Patent Description:
<CIT> (Grundfos Holding A/S) discloses a centrifugal pump including at least one pump stage. This pump stage includes an impeller which is mounted rotationally fixed on a pump shaft. Apart from the pump stage, the centrifugal pump is equipped with a turbine wheel which is arranged on the pump shaft, without a movement coupling to the pump shaft, in the delivery flow of the centrifugal pump. This turbine wheel is provided with three signal means in the form of permanent magnets and forms a transducer of a flow measuring device for measuring a delivery flow through the centrifugal pump. The flow measuring device further includes a sensor having a sensor housing inserted into an opening formed on an outer wall of the pump casing. This sensor includes a signal receiver in the form of a magnetic flux sensor which on rotation of the turbine wheel detects the magnetic fields which results from the three permanent magnets. A control device which is signal-connected to the sensor determines the rotation speed of the turbine wheel and, on the basis thereof, the delivery flow through the centrifugal pump.

However, in order to more precisely determine the delivery flow of a centrifugal pump, the delivery flow determined on the basis of a turbine wheel exposed to the delivery flow through the centrifugal pump must be corrected according to the rotational speed of the impeller or impellers of the centrifugal pump. The rotational speed of the impeller or impellers of the centrifugal pump may be determined in a number of ways. For instance, the rotational speed may be determined on the basis of a signal received from a VFD (variable-frequency drive) for an AC (alternating current) motor driving the pump.

In this case, apart from the fact that extra cabling might be needed between the VFD and the flow measuring device, a huge mix of signals/communication protocols of all existing VFD's would have to be covered. Furthermore, the direct link between motor rotation and pump rotation may not be one-to-one due to motor slip, or due to a broken coupling. In other words, this would be an indirect measurement, and as such, the measurement would not always be reliable.

Alternatively, an rpm sensor could be attached to the electric motor, whereby the rotation of a fan and/or shaft could be measured using optical or magnetic measurements. This could be done using off-the-shelf components and solutions, however, this would require extra mounting on the pump and extra cabling to the flow measuring device. Furthermore, as with the solution mentioned just above, this would be an indirect measurement, and as such, the measurement would not always be reliable.

Generally, the challenge with existing methods of providing an rpm measurement for a flow measuring device of a centrifugal pump is that they either increase the installation complexity or comes with excessive development costs (e.g. mapping all possible communication protocols for all VFD's in the world).

The object of the present invention is to provide, in a simpler way than according to existing solutions, a centrifugal pump adapted to measure delivery flow based on both the rotation of a turbine wheel and the rotational speed of the impeller or impellers of the centrifugal pump.

In view of this object, a rotatable disc is mounted on the pump shaft and fixed to the pump shaft for rotation with the pump shaft, the rotatable disc includes at least one permanent magnet, and the flow measuring device is adapted to include in the measurement of the delivery flow a second measurement signal generated by the at least one magnetic flux sensor as a result of the rotation of the rotatable disc.

In this way, because both the first measurement signal resulting from the rotation of the turbine wheel and the second measurement signal resulting from the rotation of the rotatable disc are generated by the at least one magnetic flux sensor which is arranged in the sensor housing mounted in the opening of the outer wall of the pump casing, no extra cabling is needed between the flow measuring device and other sensors. The installation of the flow measuring device is furthermore easy and simple in that the sensor housing may simply be threaded into said opening of the pump casing, which could typically be a vent hole of the pump. As an additional advantage, the measurement of the rotational speed is a direct measurement of the rotational speed of the pump shaft, and therefore, the measurement is more reliable. For instance, it would be possible to detect if the turbine wheel should get stuck on the pump shaft, because in this case, the direction of the detected rotation would be wrong. Furthermore, according to the present invention, it may be easy to check if the rotatable disc is mounted correctly.

