MAGNETIC-INDUCTIVE FLOWMETER AND METHOD FOR OPERATING SUCH A DEVICE

Description

[0001] Magneto-inductive flow meters are known from the state of the art and are described, for example, in JPH 04128614A.

[0002] The invention relates, on the one hand, to a magnetic-inductive flowmeter comprising a measuring tube, a first electrode, a second electrode, a magnetic field generator, an impedance signal generator, a coupling device and a control device.

[0003] The first electrode and the second electrode are arranged on the measuring tube for direct contact with a medium in the measuring tube. During operation of the magnetic-inductive flowmeter, a medium is present in the measuring tube, and the first and second electrodes are also in direct contact with the medium.

[0004] The magnetic field generator is designed to generate an alternating magnetic field with a positive magnetic field phase and a negative magnetic field phase in the medium in the measuring tube. The impedance signal generator is designed to generate excitation signals.

[0005] The coupling device comprises a first capacitor, a second capacitor, a first signal path, and a second signal path. The first signal path connects the impedance signal generator and the first electrode, and the second signal path connects the impedance signal generator and the second electrode for transmitting the excitation signals.

[0006] The control device is designed to determine the flow rate of a medium through the measuring tube using flow measurement signals induced by the alternating magnetic field in the medium and measurable at the first electrode and the second electrode. Furthermore, the control device is designed to determine the impedance of the medium in the measuring tube using impedance measurement signals caused by the excitation signals and measurable at the first electrode and the second electrode.

[0007] The invention also relates to a method for operating a magnetic-inductive flowmeter. The magnetic-inductive flowmeter comprises a measuring tube, a first electrode, a second electrode, a magnetic field generator, an impedance signal generator, a coupling device, and a control device.

[0008] The first electrode and the second electrode are arranged on the measuring tube for direct contact with a medium in the measuring tube.

[0009] The coupling device has a first capacitor, a second capacitor, a first signal path and a second signal path.

[0010] The first signal path connects the impedance signal generator and the first electrode and the second signal path connects the impedance signal generator and the second electrode.

[0011] The magnetic field generator generates an alternating magnetic field with a positive magnetic field phase and a negative magnetic field phase in the medium in the measuring tube.

[0012] The control device determines a flow of the medium through the measuring tube using flow measurement signals induced by the alternating magnetic field medium and measured at the first electrode and the second electrode.

[0013] Excitation signals are generated by the impedance signal generator. The excitation signals are transmitted from the impedance signal generator via the first signal path to the first electrode and via the second signal path to the second electrode.

[0014] The control device determines an impedance of the medium in the measuring tube using impedance measurement signals caused by the excitation signals and measured at the first electrode and the second electrode.

[0015] If the first and second electrodes are in direct contact with a medium, then they are in galvanic contact with the medium.

[0016] During operation of the magnetic-inductive flowmeter, the impedance signal generator generates the excitation signals. The excitation signals are routed both from the first signal path to the first electrode and from the second signal path to the second electrode. The first capacitor is located in the first signal path, and the second capacitor is located in the second signal path. The first and second capacitors galvanically isolate the impedance signal generator and the first and second electrodes from each other, while also ensuring the transmission of the excitation signals generated by the impedance signal generator to the first and second electrodes. In this sense, the first and second capacitors are coupling capacitors.

[0017] During operation of the magnetic-inductive flowmeter, the magnetic field generator generates the alternating magnetic field, and the control device determines the flow of the medium through the measuring tube using the flow measurement signals induced in the medium by the alternating magnetic field and measured at the first and second electrodes. Thus, the flow measurement signals include those measured during the positive magnetic field phase and those measured during the negative magnetic field phase. This has the advantage of at least reducing the impact of interference and parasitic effects, and making the flow determination more accurate.

[0018] It has been recognized that in the coupling device, a feedback effect occurs between the determination of the impedance of the medium and the determination of the flow rate through the medium, which affects the accuracy of the flow rate determination. The coupling results from the charge being reversed between the first and second capacitors by the flow measurement signals induced in the medium by the alternating magnetic field and applied to the first and second electrodes. Due to parasitic double-layer capacitances between the first and second electrodes and the medium, the feedback effect remains even when the first and second signal paths are each separated by a switch. One way to reduce the feedback effect is to reduce the amplitude of the excitation signals. However, this also reduces the accuracy of the determination of the impedance of the medium.

[0019] The object of the present invention is therefore to provide a magnetic-inductive flowmeter and a method for operating a magnetic-inductive flowmeter in which the feedback is reduced. Preferably, the accuracy of determining the impedance and the accuracy of determining the flow of the medium are not compromised.

