Magnetic-inductive flowmeter and method for checking for a short circuit

Abstract

The invention relates to a magnetic-inductive flowmeter (10) comprising a measuring tube (20), a housing (30) with a housing wall (31), a magnetic field-generating device (40) with at least one magnetic coil (41), two measuring electrodes (50, 51), and operating electronics (60), wherein the operating electronics (60) comprises a capacitor (62), wherein the operating electronics (60) comprises a first switch (S1) connected between a voltage source (61) and the capacitor (62), wherein the operating electronics (60) comprises a second switch (S2) connected between a voltage measuring device (63) and the at least one magnetic coil (41), wherein the first switch (S1) is closed at a first time, wherein the second switch (S2) is open at the first time, wherein the first switch (S1) is open at a second time, wherein the second switch (S2) is open at the second time.wherein the first switch is open at a third time, wherein the second switch (S2) is closed at the third time, wherein the voltage source (61) is configured to charge the capacitor (62) in a period between the first and second time, wherein the voltage measuring device (63) is configured to measure a second voltage value of an electrical voltage applied to the capacitor (62) after the third time, wherein the operating electronics (60) are configured to signal a short circuit between the at least one magnet coil (41) and the housing wall (31) if the second voltage value differs from a first voltage value.

Description

[0001] The invention relates to a magnetic-inductive flowmeter and a method for checking an electrical short circuit between a magnetic field-generating device, in particular at least one magnetic coil, and a housing wall, in particular metallic, of a housing of a magnetic-inductive flowmeter.

[0002] Magnetic-inductive flowmeters are used to determine the flow velocity and / or volumetric flow rate of a medium in a measuring tube. A magnetic-inductive flowmeter comprises a magnetic field-generating device designed to produce a magnetic field perpendicular to the longitudinal axis of the measuring tube. This is typically achieved using one or more magnetic coils. A pair of measuring electrodes attached to the outer surface of the measuring tube detects an inductively generated electrical voltage, which arises when a conductive medium flows in the direction of the longitudinal axis while a magnetic field is applied. Since the detected voltage depends on the velocity of the flowing medium according to Faraday's law of induction, the flow velocity-dependent measured quantity, e.g., the flow rate, can be derived from the voltage.The flow rate or - with the addition of a known measuring tube cross-section - the volumetric flow rate of the medium can be determined.

[0003] The magnetic field-generating device is usually attached, at least in part, directly or indirectly to the outer surface of the measuring tube and protected by a housing. A variety of housing designs are known. For example, the housing can comprise two interconnected half-shells. This is disclosed, for instance, in WO 2023 285 181 A1. However, housing types are also known that comprise a housing with a frame element and a wall element. DE 10 2016 124 975 A1 discloses a variant in which the frame element is welded to the wall element. Such housing types are also referred to as fully welded housings.

[0004] Damage to the magnetic field-generating device and / or its wiring can occur not only during the mounting of the device on the measuring tube and its connection to the operating electronics located inside the housing after installation, but also through improper handling of the magnetic-inductive flowmeter. Especially with fully welded housings, subsequent inspection requiring opening the housing is no longer possible. In the worst-case scenario, a short circuit between the magnetic field-generating device and the housing wall may only be detected during operation or (re)calibration.

[0005] The task at hand is to remedy the situation.

[0006] The problem is solved by the magnetic-inductive flow meter according to claim 1 and the method according to claim 9.

