Magnetic inductive flowmeter with conductivity measuring device and method of operation thereof

Abstract

Magnetic-inductive flowmeter with a conductivity measuring device and method for operating the same. The task of providing a magnetic-inductive flowmeter which can be used to perform an improved flow measurement is solved in that the conductivity measuring device has a measuring circuit, wherein electrodes are part of the measuring circuit, and wherein the measuring circuit has a voltage source and a measuring cell, wherein in the operating state of the conductivity measuring device the voltage source generates a measuring circuit voltage in the measuring circuit, and the measuring cell measures an actual electrode voltage which is present between the electrodes; and the conductivity measuring device has a regulating cell and an evaluation cell, wherein in the operating state of the conductivity measuring device the regulating cell regulates the actual electrode voltage to a pre-specified constant target value, and the evaluation cell determines an electrode current which flows between the electrodes, and determines a value for the electrical conductivity of the medium or a quantity which is associated with the electrical conductivity, using the determined value for the electrode current and the actual electrode voltage.

Description

TECHNICAL FIELD

[0001] The invention relates to a magnetic-inductive flowmeter having a measuring tube for conducting an electrically conductive medium, a magnetic field generating device for generating a magnetic field through the measuring tube at least partially perpendicular to the flow direction of the medium, electrodes for measuring a measuring voltage induced in the medium, and a conductivity measuring device for determining the electrical conductivity of the electrically conductive medium. The invention also relates to a method for operating such a magnetic-inductive flowmeter. BACKGROUND

[0002] Magnetic-inductive flowmeters are used for determining the flow rate of electrically conductive media. If subsequently the "conductivity" of the medium is referred to in short, this always means the electrical conductivity of the medium. The measuring principle on which the flow measurement is based is based on the principle of charge separation of particles in a magnetic field. The charge separation leads to an induced voltage, the measuring voltage, which is proportional to the flow speed of the charge carriers moving in the medium, so that from the flow speed the flow rate in the medium can be inferred. It is known from practice that a temporally alternating magnetic field is used for magnetic-inductive flow measurement.

[0003] In order that a magnetic-inductive flow measurement can be carried out on a medium, the medium must have a minimum electrical conductivity. However, the electrical conductivity or conductivity value of an electrically conductive medium is often not known. Correspondingly, magnetic-inductive flowmeters are known from the prior art which also have a conductivity measuring device with which the electrical conductivity of the electrically conductive medium can be determined.

[0004] In order to determine the electrical conductivity, a current is injected between the electrodes and the resulting voltage attached between the two electrodes is measured immediately thereafter. From the ratio of the measured voltage to the injected current, a resistance value can be calculated which serves as a basis for determining the electrical conductivity of the medium flowing in the measuring tube, wherein the electrical conductivity of the medium is proportional to the inverse of the determined resistance value.

[0005] It is also known that the conductivity measurement is carried out in the switching phase of the magnetic field generated for the magnetic-inductive flow measurement, in order to thus utilize the time required until the magnetic field has become sufficiently stable. Correspondingly, during the switching time of the magnetic field, the current required for the conductivity measurement is injected into the medium between the electrodes and the voltage falling over the electrodes as a result of the current passing through the medium is measured.

[0006] Before the actual magnetic-inductive flow measurement is started, the injected current is switched off. Despite the end of the conductivity measurement, a residual voltage related to the electrical conductivity of the medium remains between the electrodes. This residual voltage is measured in conjunction with the flow measurement and leads to an error related to the electrical conductivity of the medium, which can be noted by a voltage offset and which relates the flow value determined with the magnetic-inductive flow measurement to the electrical conductivity of the medium. SUMMARY

[0007] Correspondingly, the task of the present application is to provide a magnetic-inductive flowmeter with which an improved flow measurement can be performed. The task of the present application is also to provide a method for operating such a magnetic-inductive flowmeter.