[0020] The problem is solved by a magnetic-inductive flowmeter having the features of claim 1.

[0021] The magnetic-inductive flowmeter is characterized in that the coupling device comprises a third capacitor, a fourth capacitor, a first switch and a second switch.

[0022] The first switch, the first capacitor and the third capacitor are connected to one another in such a way, and the first switch is designed in such a way that in a first switching state of the first switch only the first capacitor and in a second switching state of the first switch only the third capacitor is connected to the first signal path. Accordingly, during operation of the magnetic-inductive flowmeter, the first switch causes either only the first capacitor or only the third capacitor to be connected to the first signal path. Furthermore, the second switch, the second capacitor and the fourth capacitor are connected to one another in such a way, and the second switch is designed in such a way that in a first switching state of the second switch only the second capacitor and in a second switching state of the second switch only the fourth capacitor is connected to the second signal path.Accordingly, during operation of the magnetic-inductive flowmeter, the second switch causes either only the second capacitor or only the fourth capacitor to be connected to the second signal path. Preferably, the first and second switches each have only the two switching states.

[0023] Furthermore, the control device is designed to set the first switch and the second switch into the first switching state for a duration of the positive magnetic field phase and into the second switching state for a duration of the negative magnetic field phase.

[0024] This prevents the first, second, third, and fourth capacitors from being recharged by flow measurement signals induced by the alternating magnetic field in the medium and applied to the first and second electrodes. This reduces the feedback effect.

[0025] The impedance signal generator is preferably designed to generate the excitation signals in specific ways, in particular as current signals. The excitation signals preferably have a rectangular profile over time. The excitation signals are preferably impressed into the medium via the first signal path and the first electrode on the one hand, and via the second signal path and the second electrode on the other hand, when the alternating magnetic field has not yet stabilized. This is because if the alternating magnetic field has not yet stabilized, the flow rate through the medium cannot yet be determined with sufficient accuracy, which is why the flow rate is only determined when the alternating magnetic field has stabilized. This means that the determination of the flow rate through the medium and the determination of the impedance of the medium are separated in time. This separation in time prevents mutual interference.The determination of the impedance also includes the determination of the conductivity of the medium.

[0026] The first and second switches can be implemented in different ways.

[0027] In one embodiment of the magnetic-inductive flowmeter, the first and second switches are each two single-pole, single-throw switches. Single-pole, single-throw switches are also referred to as single-pole, single-throw switches and abbreviated as SPST. In another embodiment, the first and second switches are each single-pole, double-throw switches. A single-pole, double-throw switch is also referred to as single-pole, double-throw switch and abbreviated as SPDT. Implementing the first and second switches using single-pole, single-throw switches and single-pole, double-throw switches is particularly simple.

[0028] It has been recognized that series leakage between switches leads to a different injection of charge carriers when the switches are switched, resulting in a feedback effect between the determination of the medium's impedance and the determination of the medium's flow rate, which impairs the accuracy of the flow rate determination. Therefore, in a further embodiment, the first and second switches are implemented with a multiplexer. By using a multiplexer, the difference between the charge induced by the first switch and the charge induced by the second switch is reduced, thereby also reducing the feedback effect.

[0029] In a further embodiment, the first and second switches are semiconductor switches. In particular, the first and second switches are implemented on the same die. In a particularly preferred embodiment, the multiplexer is implemented with semiconductor switches.

[0030] In a further embodiment, the first and second switches are arranged in the same housing. The arrangement in the same housing ensures that the first and second switches are exposed to the same environmental conditions and, in particular, have the same temperature.

[0031] In a further embodiment of the magnetic-inductive flowmeter, the first switch is located between the first and third capacitors on the one hand and the impedance signal generator on the other hand, and the second switch is located between the second and fourth capacitors on the one hand and the impedance signal generator on the other hand.

[0032] In a further embodiment, the control device is designed to measure the flow measurement signals and / or the impedance measurement signals as voltages between the first and second electrodes.

[0033] In a further embodiment, the alternating magnetic field is a pulsating DC magnetic field. The pulsating DC magnetic field alternates over time between a first magnetic field direction and a second magnetic field direction antiparallel to the first. In a steady state, the magnitude of the magnetic field strength is constant for both magnetic field directions.

[0034] The object is also achieved by a method for operating a magnetic-inductive flowmeter having the features of claim 10.

[0035] The coupling device of the magnetic-inductive flowmeter which carries out this method additionally comprises a third capacitor, a fourth capacitor, a first switch and a second switch.

