WO2005001395A1

WO2005001395A1 - Method for the operation of a process measuring apparatus

Info

Publication number: WO2005001395A1
Application number: PCT/EP2004/006510
Authority: WO
Inventors: Thomas Budmiger; Saso Jezernik
Original assignee: Endress + Hauser Flowtec Ag
Priority date: 2003-06-30
Filing date: 2004-06-17
Publication date: 2005-01-06
Also published as: JP2007506938A; RU2335740C2; DE10329540A1; CN1816734A; EP1639324A1; RU2006102492A

Abstract

Disclosed is a process measuring apparatus comprising a flow sensor that is provided with a measurement tube, an excitation arrangement, a sensor array for generating a measuring signal, and an operation and evaluation circuit. Also disclosed is a method for compensating interference potentials caused particularly by particles of foreign substances or small air bubbles in the liquid that is to be measured. According to said method, an anomaly in the progress of the measuring signal caused at least in part by an electrical, especially pulsed, interference voltage, is detected by identifying a data cluster within the stored first set of data, which digitally represents the anomaly. Additionally, the data that is part of said data cluster is removed from the stored first set of data in order to create an interference-free set of data.

Description

Process for operating a process measuring device

The invention relates to a method for operating a process measuring device with which at least one physical measured variable, in particular a flow rate, a viscosity or the like, of a medium held in a process container or flowing in a process line is to be measured. In particular, the invention relates to a method for operating a magnetic-inductive flow meter, with which the volume flow of an electrically conductive and flowing liquid is to be measured.

In industrial process measurement technology, in particular also in connection with the automation of chemical or process engineering processes, for the generation of process variables analog or digitally representing measured value signals on site, that is to say process measuring devices installed in close proximity to the process, so-called field measuring devices are used. Examples of such process measuring devices which are known per se to the person skilled in the art are described in EP-A 984 248,

EP-A 1 158 289, US-A 38 78 725, US-A 43 08 754, US-A 44 68 971, US-A 45 24 610, US-A 45 74 328, US-A 45 94 584, US -A 46 17 607, US-A 47 16 770, US-A 47 68 384, US-A 48 50 213, US-A 50 52 230, US-A 51 31 279, US-A 52 31 884, US- A 53 59 881, US-A 53 63 341, US-A 5469 748, US-A 56 04685, US-A 56 87 100, US-A 57 96 011, US-A 60 06 609,

US-B 62 36 322, US-B 63 52 000, US-B 63 97 683, WO-A 88 02 476, WO-A 88 02 853, WO-A 95 16 897, WO-A 00 36 379 , WO-A 00 14485, WO-A 01 02816 or WO-A 02 086 426.

The process variables to be recorded in each case can be, for example, a volume flow, a mass flow, a density, a viscosity, a fill level or a limit level, a pressure or a temperature or the like, a liquid, powder, vapor or gaseous process Act medium that is carried or held in a corresponding process container, such as a pipeline or a tank.

To record the respective process variables, the process measuring device has a corresponding, mostly physical-electrical, measuring sensor, which is inserted into a wall of the container carrying the process medium or in the course of a process line leading the process medium and which is used to generate at least one, in particular electrical, measurement signal that represents the primary detected process variable as precisely as possible. For this purpose, the measuring sensor is also connected to a corresponding measuring device electronics, in particular also a further processing or evaluation of the at least one measuring signal. This usually has an operating circuit driving the measuring sensor and a measuring and evaluation circuit which further processes its measuring signals.

Process measuring devices of the type described are usually also connected to one another and / or to corresponding process control computers via a data transmission system connected to the measuring device electronics, where they send the measured value signals e.g. Send via (4 mA to 20 mA) current loop and / or via digital data bus. The data transmission systems used here, especially serial, fieldbus systems, e.g. PROFIBUS-PA, FOUNDATION FIELDBUS as well as the corresponding transmission protocols. Using the process control computer, the transmitted measured value signals can be further processed and e.g. visualized on monitors and / or in

Control signals for process actuators, e.g. Solenoid valves, electric motors etc., are converted.

To accommodate the measuring device electronics, such process measuring devices further comprise an electronics housing which, e.g. in US-A 63 97 683 or the

WO-A 00 36 379 proposed, arranged away from the process measuring device and can only be connected to it via a flexible line, or as also shown, for example, in EP-A 903 651 or EP-A 1 008 836, is arranged directly on the sensor or on a sensor housing which houses the sensor separately. The electronic housing, as shown for example in EP-A 984248, US-A 45 94 584, US-A 47 16 770 or US-A 63 52 000, then often also serves to serve some mechanical components of the sensor to record, such as membrane, rod, sleeve or tube-shaped deformation or vibration bodies that deform operationally under mechanical influence, cf. also US-B 63 52 000 mentioned at the beginning.

Flow meters with a magnetic-inductive flow sensor are often used to measure electrically conductive fluids. In the following, if necessary, for the sake of simplicity, we will only speak of flow sensors or flow meters. As is known, the volume flow of an electrically conductive liquid can be measured with magnetic-inductive flow meters and mapped into a corresponding measured value that flows in a pipeline; by definition, the volume of the liquid flowing through a pipe cross-section per unit of time is measured. The structure and mode of operation of magnetic-inductive flowmeters are known per se to a person skilled in the art and are described, for example, in DE-A 43 26 991, EP-A1 275 940, EP-A 12 73 892, EP-A 1 273891, EP -A 814324, EP-A 770 855, EP-A 521 169, US-A 60 31 740, US-A 5487310, US-A 52 10 496, US-A 44 10 926, US -A 2002/0117009 or WO-A 01/90702 described in detail and in detail.

Flow transducers of the type described usually each have a non-ferromagnetic measuring tube which is used in the pipeline in a liquid-tight manner, for example by means of flanges or screw connections. The part of the measuring tube that contacts the liquid is generally electrically non-conductive, so that a voltage is not short-circuited which, according to Faraday's law of induction, is caused by a magnetic field passing through the measuring tube Liquid is induced. Metal measuring tubes are therefore usually provided on the inside with an electrically non-conductive layer, for example made of hard rubber, polyfluoroethylene etc., and also generally non-ferromagnetic; in the case of measuring tubes made entirely of a plastic or a ceramic, in particular of aluminum oxide ceramic, the electrically non-conductive layer is not required.

The magnetic field is generated by means of two coil arrangements, each of which, in the most common case, is arranged on the imaginary diameter of the measuring tube from the outside. Each coil arrangement usually consists of a coil without a core or a coil with a soft magnetic core. So that the magnetic field generated by the coils is as homogeneous as possible, in the most common and simplest case they are identical to one another and electrically connected in series in the same direction, so that the same excitation current can flow through them during operation. However, it has also already been described to have an exciting current flow through the coils alternately in the same or opposite directions, in order to be able to determine, for example, the viscosity of liquids and / or a degree of turbulence in the flow, cf. see also EP-A1 275 940, EP-A 770 855 or DE-A 4326 991. The above-mentioned excitation current is generated by a

Operating electronics generated; it is set to a constant current value of e.g. 85 mA regulated, and its current direction is periodically reversed. The reversal of the current direction is achieved in that the coils are located in a so-called T circuit or a so-called H circuit; for current regulation and reversal of direction cf. US-A 44 10 926 or US-A 6031 740.