[0008] In the case of a magnetic-inductive flowmeter according to the application, the task is solved in that the conductivity measuring device has a measuring circuit, in which the electrodes are part of the measuring circuit, and in that the measuring circuit has a voltage source and a measuring cell. In the operating state of the conductivity measuring device, the voltage source generates a measuring circuit voltage in the measuring circuit. The measuring cell measures an actual electrode voltage which is present between the electrodes. The conductivity measuring device of the magnetic-inductive flowmeter according to the application also has a regulating cell and an analysis cell. In the operating state of the conductivity measuring device, the regulating cell regulates the actual electrode voltage to a predefinable constant target value. The analysis cell determines an electrode current which flows between the electrodes and, using the value of the determined electrode current and the actual electrode voltage, determines a conductivity value of the medium and / or a quantity which is associated with the conductivity. Such a quantity can be, for example, a resistance value of the medium. For the sake of clarification, it is noted that using the measured actual electrode voltage and the determined electrode current, the conductivity value or the resistance value of the medium in the specific geometric arrangement of the electrodes and the measuring tube can first be calculated. However, it can then be inferred by a factor whether the conductivity or the resistance of the medium is the material quantity.

[0009] Unlike from what is known from the prior art, in the case of a magnetic-inductive flowmeter according to the application, in order to determine the conductivity of the medium, a constant electrode voltage is not injected between the electrodes and the resulting voltage is measured, but rather a constant electrode voltage is generated between the electrodes and the resulting electrode current is determined. From these two values, the conductivity value of the conductive medium is then determined. The magnetic-inductive flowmeter according to the application has the following advantage over the prior art: The electrode voltage which is present between the electrodes when measuring the conductivity of the medium is essentially constant and is thereby no longer dependent on or determined by the conductivity of the medium. Correspondingly, the residual voltage which remains on the electrodes after the end of the conductivity measurement is also constant, which leads to a constant, conductivity-independent offset in the magnetic-inductive flow measurement, which can thus be taken into account or calculated out much more simply.

[0010] The voltage generated in the measuring circuit by the voltage source can have any form. In one particularly preferred design, however, the voltage is an alternating voltage, preferably a harmonic alternating voltage. In one preferred design, two sinusoidal voltages are superimposed in the generated voltage. Particularly preferably, the frequency of the second sinusoidal voltage is twice the frequency of the first sinusoidal voltage.

[0011] In the first design of the magnetic-inductive flowmeter, the regulating unit and the evaluation unit are configured as separate units. In the second design of the magnetic-inductive flowmeter according to the application, however, the regulating unit and the evaluation unit are realized as a common unit, in particular by means of a microcontroller.

[0012] According to the application, the electrode current flowing through the medium between the electrodes and thereby in the measuring circuit is measured. In the first design, the measuring circuit of the conductivity measuring device has a current measuring unit which measures the electrode current and thereby the measuring circuit current. In particular, the current measuring unit transmits the value of the measured electrode current to the evaluation unit. In the second design of the magnetic-inductive flowmeter according to the application, the evaluation unit determines the voltage difference between the generated measuring circuit voltage and the actual electrode voltage and determines the electrode current from the voltage difference and the resistance value of the measuring circuit. This design has the advantage that no additional measuring unit, i.e. no additional current measuring unit, has to be provided. Rather, the electrode current flowing between the electrodes can be determined by means of the known quantities.

[0013] In a particularly preferred design of the magnetic-inductive flowmeter according to the application, the resistance value of the measuring circuit is stored in the evaluation unit. In particular, the resistance is integrated into the measuring circuit, wherein the resistance has a known resistance value which is stored in the evaluation unit.

[0014] A particularly preferred design of the magnetic-inductive flowmeter is characterized in that a constant setpoint value for the electrode voltage is stored in the regulating unit. The regulating unit compares the actual electrode voltage measured by the measuring unit with the stored setpoint value and determines a regulating deviation therefrom. That is, the regulating deviation is the difference between the setpoint value and the actual electrode voltage. Using the regulating deviation, the regulating unit adjusts the measuring circuit voltage. In a particularly preferred design, the regulating unit is configured as a P controller, a PI controller or a PID controller.