[0007] The magnetic-inductive flow meter according to the invention for determining a flow velocity-dependent measured quantity of a flowable medium comprises: - a measuring tube for guiding the medium; - a housing with a housing wall, in particular metallic, and a housing chamber bounded by the housing wall; - a magnetic field-generating device for generating a magnetic field penetrating the measuring tube, wherein the magnetic field-generating device is arranged on an outer lateral surface of the measuring tube, wherein the magnetic field-generating device comprises at least one magnetic coil, wherein the at least one magnetic coil is arranged in the housing chamber; - two measuring electrodes which are in contact with the medium during the operation of the magnetic-inductive flowmeter; and - operating electronics for operating the magnetic field-generating device and for checking whether there is a short circuit between the magnetic field-generating device, in particular the at least one magnetic coil, and the housing wall, wherein the operating electronics include a voltage source for generating a test voltage, wherein the operating electronics include a capacitor, wherein the operating electronics have a first switch which is connected between the voltage source and the capacitor, wherein the operating electronics include a voltage measuring device which is configured to measure the current voltage applied to the capacitor, wherein the operating electronics have a second switch which is connected between the capacitor and the magnetic field-generating device, in particular the at least one magnetic coil, where the first switch is closed at a first time point, where the second switch is open at the first time, where the first switch is open at a second time, where the second switch is open at the second time, where the first switch is open at a third time, where the second switch is closed at the third time, wherein the voltage source is set up to charge the capacitor in a period between the first and second time points, wherein the voltage measuring device is configured to measure a second voltage value of an electrical voltage applied to the capacitor after the third time point, wherein the operating electronics are configured to output status information regarding a short circuit between a magnetic field-generating device, in particular the at least one magnetic coil, and the housing wall, if the second voltage value deviates from a first voltage value, in particular serving as a reference value.

[0008] This makes it possible, for example, to detect a short circuit between the coil and the housing caused during assembly, in order to rectify the fault before welding the housing shut.

[0009] Advantageous embodiments of the invention are the subject of the dependent claims.

[0010] One embodiment provides that the voltage measuring device is configured to measure the first voltage value of the electrical voltage applied to the capacitor during a period between the second and third time points.

[0011] One embodiment provides that the second switch is part of an H-bridge circuit, which is configured to control the temporal behavior of the magnetic field-generating device, in particular the at least one magnetic coil. where the first switch is not part of the H-bridge circuit.

[0012] One design provides that the operating electronics include a third switch, where the third switch is open at the first time, where the third switch is open at a second time, where at the third point in time the third switch is either open or closed.

[0013] One embodiment provides that the third switch is connected to an output or an input of the magnetic field-generating device.

[0014] One embodiment provides that the second switch is connected to an input of the magnetic field-generating device, in particular the magnetic coil, when the third switch is connected to the output of the magnetic field-generating device. wherein the second switch is connected to an output of the magnetic field-generating device, in particular the magnetic coil, when the third switch is connected to the input of the magnetic field-generating device.

[0015] One design provides that the operating electronics are configured to perform the check during the ongoing operation of the magnetic-inductive flowmeter, wherein the H-bridge circuit is configured to control the magnetic field-generating device, in particular the at least one magnetic coil, during operation in such a way that it generates a magnetic field with alternating magnetic field direction, wherein the H-bridge circuit is configured to control the magnetic field-generating device, in particular the at least one magnetic coil, during operation in such a way that a rest phase is provided between changes in the magnetic field direction, in which no coil current flows through the magnetic coil, where the first to third point in time lie in the resting phase.

[0016] One embodiment provides that the second switch is closed at a fourth time, and the third switch is closed at the fourth time. wherein the voltage measuring device is configured to measure a third voltage value of the electrical voltage applied to the capacitor after the fourth time point, wherein the operating electronics are configured to output the status information regarding a short circuit between a magnetic field-generating device, in particular the at least one magnetic coil, and the housing wall, if the second voltage value and / or the third voltage value deviates from a first voltage value, in particular serving as a reference value.

[0017] The inventive method for checking a short circuit between a magnetic field-generating device, in particular at least one magnetic coil, and a, in particular metallic, housing wall of a housing of a magnetic-inductive flow meter, comprising the method steps: - Applying a test voltage to charge a capacitor, wherein the magnetic-inductive flowmeter comprises operating electronics which are in electrical connection with the at least one magnetic coil, the operating electronics include a voltage source, wherein the operating electronics include a first switch which is connected between the voltage source and the capacitor, wherein the operating electronics have a voltage measuring device in parallel to the capacitor, wherein the operating electronics include a second switch which is connected between the capacitor and the magnetic field-generating device, in particular the at least one magnetic coil, where the first switch is closed during the charging of the capacitor, the second switch remains open until the capacitor is charged; - Measuring an initial voltage value of an electrical voltage applied to the capacitor, where the first switch is open when measuring the voltage across the capacitor, where the second switch is open when measuring the voltage across the capacitor; - Closing the second switch; - Measuring a second voltage value of a voltage applied to the capacitor; - Determine whether a short circuit exists between the magnetic field-generating device, in particular the at least one magnetic coil, and the housing wall, depending on the first and second voltage values. where a short circuit is assumed if the measured voltage values ​​of the first and second voltages differ from each other, in particular by at least 10%.

