METHOD FOR DETERMINING THE FILL LEVEL OF A PIPE, EVALUATION UNIT, FLOW MEASURING SYSTEM AND COMPUTER PROGRAM PRODUCT

Description

[0001] The invention relates to a method for determining a fill level in a pipe and an evaluation unit with which the method can be carried out. Furthermore, the invention relates to a flow measurement system having such an evaluation unit. The invention also relates to a computer program product with which the operating behavior of such a flow measurement system can be simulated.

[0002] US 2017 / 131131 A1 discloses an electromagnetic flowmeter suitable for measuring impedance in a pipe. To measure the fill level of the pipe, a plurality of electrodes are arranged around its circumference. By measuring the impedances at the electrodes in pairs, it is possible to determine which of the electrodes is wetted with the fluid.

[0003] International patent application WO 2008 / 113774 A2 discloses a method for determining the electrical conductivity of a medium using a magnetic-inductive flowmeter. The flowmeter has two opposing measuring electrodes, a ground electrode, and two opposing coil arrangements. To measure the electrical conductivity, excitation signals of different frequencies are generated, and an impedance present between the measuring electrode and the ground electrode is measured.

[0004] Document DE 10 2010 020 963 A9 discloses a method for operating a magnetic flowmeter comprising a plurality of electrodes arranged along a pipe cross-section. The electrodes form electrode pairs. Signals are fed into the electrodes, and impedances and / or voltages are measured. By permuting the electrode pairs into which signals are fed, a fill level in the pipe cross-section is determined through corresponding measurements.

[0005] Flow measurement systems are used in a wide variety of applications in automation technology. In addition to flow measurement itself, additional functions such as level measurement are sought. At the same time, there are increasing demands on the compactness, reliability, and cost-effectiveness of such flow measurement systems. The invention is based on the task of providing a method for determining the level in a pipe that offers high measurement accuracy, is space-saving, robust, and cost-effective, and can be integrated into the functional spectrum of existing flow measurement systems.

[0006] The problem is solved by a method according to the invention for determining the fill level of a pipe. The pipe contains a fluid that flows through the pipe during normal operation and forms a level when the pipe is partially filled, i.e., when the fill level is below 100 percent. A first and a second controllable measuring electrode are arranged on the pipe. The measuring electrodes are controllable such that at least one electrical variable, such as voltage or current, can be specified there. The measuring electrodes extend into the lumen of the pipe and are wettable by the fluid. Furthermore, the pipe is provided with at least one grounding electrode. The method comprises a first step in which the pipe is provided in a state at least partially filled with the fluid. The fill level in the first step is therefore above 0 percent, and the first and second measuring electrodes are wetted by the fluid.

[0007] The method further comprises a second step in which the first and second measuring electrodes are excited by applying opposing measuring currents. The opposing measuring currents have current intensities of opposite signs, so that the measuring currents induce a current flow from the first to the second measuring electrode. This implements the principle of so-called push-pull excitation. Furthermore, in the second step, at least one first measured value is recorded at the first and / or second measuring electrode. The first measured value can, for example, be a voltage applied to the first or second measuring electrode. The first or second measuring electrode can be provided with suitable measuring means for this purpose.

[0008] The method also includes a third step in which the first and second measuring electrodes are excited by applying measuring currents of the same direction. Complementary to the second step, the measuring currents in the third step have current intensities with the same sign. The measuring currents in the third step therefore cause a current to flow from the first and second measuring electrodes to the first ground electrode or vice versa. This implements the principle of so-called common-mode excitation. In the third step, at least a second measured value is recorded at the first and / or second measuring electrode. The second measured value can, for example, be a voltage applied to the first or second measuring electrode, corresponding to the first measured value. The first or second measuring electrode can also be provided with suitable measuring devices for this purpose. The first and second measuring electrodes can be excited with direct current or alternating current.Excitation with alternating current also includes measuring currents with a signal coding, for example oscillation packets, so-called bursts, frequency-modulated signals and / or so-called Barker codes.

[0009] Furthermore, the method comprises a fourth step in which the fill level of the pipe is determined at least based on at least the first and second measured values, which are recorded in the second and third steps, respectively. Furthermore, in the fourth step, the determined fill level can be output to a user, for example via a display unit, or via a data interface, for example to a higher-level control unit. The invention is based, among other things, on the surprising discovery that measuring currents in the same and opposite directions lead to different characteristics, which in turn are influenced by the fill level of the pipe. These characteristics are independent of the conductivity of the medium. The method according to the invention is suitable for determining the fill level in a pipe without knowledge of the electrical conductivity of the fluid and can be classified as conductivity-agnostic.The method according to the invention is thus insensitive to changes in the composition of the fluid. Consequently, the method serves to determine the fill level in the pipe independently of conductivity or fluid. Furthermore, the method according to the invention requires a minimum of measuring electrodes or grounding electrodes and can also be implemented in existing flow measurement systems. The method according to the invention allows, in particular by utilizing the aforementioned characteristics, an essentially continuous determination of the fill level. Compared to solutions known from the prior art, the limitation of these only allowing fill level determination in discrete steps, the fineness of which is determined by the number of measuring electrodes, is thus overcome. The method according to the invention therefore offers increased measurement accuracy with a reduced number of components, in particular measuring electrodes.

[0010] According to the invention, the method can be further used in a fifth step by the first and / or second measuring electrode to measure a flow in the pipe by detecting the voltages induced by magnetic fields in the fluid. The detection of the induced voltages represents the measuring operation that can be carried out as intended with a flow measuring system. The fifth step can be carried out at any stage of the claimed method. Furthermore, the fifth step can be carried out at least partially simultaneously with one of the steps outlined above or below. Likewise, the magnetic fields, and thus the induced voltages, which are detected in the fifth step can have a different frequency or signal coding than the measuring currents according to the second and / or third step. The measured values ​​according to the fifth step can thus be clearly distinguished during evaluation.This allows the claimed method to be combined with the intended measurement operation. The claimed method increases the functional versatility of a flow measurement system accordingly. Furthermore, the fill level determined in the fourth step can be used as a correction value when measuring the flow. The claimed method thus offers increased accuracy in flow measurement.

[0011] In one embodiment of the claimed method, in the fourth step, a first impedance present in the fluid is determined based on the first measured value. Alternatively or additionally, in the fourth step, a second impedance present in the fluid is determined based on the second measured value. The first or second impedance can be determined based on the voltage present at the corresponding measuring electrode and the current intensity of the respective measuring current. Suitable measuring devices for this purpose offer increased measuring accuracy. Furthermore, flow measuring systems on which the claimed method can be carried out are already equipped with suitable measuring devices on their measuring electrodes. The claimed method thus utilizes existing components of the flow measuring system and is therefore cost-effective.Depending on the fill level of the pipe, the first and second impedances exhibit distinguishable characteristics, whose curves scale with the conductivity present in the fluid. The first and second impedances represent a reference value for each other. Regardless of the conductivity of the fluid, the curves of the corresponding characteristics have a qualitatively identical relative position to each other in a corresponding diagram. The claimed method therefore uses an easily detectable electrical property of the fluid to determine the fill level. Furthermore, corresponding characteristics can be interpolated, so that any value for the first or second impedance can be precisely evaluated. This increases measurement accuracy.

