Abstract
A sensor assembly (2) is configured to perform fault detection in a pump assembly that includes an electric motor (70) and a fluid pump (30). The sensor assembly (2) includes a housing (4) configured to be mechanically attached to the pump (30) and configured to be attached into a bore provided in the pump (30). One or more vibration sensing element(s) (16) is/are arranged in the housing (4). The sensor assembly (2) includes a calculation unit (84) configured to receive sensor signals (V.sub.1, V.sub.2, V.sub.3) from the vibration sensing element(s) (16) and perform calculations and thereby detect motor bearing faults and cavitation.
Claims
1. A sensor assembly configured to perform fault detection in a pump assembly comprising an electric motor and a fluid pump, the sensor assembly comprising: a housing configured to be attached into a bore provided in the pump; one or more vibration sensing elements arranged in the housing and a calculation unit arranged outside the housing through a wired or wireless connection, wherein the calculation unit is configured to receive sensor signals from the vibration sensing elements, and the calculation unit is configured to perform calculations and thereby detect motor bearing faults and cavitation on the basis of the sensor signals provided by the one or more vibration sensing elements.
2. A sensor assembly according to claim 1, further comprising a thermosensitive sensor arranged in the housing wherein the thermosensitive sensor is arranged to detect the temperature of fluid being pumped by the pump.
3. A sensor assembly according to claim 1, wherein the calculation unit comprises a processing unit configured to receive the sensor signals from the sensing elements, wherein the calculation unit is further configured to process the sensor signals and thereby carry out bearing fault detections by using a frequency analysis, wherein the calculation unit is further configured to carry out cavitation detection by using spectral analysis and determine if a spectral level increases in a predefined frequency band.
4. A sensor assembly according to claim 3, wherein the predefined frequency band is within the range 10-20 kHz.
5. A sensor assembly according to claim 1, further comprising a separate box and an electric cable wherein: the calculation unit is arranged in the separate box; the separate box is arranged outside the pump; and the calculation unit is electrically connected to the vibration sensing element through the electric cable.
6. A sensor assembly according to claim 1, further comprising a display unit configured to display one or more of the parameters calculated by the calculation unit.
7. A sensor assembly according to claim 1, wherein the calculations made by the calculation unit in order to detect both motor bearing faults and cavitation are carried out outside the housing.
8. A method for detection of faults in a pump assembly comprising an electric motor and a fluid pump, wherein the method comprises the steps of: providing sensor signals from at least one vibration sensing element attached into a bore provided in the fluid pump; applying a calculation unit receiving the sensor signals from the vibration sensing element; processing the sensor signals; using a frequency analysis to detect motor bearing faults.
9. A method according to claim 8, wherein a housing is configured to be mechanically attached to a pump head provided with a threaded bore configured to receive the housing, wherein the method further comprises the step of arranging the housing in the bore arranged in a pump head.
10. A method according to claim 9, wherein the method further comprises the step of applying a bearing fault detection method based on a predefined sound analysis carried out to categorize sound signals into a plurality of classes/groups, wherein corresponding sensor signals are recorded, wherein the sound signals are evaluated by using a predefined benchmarking method benchmarking each sound signal with a score or category, thereby categorizing the sound signals and the corresponding sensor signals into the classes/groups.
11. A method according to claim 10, wherein the method comprises the step of applying a data table comprising pre-recorded signals or signal patterns associated with known pump error types, wherein the method moreover comprises the step of comparing sensor signals with pre-recorded signals or signal patterns in order to associate the sensor signals with a known sensor error type.
12. A method according to claim 11 wherein a feature matrix is generated on the basis of the predefined sound analysis, wherein the feature matrix comprises a plurality of rows or columns corresponding to a number of feature vectors, wherein each feature vector is generated on the basis of a detected sensor signal, wherein the detected sensor signal is converted to a feature vector, wherein the measured sensor signal detected by the at least one vibration sensing element is converted to a measured feature vector and compared to the feature vectors of the feature matrix by using a distance measurement, wherein the distance measurement determines the distances between the point defined by the measured feature vector and the points defined by the feature vectors of the feature matrix, wherein a predefined number of points defined by the feature vector of the feature matrix having the smallest distance to the point defined by the measured feature vector are found, and wherein the score(s) or categories or a calculated average of these is adapted by the feature vector converted on the basis of the measured sensor signal detected by the at least one vibration sensing element.
