Centrifugal pump

Abstract

The centrifugal pump comprises a flow measuring device (3) which is adapted to measure a delivery flow through the pump by means of a turbine wheel (32) comprising at least one permanent magnet (42). The flow measuring device comprises at least one magnetic flux sensor (50, 51) which is arranged in a sensor housing (48) which is mounted in an outer wall of the pump housing (2). A rotatable disc (52) is fixed on the pump shaft and comprises at least one permanent magnet (53). The flow measuring device is adapted to measure the delivery flow on the basis of a first measuring signal which is generated by the at least one magnetic flux sensor as a result of the rotation of the turbine wheel and to include a second measuring signal in the measurement of the delivery flow which is generated by the at least one magnetic flux sensor as a result of the rotation of the rotatable disc.

Description

Technical Field

[0001] The present invention relates to a centrifugal pump comprising: a pump shaft; a pump housing surrounding at least one pump stage having an impeller mounted on an internal part of the pump shaft and fixed to the pump shaft for rotation with the pump shaft; a flow measuring device adapted to measure a transport flow through the centrifugal pump by means of a turbine wheel arranged rotatably about and relative to the pump shaft within the pump housing, the turbine wheel being exposed to the transport flow through the centrifugal pump, the turbine wheel including at least one permanent magnet; the flow measuring device including at least one magnetic flux sensor adapted to measure the transport flow based at least on a first measurement signal generated by the at least one magnetic flux sensor due to the rotation of the turbine wheel, and the at least one magnetic flux sensor being arranged in a sensor housing mounted in an opening formed in the outer wall of the pump housing. Background Technology

[0002] EP 3 184 823 B1 (Grundfoss Holding) discloses a centrifugal pump comprising at least one pump stage. The pump stage includes an impeller rotatably mounted on a pump shaft. In addition to the pump stage, the centrifugal pump is equipped with a turbine impeller arranged on the pump shaft, not in motion coupling, and located within the centrifugal pump's delivery flow. The turbine impeller has three signal elements in the form of permanent magnets, forming a transducer for a flow measurement device for measuring the delivery flow through the centrifugal pump. The flow measurement device also includes a sensor having a sensor housing inserted into an opening formed in the outer wall of the pump casing. The sensor includes a signal receiver in the form of a magnetic flux sensor that detects the magnetic field generated by the three permanent magnets as the turbine impeller rotates. A control device signal-connected to the sensor determines the rotational speed of the turbine impeller and, based on this speed, determines the delivery flow through the centrifugal pump.

[0003] However, to more accurately determine the delivery flow of a centrifugal pump, the delivery flow determined based on the turbine impeller exposed to the delivery flow passing through the centrifugal pump must be corrected according to the rotational speed of one or more impellers of the centrifugal pump. The rotational speed of one or more impellers of the centrifugal pump can be determined in several ways. For example, the rotational speed can be determined based on a signal received from a VFD (variable frequency drive) of an AC (alternating current) motor used to drive the pump.

[0004] In this scenario, besides the potential need for additional wiring between the VFD and the flow measurement device, the numerous and mixed signal / communication protocols of all existing VFDs must be covered. Furthermore, the direct link between motor rotation and pump rotation may not be one-to-one due to motor slip or damaged connectors. In other words, this will be an indirect measurement, and therefore, the measurement will not always be reliable.

[0005] Alternatively, a speed (rpm) sensor can be attached to the electric motor, allowing the rotation of the fan and / or shaft to be measured using optical or magnetic measurements. This can be accomplished using off-the-shelf parts and solutions; however, it requires additional mounting on the pump and additional wiring for the flow measurement device. Furthermore, as with the solutions mentioned above, this would be an indirect measurement, and therefore, the measurement is not always reliable.

[0006] The challenge with existing methods for providing speed measurement for flow measurement devices on centrifugal pumps is that they either increase installation complexity or incur excessive development costs (e.g., mapping all possible communication protocols for all VFDs worldwide). Summary of the Invention

[0007] The object of the present invention is to provide a centrifugal pump in a simpler manner than according to existing solutions, which is adapted to measure the delivery flow based on both the rotation of the turbine wheel and the rotational speed of one or more impellers of the centrifugal pump.

