WO1999015890A2

WO1999015890A2 - Method and device for process monitoring

Info

Publication number: WO1999015890A2
Application number: PCT/SE1998/001710
Authority: WO
Inventors: K. Anders BJÖRK
Original assignee: Sca Graphic Sundsvall Ab
Priority date: 1997-09-24
Filing date: 1998-09-23
Publication date: 1999-04-01
Also published as: WO1999015890A3; AU9290498A; EP1018001A2; SE9703450L; SE9703450D0

Abstract

The invention relates to a method and a device, in a manufacturing process, for example in the paper pulp, paper, pharmaceutical, food, building material industries, to indicate the characteristics and contents in a suspension in a fluid which flows through a conveying device, e.g. a conveyor line. The mechanical vibrations are recorded directly from the conveying device (12) at least at one place with minimal external influence for a precise time. The recorded vibrations from each place are graded by a data manipulating program (18) according to predetermined characteristics, e.g. frequency, angular and average differences, levels of significance or the like, and a vibration characteristics and/or at least one value related to a vibration characteristics is generated. Stored vibration characteristics and/or values in a memory (19B) relating to earlier vibration recordings with suspensions flowing through the conveyor with analysed contents are compared at each recording with acceptance of the vibration characteristics and/or the value which lies closest to that which is the case for the recorded vibrations. The recorded vibrations can then be used: for controlling the process in a suitable way; for raising alarm when there is a fault; for showing changed tendencies or the like.

Description

Method and device for process monitoring

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.

Background to the invention

A skilled paper pulp worker can through hstening to the sounds in his factory get a feeling for when the process is "feeling well or not" . Specific electronic sound measuring in order to objectively be able to determine me status and pulp characteristics from the sound characteristics has, however, not been made.

Previously, 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.

Description of related technology

Furthermore, there are a number of systems for - with the help of sound indications measuring the flow speed of flowing mixtures or suspensions in gases or liquids. In these cases it is usual to use a sound emission source and a sound recording unit which detects reflections and echoes. Such a system is described in US 5 226328, which teaches a flow speed measuring system which measures the average speed directly through using pulsed Doppler technology. A similar technology is also described in US 5 333 508. A system for investigating the effect of different adjustments in a refiner on the quality of the pulp is described in the articles "On-line modelling of refiner performance" by B.C.Strand and A.Mokvist, Pulp & Paper Canada 90:12, pp T499 to T504, 1989, "Modelling and Optimization of Full Scale-Chip Refining" by

B.C.Strand and N.Hartler, International Mechanical Pulping Conference, Stockholm 1985, and "Control and Optimization of Conical Disc Refiners" by B.C.Strand and A.Mokvist, Mech. Pulping Conf., Vancouver B.C. 1987. In this, 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 way of deterr ining the flow situation in a transport system is described in WO 89/059974. A special area of use for this measuring device is the monitoring of oil wells. In this, turbulence is produced in die flow of a transportation uirough a conveyor. One or more vibration sensors are placed by the turbulence-producing device. The signals from these are analysed using known mathematical mediods in order to give information about the actual flow situation. A disadvantage of this is that the manufactured turbulence influences the structure of the contents of that which is transported. In cases of investigation of the relationship between oil and water, the turbulence breaks apart relatively large oil bubbles to smaller. A turbulence of this kind could break apart the particles in the conveyor, .and a break apart can possibly be accepted in the oil industry where it is bubbles which are broke apart but not in die industry for paper pulp manufacturing or in other industries where solid particles of a medium .are fed through a conveyor and where settling of particles in die conveyor should be avoided. US 4,060,716 describes a method for monitoring dynamic signals, such as from vibration sensors. This method was originally developed for solving die problem to indicate if there are loose parts in a nuclear power plant or die like (see column 1, lines 11 to 42). This means mat the vibrations to be indicated are generated at selected points in a plant for continuously monitoring the operating conditions of system components (in sequence)(see me preamble of claim 1), and hence not for indicating die content in a streaming mixture in a conveyor.