13. A method according to claim 12, wherein the feature vector comprises a number of components each representing a scalar derived on the basis of a sensor signal or a signal processed on the basis of the sensor signal.
14. A method according to claim 10, wherein the method further comprises the step of establishing and training an artificial neural network or a fuzzy network to carry out bearing fault detection, wherein the artificial neural network or the fuzzy network comprises information established on the basis of the predefined sound analysis.
15. A method according to claim 10, wherein the method comprises the step of establishing an envelope on the basis of a Cepstral domain signal, wherein a motor bearing fault is defined to be present when the amplitude of the envelope exceeds a predefined level.
16. A pump comprising: an electric motor; a fluid pump; and a sensor assembly comprising: a housing configured to be attached into a threaded bore provided in a pump head; one or more vibration sensing elements arranged in the housing; and a calculation unit arranged outside the housing through a wired or wireless connection, wherein the calculation unit is configured to receive sensor signals from the vibration sensing elements and the calculation unit is configured to perform calculations and thereby detect motor bearing faults and cavitation on the basis of the sensor signals provided by the one or more vibration sensing elements, wherein the housing of the sensor assembly is mounted in the threaded bore provided in the pump head, wherein said bore is placed in a zone of the pump, in which zone the amplitude of the signals of the vibrations generated by faulty motor bearings and the amplitude of the signals generated in case of cavitation in the suction side of the pump have a magnitude sufficiently large to be detected by the vibration sensing elements.
17. A pump according to claim 16, wherein the sensor assembly further comprises a thermosensitive sensor arranged in the housing, wherein the thermosensitive sensor is arranged to detect the temperature of fluid being pumped by the pump.
18. A pump according to claim 16, wherein the calculation unit comprises a processing unit configured to receive the sensor signals from the sensing elements, wherein the calculation unit is further configured to process the sensor signals and thereby carry out bearing fault detections by using a frequency analysis, wherein the calculation unit is further configured to carry out cavitation detection by using spectral analysis and determine if a spectral level increases in a predefined frequency band.
19. A pump according to claim 18, wherein the predefined frequency band is within the range 10-20 kHz.
20. A pump according to claim 1, wherein the sensor assembly further comprises a separate box and an electric cable wherein: the calculation unit is arranged in the separate box; the separate box is arranged outside the pump; and the calculation unit is electrically connected to the vibration sensing element through the electric cable.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0131] In the drawings:
[0132] FIG. 1A is a schematic top view of a housing of a sensor assembly according to the invention;
[0133] FIG. 1B is a schematic, cross-sectional side view of the housing shown in FIG. 1A;
[0134] FIG. 1C is a schematic side view of the housing shown in FIG. 1A and in FIG. 1B;
[0135] FIG. 2A is a schematic, cross-sectional side view of one embodiment of a housing of a sensor assembly according to the invention;
[0136] FIG. 2B is a schematic, cross-sectional side view of another embodiment of a housing of a sensor assembly according to the invention;
[0137] FIG. 2C is a schematic, cross-sectional side view of a further embodiment of a housing of a sensor assembly according to the invention;
[0138] FIG. 2D is a schematic perspective view of the sensing element shown in FIG. 2C;
[0139] FIG. 3 is a schematic, cross-sectional side view of a multistage pump provided with a sensor assembly according to the invention;
[0140] FIG. 4A is a schematic, perspective, exploded view of the elements of a housing of a sensor assem bly according to the invention;
[0141] FIG. 4B is a schematic, perspective, cross-sectional view of the elements of a housing of a sensor assembly according to the invention;
[0142] FIG. 5A is a spectral diagram based on a spectral analysis of data from an accelerometer attached to a motor of a pump, wherein the detected level is plotted as function of frequency;
[0143] FIG. 5B is a spectral diagram based on a spectral analysis of data from a sensor assembly according to the invention provided with an accelerometer used as a vibration sensing element;
[0144] FIG. 5C is a spectral diagram based on a spectral analysis of data from a sensor assembly according to the invention provided with a microphone used as a vibration sensing element;
[0145] FIG. 6A is a Cepstral diagram based on a Cepstral analysis carried out on the basis of data from an accelerometer attached to a motor of a pump, wherein the detected level is plotted as function of quefrency;
