Method for determining the electrical conductivity, electromagnetic inductive flowmeter and method for operating the same

Abstract

Method for determining the conductivity of a medium with a control device and a measuring cell, wherein the control device performs the steps: generating a signal with a first frequency and a second frequency and feeding it into a first electrode and a second electrode, determining a first voltage between the first electrode and the second electrode and a first current through the medium for the first frequency and determining a first impedance (Z1) from the first voltage and the first current, determining a second voltage between the first electrode and the second electrode and a second current through the medium for the second frequency and determining a second impedance (Z2) from the second voltage and the second current, determining and comparing the phase of the first impedance with the phase of the second impedance, determining the resistance (R) of the medium according to a first formula when the phase of the first impedance is smaller than the phase of the second impedance, determining the resistance according to a second formula when the phase of the first impedance is equal to or larger than the phase of the second impedance, and determining the conductivity using the resistance and a cell constant.

Description

Technical Field

[0001] This invention relates to a method for determining the conductivity of a medium, an operating method for an electromagnetic induction flowmeter, and an electromagnetic induction flowmeter. Background Technology

[0002] The method for determining the conductivity of a medium requires a control device and a measuring cell (Messzelle). The measuring cell has a cell constant, a first electrode, and a second electrode. Here, the first and second electrodes are in direct contact with the medium. Therefore, the measuring cell is a conductivity measuring cell. The control device is the equipment.

[0003] Conductivity measuring cells are well known from the prior art. The conductivity σ of a medium is measured using a conductivity measuring cell by feeding an electrical signal S into a first and a second electrode, thereby causing a voltage U to drop across the first and second electrodes and a current I to flow through the medium. The resistance R between the first and second electrodes is then determined from the voltage and current, and the conductivity of the medium is determined from the resistance using the cell constant k of the measuring cell. Here, the conductivity is determined according to the following formula: .

[0004] The operation of an electromagnetic induction flowmeter requires a control device, a measuring tube, a first electrode, and a second electrode. Here, the first and second electrodes are arranged in direct contact with the medium in the measuring tube. Furthermore, the control device is configured to determine the flow rate of the medium through the measuring tube when using the first and second electrodes.

[0005] The electromagnetic induction flowmeter includes a control device, a measuring tube, a first electrode, and a second electrode. The first and second electrodes are arranged at the measuring tube such that they are in direct contact with the medium in the measuring tube during operation of the electromagnetic induction flowmeter. The control device is configured to determine the flow rate of the medium through the measuring tube when using the first and second electrodes.

[0006] Electromagnetic induction flow meters are well known from the prior art. In operation, an electromagnetic induction flow meter measures the flow rate of a medium through a measuring tube. For this purpose, the medium must have electrical conductivity. Electromagnetic induction flow meters typically have an electromagnet configured such that the magnetic field generated by the electromagnet at least partially permeates the medium located in the measuring tube, and the flow of the medium in the measuring tube induces a voltage in the medium. The voltage is tapped using a first electrode and a second electrode and is proportional to the flow velocity of the medium in the measuring tube. For example, the volumetric flow rate of the medium through the measuring tube is determined from the flow velocity using the inner cross-sectional area of ​​the measuring tube, or the mass flow rate of the medium through the measuring tube is determined by additionally using the density of the medium. Summary of the Invention

[0007] It is known from the practice of determining the conductivity of a medium using a conductivity measurement cell that the accuracy of the determination of the medium's conductivity is related to the actual conductivity of the medium. Therefore, the object of the present invention is to reduce the correlation between the accuracy of the determination of the medium's conductivity and the actual conductivity of the medium, thereby improving the accuracy of the determination of the medium's conductivity.

[0008] The problem concerning methods for determining the conductivity of a medium has been solved. According to the present invention, the control device performs the following steps: In one step, a signal (S) having a first frequency (f1) and a second frequency (f2) is generated and fed into a first electrode and a second electrode. This signal is, in principle, an electrical signal having only the first and second frequencies. By feeding the signal into the first and second electrodes, a signal is applied between the first and second electrodes, and thus also into the dielectric.

[0009] In one step, a first voltage (U1) between the first electrode and the second electrode and a first current (I1) through the medium are determined for a first frequency of the signal, and a first impedance (Z1) is determined from the first voltage and the first current.

