is to provide a metiiod and device which through analysis of an electrical signal gives information on non-desired components for a following process or product, such as foreign particles, stickies, printer's ink, metal, sand, oil, plastic etc.
• Yet anodier object of the invention is to provide a method and a device which can supervise a position near an adjustable unit and tiiereby give a good control of particle characteristics in a position later on in a processing system.
• die invention relates to a metiiod of measuring and a measuring device with vibration analysis especially, although not exclusively, developed for use within die paper and paper pulp industry.
• the invention is primarily intended for use in pipe lines or conveyors, where gases or fluids with solid particles or emulsions of substances witii different density and/or viscosity or the like flow between different processing stations.
• the invention consequently relates to a metiiod for indicating, during a manufac- turing process, e.g. within the paper-, paper pulp-, pharmaceutical, foodstuff- and building material industries, die characteristics and contents of a mixture in a fluid which flows tihrough a conveyor, e.g. a pipe line or a channel, characterized by - recording for a precise time me vibrations directly from die conveyor at least at one position with no or minimal mechanical influence on die mixture; - grading of die recorded vibrations for each position according to predetermined characteristics, e.g. frequency, angular and average difference, levels of significance or the like, and
• the recording of vibrations and die grading of them for the precise time is repeated for a number of time intervals after each other, and die so obtained results are combined, whereby such recordings which lie outside a predetermined deviation from die other results, are removed.
• Sampling can occur of die contents of die suspended or mixed substances at precise time relationships with generating of a vibration characteristic and/or value with determination of die contents and storage in a table for the contents against vibration characteristics and/or values for producing comparison data.
• die word content is meant also the amount, quality and volume either totally for the mixture or suspension or for at least one component, compound or substance in die mixture.
• Dete ⁇ nination of the amount, quantity, or volume of tihe flow totally or for at least one component, compound or substance is provided from analyse results and for example from dwell time and calculations in a later process step.
• the determinations of die content can also be done before installation of die measuring equipment.
• the position for recording of die vibrations and die sample-taking position can be placed at a distance from each other so that there is a time delay between die passage of die material tiirough the two places, whereby said time relationship corresponds with said time delay.
• the vibration-recording place can He in a pipe line near a process changing means which is controllable under die guid.ance of analysis results of the obt.ained vibration characteristics, but in such a position tihat the vibrations originating from die process-changing means are attenuated in it.
• a value can be calculated using known mathematical methods, whereby for each calculated value a control value is allocated such tiiat a control of die servo type can be obtained for die process-changing means in order to counteract deviations in die calculated value from a desired value.
• die measuring means for performing die metiiod comprises a sound or vibration measurer, preferably in die shape of an accelerometer or surface sensor placed on or screwed into die conveyor.
• the vibrations could also be captured by using laser techniques, for example by directing a laser beam onto e conveyor and to record die beam reflected from me conveyor and modulated with the vibrations from die flowing content in the conveyor.
• the vibration measure will be called below a sensor or vibration sensor.
• the measuring device converts vibrations in die conveyor to an electrical signal. The signal is registered during several, relatively short periods of time after each other.
• the signal in each period of time can, for example, be divided into its frequency components, for example and preferably with Fast Fourier,Transform (FFT), whereby a frequency characteristics is created.
• FFT Fast Fourier,Transform
• Each type of flow with its contents of sotid particles and its flow speed gives a typical frequency characteristics.
• This frequency characteristics is analysed in order to obtain die characteristics of the flow.
• Otiier predetermined characteristics to grade die signal are angular and average difference, levels of significance or die like.
• the industrial application for the appHcation lies in tihat the analysis of die obtained vibration characteristics can be used to control processes or to check the quaHty during manufacturing, to control die process from new characteristics which up to now have not been possible to control and/or in order to give an alarm if error occur.
• An electrical signal from at least one sensor attached to a conveyor is frequency-analysed and at least one value derived tiierefrom is used for controlling at least part of die process, e.g. to add more gas or fluid, to increase die flow of a main reactant, adjust withdrawal of Hquid/gas, increase revolution speed/power on a feed screw, to change die pH-value, to add functional chemical(s) or the like.