[0015] In a particularly preferred design, the setpoint value for the electrode voltage is 1 mV, so that the actual electrode voltage is regulated to 1 mV. However, smaller or larger values of the setpoint value are equally conceivable.

[0016] A further design variant of the magnetic-inductive flowmeter is characterized in that the measuring circuit has at least two alternative measuring paths which can be integrated into the measuring circuit by means of at least one switch, respectively. Each of the at least two measuring paths has an electrical resistance, wherein at least two of the electrical resistances of the at least two measuring paths have different electrical resistance values from one another. The resistance values of the different electrical resistances are stored in an adjustment unit. The adjustment unit is further configured such that it can switch the switches and thereby can alternatively switch the alternative measuring paths into the measuring circuit. In a preferred design variant, the measuring circuit has three measuring paths which can be integrated into the measuring circuit by means of at least one switch, respectively.

[0017] It is particularly preferred that the adjustment unit is configured such that it makes a decision as to which measuring path should be switched into the measuring circuit depending on the adjustment deviation, i.e. the difference between the setpoint value and the measured actual electrode voltage, and a characteristic of the voltage source operating at a limit of its adjustment range. Thus, it is preferred that a switch from one measuring path to another measuring path is performed each time the voltage source operates at a limit of its adjustment range, whereas the adjustment deviation still exists or exceeds a tolerable value. Thereby, the magnetic-inductive flowmeter has the great advantage that a very wide measuring range can be achieved. The measuring range of the conductivity measuring device can be adjusted and changed accordingly by switching on the alternative measuring paths.

[0018] In a further design variant of the magnetic-inductive flowmeter according to the application, a capacitor is provided in the measuring circuit. In the design variant in which the measuring circuit has a plurality of alternatively switchable measuring paths, a capacitor is provided in each measuring path. The capacitor serves to filter, i.e. to suppress, a direct current component in the measuring circuit. Such a direct current component can have a disadvantageous effect on the electrode voltage and thus also on the flow measurement, which is prevented by filtering with the capacitor. The capacitance of the capacitor is chosen to be so large that the voltage drop over the capacitor can actually be neglected, for example compared to the voltage drop (which can be measured at the electrodes) over the medium section and for example compared to the voltage drop over the additional ohmic resistance.

[0019] In addition to the magnetic induction flowmeter, the present invention also relates to a method for operating the magnetic induction flowmeter according to the invention, namely, a method for operating a magnetic induction flowmeter having: a measuring tube for guiding a conductive medium; a magnetic field generating device for generating a magnetic field that penetrates the measuring tube at least partially perpendicular to the flow direction of the medium; electrodes for measuring a measuring voltage induced in the medium; and a conductivity measuring device having a measuring circuit, wherein the electrodes are part of the measuring circuit, and wherein the measuring circuit has a voltage source and a measuring unit, and wherein the conductivity measuring device has an adjustment unit and an analysis unit.

[0020] In the method according to the invention, in the generation step, a voltage source generates a measurement circuit voltage in the measurement circuit, and in the measurement step, a measurement unit measures the actual electrode voltage between the electrodes. In the comparison step, an adjustment unit compares the measured actual electrode voltage with a predetermined rated value and determines the adjustment deviation.

[0021] If the adjustment deviation exceeds a predetermined value, the adjustment unit adjusts the voltage of the measuring circuit during the adjustment step until the adjustment deviation is lower than or corresponds to the predetermined value. This predetermined value is, for example, stored in the adjustment unit.

[0022] In the determination step, the analysis unit determines the electrode current flowing between the electrodes, while in the calculation step, the analysis unit calculates the conductivity value and / or parameters associated with the conductivity based on the electrode current and the actual electrode voltage. Parameters associated with conductivity may, for example, be the resistance of the dielectric.

[0023] In a particularly preferred embodiment of the method according to the invention, in the determination step, the electrode current is determined based on the difference between the applied measuring circuit voltage and the actual electrode voltage and the resistance value of the measuring circuit. Particularly preferably, the resistance value of the measuring circuit is stored in the analysis unit.