Obiects of the invention

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.

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 anodier object of die invention is to determine die quantity and/or different pro- portions of solid particles in flowing water or gas. Yet anodier object of die invention is to provide a method and a device which through the analysis of an electrical signal gives information about die characteristics of the different particles in a flowing mixture or suspension being investigated, for example different particle dimensions and -distributions, if the particles are hard or soft, smooth or sticky, different pro-portions of particles with different characteristics, die particle surface chemistry, the particle flexibility, ash contents, die particle specific surface, particle weighζ particle wall thickness, characteristics from standardised fibre network testing procedures, etc.

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.

The invention

The above mentioned objects are achieved by a method which has the characteristics stated in claim 1. Further features and developments and a device for performing the method .are evident from die otiier cl.aims.

Consequently, 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

- generating a vibration characteristics and/or

- generating at least one value related to a vibration characteristics; - comparing with stored vibration characteristics and/or values originating from earlier vibration recordings with mixtures with analysed content flowing dirough the conveyor at each recording and/or calculating the mass or volume flow at each recording witii acceptance of die vibration characteristics and/or die value which is closest to that which is die case for the recorded vibrations and/or indicating if the actually recorded vibration characteristic and/or value lies outside a determined allowed calibration region. The mixture is most often a liquid suspension or streaming particles in gas. However, me suspension could be provided in different liquids and tiien the detected features could give another signal characteristics adapted to tihe combined mixture of liquid and suspension.

Preferably, 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. By 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. Deteπnination 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. For each vibration characteristic with sorted contents 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.

Consequently, for each measuring point 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. However, 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. 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.

Advantages of die invention

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, e.g. a pipe line, 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). 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. For each step, 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.

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. Previously it has sometimes not been possible to make measurements in a position nearby the locaHty for a control action. Therefore, measurements have been made on die features to be controUed in a process step later on in the process. The value so derived has been used as a base for the control action.

In die case when die content in a conveyor in a step further along in the process flow is the important feature to be monitored, and die control of it must be made at an essentially eariier step in die process, 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.

Even if the invention is described especiaUy in connection with use in die paper and paper pulp industry, it has a wide field of appHcation and can, for example, also be used in the pharmacεuptical, food and building material industries amongst others.

Short description of die figures

The invention is described in more detail below with reference to die accompanying drawings which show examples of die invention, where:

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.

Detailed description of tihe embodiments

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. It should be noticed 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.

In Fig. 1A, 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. It should be noticed tiiat 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.

Furthermore, 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.

In addition to tihose mentioned above and shown in Figs. 1A and IB, vibration sensors can be placed at several places in a process step.

As is shown in Fig. 2, 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.

If possible, a hole can be drilled in tihe pipe 12 and a stud 11 ti readed in and die vibration sensor 10 attached to die stud 11. 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.

However, 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. Hi order to achieve a good idea of die state of tihe suspension, 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 faπniy of wave functions.

It can also be necessary to pre-treat the time discrete signals before they are processed with any of die above mentioned transforms in such ways which are well known to die man skiUed in the art and which therefore do not need to be described more closely. The conditions which are to be placed upon die transforms used are 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. For example, different fibre lengths in a fibre proportion give rise to different frequencies or frequency regions seen in relationship to the flow speed tihrough the pipe. Each type of so graded vibration characteristics can be filtered with some suitable filter characteristic (not shown), which for example is stored by die control unit 17.

By usmg several of these different types of in themselves known transformations and combining them, specific combinations of signal characteristics can be produced, which iUustrate die content of suspended material, different proportions of e.g. long and short fibres, contents of ash, clay or other small particles, proportions of hard and/or soft particles, proportions of sticky or smooth particles etc.