[0018] One embodiment provides that the procedure is carried out during the ongoing operation of the magnetic-inductive flowmeter.

[0019] One design includes the following procedural step: - Closing a third switch; - Measuring a third voltage value of the voltage applied to the capacitor; - Determine whether there is a short circuit between the magnetic field-generating device, in particular the at least one magnetic coil, and the housing wall, taking into account the third voltage value.

[0020] The invention is explained in more detail with reference to the following figures. They show: Fig. 1: A partially cutaway view of a magnetic-inductive flow meter; Fig. 2: a simplified representation of a first embodiment of a circuit according to the invention at three different times; Fig. 3: a simplified representation of a second embodiment of a circuit according to the invention at three different times; Fig. 4: a simplified representation of the circuit according to Fig. 3 at a fourth time; Fig. 5: an embodiment of the process sequence according to the invention.

[0021] Fig. Figure 1 shows a partially cutaway view of a magnetic-inductive flowmeter (10) for determining a flow velocity-dependent measured quantity of a flowable medium. The flow velocity-dependent measured quantity can be, for example, a flow velocity, a volumetric flow rate, or a mass flow rate of the flowable medium. The medium to be monitored typically has a minimum conductivity of 5 µS / cm.

[0022] The magnetic-inductive flowmeter (10) comprises a measuring tube (20) for guiding the medium to be monitored. The measuring tube (20) is electrically insulating, at least in the area in contact with the medium. This can be achieved by fitting an electrically insulating liner (e.g., rubber, PFA, PU) to the inner surface of a metallic support tube (e.g., steel tube) facing the medium, or alternatively, by using a tube made entirely of an electrically insulating material (e.g., PEEK tube, ceramic tube, glass tube). In the latter case, a liner is not required.

[0023] The magnetic-inductive flowmeter (10) comprises a housing (30) with a housing wall (31), in particular a metallic one, and a housing chamber (32) bounded by the housing wall (31). The housing chamber (32) describes the internal volume of the housing (30) and need not be understood as a single space within the housing. The housing (30) can, for example, be a sheet metal housing with a housing wall (31) formed from sheet metal. The housing (30) can be multi-part, i.e., it can comprise more than two housing parts that together form the housing wall (31). The housing wall (31) can be connected to an electrical reference potential directly via a reference terminal or indirectly via the electrically conductive support tube.

[0024] The magnetic-inductive flowmeter comprises a magnetic field-generating device (40) for generating a magnetic field penetrating the measuring tube (20). This device is arranged either indirectly or directly on an outer surface (MF) of the measuring tube (20) and connected to it. The magnetic field-generating device (40) comprises at least one magnetic coil (41). Magnetic-inductive flowmeters (10) are known with exactly one magnetic coil, with exactly two opposing magnetic coils, and with more than two magnetic coils (e.g., four or eight). The at least one magnetic coil (41) can be a cylindrical coil, particularly in conjunction with a pole shoe, or a saddle coil. The at least one magnetic coil (41) is arranged in the housing chamber (32).Due to increasingly stringent requirements for the compactness of the magnetic-inductive flowmeter (10), the distance between the magnetic field-generating device (40) and the housing wall (31) is also reduced. Therefore, incorrect assembly can lead to an electrical short circuit between the magnetic field-generating device (40), in particular the at least one magnetic coil (41), and the electrically conductive housing wall (31), which is usually connected to a reference potential and is primarily metallic. Another potential source of error lies in the wiring of the coil connections. The magnetic coil (41) may also be defective before assembly due to faulty copper insulation. This must be detected before the housing is closed, e.g., by welding or crimping.