[0012] Furthermore, the claimed method can comprise a sixth step in which a measured value is recorded at the first grounding electrode and / or a second grounding electrode to detect a drop in the fill level. As the fill level drops, one of the grounding electrodes is exposed so that it is no longer wetted with fluid. The recorded measured value relates to an electrical quantity, for example a grounding current strength, which essentially becomes zero as a result of the drop. The corresponding grounding electrode can be positioned in the region of an apex of the pipe, i.e., the pipe cross-section. Correspondingly, a change in a measured value recorded at the other grounding electrode can be recorded simultaneously. The corresponding grounding electrode can, for example, be positioned in the region of a low point of the pipe, i.e., the pipe cross-section.In particular, the first grounding electrode can be mounted near the lowest point of the pipe, and the second grounding electrode near the highest point of the pipe. In particular, by positioning a measuring electrode at the highest point, a drop in the fill level below 100 percent can be reliably detected. As long as the fill level is essentially 100 percent, an evaluation of further characteristics is unnecessary, thus saving computational effort. This, in turn, allows for the saving of electrical energy, particularly if the flow measurement system has a battery-operated evaluation unit. Furthermore, the measuring electrodes and the at least one grounding electrode can be arranged in a plane along the pipe or one behind the other.

[0013] Furthermore, the measuring currents excited in the second and / or third step can be essentially the same in magnitude. This implements the principle of symmetrical excitation. Likewise, the first and second measuring electrodes can be arranged opposite each other on the pipe, i.e., at a maximum distance from each other. With measuring currents of equal magnitude, a symmetrical distribution of electrical current densities is achieved in the fluid, which can be easily determined using the first and / or second measured value. In particular, the first grounding electrode can be attached to the pipe near a low point relative to the fluid level. With measuring currents of equal magnitude in the second step, the measured value at the first grounding electrode is essentially zero. Furthermore, a second grounding electrode can be attached to an apex of the pipe opposite the first grounding electrode.In the second step, the ground current at the second ground electrode at the apex of the pipe is also essentially zero when the measuring currents are essentially the same. In the third step, the ground current at the first and second ground electrode is essentially the same when the measuring currents at the first and second measuring electrodes are wetted by the fluid. For a corresponding fill level, in particular a 100 percent fill level, a defined state results which is expressed in the first and second measured values ​​recorded in the second and third steps. For fill levels where one of the ground electrodes is exposed, the same electrical quantities are present at the first and second measuring electrodes in the second and third steps.In particular, the first measured values ​​at the first and second measuring electrodes depend solely on the conductivity of the fluid, i.e., the impedance present in the fluid. Furthermore, with symmetrical excitation, identical second measured values ​​are available in the third step in the first and, if applicable, second measuring electrode. The claimed method is thus capable of automatically detecting an eigenstate in which measurement can be carried out with increased accuracy. Consequently, the claimed method is robust against interference. Correspondingly, in the event of deviations between the first measured values ​​at the measuring electrodes and / or between the second measured values ​​at the measuring electrodes, contamination of one of the measuring electrodes or misalignment of the flow measuring system can be detected. A corresponding warning can be issued.

[0014] Furthermore, in the second step, an asymmetry between the first and second measuring electrodes can be detected based on first measured values. An asymmetry in the first measured values ​​expresses an asymmetry in the existing current density distribution with respect to an axis of symmetry between the first and second measuring electrodes, which asymmetry can thus be detected using the first measured values ​​at the first and second measuring electrodes. Such an asymmetry can be caused, for example, by contamination on the first and / or second measuring electrode. Alternatively, such an asymmetry can be caused by a tilt of the pipe, i.e. an angular offset around a pipe axis along which the pipe extends.

[0015] During the third step, an asymmetry can be detected between the second measured values ​​at the first and second measuring electrode, which is caused by an asymmetry of the current density present in the pipe cross-section. This can also be used to detect contamination of the first and / or second measuring electrode, or a tilt of the pipe. An asymmetry can also be detected between the measured values ​​recorded at the first and second grounding electrode. For example, a grounding electrode located near a low point in the pipe may be covered with sunken contamination. In normal operating conditions, however, the first and second measured values ​​from the second and third steps respectively reflect the electrical conductivity of the fluid in the pipe.In the case of contamination, however, the characteristic curves of the electrical conductivity under common-mode and differential-mode excitation differ from the intended state. By comparing the asymmetries determined in the second and third steps, different types of contamination on the pipe wall or inclinations of the pipe can be automatically distinguished. Furthermore, reduced asymmetries in the measured values ​​at a grounding electrode in the region of the low point of the pipe and a grounding electrode in the region of an apex of the pipe cross-section can indicate regionally different electrical conductivities of the fluid. This can, for example, detect a separation of the fluid into differently conductive components, which are at least partially layered in the pipe cross-section when separated. This also provides an additional diagnostic option through the claimed method.

[0016] Furthermore, in a further seventh step of the method, measuring currents can be excited that are unequal in magnitude. This implements the principle of asymmetric excitation. Corresponding to the second or third step, in the seventh step at least one comparison measured value is recorded at the first and / or second measuring electrode. In particular, at least one of the measuring currents in the seventh step can be substantially equal to zero. When the fill level drops, at which the second grounding electrode is exposed, a decrease in a measured value, in particular the grounding current strength, at the second grounding electrode can be recorded and, at the same time, an increase in a measured value, in particular the grounding current strength, at the first grounding electrode can be recorded. Likewise, a change in the at least one comparison measured value at the first and / or second measuring electrode can be recorded simultaneously.In particular, in the seventh step, a measuring current of essentially zero can be applied alternately to the first and second measuring electrodes. Correspondingly, a measuring current other than zero is applied to the other measuring electrode. This allows for further plausibility checks of the fill level determined in the fourth step.

[0017] Furthermore, the asymmetric excitation in the second pass of the method can be combined with the symmetric excitation in the first pass. In the claimed method, a deviation can also be detected between the fill levels determined in the fourth and seventh steps. This deviation can be caused by contamination of one of the measuring electrodes or a misalignment of the measuring electrodes and / or at least one grounding electrode. A corresponding warning can also be issued. The warning function thus implemented further increases the versatility of a flow measuring system on which the method is carried out. Alternatively or additionally, an asymmetric arrangement of the first and second measuring electrodes can also be detected and / or compensated for in the case of asymmetric excitation. The claimed method can therefore also be carried out with measuring electrodes in any arrangement on the pipe, including asymmetric arrangements.Consequently, the claimed method can be retrofitted to a wide range of flow measurement systems.