[0008] For this purpose, a rotatable disc is mounted on and fixed to the pump shaft to rotate with the pump shaft. The rotatable disc includes at least one permanent magnet, and the flow measurement device is adapted to include a second measurement signal generated by at least one magnetic flux sensor due to the rotation of the rotatable disc in the measurement of the conveyed flow.

[0009] Thus, since both the first measurement signal generated by the rotation of the turbine wheel and the second measurement signal generated by the rotation of the rotatable disc are generated by at least one magnetic flux sensor arranged in a sensor housing installed in an opening in the outer wall of the pump casing, no additional wiring is required between the flow measuring device and other sensors. Installation of the flow measuring device is easier and simpler because the sensor housing can be easily screwed into the opening in the pump casing, which is typically a vent hole for the pump. As an additional advantage, the measurement of rotational speed is a direct measurement of the pump shaft speed, thus making the measurement more reliable. For example, it is possible to detect whether the turbine wheel is stuck on the pump shaft, because in this case, the detected direction of rotation would be incorrect. Furthermore, according to the invention, it is easy to check whether the rotatable disc is correctly installed.

[0010] In one embodiment, the pump shaft extends through a shaft seal arranged in the outer wall of the pump housing. The external part of the pump shaft has a connecting end for connection with the motor shaft, and a rotatable disc is mounted on the external part of the pump shaft. Therefore, the rotatable disc is easily accessible from the outside of the pump housing and does not occupy space inside the pump housing. This is indeed an advantage, as the rotatable disc can be directly accessed and seen, allowing for proper installation control and easy maintenance if necessary. Furthermore, it is advantageous that the magnet of the rotatable disc does not need to be in contact with the fluid pumped by the centrifugal pump. Therefore, a wider range of materials can be chosen for the magnet. For example, neodymium magnets, which are much stronger than standard permanent magnets, can be used. Neodymium magnets should not be used in contact with drinking water.

[0011] In a particularly advantageous embodiment, the rotatable disc consists of two disc halves that are clamped together, thereby clamping the pump shaft in a central hole passing through the rotatable disc. Therefore, the rotatable disc can be easily mounted on the pump shaft.

[0012] A rotatable disc can be clamped onto the ring of a shaft seal, for example.

[0013] In one embodiment, at least one magnetic flux sensor includes a first magnetic flux sensor and a second magnetic flux sensor. The first magnetic flux sensor is adapted to generate a first measurement signal due to the rotation of the turbine wheel, and the second magnetic flux sensor is adapted to generate a second measurement signal due to the rotation of the rotatable disk. Therefore, the first and second measurement signals do not need to be separated in software via demodulation, as these signals have already been generated independently. Furthermore, the first and second magnetic flux sensors can be positioned at different locations within the sensor housing, allowing the position of each magnetic flux sensor relative to the magnets of the turbine wheel and the rotatable disk to be optimized. Therefore, the provided first and second measurement signals can be more reliable.

[0014] In one embodiment, the sensor housing is elongated and extends through an opening formed in the outer wall of the pump housing. The sensor housing includes a first part disposed inside the pump housing and a second part disposed outside the pump housing. A first magnetic flux sensor is disposed in the first part of the sensor housing, and a second magnetic flux sensor is disposed in the second part of the sensor housing. Therefore, specifically, the position of the first magnetic flux sensor can be optimized because it can be positioned very close to the magnet of the turbine wheel and located inside the pump housing, so that it is not necessary to penetrate the pump housing to detect the magnetic field of the turbine wheel. The short distance between the first magnetic flux sensor and the magnet of the turbine wheel will reduce possible signal interference. On the other hand, the position of the second magnetic flux sensor can also be optimized because it can be located outside the pump housing, so that it is not necessary to penetrate the pump housing to detect the magnetic field of the rotating disk's magnet. Therefore, the provided first and second measurement signals can be more reliable.

[0015] In one embodiment, a first magnetic flux sensor and a second magnetic flux sensor are arranged in a sensor housing, having a first distance from each other in the longitudinal direction of the sensor housing. The first magnetic flux sensor is arranged at a minimum second distance from at least one permanent magnet of the turbine wheel during turbine wheel rotation, and the second magnetic flux sensor is arranged at a minimum third distance from at least one permanent magnet of the rotatable disk during rotatable disk rotation. The minimum third distance is at least twice, preferably at least 2.5 times, and most preferably at least three times the minimum second distance. Therefore, the provided first and second measurement signals can be more reliable.

