Method for operating magnetic inductive flow meter

Abstract

The invention relates to a method for operating a magnetic-inductive flow meter (1), comprising the following method steps:-applying an operating signal (11), the operating signal (11) having a first time section (I) having a first partial time section (i) in which the operating signal (11) is in the first direction of time, and a second partial time section (ii) in which the operating signal (11) is in the second direction of time; in the first partial time section (ii), a signal value # imgabs0 # is applied for a duration # imgabs1 #, and in the second partial time section (ii), a signal value # imgabs2 # is applied for a duration # imgabs3 #, the duration # imgabs4 # being longer than the duration # imgabs5 #, the magnetic field polarity during the duration # imgabs6 # being different from the magnetic field polarity during the duration # imgabs7 #, and the magnetic field polarity during the duration # imgabs6 # being different from the magnetic field polarity during the duration # imgabs7 #. Wherein the operating signal has a second time section (II) having a third partial time section (iii) and a fourth partial time section (iv), in which the signal value # imgabs8 # is applied for a duration # imgabs9 # in the third partial time section (iii) and the signal value # imgabs10 # is applied for a duration # imgabs11 # in the fourth partial time section (iv), wherein the duration of time # imgabs 12 # is longer than the duration of time # imgabs 13 #; measuring a first measurement voltage value # imgabs14 # of the inductive measurement voltage during a measurement section of the first time section (I) and measuring a second measurement voltage value # imgabs15 # of the inductive measurement voltage during a measurement section of the second time section (II); and-determining the flow rate-dependent measurement variable on the basis of the first measurement voltage value # imgabs16 # and the second measurement voltage value # imgabs17 #.

Description

Technical Field

[0001] The invention relates to a method for operating a magnetic-inductive flowmeter, a magnetic-inductive flowmeter and a magnetic-inductive flow measuring probe. Background Art

[0002] Magnetic inductive flowmeters are used to determine the flow velocity and volume flow of a flowing medium in a pipeline. The distinction here is between an online magnetic inductive flowmeter and a magnetic inductive flow measuring probe, which are inserted into a transverse opening of a pipeline. The magnetic inductive flowmeter has a magnetic field generating device for generating a magnetic field. The main axis of the magnetic field extends substantially perpendicular to the flow direction of the flowing medium. Saddle coils or solenoids are generally used for this purpose. In order to achieve a uniformly dominant magnetic field, the pole shoes are additionally formed and attached relative to the flow direction so that the magnetic field lines extend over the entire tube cross section substantially perpendicular to the transverse axis or parallel to the vertical axis of the measuring tube. In addition, the magnetic inductive flowmeter has a measuring tube, which is used to guide the medium on the outer side of which the magnetic field generating device is arranged. A pair of measuring electrodes attached to the side surface of the measuring tube taps a measuring voltage or potential difference perpendicular to the flow direction and the magnetic field, and appears when flowing in the flow direction when the magnetic field is applied. Since the tapped measuring voltage depends on the velocity of the flowing medium according to Faraday's law of induction, it is possible to determine the flow velocity and / or the volume flow including the case of a known pipeline cross section based on the measured induced measuring voltage.

[0003] Compared to the magneto-inductive flowmeter, which includes a device for conducting a medium with an attachment device to generate a magnetic field penetrating the measuring tube and also includes measuring electrodes, the magnetic inductive flow measuring probe is inserted into the lateral opening of the tube with their cylindrical housing, which is usually circular, and is fastened in a fluid-tight manner. A special measuring tube is no longer required. The measuring electrode arrangement and coil arrangement on the side surface of the measuring tube mentioned at the beginning are omitted, and the measuring electrode arrangement and coil arrangement are replaced by a device for generating a magnetic field, which is arranged inside the housing and directly close to the measuring electrodes and is designed so that the axis of symmetry of the magnetic field lines of the generated magnetic field intersects perpendicularly with the front face or face between the measuring electrodes. In the prior art, there are already a number of different magnetically sensitive flow measuring probes.

[0004] Magnetic-inductive flowmeters are commonly used in process and automation engineering for fluids starting with a conductivity of approximately 5. The applicant markets corresponding flow measuring devices in various embodiments for various fields of application, for example under the names PROMAG or MAGPHANT.