[0036] The method described above is modified as follows: The control device sets the first switch and the second switch into a first state for a duration of the positive magnetic field phase, so that only the first capacitor is connected to the first signal path and only the second capacitor is connected to the second signal path.

[0037] Furthermore, the control device sets the first switch and the second switch into a second state for a duration of the negative magnetic field phase, so that only the third capacitor is connected to the first signal path and only the fourth capacitor is connected to the second signal path.

[0038] In one embodiment, the magnetic-inductive flowmeter which carries out the method is designed according to at least one of the previously described embodiments.

[0039] Furthermore, the statements regarding the magnetic-inductive flowmeter apply accordingly to the method for operating a magnetic-inductive flowmeter and vice versa.

[0040] In detail, there are numerous possibilities for designing and developing the magnetic-inductive flowmeter and the method. Reference is made to the claims subordinate to the independent claims as well as to the following description of a preferred embodiment in conjunction with the drawings.

[0041] The drawing shows Fig. 1 an embodiment of a magnetic-inductive flowmeter and Fig. 2a temporal course of signals during operation of the magnetic-inductive flowmeter.

[0042] Fig. 1 shows essential elements of an embodiment of a magnetic-inductive flowmeter 1 in abstract form and in operation. The magnetic-inductive flowmeter 1 comprises a measuring tube 2, a first electrode 3, a second electrode 4, a magnetic field generator 5, an impedance signal generator 6, a coupling device 7, and a control device 8.

[0043] As the magnetic-inductive flowmeter 1 is in operation, a medium 9 flows through the measuring tube 2. The first electrode 3 and the second electrode 4 are arranged on the measuring tube 2 for direct contact with the medium 9. In this case, the first electrode 3 and the second electrode 4 are in direct contact with the medium 9.

[0044] The coupling device 7 has a first capacitor 10, a second capacitor 11, a third capacitor 12, a fourth capacitor 13, a first switch 14, a second switch 15, a first signal path 16 and a second signal path 17.

[0045] The first signal path 16 connects the impedance signal generator 6 and the first electrode 3 and the second signal path 17 connects the impedance signal generator 6 and the second electrode 4.

[0046] The magnetic field generator 5 has a yoke 18, a coil 19, and a source 20. The source 20 is controllable by the control device 8 and feeds the coil 19. The magnetic field generator 5 is designed to generate an alternating magnetic field 21 with a positive magnetic field phase 22 and a negative magnetic field phase 23 in the medium 9 in the measuring tube 2. In the present embodiment, the alternating magnetic field is a pulsating DC magnetic field. The pulsating DC magnetic field alternates over time with a first magnetic field direction and a second magnetic field direction antiparallel to the first. An amount B 0 of a magnetic flux density B in a steady state is constant for both magnetic field directions. See Fig. 2a .

[0047] The control device 8 is designed to determine a flow rate of the medium 9 through the measuring tube 2 using flow measurement signals induced in the medium by the alternating magnetic field 21 and measurable at the first electrode 3 and the second electrode 4. In this exemplary embodiment, the control device 8 is designed to measure the flow measurement signals as voltages u between the first electrode 3 and the second electrode 4.

[0048] The impedance signal generator 6 is designed to generate excitation signals. In this embodiment, the excitation signals are current signals i, see Fig. 2c which are impressed into the medium 9 via the first signal path 16 and the first electrode 3 and via the second signal path 17 and the second electrode 4.

[0049] Furthermore, the control device 8 is configured to determine an impedance of the medium 9 in the measuring tube 2 using impedance measurement signals generated by the excitation signals i and measurable at the first electrode 3 and the second electrode 4. In this exemplary embodiment, the control device 8 is configured to measure the impedance measurement signals as voltages u between the first electrode 3 and the second electrode 4.

[0050] In the present embodiment, the first switch 14 and the second switch 15 are each implemented as a multiplexer. The multiplexers are semiconductor switches implemented on the same die. The first switch 14 and the second switch 15 are also arranged in the same housing.

[0051] The first switch 14 is arranged between, on the one hand, the first capacitor 10 and the third capacitor 12 and, on the other hand, the impedance signal generator 6. The second switch 15 is arranged between, on the one hand, the second capacitor 11 and the fourth capacitor 13 and, on the other hand, the impedance signal generator 6. Furthermore, a resistor 24 is arranged in the first signal path 16 between, on the one hand, the first capacitor 10 and the second capacitor 12 and, on the other hand, the first electrode 3. Accordingly, a second resistor 25 is arranged in the second signal path 17 between, on the one hand, the second capacitor 11 and the fourth capacitor 13 and, on the other hand, the second electrode 4. The first resistor 24 and the second resistor 25 serve to limit the current i.