In an embodiment, the pump shaft extends through a shaft seal arranged in the outer wall of the pump casing, an external part of the pump shaft has a coupling end for connection with a motor shaft, and the rotatable disc is mounted on the external part of the pump shaft. Thereby, the rotatable disc is easily accessible outside the casing of the pump and does not take up space inside the pump casing. It is indeed an advantage that the rotatable disc is directly accessible and visible so that is may be controlled that it is correctly mounted and so that is may be easily serviced, if necessary. It is furthermore an advantage that the magnets of the rotatable disc do not have to come into contact with the fluid pumped by the centrifugal pump. Therefore, the choice of material for the magnets is greater. For instance, neodymium-magnets may be used which are much stronger than standard permanent magnets. Neodymium-magnets should not be used in contact with drinking water.

In a structurally particularly advantageous embodiment, the rotatable disc is composed by two disc halves clamped together and thereby clamping the pump shaft in a central hole through the rotatable disc. Thereby, the rotatable disc may easily be mounted on the pump shaft.

The rotatable disc may for instance be clamped on a ring of the shaft seal.

In an embodiment, the 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 the first measurement signal as a result of the rotation of the turbine wheel, and the second magnetic flux sensor is adapted to generate the second measurement signal as a result of the rotation of the rotatable disc. Thereby, the first and second measurement signals need not be separated in software by demodulation, as the signals are already created separately. Furthermore, the first and second magnetic flux sensors may be positioned differently in the sensor housing, so that the position of each magnetic flux sensor may be optimised in relation to the position of the magnets of the turbine wheel and the magnets of the rotatable disc, respectively. Thereby, the provided first and second measurement signals may be more reliable.

In an embodiment, the sensor housing is elongated and extends through the opening formed in the outer wall of the pump casing, the sensor housing includes a first part arranged inside the pump casing and a second part arranged outside the pump casing, the first magnetic flux sensor is arranged in the first part of the sensor housing, and the second magnetic flux sensor is arranged in the second part of the sensor housing. Thereby, in particular the position of the first magnetic flux sensor may be optimised in that it may be positioned very close to the position of the magnets of the turbine wheel and inside the pump casing, so that the magnetic field of the turbine wheel does not have to be detected through the pump casing. A short distance between the first magnetic flux sensor and the magnets of the turbine wheel will reduce possible disturbances of the signal. On the other hand, also the position of the second magnetic flux sensor may be optimised in that it may be positioned outside the pump casing, so that the magnetic field of the magnets of the rotatable disc does not have to be detected through the pump casing. Thereby, the provided first and second measurement signals may be even more reliable.

In an embodiment, the first magnetic flux sensor and the second magnetic flux sensor are arranged in the sensor housing with a mutual first distance in a longitudinal direction of the sensor housing, the first magnetic flux sensor is arranged at a, during rotation of the turbine wheel, shortest second distance from the at least one permanent magnet of the turbine wheel, the second magnetic flux sensor is arranged at a, during rotation of the rotatable disc, shortest third distance from the at least one permanent magnet of the rotatable disc, and the shortest third distance is at least <NUM> times, preferably at least <NUM> times, and most preferred at least <NUM> times, the shortest second distance. Thereby, the provided first and second measurement signals may be even more reliable.

In an embodiment, the mutual first distance is within ±<NUM> per cent, preferably within ±<NUM> per cent, and most preferred within ±<NUM> per cent of the shortest third distance. Thereby, the provided first and second measurement signals may be even more reliable.

In an embodiment, at least the second magnetic flux sensor is of an omnidirectional type. Thereby, the exact position of the rotatable disc in relation to the second magnetic flux sensor may not be critical. This may be an advantage, for instance because the same sensor housing design may be used for centrifugal pumps of different size, whereby a preferred position of the rotatable disc on the pump shaft may vary due to various constructional considerations.

In an embodiment, the first magnetic flux sensor has a direction of maximum sensitivity, and the first magnetic flux sensor is arranged with its direction of maximum sensitivity extending in the longitudinal direction of the sensor housing and in the direction of the, during rotation of the turbine wheel, closest position of the at least one permanent magnet of the turbine wheel. Thereby, the sensitivity of the first magnetic flux sensor may be maximised. This may be advantageous in order to obtain a reliable first measurement signal without using special magnets providing a stronger magnetic field.