• the analysis is performed relatively "on-line", i.e. die investigation takes a relatively short time, only a few seconds and in certain cases even down to fractions of a second, and die control can take place almost directly after the result is obtained.
• One difficulty with vibration analysis of this type is obtaining sufficiently clear and unambiguous results, and with as Httie influence from surrounding disturbing effects as possible. Therefore the obtained sound signal, e.g. FFT (Fast Fourier Transform), AMT (Angle Measure Technique) or wavelets (where die signals are decomposed in levels of significance), is transformed in order to obtain typical vibration characteristics (in FFT, e.g. power spectrum having windows, e.g. Hamming windows).
• FFT Fast Fourier Transform
• AMT Angle Measure Technique
• wavelets where die signals are decomposed in levels of significance
• AMT is based upon tiiat, in a set of sampled/time-series values, a number of points in die set is used as a centre point for a circle which is expanded stepwise.
• the angle and die distance in die y-direction are measured for the two points in die signal set provided at the edge of die circle.
• the mean value for the whole set is calculated for the angle and die average difference Y as a function of die stripping factor (the expansion degree of the circle) using die values for each circle and expanding step,.
• Subsequent calibration can tiien take place preferably with multivariate statistical methods, e.g. PLS (Partial Least Squares). Analysis with neural networks is also conceivable and also combination of multivariate statistics and neural networks.
• PLS Partial Least Squares
• Vibration measuring can, with die method according to die invention, take place at a measuring position in a conveyor with flowing suspension or die like in die direction of flow near a unit which is to be controlled.
• the obtained analysis values in monitoring position could be compared witii die analysis values of die contents in die suspension at another analysis position in die pulp manufacturing plant, which Hes further in die direction of flow.
• On-line control from the analysis position is impossible because of die time delay, although rn.anu.al control has been possible to use.
• Comparison values could be recorded with the time delay which occurs between die measuring position and die analysis position.
• the obtained comparison values could be stored in a data bank and used during the control of the unit.
• a quantity/mass flow measurement totally and/or for each, chosen component can be obtained, where the suspension or mixture need not be in direct contact with die measuring sensor, as it for example must be at different kinds of spectroscopy. This is very important when die measurement of a mixture or suspension is made which is corroding or caustic or the like. EarHer, samples could sometimes not be taken continuously to a test equipment. A very large test stream had instead to be taken manuaUy for test at intervals. The invention takes care of tiiat problem.
• Figs. 1A and IB exemplify schematic outline characteristics of a paper miU with different processing stations/process steps for the manufacturing of paper pulp, partly with mechanical processing and pardy from recycled paper and showing die positions in the system where measuring units can be placed.
• Fig. 2 shows a block diagram of an embodiment of a measuring device according to the invention.
• Figs. 3A and 3B show curves obtained in experiments with die invention and processing with FFT.
• Fig. 4 shows schematically a subsystem in a paper miU, where a first embodiment of a device according to die invention has been placed.
• Fig. 5 shows schematically a different subsystem to that shown in Fig. 4 in a paper mill, where a second embodiment of a device according to die invention has been placed.
• Fig. 6 shows schematically yet another subsystem different to those shown m Figs. 4 and 5 in a paper mill, where a third embodiment of a device according to the invention has been placed.
• Fig. 7 shows schematically anodier subsystem in a pulp mill in which the device according to die invention has been positioned in different pipe lines.
• Fig. 1A In the process treatment stages of paper pulp manufacturing of the mechanical type (such as in RMP, TMP, CTMP etc.), shown in die examples of Fig. 1A, one starts from wood chips which are cleaned in a chip wash unit 1 and then dewatered and moistened in a unit 2. A certain feedback of mainly water takes place from die unit 2 to die chip cleaner 1. Possible chemical impregnation occurs in a unit 3, whereafter the chips are fed to a refiner 4. The wood chips ground in tihe refiner 4 (die beaten chips are now pulp) are diluted and further diluted and screened in a unit 5 and then fed to a vortex cleaner unit 6, whereafter they are dewatered 7.
• the low fibre content water is fed back to most of die stages in d e process, as shown in Fig. 1.
• the dewatered pulp is bleached 8. Thereafter the so manufactured pulp is stored 9 while waiting for paper manufacturing 10.