[0052] The first switch 14, the first capacitor 10, and the third capacitor 12 are connected to one another in such a way, and the first switch 14 is designed such that in a first switching state S1, only the first capacitor 10 and in a second switching state S2, only the third capacitor 12 is connected to the first signal path 16. The second switch 15, the second capacitor 11, and the fourth capacitor 13 are connected to one another in such a way, and the second switch 15 is designed such that in a first switching state S1, only the second capacitor 11 and in a second state S2, only the fourth capacitor 13 is connected to the second signal path 17. Fig. 1 the first switch 14 and the second switch 15 are each shown in the first switching state S 1.

[0053] The control device 8 is designed to set the first switch 14 and the second switch 15 into the first switching state S 1 for a duration of the positive magnetic field phase 22 and into the second switching state S 2 for the duration of the negative magnetic field phase 23.

[0054] During operation, the magnetic-inductive flowmeter 1 carries out the following process: The magnetic field generator 5 generates the alternating magnetic field 21 with the positive magnetic field phase 22 and the negative magnetic field phase 23 in the medium 9 in the measuring tube 2.

[0055] The control device 8 determines a flow of the medium 9 through the measuring tube 2 using voltages u induced by the alternating magnetic field 21 in the medium 9 and measured at the first electrode 3 and the second electrode 4 as flow measurement signals.

[0056] The excitation signals are generated by the impedance signal generator 6. The excitation signals are then impressed into the medium 9 when the alternating magnetic field 21 has not yet stabilized. This separates the determination of the flow rate of the medium 9 and the determination of the conductivity of the medium 9 from each other in time.

[0057] The control device 8 sets the first switch 14 and the second switch 15 to the first state S 1 for the duration of the positive magnetic field phase 22, so that only the first capacitor 10 is connected to the first signal path 16 and only the second capacitor 11 is connected to the second signal path 17.

[0058] Furthermore, the control device 8 sets the first switch 14 and the second switch 15 to the second state S 2 for the duration of the negative magnetic field phase 23, so that only the third capacitor 12 is connected to the first signal path 16 and only the fourth capacitor 13 is connected to the second signal path 17.

[0059] Furthermore, the control device determines a conductivity of the medium 9 in the measuring tube using voltages u caused by the excitation signals i and measured at the first electrode 3 and at the second electrode 4 as impedance measurement signals. Reference symbol

[0060] 1 magnetic-inductive flowmeter 2 measuring tube 3 first electrode 4 second electrode 5 magnetic field generator 6 impedance signal generator 7 coupling device 8 control device 9 medium 10 first capacitor 11 second capacitor 12 third capacitor 13 fourth capacitor 14 first switch 15 second switch 16 first signal path 17 second signal path 18 yoke 19 coil 20 source 21 alternating magnetic field 22 positive magnetic field phase 23 negative magnetic field phase 24 first resistor 25 second resistor B magnetic flux density B 0 magnitude of the magnetic flux density in steady state i current u voltage

Claims

1. Magnetic-inductive flowmeter (1) comprising a measuring tube (2), a first electrode (3), a second electrode (4), a magnetic field generator (5), an impedance signal generator (6), a coupling device (7) and a control device (8), wherein the first electrode (3) and the second electrode (4) are arranged on the measuring tube (2) for direct contact with a medium (9) in the measuring tube (2), wherein the magnetic field generator (5) is designed to generate an alternating magnetic field (21) with a positive magnetic field phase (22) and a negative magnetic field phase (23) in the medium (9) in the measuring tube (2), wherein the impedance signal generator (6) is designed to generate excitation signals (i), wherein the coupling device (7) comprises a first capacitor (10), a second capacitor (12), a first signal path (16) and a second signal path (17), wherein the first signal path (16) interconnects the impedance signal generator (6) and the first electrode (3) and the second signal path (17) interconnects the impedance signal generator (6) and the second electrode (4) for transmitting the excitation signals (i), wherein the control device (8) is designed for determining a flow rate of a medium (9) through the measuring tube (2) using flow rate measurement signals caused by the alternating magnetic field (21) in the medium (9) and measurable at the first electrode (3) and the second electrode (4), and wherein the control device (8) is designed to determine an impedance of the medium (9) in the measuring tube (2) using impedance measurement signals induced by the excitation signals (i) and measurable at the first electrode (3) and the second electrode (4), characterized in that the coupling device (7) has a third capacitor (12), a fourth capacitor (13), a first switch (14) and a second switch (15) that the first switch (14), the first capacitor (10) and the third capacitor (12) are connected to one another in such a way and the first switch (14) is designed in such a way that, in a first switching state (S1), only the first capacitor (10) and, in a second switching state (S2), only the third capacitor (12) are connected in the first signal path (16) that the second switch (15), the second capacitor (11) and the fourth capacitor (13) are connected to one another in such a way and the second switch (15) is designed in such a way that, in a first switching state (S1), only the second capacitor (11) and, in a second switching state (S2), only the fourth capacitor (13) is connected into the second signal path (17), and that the control device (8) is designed to set the first switch (14) and the second switch (15) to the first switching state (S1) for a duration of the positive magnetic field phase (22) and to set them to the second switching state (S2) for a duration of the negative magnetic field phase (23).