[0010] In one step, a second voltage (U2) between the first electrode and the second electrode and a second current (I2) through the medium are determined for a second frequency of the signal, and a second impedance (Z2) is determined from the second voltage and the second current.

[0011] The voltage and current determined for the frequency of a signal should, in principle, only have that frequency, even if the signal should have other frequencies.

[0012] In one step, the phase of the first impedance ( 1) The phase of the second impedance ( 2) Determine and compare them. Based on the values ​​(|Z1|, |Z2|) and phase ( 1, 2) The impedance is determined by the real part (Re(Z1), Re(Z2)) and the imaginary part (Im(Z1), Im(Z2)).

[0013] In one step, when the phase of the first impedance is less than the phase of the second impedance ( 1< 2) When, according to the first formula Determine the resistance (R) of the medium.

[0014] In one step, when the phase of the first impedance is equal to or greater than the phase of the second impedance ( 1≥ 2) When, according to the second formula Determine the resistance.

[0015] Therefore, the two steps described above are mutually exclusive, and are performed according to the ratio of the phase of the first impedance to the phase of the second impedance.

[0016] In one step, the conductivity of the medium is determined using resistance and cell constant.

[0017] By determining the resistance according to either the first formula or the second formula based on the ratio of the phase of the first impedance to the phase of the second impedance, the conductivity can be determined more accurately than that known from the prior art.

[0018] This invention is based on the understanding that the phase of impedance changes with the conductivity of the medium and is related to the frequency of the signal. = f(f,σ)), and at different frequencies of the signal ( 1 = f(f1,σ), The deviation between the phase changes under the condition of 2 = f(f2,σ) is applicable to selecting a suitable formula to determine the resistance. Furthermore, this invention is based on finding two suitable formulas.

[0019] In one design of this method, the control device has a circuit that connects the control device to a first electrode on one side and a second electrode on the other. If the phase of the first impedance is now less than the phase of the second impedance ( 1< 2) Then subtract the line resistance from the total resistance. By additionally considering the line resistance, the accuracy of determining the conductivity of the medium is further improved.

[0020] In another design, the signal comprises a first portion of the signal having a first frequency and a second portion of the signal having a second frequency. Therefore, the first portion of the signal has the first frequency, and the second portion of the signal has the second frequency. Furthermore, the first and second portions of the signal overlap in the time domain. This means that the first and second portions of the signal occur simultaneously at least within one interval. This time-domain overlap reduces the time required to perform the method compared to feeding the first and second portions of the signal sequentially into the first and second electrodes in time. Preferably, the first and second portions of the signal are sinusoidal in principle.

[0021] In another design, the quotient generated by dividing the second frequency by the first frequency is in the range of 1.8 to 2.2. This quotient is preferably in the range of 1.9 to 2.1. The quotient is particularly preferably 2. A quotient with the above values ​​is advantageous because signals, such as voltages and currents, with frequencies having such intervals can be easily distinguished by the control device. To implement this method, it is necessary to distinguish the signals based on their frequencies.

[0022] In an improved version of the above design, the first frequency is in the range of 450 Hz to 550 Hz. Preferably, the first frequency is in the range of 480 Hz to 520 Hz. Particularly preferably, this frequency is in the range of 490 Hz to 510 Hz. Having these values ​​for the first frequency is advantageous because these values ​​can be generated and processed in a simple manner. For example, the control device selects 500 Hz as the first frequency and selects 2 as the quotient, thus the second frequency is 1 kHz.

[0023] In another design of this method, the signal has a signal voltage (U) and a signal current (I). Furthermore, the control device performs the following steps: In one step, a signal current is injected into the medium.

[0024] In one step, a first voltage (U1) is determined by generating a first rectangular signal having a first frequency and multiplying the first rectangular signal by a signal voltage.

[0025] In one step, the second voltage (U2) is determined by generating a second rectangular signal with a second frequency and multiplying the second rectangular signal by the signal voltage.

[0026] As already explained, the first voltage has a first frequency. Therefore, the first voltage is rectified by multiplying it by a first rectangular signal that also has a first frequency. The rectified voltage is then used for subsequent steps. Correspondingly, the second voltage is rectified by multiplying it by a second rectangular signal. This design is advantageous because it allows for the simple determination of the first and second voltages. The determination of the first and second currents is eliminated because they are injected by the control device and are therefore determined from the generation process. This design is particularly advantageous when combined with a design in which the first and second portion signals are superimposed on each other in the time domain. This is because not only is the time required to perform the method small, but the cost of determining the first and second voltages is also low.