[0025] The magnetic-inductive flowmeter (10) comprises at least two measuring electrodes (50, 51) which are in contact with the medium during operation of the magnetic-inductive flowmeter (10). These can be arranged opposite each other, as shown, and each in a medium-tight manner within designated measuring electrode openings. Magnetic-inductive flowmeters are known in which more than two measuring electrodes (50, 51) are used. For example, two or three measuring electrodes can be arranged on each side of the measuring tube (20), which is conceptually divided by a longitudinal plane.

[0026] According to the invention, the magnetic-inductive flowmeter (10) comprises operating electronics (60) for operating the magnetic field-generating device (40) and for checking whether an electrical short circuit exists between the magnetic field-generating device (40), in particular the at least one magnetic coil (41), and the housing wall (31). An electrical short circuit between two components of the magnetic-inductive flowmeter (10) is understood to be a virtually resistance-free connection between two circuit points with normally different potentials, causing the electrical voltage between these components to drop to a value close to zero. The operating electronics (60) are electrically connected to the magnetic field-generating device (40), in particular the at least one magnetic coil (41), via electrical connectors (80, 81).

[0027] For this purpose, the operating electronics (60) includes a voltage source for generating a test voltage, a capacitor, a first switch connected between the voltage source and the capacitor, a voltage measuring device configured to measure the current voltage value of the voltage applied to the capacitor, and a second switch connected between the capacitor and the magnetic field-generating device, in particular the at least one magnetic coil (see Fig. 2-4). The operating electronics (60) may include further electronic components, such as transformers, amplifiers, microprocessors and / or microcontrollers, which may be necessary to operate the magnetic field-generating device.

[0028] The voltage source (61) can be a switching regulator or a linear regulator. The test voltage to be generated can take on values ​​between 1 and 100 V.

[0029] The respective switches (S1, S2) can be integrated switches (e.g., MOSFETs or bipolar transistors). Alternatively, mechanical or electronic relays are also conceivable.

[0030] The voltage measuring device (63) can be a discrete analog-to-digital converter or an analog-to-digital converter integrated into a microprocessor / microcontroller.

[0031] The operating electronics (60) are suitable or designed to perform the functions in Fig. to carry out the 5 outlined procedural steps.

[0032] Fig. 2 outlines a simplified representation of a first embodiment of a circuit according to the invention - which is part of the operating electronics (see Fig. 1) is - at three different times (T1, T2, T3). The circuit comprises a voltage source (61), a first switch (S1), a second switch (S2), a capacitor (62), a voltage measuring device (63), and the magnetic coil (41) of the magnetic field-generating device. The first switch (S1) is located between the voltage source (61) and the capacitor (62). The voltage measuring device (63) is connected in parallel with the capacitor (62). The second switch (S2) is located between the voltage measuring device (63) and the input of the magnetic coil (41). The magnetic coil (41) is connected in parallel with the voltage measuring device (63).

[0033] To detect a short circuit, it is necessary that there is a first point in time (T1) from which the first switch (S1) is closed, i.e., that it is conductive for the electric current, and that the second switch (S2) is open, i.e., that it is not conductive.

[0034] Furthermore, there is a second point in time (T2) from which the first switch (S1) is open and the second switch (S2) is also open.

[0035] Furthermore, there is a third point in time (T3) from which the first switch (S1) is open and the second switch (S2) is closed.

[0036] The voltage source (61) is configured to charge the capacitor (62) during the period between the first and second time points (T1, T2). This is achieved by supplying the test voltage. This voltage can be fixed and defined by a specific voltage value. During the period between the two time points (T1, T2), an approximately constant voltage other than 0 V is established across the capacitor (62). By opening the two switches (S1, S2), the capacitor (62) is disconnected from the voltage source (61) and the solenoid (41).