[0018] In a further embodiment of the claimed method, an expected value for the comparison measured value acquired in the seventh step can be determined in an eighth step. In particular, the measuring currents in the seventh step can be configured such that they each correspond to a superposition of the measuring currents from the second and third steps. Accordingly, in the eighth step, superpositions of the first and second measured values ​​are determined that correspond to the respective measuring currents. A superposition of a first and a second measured value from a corresponding second and third step forms the expected value for the comparison measured value acquired in the seventh step. In the eighth step, the comparison measured value is compared with the expected value. If a deviation between the comparison measured value and the expected value exceeds an adjustable tolerance value, an improper operating state of the flow measuring system is detected.Accordingly, a warning can be issued. The invention is based, among other things, on the surprising discovery that the symmetrical excitation and the asymmetrical excitation are linked via the superposition principle. The claimed method can thus be reliably and automatically tested for its functionality.

[0019] The method can further comprise a ninth step in which a temporal gradient of a drop and / or rise in the fill level is recorded. Alternatively or additionally, a duration between the drop and rise in the fill level can also be recorded in the ninth step. The drop or rise in the fill level can be carried out using one of the methods outlined above. Furthermore, in the ninth step, the presence of a multi-phase flow is detected based on the recorded temporal gradient and / or the recorded duration. In a multi-phase flow, the fluid comprises a first component and a second component which has a lower electrical conductivity than the first component. The first component can be water, for example, and the second component air or oil, and thus represent a foreign phase to the first component.If a foreign phase, for example a bubble or a drop, flows along a pipe wall at the first or second grounding electrode, this is detected as a drop in the fill level, as outlined in the second, third or sixth step. If the foreign phase passes the first or second grounding electrode, this is analogously detected as a rise in the fill level. In the ninth step, a temporal gradient is determined for the drop and / or rise in the fill level. The temporal gradient can be compared with an adjustable multi-phase tolerance value. If the temporal gradient exceeds the multi-phase tolerance value in terms of magnitude, the passing of a foreign phase in the pipe and thus the presence of multiphase flow is detected. The foreign phase can be in the form of a gas phase or a drop, for example an oil drop.Alternatively or additionally, the duration for which the fill level is temporarily reduced can be determined in the ninth step and compared with an adjustable multiphase limit value. If the determined duration falls below the multiphase limit value, the passage of a foreign phase in the fluid, and thus the presence of multiphase flow, is detected. Furthermore, the ninth step can be used to determine whether the reduced fill level returns to the previous level. This makes it possible to verify the detection of multiphase flow in the pipe. In the ninth step, for example, plug flow or slug flow can be detected. Furthermore, a warning is issued to a user or a data interface in the ninth step. The claimed method is thus suitable for detecting multiphase flow during measurement operation of a flow measuring system and is therefore functionally versatile.

[0020] Furthermore, the method can comprise a tenth step in which a difference between measured values ​​from the first and second grounding electrodes is recorded. These can in particular be measured values ​​from essentially synchronously output measuring currents. If a bubble or a drop of the second component flows eccentrically past the measuring electrodes in the pipe, the foreign phase represents a constriction of an electrically conductive region in the fluid. In particular during the third step, a current flow of the measuring current to the first or second grounding electrode is inhibited. Consequently, a difference can be recorded between measured values ​​recorded at the first and second grounding electrodes in the tenth step. If the amount of the recorded difference exceeds a multiphase threshold, the presence of a multiphase flow in the pipe is detected in the tenth step.If multiphase flow is present, a warning is issued to a user or a data interface in the tenth step. In particular, so-called bubbly flow can be detected in this way. The functional versatility of the claimed method is thus further increased.

[0021] Alternatively or additionally, the position of the extraneous phase can be detected in the tenth step. For this purpose, the second measured values ​​detected in the third step, i.e. a common-mode excitation, can be evaluated together with at least one measured value at the first and / or second grounding electrode. For this purpose, the first and / or second grounding electrode are connected to non-grounding in the tenth step and are provided with suitable switching means that can be actuated by the evaluation unit. In particular, it can be detected at which of the measuring electrodes and at least one grounding electrode the greatest change in the corresponding measured value occurs, which indicates a decrease in electrical conductivity in the area of ​​the corresponding measuring electrode or grounding electrode. In particular, an existing electrical voltage can be detected at the corresponding measuring electrode or grounding electrode.The position of the extraneous phase is identified as a sector in the pipe cross-section that is closest to the corresponding measuring electrode or grounding electrode. In the tenth step, the position of the extraneous phase can thus be identified based on second measured values ​​and at least one measured value from the first and / or second grounding electrode.

[0022] Furthermore, alternatively or additionally, the first measured values ​​at the measuring electrodes, which are caused by a differential mode excitation, such as in the second step, can also be evaluated in the tenth step. These are evaluated together with at least one measured value at the first and / or second grounding electrode. For this purpose, the first and / or second grounding electrodes are switched to non-grounding in the tenth step and are provided with suitable switching means that can be actuated by the evaluation unit. This makes it possible to identify the position of the extraneous phase along a connecting line between the first and second measuring electrodes. Based on the first measured values ​​at the first and second measuring electrodes, it is possible to identify whether an extraneous phase is located in the region of the connecting line. If an extraneous phase is present in the region of the connecting line, for example, a voltage recorded at the first and second measuring electrode increases.Furthermore, depending on the sign of the at least one measured value at the first and / or second grounding electrode, it is possible to determine whether the extraneous phase is located closer to the first measuring electrode, the second measuring electrode, or in a central region of the connecting line. Accordingly, in the tenth step, the position of the extraneous phase can be determined by evaluating the first measured values ​​and the sign of the at least one measured value at the first and / or second grounding electrode. The detected position of the extraneous phase can be output to a user and / or a data interface.

[0023] The evaluations of the first measured values ​​and the second measured values ​​from the second and third steps, respectively, in conjunction with the measured values ​​from non-grounded grounding electrodes, can also be compared to verify the plausibility of detected extraneous phases, and thus of existing multiphase flows. This enables reliable detection of multiphase flows, especially slug and plug flows.

[0024] Furthermore, in a substantially horizontally aligned pipe, the material of which the foreign phase consists can be determined by detecting the position of the foreign phase. For example, in a fluid that has a liquid as its first component, a foreign phase predominantly present in a region of the apex of the pipe cross-section is typically a gas or a liquid with a lower density than the first component. Liquids or solids, i.e. particles, with a higher density than the first component of the fluid, on the other hand, typically flow along in the region of a low point of the pipe cross-section. Consequently, the claimed method allows a more detailed characterization of the multiphase flow to be carried out automatically. In the tenth step, information about the foreign phase of the multiphase flow can thus be output to a user and / or a data interface.

[0025] In a further embodiment of the claimed method, signal noise is detected for the first and / or second measured values. Based on the signal noise, the fill level in the pipe can be determined essentially continuously. The invention is based, among other things, on the surprising finding that there is an analyzable relationship between the fill level in the pipe and the signal noise. For this purpose, characteristic curves determined, for example, by calibration runs of the flow measuring system can be used in the claimed method. The fill level can thus be additionally determined by evaluating the signal noise. This allows a plausibility check of the fill level determined, for example, in the fourth step. Furthermore, the pipe can be equipped with an annular first grounding electrode. The claimed method is therefore applicable to a wider range of flow measuring systems.