The induced voltage mentioned arises between at least two galvanic measuring electrodes, that is to say wetted by the liquid, or between at least two capacitive measuring electrodes, that is, for example, arranged within the tube wall of the measuring tube, each of the electrodes tapping a potential for itself. In the most common case, the measuring electrodes are diametrically opposed to one another arranged opposite one another so that their common diameter is perpendicular to the direction of the magnetic field and thus perpendicular to the diameter on which the coil arrangements lie. The induced voltage is amplified and processed by means of an evaluation circuit to form a measurement signal that is registered, displayed or in turn processed. Corresponding measuring electronics are also known to the person skilled in the art, for example from EP-A 814 324, EP-A 521 169 or WO-A 01/90702.

In principle, the absolute value of the potential at the respective electrode is irrelevant for the measurement of the volume flow, but only on the condition that, on the one hand, the potentials are in the modulation range of a differential amplifier following the measuring electrodes, i.e. So that this amplifier must not be overdriven by the potentials, and that on the other hand the frequency of potential changes differs significantly from the frequency of the current direction reversal mentioned.

The potential at each electrode is not only dependent on the magnetic field due to the Faraday law - this depends on the geometrical / spatial dimensions of the measuring tube and the properties of the liquid - but also on the Faraday law and as a purely desired use -Measurement signal, as already discussed in EP-A 12 73 892 or also in EP-A 1 273 891, has interference potentials of different origins superimposed, which in turn can make a considerable contribution to the deterioration of the measurement result.

A first type of interference potential comes from inductive and / or capacitive interference, which emanate from the coil arrangements and their feed lines and change the electrical charge of the capacitor that exists at the interface between the electrode and the liquid. Because of asymmetries in the specific structure of the flow sensor, especially as regards the wiring to the coil arrangements and the measuring electrodes As a result, the interference potential of one electrode generally deviates from the interference potential of the other electrode.

This - first - effect can on the one hand lead to a limitation of the dynamics of the differential amplifier mentioned. On the other hand, the value of the interference potential difference caused by the interference potential of each electrode is subject to sample variations due to the manufacturing tolerances of the flow sensors. The detectable dependence of the potentials of the measuring electrodes on the speed of the liquid is partly due to this effect, since at low speeds the mentioned

Charges at the interface between the electrode and the liquid are not cleared by the latter.

A second type of interference potential originates from particles of a foreign substance or from air bubbles which are carried along by the liquid and which, when they strike an electrode, cause sudden changes in their potential. The decay time of these changes depends on the type of liquid and is usually longer than the rise time of the changes.

This - second - effect also leads to a disturbed useful measurement signal. The error caused by this also depends on the potential of the electrode. However, since this has - as already explained above - specimen scatter, the second effect is added to the first effect, so that the individual specimens of the flow sensor show very different behavior, which is of course extremely undesirable.

A third type of interference potential, as also described, for example, in US Pat. No. 5,210,496, is caused by deposits on the measuring electrodes, which are deposited there by the liquid. The formation of the deposits depends very much on the speed of the liquid. The differences in the behavior of the individual specimens of the flow transducers can be increased even further by the formation of deposits. EP-A 1 273 892 proposes a method for operating a magnetic induction flow sensor, whereby the occurrence of the mentioned interference potentials, of whatever type, is thereby prevented or at least their effect is significantly reduced by using at least one of the two measuring electrodes by means of the evaluation and operating circuit generated voltage pulses are applied at least temporarily. The application of this method can primarily with single-phase or also with well-mixed multi-phase liquids to a considerable improvement in the measuring accuracy of magnetic-inductive

Flow meters. In addition, methods are described, for example, in EP-A 337 292 or WO-A 03/004977 in which the measuring electrodes, in particular by short-circuiting to ground or by applying a harmonic alternating voltage, over a longer period of time with an extinction voltage which eliminates the potential of the current be charged.

A disadvantage of the above-described measuring method or corresponding flow sensor, however, is that, for example, in the case of multi-phase liquids with a pronounced separation of the individual liquid phases or in mushy-viscous liquids with a rather stochastic, previously practically no longer sensible and therefore hardly calibratable distribution any foreign matter particles or gas bubbles that have been carried along are to be expected. To a corresponding extent, interference potentials of the second type can no longer be removed from the measuring electrodes to a sufficiently safe degree.

It is therefore an object of the invention to provide a method with which interference potentials coupled into the measurement signals from flow measuring sensors, in particular the interference potentials of the second type, can be largely compensated for and a measured value can thus be generated which is largely independent of such interference potentials. esp. from interference potentials of the second type. To achieve this object, the invention consists in a method for operating a process measuring device, in particular a magnetic-inductive flow meter, with a measuring tube which is inserted into the course of a line through which a medium, particularly a fluid, flows, which method comprises the following steps comprising:

Allowing the medium to flow through the measuring tube,

Allowing an electrical, in particular bi-polar, excitation current to flow through an operating circuit of the flow meter for driving an excitation arrangement arranged on the measuring tube and acting on it and / or the medium flowing through it,

Generating at least one electrical measurement signal corresponding to the physical measurement variable by means of a sensor arrangement arranged on the measuring tube, digitizing the measurement signal or at least a portion thereof to generate a digital scanning sequence which represents a time course of the measurement signal,

Storing at least part of the digital scanning sequence for generating a first data record which currently represents a temporal course of the measurement signal within a predefinable time interval, and

- Detection of an anomaly in the temporal course of the measurement signal, which is at least partially caused by an interference potential contained in the measurement signal, in particular pulse-shaped, by detecting a data group within the stored first data record, which digitally represents the anomaly, and

- Extracting the data belonging to the data group from the stored first data record in order to generate an interference-free second data record and

- Determining a measured value representing a physical quantity of the flowing fluid using the second data set.

Furthermore, the invention consists in a magnetic-inductive flow meter for a fluid flowing in a line, which comprises: a measuring tube that can be inserted into the line for guiding the fluid,

- an evaluation and operating circuit,

means fed by the evaluation and operating circuit for generating a magnetic field passing through the measuring tube with a coil arrangement arranged on the measuring tube and through which an excitation current flows,

- At least two measuring electrodes for tapping potentials which are induced in the fluid flowing through the measuring tube and permeated by the magnetic field, - Means at least temporarily connected to the measuring electrodes for generating at least one measuring signal derived from the tapped potentials and

Means for storing a first data record comprising digitized measurement data, which currently represents a temporal course of the measurement signal within a predefinable time interval,

the evaluation and operating circuit - detects an anomaly in the measurement signal based on the first data set, which is caused by at least one of the measuring electrodes applied interference, - extracts the detected anomaly from the stored first data set and generates a second data set free of the detected anomaly, and - by means of the second data record freed from the anomaly, generates at least one measured value which represents a physical quantity of the flowing fluid.