[0037] The voltage measuring device (63) is configured to measure a second voltage value (U2) of the electrical voltage applied to the capacitor (62) after the third time (T3), i.e., after the second switch (S2) has been closed. Closing the second switch (S2) connects the electrical potential of the solenoid coil to the potential of the capacitor or, if present, to the potential of the H-bridge circuit. This establishes an electrical voltage, which is measured by the voltage measuring device (63). If there is no low-resistance connection between the solenoid coil and a reference potential, the previously set voltage remains approximately constant or may even increase slightly due to parasitic effects.

[0038] According to the invention, the operating electronics (60) are configured to output status information regarding a short circuit between the magnetic field-generating device (40), in particular the at least one magnetic coil (41), and the housing wall (31), if the second voltage value (U2) deviates from a first voltage value (U1), which is provided, in particular, as a reference value. The voltage value (U1) provided as a reference value can be stored in a memory in the operating electronics. The first voltage value (U1) can be predefined. Alternatively, the voltage measuring device (63) can be configured to measure the first voltage value (U1) of the electrical voltage applied to the capacitor (62) during a period between the second and third time points (T1, T3). The operating electronics (60) are configured to determine the status information depending on the first and second voltage values ​​(U1, U2).For this purpose, for example, the difference or quotient of the two voltage values ​​(U1, U2) can be determined. Alternatively, the two voltage values ​​(U1, U2) can be compared with each other to determine the state information.

[0039] Fig. Figure 3 outlines a simplified representation of a second embodiment of a circuit according to the invention at three different times (T1, T2, T3). In the second embodiment, the second switch (S2) is part of an H-bridge circuit (64) configured to control the temporal behavior of the magnetic field-generating device, in particular the at least one magnetic coil (41) represented by electrical resistance and induction. Such a circuit is known, for example, from DE 10 2022 134 361 A1 and DE 10 2017 107 417 A1. The first switch (S1), on the other hand, is not part of the H-bridge circuit (64) but can be part of the coil current control. In the second embodiment, the second switch (S2) is connected to an input of the magnetic field-generating device, in particular the at least one magnetic coil (41).The H-bridge circuit (64) comprises the second switch, a third switch (S3) connected in parallel to the second switch, a fourth switch (S4) connected in series with the third switch (S3), and a fifth switch (S5) connected in parallel with the fourth switch (S4) and in series with the second switch (S2). The magnetic field-generating device (40), in particular the at least one magnetic coil (41), is located in the bridge branch.

[0040] An amplifier circuit (66) located at the top of the H-bridge circuit (64) allows the electrical voltage applied to the bridge or capacitor (62) to be tapped at high impedance and converted into a voltage value proportional to it, which can be converted into a digital value by an integrated analog-to-digital converter of the microprocessor / microcontroller.

[0041] To detect a short circuit, it is necessary that there is a first point in time (T1) from which the first switch (S1) is closed, i.e., that it is conductive for the electric current, and that the second switch (S2) is open, i.e., that it is not conductive.

[0042] Furthermore, there is a second point in time (T2) from which the first switch (S1) is open and the second switch (S2) is also open.

[0043] As shown in the second embodiment, the operating electronics (60) can include a third switch (S3) which is open at the first time (T1) and the second time (T2).

[0044] Furthermore, there is a third point in time (T3) from which the first switch (S1) is open and the second switch (S2) is closed.

[0045] The H-bridge circuit has further switches, namely the fourth switch (S4) and the fifth switch (S5). These are also open at least from the third time point (T3).

[0046] In the second embodiment, the third switch (S3) is open at the third time (T3). Alternatively, the third switch (S3) can be closed at the third time (T3). The third switch (S3) is electrically connected to an output of the magnetic field-generating device, in particular to the at least one magnetic coil (41).

[0047] Alternatively, the second switch (S2) can be connected to an output of the magnetic field-generating device (40), in particular the magnetic coil (41), if the third switch (S3) is connected to the input of the magnetic field-generating device (40).