[0026] Furthermore, the second step and the third step can be carried out at least partially simultaneously. For at least partially simultaneous implementation of the so-called common-mode excitation and differential-mode excitation in the second and third steps, respectively, the respective measuring currents can be excited at different frequencies. The measuring currents can be designed as alternating currents with an adjustable frequency. For easy differentiation, there can be an adjustable frequency difference between the frequencies of the measuring currents in the second and third steps. The claimed method can thus be carried out in a time-saving manner and integrated into the measuring operation of a corresponding flow measuring system. Likewise, first and second measured values ​​with essentially the same time stamp can be generated in the second and third steps. Inaccuracies due to time offsets between the second and third steps can thus be avoided.Overall, this ensures reliable determination of the fill level.

[0027] The underlying problem is also solved by an evaluation unit according to the invention. The evaluation unit is designed to determine the fill level of a pipe. The evaluation unit is also designed to receive and process measurement signals from measuring devices that can be coupled to the evaluation unit. The measuring devices include a first measuring electrode, a second measuring electrode, and a first grounding electrode, which can be coupled to the evaluation unit separately or in combination. The measurement signals correspond to the measured values ​​outlined above from the measuring electrodes and / or the grounding electrodes. The at least one grounding electrode serves, among other things, to ground the fluid so that, for example, a current flow can occur in the fluid upon common-mode excitation.For the flow measurement according to the fifth step, at least one grounding electrode is used to reduce interference and limit common-mode signals. In particular, at least one of the grounding electrodes can be designed for frequency-dependent grounding, so that, for example, grounding exists for the measurement in the fifth step, but for example, for the measurement according to the third step, one of two grounding electrodes cannot divert any measuring current. The first measuring electrode, the second measuring electrode, and the first grounding electrode can be attached to an inner side of the wall of a pipe in which the fill level is to be determined, such that they are wetted by a fluid. According to the invention, the evaluation unit is designed to carry out at least one embodiment of the method described above.The features of the claimed method described above therefore also apply analogously to the claimed evaluation unit and are readily transferable to it. The evaluation unit can be equipped with a computer program product designed to carry out a corresponding method. Alternatively or additionally, the evaluation unit can be equipped with a chip, microcontroller, or FPGA, each of which can be used to implement the claimed method. The claimed method can essentially be implemented by an evaluation unit according to the invention on existing measuring electrodes or grounding electrodes, for example, during a retrofit.

[0028] Likewise, the problem outlined at the outset is solved by a flow measuring system according to the invention, which comprises a first measuring electrode, a second measuring electrode, and a first grounding electrode. The first measuring electrode, the second measuring electrode, and the first grounding electrode are coupled to an evaluation unit, which is also part of the flow measuring system. The evaluation unit is designed to determine a fill level in a pipe, to which the first measuring electrode, the second measuring electrode, and the first grounding electrode are connected when the flow measuring system is in the assembled state. According to the invention, the evaluation unit of the flow measuring system is designed according to one of the embodiments outlined above. The features of the claimed evaluation unit and the claimed method are therefore also transferable to the flow measuring system according to the invention.Overall, the flow measuring system according to the invention is compact and offers a wide range of functions by measuring the flow through the pipe and determining the fill level therein. The first and second measuring electrodes can be arranged symmetrically, i.e. essentially opposite one another on a diameter line in a circular cross-section of the pipe. Alternatively, the first and second measuring electrodes can also be arranged asymmetrically on the pipe, i.e. essentially on a secant in the cross-section of the pipe. Furthermore, the measuring electrodes and / or the at least one grounding electrode can each be designed as capacitively coupled electrodes. An insulating layer is provided on the measuring electrodes or the at least one grounding electrode, which insulates them from the fluid.Furthermore, in the first and / or second step, the measuring currents can be excited at adjustable frequencies, allowing the dielectric properties of the fluid to be determined. Furthermore, the claimed method can also use measurement signals to determine frequency-dependent electrical or dielectric properties of the fluid. This allows for further refinement of the flow measurement.

[0029] Furthermore, the underlying problem is solved by a computer program product according to the invention, which is designed to simulate the operating behavior of a flow measuring system mounted on a pipe in a measuring section. According to the invention, the computer program product has a digital image of at least the measuring section, which includes a first measuring electrode mounted there, a second measuring electrode, and a first grounding electrode. The first measuring electrode, the second measuring electrode, and the grounding electrode thus belong to the flow measuring system to be simulated. According to the invention, the flow measuring system is designed according to one of the embodiments described above. The features of the claimed flow measuring system, the claimed evaluation unit, and the claimed method are thus transferable to the computer program product according to the invention.The computer program product may include instructions that cause a computer executing the computer program product to simulate the operating behavior of the corresponding flow measurement system. In particular, the operating behavior of the flow measurement system can be simulated using the computer program product while an embodiment of the claimed method is being performed thereon. The claimed method can be performed on the underlying real, i.e., physically existing, flow measurement system and / or simulated on the digital flow measurement system, i.e., simulated using the claimed computer program product.

[0030] The computer program product can have a physics module for simulation purposes, in which the flow measurement system is at least partially mapped. For this purpose, the flow measurement system can be simulated, for example, in its structure and functionality, particularly in the digital image that is part of the computer program product. Alternatively or additionally, the flow measurement system can also be implemented as a computer model in the physics module. The physics module can be designed to simulate, among other things, the thermal or flow-dynamic behavior of the fluid and the resulting measurement behavior of the flow measurement system under adjustable operating conditions.The adjustable operating conditions include, for example, a flow velocity, a temperature of the fluid, an electrical conductivity of the fluid and / or the pipe wall, an electrical current flow distribution in the fluid, a phase specification of the fluid, a thermal conductivity and / or electrical conductivity of a gas or vapor phase in the fluid, a delivery pressure in the fluid, and / or a viscosity of the fluid. The computer program product can have a data interface via which corresponding data can be specified via a user input and / or other simulation-oriented computer programs. Likewise, the computer program product can have a data interface for outputting simulation results to a user and / or other simulation-oriented computer program products.Using the computer program product, for example, a defective measuring electrode or grounding electrode, insulating contamination of a measuring or grounding electrode, and / or an improper installation position of a measuring or grounding electrode can be detected. In particular, the operating behavior of the flow measuring system, expressed by measurement signals at the first and / or second measuring electrode, can be checked for plausibility by comparing it with the simulated flow measuring system. Furthermore, the flow measuring system can be easily modeled, i.e., its operating behavior can be recalculated with a minimum of CFD calculations. In particular, the flow behavior in the pipe can be approximated with sufficient precision through algebraic calculation. The computer program product according to the invention thus allows modeling of the underlying flow measuring system with reduced computing power requirements.This also makes it possible to simulate a large number of such flow measurement systems, for example, in a higher-level control unit of an automation system. This makes it easy to provide a particularly realistic process image of the operation of a corresponding automation system. The computer program product can be designed as a so-called digital twin, as described, for example, in the publication.

[0031] US 2017 / 286572 A1. The computer program product can be monolithic, i.e., executable entirely on a single hardware platform. Alternatively, the computer program product can be modular and comprise a plurality of subprograms that are executable on separate hardware platforms and interact via a communicative data connection. Such a communicative data connection can be a network connection, an internet connection, and / or a mobile phone connection. Furthermore, the computer program product according to the invention can be used to test and / or optimize a flow measurement system via simulation.