• tiiat the different process treatments described above can change places with each other and tiiat tihey furthermore can be performed several times in a process, e.g. grinding, filtering etc. Chemical treatment of different types can naturally take place in different stations in the process.
• an X indicates an example of such places in die process where tihere can be a pulp transportation through a conveyor or pipe line in which it is suitable to place at least one sensor of tihe type used according to die invention.
• the measuring units in principle can be placed in all of the places in a paper pulp factory, where the pulp is transported in pipes or another type of transporter, e.g. a screw press, a blow line or die like, i.e. in a process tiiere are several places where a sensor can be placed.
• Fig. IB shows in a similar way the different stages in recycled fibre converting with die illustration by an X of places where an arrangement according to die invention can be placed.
• the figure can be easily interpreted by a skilled person and speaks for itself and does not need to be described more closely.
• the device according to die invention can naturaUy also be placed between die many stages in chemical pulp manufacturing of different types, e.g. at re-burning lime sludge (Calcium carbonate to re-burned (unkilled) lime) at a continuous digester as well as at black Hquor to a kraft recovery boiler, various bleaching steps, and also at a fluidizing bed, even if this is not shown specially in any figure.
• the measuring arrangement -with vibration sensors can even be placed during die manufacturing of soft paper types, such as ceUulose tissue and tissue paper, and hygienic products, such as diapers, inconti-nence protectors, sanitary protectors etc.
• At least one sensor can also be placed in paper machines for different products, such as e.g. test liners, tissue, newspaper, cartoon-board. SC-paper. e.g. where pulp suspensions are transported.
• the invention is not limited to appHcation in die paper industry but can also well be used in the pharmaceutical industry, die food industry etc. The invention has consequently a wide field of application and only some of die manufacturing processes where it is usable have been exemplified above.
• vibration sensors can be placed at several places in a process step.
• At least one sound or vibration sensor 10, 10' e.g. of die accelerometer type, is firmly attached to a pipe line 12 with a flowing suspension 13 which is to be investigated. That which limits tihe possibiHties to measure in different media is die surrounding vibration and sound levels in relation to die vibrations caused by tihe flow inside die pipe Hne. Therefore, the attachment of die vibration sensor 10 is important as weU as its position in relation to noisy units in die sur- roundings. In order to further minimise the influence of noise in tihe surroundings, a sensor or sensors can be shielded, as is indicated by die dashed Hne 10A.
• a stud mounting is suitable when one wishes to measure high frequency vibrations, where die highest vibration frequency for the vibration sensor 10 is needed, i.e. an accelerometer' s performance can be used to the maximum.
• a stud mounting is also suitable for the places where die vibration sensor can be permanently mounted.
• the important tiling is tiiat the sound or vibration sensor 10 is attached as firmly as possible to the pipe 12, and otiier types of mounting are therefore conceivable, e.g. self-adhesive mounting, welding, direct gluing or gluing of a stud with an attachment plate.
• a sensor with mounting should, however, not be placed in die pipe line such tiiat any part projects into the cavity itself, or at least not so far out tiiat it will cause disturbances in tihe feeding of die suspension, as this would give rise to currents and vortexes which in turn can cause depositing of die substances in die pipe itself in connection to such a disturbance.
• Another possible mounting is a tube section which is optimised for a particular kind of sensor and which is mounted in a common kind of flange joint, i.e. in stead of anodier tube section without a sensor.
• die vibration measuring consequently measures the normal flow through the pipe.
• Another possibiHty for vibration measurements is to use laser-techniques in order to provide a non-touching measurement.
• the signal from each vibration sensor 10,10' is amplified and at least low-pass- or band-pass-filtered in a signal conditioning circuit 14 in order to obtain a signal which is easy to analogue/digital convert in an A/D-converter 15.
• the vibration sensor should have a high sensitivity, however adapted to die measuring position.
• the AD-converter should convert with a high resolution, preferably 16 bits or more.
• Data is collected and stored in a data collection circuit 16 for a predetermined periods of time.
• a control device 17 controls the co-operation between tihe units 10, 14, 15 and 16.
• Each digitalized data coUection is stored in an individual storage space until aU the data coUection needed for an evaluation is ready.