[0027] This task relates to the operation method of an electromagnetic induction flowmeter. According to the invention, a measuring cell with a cell constant is constituted by a first electrode, a second electrode, and a measuring tube for determining the conductivity of the medium. Therefore, the electromagnetic induction flowmeter implicitly possesses the previously described conductive measuring cell. According to the invention, the control device further performs the following steps: In one step, a signal (S) having a first frequency (f1) and a second frequency (f2) is generated and the signal is fed into the first electrode and the second electrode.

[0028] In one step, a first voltage (U1) between the first electrode and the second electrode and a first current (I1) through the medium are determined for a first frequency of the signal, and a first impedance (Z1) is determined from the first voltage and the first current.

[0029] In one step, a second voltage (U2) between the first electrode and the second electrode and a second current (I2) through the medium are determined for a second frequency of the signal, and a second impedance (Z2) is determined from the second voltage and the second current.

[0030] In one step, the phase of the first impedance ( 1) The phase of the second impedance ( 2) Determine and compare them.

[0031] In one step, when the phase of the first impedance is less than the phase of the second impedance ( 1< 2) When, according to the first formula Determine the resistance (R) of the medium.

[0032] In one step, when the phase of the first impedance is equal to or greater than the phase of the second impedance ( 1≥ 2) When, according to the second formula Determine the resistance.

[0033] In one step, the conductivity of the medium is determined using resistance and cell constant.

[0034] Therefore, in principle, no structural changes are required to the electromagnetic induction flowmeter to implement this operating method.

[0035] In one design of the operating method, the flow rate of the medium through the measuring tube is determined by a control device using a first electrode and a second electrode by executing an electromagnetic induction flow measurement method. The electromagnetic induction flow measurement method is well known from the prior art. However, here the first and second electrodes are used, on the one hand, to execute the electromagnetic induction flow measurement method to determine the flow rate of the medium through the measuring tube, and on the other hand, to use in a method for determining the conductivity of the medium in the measuring tube. One significant advantage of this design is that it eliminates the need for other sensors, such as other electrodes, thereby reducing costs. Other electrodes in direct contact with the medium would also increase the probability of medium leakage in the measuring tube.

[0036] In an improved version of the above design, in the case of the electromagnetic induction flow measurement method, an alternating magnetic field for determining the flow rate is generated by a control device. The alternating magnetic field is preferably a rectangular alternating field. Here, the control device feeds a signal (S) into the first and second electrodes in the transient region of the alternating magnetic field. One advantage of using an alternating magnetic field is that it reduces interference with flow rate determination, thereby improving the accuracy of flow rate determination. The transient region of the alternating magnetic field is characterized in that the flow rate of the medium is not determined by the voltage induced by allowing the medium to flow into the first and second electrodes. Therefore, the advantage of this improved version is that the electromagnetic induction flow measurement method is not affected by the method for determining the conductivity of the medium, or the duration of the operation is increased. When the method for determining the conductivity of the medium is additionally implemented, it is generally not necessary to change the electromagnetic induction flow measurement method.

[0037] In another design, the control device has wiring that connects the control device to a first electrode on one side and a second electrode on the other. One of the previously described methods is preferably executed by the control device of an electromagnetic induction flowmeter.

[0038] Furthermore, the explanation of the method applies accordingly to running the method and vice versa.

[0039] This task relates to an electromagnetic induction flowmeter. According to the invention, a first electrode, a second electrode, and a measuring tube constitute a measuring cell with a cell constant for determining the conductivity of the medium. Therefore, the electromagnetic induction flowmeter implicitly possesses the previously described conductive measuring cell. According to the invention, the control device further performs the following steps: In one step, a signal (S) having a first frequency (f1) and a second frequency (f2) is generated and the signal is fed into the first electrode and the second electrode.

[0040] In one step, a first voltage (U1) between the first electrode and the second electrode and a first current (I1) through the medium are determined for a first frequency of the signal, and a first impedance (Z1) is determined from the first voltage and the first current.