[0032] The object is also achieved by a monitoring method according to the invention for a flow measuring system. The monitoring method serves to monitor the operation of a flow measuring system. The monitoring method comprises a first step in which the flow measuring system is provided in an active operating state. Likewise, in the first step, at least one measured value is provided which results at the first and / or second measuring electrode as a result of a fluid flow in the pipe to which the flow measuring system is attached. Likewise, at least one operating variable is recorded and provided which predetermines the current operating state of the flow measuring system. The method further comprises a second step in which the at least one operating variable is provided as input to a computer program product.Based on the provided operating variable, the computer program product determines a target measured value in a second step, which corresponds to the measured value provided in the first step. The method comprises a third step in which the target measured value and the measured value are compared. If the difference between the measured value and the target measured value exceeds an adjustable threshold, a warning is issued to a user and / or an evaluation unit of the flow measuring system. In addition, in a fourth step, a cause for the difference between the measured value and the target measured value can be identified using a recognition algorithm based on the target measured value and the measured value. The recognition algorithm can, for example, be designed as a neural network.According to the invention, the computer program product used in the second step is designed according to one of the embodiments described above. Each of the steps of the claimed monitoring method can be executed on different hardware platforms, regardless of location. Intermediate results of individual steps can be exchanged between the hardware platforms via a communicative data connection, for example, via a network connection, an internet connection, or a radio connection, in particular a mobile radio connection.

[0033] The invention is explained in more detail below with reference to individual embodiments in the figures. The figures are to be read as complementary to one another insofar as identical reference numerals in different figures have the same technical meaning. The features of the individual embodiments can also be combined with one another. Furthermore, the features outlined above can also be combined with the features of the embodiments shown in the figures. They show in detail: FIG 1 schematically shows a first embodiment of the claimed method in a first stage in cross-section; FIG 2 schematically shows the first embodiment of the claimed method in a second stage in cross-section; FIG 3 schematically shows a second embodiment of the claimed method in a first stage in cross-section; FIG 4 schematically shows the second embodiment of the claimed method in a second stage in cross-section; FIG 5 schematically shows a fourth step of the claimed method according to the first or second embodiment in a diagram; FIG 6 schematically shows a third embodiment of the claimed method in a first stage in cross-section; FIG 7 schematically shows the third embodiment of the claimed method in a second stage in cross-section; FIG 8 schematically shows a fourth embodiment of the claimed method in a third stage.FIG 9 schematically shows a fifth embodiment of the claimed method in a fourth stage in cross-section. ;

[0034] In FIG 1 A first embodiment of the claimed method 100 is shown in a first stage in cross-section, which belongs to a first passage 52 of the method 100. The method 100 serves to determine a fill level 18 in a pipe 10, which has a wall 12 in which a fluid 15 is accommodated, which flows through the pipe 10. The fill level 18 according to FIG 1 is maximum, i.e. 100 percent. The flow in pipe 10 causes a flow 13, which is FIG 1 is symbolized as a filled arrow. The method 100 is carried out on a flow measuring system 60, which has measuring electrodes 20 positioned opposite one another on the wall 12. The measuring electrodes 20 can be controlled via an evaluation unit 40. The measuring electrodes 20 are attached to the wall 12 of the pipe 10 in such a way that they can be wetted by the fluid 15. A first and a second measuring electrode 22, 24 are positioned essentially horizontally opposite one another. Furthermore, the measuring electrodes 20 can be controlled such that adjustable measuring currents 25 can be excited thereat. The flow measuring system 60 further comprises grounding electrodes 30, which are arranged on the wall 12 of the pipe 10 so that they can be wetted by the fluid 15. The grounding electrodes are arranged opposite one another, with a first grounding electrode 32 positioned at a low point of the pipe 10 and a second grounding electrode 34 positioned at an apex of the pipe 10.Both the measuring electrodes 20 and the grounding electrodes 30 are each provided with measuring devices 21, each designed to detect at least one electrical variable. The measuring devices 21 are each coupled to the evaluation unit 40, which is also part of the flow measuring system 60. The method 100 is based on an initial situation in which the pipe 10 is provided in a state at least partially filled with the fluid 15, thus completing a first method step 110. The fluid 15 has an electrical conductivity 17, so that impedances 45 for the measuring currents 25 result from the amount of fluid 15 present in the pipe 10, i.e., the fill level 18.

[0035] The method 100 further comprises a second step 120 in which the first and second measuring electrodes 22, 24 are excited, thereby generating opposing measuring currents 25. The opposing measuring currents 25 are of equal magnitude and implement the principle of a so-called push-pull excitation. Furthermore, in the second step 120 of the method 100, a first measured value 26 is recorded at each of the first and second measuring electrodes 22, 24. The first measured values ​​26 are transmitted to the evaluation unit 40. The evaluation unit 40 has a computing unit 42 and a control unit 44, which are designed to execute a computer program product 50 by which at least the first measured values ​​26 can be evaluated. For the push-pull excitation, as in FIG 1 As shown, an impedance 45 for the fluid 15 results, which can be determined via the first measured values ​​26. The evaluation unit 40 is further coupled to a display unit 46, via which determined results, in particular determined fill levels 18, can be output to a user. The evaluation unit 40 is likewise connected to a data interface 48, via which determined results, in particular determined fill levels 18, can be forwarded, for example to a higher-level control unit (not shown). At least partially simultaneously or staggered in time to the second step 120, a fifth step 195 is carried out in the method 100, in which voltages 29 induced by magnetic fields are detected via the first measuring electrode 22, by means of which the flow rate 13, i.e. the amount of fluid 15 flowing through per unit of time, can be determined. The fifth step 195 belongs to a measuring operation, to which the method 100 can be carried out concurrently.The flow rate 13 is also determined by the evaluation unit 40. FIG 1 shows a cross-sectional view of a measuring section along pipe 10, which is depicted in a digital image belonging to a computer program product 80 designed to simulate the operating behavior of flow measurement system 60. For this purpose, computer program product 80 is designed as a digital twin.