According to a preferred first embodiment of the method of the invention, the second data set also includes digital measurement data originally contained in the first data set.

According to a preferred second embodiment of the method of the invention, the step of detecting the anomaly comprises the step of determining a first time value based on the first data record, which time value is one Represents the time of onset of an interference voltage corresponding to the interference potential.

According to a preferred third embodiment of the method of the invention, the step of determining the first time value comprises the steps of comparing the digital data of the first data record with a predeterminable first threshold value and generating a first comparison value which signals that the first threshold value has been exceeded.

According to a preferred fourth embodiment of the method of the invention, the step of detecting the anomaly comprises the step of determining a second time value on the basis of the first data record, which time value represents a point in time of the disappearance of the interference voltage.

According to a preferred fifth embodiment of the method of the invention, the step of determining the second time value comprises the steps of comparing the digital data of the first data record with a predeterminable second threshold value and generating a second comparison value which signals that the second threshold value has been fallen below.

According to a preferred sixth embodiment of the method of the invention, the step of detecting the anomaly comprises the step of determining an amplitude value on the basis of the first data record, which amplitude value represents an amplitude of the measurement signal within the predefinable time interval, in particular the largest amount.

According to a preferred seventh embodiment of the method of the invention, the step of detecting the anomaly comprises the step of determining a third time value on the basis of the first data record, which time value represents a time of occurrence of the amplitude of the measurement signal within the predefinable time interval, in particular the largest amount. According to a preferred eighth embodiment of the method of the invention, the step of detecting the anomaly comprises the step of forming a time difference between the first and the second time value for determining a fourth time value representing the duration of the occurrence of the interference voltage.

According to a preferred ninth embodiment of the method of the invention, the step of detecting the anomaly comprises the step of comparing the amplitude value with a predefinable, in particular variable third threshold value and generating a third comparison value which signals that the third threshold value has been exceeded.

According to a preferred tenth embodiment of the method of the invention, the step of generating the interference-free second data record comprises the step of determining an average value for the voltage induced in the flowing fluid using the measurement signal, in particular already digitized.

According to a preferred eleventh embodiment of the method of the invention, the step of generating the interference-free second data set comprises the step of determining an average value for the voltage induced in the flowing fluid using digital data of the first data set.

According to a preferred twelfth embodiment of the method of the invention, the step of generating the interference-free second data record comprises the step of determining an average value for the voltage induced in the flowing fluid using digital data with a time value that is less than the first time value.

According to a preferred thirteenth embodiment of the method of the invention, the step of generating the suppressed second comprises

Record the step of determining an average for that in the flowing fluid induced voltage using digital data with a time value greater than the second time value.

According to a preferred fourteenth embodiment of the method of the invention, the step of generating the suppressed second data record comprises the step of generating an artificial third data record of digital data approximating the temporal course of the interference voltage, using at least part of the data from the data group representing the anomaly.

According to a preferred fifteenth embodiment of the method of the invention, the step of generating the artificial third data record comprises the step of determining at least one compensation function for at least some of the digital data from the data group representing the anomaly.

According to a preferred sixteenth embodiment of the method of the invention, the step of generating the artificial third data record comprises the step of generating digital data using data values from the data group representing the anomaly and using the determined compensation function.

According to a preferred seventeenth embodiment of the method of the invention, the step of generating the faulty second data record comprises the step of forming a difference between one of the data values from the data group representing the anomaly and one of the data values from the artificial third data record, the two each being Form the difference used data values have mutually corresponding, in particular the same, time values.

According to a preferred eighteenth embodiment of the method of the invention, the step of generating the at least one comprises Compensation function the step of determining at least one coefficient, in particular a time constant, for the compensation function using data values from the data group representing the anomaly.

According to a preferred nineteenth embodiment of the method of the invention, the step of generating the at least one compensation function comprises the step of determining a coefficient, in particular a time constant, for the compensation function using the mean value currently determined for the voltage induced in the flowing fluid.

According to a preferred twentieth embodiment of the method of the invention, the step of determining the coefficient for the compensation function comprises the steps of forming a first difference between a first data value from the data group representing the anomaly and the mean value currently determined for the voltage induced in the flowing fluid, Forming a second difference between a second data value from the data group representing the anomaly and the mean value currently determined for the voltage induced in the flowing fluid and forming a quotient of the first and the second difference.

According to a preferred twenty-first embodiment of the method of the invention, the step of determining the coefficient for the compensation function comprises the steps of generating a digital coefficient sequence of provisional coefficients for the compensation function and digital, in particular recursive, filtering of the coefficient sequence.

According to a preferred twenty-second embodiment of the method of the invention, the step of generating the third data record comprises the step of determining at least one second compensation function for at least a second part of the digital data from the data group representing the anomaly. According to a preferred development of the method of the invention, the exciter arrangement used comprises a coil arrangement for generating a magnetic field, in particular also penetrating the medium carried in the measuring tube.

According to an embodiment of this development of the invention, the sensor arrangement used comprises measuring electrodes arranged on the measuring tube and the method comprises the following further steps:

Generating a magnetic field which also penetrates the fluid by means of the exciter arrangement, inducing a voltage in the flowing fluid for changing potentials applied to measuring electrodes and

- Removal of potentials applied by the measuring electrodes for generating the at least one measuring signal.

A basic idea of the invention is to detect the highly variable interference potentials in the at least one measurement signal on the basis of anomalies corresponding to the interference potentials, in particular directly and in the time range or rather in the scanning range, which in at least one are provided by the sensor arrangement of the flow sensor

Measurement signal or occur in digitally stored data records derived from the measurement signal. By extracting the digital data corresponding to the anomalies and replacing them with calculated data, practically data sets are created, some of which consist of original measurement data and some of which are artificial computing data.

The invention is based on the surprising finding that interference potentials of the type described can be distributed in a highly stochastic manner, but the anomalies to be detected mostly have a typical course or a typical form, the detection of which both identifies such interference potentials in the digitally stored data records derived from the measurement signal and also a Clean them up by manipulation, in particular a non-linear digital filtering, which enables digital data affected by the interference potentials, the actual information contained in the measurement signal originally about the physical quantity to be measured being largely retained on the one hand and also for determining the measurement value on the other hand is made available very quickly.

The method of the invention and further advantages will now be explained in greater detail on the basis of time diagrams and schematic circuit diagrams of a magnetic-inductive flow meter shown in the figures of the drawing.

1a, b show schematically and partly in the form of a block diagram a process measuring device which is suitable for the execution of the method of the invention, here a magnetic-inductive flow meter,

2a schematically shows a time diagram of an excitation current flowing during operation of the process measuring device according to FIGS. 1a, 1b,

2b, c schematically show time diagrams of potentials measurable during operation of FIGS. 3a, b process measuring device according to FIGS. 1a, 1b and FIGS. 4a, b, 5a, b

6a, b schematically show digitally stored curves of measured potentials during operation of the process measuring device according to FIGS. 1a, 1b.