[0005] WO 2020 / 001876 A1 discloses a method for operating a magnetic-inductive flow meter, wherein, before the start of a measuring phase, in which the operating voltage alternates at a first frequency, there is a switch to a higher second frequency. This allows the magnetic field generating device to heat up faster and thus reduces the stabilization time that must be waited until the magnetic field stabilizes. However, WO 2020 / 001876 A1 does not address how the zero point can be stabilized during the measurement phase.

[0006] A magnetic-inductive flowmeter is known from JP 2002-310751 A, which operates with a dual-frequency operating signal. This means that during the measuring phase, the excitation current changes direction at a first frequency and at the same time alternates between maximum excitation current and no excitation current at a second frequency higher than the first frequency. The advantage of such an operating signal is the stabilization of the zero point. The disadvantage is the provision of time sections in which no magnetic field is generated or a residual magnetic field is present, which usually only corresponds to a few percent of the nominal magnetic field. On the one hand, this leads to the fact that in these time sections no voltage is induced at the measuring electrodes and therefore no flow rate-dependent process variables can be measured, and on the other hand, the amplitude of the measuring signal is temporarily very low. This leads to increased measurement errors in applications with very high flow rate variations. Summary of the invention

[0007] The object of the present invention is to solve this problem.

[0008] This object is achieved by a method according to claim 1 , a magnetic-inductive flow meter according to claim 14 and a magnetic-inductive flow measuring probe according to claim 15 .

[0009] According to the method of the invention for operating a magnetic-inductive flowmeter for determining a flow rate-related measured variable of a flowable medium, the magnetic-inductive flowmeter comprising a magnetic field generating device for generating a magnetic field and a device for detecting an induced measurement voltage in the medium, the method comprises the following method steps:

[0010] - applying an operating signal to the magnetic field generating device to generate a magnetic field,

[0011] The operation signal has a first time segment.

[0012] The first time segment at least includes a first partial time segment and a second partial time segment.

[0013] In this case, in the first partial time period, the signal value is applied in each case Duration ,

[0014] In the second time segment, the signal value is applied Duration ,

[0015] Among them, the duration Longer than duration ,

[0016] Among them, in duration The magnetic field polarity during the period is different from that during the duration The magnetic field polarity during

[0017] The operating signal has a second time segment, which is particularly immediately after the first time segment.

[0018] The second time segment includes at least a third time segment and a fourth time segment.

[0019] In the third time segment, the signal value is applied Duration ,

[0020] In the fourth time segment, the signal value is applied Duration ,

[0021] Among them, the duration Longer than duration ,

[0022] Among them, in duration The magnetic field polarity during the period is different from that during the duration The polarity of the magnetic field during the period;

[0023] - measuring a first measured voltage value of the induced measured voltage in a measuring section of the first time section ;

[0024] - measuring a second measured voltage value of the induced measured voltage in the measuring section of the second time section ;as well as

[0025] - Based on the first measured voltage value and the second measured voltage value Determine the current zero point in order to compensate flow-dependent measured variables.

[0026] The operating signal can be a voltage signal applied to the magnetic field generating device. In this case, the voltage signal includes a time-varying voltage, which is generated by means of an operating circuit and applied to the magnetic field generating device. The magnetic field generating device is designed so that it generates a time-varying magnetic field based on the applied operating signal. Typically, the magnetic field generating device includes at least one coil electrically connected to the operating circuit. Alternatively, the operating signal can also be a current signal set or specified at the magnetic field generating device. In this case, the operating circuit is configured to generate a current signal and provide it to the magnetic field generating device.

[0027] The operating signal causes the first time segment to start again after the second time segment and the second time segment to start again after the first time segment. While the operating signal is being applied, at the device for detecting the induced measuring voltage, the measuring circuit measures the induced measuring voltage in the medium and the potential present at the respective measuring electrodes. Thus, the operating signal is applied during the measuring phase. The evaluation circuit is designed to determine the flow rate-related measured variable based on the measured measuring voltage or the potential at different partial time intervals. The flow rate-related measured variable can be the flow rate, the volume flow, the mass flow and / or a variable derived therefrom.