2. Magnetic-inductive flowmeter (1) according to claim 1, characterized in that the first switch (14) and the second switch (15) are each two single pole single throw switches.

3. Magnetic-inductive flowmeter (1) according to claim 1, characterized in that the first switch (14) and the second switch (15) are each a single-pole changeover switch.

4. Magnetic-inductive flowmeter (1) according to any one of claims 1 to 3, characterized in that the first switch (14) and the second switch (15) are implemented with a multiplexer.

5. Magnetic-inductive flowmeter (1) according to any one of claims 1 to 4, characterized in that the first switch (14) and the second switch (15) are semiconductor switches, in particular implemented on the same die.

6. Magnetic-inductive flowmeter (1) according to any one of claims 1 to 5, characterized in that the first switch (14) and the second switch (15) are arranged in the same housing.

7. Magnetic-inductive flowmeter (1) according to any one of claims 1 to 6, characterized in that the first switch (14) is located between, on the one hand, the first capacitor (10) and the third capacitor (12) and, on the other hand, the impedance signal generator (6), and that the second switch (15) is located between, on the one hand, the second capacitor (11) and the fourth capacitor (13) and, on the other hand, the impedance signal generator (6).

8. Magnetic-inductive flowmeter (1) according to any one of claims 1 to 7, characterized in that the control device (8) is designed to measure the flowmeter signals and / or the impedance measurement signals as voltages (u) between the first electrode (3) and the second electrode (4).

9. Magnetic-inductive flowmeter (1) according to any one of claims 1 to 8, characterized in that the alternating magnetic field (21) is a pulsating DC magnetic field.

10. Method for operating a magnetic-inductive flowmeter (1) comprising a measuring tube (2), a first electrode (3), a second electrode (4), a magnetic field generator (5), an impedance signal generator (6), a coupling device (7) and a control device (8), wherein the first electrode (3) and the second electrode (4) are arranged on the measuring tube (2) for direct contact with a medium (9) in the measuring tube (2), wherein the coupling device (7) comprises a first capacitor (10), a second capacitor (11), a third capacitor (12), a fourth capacitor (13), a first switch (14), a second switch (15), a first signal path (16) and a second signal path (17), wherein the first signal path (16) interconnects the impedance signal generator (6) and the first electrode (3) and the second signal path (17) interconnects the impedance signal generator (6) and the second electrode (4), wherein an alternating magnetic field (21) with a positive magnetic field phase (22) and a negative magnetic field phase (23) is generated in the medium (9) in the measuring tube (2) by the magnetic field generator (5), wherein a flow rate of the medium (9) through the measuring tube (2) is determined by the control device (8) using flow rate measurement signals induced by the alternating magnetic field (21) in the medium (9) and measured at the first electrode (3) and the second electrode (4), wherein excitation signals are generated by the impedance signal generator (6), wherein the excitation signals are transmitted from the impedance signal generator (6) via the first signal path (16) to the first electrode (3) and via the second signal path (17) to the second electrode (4), wherein the first switch (14) and the second switch (15) are set to a first state (S1) by the control device (8) for a duration of the positive magnetic field phase (22), so that only the first capacitor (10) is switched into the first signal path (16) and only the second capacitor (11) is switched into the second signal path (17), wherein the first switch (14) and the second switch (15) are set to a second state (S2) by the control device (8) for a duration of the negative magnetic field phase (23), so that only the third capacitor (12) is connected in the first signal path (16) and only the fourth capacitor (13) is connected in the second signal path (17), and wherein an impedance of the medium (9) in the measuring tube (2) is determined by the control device (8) using impedance measurement signals caused by the excitation signals and measured at the first electrode (3) and the second electrode (4).

11. Method according to claim 10, wherein the magnetic-inductive flowmeter (1) is configured according to any one of claims 1 to 9.