[0041] In one step, a second voltage (U2) between the first electrode and the second electrode and a second current (I2) through the medium are determined for a second frequency of the signal, and a second impedance (Z2) is determined from the second voltage and the second current.

[0042] In one step, the phase of the first impedance ( 1) The phase of the second impedance ( 2) Determine and compare them.

[0043] In one step, when the phase of the first impedance is less than the phase of the second impedance ( 1< 2) When, according to the first formula Determine the resistance (R) of the medium.

[0044] In one step, when the phase of the first impedance is equal to or greater than the phase of the second impedance ( 1≥ 2) According to the second formula Determine the resistance.

[0045] Therefore, the two steps described above are directly interchangeable steps, which are performed according to the ratio of the phase of the first impedance to the phase of the second impedance.

[0046] In one step, the conductivity of the medium is determined using resistance and cell constant.

[0047] In one design of the electromagnetic induction flowmeter, the control device has wiring that connects the control device to a first electrode on one side and a second electrode on the other. The control device is preferably configured to perform one of the previously described methods and / or operating methods.

[0048] Furthermore, the explanations regarding the methods and operating procedures apply accordingly to electromagnetic induction flow meters and vice versa. Attached Figure Description

[0049] Specifically, numerous possibilities are given for configuring and improving methods for determining the conductivity of a medium, methods for operating an electromagnetic induction flowmeter, and electromagnetic induction flowmeters. For this purpose, reference is made not only to the claims dependent on the independent claims but also to the following description of preferred embodiments taken in conjunction with the accompanying drawings. The drawings are as follows: Figure 1 An embodiment of an electromagnetic induction flow meter is shown. Figure 2 The signal change process of the electromagnetic induction flowmeter over time is shown, and Figure 3 The equivalent circuit diagram of the medium is shown, and Figure 4 This shows the change in impedance phase with dielectric conductivity at two different frequencies of the signal. Detailed Implementation

[0050] Figure 1 An embodiment of an electromagnetic induction flowmeter 1 is shown in operation when performing an operating method. The electromagnetic induction flowmeter 1 has a control device 2, a measuring tube 3, a first electrode 4, a second electrode 5, and an electromagnet 6. A medium 7 having electrical conductivity flows through the measuring tube 3. The first electrode 4 and the second electrode 5 are arranged at the measuring tube 3 such that the first electrode 4 and the second electrode 5 are in direct contact with the medium 7 in the measuring tube 3.

[0051] The electromagnet 6 has a yoke 8 and a coil 9 arranged around the yoke 8. The coil 9 is driven by a driver 10, and the driver 10 is controlled by a microcontroller 11. Figure 1 The double arrows indicate this. The driver 10 and microcontroller 11 are arranged in the control unit 2. The electromagnet 6 is configured such that the magnetic field 12 generated by the electromagnet partially permeates the medium 7 located in the measuring tube 3, wherein the magnetic field... Figure 1 The measuring tube 3 is indicated by multiple parallel arrows and has a magnetic flux density B. The flow of medium 7 in the measuring tube 3 induces a voltage in the medium 7, which can be tapped between the first electrode 4 and the second electrode 5. The induced voltage is proportional to the flow rate of medium 7 in the measuring tube 3.

[0052] The control device 2 has a first line 13 and a second line 14, wherein the first line 13 connects the microcontroller 11 to the first electrode 4, and the second line 14 connects the microcontroller 11 to the second electrode 5, such that an induced voltage is applied to the control device 2. The microcontroller 11 is configured to evaluate the induced voltage. The first line 13 and the second line 14 together have a line resistance R. L In this sense, the control device 2 is connected to the first line 13 and the second line 14.

[0053] The control device 2 is configured to determine the flow rate of the medium 7 through the measuring tube 3 within the range of the operating method, using the first electrode 4 and the second electrode 5. Currently, the operating method is configured such that the control device 2 determines the flow rate of the medium 7 through the measuring tube 3 by executing an electromagnetic induction flow measurement method using the first electrode 4 and the second electrode 5. In the case of the electromagnetic induction flow measurement method, the control device 2 generates a rectangular alternating magnetic field with a magnetic flux density B to determine the flow rate. Here, the microcontroller 11 manipulates the driver 10 to generate the rectangular alternating magnetic field. The change process of the magnetic flux density B of the rectangular alternating magnetic field with time t is described in... Figure 2 The first row of the graph shows that the successive constant regions of magnetic flux density B are interconnected through transient regions. The flow velocity of the medium 7 in the measuring tube 3 is first determined by the microcontroller 11 from the induced voltage, and then the volumetric flow rate of the medium 7 through the measuring tube 3 is determined from the flow velocity using the inner cross-sectional area of ​​the measuring tube 3.