• the data coUection cam take place with the use of digital filtering with a filter characteristic stored in a memory and possibly adaptable according to die acmal measuring place.
• the recorded sound or vibration is to be converted to a sound characteristics, which as clearly as possible is indicative of the condition and contents of die suspension flowing drough the pipe. That which causes die vibration is tihe bumping of tihe suspended substances against each other and against the waU of die pipe.
• the characteristics of die substances such as softness, dimensions, stickiness etc. give different sound characteristics. Different fluids in which tihe mixture is provided could also give different sound characteristics to die mixture flow. Therefore, the stored collected data is used in a data manipulating program 18, which, dirough transforming of die data gives a transformed sound characteristics and/or a value or several values which can be used for regulating, producing a clear indication of die contents and/or deviation from a desired contents.
• a suitable data manipulation is, for example, to form a spectral characteristics and diereby, for example, to use FFT (Fast Fourier Transform) in order to obtain a signal characteristic of die frequency in relation to amplitude, or to use AMT (Angle Measure Technique) in order to obtain an average angle, which depends on scaling factors which also give a scaled average difference, or WT (Wavelet Transform) in order to break down die sampled signal in levels of graded signal significance with the help of a fa ⁇ niy of wave functions.
• FFT Fast Fourier Transform
• AMT Average Measure Technique
• WT Widelet Transform
• tiiat tihe recorded sound of vibration shall be divided effectively into at least one characteristic, for example according to frequency, angular or average difference, levels of significance or the like, which for the mixture one is measuring gives a clear differentiabiHty as possible with respect to tihe same transform on other sound or vibration recordings so tiiat die different characteristics of die content, which die sound or vibration recording takes place on, wiU be able to be read from die characteristics.
• Fig. 3 A shows an example of spectra of signal characteristics obtained after FFT transformation.
• Fig. 3B shows median- and average values ⁇ of the same spectra . It should be observed that one or some of die spectra characteristics in Fig. 3 A, such as Al, A2 and A3, can have values which He completely outside of die otiier characteristics. Such characteristics can be discriminated away before combination of spectra characteristics.
• the transformations are performed on each stored data collection, where after median values B 1 and average values B2 can be formed from tihese, so that two signal characteristics are obtained, as combinations of a relatively large number of measuring sequences.
• characteristics of the type Al, A2, A3 are discriminated away completely automaticaUy.
• the median value- producing signal characteristic can, however, if so desired, be smoothed out dirough performing a low pass filtering of the signal characteristic itself. This can be of interest in such circumstances where the flow speed can vary and tihe peaks therefore shift in tihe characteristics, e.g. in pipe lines with suspensions in steam.
• the signal characteristics can tiien in turn be manipulated in a mathematical method known to die skiUed man, such as for example multivariate statistical analysis, e.g. PLS, PCA (Principal Component Analysis), ICA (Independent Component Analysis) or multiple regression or neural networks or die like, in order to produce at least one control value which can be used for regulating different parts of the process in order to obtain a predetermined desirable result.
• a suitable such manipulation which in most cases gives a clear result, is data-processing witii multivariate statistical methods. It should, however, be observed tiiat different types of mathematical models can give optimal results for measuring at different process steps, whereafter before each permanent installation the different methods for data-processing can be tried in parallel in order to obtain die best possible result for the position in question.
• - weighting which is used when die influence of certain variables in the graded signal must be reduced, for example if certain parts in the signal characteristic contain noise or special influences from the surroimdings, - centering in order to centre variables so that if a new co-ordinate system is produced tiien tihey wiU have their centres at the origin,
• MultipHcative Scatter Correction can be used in order to minimise the influence of varying flow rate on tihe signal characteristics before the modelling.
• - NormaHsing of the signal characteristic i.e. addition of die ampHtudes of for example all or chosen frequencies and tiien to divide die ampHtude of each frequency with the sum of the addition.
• ti at wavelets also could be used as pre- treatment method.
• OSC Orthogonal Signal Correction
• tiiat unambiguous control signals can be produced (or, in case of fuzzy logic, also ambiguous signals if several control signals are used simultaneously in a fuzzy control), which after possible transforming can be used for preferably automatic control or adjustment of controUable units in order to obtain a pulp, which the whole time has as even and similar characteristics as possible, and also a possibiHty to obt.ain values, which are usable in order to quickly and reHably raise die alarm.