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. During median value forming, characteristics of the type Al, A2, A3 are discriminated away completely automaticaUy. In the composite characteristics B 1 of die median values in Fig. 3 A, a number of relatively marked peaks can be seen and tiiese can in a number of circumstances be specially interesting for determining die contents of tihe suspension. 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.

Further pre-treatments of data before the data-processing, ?.g. of the multivariate statistical type, can amongst others be:

- 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,

- scaling in order to obtain variables in tihe used mathematical model which are similar irrespective of their dynamic range,

- auto-scaling, which is a combination of centering and scaling, - Hnearizating in order to obtain more stable calculations of die principal components when die variable values have extremely large variations, i.e. in order to obtain smaU values which are worth as much as large values in the mathematical model used,

- MSC (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. Note ti at wavelets also could be used as pre- treatment method. - OSC (Orthogonal Signal Correction) can be appHed for removing variation in the vibration or sound characteristics not related to die characteristics tihat is subject to tihe model. It can also be apptied for making model transfer between sensors of the same kind which can bee regarded as a way to transfer of caHbration done on one particular sensor to another similar sensor without doing an entire new caHbration, i.e. only to a new caHbration to a certain extent. It should be observed tiiat the above stated mathematical methods are given as examples and tiiat also other types of known mathematical manipulation can be used. What is important for the manipulation is that unambiguous vibration characteristics and/or values, or combinations of them, can.be obtained for the type of suspended material which is in die conveyor or pipe Hne concerning its contents of different types of material parts and/or emulsions. It is also important 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.

It should also be observed tiiat one normaUy knows die contents in a pipe Hne with certain variations around desired proportions. NormaUy one desires to control these proportions to desired normal values, and die invention offers a possibiHty to obtain values which make it possible to control on-line treatment units upstream of die pipe Hne on which die measuring equipment is placed.

AU the above described data-processing is performed in a data manipulating circuit 18 controUed by the control unit 17. During process regulating, 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. In die memory is stored a table for different pulp compositions which is related to each of tiheir own individual vibration characteristics and/or vibration values. 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 tiϋs 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 tiϋs 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.

Thereafter, 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. Suitably, all the units 14-18 are implemented in a computer.

Instead it is also be possible to let 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. At die same time 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.

Examples of media and situations where a measuring equipment according to die invention is suitable due to tiiat a high acoustic emission is obtained without any extra actions on the flow:

- Two-phase flow with gases/Hquids in combination with soHd particles or compo- nents in a soHd phase.

- Emulsions of substances with different densities and/or viscosities.

- High but almost even flow speeds for flows with soHd particles of different types and/or with emulsions.

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.

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. Previously, random sampling (spot checks) have dierefore been made at a checking station 33. FoUow- ing deviations from desired proportions, either the screw unit 21 or the refiner 24 or the water supply to the chips has had to be changed. Hi tiiat case, a disadvantage has been tihe long time which passes from the passage of the pulp from the refiner to the sample measuring position. On-line measuring in the pipe Hne 29 and regulating have not been possible to perform but the lag in the control has been unfavourable with swings in the result as a consequence.

Previously, it has been possible to manuaUy take samples of the pulp, i.e. when it passes dirough die pipe Hne 29, but here die fibre pulp is so hot and at such a high pressure diat this has been difficult for practical reasons. Eariier, however, comparative investigations as to pulp characteristics in die pipe Hne 29 in relation to the pulp characteristics in the pipe Hne 32 have been made. A table has been set up for these. Since it is apparent that it is better to indicate the signal(s) to control a unit, such as the refiner, as near to the unit as possible, tiien a table can be set up concerning manual investigations directly made on pulp characteristics in die pipe line 32 in relation to measuring results obtained with die automatic vibration measuring on the pipe Hne 29 according to die invention. Thereby the vibration measuring on d e pipe Hne 29 dirough conversion in the table can be made to apply also for comparisons concerning die pulp characteristics in the pipe line 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.

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. It should be observed 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.