[0054] The segments of the first electrode 4, the second electrode 5, and the measuring tube 3 constitute a conductivity measuring cell 15 with a cell constant (Zellkonstanten) k for determining the conductivity σ of the dielectric 7. Here, the conductivity σ of the dielectric 7 is determined according to the following formula. .

[0055] Figure 2 An equivalent circuit diagram 16 is shown for the dielectric 7 used between the first electrode 4 and the second electrode 5. Equivalent circuit diagram 16 is an approximation of the dielectric 7 used for alternating signals. Equivalent circuit diagram 16 has a parallel circuit consisting of a series circuit and a parallel capacitor 17. The series circuit has a dielectric resistor 18 with a resistance R and a series capacitor 19. Using the resistance R and the cell constant k, the conductivity σ is determined according to the formula described above. Therefore, the resistance R is the resistance of the dielectric 7 between the first electrode 4 and the second electrode 5.

[0056] The control device 2 includes a sine wave generator 20 and a control device 21 for feeding an electrical signal S into the first electrode 4 and the second electrode 5. The sine wave generator 20 is controlled by a microcontroller 11, which... Figure 1The signal S is indicated by a double arrow and is configured to generate a generator signal G having at least one first frequency f1 and a second frequency f2. The control device 21 has a first branch 22 and a second branch 23, into which the generator signal G is fed during operation. The first branch 22 leads to a first line 13, and the second branch leads to a second line 14. The first branch 22 includes a series circuit having a first amplifier 24, a first resistor 25, and a first capacitor 26. The first amplifier 24 has a gain of +1. The first resistor 25 and the first capacitor 26 constitute a first high-pass filter. The second branch 23 has a second amplifier 27, a second resistor 28, and a second capacitor 29. The second amplifier 27 has a gain of -1. The second resistor 28 and the second capacitor 29 constitute a second high-pass filter. The first amplifier 24 only buffers the generator signal G, which is additionally inverted by the second amplifier 27. The signal S has a signal voltage U and a signal current I. The control device 21 generates the signal S from the generator signal G, which is a differential signal.

[0057] The cutoff frequencies of the first and second high-pass filters are chosen such that the signal S is not significantly attenuated. These high-pass filters are used to prevent the feeding of a DC signal (Gleich signal) into the first electrode 4 and the second electrode 5. The values ​​of the first resistor 25 and the second resistor 28 are chosen such that the resistance R is negligible when approximating the signal current I. Furthermore, the signal current I is determined by the microcontroller 11, i.e., by the control device 2, by dividing the voltage of the generator signal G by half the sum of the values ​​of the first resistor 25 and the second resistor 28. The approximate determination of the signal current includes both numerical value and phase, and is sufficiently accurate for the described method.

[0058] In addition to the previously described electromagnetic induction flow measurement method, the control device 2 also performs the following steps within the scope of the operating method, wherein the control device is also configured to perform the following steps: In one step, a signal S having a first frequency f1 = 500 Hz and a second frequency f2 = 1 kHz is generated and fed into the first electrode 4 and the second electrode 5. Currently, the signal S is fed in by injecting a signal current I into the dielectric 7 via the first electrode 4 and the second electrode 5. The quotient generated by dividing the second frequency f2 by the first frequency f1 is 2. For this purpose, a generator signal G having not only the first frequency f1 but also the second frequency f2 is first generated by the sine wave generator 20. The generator signal G is then fed into the first branch 22 and the second branch 23 of the control device 21. The control device 21 then generates the signal S from the generator signal G, which is fed into the first electrode 4 and the second electrode 5.

[0059] Signal S comprises a first part of the signal having a first frequency f1 and a second part of the signal having a second frequency f2. The first part of the signal and the second part of the signal overlap with each other in time. Figure 2 The second line shows a signal S with two partially overlapping signals in time. Signal S is fed into the first electrode 4 and the second electrode 5 only in the transient region of the alternating magnetic field B. This does not affect the determination of the flow rate. There is no loss of mass, nor is the duration of the flow rate determination increased.