[0146] FIG. 6B is a Cepstral diagram based on a Cepstral analysis carried out on the basis of data from a sensor assembly according to the invention provided with an accelerometer used as a vibration sensing element, wherein the detected level is plotted as function of quefrency,
[0147] FIG. 6C is a Cepstral diagram based on a Cepstral analysis carried out on the basis of data from a sensor assembly according to the invention provided with a microphone used as a vibration sensing element, wherein the detected level is plotted as function of quefrency;
[0148] FIG. 7A is a spectral diagram based on a spectral analysis of data from an accelerometer attached to a motor of a pump, during cavitation and under normal operation, wherein the detected level is plotted as function of frequency;
[0149] FIG. 7B is a spectral diagram based on a spectral analysis of data from a sensor assembly according to the invention provided with an accelerometer used as a vibration sensing element, during cavitation and under normal operation, wherein the detected level is plotted as function of frequency;
[0150] FIG. 8A is a schematic, side view of the elements of a sensor assembly according to the invention, wherein the housing is arranged in a bore of a multistage pump;
[0151] FIG. 8B is a schematic, side view of the elements of another sensor assembly according to the invention, wherein the housing is arranged in a bore of a multistage pump and wherein the sensor assembly is configured to communicate with a cloud-based server;
[0152] FIG. 8C is a schematic, side view of the elements of a further sensor assembly according to the invention, wherein the housing is arranged in a bore of a multistage pump and wherein the sensor assembly is configured to communicate with a cloud-based server;
[0153] FIG. 8D is a schematic, side view of the elements of a sensor assembly according to the invention, wherein the housing is arranged in a bore of a multistage pump and wherein the sensor assembly comprises a display attached to the housing;
[0154] FIG. 9A is a schematic, perspective, cross-sectional view of the elements of a housing of a sensor assembly according to the invention;
[0155] FIG. 9B is a schematic, perspective, cross-sectional view of the elements of a housing of another sensor assembly according to the invention;
[0156] FIG. 10 is a schematic, cross-sectional side view of a multistage pump provided with a sensor assembly according to the invention;
[0157] FIG. 11A is a schematic view of a sound analysis carried out to categorize sound signals into a plurality of classes/groups, wherein corresponding sensor signals are recorded, and the sound signals are evaluated by using a predefined benchmarking method;
[0158] FIG. 11B is a schematic view of a method that comprises the step of applying a data table comprising pre-recorded signals or signal patterns associated with known pump error types and comparing sensor signals with pre-recorded signals or signal patterns in order to associate the sensor signals with a known sensor error type;
[0159] FIG. 12A is a schematic view of the process of associating a detected sensor signal with a known sensor error type by using a method according to the invention and FIG. 12B is a close-up view of the process illustrated in FIG. 12A.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0160] Referring to the drawings, for the purpose of illustrating preferred embodiments of the present invention, a housing 4 of a sensor assembly 2 of the present invention is illustrated in FIG. 1A. FIG. 1A illustrates a schematic top view of a housing 4 of a sensor assembly 2 according to the invention. The housing 4 comprises a hexagonal nut-structure that is integrated in the proximal end of the housing 4. Accordingly, the nut structure can be applied as an engagement structure during mounting of the housing 4 into a threaded bore in a pump. A section line A is indicated.
[0161] FIG. 1B illustrates a schematic, cross-sectional side view of the housing 4 shown in FIG. 1A. It can be seen that the housing 4 comprises a bottom wall 8 having a thickness that is smaller than the thickness of the remaining wall portions of the housing 4. The bottom wall 8 is arranged in the distal end 46 of the housing 4 and is formed as a plate-shaped end portion. A threaded portion 6 is provided at the outer structure of the part of the housing 4 that is configured to be inserted into a threaded bore. The threads of the treaded portion 6 are configured to engage with inner threads of a corresponding bore (see FIG. 3 and FIG. 10). The hexagonal nut structure protrudes from the proximal end 48 of the housing 4. The housing 4 is provided with a hollow inner portion 26 configured to receive a number of sensor members. The hollow inner portion 26 is provided with an inner threaded portion 24 that has been brought into engagement with the treads of a threaded connection structure. This connection structure may (as shown in FIG. 4B) be provided with electrical socket structures for receiving an electrical plug (e.g. provided in the distal end of an electric cable).