It should be observed tiiat during measuring of different types of flowing mixtures, it can be expedient to have 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. For example, during control of the refiner discs of the refiner in order to obtain another proportion of long and short fibres, respectively, 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. In order to further reduce die influence of sound from die refiner 24, a vibration sensor 35 can be placed at a place on die refiner with a sound characteristics from the refiner as simtiar as possible 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 simtiar 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. Preferably, 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.

As shown, even a value calculated in some otiier way but with die same metiiod can give rise to regulating of e.g. die plug screw in die screw unit 21. What hereby has been achieved with die sensor arrangement according to the invention is a method for on-line control which has not existed eariier. It is also to be noted tiiat also mass flow of fibres as weU as steam can be indicated by a sensor provided in the pipe line 29 at approximately the same position as the sensor 34. Hi such a case the signal processing of the signal characteristics from the sensor or sensors is adapted to die particular appHcation. The result of the signal processing can then be used as a control parameter. For example, the input set value, output actual pressure as weU as the rotation rate of the refiner can be controUed by means of these parameters.

In die reject piping case with system alarm shown in Fig. 5, also with the parts which are not important for the invention not shown, is 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.

Thus, each Hne 41 and 42 is provided with their own vibration sensor 44 respectively 45. There are different flows, flow speeds and concentrations in die two lines. 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.

Of course it is also possible to use the results obtained from die two vibration sensors in order to optimise screening so tihat it is possible to separate out in order to obtain a more desired quaHty for the accepted pulp indicated through comparison between the signal results. Different result combinations give reasons to control the reject aUowance from the screen and/or the incoming concentration to the screen and/or die dUution water in die screen.

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. From the bleachery, 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. Here 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.

Hi certain cases it can happen that 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. In order to raise the general vibration or sound level, it can be advantageous to place 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. Alternatively, 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.

It is important to keep a constant fibre flow into and out of (the delignified rest) die continuous digester 60. Therefore, 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.

In the embodiment in Fig. 7 die signal characteristics froπ different sensors can be monitored and processed simultaneously to be combined with each other in order to provide signal valuation results suitable to perform several controls of feeding materials and/or solutions to the digester. The control of these parameters can be made quite complex in tiϋs embodiment.

The results of experiments with the invention where internal vaHdation is compared with cross-validation are appended as appendices. Hi the internal vaHdation a model is butit with ati of the tests. As mentioned eariier in e description, naturaUy certain deviant tests are removed in order to get die model to function. Characteristics are predicted from this model for aU of the tests. With cross vaHdation a model is butit with aU the tests except one. The characteristics of this single test are predicted with the help of this model. The process is repeated until aU the tests have predicted values. Investigations have been made, on one hand, for the medium consistency pump according to Fig. 6 (however, without using an extra vibration or sound source), shown in Appendix 1, and, on die other hand, for the refiner according to Fig. 4 and for die screen Accept and screen Reject according to Fig. 5, shown in appendix 2. The cross- vaHdated model gives actuaUy a more true idea of die result tiian the internaUy vaHdated model.

Appendix 1 shows for the medium consistency pump two plots for the CSF

(Canadian Standard Freeness) measured with the invention in relation to the CSF which has been predicted with sample-taking. One can see in tihese plots good correspondence between die measured values and die sampled values, especially in die internaUy vaHdated model but also in the cross-validated model., and diere especiaUy in the upper region with higher values. Hi the table on top of the page one can see tiiat the correspondence is good for most of the characteristics one is able to measure with the invention.

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.

Sometimes for caHbration purposes it is appropriate to coUect vibrations during predetermined times having a predetermined length. Thereafter spectral or vibration characteristics are created. 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.