[0048] The operating electronics (60) can be configured to perform the check during the operation of the magnetic-inductive flowmeter (10). It is advantageous to generate an alternating magnetic field in the measuring tube. Therefore, the H-bridge circuit (64) can be configured to connect the magnetic field-generating device (40), in particular the at least one magnetic coil (41), to the voltage source during operation via the individual switches (S2-S5) such that a time-varying operating signal is provided from a time-varying voltage waveform at the magnetic field-generating device (40), in particular the at least one magnetic coil (41).To perform the check during operation, the H-bridge circuit (64) can be configured to control the magnetic field-generating device (40), in particular the at least one magnetic coil (41), during operation such that a rest phase is provided between changes in the magnetic field direction, during which no coil current flows through the magnetic coil (41). The first to third time points (T1, T2, T3) occur during this rest phase. Thus, the short-circuit monitoring does not affect the measurement of the flow velocity-dependent quantity.

[0049] Fig. Figure 4 outlines a simplified representation of the circuit according to Fig. 3 at a fourth time point (T4). Alternatively, the circuit situation of the two switches (S2, S3) shown can also exist at the third time point (T3).

[0050] The second switch (S2) and the third switch (S3) are closed at a fourth time (T4). The voltage measuring device (63) is configured to measure a further, third voltage value (U3) of the electrical voltage applied to the capacitor (62) after the fourth time (T4). The third voltage value (U3) can be used as a reference value. The operating electronics (60) are configured to output status information regarding a short circuit between the magnetic field-generating device (40), in particular the at least one magnet coil (41), and the housing wall (31), if the second voltage value (U2) and / or the third voltage value (U3) deviates from the first voltage value (U1), which serves in particular as a reference value.Based on the voltage values ​​thus determined (U1, U2, U3), it can be determined whether the short circuit to the housing wall occurs via the at least one magnetic coil or via the electrical connectors (see . Fig. 1) is done.

[0051] Fig. 5: an embodiment of the inventive method for checking a short circuit between a magnetic field-generating device, in particular at least one magnetic coil, and a, in particular metallic, housing wall of a housing of a magnetic-inductive flow meter, in particular of a magnetic-inductive flow meter according to the invention (see Fig. 1-4).

[0052] The procedure includes the following steps: I. Applying a test voltage to charge a capacitor, see ( Fig.2-4). The test voltage can, for example, be a target voltage that is also applied to at least one magnetic coil during operation in order to generate a substantially constant magnetic field over time, and at which the induced measuring voltage necessary for determining the flow velocity-dependent measured quantity is also measured. II. Measuring a first voltage value (U1) of an electrical voltage applied to the capacitor.

[0053] The first switch (S1) and the second switch (S2) are open when measuring the first voltage value (U1). III. Closing the second switch (S2) so that the potential of the capacitor is connected to that of the magnetic coil (41) with low resistance. IV. Measuring a second voltage value (U2) of a voltage applied to the capacitor (62). V. Determine whether a short circuit exists between the magnetic field-generating device (40), in particular the at least one magnetic coil (41), and the housing wall (31) depending on the first and second voltage values ​​(U1, U2), where a short circuit is assumed if the measured voltage values ​​of the first and second voltages (U1, U2) differ from each other, in particular by at least 10%.

[0054] Further training includes additional procedural steps: - Closing a third switch, which is connected in parallel to the second switch and which is connected to the second switch via the bridge branch having at least one magnetic coil. - Measuring a third voltage value of the voltage applied to the capacitor. - Determine whether there is a short circuit between the magnetic field-generating device, in particular the at least one magnetic coil, and the housing wall, taking into account the third voltage value.

[0055] And optionally: identifying a possible source of the electrical short circuit. For example, the short circuit could be caused by at least one solenoid coil or by the electrical connections between the solenoid coil and the operating electronics.

[0056] Some embodiments of the present disclosure are described in more detail below with reference to the accompanying figures. The figures show some, but not all, embodiments of the disclosure. In fact, these disclosures can be embodied in many different forms and should not be interpreted as being limited to the embodiments presented here. Different embodiments, each showing individual details of the subject matter of the invention, can be combined with one another to form new embodiments not shown in the figures. Identical numbers refer throughout to identical elements.