[0036] The first embodiment of the claimed method 100 is shown in FIG 2 in a second stage, which is based on the FIG 1 shown first stage follows and still belongs to the first pass 52 of the method 100. There is still a maximum fill level 18 in the pipe 10, i.e. 100 percent. In the second stage, a third step 130 takes place in which measuring currents 25 are excited in the same direction, so that a current flows from the first and second measuring electrodes 22, 24 to the first and second grounding electrodes 32, 34. The measuring currents 25 excited by the first and second measuring electrodes 22, 24 are of equal magnitude. This results in symmetrical current flow lines 16 in the cross-section of the pipe 12 with respect to a connecting line 19 between the first and second grounding electrodes 32, 34. The excitation of the first and second measuring electrodes 22, 24 in the third step 130 implements the principle of so-called common-mode excitation.During the third step 130, second measured values ​​28 are recorded via the measuring devices 21 at the first and second measuring electrodes 22, 24 and forwarded to the evaluation unit 40. For the measuring currents 25 that are excited in the third step 130, impedances 45 of the fluid 15 can be determined based on the second measured values ​​28. Furthermore, in the third step 130, a grounding current strength can be recorded as a measured value 35 via the measuring devices 21 at the grounding electrodes 30, which is forwarded to the evaluation unit 40. Due to the maximum fill level 18, as shown in . FIG 1 and FIG 2 As shown, the first and second grounding electrodes 32, 34 are wetted by the fluid 15. The presence of the maximum fill level 18 can thus be determined by the measured values ​​35 from the first and second grounding electrodes 32, 34. The determination of the maximum fill level 18 based on the measured values ​​35 from the grounding electrodes 30 takes place alongside a determination of the fill level 18 in a fourth step 140 of the method 100. In the fourth step 140, the fill level 18 is determined based on the first measured values ​​26 and second measured values ​​28 determined in the second and third steps 120, 130 via the first and second measuring electrodes 22, 24. The first and second measured values ​​26, 28 from the second and third steps 120, 130, respectively, result in an essentially continuous characteristic that allows a continuous determination of the fill level 18.For this purpose, the first and second measured values ​​26, 28 from the second and third steps 120, 130 are evaluated in the evaluation unit 40 using the computer program product 50 executed therein. The fourth step 140 is described below in . FIG 5 presented in more detail. The FIG 2 The steps shown can be reproduced via the computer program product 80 designed as a digital twin, which is designed to simulate the operating behavior of the flow measuring system 60.

[0037] A second embodiment of the claimed method 100 is shown in FIG 3 in a first stage belonging to a first pass 52 of the method 100. The method 100 is carried out on a flow measuring system 60 which is similar in structure to the flow measuring system 60 according to FIG 1 and FIG 2 The descriptions for the structure from FIG 1 and FIG 2 apply to FIG 3 therefore analogous. In FIG 3 a first step 110 of the method 100 is completed, in which the tube 10 is provided in a state at least partially filled with fluid 15.

[0038] In the first stage of the procedure 100 under FIG 3 there is a reduced fill level 18 which is below 100 percent. Furthermore, in the method 100, a second step 120 is carried out in which opposing measuring currents 25 which are of equal magnitude are excited at the first and second measuring electrodes 22, 24. The opposing excited measuring currents 25 cause a current to flow from the first measuring electrode 22 to the second measuring electrode 24, and the principle of push-pull excitation is implemented. The measuring currents 25 pass through the cross-section of the pipe 10, with the fluid 15 serving as an electrical conductor. Due to the reduced fill level 18, a reduced conductor cross-section is therefore available between the first and second measuring electrodes 22, 24. Furthermore, in the second step 120, first measured values ​​26 are recorded at the first and second measuring electrodes 22, 24. The first measured values ​​26 are characteristic of the impedances 45 present in the fluid 15 during push-pull excitation.Accordingly, first measured values ​​26 from the second step 120 are according to . FIG 3 and FIG 1 distinguishable. This results in an essentially continuous characteristic for different fill levels 18. The first measured values ​​26 are forwarded to the evaluation unit 40 in the second step 120.

[0039] Furthermore, at the apex of the wall 12 of the tube 10, in the area of ​​the second grounding electrode 34, a gas phase 11 is present due to the reduced fill level 18. The second grounding electrode 34 is separated from the fluid 15 by the gas phase 11. Furthermore, in the first stage, FIG 3 a fifth step 195 of the method 100, in which voltages 29 induced by magnetic fields are measured at the first measuring electrode 22 to detect the flow 13 in the pipe 10. The fifth step 195 is also carried out at least partially simultaneously with the second step 120 or with a time delay therefrom. The method 100 is thus integrated into the measuring operation of the flow measuring system 60. The FIG 3 The steps outlined can be reproduced by the computer program product 80 designed as a digital twin, which is designed to simulate the operating behavior of the flow measuring system 60.

[0040] The second embodiment of the claimed method 100 is shown in FIG 4 shown in a second stage, which follows the first stage according to FIG 3 and also belongs to the first pass 52 of the process 100. The fill level 18 according to FIG 4 corresponds to the reduced filling level 18 as in FIG 3 The structure of the flow measurement system 60 in FIG 4 corresponds to the structure of FIG 3 In the second stage of the method 100, a third step 130 is carried out in which measuring currents 25 are excited in the same direction at the first and second measuring electrodes 22, 24, which are of equal magnitude. In the third step 130, a current essentially flows from the first and second measuring electrodes 22, 24 to the first ground electrode 32 through the gas phase 11 at the apex of the tube 10, i.e., at the second ground electrode 34. Accordingly, current flow lines 16 are present in a correspondingly dense manner between the measuring electrodes 20 and the first ground electrode 32. Due to the reduced fill level 18, a reduced conductor cross-section in the form of the fluid 15 exists between the measuring electrodes 20 and the first ground electrode 32. Accordingly, for reduced fill levels 18, a substantially continuous characteristic of the impedances 45 in the fluid 15 results.These impedances 45 can be determined via second measured values ​​28, which can be detected at the first and second measuring electrodes 22, 24. The second measured values ​​130 are detected in the third step 130 and forwarded to the evaluation unit 40. The first measured values ​​26 from the second step 120, as shown in . FIG 3 shown, and the second measured values ​​28 from the third step 130 can be evaluated in a fourth step 140. In particular, in the fourth step 140, the current fill level 18 is determined based on the first and second measured values ​​26, 28. For this purpose, the evaluation unit 40 is equipped with the computer program product 50 executed thereon. The fourth step 140 is described below in FIG 5 shown in more detail.

[0041] Furthermore, a sixth step 150 is carried out in which the drop 36 in the fill level 18 is detected. In this step, at least one measured value 35 is recorded at the first and / or second grounding electrode 32, 34. Due to the drop 36 in the fill level 18, the second grounding electrode 34, which is arranged in the region of an apex of the pipe 10, is no longer wetted. As a result of the drop 36 in the fill level 18, the density of streamlines 16 in the region of the first grounding electrode 32, which is arranged in the region of the lowest point of the pipe 10, is also increased. A measured value 35 recorded at the first grounding electrode 32 also shows a significant change due to the drop 36 in the fill level 18, which indicates the drop 36 in the fill level 18. FIG 3 The steps outlined can be reproduced by the computer program product 80 designed as a digital twin, which is designed to simulate the operating behavior of the flow measuring system 60.