[0024] The method according to the invention can be performed in different embodiments. In one embodiment, when the adjustment deviation corresponds to or is lower than the predetermined value, a determination step and a calculation step are performed. Here, the predetermined value corresponds to a tolerable deviation between the actual electrode voltage and the rated value and can be, for example, predetermined by the user. If the adjustment deviation corresponds to or is even lower than the predetermined value, the actual electrode voltage is adjusted accordingly.

[0025] In another embodiment, the determining and calculating steps are performed regardless of the value of the determined adjustment deviation, i.e., regardless of whether the actual electrode voltage already corresponds to the rated value. Simultaneously, the adjustment steps are performed until the actual electrode voltage corresponds to the rated value. In this embodiment, the steps are repeated multiple times, preferably continuously, until the adjustment deviation finally corresponds to the predetermined value.

[0026] If the measuring circuit of the magnetic induction flowmeter has at least two alternative measuring paths that can be integrated into the measuring circuit via switches, and each of the at least two measuring paths further has a resistor, wherein at least two resistors of the at least two measuring paths have different resistance values, and wherein the at least two resistance values ​​are stored in an adjustment unit, then an extension of the method according to the invention is characterized in that, in the switching step, one of these switches is closed by the adjustment unit, thereby effectively switching one of these measuring paths into the measuring circuit. Preferably, the adjustment unit switches exactly one of these measuring paths into the measuring circuit. Through this embodiment, the measuring range of the conductivity measuring device is changed in a concise manner and method.

[0027] Particularly preferably, in the checking step, the adjustment unit checks whether the voltage source is operating at the limits of its adjustment range. Additionally, the checking step checks whether the adjustment deviation is higher than the predetermined value. In the decision step following the checking step, the adjustment unit decides whether to effectively switch another alternative measurement path into the measurement circuit. When the voltage source is operating at the limits of its adjustment range (where this could be not only the upper limit but also the lower limit), and when the adjustment deviation is simultaneously higher than the predetermined value, i.e., when the actual electrode voltage still does not correspond to the rated value, it is definitively decided to switch another measurement path into the measurement circuit. Preferably, the adjustment unit selects the measurement path having the next higher or lower resistance value, depending on whether the voltage source is operating at its upper or lower limit. Attached Figure Description

[0028] Now, various possibilities for designing and extending the magnetic induction flowmeter according to the invention and the method according to the invention are given in detail. For this purpose, reference is made to the description of particularly preferred embodiments in conjunction with the accompanying drawings. In the drawings:

[0029] Figure 1 A first embodiment of a magnetic induction flowmeter with a conductivity measuring device is shown;

[0030] Figure 2 A second design scheme for a magnetic induction flowmeter with a conductivity measuring device is shown;

[0031] Figure 3 A block diagram of a first embodiment of the method is shown; while

[0032] Figure 4 A block diagram of a second embodiment of the method is shown. Detailed Implementation

[0033] Figure 1 A magnetic induction flow meter 1 is shown. The magnetic induction flow meter 1 has: a measuring tube 2 for guiding a conductive medium; and a magnetic field generating device 3. Two electrodes 4 are used to measure the voltage induced in the medium. To similarly determine the conductivity of the conductive medium, the magnetic induction flow meter 1 has a conductivity measuring device 5. The conductivity measuring device 5 has a measuring circuit 6, in which the two electrodes 4 are part. The measuring circuit 6 also has a voltage source 7 and a measuring unit 8. The voltage source 7 generates a measuring circuit voltage in the measuring circuit 6, while the measuring unit 8 measures the actual electrode voltage attached between the electrodes 4. The conductivity measuring device 5 also has an adjustment unit 9 and an analysis unit 10, which, in the currently shown embodiment, are implemented as a common unit, i.e., a microcontroller. During operation of the conductivity measuring device 5, the adjustment unit 9 adjusts the actual electrode voltage to a pre-given constant rated value. The analysis unit 10 determines the electrode current flowing between the electrodes 4, and uses the determined electrode current value and the actual electrode voltage to calculate the conductivity value of the medium and / or parameters associated with the conductivity of the medium, such as the resistance value of the medium.