In an embodiment, the flow measuring device includes a processor adapted to calculate an uncorrected delivery flow on the basis of the first measurement signal generated by the at least one magnetic flux sensor as a result of the rotation of the turbine wheel, and the processor is adapted to calculate a corrected delivery flow by correcting the uncorrected delivery flow by means of a correction factor based on the second measurement signal generated by the at least one magnetic flux sensor as a result of the rotation of the rotatable disc. Thereby, the flow measuring device may be provided as a single unit adapted to provide a delivery flow measurement corrected on the basis of the rotation of the impeller or impellers of the centrifugal pump. The flow measuring device may further be provided with a single sensor housing including the entire flow measuring device apart from the turbine wheel and the rotatable disc.

The invention will now be explained in more detail below by means of examples of embodiments with reference to the very schematic drawing, in which.

<FIG> illustrate an embodiment of a centrifugal pump <NUM> according to the present invention. The centrifugal pump <NUM> includes a pump casing <NUM> having a casing lower part <NUM>, a casing upper part <NUM>, and a hollow-cylindrical casing middle part <NUM> arranged there between. A fluid inlet <NUM> and a fluid outlet <NUM> of the centrifugal pump <NUM> are formed on the casing lower part <NUM>. The fluid inlet <NUM> is flow-connected to five pump stages <NUM> of the centrifugal pump <NUM> which are arranged in the region of the casing middle part <NUM> over one another in the direction of the casing upper part <NUM>. Each of the pump stages <NUM> includes a housing <NUM> which is arranged in the pump casing <NUM> in a stationary manner and in which an impeller <NUM> and a diffuser <NUM> are arranged in a manner well-known to the skilled person. The housings <NUM> are each flow-connected to adjacent housings <NUM>, wherein a housing <NUM> which is last in the direction of the casing upper part <NUM> is flow-connected via an opening <NUM> to a pressure chamber <NUM> which is formed in the region of the casing upper part <NUM>.

The impellers <NUM> of the pump stages <NUM> are connected to a pump shaft <NUM> in a rotationally fixed manner, said pump shaft extending concentrically to the casing middle part <NUM> through the pump casing <NUM> and projecting out of the pump casing <NUM> at the casing upper part <NUM>. There, an external part <NUM> of the pump shaft <NUM> has a coupling end which by means of a coupling <NUM> is connected to a motor shaft of a drive motor which is not represented and which is mounted on a motor stool <NUM> which is formed on the casing upper part <NUM>. When the pump shaft <NUM> is driven, the impellers <NUM> of the individual pump stages deliver a fluid from the fluid inlet <NUM> through the pump stages <NUM> to the pressure chamber <NUM>, from where the fluid flows via an annular gap <NUM> between the wall of the casing middle part <NUM> and the housing <NUM> of the pump stages, to the fluid outlet <NUM> of the centrifugal pump <NUM>. Alternatively, the fluid outlet <NUM> could also be situated at the opposite axial end of the centrifugal pump <NUM>.

A turbine wheel <NUM> is rotatably mounted in the pressure chamber <NUM>, downstream of the pump stage <NUM> which is last in the flow direction and which is directly adjacent the pressure chamber <NUM>. This turbine wheel <NUM> is arranged around the pump shaft <NUM>, wherein the pump shaft <NUM> engages through a hub <NUM> of the turbine wheel <NUM>, and the turbine wheel <NUM> is rotatably mounted in relation to the pump shaft <NUM>. Several blades <NUM>, departing from the hub <NUM>, extend outwards in the radial direction, where they are connected to an outer ring <NUM> of the turbine wheel <NUM>. Hereby, the blades <NUM> of the turbine wheel <NUM> in the flow direction of the centrifugal pump are arranged directly above the opening <NUM> which is formed on the last pump stage <NUM> and via which the delivery flow in the axial direction of the pump housing flows through the centrifugal pump <NUM> into the pressure chamber <NUM>. The delivery flow exerts a torque upon the turbine wheel <NUM> by way of it hitting the blades <NUM> of the turbine wheel <NUM>, by which means this is brought into a rotational movement. The torque which is exerted by the delivery flow onto the turbine wheel <NUM> is hereby directed counter to the torque which is exerted upon the impeller <NUM> via the pump shaft <NUM> for the purpose of fluid delivery. This is due to the fact that the blades <NUM> of the turbine wheel <NUM> are aligned quasi counter to blades <NUM> of the impeller <NUM>. Thus, the turbine wheel <NUM> rotates oppositely to the pump shaft <NUM> in operation.