• die control unit 17 shaU output at least one value suitable for servo-control of a unit 171 in die process, such as increasing/reducing tihe water supply, changing some adjustment screw, increasing/reducing some chemical, changing the distance between refiner discs in a refiner or die like. It shall alternatively or as a complement control at least one alarm unit 172, if the obtained signal characteristic or die obtained signal value is outside an acceptance range, or if a quaHty investigation station detects a tendency which could lead to worse quality if no extra action is taken. Therefore a vibration memory 19A is connected to die control device 17.
• a control memory 19B connected to die control device 17 comprises suitable regulating action or actions for suitable process improving means.
• the control device 17 compares the results from the data manipulating program 18, compares these with those which are stored in die table 19B and performs the regulating action which is tihe consequence of tihe comparison. It is possible, for example, to have different desires for the desired vibration characteristics or vibration values for different sorts of manufacturing object, e.g. paper pulp, which sh.aU be manufactured with the same plant.
• the table 19A gives information of the different desired values (set points) which should be set for a possible servo-control. Thereafter, control takes place towards die predicted value until ti ⁇ s is achieved, and then servo-control occurs in order to keep die obtained actual value so near the set point as possible in the case in question.
• the circuit 18 can begin its grading of each stored signal characteristic directly after its storage and store each graded signal characteristic in a memory for these. It is also possible that die circuit 18 first investigates each coUected signal characteristic stored in d e data coUection unit 16 to check whether it differs so much from the others that it should be sorted out. It is, however, also possible to perform the sorting out directly, namely when a measuring occurs continuously in tihe same place where the measuring differences are relatively smaU. A large measurement difference in ti ⁇ s case is noted directly and can be discriminated away. If several large measuring deviations should occur after each other, then the circuit 18 can raise die alarm after a predetermined number of deviations as tiiis indicates tiiat a fault has occurred.
• the circuit 18 performs grading and forms median values and average values in consecutive order, which can take place without individual storage of each graded signal characteristic but preferably occurs after intermediate storage of die graded results. It is tihereby obvious tiiat deviation measuring can take place either before or after grading. Thereafter foUows further manipulation and comparison against stored values corresponding to suitable control values for the object which is to be controUed, or for the alarm to be raised.
• all the units 14-18 are implemented in a computer.
• die data coUection, manipulation and control take place in separate computers.
• the latter can be specially suitable during die construction of a correspondence table between die obtained signal values and die sampling results in order to provide suitable guidance values to such units which are to be controUed with the guidance of the obtained signal values. Hi such a construction one varies the characteristics of the suspension.
• a control of tihe object, which then shaU be servo-controUed, takes place, at least to the extent tiiat one can see in which direction the control is to be performed. If, for example, refiner discs should be controUed towards or from each other or die like.
• Fig. 4 shows the refiner part of a process flow. Only the important parts for describing die invention are shown, and tiierefore return lines and supply lines for water and lines with pressure release valves etc. are not shown.
• Pre-treated wood chips 20 are fed to a pressurising unit and screw device 21, and from mere in a unit 22 to a feed screw 23, where tiiey are then mixed witii water and fed into a refiner 24.
• Hi the refiner the mixture is ground between refiner discs 25 and 26.
• Hi Fig. 4 the refiner (of the double disc type) is shown having a motor 27 and 28 for each refiner disc, but it is also possible to only rotate one of die refiner discs (single disc type) and to let the other refiner disc be fixed.
• die ground pulp fibres After refining, die ground pulp fibres, greatly warmed up during the grinding, in highly heated water mixture at high pressure are fed to a pipe line 29. Then the high pressure is reduced, and some of die heated water is evaporated into steam.
• the pipe Hne 29 leads to a cyclone 30 for separating the steam from the fibre mixture. From the bottom of the cyclone the fibres are conveyed via a screen feeder to a storage tank 31. The pulp is now aUowed to rest in the storage tank 31, where it can stay for approximately twenty minutes and tiien be fed further dirough a pipe Hne 32 to tihe next stage in the process. It is important to keep a predetermined proportion of short and long fibres in the mixture which is fed dirough die pipe 32.