Several weighting tables could be created, one for each independent or orthogonal signal component related to a variation of the feature in each signal characteristics, which variation represents an underlying variation of said signal component. An addition to die weighted features could tiien provide a final value(s) which could indicate die process state. APPENDIX

Page 1

MEDIUM CONSISTENCY PUMP

APPENDIX

Page 2

^0 5 50 55 60

MEDIUM CONSISTENCY PUMP CROSS VAUDATED MODELL No. PC 4

0 45 50 55 60 55

MEDIUM CONSISTENCY PUMP INTERNALLY VAUDATED MODELL No. PC 4 RESULTS FROM TRIALS APPENDIX II Page 1

REFINER

SCREEN ACCEPT

APPENDIX Page 2

SCREEN REJECT

Claims

1. Method, in a manufacturing process, e.g. in the paper-, paper pulp-, pha╧Çnaceuptical-, food- and building material industry, to indicate characteristics and contents of a mixture in a fluid which flows through, a conveyor, e.g. a pipe line, characterized by

Γûá recording for a precise time the vibrations directly from the conveyor in at least one position with no or minimal mechanical influence on the mixture;

Γûá grading of the recorded vibrations for each position according to predete╧Çriined characteristics, e.g. frequency, angular and average difference, levels of significance or the like and

Γûá generating vibration characteristics and/or

Γûá generating at least one value relating to vibration characteristics;

Γûá comp-aring with stored vibration characterisic(s) and/or value(s) referring to earlier vibration recordings with mixtures with analysed contents flowing through the conveyor at each recording with the acceptance of the vibration characteristic and/or the value which lies nearest to that which is the case for the recorded vibrations and/or indicating if the actu-ally recorded vibration ch.aracteristic and/or value lies outside a determined allowed region.

2. Method according to Claim 1, characterized by

Γûá recording of vibrations and grading them during the precise time during a number of intervals after each other; and

Γûá combining the so obtained results with discrimination of recordings which he outside the predetermined deviation from me other results.

3. Method according to claim 1 or 2, characterized in tiiat the content to be analysed can be at least one of the following categories: different materials, fluids, liquid or gaseous, mixtures, suspensions, percentage of material, amounts, quantities, qualities, mass flow, volume of the flow totally or for at least one component- compound or substance.

4. Method according to any or the preceding Claims, characterized by sampling of the contents of mixed materials with a predetermined time relationship between generation of a vibration characteristics and/or values with determination of the contents and storage in a table for contents against the vibration characteristics and/or values in order to produce comparison data.

5. Method according to Claim 4, characterized in that the vibration measuring position and the sampling position He at a distance from each other so that there is a time delay between the passage of material through the two positions, whereby said time relationship corresponds to said time delay.

6. Method according to any of the previous claims, characterized in that the vibration characteristics and/or value is used to control the process.

7. Method according to any of the previous claims, characterized in that the vibration recording place Hes in a conveyor near a process changing means, which is controllable with the guidance of analysis results of the obtained vibration characteristics, but in such a position that vibrations originating from the process changing means are damped in it.

8. Method according to Claim 7, characterized in that for each vibration characteristics with graded contents a value is calculated with known mathematical methods, whereby for each calculated value a control value is allocated such that a control of servo type is made for the process changing means in order to counteract changes in the calculated value from a desired value.

9. Method according to any of the previous claims, characterized in that several of the different types of grading are performed and the results of them are combined in order to obtain the optimal measuring result depending on the actual mixture characteristics which are to be measured in an intended measuring position.

10. Method according to any of the previous claims, characterized in that for each actual measuring place, where the vibration measuring is to be performed, an investigation at least concerning the grading characteristics is performed in order to determine the one or ones which are most suitable for that measuring position.

11. Method according to any of the preceding claims, characterized by extra addition of vibration to the conveyor during the measuring of vibrations.

12. Method according to any of the preceding claims, characterized by creating a weighting table based on reference analyses and/or calculations of determined features, for example dwell times, and using this table as said recording to which comparing are to be done.

13. Method according to claim 12, characterized in that the weighting table takes the form of a composed weighting net.

14. Method according to claim 12 or 13, characterized in that the signal characteristics is weighted using die weighting table, and the value for a desired feature is calculated.