[0034] The illustrated magnetic induction flowmeter 1 has the following advantages: the actual electrode voltage between the electrodes 4 is adjusted to a constant value. Since conductivity measurement is affected by the residual voltage between the electrodes 4, the illustrated magnetic induction flowmeter 1 achieves a constant residual voltage that is independent of or not determined by the conductivity of the medium. The residual voltage causes errors in flow measurement, particularly noticeable through voltage deviation in the measured voltage induced in the medium by the magnetic field. By maintaining a constant actual electrode voltage between the electrodes 4 and thereby a constant residual voltage, a constant deviation value is obtained, making the magnetic induction flow measurement no longer dependent on the conductivity of the medium.

[0035] Figure 2 Another design scheme for a magnetic induction flowmeter 1 with a conductivity measuring device 5 is shown. Unlike in... Figure 1In the embodiment shown, the measurement circuit 6 has three alternative measurement paths 12, 12', 12" that can be integrated into the measurement circuit 6 via switches 11, 11', 11" respectively. In the illustrated embodiment, switch 11' is closed while the two switches 11, 11" are open, so that measurement path 12' is effectively integrated into the measurement circuit 6.

[0036] Each of the measurement paths 12, 12', 12" has an ohmic resistor 13, 13', 13" with different resistance values. Additionally, each measurement path 12, 12', 12" has a capacitor 14, 14', 14" which filters out the DC voltage component from the measurement circuit voltage.

[0037] Unlike in Figure 1 The embodiments shown in the figure are in Figure 2 Another advantage of the embodiment shown is that the measurement range of the conductivity measuring device 5 can be changed and adapted to the medium by correspondingly switching on one of the measurement paths 12, 12', and 12" respectively. In this case, the adjustment unit 9 is designed to check whether the voltage source 7 is operating at the limits of its adjustment range and whether the adjustment deviation determined by the adjustment unit 9 is higher than a predetermined value. If the voltage source 7 is operating at the limits of its adjustment range and the adjustment deviation is higher than the predetermined value, the adjustment unit 9 switches another measurement path 12, 12', or 12" to the measurement circuit 6. Here, the voltage source 7 is implemented by a digital-to-analog converter. Correspondingly, the measurement unit 8 is implemented as an analog-to-digital converter.

[0038] Figure 3 A block diagram illustrating an embodiment of a method 100 for operating the described magnetic induction flowmeter 1 is shown. In the generation step 101, a measurement circuit voltage is generated in the measurement circuit 6 by a voltage source 7. In the measurement step 102, the actual electrode voltage between the electrodes 4 is measured by a measurement unit 8. In the comparison step 103, the measured actual electrode voltage is compared with a pre-given rated value by an adjustment unit 9, and an adjustment deviation is determined. In the determination step 104, the electrode current flowing between the electrodes 4 is determined by an analysis unit 10, and in the calculation step 105, the analysis unit calculates the conductivity value and / or calculates parameters associated with the conductivity based on the electrode current and the actual electrode voltage.

[0039] If the adjustment deviation exceeds the predetermined value, then in adjustment step 106, the adjustment unit 9 adjusts the voltage of the measuring circuit until the adjustment deviation is lower than or corresponds to the predetermined value.

[0040] In the method shown, in step 104, the electrode current is determined based on the difference between the applied measuring circuit voltage and the actual electrode voltage and the resistance value of the measuring circuit 6.