[0042] FIG 5 shows in a diagram 70 a fourth step 140 of the claimed method 100, which, for example, in the embodiments according to FIG 1 , FIG 2 , FIG 3 or FIG 4 is feasible. The fourth step 140 is carried out in the first pass 52 of the method 100 and serves to determine a fill level 18 present in the pipe 10 based on first and second measured values ​​26, 28, which are recorded in the second and third steps 120, 130, respectively. To do this, the fourth step 140 uses the relationships shown in the diagram 70. The diagram 70 has a horizontal fill level axis 72, which indicates an increasing fill level 18 from left to right. The diagram 70 also includes a vertical impedance axis 74. The diagram 70 has two characteristic curves 73, each of which represents a relationship between the fill level 18 and an existing impedance 45. The characteristic curves 73 are limited on the left by a minimum detectable fill level 18 and on the right by a maximum detectable fill level 18. The minimum and maximum detectable fill levels 18 can be 0 or 100 percent, depending on the position of the electrodes.The characteristic curve 73 used in the third step 130 has a step-like decrease in the area of ​​the maximum detectable fill level 18, which occurs because a second grounding electrode 34 is wetted at an apex of the pipe 12. The characteristic curves 73 in the diagram 70 can each be provided by calculation, simulation or measurement. The characteristic curves 73 each form characteristics which describe a relationship between the determined impedance 45 and the fill level 18 for differential mode excitation or common mode excitation in the second or third step 120, 130 of the method 100. The position of the characteristic curves 73 along the impedance axis 74 depends on the conductivity 17 present in the fluid 15. However, the relative position of the characteristic curves 73 to one another is the same. This results in a sliding coupling 75 related to the conductivity 17 of the fluid 15, which is shown in . FIG 5 symbolized by a double arrow. To determine the fill level 18, the respective impedances 45 are determined based on the first and second measured values ​​26, 28 from the second and third steps 120, 130, and an impedance ratio 76 is determined. The impedance ratio 76, in turn, is characteristic of up to two positions along the characteristic curves 73. One of these positions represents the current fill level 18, and the other position a hypothetical fill level 79. The hypothetical fill level 79 is theoretically possible, but not plausible. Based on a known historical value 77 for the fill level 18, it can be determined that a slow downward trend 78 is more realistic than a sudden drop to the hypothetical fill level 79.In the fourth step 140, if two computationally possible fill levels are present, i.e., the actual fill level 18 and the hypothetical fill level 79, the one that is closer to the known historical fill level 77 is recognized as the actual fill level 18. A repetition rate at which the method 100 is performed can be adjusted such that the comparison with the known historical value 77 allows a plausible distinction. Overall, the fourth step 140 allows for a substantially continuous detection of the fill level 18 of fluid 15 in the pipe 10, independent of the electrical conductivity 17 present in the fluid 15. The fourth step 140 is performed by means of the evaluation unit 40 of the flow measurement system 60 (not shown in detail), for example, by the computer program product 50 executed in the evaluation unit 40.

[0043] FIG 6 shows a third embodiment of the claimed method 100 in a first stage in cross-section. The method 100 is carried out on a flow measuring system 60 which is similar in design to the flow measuring systems 60 according to FIG 1 bis FIG 4 The current fill level 18 is maximum, i.e. 100 percent. In the process 100 according to FIG 6 A sixth step 160 is carried out in which measuring currents 25 are excited at the first and second measuring electrodes 22, 24, which differ in magnitude. The sixth step 160 belongs to a second pass 54 of the method 100, which follows the first pass 52 according to, for example, FIG 1 bis FIG 4 This results in asymmetrically formed current density lines 16 in the fluid 15 relative to a connecting line 19 between the first and second grounding electrodes 32, 34. Likewise, in the seventh step 160, at least one comparison measured value 27 is recorded at the first and second measuring electrodes 22, 24, which is forwarded to the evaluation unit 40. Likewise, measured values ​​35 can be recorded at the first and second grounding electrodes 32, 34 and forwarded to the evaluation unit 40.

[0044] In the first stage, as in FIG 6 shown, a seventh step 170 is also carried out. In the eighth step 170, the first and second measured values ​​26, 28 from the second and third steps 120, 130, as in FIG 1 bis FIG 4 depicted, at least one expected value 33 is determined. The at least one expected value 33 is formed in the eighth step 170 by superposition. The measuring currents 25 excited in the seventh step 160 likewise correspond to a superposition of the corresponding measuring currents 25 from the first pass 52. The at least one comparison measured value 27 recorded in the seventh step 160 is thus compared with the corresponding expected value 33 in the eighth step 170. For this purpose, a difference is determined between the at least one comparison measured value 27 and the corresponding expected value 33 and compared with an adjustable tolerance value. If the determined difference exceeds the adjustable tolerance value in terms of amount, a warning is issued. If the difference is less than the adjustable tolerance value in terms of amount, a normal state of the flow measuring system 60 is recognized.The seventh step 160 and the eighth step 170 thus make it possible to detect an improper condition of the flow measurement system 60, which is integrated into its measuring operation. An improper condition can, for example, consist of a contaminated measuring electrode 20, a contaminated grounding electrode 30, or a misplaced mounting position of the latter. The functional spectrum of the method 100 is thus further enhanced by the asymmetric excitation. The operating behavior of the flow measurement system 60 can also be simulated by the computer program product 80, designed as a digital twin, and thus further monitored for improper conditions.

[0045] The third embodiment of the claimed method 100 is shown in FIG 7 in a second stage, which is similar to the FIG 6 The structure of the flow measurement system 60 in FIG 7 corresponds to that of the flow measuring system 60 from FIG 6 Compared to the first stage, the fill level 18 is reduced in the second stage, i.e., below 100 percent. In the second stage, which also belongs to the second pass 54 of the method 100, the sixth and seventh steps 160, 170 are carried out corresponding to the first stage according to FIG 6 The measuring currents 25 excited by the first and second measuring electrodes 22, 24 are of unequal magnitude, resulting in asymmetrically arranged current density lines 16. In the seventh and eighth steps 160, 170, the superposition principle can be used even with a reduced fill level 18 to verify the plausibility of the fill level 18 determined in the first pass 52 and / or to detect an abnormal condition of the flow measuring system 60. Likewise, the operating behavior of the flow measuring system 60 with a reduced fill level 18 and asymmetric excitation can be simulated in the computer program product 80 and further monitored for abnormal conditions.

[0046] A fourth embodiment of the claimed method 100 is shown in FIG 8 shown in a diagram 90. The fourth embodiment includes a ninth step 180, which is performed in a third stage of the method 100. The third stage may follow a second stage, as in FIG 3 and FIG 4 shown. The eighth step serves to detect a multiphase flow in the cross-section of the pipe 12. The diagram 90 has a horizontal time axis 92 and a vertical magnitude axis 94, on which the current fill level 18 in the pipe 10 can be read.

[0047] The filling level 18 is at a substantially constant level. In the fluid 15, a gas phase 11 moves with the flow 13. The gas phase 11 passes through a measuring section of the tube 10, in which at least measuring electrodes 20, as in FIG 1 bis FIG 4 shown, are arranged. By means of the claimed method 100, a drop 36 in the fill level 18 in the pipe 10 is first detected as the gas phase 11 passes through the measuring section. Subsequently, a rise 38 in the fill level 18 to the previous level is detected. In the ninth step 180, the drop 36 and / or the rise 38 in the fill level 18 is detected. A temporal gradient 93 is determined for each drop 36 and / or the fall 38 in the fill level 18. In the ninth step 180, the temporal gradient 93 is further compared with a multi-phase tolerance value (not shown in detail). If the magnitude of the temporal gradient 93 exceeds the adjustable multi-phase tolerance value, a passage of the gas phase 11 is detected. The eighth step 180 is based, among other things, on the finding that gas phases 11 in the claimed method 100 lead to apparently abruptly decreasing or increasing determined fill levels 18.