1 schematically and partly in the form of a block diagram shows a process measuring device which is suitable for the execution of the method of the invention - here designed as a magnetic-inductive flow meter - by means of which measured values for at least one physical quantity of a - Not shown here - pipeline flowing medium, in particular a fluid, can be generated. For example, the flow meter can be used to measure a volume flow and / or a flow rate of an electrically conductive liquid.

The flow meter shown here comprises a flow sensor 1 for generating measurement potentials corresponding to the physical quantity to be measured, an operating circuit 2 for detecting the measurement potentials and for generating at least one measurement signal corresponding to the physical quantity, as well as an evaluation circuit 3 which serves the operating circuit 2 and thus also to control the flow sensor 1 and to generate measured values representing the physical quantity using the at least one measurement signal. The operating circuit 2, and possibly also some components of the flow sensor 1, can be accommodated in an electronics housing 10 of the flow meter, for example, as indicated schematically in FIG. 1a.

The flow sensor 1 includes a measuring tube 11 which can be inserted in the course of the above-mentioned pipeline and which has a tube wall and through which the fluid to be measured flows in operation in the direction of a measuring axis.

To avoid short-circuiting of voltages induced in the fluid, an inner part of the measuring tube 11 that contacts the fluid is designed to be electrically non-conductive. Metal measuring tubes are usually provided with an electrically non-conductive layer, e.g. made of hard rubber, polyfluoroethylene etc., and also i.a. non-ferromagnetic; in the case of measuring tubes consisting entirely of a plastic or a ceramic, in particular of aluminum oxide ceramic, the electrically non-conductive layer is not required.

An excitation arrangement of the flow meter controlled by driver electronics 21 provided in the operating circuit 2 has been shown in FIG Embodiment a first field coil 12 arranged on the measuring tube 11 and a second field coil 13 arranged on the measuring tube 11. The field coils 12, 13 lie on a first diameter of the measuring tube 11. The exciter arrangement is used in operation to generate a magnetic field H passing through the tube wall and the fluid flowing through it. This occurs when one of the field coils 12, 13 connected here in series the driver electronics 21 driven excitation current I is allowed to flow. The excitation current I, in particular bipolar, can be rectangular, triangular or sinusoidal, for example.

In Fig. 1b it is shown that the field coils 12, 13 do not contain a core, that is to say they are so-called air coils. The field coils 12, 13 can, however, as is customary in the case of such coil arrangements, be wound around a core which in general. is soft magnetic, whereby the cores can interact with pole pieces, cf. e.g. US-A 55 40 103.

The exciter arrangement, which in the exemplary embodiment shown acts as an electromagnetic coil acting on the medium, is designed here, in particular the two field coils 12, 13 are shaped and dimensioned such that the magnetic field H thus generated within the measuring tube 11 at least with respect to a second one perpendicular to the first diameter Diameter is symmetrical, especially rotationally symmetrical.

According to one embodiment of the invention, the driver electronics 21 generate a direct current, in particular regulated to a constant amplitude, which is then periodically switched by means of a corresponding switching mechanism configured, for example, in an H or T circuit, and thus to an alternating current with regulated Amplitude is modulated. As a result, the excitation current I is allowed to flow through the coil arrangement such that the coils 12, 13, as shown schematically in FIG. 2a, during a first switching phase PH 11 in each case in a first current direction and during a second switching phase PH12 following the first switching phase in one for flow through the opposite direction in the first current direction, cf. for current regulation and polarity reversal, for example, also US-A 44 10 926 or US-A 60 31 740.

The second switching phase PH 12 is followed by a third switching phase PH21, during which the excitation current I flows again in the first current direction. The third switching phase is followed by a fourth switching phase PH22, during which the excitation current I flows again in the opposite direction. This is followed by a corresponding switching phase PH31 etc. With regard to the reversal of the direction of the excitation current I, two of the successive switching phases form a switching period P1, P2, P3, etc. Along with the polarity reversal of the excitation current I flowing through the coil arrangement, apart from a possible switching phase shift essentially in sync with it, the magnetic field H is also reversed, see FIG. Fig. 2a.

To generate at least one electrical measurement signal corresponding to the measured variable, a sensor arrangement arranged on the measuring tube or at least in the vicinity thereof is also provided in the measuring sensor. According to one embodiment of the invention, the sensor arrangement has electrodes practically directly attached to the measuring tube. One on the inside of the

The tube wall of the measuring tube 11 arranged first electrode 14 serves to tap a first potential e induced by the magnetic field H - A second electrode 15 arranged in the same way also serves to tap a second potential eι ₅ induced by the magnetic field. The measuring electrodes 14, 15 lie on the second diameter of the measuring tube 11 perpendicular to the first diameter and to the longitudinal axis of the measuring tube, but they can, for example, also lie on a chord of the measuring tube 11 parallel to the second diameter, cf. see also US-A 56 46 353.

In Fig. 1b, the measuring electrodes 14, 15 are shown as galvanic measuring electrodes, that is to say as those which touch the fluid. However, two capacitive ones, that is to say for example arranged inside the tube wall of the measuring tube 11, Measuring electrodes are used. Each of the measuring electrodes 14, 15 taps an electrical potential eu, e- ₁₅ which is induced in the fluid flowing through during operation due to Faraday's law.

As shown in FIG. 1 b, the measuring electrodes 14, 15 are at least temporarily connected to an inverting or non-inverting input of a differential amplifier 22 during operation. A potential difference of the two potentials e ₁ , ice tapped by the measuring electrodes 14, 15 is thus formed, which corresponds to a voltage built up in the fluid flowing through and thus also to the physical quantity to be measured. The potentials e, ice applied to the measuring electrodes 14, 15 are usually approximately in the range from 10 mV to 100 mV.

The measurement signal u present in the exemplary embodiment shown output of the differential amplifier 22 is, as shown schematically in FIGS. 1b, supplied to the evaluation circuit 3 provided in the flow meter. According to the invention, the evaluation circuit 3 serves, in particular, to digitize the supplied measurement signal u and to store sections of it in a first data record DS ₁ , so that information about the temporal course of a section of the measurement signal u is available in digital form for determining the measured value XM ,

For this purpose, the measurement signal u is fed to the evaluation circuit 3, as shown schematically in FIG. 1 a, in the exemplary embodiment shown via a low-pass filter 31 of a predefinable filter order, for example a passive or an active RC filter, and an adjustable cut-off frequency. The low-pass filter 31 serves to limit the measurement signal u in order to avoid aliasing errors and thus to preprocess it accordingly for digitization. According to the known Nyquist sampling theorem, the cut-off frequency is set to less than 0.5 times a sampling frequency with which the portion of the measurement signal u that is passed is sampled. In case that the measurement signal u is already band-limited in the required manner, the low-pass filter 31 can optionally also be dispensed with.