[0028] The current zero point can be determined as follows. In a first method step, the difference or average value of two measured voltages from preferably consecutive time intervals of opposite magnetic field polarity of a first time interval is determined. A first measured voltage value is generated from the difference value. This is used to determine a flow rate-related measured variable. In a second method step, the difference or average value of two measured voltages from preferably consecutive partial time intervals of a second time interval with opposite magnetic field polarity is also determined. A second measured voltage value This is also used to determine the flow rate-dependent measured variable. First measured voltage value and the second measured voltage value is input into the determination of the zero point effect. For example, the difference between the respective absolute values ​​of two determined measured voltage values ​​is determined, which itself has no flow rate-dependent components and depends essentially only on the zero point effect. The currently determined measured value of the flow rate-dependent measured variable is then corrected by the current zero point.

[0029] The solution according to the invention has the advantage that time periods are avoided in which no current flows through the magnetic field generating device or no voltage is applied to the magnetic field generating device and therefore no magnetic field is generated. Thus, an induced voltage proportional to the flow rate of the medium can always be detected at the device for detecting the induced measurement voltage. Precisely in applications in which the flow rate changes rapidly, such as during a filling process, it is advantageous if the induced measurement voltage can be detected continuously throughout the entire measuring cycle.

[0030] Another advantage is that by applying the signal value , , and — (all different from 0) enables significantly higher signal amplitudes to be achieved compared to the method according to JP2002-310751 A, and thus The sensitivity to noise is small. Furthermore, the operating signal according to the invention leads to a significant simplification of the control method, since no sections are provided in which no current flows.

[0031] Advantageous embodiments of the invention are subject matter of the dependent claims.

[0032] One embodiment provides that during the first time period, the first partial time interval, in particular the signal value and the second part, the time interval, in particular the signal value At least temporarily at the first frequency alternately.

[0033] One embodiment provides that during the second time period, the third partial time interval, in particular the second signal value and the fourth part of the time interval, especially the second signal value At least temporarily at the second frequency alternately.

[0034] This not only means operating on a signal more than once presents the signal value and signal value , and is presented periodically. The same applies to signal values and signal value This has the advantage that a more stable flow rate-related measured variable can be determined from the measured voltage measured during the repeated partial time intervals.

[0035] One embodiment provides that the first time segment and the second time segment are transmitted at a third frequency alternately.

[0036] One embodiment provides that the third frequency Below the first frequency and the second frequency .

[0037] One embodiment provides that the third frequency and the first frequency and / or a second frequency The ratio lies between 2 and 1000, in particular between 2 and 10 and preferably between 3 and 5.

[0038] One embodiment provides that the duration and duration The ratio lies between 1 and 10, in particular between 1.5 and 5, and preferably between 2 and 3.

[0039] One embodiment provides that the duration and duration The ratio is between 1 and 10, in particular between 1.5 and 5 and preferably between 2 and 3.

[0040] One embodiment provides that the duration Equal to duration , and / or duration Equal to duration .

[0041] The measured values ​​of the coil current and the coil voltage can also be used to control the operating signal. Thus, the time profile and / or measured values ​​of the coil current and the coil voltage during a longer time interval can be determined and used to control the duration of the short time interval and to determine the inductance of the magnetic field generating device. This means that the shorter time interval can be selected to be shorter than in the case of operation with constant partial time intervals. This is useful for suppressing Interference signals are particularly advantageous. The determined inductance can be used for diagnostics, compensation and / or flux density control in order to ensure that flow rate-related measured values ​​are correct and reliable even in the event of changes to the magnetic field generating device or under the influence of external disturbances.

[0042] One embodiment provides that the first time period lasts for a duration .

[0043] One embodiment provides that the duration and duration The ratio lies between 2 and 1000, in particular between 3 and 10 and preferably between 5 and 7.

[0044] One embodiment provides that the duration and duration The ratio lies between 4 and 2000, in particular between 6 and 20 and preferably between 10 and 14.

[0045] One embodiment provides that during the first partial time period and / or the third partial time period, the transmission signal value is applied Duration , and / or

[0046] During the second time segment and / or the fourth time segment, the transmission signal value is applied. Duration .