[0048] Alternatively or additionally, a duration 95 between a decrease 36 and a rise 38 of the fill level 18 can also be recorded in the ninth step 180. Gas phases 11 typically pass through the pipe 10 in the fluid 15 at increased speed, so that the fill level 18 in the claimed method 100 appears to temporarily drop for a short time. This also makes the presence of a multiphase flow in the pipe 10 recognizable. The claimed method 100 can be carried out so quickly that a passing gas phase 11 can be reliably recognized. This makes plug flow or slug flow recognizable in the pipe 10.

[0049] FIG 9 shows schematically a fifth embodiment of the claimed method 100 in a fourth stage, which is for example based on the first stage as in FIG 1 or FIG 2 shown, or to the third stage after FIG 8 In the fifth embodiment of the claimed method 100, a tenth step 190 is performed, which serves to detect a multiphase flow. The flow measurement system 60 corresponds in structure to the flow measurement systems 60 as shown in FIG 1 bis FIG 4 , FIG 6 and FIG 7shown. With the flow 13 of the fluid 15, an extraneous phase 31, which is in the form of drops, for example made of oil, flows through the pipe 10. The extraneous phase 31 has a lower electrical conductivity 17 than the fluid 15. In the tenth step 190, as in the third step 130 of the method 100, measuring currents 25 of the same direction are excited at the first and second measuring electrodes 22, 24, thus realizing common-mode excitation. With respect to a connecting line 19, which runs essentially horizontally between the first and second measuring electrodes 22, 24, asymmetrical current flow lines 16 are established by the extraneous phase 31. Between the second grounding electrode 34 and the first or second measuring electrode 22, 24, the usable conductor cross-section present in the fluid 15, i.e. the fluid 15 itself, is thus reduced by the extraneous phase 31.Furthermore, in the tenth step 190, a measured value 35 is recorded at the first and second grounding electrodes 32, 34 and forwarded to the evaluation unit 40. The measured values ​​35 recorded at the grounding electrodes 30 in the tenth step 190 correspond to one another, thus relating to the same electrical quantity. Likewise, in the tenth step 190, a difference is calculated between the measured values ​​34 thus recorded at the first and second grounding electrodes 32, 34. If the difference exceeds an adjustable multiphase threshold value, the presence of a multiphase flow in the pipe 10 is detected. The tenth step 190 can be integrated into the third step 130 or combined with the other embodiments shown. The claimed method 100 is thus also capable of detecting plug flow or slug flow.If it is known which substance the foreign phase 31 is, a volume fraction of the foreign phase 31 in the fluid 15 can be determined using a table or corresponding characteristic.

Claims

1. Method (100) for ascertaining a fill level (18) of a pipe (10) on which are arranged a first and a second drivable measuring electrode (22, 24) and which is provided with at least one earth electrode (30, 32, 34), comprising the steps of: a) providing the pipe (10) in a state at least in part filled with a fluid (15); characterised in that the method (100) further comprises the steps of: b) exciting the first and second measuring electrodes (22, 24) with contradirectional measuring currents (25), wherein the measuring currents (25) bring about current flow from the first measuring electrodes (22) to the second measuring electrode (24), and detecting at least one first measured value (26) at each of the first and / or second measuring electrodes (22, 24); c) exciting the first and second measuring electrodes (22, 24) with equidirectional measuring currents (25), wherein the measuring currents (25) bring about current flow from the first and second measuring electrodes (22, 24) to a first earth electrode (32) or vice versa, and detecting a second measured value (28) at each of the first and / or second measuring electrodes (22, 24); d) ascertaining the fill level (18) of the pipe (10) on the basis of at least the first and second measured values (26, 28) according to steps b) and c), wherein, in a further step e), a voltage (29) induced in the fluid (15) by a magnetic field is detected by the first and / or second measuring electrodes (22, 24) in order to measure flow (13) in the pipe (10).

2. Method (100) according to claim 1, characterised in that, in step d), a first impedance (45) is ascertained on the basis of the first measured value (26) and / or a second impedance (45) is ascertained on the basis of the second measured value (28).

3. Method (100) according to claim 1 or 2, characterised in that, in a further step f), a measured value (35) is detected at the first earth electrode (32) and / or a second earth electrode (34) in order to identify a fall (36) in the fill level (18).

4. Method (100) according to one of claims 1 to 3, characterised in that the measuring currents (25) excited in steps b) and / or c) are identical in magnitude in at least one first pass (52) of the method (100).

5. Method (100) according to one of claims 1 to 4, characterised in that, in a further step g), measuring currents (25) are excited in the first and / or second measuring electrodes (22, 24) that are non-identical in magnitude and at least one comparison measured value (27) is detected at the first and / or second measuring electrodes (22, 24).

6. Method (100) according to claims 4 and 5, characterised in that, in a further step h), an expected value (33) is formed on the basis of the first and second measured values (26, 28) from the first pass (52), which expected value (33) is compared with the comparison measured value (27).

7. Method (100) according to one of claims 1 to 6, characterised in that, in a further step i), a time gradient (93) of the fall (36) and / or a rise (38) in the fill level (18) and / or a duration (95) between the fall (36) and rise (38) is detected and multiphase flow is identified on the basis of the temporal gradient (93) and / or the duration (95).

8. Method (100) according to one of claims 1 to 7, characterised in that, in a further step j), a difference is detected between the measured values (35) of the first and second earth electrodes (32, 34) in order to ascertain the presence of multiphase flow.

9. Method (100) according to claim 8, characterised in that, in step j), a position of a foreign phase (31) in a pipe cross-section of the pipe (12) is identified on the basis of first measured values (26) from step b) and / or second measured values (28) from step c) together with at least one measured value (35) at the first and / or second earth electrodes (32, 34).

10. Method (100) according to one of claims 1 to 9, characterised in that signal noise is detected for the first and / or second measured values (26, 28) and the fill level (18) is ascertained on the basis of the signal noise.

11. Method (100) according to one of claims 1 to 10, characterised in that step b) and step c) are carried out at least in part simultaneously.

12. Evaluation unit (40) for ascertaining a fill level (18) of a pipe (10) that is configured to receive and process measurement signals (26, 27, 28, 35) from measuring devices (21) and is couplable with a first measuring electrode (22), a second measuring electrode (24), and a first earth electrode (32), characterised in that the evaluation unit (40) is configured to carry out at least one method (100) according to one of claims 1 to 11.

13. Flow measuring system (60) comprising a first measuring electrode (22), a second measuring electrode (24), and a first earth electrode (32) that are coupled with an evaluation unit (40) for ascertaining flow (13) in a pipe (10), characterised in that the evaluation unit (40) is configured according to claim 12.

14. Computer program product (80) for simulating the operating behaviour of a flow measuring system (60) that is mounted on a pipe (10) in a measuring portion, and has a digital model at least of the measuring portion with a first measuring electrode (22), a second measuring electrode (24), and a first earth electrode (32) of the flow measuring system (60), characterised in that the flow measuring system (60) is configured according to claim 13.