The turbine wheel <NUM> forms a transducer of a flow measuring device <NUM>, with which the delivery flow through the centrifugal pump <NUM> may be continuously determined during the operation of the centrifugal pump, in order to e.g. subsequently be included in the activation of the not shown drive motor for the centrifugal pump <NUM>. The turbine wheel <NUM>, which is represented in <FIG> and <FIG>, for forming a transducer is provided with three signal means in the form of permanent magnets <NUM> which are arranged in three corresponding recesses <NUM> formed on the outer peripheral side of the outer ring <NUM> of the turbine wheel <NUM> at varying angular distance in order to be able to determine the rotation direction of the turbine wheel <NUM>.

An threaded opening <NUM> is formed on the casing upper part <NUM> of the pump casing <NUM>. A sensor housing <NUM> of the flow measuring device <NUM> which extends down to the direct vicinity of the outer ring <NUM> of the turbine wheel <NUM> is in threaded connection with this opening <NUM>. The opening <NUM> may additionally serve as a vent opening for the centrifugal pump <NUM>, and a vent opening of an existing pump design may serve for the integration of a flow measuring device <NUM> according to the present invention.

This sensor housing <NUM> includes a first magnetic flux sensor <NUM> which on rotation of the turbine wheel <NUM> detects the varying magnetic field resulting from the three permanent magnets <NUM> of the turbine wheel <NUM>.

As seen in <FIG> and <FIG>, a rotatable disc <NUM> is mounted on the pump shaft <NUM> and fixed to the pump shaft for rotation with the pump shaft. The rotatable disc <NUM> includes a number of permanent magnets <NUM> arranged at its periphery. Furthermore, the sensor housing <NUM> includes a second magnetic flux sensor <NUM> which on rotation of the rotatable disc <NUM> detects the varying magnetic field resulting from the number of permanent magnets <NUM> of the rotatable disc <NUM>.

The sensor housing <NUM> is preferably made of corrosion resistant metal, however it could also be made of plastic. However, the sensor housing <NUM> should generally not be ferromagnetic, as this could disturb the magnetic fields detected by the magnetic flux sensors <NUM>, <NUM>.

The flow measuring device <NUM> is adapted to measure, during operation of the centrifugal pump <NUM>, the delivery flow of the pump on the basis of a first measurement signal generated by the first magnetic flux sensor <NUM> as a result of the rotation of the turbine wheel <NUM>. Furthermore, according to the present invention, the flow measuring device <NUM> is adapted to include in the measurement of the delivery flow a second measurement signal generated by the second magnetic flux sensor <NUM> as a result of the rotation of the rotatable disc <NUM>.

According to an alternative embodiment of the present invention, a single magnetic flux sensor may be used for generating both the first measurement signal and the second measurement signal. Such single magnetic flux sensor may be arranged at any suitable position in the sensor housing <NUM>. However, by using a separate first magnetic flux sensor <NUM> for generating the first measurement signal and a separate second magnetic flux sensor <NUM> for generating the second measurement signal, the first and second measurement signals need not be separated in software by demodulation, as the signals are already created separately. Furthermore, the first and second magnetic flux sensors <NUM>, <NUM> may be positioned differently in the sensor housing <NUM>, so that the position of each magnetic flux sensor may be optimised in relation to the position of the magnets <NUM> of the turbine wheel <NUM> and the magnets <NUM> of the rotatable disc <NUM>, respectively. Thereby, the provided first and second measurement signals may be more reliable.