[0047] An advantage of this embodiment is that the additional application of transmit signal values ​​in separate time intervals results in a faster settling and thus a stabilization of the generated magnetic field.

[0048] The magnetic-inductive flowmeter according to the invention for determining a flow velocity-dependent measured variable of a flowable medium comprises:

[0049] - Measuring tubes for conducting media;

[0050] - Devices for detecting induced measuring voltages in media

[0051] - a magnetic field generating device, which is arranged on the measuring tube to generate a magnetic field penetrating the measuring tube;

[0052] - A measuring, operating and / or evaluating circuit designed to carry out the method according to the invention.

[0053] The magnetic-inductive flow measuring probe according to the invention for determining a flow velocity-dependent measured variable of a flowable medium comprises:

[0054] - a housing having a front portion to be acted upon by the medium,

[0055] - devices for detecting induced measuring voltages in a medium;

[0056] - a magnetic field generating device arranged in the housing to generate a magnetic field penetrating the housing, in particular the front part; and

[0057] - A measuring, operating and / or evaluating circuit designed to carry out the method according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will be described in more detail with reference to the following drawings, in which:

[0059] Figure 1 An embodiment of a magnetic induction flow meter is shown;

[0060] Figure 2 A perspective view showing a partial cross section of an embodiment of a magnetic-inductive flow measurement probe;

[0061] Figure 3 A schematic diagram showing a first embodiment of an operating signal;

[0062] Figure 4 It shows that the flow rate is 0m / s. Figure 3 Schematic representation of the measurement signal generated by the operating signal.

[0063] Figure 5 A schematic diagram showing a second embodiment of an operating signal;

[0064] Figure 6 An embodiment of the method according to the invention is shown. DETAILED DESCRIPTION

[0065] Figure 1A cross section through a magnetic-inductive flowmeter 1 is shown. The structure and measuring principle of the magnetic-inductive flowmeter 1 are known in principle. A flowable medium with electrical conductivity is conducted through a measuring tube 2. The measuring tube 2 comprises a medium-contacting carrier tube 3, which is usually made of steel, or at least comprises steel, ceramic, plastic or glass. A magnetic field generating device 5 for generating a magnetic field is arranged on the carrier tube 3 so that the magnetic field lines are oriented substantially perpendicular to the longitudinal direction defined by the measuring tube axis. The magnetic field generating device 5 usually comprises a saddle coil or at least one solenoid 6i. The coil core 14i usually extends through the socket 15 of the coil 6i. The socket 15 is understood to be a volume defined by the coil wire forming the coil 6i. The socket 15 of the coil 6i can therefore be formed by a coil holder or by an imaginary closed volume. The latter occurs when the coil wire of the coil 6i is directly wound around the coil core 14i. The coil core 14i is formed by a magnetically conductive, in particular soft magnetic material. The device 5 for generating a magnetic field comprises a pole shoe 21i arranged at one end of the coil core 14i. The pole shoe 21i can be a separate component or can be integrally connected to the coil core 14i. Figure 1 In the embodiment shown, two radially arranged coils 6a, 6b each have a coil core 14a, 14b and a pole shoe 21a, 21b. The two coil cores 14a, 14b are connected to each other via a field return 22. The field return 22 connects each side of the coil cores 14a, 14b that are opposite to each other. However, a magneto-inductive flowmeter having exactly one coil 6 with exactly one coil core 14 and without a field return is also known. The coil 6 is connected to an operating circuit 7, which operates the coil 6 by means of an operating signal. The operating signal can be a voltage with a time-variable curve and is characterized by operating signal parameters, at least one of which is controllable. The magnetic field generated by the device 5 for generating a magnetic field is generated by means of a pulsed direct current of alternating polarity provided by the operating circuit 7. This ensures a stable zero point and makes the measurement insensitive to influences due to electrochemical disturbances. The two coils 6a, 6b can be connected to the operating circuit 7 separately or connected in series or in parallel with each other.