[0016] In one embodiment, the first distance between them is within ±30%, preferably within ±20%, and most preferably within ±10% of the shortest third distance. Therefore, the provided first and second measurement signals can be more reliable.

[0017] In one embodiment, at least the second magnetic flux sensor is omnidirectional. Therefore, the precise position of the rotatable disk relative to the second magnetic flux sensor may not be critical. This can be an advantage, for example, because the same sensor housing design can be used for centrifugal pumps of different sizes, which may result in different preferred positions of the rotatable disk on the pump shaft due to various structural considerations.

[0018] In one embodiment, the first magnetic flux sensor has a direction of maximum sensitivity, and is arranged such that this direction extends longitudinally along the sensor housing and, during turbine wheel rotation, in the direction of closest proximity to at least one permanent magnet of the turbine wheel. Therefore, the sensitivity of the first magnetic flux sensor can be maximized. This can be advantageous for obtaining a reliable first measurement signal without using a special magnet that provides a stronger magnetic field.

[0019] In one embodiment, the flow measurement device includes a processor adapted to calculate an uncorrected transport flow based on a first measurement signal generated by at least one magnetic flux sensor due to the rotation of a turbine impeller, and the processor adapted to calculate a corrected transport flow by correcting the uncorrected transport flow based on a second measurement signal generated by at least one magnetic flux sensor due to the rotation of a rotatable disk. Therefore, the flow measurement device can be provided as a single unit adapted to provide a transport flow measurement corrected based on the rotation of one or more impellers of a centrifugal pump. The flow measurement device may also be provided with a single sensor housing comprising the entire flow measurement device except for the turbine impeller and the rotatable disk. Attached Figure Description

[0020] The invention will now be explained in more detail below with reference to the schematic diagrams and examples of embodiments, wherein:

[0021] Figure 1 This is an axial cross-sectional view of an embodiment of the centrifugal pump according to the present invention.

[0022] Figure 2 Shown at a larger scale Figure 1 Details

[0023] Figure 3 It shows Figure 1 A three-dimensional view of a part of a centrifugal pump.

[0024] Figure 4 It shows Figure 1 A three-dimensional diagram of the rotating disc of a centrifugal pump, and

[0025] Figure 5 It shows Figure 4 An exploded 3D diagram of a rotating disk. Detailed Implementation

[0026] Figures 1 to 3An embodiment of a centrifugal pump 1 according to the present invention is shown. The centrifugal pump 1 includes a pump casing 2 having a lower casing portion 4, an upper casing portion 8, and a hollow cylindrical intermediate casing portion 6 disposed therebetween. A fluid inlet 10 and a fluid outlet 12 of the centrifugal pump 1 are formed on the lower casing portion 4. The fluid inlet 10 is flow-connected to five pump stages 14 of the centrifugal pump 1, which are arranged one after another in the region of the intermediate casing portion 6 in the direction of the upper casing portion 8. Each pump stage 14 includes a housing 16, which is fixedly arranged in the pump casing 2, and an impeller 18 and a diffuser 20 are arranged in the housing in a manner known to those skilled in the art. Each housing 16 is flow-connected to an adjacent housing 16, wherein the last housing 16 in the direction of the upper casing portion 8 is flow-connected via an opening 22 to a pressure chamber 24 formed in the region of the upper casing portion 8.

[0027] The impeller 18 of pump stage 14 is rotatably fixed to pump shaft 26, which extends concentrically through pump housing 2 with housing intermediate portion 6 and protrudes beyond pump housing 2 at upper portion 8. Here, the outer portion 27 of pump shaft 26 has a connecting end connected by means of connector 29 to the motor shaft of drive motor (not shown), which is mounted on motor bracket 28 formed on upper portion 8. When pump shaft 26 is driven, the impellers 18 of each pump stage deliver fluid from fluid inlet 10 through pump stage 14 to pressure chamber 24, from which fluid flows through an annular gap 30 between the wall of housing intermediate portion 6 and pump stage housing 16 to fluid outlet 12 of centrifugal pump 1. Alternatively, fluid outlet 12 may also be located at the opposite axial end of centrifugal pump 1.