[0060] In one step, a first voltage U1 between the first electrode 4 and the second electrode 5 and a first current I1 through the medium 7 are determined for a first frequency f1 of the signal S, and a first impedance Z1 is determined from the first voltage U1 and the first current I1. The following sub-step belongs to this step, wherein the first voltage U1 is determined by generating a first rectangular signal T1 having a first frequency f1 and multiplying the first rectangular signal T1 by the signal voltage U. A copy T1' of the first rectangular signal T1 also belongs to the first rectangular signal T1, the copy having a phase shift of preferably 90° relative to the first rectangular signal T1. The first rectangular signal T1 in... Figure 2 As shown in line 3, and its copy T1' shown in line 4. Therefore, not only the first rectangular signal T1 but also its copy T1' is multiplied by the signal voltage U, such that the voltage U1 is determined based on its value and phase. The first current I1 is also determined according to the previously described approximation, and similarly based on its value and phase. The first impedance Z1 is also determined based on its value and phase. 1. Determine.

[0061] In one step, a second voltage U2 between the first electrode 4 and the second electrode 5 and a second current I2 through the medium 7 are determined for a second frequency f2 of the signal S, and a second impedance Z2 is determined from the second voltage U2 and the second current I2. The following sub-step also belongs to this step, namely, in which the second voltage U2 is determined by generating a second rectangular signal T2 having a second frequency f2 and multiplying the second rectangular signal T2 by the signal voltage U. A copy T2' of the second rectangular signal T2 also belongs to the second rectangular signal T2, the copy having a phase shift of preferably 90° relative to the second rectangular signal T2. The second rectangular signal T2 in... Figure 2 As shown in line 5, and its copy T2' shown in line 6. Therefore, not only the second rectangular signal T2 but also its copy T2' is multiplied by the signal voltage U, such that voltage U2 is determined based on its value and phase. The second current I2 is determined according to the previously described approximation, and also based on its value and phase. The second impedance Z2 is also determined based on its value and phase. 2. Determine.

[0062] In one step, after determining the phase of the first impedance Z1... Phase of the second impedance Z2 2. Then the phase of the first impedance Z1 Phase of the second impedance Z2 2. Compare with each other.

[0063] In one step, when the phase of the first impedance Z1 1 is less than the phase of the second impedance Z1 2, that is 1< At 2 o'clock, according to the first formula To determine the resistance R of the dielectric, the line resistance R is additionally subtracted from the first formula. L .

[0064] In one step, when the phase of the first impedance Z1 1 is equal to or greater than the phase of the second impedance Z2 2, that is 1≥ At 2 o'clock, according to the second formula To determine the resistance R.

[0065] The two steps described above are directly interchangeable, and these steps are based on the phase of the first impedance Z1. Phase of 1 with the second impedance Z2 How is the 2 ratio implemented? From Figure 4 This demonstrates the suitability of using the phase of the impedance as a selection criterion for the first or second formula. Figure 1 The aspect shows the phase of the first impedance Z1 The process of change of conductivity σ with respect to the second impedance Z2 is shown, and the phase of the second impedance Z2 is also shown. 2. The process of change with conductivity σ.

[0066] In one step, the conductivity σ of dielectric 7 is determined according to the following formula, using the resistance R and the cell constant k: .

[0067] Figure Labels 1. Electromagnetic induction flow meter 2. Control device 3. Measuring tube 4. First electrode 5. Second electrode 6. Electromagnets 7. Medium 8. Magnetic yoke 9. Coil 10. Driver 11. Microcontroller 12. Magnetic field 13. Route 1 14. Second Route 15. Measuring pool 16. Equivalent Circuit Diagram 17. Dielectric resistance 18. Series capacitor 19. Parallel capacitors 20. Sine wave generator 21. Control device 22. First branch road 23. Second branch road 24. First Amplifier 25. First resistor 26. First capacitor 27. Second Amplifier 28. Second resistor 29. Second capacitor.