[0066] When a magnetic field is applied, a flow rate-dependent potential distribution is generated in the measuring tube 2, which can be detected, for example, in the form of an induced measurement voltage. A device 8 for tapping the induced measurement voltage is arranged on the measuring tube 2. In the embodiment shown, the device 8 for tapping the induced measurement voltage is formed by two measuring electrodes 17, 18 arranged oppositely so as to form an electrical contact with the medium. However, this is known from a magnetic induction flowmeter comprising measuring electrodes arranged on the outer wall of the carrier tube 3 that are not in contact with the medium. The measuring electrodes 17, 18 are usually arranged along the diameter and form an electrode axis, or intersect with a transverse axis extending perpendicular to the magnetic field lines and the longitudinal axis of the measuring tube 2. However, a device 8 for tapping the induced measurement voltage and having more than two measuring electrodes is also known. The measured variable related to the flow rate can be determined based on the measured measurement voltage. The measured variable related to the flow rate includes the flow rate, volume flow rate and / or mass flow rate of the medium. The measuring circuit 23 is configured to detect the induced measurement voltage applied to the measuring electrodes 17, 18, and the evaluation circuit 24 is designed to determine the measured variable related to the flow rate. The evaluation circuit 24 can be part of the transmitter.

[0067] The carrier tube 3 is usually formed of an electrically conductive material such as steel. To prevent the measuring voltage applied to the first and second measuring electrodes 2, 3 from being conducted away via the carrier tube 3, the inner wall is lined with an insulating material, such as a lining 4 (made of plastic).

[0068] Commercially available magnetic-inductive flow meters have two further electrodes 19 and 20 in addition to the measuring electrodes 17, 18. In the first case, the fill level monitoring electrode 19, which is optimally attached at the highest point of the measuring tube 2, serves to detect partial filling of the measuring tube 1 and is configured to convey this information to the user and / or to take the fill level into account when determining the volume flow. In addition, a reference electrode 20, which is usually connected diametrically to the fill level monitoring electrode 19 or at the lowest point of the measuring tube cross section, serves to set a controlled potential in the medium. As a rule, the reference electrode 20 is used to connect the flowing medium to ground potential.

[0069] The operating circuit 7, the controller circuit 10, the measuring circuit 23 and the evaluation circuit 24 can be part of a single electronic circuit or can form a separate circuit. The measuring, operating and / or evaluation circuits 7, 23, 24 are designed to perform the method according to the invention. For this purpose, they can have a microprocessor and / or electrical components (electrical wiring, electromechanical components, passive and / or active components). For this purpose, the operating circuit is designed to generate an operating signal and provide it to the magnetic field generating device. In addition, the measuring circuit is designed to determine the measured voltage values ​​and forward them to the evaluation circuit. The evaluation circuit is designed to determine the current zero point and take into account the determination of the measured variable related to the flow rate.

[0070] First, based on Figure 2The perspective view and the partial cross-sectional view illustrate the measuring principle on which the present invention is based. The flow measurement probe 101 comprises a substantially circular cylindrical housing 102 having a predetermined outer diameter. The housing is adapted to the diameter of the hole located in the pipeline ( Figure 1 116 , which is a front end 116 of the housing 102 that protrudes into the medium, is sealed in a fluid-tight manner with a front body 115 made of an insulating material. With the aid of a coil arrangement 106 arranged in the housing 102, a magnetic field 109 extending through the end portion into the medium can be generated. A coil core 111 that is at least partially composed of a soft magnetic material and arranged in the housing 102 terminates at or near the end 116. A field return body 114 that surrounds the coil arrangement 106 and the coil core 111 is configured to return the magnetic field 109 extending through the end portion to the housing 102. The coil core 111, the pole shoe 112 and the field return body 114 are each a field conduction body 110 that together form a field conduction arrangement 105. The first and second measuring electrodes 104i which form an electrical contact with the medium to be conducted form a device 103 and are arranged in the front body 115, which serves to detect the measuring voltage induced in the medium and, like the outer wall of the housing, touches the medium. The voltage caused by Faraday's law of induction can be tapped at the measuring electrodes 104i by means of a measuring and / or evaluation circuit. When the flow measurement probe 101 is installed in the pipeline, it is at a maximum value so that the plane spanned by the straight line intersecting the two measuring electrodes 104i and by the longitudinal axis of the flow measurement probe extends perpendicular to the flow direction 118 or perpendicular to the longitudinal axis of the pipeline. The operating circuit 107 is electrically connected to the coil arrangement 106, in particular to the coil 113, and is configured to apply a clocked operating signal to the coil 113, thereby generating a clocked magnetic field 109.