On the output side, the low-pass filter 31 is coupled to a signal input of an A / D converter (analog-to-digital converter) 32 of the evaluation circuit 3, which serves to convert the measurement signal u supplied via the low-pass filter 31 into a digital measurement signal UD representing it. For this purpose, the A / D converter 32 known to the person skilled in the art, e.g. serial or parallel converting, A / D converters can be used, which can be clocked with the sampling frequency mentioned above. A suitable A / D converter type is e.g. that of a delta-sigma A / D converter ADS 1252 from Texas Instruments Inc. with a resolution of 24 bits and a permissible sampling frequency of less than or equal to 40 kHz, wherein sampling frequencies of less than 10 kHz may be sufficient to implement the method according to the invention.

In the event that the A / D converter 32 used, e.g. The aforementioned ADS 1252 is provided for converting only positive signal values, a reference voltage of the A / D converter 32 is to be set accordingly so that an expected minimum signal value input of the converter is at least one bit, especially the highest significant bit (MSB). , of the measurement signal UD. In other words, a DC component must be added to the signal present at the output of the low-pass filter 31 in such a way that it acts on the A / D converter 32 practically as a DC signal of variable amplitude.

The digital measurement signal u _{D present on the} output side of the A / D converter 32 is loaded segment by segment, for example via an internal data bus, into a volatile data memory 33 of the evaluation circuit 3 and there as a finite scan sequence AF inform representing the measurement signal u of an ensemble of digitally stored measurement data , in particular for a digital flow computer 34 of the evaluation circuit 3. As

In this case, data memories 33 can serve, for example, static and / or dynamic read / write memories. A width for a current scanning window, i.e. a time length of the section of the scanning sequence AF to be stored, which currently represents the measurement signal u, can be, for example, in the range of the entire duration of one of the switching periods P1, P2 with which the excitation current I is clocked or also in the range of Duration of one of the switching phases PH11, PH12, PH21, PH22, the clocking with which data is read into the data memory 33 being accordingly essentially in phase with the clocking of the excitation current. Typical cycle times are in conventional Durchflußmesern of the type described for example in the range of 10 to 100 ms, which in turn at a sampling frequency f _a A / D converter 32 of 10 kHz, respectively, a number of 100 to 1000 samples, so in 1000 the stored samples from the sampling sequence AF or the first record would result.

If necessary, for example due to a smaller storage capacity of the data memory 33 or for the upstream elimination of field reversal-related voltage transients, it is also possible to read only a portion of the measurement signal u generated per switching phase, rather the digital measurement signal UD into the data memory 33. For this purpose, the switching phases PH11, PH12, PH21, PH22, PH31 mentioned above are each illustrated in an associated first partial period T111, T121, T211, T221, T311 and the associated second partial period serving as a measuring phase T112, T122, T212, T222, T312 divided, see 2a, 2b and 2c. Preferably this

Embodiment of the invention in each case only virtually in the course of the measurement signal u associated with the respectively current second of the partial period durations T112, T122, T212, T222 or T312 in the data memory 33, the evaluation of the measurement data and the generation of the measurement value then in each case during the next Magnetic field build-up phase T121, T211, T221, T311 can take place. To generate the measured value XM from the scanning sequence AF, the flow computer 34 has, at least temporarily, access to the data memory 33 and the data records stored therein, in particular via data bus, for example via an internal data bus. The flow computer 34 can, for example, as shown schematically in FIG. 1 a, be advantageously implemented by means of a microprocessor 30 and computer programs running in it.

According to a preferred embodiment of the invention, the evaluation circuit 3 further comprises a memory manager 35 designed as a separate subcircuit, which communicates with the microprocessor 30, for example via an internal data bus, to manage the data memory 33, in particular the sampling of the digital measurement signal u _D and control the generation of the scan sequence AF, and thus relieve the microprocessor 30. The memory manager 35 is preferably implemented in a programmable functional memory, for example a PAL (programmable array logic) or an FPGA (field programmable gate array). If necessary, the memory manager 35 can also be implemented by means of the microprocessor 30 or another microprocessor (not shown here) and corresponding computer programs running therein. By means of the memory manager 35 it is also possible, for example, to implement a mean or median formation, customary for such flowmeters, over a plurality of scanning sequences.

As already mentioned several times, the measurement signal u can be disturbed to a considerable extent due to interference potentials E112, E122, E222, E312 occurring at the measurement electrodes 14, 15, and can therefore be falsified, cf. see also Fig. 2b, 2c. For illustration, FIGS. 3a, 3b also show curves of the potentials eι ₄ , e-ι ₅ recorded over approximately 10 seconds, which are temporarily superimposed by interference potentials, with a region of the recorded potential curves βι ₄ , ice which is disturbed in the manner described 4a, 4b are shown again in a different time scale; compared 5a, 5b, undisturbed areas of the potential curves e <ι, e ^ shown in FIGS. 3a and 3b are shown again.

Examinations of the temporal profiles of such interference potentials have shown that, as can also be seen in FIGS. 3a, 3b, the height of their amplitude or the times of their occurrence cannot be predicted, but a typical amplitude profile is postulated for at least a large number of the interference potentials and can be taken into account in the sense of a priori information when evaluating the measurement signal u and determining the measurement values. Surprisingly, it has been shown that the interference potentials in the course of the measurement signal u inform are reflected in distinctive anomalies which can be determined beforehand at least qualitatively in terms of their shape. In addition, it has been shown that these anomalies can be detected relatively reliably during operation within the scanning sequence AF or rather on the basis of the current data record DSi derived therefrom and can be eliminated from the data record at the expense of a comparatively very low loss of information.

Accordingly, in the method according to the invention, an anomaly in the temporal course of the measurement signal u, which is at least partially caused by an interference potential, in particular pulse-shaped interference voltage, applied at least to one of the measurement electrodes 14, 15, is detected by the fact that, as shown schematically in FIG. a data group DSA is determined within the stored first data record DSi, which digitally represents the anomaly. Furthermore, the anomaly detected in this way is extracted from the stored first data record DSi in order to generate an interference-free second data record DS _2, the interference-suppressed data record DS ₂ finally being used to determine the measured value XM representing the physical quantity of the flowing fluid to be measured.

According to one embodiment of the method of the invention is vorgsehen, for generating the interference-free data set DS ₂ an average value for the U in flowing fluid induced voltage using a range of the measurement signal u or the already digitized measurement signal UD ZU to determine and keep available in the data memory 33 for further calculations. In an advantageous manner, the determination of the mean value U can be derived from the measurement signal u using the currently stored data record DSi and / or using an earlier point in time using a current switching phase, preferably the immediately preceding switching phase or the preceding switching phase and cached data set. For the formation of the mean value U, preference is given to using data which do not belong to the data group DSA representing the anomaly and which can therefore be regarded as essentially free of interference.

Using the mean value U, for example, simply by deleting the individual data of the data group DSA representing the anomaly from the currently stored data record DSi and inserting the current mean value U into the "vacant" positions of the data record DSi a very effective interference suppression of the data set DSi. However, a considerable amount of measurement information can also be lost in this way if the flow fluctuates greatly.