• the embodiment shown tiierefore dlustrates that a sensor equipment 34 according to die invention can be placed in die pipe Hne 29 and its results can with good correspondence be compared to manual investigations of the characteristics in a pipe Hne 32 in a completely different place in the manufacturing chain.
• the sensor equipment 34 has in this embodiment preferably a position 34 on the pipe Hne 29 where the vibration sound from e refiner 24 is sufficiently low so that the influence of this sound wiU be negHgible or filtered away.
• Figs. 3A and 3B The spectral characteristics in Figs. 3A and 3B have been obtained during an experiment with this embodiment.
• the remaining refiner sounds are first of aU in the low-frequent frequency range, and tiierefore this frequency range is discriminated away, as indicated witii the shaded region X in Fig. 3B.
• tiiat the curves in Fig. 3 A and 3B have been recorded with die use of a low-pass filter with a high cut off frequency, about 25 kHz, which Hes only a small amount under the upper limit frequency of tihe vibration sensor itself, where sound recording can take place relatively undistorted.
• a band-pass filter can instead be used which only lets dirough frequencies suitable for producing the required sound characteristics.
• a filter for filtering die obtained spectral characteristics, which filter discriminate away other parts of the signal characteristic in order to accentuate die parts of it which are sensitive to just those characteristics which can be taken care of by control.
• some of die frequency regions around signal peaks in the middle and in die vicinity of die upper part of the frequency interval can be accentuated before the transformation.
• a vibration sensor 35 can be placed at a place on die refiner with a sound characteristics from the refiner as feasible to that which is superimposed on die sound characteristics obtained from the sensor at place 34.
• the sound characteristics obtained from the vibration sensor 35 can, after suitable delay and ampHtude adaptation, for example be superimposed in counter phase on tihe signal from the vibration sensor 34. It is also possible to perform a Balar data manipulation such as that shown in Fig. 2 and take away die result from the resulting sound contribution from the sound contribution from the ordinary sensor 34.
• the evaluation circuit 36 which is connected to die sensor 29 and possibly to die sensor 35, performs the above mentioned data manipulations. At least one value is obtained where each value is fitted witiiin a value range to the desired fibre contents which is to be found at die eartier measuring point 33. This unambiguousness is obtained dirough eariier comparative measurements with the sensor arrangement 34,36 and spot checks at 33 witii reference taken to the time delay between die positions 34 and 33, wherein die measured results are stored in a table in a memory in die evaluation unit 36.
• the investigated values have tihereby been lying within a suitable interval around die desired value or die desired values.
• the control for the refiner 24 for driving the refiner discs towards or from each otiier is adapted to die values in die interval to, in a sort of servo-control, bring die actual value from the measurement to the set point value which corresponds to tihe desired sampled value.
• no large distance changes of the refiner discs are made after each measurement but these changes take place stepwise in die direction indicated by die deviation and tihe direction of deviation of tihe actual value from he set point value.
• a screen 38 such as e.g. the CENTRI SORTER-screen which works under positive pressure, placed in order to separate different types of deviating material parts, such as over-large fibre bundles and/or fragments or die like, out of the fibre suspension 39 which is introduced through the Hne 39.
• the rotation speed of die screen is a parameter which can be controUed by means of tihe processed measuring signals. Fluid is introduced dirough die Hne 40. The pulp accepted during sieving in die screen 38 is fed dirough an acceptance pipe 41 for further treatment.
• the separated material parts are fed dirough a reject pipe 42 to a holding tank 43 in order for thereafter be fed away or re-fed for renewed treatment in order to be subsequentiy returned to die screen 38. It is also possible to control circulated stream of rejected or accepted material by means of processed signals from vibration sensors 44 and 45 in me lines 41 and 42, respectively.
• each Hne 41 and 42 is provided with their own vibration sensor 44 respectively 45.
• the output signals treated by tihe sensors are caHbrated against laboratory- obtained characteristics of die pulp in die two pipe lines.
• the caHbrated values can tiien be compared witii each other in different ways, such as quotient-forming, subtraction or in some other more compHcated way, and if die comparison between dieir values and/or die value from die one or the otiier sensor Hes within a value region which means danger, an alarm is given to an operator who, depending on die type of alarm or alarms, can conclude where in die system before the screen an error has occurred which needs to be righted.