[0071] The measuring, operating and / or evaluating circuit 107, 120, 121 is suitable and configured to perform the method according to the invention. For this purpose, it can have a microprocessor and / or electrical components (electrical wiring, electromechanical components, passive and / or active components). For this purpose, the operating circuit is designed to generate an operating signal and provide it to the magnetic field generating device. In addition, the measuring circuit is designed to determine the measured voltage values ​​and forward them to the evaluation circuit. The evaluation circuit is designed to determine the current zero point and take into account the determination of the measured variable related to the flow rate.

[0072] Figure 3A first embodiment of an operating signal (solid line) and a simplified schematic representation of an operating signal according to the prior art (dashed line) are shown. The operating signal can be a voltage signal or a current signal. In case the operating signal is a voltage signal, this comprises a time-varying voltage value applied to the magnetic field generating device. In case the operating signal is a current signal, this comprises a time-varying current value set at the magnetic field generating device. The depicted graph shows the current or voltage as a function of time. According to the prior art, the operating signal varies periodically between two time intervals. In a first time interval, the operating signal varies between signal values ​​​​of and signal value 0. The first part of the time interval has a time interval in which the operating signal has a signal value In the second time interval, the generated magnetic field changes the magnetic field polarity. In the second time interval, the operating signal changes between the signal values. and signal value 0. The second part of the time interval has a time interval in which the operating signal has a signal value and three partial time intervals in which the operating signal is 0. or The corresponding duration of is the same as the duration in which the operating signal assumes the signal value 0. The operating signal shown is referred to as a dual-frequency operating signal.

[0073] The operating signal according to the present invention differs from the prior art mainly in that there is no partial time interval in which the operating signal presents a signal value of zero. and or and The durations of the time intervals i, ii, iii, iv are different. In the embodiment shown, the duration and Presents a 1:2 ratio and duration and A ratio of 2:1 is presented. The ratio changes at a change from a first time interval to a second time interval or from a second time interval to a first time interval. The first time interval lasts for a duration In the illustrated embodiment, the duration of the first time interval is the same as the duration of the second time interval. and and signal value and or four signal values , , and The absolute value of is also the same. Duration With duration Same and duration With duration Same. Alternatively, the duration and duration The ratio can be between 1 and 10, in particular between 1.5 and 5, and preferably between 2 and 3. Alternatively, the duration and duration The ratio can be between 1 and 10, in particular between 1.5 and 5, and preferably between 2 and 3. For an optimal configuration of the operating signal, the duration and duration The ratio can be set between 2 and 1000, in particular between 3 and 10, and preferably between 5 and 7, and the duration and duration The ratio can be set between 4 and 2000, in particular between 6 and 20, and preferably between 10 and 14.

[0074] Figure 4 It is shown that according to the present invention Figure 3 Schematic representation of the operating signal in and the measured signal according to the prior art at a flow velocity of 0 m / s. The measured signal comprises a measured voltage induced by the flowing medium with a simplified interference signal (the measured voltage is zero in this case), which provides an exponentially decaying part. The interference signal is caused by crosstalk from the magnetic field generating device to the device for detecting the induced measured voltage. Usually, the measured voltage observed over time is measured in the later part of the time interval of constant magnetic field polarity, because the influence of the interference is minimal there. Operating the magnetic field generating device at a higher frequency produces a larger zero point (see and ), because the disturbance induced when switching the coil current direction is able to decay to a small extent before the next switching occurs. Such disturbance cannot be reliably distinguished from the actual flow. For example, the average value of two measured voltages with opposite magnetic field polarity (red double arrows) in two consecutive time intervals and without corresponding flow-related signal components does not depend on zero-point effects.

[0075] According to the measurement signal generated by the operating signal 11 according to the prior art (dashed line), the advantages of the operating signal according to the invention are clearly evident. The measurement signal generated by the operating signal according to the invention has a significantly higher measurement signal amplitude for all partial time intervals. Exactly at the beginning of the switching process, the amplitude in the conventional solution is very low and close to 0V. Only after a few partial time intervals, the amplitude of the partial time intervals in which no coil current flows through the magnetic field generating device increases until it reaches essentially half of the maximum amplitude.