As seen in <FIG>, the pump shaft <NUM> extends through a shaft seal <NUM> arranged in the outer wall of the pump casing <NUM>. As mentioned above, the external part <NUM> of the pump shaft <NUM> has a coupling end for connection with a not shown motor shaft, and the rotatable disc <NUM> is mounted on the external part <NUM> of the pump shaft <NUM>. In the illustrated embodiment, the rotatable disc <NUM> is clamped on a ring of the shaft seal <NUM>. However, in the case of larger pumps, it may be preferred that the rotatable disc <NUM> is arranged higher on the pump shaft <NUM>, nearer to the coupling <NUM>. The rotatable disc <NUM> is easily accessible outside the casing <NUM> of the pump <NUM> and does not take up space inside the pump casing. The rotatable disc <NUM> is directly accessible and visible so that is may be controlled that it is correctly mounted and so that is may be easily serviced. It is furthermore an advantage that the magnets <NUM> of the rotatable disc <NUM> do not have to come into contact with the fluid pumped by the centrifugal pump <NUM>. Therefore, the choice of material for the magnets <NUM> is greater. For instance, neodymium-magnets may be used which are much stronger than standard permanent magnets. Neodymium-magnets should not be used in contact with drinking water.

In the embodiment illustrated in <FIG>, the rotatable disc <NUM> is composed by two disc halves <NUM>, <NUM> clamped together and thereby clamping the pump shaft <NUM> in a central hole <NUM> through the rotatable disc <NUM>. The disc halves <NUM>, <NUM> are clamped together by means of screws mounted in screw holes <NUM>. As indicated in <FIG>, the permanent magnets <NUM> of the rotatable disc <NUM> may be mounted in the disc in that they are inserted in the radially outer parts of centrally open holes <NUM>. However, the rotatable disc <NUM> may be constructed in any other suitable way. The material of the rotatable disc <NUM> is preferably metal, such as aluminium, but any suitable material may be used. In the illustrated embodiment, two permanent magnets <NUM> are arranged symmetrically at the periphery of the rotatable disc <NUM>. However, any other suitable number of permanent magnets <NUM> could be used, including one, as well as three or more. Furthermore, the permanent magnets <NUM> could be arranged at varying angular distance in order to be able to determine the rotation direction of the rotatable disc <NUM>.

As seen in <FIG>, the sensor housing <NUM> is elongated and extends through the opening <NUM> formed in the outer wall of the pump casing <NUM>. The sensor housing <NUM> includes a first part <NUM> arranged inside the pump casing <NUM> and a second part <NUM> arranged outside the pump casing. The first magnetic flux sensor <NUM> is arranged in the first part <NUM> of the sensor housing <NUM>, and the second magnetic flux sensor <NUM> is arranged in the second part <NUM> of the sensor housing <NUM>. The position of the first magnetic flux sensor <NUM> may be optimised in that it may be positioned very close to the position of the magnets <NUM> of the turbine wheel <NUM> and inside the pump casing, so that the magnetic field of the turbine wheel does not have to be detected through the pump casing <NUM>. A short distance between the first magnetic flux sensor <NUM> and the magnets <NUM> of the turbine wheel <NUM> will reduce possible disturbances of the signal. On the other hand, also the position of the second magnetic flux sensor <NUM> may be optimised in that it may be positioned outside the pump casing <NUM>, so that the magnetic field of the magnets <NUM> of the rotatable disc <NUM> does not have to be detected through the pump casing. Thereby, the provided first and second measurement signals may be even more reliable.