[0057] The components depicted in the figures represent components that may or may not be present in various embodiments of the present disclosure described herein, so that the embodiments may contain fewer or more components than those depicted in the figures without thereby departing from the scope of the present disclosure. Some components may be omitted or shown with dashed lines in one or more figures to make the underlying components visible. The expressions "in one exemplary embodiment," "some embodiments," "various embodiments," and the like generally mean that the particular feature, structure, or property following the expression may be included in at least one embodiment of the present disclosure and may be included in more than one embodiment of the present disclosure.Such expressions do not necessarily have to refer to the same design.

[0058] The word "example" or "exemplary" is used here in the sense of "serving as an example or illustration." Each implementation described here as "exemplary" is not necessarily to be understood as preferable or advantageous over other implementations.

[0059] If the figure description states that a component, part, or feature is "preferably," "possibly," "typically," "optionally," or "for example" (or any other such wording), or that a feature "may" be included, or that a feature "could" or "should" have a property, it is not necessary that a specific component or feature be included or possess the feature. Such components or features may be optional in some embodiments, but they may also be excluded. An embodiment not shown in the figures may also include all the features—provided they do not contradict each other—of the embodiments shown. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2023 285 181 A1

[0003] DE 10 2016 124 975 A1

[0003] DE 10 2022 134 361 A1

[0039] DE 10 2017 107 417 A1

[0039]