[0076] Figure 51 shows a schematic representation of a second embodiment of the operating signal 11. The second embodiment of the operating signal 11 differs from the first embodiment mainly in that during the first partial time period i and the third partial time period iii, the transmission signal value is additionally applied. (e.g., transmit voltage) for a duration , and during the second partial time period ii and the fourth partial time period iv, the transmission signal value is additionally applied (e.g., transmit voltage) for a duration In the case of the exemplary embodiment shown, the absolute values ​​of the individual transmit signal values ​​and the durations are identical. The absolute values ​​of the individual transmit signal values ​​as well as the durations for which the corresponding transmit signal values ​​are applied can differ from one another.

[0077] Figure 6 An embodiment of the method according to the invention is shown. An operating signal is applied to a magnetic field generating device to generate a magnetic field (method step I). The operating signal has a first time section having at least a first partial time section and a second partial time section. In the first partial time section, a signal value is applied for a duration of , and in the second part of the time period, the signal value is applied Duration During the duration , the magnetic field generated has a magnetic field polarity different from that in the duration According to the present invention, the duration Longer than duration Thus, during the first duration, in which the signal value is applied The time portion is longer than the value in which the signal is applied The time portion.

[0078] The operating signal also includes a second time segment directly following the first time segment. However, it is possible to provide a further time segment with a signal value of 0 between the first duration and the second duration. The second time segment has at least a duration in which the application The signal value The third part of the time period and the duration of application The signal value The fourth part of the time period. The magnetic field polarity during the period is different from that during the duration According to the present invention, the duration Longer than duration Therefore, in the second time segment, the signal value is applied The time portion is longer than the value in which the signal is applied The time portion.

[0079] It is essential for the invention that during the first duration the signal value and signal value At least temporarily at a first frequency Alternately, and during the second duration, the second signal value and the second signal value At least temporarily at a second frequency At the same time, the first time segment and the second time segment are at a frequency lower than the first frequency and the second frequency The third frequency Therefore, the operating signal according to the present invention is also a dual-frequency operating signal.

[0080] While applying the operating signal, measuring a first measured voltage value of the induced measured voltage during a measuring section of a first time section (I) (Method step II).

[0081] During a measuring period of the second time period (II) offset in time relative to the first time period (I), a second measured voltage value of the induced measured voltage is measured (Method step III).

[0082] According to the first measured voltage value measured and the second measured voltage value , determine the current zero point for compensating the flow rate-dependent measured variable (method step IV). This can be done by measuring the current zero point at two measured voltage values. and The flow rate-dependent measured variable is determined based on the measured voltage values ​​at different partial time intervals and is compensated by the current zero point.

[0083] Method steps I to IV are not to be interpreted as sequential method steps. For example, in method step I the induced measurement voltage is measured during the application of the operating signal.