[0041] Figure 4 A block diagram of a second method 100' for operating a magnetic induction flowmeter 1 is shown. Method 100' is performed in the magnetic induction flowmeter 1 having a conductivity measuring device 5, wherein a measuring circuit 6 has at least two alternative measuring paths 12, 12', 12" that can be integrated into the measuring circuit 6 respectively via switches 11, 11', 11" , wherein each of the at least two measuring paths 12, 12', 12" has a resistor 13, 13', 13" . Resistors 13, 13', 13" have different resistance values ​​from each other. The corresponding resistance values ​​are stored in an adjustment unit 9. Figure 4 The method 100' shown in the figure is the same as that in the figure. Figure 3 The difference in method 100 shown is that the following method steps are performed. After comparison step 103, the adjustment unit 9 performs check step 107. In check step 107, the adjustment unit 9 checks whether the voltage source 7 is operating at the limits of its adjustment range and whether the adjustment deviation is higher than a predetermined value, i.e., whether the actual electrode voltage deviates from the rated value by more than a tolerable value. In the immediately following decision step 108, the adjustment unit 9 decides whether another measurement path 12, 12', 12" should be switched to the measurement circuit 6 and which measurement path 12, 12', 12" should be switched to the measurement circuit 6. If voltage source 7 operates at the limits of its adjustment range and the adjustment deviation is greater than the predetermined value, then adjustment unit 9 decides to perform switching step 109 and switch the other measurement paths 12, 12', 12" to measurement circuit 6. Then, adjustment step 106 is performed. If adjustment unit 9 decides in decision step 108 that switching should not be performed, then adjustment step 106 is performed without switching the other measurement paths 12, 12', 12" to measurement circuit 6.

[0042] Figure Labels

[0043] 1. Magnetic induction flow meter

[0044] 2 Measuring tube

[0045] 3. Magnetic field generating device

[0046] 4 electrodes

[0047] 5. Conductivity measuring device

[0048] 6. Measurement Circuit

[0049] 7. Voltage source

[0050] 8 Measurement Units

[0051] 9 Adjustment Units

[0052] 10 Analysis Units

[0053] 11 Switches

[0054] 12 Measurement Path

[0055] 13 Resistors

[0056] 14 Capacitors

[0057] 100 methods

[0058] 100' method

[0059] 101 Generation Steps

[0060] 102 Measurement Procedure

[0061] 103 Comparison Steps

[0062] 104 Determine the steps

[0063] 105 Calculation Steps

[0064] 106 Adjustment Steps

[0065] 107 Inspection Steps

[0066] 108 Decision Steps

[0067] 109 Switching Steps

Claims

1. A magnetic induction flowmeter (1) comprising: a measuring tube (2) for guiding a conductive medium; a magnetic field generating device (3) for generating a magnetic field penetrating the measuring tube (2) at least partially perpendicular to the flow direction of the medium; an electrode (4) for measuring a voltage induced in the medium; and a conductivity measuring device (5) for determining the conductivity of the conductive medium. in, The conductivity measuring device (5) has a measuring circuit (6), wherein the electrode (4) is part of the measuring circuit (6), wherein the measuring circuit (6) has a voltage source (7) and a measuring unit (8), wherein, in the operating state of the conductivity measuring device (5), the voltage source (7) generates a measuring circuit voltage in the measuring circuit (6). Its features are, The measuring unit (8) measures the actual electrode voltage between the electrodes (4); Furthermore, the conductivity measuring device (5) has an adjustment unit (9) and an analysis unit (10), wherein, in the operating state of the conductivity measuring device (5), the adjustment unit (9) adjusts the actual electrode voltage to a predetermined constant rated value, and the analysis unit (10) determines the electrode current flowing between the electrodes (4), and uses the determined electrode current value and the actual electrode voltage to calculate the conductivity value of the medium or a parameter associated with the conductivity; Furthermore, the measurement circuit (6) has at least two alternative measurement paths that can be integrated into the measurement circuit by switching, each of the at least two measurement paths having a resistor, and the at least two resistors of the at least two measurement paths having different resistance values; and the resistance values ​​of the resistors are stored in the adjustment unit (9); and the adjustment unit (9) is configured such that the adjustment unit can switch the switch and thereby can alternatively and effectively switch the alternative measurement paths into the measurement circuit (6).

2. The magnetic induction flowmeter (1) according to claim 1, characterized in that, The measurement circuit (6) has a current measurement unit that measures the electrode current and transmits the value of the electrode current to the analysis unit (10).