[0028] The turbine wheel 32 is rotatably mounted in the pressure chamber 24, downstream of the last pump stage 14 in the flow direction and directly adjacent to the pressure chamber 24. The turbine wheel 32 is arranged around a pump shaft 26, which is engaged by a hub 34 of the turbine wheel 32, and the turbine wheel 32 is rotatably mounted relative to the pump shaft 26. A plurality of blades 36 extending radially outward from the hub 34 are connected to the outer ring 38 of the turbine wheel 32. Thus, the blades 36 of the turbine wheel 32 are directly positioned above an opening 22 formed on the last pump stage 14 in the flow direction of the centrifugal pump, through which the axial flow of the pump casing flows through the centrifugal pump 1 into the pressure chamber 24. The flow of the pump applies torque to the turbine wheel 32 by impacting the blades 36, thereby causing rotational motion. The torque exerted on the turbine wheel 32 by the transport flow is therefore in the opposite direction to the torque exerted on the impeller 18 via the pump shaft 26 for fluid transport purposes. This is because the blades 36 of the turbine wheel 32 are quasi-counteraligned with the blades 40 of the impeller 18. Therefore, in operation, the turbine wheel 32 rotates in the opposite direction to the pump shaft 26.

[0029] The turbine wheel 32 forms a converter for the flow measurement device 3, which allows the delivery flow through the centrifugal pump 1 to be continuously determined during operation of the centrifugal pump so that the delivery flow can be subsequently incorporated into the activation of the drive motor (not shown) of the centrifugal pump 1. Figure 1 and Figure 2 The turbine wheel 32 shown for forming the converter is provided with three signal components in the form of permanent magnets 42. These three signal components are arranged in three corresponding recesses 44 formed at different angular distances on the outer peripheral side of the outer ring 38 of the turbine wheel 32 so as to determine the rotation direction of the turbine wheel 32.

[0030] A threaded opening 46 is formed on the upper portion 8 of the pump housing 2. The sensor housing 48 of the flow measuring device 3 is threadedly connected to this opening 46, and the sensor housing extends downwards to the outer ring 38 directly adjacent to the turbine wheel 32. The opening 46 can also be used as a vent opening for the centrifugal pump 1, and vent openings in existing pump designs can be used as an integral part of the flow measuring device 3 according to the invention.

[0031] The sensor housing 48 includes a first magnetic flux sensor 50, which detects the changing magnetic field generated by the three permanent magnets 42 of the turbine wheel 32 as the turbine wheel 32 rotates.

[0032] like Figure 1 and Figure 2As shown, a rotatable disk 52 is mounted on and fixed to the pump shaft 26 so as to rotate with the pump shaft. The rotatable disk 52 includes a plurality of permanent magnets 53 arranged on its periphery. In addition, the sensor housing 48 includes a second magnetic flux sensor 51, which detects the changing magnetic field generated by the plurality of permanent magnets 53 of the rotatable disk 52 as the rotatable disk 52 rotates.

[0033] The sensor housing 48 is preferably made of a corrosion-resistant metal, but it can also be made of plastic. However, the sensor housing 48 should generally not be ferromagnetic, as ferromagnetism would interfere with the magnetic field detected by the magnetic flux sensors 50 and 51.

[0034] The flow measurement device 3 is adapted to measure the pump's delivery flow based on a first measurement signal generated by a first magnetic flux sensor 50 due to the rotation of the turbine wheel 32 during operation of the centrifugal pump 1. Furthermore, according to the invention, the flow measurement device 3 is adapted to include a second measurement signal in the measurement of the delivery flow, generated by a second magnetic flux sensor 51 due to the rotation of a rotatable disk 52.

[0035] According to an alternative embodiment of the invention, a single magnetic flux sensor can be used to generate both the first and second measurement signals. This single magnetic flux sensor can be arranged at any suitable location within the sensor housing 48. However, by using a separate first magnetic flux sensor 50 to generate the first measurement signal and a separate second magnetic flux sensor 51 to generate the second measurement signal, the first and second measurement signals do not need to be separated in software via demodulation, since these signals have already been generated separately. Furthermore, the first magnetic flux sensor 50 and the second magnetic flux sensor 51 can be positioned in different locations within the sensor housing 48, such that the position of each magnetic flux sensor is optimized relative to the position of the magnet 42 of the turbine wheel 32 and the position of the magnet 53 of the rotatable disk 52. Therefore, the provided first and second measurement signals can be more reliable.