Based on the knowledge that most disturbance potentials have a qualitatively essentially comparable form of course and thus can be determined at least qualitatively in advance or at least well estimated in terms of their temporal course, the suppressed second data record DS ₂ , as in FIG 6b, using a third data set DS of artificially generated digital data approximating the temporal course of the interference voltage. These data are generated during operation by means of the evaluation circuit 3 on the basis of at least a portion of the data from the previously located Anomaly representing data group DSA is calculated and possibly also buffered again in data memory 33.

Furthermore, the suppressed second data record DS ₂ can now be generated in an advantageous manner by first selecting a data value x from the data group DSA representing the anomaly and from the third data record DSK, the two selected data values x corresponding to one another, in particular, have the same time values i, and that a difference between the two currently selected data values x is formed numerically. This is repeated until all data values x from the data group representing the anomaly DSA have been used. In this way, an interference potential approximated in its shape, in particular in terms of its height and duration, is virtually subtracted from the measurement signal u, which, assuming that the voltage superior to the approximated shape of the interference potential, essentially the measurement voltage that is actually of interest is, practically only the portion of the measurement signal corresponding to the physical quantity remains in the suppressed data record DS ₂ .

In order to generate the artificial data record DSK, at least one compensation function for at least some of the digital data from the data group representing the anomaly, DSA, is determined by means of the evaluation circuit 3 during operation, and the artificial data record DSK is determined using the compensation function. According to an embodiment of this development of the method of the invention, for determining the at least one compensation function, provision is also made to determine at least one, but preferably two or more, coefficients Ti for the compensation function using data values x from the data group DSA representing the anomaly ,

To determine the compensating function, in particular the coefficient Ti for the compensating function, one can, for example, use the Gaussian principle of algorithm based on the smallest error squares are programmed into the evaluation circuit 3 and are used by means of the same to the data group DSA currently held in the data memory 33.

In comparison to the embodiment mentioned above, in which only the current mean U is used as a replacement for the data from the data group DS _A representing the anomaly, it was possible to use a suitable compensation function, in particular when using the interference-free data record DS generated in this way ₂ for the flow measurement, at least halving and thus a further significant reduction in the measurement error.

Investigations of representative applications have also shown that a particularly frequently occurring form of disturbance potentials of the type described, for example that of short needle-shaped ones

Voltage pulses is very similar. The interference potentials usually have a relatively steep rising edge followed by an essentially exponentially falling edge. Based on this knowledge, according to another embodiment of the aforementioned development of the invention, for determining the at least one compensation function, provision is made to determine at least one coefficient as a time constant of an exponentially declining compensation function, for example a declining e-function of the first or higher order.

According to a further embodiment of the invention, provisional coefficients, in particular a sequence of provisional coefficients, are first generated for the compensation function, for example by repeatedly applying the aforementioned calculation rule sequentially to different data pairs from the data group DSA representing the anomaly. According to a further development, the provisional coefficients determined are digitally filtered, for example individually in each case immediately after their calculation or only after the calculation of the entire coefficient sequence. Investigations have shown that, in particular using a recursive digital filter on the coefficient sequence, even with a low filter order, good, in particular robust and also reproducible measurement results can be achieved even with a large spectrum in the resulting interference potentials. According to an advantageous embodiment, the sequence of the provisional coefficients can be determined in accordance with the following instruction:

f _n = λ T _{n +} (l-λ) f _n,, (1)

where f _n - a preliminary coefficient for the compensation function, f _n _, calculated in the calculation step currently being carried out. - a provisional coefficient for the compensation function calculated in the previously performed calculation step, T _n - an intermediate value previously determined for the current calculation step and λ, (1-λ) - predetermined filter coefficients for the digital filter, with 0 <λ <1.

It is possible to store the provisionally determined coefficients individually as well as to always only keep the current and the previous coefficients in the data memory 33. The calculation rule is now applied until a predetermined number, for example the amount of data in the data group DSA representing the anomaly, has been subjected to arithmetic loops and / or until a previously selected termination criterion, for example a sufficiently low change between the last calculated preliminary coefficients , are fulfilled. The last calculated coefficient then corresponds to the coefficient T-ι searched for the compensation function. In the event that an interference potential is present at the measuring electrodes over a longer period of time and thus also over several measuring phases, the calculation of the coefficient is carried out using a corresponding coefficient determined in an immediately preceding measuring phase, this older coefficient then, for example, as one current provisional coefficient f _n . can serve.

According to a further embodiment of the method of the invention, to generate the at least one compensation function, the coefficient or coefficients for the compensation function is calculated using the mean value U currently determined for the voltage induced in the flowing fluid. Advantageously, this can e.g. are already numerically implemented when determining the intermediate values for the provisional coefficients based on the following calculation rule:

(2)

where xιι, Xj ₂ - a first and a second data value from the data group representing the anomaly DS _A and, i ₂ - are their indicia corresponding to the respectively associated time value.

According to Eq. (2) in this embodiment of the method, a first difference between a first data value XK from the data group representing the anomaly DSA and the mean value U currently determined for the voltage induced in the flowing fluid and a second difference between a second data value Xj ₂ the the anomaly representing data group DSA and the mean value U currently determined for the voltage induced in the flowing fluid. The natural logarithm is also determined numerically from a quotient determined from the first and the second difference, to which a previously formed difference between the time values or indicia h, i _{2 of} the currently used data values Xu, Xj _{2 is then} standardized.

To detect the anomaly, according to a further embodiment of the invention, a first time value t _{s is} determined on the basis of the first data set DSi, which represents a point in time at which the interference voltage is set. For this purpose, the digital data of the first data record DSi can be compared, for example, with a predeterminable first threshold value TH _S , which can be changed during operation, and a corresponding first comparison value can be generated which signals that the first threshold value TH _{S has been} exceeded. The first time value t _s can be calculated as t _s = i _s / f _a , where i _{s is} the index of the determined data value, which first exceeds the threshold value. Furthermore, to detect the anomaly, a second time value t _{e is} determined on the basis of the first data record DSi, for example based on t _e = i _e / f _a , which represents a point in time of the disappearance of the interference voltage. In an analogous manner, the digital data of the first data record DSi can be compared, for example, with a predefinable second threshold value TH _e , which can be changed during operation, and a corresponding second comparison value can be generated, which signals that the second threshold value TH _{e is} undershot. It should also be mentioned at this point that the aforementioned comparisons actually relate to the magnitude of the measurement signal u. In the event that these comparisons are also to be made taking into account the sign of the measurement signal u, the threshold values TH _S , TH _e for negative voltages are to be determined vice versa.

Based on the assumption that, for example, the flow between two successive measurement phases T112 and T122 changes only to a comparatively small extent due to physical or technological reasons can, according to a further embodiment of the invention, at least one of the threshold values TH _S , TH _{e is} determined during operation and adapted to the fluid currently flowing in the measuring tube 11, in particular to a flow measurement value determined for an earlier switching phase. For example, the threshold value TH _S or TH _e can advantageously be formed using an average value U of the measurement signal u determined in an earlier, especially an immediately preceding or a recent, undisturbed measurement phase. This can be implemented in a particularly simple manner, for example, by increasing the threshold value during operation by a value that corresponds to the maximum increase in the measured value to be expected within the time that has now passed, or by a corresponding percentage.