Claims

[1] Magnetic-inductive flow meter (10) for determining a flow velocity-dependent measured quantity of a flowable medium, comprising: - a measuring tube (20) for guiding the medium; - a housing (30) with a housing wall (31), in particular metallic, and a housing chamber (32) bounded by the housing wall (31); - a magnetic field-generating device (40) for generating a magnetic field penetrating the measuring tube (20), wherein the magnetic field generating device (40) is arranged on an outer lateral surface (MF) of the measuring tube (20), wherein the magnetic field generating device (40) comprises at least one magnetic coil (41), wherein the at least one magnetic coil (41) is arranged in the housing chamber (32); - two measuring electrodes (50, 51) which are in contact with the medium during operation of the magnetic-inductive flowmeter (10); and - an operating electronics (60) for operating the magnetic field-generating device (40) and for checking whether there is a short circuit between the magnetic field-generating device (40), in particular the at least one magnetic coil (41), and the housing wall (31), wherein the operating electronics (60) includes a voltage source (61) for generating a test voltage, wherein the operating electronics (60) includes a capacitor (62), wherein the operating electronics (60) has a first switch (S1) which is connected between voltage source (61) and capacitor (62), wherein the operating electronics (60) includes a voltage measuring device (63) which is configured to measure a current voltage value of the electrical voltage applied to the capacitor (62), wherein the operating electronics (60) has a second switch (S2) which is connected between the capacitor (62) and the magnetic field-generating device (40), in particular the at least one magnetic coil (41), where the first switch (S1) is closed (i.e. conducting) at a first time (T1), where the second switch (S2) is open (i.e. non-conducting) at the first time (T1), where the first switch (S1) is open at a second time (T2), where the second switch (S2) is open at the second time (T2), where the first switch is open at a third time (T3), where the second switch (S2) is closed at the third time (T3), wherein the voltage source (61) is configured to charge the capacitor (62) during a period between the first and second time (T1, T2), wherein the voltage measuring device (63) is configured to measure a second voltage value (U2) of an electrical voltage applied to the capacitor (62) after the third time (T3), wherein the operating electronics (60) is configured to output status information regarding a short circuit between the magnetic field-generating device (40), in particular the at least one magnetic coil (41), and the housing wall (31), if the second voltage value (U2) deviates from a first voltage value (U1), in particular provided as a reference value. [2] Magnetic-inductive flowmeter according to claim 1, wherein the voltage measuring device (63) is configured to measure the first voltage value (U1) of the electrical voltage applied to the capacitor (62) during a period between the second and third time (T1, T3). [3] Magnetic-inductive flow meter according to claim 1 or 2, wherein the second switch (S2) is part of an H-bridge circuit (64) which is configured to control the temporal behavior of the magnetic field-generating device (40), in particular the at least one magnetic coil (41), where the first switch (S1) is not part of the H-bridge circuit (64). [4] Magnetic-inductive flow meter according to any of the preceding claims, wherein the operating electronics (60) includes a third switch (S3), where the third switch (S3) is open (i.e. non-conducting) at a first time (T1), where the third switch (S3) is open at a second time (T2), where at the third time (T3) the third switch (S3) is open or closed. [5] Magnetic-inductive flow meter according to claim 4, wherein the third switch (S3) is connected to an output or an input of the magnetic field generating device (40). [6] Magnetic-inductive flow meter according to claim 5, wherein the second switch (S2) is connected to an input of the magnetic field-generating device (40), in particular the magnetic coil (41), when the third switch (S3) is connected to the output of the magnetic field-generating device (40), wherein the second switch (S2) is connected to an output of the magnetic field generating device (40), in particular the magnetic coil (41), when the third switch (S3) is connected to the input of the magnetic field generating device (40). [7] Magnetic-inductive flow meter (10) according to claim 3 or 4, wherein the operating electronics (60) are configured to perform the check during the ongoing operation of the magnetic-inductive flow meter (10), wherein the H-bridge circuit (64) is configured to control the magnetic field-generating device (40), in particular the at least one magnetic coil (41), during operation such that it generates a magnetic field with alternating magnetic field direction, wherein the H-bridge circuit (64) is configured to control the magnetic field-generating device (40), in particular the at least one magnetic coil (41), during operation in such a way that a rest phase is provided between the change of a magnetic field direction in which no coil current flows through the magnetic coil (41), where the first to third time points (T1, T2, T3) lie in the resting phase. [8] Magnetic-inductive flow meter according to any of the preceding claims, where the second switch (S2) is closed at a fourth time (T4), where the third switch (S3) is closed at the fourth time (T4), wherein the voltage measuring device (63) is configured to measure a third voltage value (U3) of the electrical voltage applied to the capacitor (62) after the fourth time (T4), wherein the operating electronics (60) is configured to output the status information regarding a short circuit between the magnetic field-generating device (40), in particular the at least one magnetic coil (41), and the housing wall (31), if the second voltage value (U2) and / or the third voltage value (U3) deviates from a first voltage value (U1), in particular serving as a reference value. [9] Method for checking for a short circuit between a magnetic field-generating device, in particular at least one magnetic coil (41), and a housing wall (31), in particular metallic, of a housing (30) of a magnetic-inductive flow meter (10), comprising: - Applying a test voltage to charge a capacitor (62), wherein the magnetic-inductive flowmeter (10) comprises operating electronics (60) which are in electrical connection with the at least one magnetic coil (41), wherein the operating electronics (60) includes a voltage source (61), wherein the operating electronics (60) includes a first switch (S1) which is connected between the voltage source (61) and the capacitor (62), wherein the operating electronics (60) has a voltage measuring device (63) in parallel to the capacitor (62), wherein the operating electronics (60) comprises a second switch (S2) which is connected between the capacitor (62) and the magnetic field-generating device (40), in particular the at least one magnetic coil (41), where the first switch (S1) is closed when the capacitor (62) is charging, wherein the second switch (S2) remains open until the capacitor (62) is charged; - Measuring a first voltage value (U1) of an electrical voltage applied to the capacitor (62), where the first switch (S1) is open when measuring the voltage applied to the capacitor (62), where the second switch (S2) is open when measuring the voltage applied to the capacitor (62); - Closing the second switch (S2); - Measuring a second voltage value (U2) of a voltage applied to the capacitor (62); - Determine whether a short circuit exists between the magnetic field-generating device (40), in particular the at least one magnetic coil (41), and the housing wall (31) depending on the first and second voltage values ​​(U1, U2), where a short circuit is assumed if the measured voltage values ​​of the first and second voltages (U1, U2) differ from each other, in particular by at least 10%. [10] Method according to claim 9, wherein the method is carried out during the operation of the magnetic-inductive flow meter (10).

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