15. Method according to any of die claims 12 to 14, characterized in that several weighting tables are created, one for each independent or orthogonal signal component related to a variation of said feature in each signal characteristics, said variation represents an underlying variation of said signal component.

16. Device, in a manufacturing procedure, for example manufacturing in the paper- or paper pulp-, pha╧Çnaceuprical-, food-, building material-industries, to indicate the characteristics and/or contents and/or proportions of different substances in a suspension in a fluid, which flows through a conveyor, e.g. a conveyor line, where at least one sound- or vibration sensor means is positioned to pick up the vibrations from a conveyor, e.g. a pipe line, and die sensor meΓêæms signals are treated in a data manipulation unit (18) with mathematical methods known in themselves, in order to produce a typical vibration characteristics or a vibration value for the characteristics and/or contents and/or proportions, characterized by Γûá a control unit (17) connected to the data manipulation unit (18);

Γûá at least one memory means (19A,19B) connected to the control unit (17) for suitable regulating of at least one action unit (24,21) based on the obtained vibration characteristics or vibration values;

Γûá whereby the control unit (17) having obtained die vibration characteristics or a vibration value compares it against at least one vibration characteristics and/or value stored in the memory means (19A,19B) and gives suitable control towards tihe suitable action unit or units (24,21) and/or indication if the actually recorded vibration characteristics and/or value Hes outside a determined allowed region.

17. Device according to Claim 16, characterized in that the data manipulation unit (18) is arranged to record sensor signals for a precise time and to grade and record die vibrations according to predetermined characteristics, e.g. frequency, angular and average differences, levels of significance or the like, and tiierefrom generate the vibration characteristics or die vibration value.

18. Device according to Claim 17, characterized in that the content to be analysed can be at least one of die following categories: different materials, fluids, Hquid or gaseous, mixtures, suspensions, percentage of material, amounts, quantities, qualities, mass flow, volume of the flow totally or for at least one component. compound or substance.

19. Device according to any of Claims 16 to 18, characterized in tiiat said memory means (19A,19B) connected to the control unit (17) stores at least one table for different mass compositions for different vibration characteristics and/or vibration values.

20. Device according to claim 19, characterized in that the table is a weighting table based on reference analyses and/or calculations of determined features, for example dwell times, said control unit (17) compares the at least one vibration characteristics and/or value to this table.

21. Device according to claim 20, characterized in that the weighting table takes tihe form of a composed weighting net.

22. Device according to claim 20 or 21, characterized in that the control unit (17) weights the obtained signal characteristics against tiie weighting table, and calculates the value for a desired feature.

23. Device according to any of die claims 20 to 12, characterized in that several weighting tables are stored in the memory means (19A,19B), one for each independent or orthogonal signal component related to a variation of said feature in each signal characteristics, said variation represents an underlying variation of said signal component.

24. Device according to any of Claims 16-23, characterized in that memory means (19.A_.19B) has/have stored acceptance limits, and that the control unit (17) controls an alarm unit when it receives values outside these limits.

25. Device according to any of Claims 16-24, characterized in that the memory means (19A,19B) has stored desired vibrations characteristics or vibration values and at least regulating directions for the action unit or action units during deviations from the desired vibration characteristics or vibration values, depending on the type of deviation of the obtained vibration characteristics or vibration values from the desired ones.

26. Device according to any of Claims 16-24, characterized in that the control unit (17) is arranged, at short intervals, to perform vibration measuring with evaluation of them and to perform control of the action unit or action units (24,21) on-line, similar to servo-control.

27. Device according to any of Claims 18-26, characterized in that the memory means (19A, 19B) also contain(s) suitable control values in the table.

28. Device according to any of Claims 16-27, characterized by a vibration or sound emitting unit (58) placed on or at the conveyor (55).

29. Device according to any of Claims 16-27, characterized by a laser arrangement to indicate the vibrations of the conveyor.