Claims

1. A method for determining the conductivity (σ) of a medium (7) using a control device (2) and a measuring cell (15), The measuring cell (15) has a cell constant (k), a first electrode (4), and a second electrode (5). The first electrode (4) and the second electrode (5) are in direct contact with the medium (7), and The control device (2) performs the following steps: - Generate a signal (S) having a first frequency (f1) and a second frequency (f2) and feed the signal (S) into the first electrode (4) and the second electrode (5). - Determine the first voltage (U1) between the first electrode (4) and the second electrode (5) and the first current (I1) through the medium (7) for the first frequency (f1) of the signal (S), and determine the first impedance (Z1) from the first voltage (U1) and the first current (I1). - Determine the second voltage (U2) between the first electrode (4) and the second electrode (5) and the second current (I2) through the medium (7) for the second frequency (f2) of the signal (S), and determine the second impedance (Z2) from the second voltage (U2) and the second current (I2). - Phase of the first impedance (Z1) 1) Phase with the second impedance (Z2) 2) To determine and compare, -When the phase of the first impedance (Z1) ( 1) The phase smaller than the second impedance (Z2) 2) When, according to the first formula Determine the resistance (R) of the medium (7). Where Re(Z1) is the real part of the first impedance (Z1), Re(Z2) is the real part of the second impedance (Z2), and Im(Z1) is the imaginary part of the first impedance (Z1), and Im(Z2) is the imaginary part of the second impedance (Z2). -When the phase of the first impedance (Z1) ( 1) The phase of the second impedance (Z2) is equal to or greater than the phase of the second impedance (Z2). 2) When, according to the second formula Determine the resistance (R), and - Determine the conductivity (σ) of the medium (7) using the resistance (R) and the cell constant (k).

2. The method according to claim 1, wherein the control device (2) has lines (13, 14) connecting the control device (2) to the first electrode (4) and the second electrode (5), wherein if the phase of the first impedance (Z1) is ( 1) The phase smaller than the second impedance (Z2) 2), then subtract the line resistance (R) of the lines (13, 14) from the resistor (R). L ).

3. The method according to claim 1 or 2, wherein the signal (S) comprises a first portion signal having the first frequency (f1) and a second portion signal having the second frequency (f2), and wherein the first portion signal and the second portion signal are overlapped in the time domain.

4. The method according to claim 1 or 2, wherein the quotient generated by dividing the second frequency (f2) by the first frequency (f1) is in the range between 1.8 and 2.

2.

5. The method of claim 4, wherein the quotient generated by dividing the second frequency (f2) by the first frequency (f1) is in the range between 1.9 and 2.

1.

6. The method of claim 4, wherein the quotient generated by dividing the second frequency (f2) by the first frequency (f1) is 2.

7. The method of claim 4, wherein the first frequency (f1) is in the range between 450 Hz and 550 Hz.

8. The method of claim 7, wherein the first frequency (f1) is in the range between 480 Hz and 520 Hz.

9. The method of claim 7, wherein the first frequency (f1) is in the range between 490 Hz and 510 Hz.

10. The method according to claim 1 or 2, wherein the signal (S) has a signal voltage (U) and a signal current (I), and wherein the control device (2) performs the following steps: - Inject the signal current into the medium (7), - The first voltage (U1) is determined by generating a first rectangular signal (T1, T1') having the first frequency (f1) and multiplying the first rectangular signal (T1, T1') by the signal voltage (U), and - The second voltage (U2) is determined by generating a second rectangular signal (T2, T2') having the second frequency (f2) and multiplying the second rectangular signal (T2, T2') by the signal voltage (U).