[0084] Reference numerals list

[0085] Magnetic induction flowmeter 1

[0086] Measuring tube 2

[0087] Loading tube 3

[0088] Lining 4

[0089] Magnetic field generating device 5

[0090] Operation circuit 7

[0091] Device for detecting inductive measuring voltage 8

[0092] Controller circuit 10

[0093] Operation signal 11

[0094] Coil 13i

[0095] Coil core 14i

[0096] Measuring electrode 17i

[0097] Field returns to the main body 19

[0098] Pole shoe 21i

[0099] Measurement circuit 23

[0100] Evaluation circuit 24

[0101] Magnetic induction flow measurement probe 101

[0102] Housing 102

[0103] Device for measuring induced measuring voltage 103

[0104] Measuring electrode 104i

[0105] Magnetic field generating device 105

[0106] Coil Arrangement 106

[0107] Operation circuit 107

[0108] Magnetic Field 109

[0109] Field conduction body 110

[0110] Coil core 111

[0111] Pole shoe 112

[0112] Coil 113

[0113] Field return main body 114

[0114] Front body 115

[0115] End 116

[0116] Flow direction of the medium 118

[0117] Measurement circuit 120

[0118] Evaluation circuit 121

Claims

1. A method for operating a magnetic-inductive flowmeter for determining a flow rate-related measured variable of a flowable medium, the magnetic-inductive flowmeter comprising a magnetic field generating device (5, 105) for generating a magnetic field and a device (8, 103) for detecting an induced measurement voltage in the medium, the method comprising the following method steps: - applying an operating signal (11) to the magnetic field generating device (5) to generate the magnetic field, in, The operating signal (11) has a first time section (I), The first time segment (I) at least includes a first partial time segment (i) and a second partial time segment (ii). Therein, in the first partial time period (i), a signal value is applied in each case Duration , In the second time segment (ii), the signal value is applied Duration , The duration Longer than stated duration , wherein, during the duration The magnetic field polarity during the duration is different from that in the The magnetic field polarity during The operation signal has a second time segment (II), and the second time segment (II) is particularly immediately after the first time segment (I). The second time segment (II) at least includes a third time segment (iii) and a fourth time segment (iv). In the third time segment (iii), the signal value is applied Duration , In the fourth time segment (iv), the signal value is applied Duration , The duration Longer than stated duration , wherein, during the duration The magnetic field polarity during the duration is different from that in the The polarity of the magnetic field during the period; - measuring a first measured voltage value of the induced measurement voltage during a measuring section of the first time section (I) ; - measuring a second measured voltage value of the induced measured voltage during a measuring section of the second time section (II) ;as well as - Based on the first measured voltage value and the second measured voltage value The current zero point is determined in order to compensate the flow rate-dependent measured variable.

2. The method according to claim 1, wherein: in, During the first time period (I), the signal value and the signal value At least temporarily at the first frequency alternately.

3. The method according to claim 1 or 2, wherein: in, During the second time period (II), the second signal value and the second signal value At least temporarily at the second frequency alternately.

4. The method according to one of the preceding claims, in, The first time segment (I) and the second time segment (II) are transmitted at a third frequency. alternately.

5. The method according to any one of claims 2 to 4, in, The third frequency Below the first frequency and the second frequency .

6. The method according to any one of claims 2 to 5, in, The third frequency With the first frequency and / or the second frequency The ratio lies between 2 and 1000, in particular between 2 and 10 and preferably between 3 and 5.

7. The method according to one of the preceding claims, in, The duration and the duration The ratio lies between 1 and 10, in particular between 1.5 and 5, and preferably between 2 and 3.

8. The method according to one of the preceding claims, in, The duration and the duration The ratio lies between 1 and 10, in particular between 1.5 and 5, and preferably between 2 and 3.

9. The method according to one of the preceding claims, in, The duration Equal to the duration , and / or the duration Equal to the duration .

10. The method according to one of the preceding claims, in, The first time period (I) lasts for a duration .

11. The method according to claim 10, wherein: in, The duration and the duration The ratio lies between 2 and 1000, in particular between 3 and 10 and preferably between 5 and 7.

12. The method according to claim 10 or 11, wherein: in, The duration With the duration The ratio lies between 4 and 2000, in particular between 6 and 20 and preferably between 10 and 14.

13. The method according to one of the preceding claims, in, During the first part of the time period (i) and / or the third part of the time period (iii), a transmission signal value is applied Duration , and / or During the second time segment (ii) and / or the fourth time segment (iv), the transmission signal value is applied. Duration .

14. A magnetic-inductive flowmeter (1) for determining a flow velocity-dependent measured variable of a flowable medium, include: - a measuring tube (2) for conducting the medium; - Device for detecting an induced voltage in the medium (8) - a magnetic field generating device (5) arranged on the measuring tube (2) to generate a magnetic field penetrating the measuring tube (2); - a measuring circuit, an operating circuit and / or an evaluation circuit (7, 23 and 24) designed to carry out a method according to any of the preceding claims.

15. A magnetic-inductive flowmeter (101) for determining a flow velocity-dependent measured variable of a flowable medium, include: - a housing (102) having a front portion (116) on which the medium is to act, - a device (103) for detecting an induced voltage in a medium; - a magnetic field generating device (105) arranged in the housing (102) to generate a magnetic field penetrating the housing (102), in particular the front part (116); and - a measuring, operating and / or evaluating circuit (107, 120, 121) designed to carry out a method according to any of claims 1 to 13.

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