As illustrated in <FIG>, the first magnetic flux sensor <NUM> and the second magnetic flux sensor <NUM> are arranged in the sensor housing <NUM> with a mutual first distance d1 in a longitudinal direction L of the sensor housing <NUM>. The first magnetic flux sensor <NUM> is arranged at a, during rotation of the turbine wheel <NUM>, shortest second distance d2 from the at least one permanent magnet <NUM> of the turbine wheel <NUM>. The second magnetic flux sensor <NUM> is arranged at a, during rotation of the rotatable disc <NUM>, shortest third distance d3 from the at least one permanent magnet <NUM> of the rotatable disc <NUM>. The shortest third distance d3 is at least <NUM> times, preferably at least <NUM> times, and most preferred at least <NUM> times, the shortest second distance d2. The mutual first distance d1 is within ±<NUM> per cent, preferably within ±<NUM> per cent, and most preferred within ±<NUM> per cent of the shortest third distance d3.

Preferably, at least the second magnetic flux sensor <NUM> is of an omnidirectional type. Thereby, the exact position of the rotatable disc <NUM> in relation to the second magnetic flux sensor <NUM> may not be critical. This may be an advantage, for instance because the same sensor housing design may be used for centrifugal pumps of different size, whereby a preferred position of the rotatable disc <NUM> on the pump shaft <NUM> may vary due to various constructional considerations.

Preferably, the first magnetic flux sensor <NUM> has a direction of maximum sensitivity, and the first magnetic flux sensor <NUM> is arranged with its direction of maximum sensitivity extending in the longitudinal direction L of the sensor housing <NUM> and in the direction of the, during rotation of the turbine wheel <NUM>, closest position of the at least one permanent magnet <NUM> of the turbine wheel <NUM>. Thereby, the sensitivity of the first magnetic flux sensor <NUM> may be maximised. This may be advantageous in order to obtain a reliable first measurement signal without using special magnets providing a stronger magnetic field.

According to the present invention, the flow measuring device <NUM> includes a not shown processor adapted to calculate an uncorrected delivery flow on the basis of the first measurement signal generated by at least one magnetic flux sensor <NUM>, <NUM> as a result of the rotation of the turbine wheel <NUM>. The processor is adapted to calculate a corrected delivery flow by correcting the uncorrected delivery flow by means of a correction factor based on the second measurement signal generated by the at least one magnetic flux sensor <NUM>, <NUM> as a result of the rotation of the rotatable disc <NUM>.

Claim 1:
A centrifugal pump (<NUM>) including a pump shaft (<NUM>), a pump casing (<NUM>) enclosing at least one pump stage (<NUM>) with an impeller (<NUM>) mounted on an internal part of the pump shaft (<NUM>) and fixed to the pump shaft for rotation with the pump shaft, a flow measuring device (<NUM>) adapted to measure a delivery flow through the centrifugal pump (<NUM>) by means of a turbine wheel (<NUM>) arranged in the pump casing (<NUM>) rotationally about the pump shaft (<NUM>) and rotationally in relation to the pump shaft, the turbine wheel (<NUM>) being exposed to the delivery flow through the centrifugal pump, the turbine wheel (<NUM>) including at least one permanent magnet (<NUM>), the flow measuring device (<NUM>) including at least one magnetic flux sensor (<NUM>, <NUM>), the flow measuring device (<NUM>) being adapted to measure the delivery flow on the basis of at least a first measurement signal generated by the at least one magnetic flux sensor (<NUM>, <NUM>) as a result of the rotation of the turbine wheel (<NUM>), and the at least one magnetic flux sensor (<NUM>, <NUM>) being arranged in a sensor housing (<NUM>) mounted in an opening (<NUM>) formed in an outer wall of the pump casing (<NUM>), characterised in that a rotatable disc (<NUM>) is mounted on the pump shaft (<NUM>) and fixed to the pump shaft for rotation with the pump shaft, in that the rotatable disc (<NUM>) includes at least one permanent magnet (<NUM>), and in that the flow measuring device (<NUM>) is adapted to include in the measurement of the delivery flow a second measurement signal generated by the at least one magnetic flux sensor (<NUM>, <NUM>) as a result of the rotation of the rotatable disc (<NUM>).