• FIG. 6 Another embodiment for system alarming during storage of pulp from the bleachery, shown in Fig. 6, also with the parts which are not important for the invention not shown, where the sensor arrangement according to die invention is suitable to use, is in connection with a medium consistency pump50.
• the pulp is fed with a pulp concentration of 7 to 10% to two presses 51 and 52, which increases die pulp with concentration to approximately 30% to a feed screw 53, which with the addition of water for dilution of the pulp, feeds this to a medium consistency pump54.
• the pump 54 feeds die pulp, which at its outlet has a concentration of approximately 10%, via a pipe line 55 before the pulp is fed to a holding tank 56, from which it later is fed further for further treatment.
• a vibration sensor 57 is placed on die pipe Hne 55 for monitoring me quaHty of the final product.
• die trend is investigated, i.e. die deviation and die direction of deviation from a desired final product value, and is tiien shown on a printer, a screen or the like in relation to the desired quaHty value.
• a vibration sensor is placed in such a position or on such a conveyor that the vibrations which are to be sensed are so small tiiat they are difficult to sense by die sensor.
• the situation shown in Fig. 6 can, for example. be one of those.
• a sound- or vibration-emitting unit 58 on or by the convevor 55.
• the addition of energy in die form of vibrations or sound can make it possible to evaluate die tihen measured vibrations in die same way as without the addition of vibrations.
• the unit 58 can, for example, emit so-caUed white noise with the sound evenly divided over the frequency region which is sensed by die sensor 57.
• the unit 58 can emit sound over an extremely narrow frequency region which tiien can be discriminated away from die obtained vibration characteristics. Even other types of sound or vibrations from die unit are conceivable which, for example, can be speciaUy adaptable for discriminating away during use of AMT or WT via data manipulation.
• the measuring equipment according to die invention can be mounted in a pipe Hne before as weU as after a continuous digester 60 and possibly also before an impregnation vessel 61. This is iUustrated in Fig. 7.
• a production measurement equipment which measures the fibre flow which is fed into die impregnation vessel 61 or the digester 60 may be used to control a dosing feeding out screw or otiier kind of dosing feeding out device which provides die feeding by a controUed pressure change dirough a valve.
• the measuring sensor can en be positioned in a pipe Hne before 63 or after 64 die feeding device 62, and before 65 or 66 a feeding out device 67 positioned between die impregnation vessel 61 and die digester 60.
• Another important factor in continuous digesting processs is to keep die degree of released substance at least in e initial and bulk phase constant.
• This can be obtained by providing tihe measuring head of die inventive device at the circulations and control the additive of white liquor, an also control die temperature in die initial an bulk phase and/or die additive of polysulfides or some other deHgnifying additive. Therefore, the measuring equipment according to die invention, such as the equipments 68 to 74 can be provided at die different inputs and outputs of the continuous digester for the different parts of the digester between die extraction screens 75 to 77, as weU as in die blow Hne 78 after the wash zone 79 to die blow tank 80, in order to adapt the different processing facitities for mass flow indication and different otiier relevant control parameters.
• Appendix 1 shows for the medium consistency pump two plots for the CSF
• Appendix 2 shows for the refiner very good correspondence between a large number of different characteristics measured with tihe invention and at sample-taking. For the screen Accept and for the screen Reject, extremely good correspondence for the characteristics which are meaningful to measure with this type of placements for vibration measuring according to the invention.
• Eariier at least one weighting table has been created based on reference analyses and/or calculations of determined features, for example dweU times. This table is used as said recording to which comparing is done.
• the weighting table which could take the form of a composed weighting net could be used such tiiat the signal characteristics is weighted using die weighting table, and the value for a desired feature is calculated.

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• 1997
  • 1997-09-24 SE SE9703450A patent/SE9703450L/ not_active Application Discontinuation
• 1998
  • 1998-09-23 WO PCT/SE1998/001710 patent/WO1999015890A2/en not_active Application Discontinuation
  • 1998-09-23 EP EP98945727A patent/EP1018001A2/de not_active Withdrawn
  • 1998-09-23 AU AU92904/98A patent/AU9290498A/en not_active Abandoned

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