[0036] like Figure 2As shown, the pump shaft 26 extends through a shaft seal 54 arranged in the outer wall of the pump housing 2. As described above, the outer portion 27 of the pump shaft 26 has a connecting end for connection with a motor shaft (not shown), and a rotatable disc 52 is mounted on the outer portion 27 of the pump shaft 26. In the illustrated embodiment, the rotatable disc 52 is clamped onto the ring of the shaft seal 54. However, for larger pumps, it may be preferable that the rotatable disc 52 is arranged higher on the pump shaft 26, closer to the connector 29. The rotatable disc 52 is easily accessible from the outside of the pump housing 2 and does not occupy space inside the pump housing. The rotatable disc 52 is directly accessible and visible, and therefore can be controlled to ensure proper installation and thus can be easily maintained. Furthermore, it is advantageous that the magnet 53 of the rotatable disc 52 does not need to be in contact with the fluid pumped by the centrifugal pump 1. Therefore, there is a greater range of choices for the material of the magnet 53. For example, neodymium magnets, which are much stronger than standard permanent magnets, can be used. Neodymium magnets should not be used in contact with drinking water.

[0037] exist Figure 4 and Figure 5 In the illustrated embodiment, the rotatable disc 52 consists of two disc halves 55 and 56, which are clamped together to clamp the pump shaft 26 in a central hole 57 passing through the rotatable disc 52. The disc halves 55 and 56 are clamped together by means of screws installed in screw holes 62. Figure 4 As shown, the permanent magnets 53 of the rotatable disk 52 can be mounted in the disk, i.e., they are inserted into the radially outer portion of the central opening 63. However, the rotatable disk 52 can also be constructed in any other suitable manner. The material of the rotatable disk 52 is preferably a metal (e.g., aluminum), but any suitable material can be used. In the illustrated embodiment, two permanent magnets 53 are symmetrically arranged on the periphery of the rotatable disk 52. However, any other suitable number (including one and three or more) of permanent magnets 53 can be used. Furthermore, the permanent magnets 53 can be arranged at different angular distances to determine the direction of rotation of the rotatable disk 52.

[0038] like Figure 2As shown, the sensor housing 48 is elongated and extends through an opening 46 formed in the outer wall of the pump housing 2. The sensor housing 48 includes a first portion 58 disposed inside the pump housing 2 and a second portion 59 disposed outside the pump housing 2. A first magnetic flux sensor 50 is disposed in the first portion 58 of the sensor housing 48, and a second magnetic flux sensor 51 is disposed in the second portion 59 of the sensor housing 48. The position of the first magnetic flux sensor 50 can be optimized because it can be positioned very close to the magnet 42 of the turbine wheel 32 and located inside the pump housing, so that it is not necessary to pass through the pump housing 2 to detect the magnetic field of the turbine wheel. The short distance between the first magnetic flux sensor 50 and the magnet 42 of the turbine wheel 32 will reduce possible signal interference. On the other hand, the position of the second magnetic flux sensor 51 can also be optimized because it can be located outside the pump housing 2, so that it is not necessary to pass through the pump housing to detect the magnetic field of the magnet 53 of the rotating disk 52. Therefore, the provided first and second measurement signals can be more reliable.

[0039] like Figure 2 As shown, a first magnetic flux sensor 50 and a second magnetic flux sensor 51 are arranged in a sensor housing 48, having a first distance d1 between them in the longitudinal direction L of the sensor housing 48. The first magnetic flux sensor 50 is arranged at a minimum second distance d2 from at least one permanent magnet 42 of the turbine wheel 32 during rotation. The second magnetic flux sensor 51 is arranged at a minimum third distance d3 from at least one permanent magnet 53 of the rotatable disk 52 during rotation. The minimum third distance d3 is at least twice the minimum second distance d2, preferably at least 2.5 times, and most preferably at least three times. The mutual first distance d1 is within ±30%, preferably within ±20%, and most preferably within ±10% of the minimum third distance d3.