11. A method for operating an electromagnetic induction flowmeter (1) having a control device (2), a measuring tube (3), a first electrode (4), and a second electrode (5), The first electrode (4) and the second electrode (5) are arranged in direct contact with the medium (7) in the measuring tube (3). The control device (2) is configured to determine the flow rate of the medium (7) through the measuring tube (3) using the first electrode (4) and the second electrode (5). The first electrode (4), the second electrode (5), and the measuring tube (3) constitute a measuring cell (15) with a cell constant (k) for determining the conductivity (σ) of the medium (7), and the control device (2) performs the following steps: - Generate a signal (S) having a first frequency (f1) and a second frequency (f2) and feed the signal (S) into the first electrode (4) and the second electrode (5). - Determine the first voltage (U1) between the first electrode (4) and the second electrode (5) and the first current (I1) through the medium (7) for the first frequency (f1) of the signal (S), and determine the first impedance (Z1) from the first voltage (U1) and the first current (I1). - Determine the second voltage (U2) between the first electrode (4) and the second electrode (5) and the second current (I2) through the medium (7) for the second frequency (f2) of the signal (S), and determine the second impedance (Z2) from the second voltage (U2) and the second current (I2). - Phase of the first impedance (Z1) 1) Phase with the second impedance (Z2) 2) To determine and compare, -When the phase of the first impedance (Z1) ( 1) The phase smaller than the second impedance (Z2) 2) When, according to the first formula Determine the resistance (R) of the medium (7). Where Re(Z1) is the real part of the first impedance (Z1), Re(Z2) is the real part of the second impedance (Z2), and Im(Z1) is the imaginary part of the first impedance (Z1), and Im(Z2) is the imaginary part of the second impedance (Z2). -When the phase of the first impedance (Z1) ( 1) The phase of the second impedance (Z2) is equal to or greater than the phase of the second impedance (Z2). 2) When, according to the second formula Determine the resistance (R), and - Determine the conductivity (σ) of the medium (7) using the resistance (R) and the cell constant (k).

12. The operating method according to claim 11, wherein the flow rate of the medium (7) through the measuring tube (3) is determined by the control device (2) by performing an electromagnetic induction flow measurement method using the first electrode (4) and the second electrode (5).

13. The operating method according to claim 12, wherein in the case of the electromagnetic induction flow measurement method, the control device (2) generates an alternating magnetic field for determining the flow rate, and wherein the control device (2) feeds the signal (S) into the first electrode (4) and the second electrode (5) in the transient region of the alternating magnetic field.

14. The operating method according to claim 13, wherein the alternating magnetic field is a rectangular alternating field.

15. The operating method according to any one of claims 11 to 14, wherein the control device (2) is constructed according to claim 2 and / or the control device (2) performs the method according to any one of claims 2 to 10.

16. An electromagnetic induction flowmeter (1) having a control device (2), a measuring tube (3), a first electrode (4), and a second electrode (5). The first electrode (4) and the second electrode (5) are arranged at the measuring tube (3) so that the first electrode (4) and the second electrode (5) are in direct contact with the medium (7) in the measuring tube (3) during the operation of the electromagnetic induction flowmeter (1). The control device (2) is configured to determine the flow rate of the medium (7) through the measuring tube (3) using the first electrode (4) and the second electrode (5). The first electrode (4), the second electrode (5), and the measuring tube (3) are configured to form a measuring cell (15) with a cell constant (k) for determining the conductivity (σ) of the medium (7), and the control device (2) is configured to perform the following steps: - Generate a signal (S) having a first frequency (f1) and a second frequency (f2) and feed the signal (S) into the first electrode (4) and the second electrode (5). - Determine the first voltage (U1) between the first electrode (4) and the second electrode (5) and the first current (I1) through the medium (7) for the first frequency (f1) of the signal (S), and determine the first impedance (Z1) from the first voltage (U1) and the first current (I1). - Determine the second voltage (U2) between the first electrode (4) and the second electrode (5) and the second current (I2) through the medium (7) for the second frequency (f2) of the signal (S), and determine the second impedance (Z2) from the second voltage (U2) and the second current (I2). - Phase of the first impedance (Z1) 1) Phase with the second impedance (Z2) 2) To determine and compare, -When the phase of the first impedance (Z1) ( 1) The phase smaller than the second impedance (Z2) 2) When, according to the first formula Determine the resistance (R) of the medium (7). Where Re(Z1) is the real part of the first impedance (Z1), Re(Z2) is the real part of the second impedance (Z2), and Im(Z1) is the imaginary part of the first impedance (Z1), and Im(Z2) is the imaginary part of the second impedance (Z2). -When the phase of the first impedance (Z1) ( 1) The phase of the second impedance (Z2) is equal to or greater than the phase of the second impedance (Z2). 2) When, according to the second formula Determine the resistance (R), and - Determine the conductivity (σ) of the medium (7) using the resistance (R) and the cell constant (k).

17. The electromagnetic induction flowmeter (1) according to claim 16, wherein the control device (2) is constructed according to claim 2, and / or wherein the control device (2) is configured to perform the method according to any one of claims 2 to 10 or the operating method according to any one of claims 12 to 14.

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