According to a further embodiment of the method of the invention, the anomaly is further detected in that at least one amplitude value and an associated third time value are determined on the basis of the first data set DSi, the amplitude value representing an amplitude of the measurement signal within the predefinable time interval, in particular the largest amplitude , Furthermore, it is provided to compare several or all of the data of the first data set DSi or only the amplitude value with a predeterminable third threshold value TH _{a, which} can be changed during operation, in order to detect the anomaly. This threshold value is chosen to be larger than the first threshold value TH _S and represents a predetermined minimum amplitude for a voltage surge to be detected as an anomaly. In addition, a corresponding third comparison value is generated, the signal exceeding the threshold value TH _a.

According to another embodiment of the invention, the digital data of the first record DSi for detecting the anomaly to be compared with a predetermined third threshold value TH _A and is generated in a corresponding manner, the third comparison value, which signals exceeding the threshold value TH _a. According to a further embodiment of the invention, a time difference t _e - t _{s is also formed} between the previously determined first time value t _s representing the onset of the interference voltage and the second time value t _e representing the disappearance of the interference voltage to detect the anomaly, which represents the duration of the occurrence of the interference voltage. Furthermore, this fourth time value can in turn be compared with a corresponding fourth threshold value, which represents a predefinable minimum duration for a voltage pulse to be regarded as an anomaly to be eliminated.

Furthermore, in the case of a first data record DSi which is not completely disturbed, the mean value U for the voltage induced in the flowing fluid can be calculated using digital measurement data from the data record DSi, to which a time value is assigned which is less than the previously determined first time value t _s and / or of digital measurement data of the data set DSi with a time value that is greater than the second time value t _e .

In addition to the one compensation function mentioned, it is also possible, during operation, to determine a further compensation function for at least a second part of the digital data from the data group DSA ZU representing the anomaly, for example a simple rising straight line for the rising edge of the interference voltage pulse, and the data of the to generate artificial data set DSK using this second compensation function.

Following the generation of the faulty data record DS ₂ , the evaluation circuit 3 can now be used in the usual manner, for example in US Pat. No. 4,382,387, US Pat. No. 4,422,337 or US Pat. No. 4,7 04,908 Flow measured value described, the measured value representing the physical quantity to be measured are calculated accordingly. As already mentioned, the determination of the flow, for example, is based on the

Evaluation of an amplitude curve of the voltage tapped between the two measuring electrodes 14, 15 which is dependent on the current flow rate can now be determined with high precision in a conventional manner by means of the interference-free data record DS ₂ kept available in the data memory 33. Likewise, the current fault-cleared data record DS ₂ or a plurality of such stored data records can be used to determine further physical quantities of interest, for example a viscosity of the fluid

Flow index, a degree of turbulence of the flow or the like can be used.

At this point, it should be pointed out that, instead of a single differential amplifier for the measuring electrodes 14, 15 which serves to generate an analog difference signal, a corresponding signal amplifier can of course also be provided separately for each of the measuring electrodes 14, 15. Accordingly, for example, the potential difference between the two potentials tapped by the measuring electrodes 14, 15 e-ι ₄ , e-ι ₅ can also be calculated numerically using two separately digitized measuring signals.

Both the evaluation methods required to generate the interference-free data record DS ₂ by means of the data record DSi and the evaluation methods required to determine the measured values X _M based on the interference-free data record DS ₂ can be implemented in the manner known to the person skilled in the art, for example as a computer program running in the microprocessor 30. The program codes required for this can also be easily implemented in an, in particular permanent, writable memory 36 of evaluation stage 3, for example an EPROM, a flash EEPROM or EEPROM, to which the microprocessor 30 reads data during operation.

According to an advantageous embodiment, it is provided that the microprocessor 30 is implemented by means of a digital signal processor, for example of the TMS 320 C 33 type from Texas Instruments, Inc. If necessary, an additional signal processor can also be provided in the control unit 3, for example in addition to the microprocessor 30. The flow meter can, for example, be connected to a fieldbus, not shown, and can thus be connected to a remote control room and to an external power supply that feeds the flow meter, set via an internal supply unit 4. To send measuring device data, in particular also the flow measurement value, to the fieldbus, the flow measuring device further comprises a communication unit 5 with corresponding data interfaces 51. Furthermore, the communication unit 5 can also, in particular for visualizing measuring device data and / or for setting the flow measuring device on site to enable having a corresponding display and control unit 52.

An advantage of the invention can also be seen in the fact that the determination of the measured values using the current first data record DS-ι, in particular when there is no comparatively sluggish higher-order digital filter for the scanning sequence AF or for the first data record and when there is also no complex spectral analysis of the scanning sequence AF or the first data set in the frequency domain, performed comparatively promptly, even if the data set used is completely or partially disturbed. This can even be achieved for disturbances in the measurement signal u which are present over two or more measurement phases. In addition, the method according to the invention has, in addition to a very short computing time compared to digital filters of correspondingly higher order, which are comparable in effect, a much higher selectivity with regard to interference of the type described. In particular, very good results can also be achieved for the interference potential of the second type mentioned at the outset or for highly viscous liquids, such as pulp. Another advantage of the invention is that both conventional flow sensors and conventional operating circuits can be used to implement the method. Even conventional evaluation circuits can essentially continue to be used if the implemented software is modified accordingly. Another advantage of the method according to the invention is that it can also be used for process measuring devices other than those shown in the exemplary embodiment can be applied. For example, the method can also be used very advantageously in flowmeters which operate by means of ultrasonic sensors or by means of measuring tubes which vibrate during operation.

Claims

1. A method for operating a process measuring device, in particular a magnetic inductive flow meter, with a measuring tube (11) which is inserted into the course of a line through which an, in particular fluid, medium flows, which method comprises the following steps

- Letting the medium flow through the measuring tube (11),

Allowing an electrical, in particular bi-polar, excitation current (I) to flow through an operating circuit (21) of the flow meter to drive an excitation arrangement (12, 13) arranged on the measuring tube (11) and acting on it and / or the medium flowing through it,

Generating at least one electrical measurement signal (u) corresponding to the physical measured variable by means of a sensor arrangement (14, 15) arranged on the measuring tube (11),

Digitizing the measurement signal (u) or at least a portion thereof to generate a digital scan sequence (AF) which represents a time course of the measurement signal (u),

- Storage of at least part of the digital scanning sequence (AF) for generating a first data record (DSi), which currently represents a temporal course of the measurement signal (u) within a predefinable time interval, and

- Detecting an anomaly in the course of the measurement signal over time, which is at least partially caused by a pulse-shaped interference potential (E222) contained in the measurement signal, by detecting a data group (DS _A ) within the stored first data record (DSi) represents the anomaly digitally, and

- Extracting the data belonging to the data group (DS _A ) from the stored first data record in order to generate an interference-free second data record (DS ₂ ) and - Determining a measured value (XM) representing a physical quantity of the flowing fluid using the second data set (DS ₂ ).