[0040] Preferably, at least the second magnetic flux sensor 51 is omnidirectional. Therefore, the precise position of the rotatable disk 52 relative to the second magnetic flux sensor 51 may not be important. This can be an advantage, for example, because the same sensor housing design can be used for centrifugal pumps of different sizes, which may result in different preferred positions of the rotatable disk 52 on the pump shaft 26 due to various structural considerations.

[0041] Preferably, the first magnetic flux sensor 50 has a direction of maximum sensitivity, and the first magnetic flux sensor 50 is arranged such that its direction of maximum sensitivity extends in the longitudinal direction L of the sensor housing 48, and extends in the direction closest to the position of at least one permanent magnet 42 of the turbine wheel 32 during rotation of the turbine wheel 32. Therefore, the sensitivity of the first magnetic flux sensor 50 is maximized. This is advantageous for obtaining a reliable first measurement signal without using a special magnet that provides a stronger magnetic field.

[0042] According to the invention, the flow measurement device 3 includes a processor (not shown) adapted to calculate an uncorrected transport flow based on a first measurement signal generated by at least one magnetic flux sensor 50, 51 due to the rotation of the turbine wheel 32. The processor is adapted to calculate a corrected transport flow by correcting the uncorrected transport flow based on a second measurement signal generated by at least one magnetic flux sensor 50, 51 due to the rotation of a rotatable disk 52 using a correction factor.

[0043] The first magnetic flux sensor 50 and the second magnetic flux sensor 51 can be Hall sensors; however, coil sensors may be preferred because they are more sensitive.

[0044] Explanation of reference numerals in the attached figures

[0045] L: Longitudinal direction of the sensor housing

[0046] 1: Centrifugal pump

[0047] 2: Pump casing

[0048] 3: Flow measurement device

[0049] 4: Lower part of the shell

[0050] 6: Middle part of the shell

[0051] 8: Upper part of the shell

[0052] 10: Fluid inlet

[0053] 12: Fluid outlet

[0054] 14: Pump stage

[0055] 16: Shell

[0056] 18: Impeller

[0057] 20: Diffuser

[0058] 22: Opening

[0059] 24: Pressure Chamber

[0060] 26: Pump shaft

[0061] 27: External part of the pump shaft

[0062] 28: Motor frame

[0063] 29: Connector

[0064] 30: Annular gap

[0065] 32: Turbine wheel

[0066] 34: Hub of a turbine wheel

[0067] 36: Turbine wheel blades

[0068] 38: Outer ring of the turbine wheel

[0069] 40: Impeller blades

[0070] 42: Permanent magnets of turbine wheels

[0071] 44: The recess of the turbine wheel

[0072] 46: Ventilation opening in the upper part of the shell

[0073] 48: Sensor housing

[0074] 50: First magnetic flux sensor

[0075] 51: Second magnetic flux sensor

[0076] 52: A rotating disc

[0077] 53: A permanent magnet that can rotate.

[0078] 54: Shaft seal

[0079] 55, 56: The half of a rotating disk

[0080] 57: The central hole of the rotating disc

[0081] 58: The first part of the sensor housing

[0082] 59: The second part of the sensor housing

[0083] 60: Ring of shaft seal

[0084] 61: Screw

[0085] 62: Screw hole

[0086] 63: Hole for magnets

[0087] 64: Electrical connection for sensor housing

Claims

1. A centrifugal pump (1), comprising: Pump shaft (26); pump housing (2) surrounding at least one pump stage (14) having an impeller (18) mounted on an internal portion of the pump shaft (26) and fixed to the pump shaft for rotation with the pump shaft; flow measuring device (3) adapted to measure the conveyed flow through the centrifugal pump (1) by means of a turbine wheel (32) rotatably arranged in the pump housing (2) about and relative to the pump shaft, the turbine wheel (32) being exposed to the conveyed flow through the centrifugal pump, the turbine wheel (32) including at least one permanent magnet (42), the flow measuring device (3) including at least one magnetic flux sensor (50, 51), the flow measuring device (3) adapted to measure the conveyed flow based at least on a first measurement signal, The first measurement signal is generated by the at least one magnetic flux sensor (50, 51) due to the rotation of the turbine wheel (32), and the at least one magnetic flux sensor (50, 51) is arranged in a sensor housing (48) which is mounted in an opening (46) formed in the outer wall of the pump housing (2). The device is characterized in that a rotatable disk (52) is mounted on the pump shaft (26) and fixed to the pump shaft to rotate with the pump shaft. The rotatable disk (52) includes at least one permanent magnet (53). The flow measurement device (3) is adapted to include a second measurement signal in the measurement of the transport flow, the second measurement signal being generated by the at least one magnetic flux sensor (50, 51) due to the rotation of the rotatable disk (52).