3. The magnetic induction flowmeter (1) according to claim 1, characterized in that, The analysis unit (10) determines the voltage difference between the generated measurement circuit voltage and the actual electrode voltage and determines the electrode current based on the voltage difference and the resistance value of the measurement circuit (6).

4. The magnetic induction flowmeter (1) according to any one of claims 1 to 3, characterized in that, The adjustment unit (9) stores the pre-given constant rated value, and the adjustment unit (9) compares the actual electrode voltage measured by the measurement unit (8) with the rated value and thus determines the adjustment deviation, and the adjustment unit adjusts the voltage of the measurement circuit in the case of the adjustment deviation, wherein the adjustment unit (9) is configured as a P controller, PI controller or PID controller.

5. The magnetic induction flowmeter (1) according to claim 4, characterized in that, The adjustment unit (9) makes a decision on which measurement path to effectively switch to the measurement circuit (6) based on whether the adjustment deviation is higher than a pre-given value and whether the voltage source (7) is operating at the limit of its adjustment range.

6. The magnetic induction flowmeter (1) according to any one of claims 1 to 3, characterized in that, Each measurement path has a capacitor connected in series with the resistor to filter the DC voltage component in the measurement circuit voltage.

7. A method for operating a magnetic induction flow meter (1), wherein the magnetic induction flow meter (1) comprises: a measuring tube (2) for guiding a conductive medium; a magnetic field generating device (3) for generating a magnetic field that penetrates the measuring tube (2) at least partially perpendicular to the flow direction of the medium; an electrode (4) for measuring a measuring voltage induced in the medium; and a conductivity measuring device (5) having a measuring circuit (6), wherein the electrode (4) is part of the measuring circuit (6), and wherein the measuring circuit (6) has a voltage source (7) and a measuring unit (8), and wherein the conductivity measuring device (5) has an adjustment unit (9) and an analysis unit (10). In the generation step (101), the voltage source (7) generates the measurement circuit voltage in the measurement circuit (6). In measurement step (102), the measurement unit (8) measures the actual electrode voltage between the electrodes (4). In the comparison step (103), the adjustment unit (9) compares the measured actual electrode voltage with a pre-given rated value and determines the adjustment deviation. If the adjustment deviation exceeds a predetermined value, in adjustment step (106), the adjustment unit (9) adjusts the voltage of the measuring circuit until the adjustment deviation is lower than or corresponds to the predetermined value. In step (104), the analysis unit (10) determines the electrode current flowing between the electrodes (4). Furthermore, in the calculation step (105), the analysis unit (10) calculates the conductivity value and / or calculates parameters associated with the conductivity based on the actual electrode voltage and the electrode current. Furthermore, the measuring circuit (6) has at least two alternative measuring paths that can be integrated into the measuring circuit (6) by switching, each of the at least two measuring paths having a resistor, and the at least two resistors of the at least two measuring paths having different resistance values ​​from each other, and the at least two resistance values ​​of the resistors being stored in the adjustment unit (9), characterized in that, In the switching step (109), one of the switches is closed by the adjustment unit (9), thereby effectively switching one of the measurement paths into the measurement circuit (6).

8. The method according to claim 7, characterized in that, In the determination step (104), the electrode current is determined based on the difference between the applied measurement circuit voltage and the actual electrode voltage and the resistance value of the measurement circuit (6).

9. The method according to claim 7 or 8, characterized in that, When the adjustment deviation corresponds to or is lower than the predetermined value, the determination step (104) and the calculation step (105) are performed; or the determination step (104) and the calculation step (105) are performed regardless of the value of the determined adjustment deviation.

10. The method according to claim 7 or 8, characterized in that, In the inspection step (107), the adjustment unit (9) checks whether the voltage source (7) is operating at the limit of its adjustment range and whether the adjustment deviation is higher than the pre-given value; while in the decision step (108), the adjustment unit (9) decides whether to effectively switch another measurement path to the measurement circuit (6) and which measurement path to effectively switch to the measurement circuit (6).

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