2. The method according to claim 1, wherein the second data set (DS ₂ ) also includes original digital measurement data contained in the first data set (DSi).

3. The method according to claim 1 or 2, wherein the step of detecting the anomaly comprises the step of determining a first time value (t _s ) on the basis of the first data record (DSi), which time value (t _s ) represents a point in time at which one with the interference potential ( E222) represents the corresponding interference voltage.

4. The method according to the preceding claim, wherein the step of determining the first time value (t _s ) comprises the steps of comparing the digital data of the first data set (DSi) with a predeterminable first threshold value (TH _S ) and generating a first comparison value which exceeds of the first threshold (TH _S ) signals.

5. The method according to any one of the preceding claims, wherein the step of detecting the anomaly comprises the step of determining a second time value (t _e ) on the basis of the first data record (DS _t ), which time value (t _e ) represents a point in time of the disappearance of the interference voltage.

6. The method according to the preceding claim, wherein the step of determining the second time value (t _e ) comprises the steps of comparing the digital data of the first data record (DSi) with a predeterminable second threshold value (TH _e ) and generating a second comparison value which is less than the value of the second threshold (TH _e ) signals.

7. The method according to any one of the preceding claims, wherein the step of detecting the anomaly, the step of determining an amplitude value based on of the first data set (DSi), which amplitude value represents an, in particular largest, amplitude of the measurement signal (u) within the predefinable time interval.

8. The method according to the preceding claim, wherein the step of detecting the anomaly comprises the step of determining a third time value on the basis of the first data record, which time value represents a time of occurrence of the, in particular largest, amplitude of the measurement signal within the predeterminable time interval.

9. The method according to claim 6, wherein the step of detecting the anomaly comprises the steps of comparing the amplitude value with a predefinable, in particular variable, third threshold value (TH _a ) and generating a third comparison value which exceeds the third threshold value (TH _a ) signals.

10. The method according to claim 2 and 4, wherein the step of detecting the anomaly comprises the step of forming a time difference (t _e - t _s ) between the first and the second time value (t _s , t _e ) for determining the duration of the occurrence of the interference voltage representing fourth time value.

11. The method according to any one of the preceding claims, wherein the step of generating the interference-free second data set (DS ₂ ) comprises the step of determining an average value (U) for the voltage induced in the flowing fluid using the, in particular already digitized, measurement signal (u) ,

12. The method according to any one of the preceding claims, wherein the step of generating the suppressed second data set (DS ₂ ) comprises the step of determining an average value (U) for the voltage induced in the flowing fluid using digital data of the first data set (DSi).

13. The method according to any one of the preceding claims, wherein the step of generating the interference-free second data set, the step of generating an artificial third data set (DSK) of digital data approximating the time profile of the interference voltage using at least part of the data from the data group representing the anomaly (DSA).

14. The method according to the preceding claim, wherein the step of generating the artificial third data record (DSK) comprises the step of determining at least one compensation function for at least some of the digital data from the data group representing the anomaly (DSA).

15. The method according to claim 12 or 13, wherein the step of generating the artificial third data record (DSK) the step of generating digital data using data values from the data group representing the anomaly (DSA) and using the determined compensation function.

16. The method according to any one of claims 12 to 14, wherein the step of generating the second data set (DS ₂ ) the step of forming a difference between one of the data values from the data group representing the anomaly (DSA) and one of the data value from the artificial third Data set (DSK) comprises, the two data values used to form the difference each have corresponding, in particular the same, time values.

17. The method according to claim 13, wherein the step of generating the at least one compensation function comprises the step of determining at least one coefficient (Ti), in particular a time constant, for the compensation function using data values from the data group representing the anomaly ( DSA).

18. The method according to any one of claims 13 to 16, wherein the step of generating the at least one compensation function, the step of determining a coefficient (T-ι), in particular a time constant, for the compensation function using that currently determined for the voltage induced in the flowing fluid Average (U) includes.

19. The method according to the preceding claim, wherein the step of determining the coefficient (T-i) for the compensation function comprises the steps:

Forming a first difference between a first data value from the data group (DSA) representing the anomaly and the mean value (U) currently determined for the voltage induced in the flowing fluid,

- Forming a second difference between a second data value from the data group representing the anomaly (DSA) and the mean value (U) and currently determined for the voltage induced in the flowing fluid

- Forming a quotient of the first and the second difference.

20. The method according to any one of claims 12 to 18, wherein the step of determining the coefficient for the compensation function comprises the steps:

- Generation of a digital coefficient sequence (T _n ) of provisional coefficients for the compensation function and

- digital, especially recursive, filtering of the coefficient sequence (T _n ).

21. The method according to any one of claims 12 to 19 wherein the step of

Generating the third data record (DSK) comprises the step of determining at least one second compensation function for at least a second part of the digital data from the data group (DSA) representing the anomaly.

22. The method according to any one of the preceding claims, wherein the

Exciter arrangement (12, 13) a coil arrangement for generating a, esp. also includes the magnetic field (H) passing through the medium guided in the measuring tube.

23. The method according to the preceding claim, wherein the sensor arrangement (14, 15) comprises measuring electrodes arranged on the measuring tube (11), comprising the following further steps:

Generating a magnetic field (H) which also penetrates the medium guided in the measuring tube (11) by means of the exciter arrangement (12, 13),

- Inducing a voltage in the flowing fluid to change potentials applied to measuring electrodes (e <ι, e ₁₅ ) and

- _{Removal of} potentials applied by the measuring _electrodes (e-ι _4j eis) for generating the at least one measuring signal (u).

24. Magnetic-inductive, especially suitable for realizing the method according to one of the preceding claims 1 to 20, flow meter for a fluid flowing in a line, which comprises:

a measuring tube (11) that can be inserted into the line for guiding the fluid,

- an evaluation and operating circuit (2, 3), - means fed by the evaluation and operating circuit (2, 3) for generating a magnetic field passing through the measuring tube (11) with a arranged on the measuring tube (1) and an excitation current (i ) flowing through the coil arrangement (12, 13),

- At least two measuring electrodes (14, 15) for tapping potentials (e ₄ , e ₅ ), which are induced in the fluid flowing through the measuring tube and penetrated by the magnetic field,

- At least at times connected to the measuring electrodes (14, 15) means for generating at least one of the tapped potentials (eι ₄ , eι ₅ ) derived measurement signal (u) and - Means for storing a first data record (DS), which shows a time course of the Measurement signal (u) currently represented within a predeterminable time interval, - The evaluation and operating circuit (2, 3) - using the first data set (DS) detects an anomaly in the measurement signal (u), which is caused by at least one of the measuring electrodes (14, 15) applied interference potential, - the detected anomaly extracted from the stored first data record (DSi) and generates a second data record (DS ₂ ) free of the detected anomaly and - by means of the interference-free data record (DS ₂ ) freed from the anomaly, generates at least one measured value (XM) which is a physical quantity of the flowing Represents fluids.