2. The centrifugal pump according to claim 1, wherein, The pump shaft (26) extends through a shaft seal (54) arranged in the outer wall of the pump housing (2), wherein the outer portion (27) of the pump shaft (26) has a connecting end for connection with a motor shaft, and wherein the rotatable disc (52) is mounted on the outer portion (27) of the pump shaft (26).

3. The centrifugal pump according to claim 2, wherein, The rotatable disc (52) consists of two disc halves (55, 56) that are clamped together to clamp the pump shaft (26) in the central hole (57) passing through the rotatable disc (52).

4. The centrifugal pump according to any one of claims 1 to 3, wherein, The at least one magnetic flux sensor (50, 51) includes a first magnetic flux sensor (50) and a second magnetic flux sensor (51), wherein the first magnetic flux sensor (50) is adapted to generate a first measurement signal due to the rotation of the turbine wheel (32), and wherein the second magnetic flux sensor (51) is adapted to generate a second measurement signal due to the rotation of the rotatable disk (52).

5. The centrifugal pump according to claim 4, wherein, The sensor housing (48) is elongated and extends through an opening (46) formed in the outer wall of the pump housing (2). The sensor housing (48) includes a first portion (58) disposed inside the pump housing (2) and a second portion (59) disposed outside the pump housing. The first magnetic flux sensor (50) is disposed in the first portion (58) of the sensor housing (48), and the second magnetic flux sensor (51) is disposed in the second portion (59) of the sensor housing (48).

6. The centrifugal pump according to claim 4, wherein, The first magnetic flux sensor (50) and the second magnetic flux sensor (51) are arranged in the sensor housing (48) having a first distance (d1) between them in the longitudinal direction of the sensor housing (48), wherein the first magnetic flux sensor (50) is arranged at a minimum second distance (d2) from at least one permanent magnet (42) of the turbine wheel (32) during the rotation of the turbine wheel (32), wherein the second magnetic flux sensor (51) is arranged at a minimum third distance (d3) from at least one permanent magnet (53) of the rotatable disk (52) during the rotation of the rotatable disk (52), and wherein the minimum third distance (d3) is at least twice the minimum second distance (d2).

7. The centrifugal pump according to claim 6, wherein, The first mutual distance (d1) is within ±30% of the shortest third distance (d3).

8. The centrifugal pump according to claim 4, wherein, At least the second magnetic flux sensor (51) is omnidirectional.

9. The centrifugal pump according to claim 6, wherein, The first magnetic flux sensor (50) has a maximum sensitivity direction, and wherein the first magnetic flux sensor (50) is arranged such that its maximum sensitivity direction extends in the longitudinal direction (L) of the sensor housing (48) and extends in the direction of the closest position of the at least one permanent magnet (42) of the turbine wheel (32) during the rotation of the turbine wheel (32).

10. The centrifugal pump according to any one of claims 1 to 3, wherein, The flow measurement device (3) includes a processor adapted to calculate an uncorrected transport flow based on a first measurement signal generated by the at least one magnetic flux sensor (50, 51) due to the rotation of the turbine wheel (32), and wherein the processor is adapted to calculate a corrected transport flow by correcting the uncorrected transport flow based on a second measurement signal generated by the at least one magnetic flux sensor (50, 51) due to the rotation of the rotatable disk (52).

11. The centrifugal pump according to claim 6, wherein, The shortest third distance (d3) is at least 2.5 times the shortest second distance (d2).

12. The centrifugal pump according to claim 6, wherein, The shortest third distance (d3) is at least three times the shortest second distance (d2).

13. The centrifugal pump according to claim 7, wherein, The first mutual distance (d1) is within ±20% of the shortest third distance (d3).

14. The centrifugal pump according to claim 7, wherein, The first mutual distance (d1) is within ±10% of the shortest third distance (d3).

Images