[0162] FIG. 1C illustrates a schematic side view of the housing 4 shown in FIG. 1A and in FIG. 1B. It can be seen that the hexagonal nut structure protrudes from the proximal end 48 of the housing 4, and that the hexagonal nut-structure has a larger width that the more distal portion of the housing 4. The bottom wall 8 is arranged as an end portion arranged next to a conical portion that is arranged next to a cylindrical portion provided with a threaded portion 6.
[0163] FIG. 2A illustrates a schematic, cross-sectional side view of one embodiment of a housing 4 of a sensor assembly 2 according to the invention. The housing 4 corresponds to the one shown in FIG. 1B. Accordingly, some of the structures of the housing 4 have already been defined with reference to FIG. 1B. Several electric elements are arranged in the hollow inner portion 26 of the housing 4. A PCB 12 is arranged in the hollow inner portion 26. The PCB 12 is centrally arranged. However, it may be arranged differently in order to meet specific requirements. A thermosensitive sensor 14 and vibration sensing element 16 are electrically connected to the PCB 12. An ultrasonic sensor 10 is arranged in the distal portion of the hollow inner portion 26. The ultrasonic sensor 10 is arranged close to the distal end portion of the housing 4 close to the bottom wall 8. Accordingly, the ultrasonic sensor 10 can be used as a dry run sensor configured to detect if there is air or a liquid in the space into which the distal end 48 of the housing 4 is inserted. The ultrasonic sensor 10 is electrically connected to the PCB 12 by means of two legs 18, 18. Although not shown, it may be an advantage that the housing 4 is filled with resin in order to enable vibration signals to be detected by the vibration sensing element 16 in the most efficient manner.
[0164] FIG. 2B illustrates a schematic, cross-sectional side view of an embodiment of a housing 4 of a sensor assembly 2 according to the invention corresponding to the one shown in FIG. 2A. Accordingly, some of the structures of the housing 4 have already been defined and explained with reference to FIG. 2A. A PCB 12 is centrally arranged in the hollow inner portion 26, however, it may be arranged differently (e.g. close to one of the side walls) if desired. A vibration sensing element 16 is electrically connected to the PCB 12. A sensing element 20 comprising a thermosensitive sensor and an ultrasonic sensor is arranged in the distal portion of the hollow inner portion 26. The sensing element 20 is a combined sensing element 20 arranged in the same sensor housing member. It can be seen that the sensing element 20 is brought into contact with the bottom wall 8 in the distal end 46 of the housing 4. Accordingly, the thermal resistance can be minimized in order to optimize the temperature measurement conditions by using the thermosensitive sensor. Similarly, this position enables optimal conditions for providing dry run detection by using the ultrasonic sensor of the sensing element 20. The bottom wall 8 may preferably be made in a material having a high thermal conductance. In a preferred embodiment according to the invention, the housing 4 including the bottom wall 8 is made in steel, e.g. stainless steel. The sensing element 20 is arranged in a cavity filled with an ultrasound gel 22. Hereby, it is possible to achieve a good acoustical connection between the ultrasonic sensor of the sensing element 20 and the wall members being in contact with the fluid, of which the temperatures are being measured.
[0165] FIG. 2C illustrates a schematic, cross-sectional side view of an embodiment of a housing 4 of a sensor assembly 2 according to the invention corresponding to the one shown in FIG. 2A and FIG. 2B. The components inside the hollow inner portion 26 of the housing 4, however, are slightly different. A PCB 12 extends along the longitudinal axis of the housing 4. A vibration sensing element 16 is mechanically and electrically connected to the PCB 12.
[0166] A sensing element 20 comprising an ultrasonic sensor 20 is arranged in the distal portion of the hollow inner portion 26. The sensing element 20 is brought into contact with the bottom wall 8 in the distal end 46 of the housing 4. Accordingly, the position enables optimal conditions for providing dry run detection by using the ultrasonic sensor of the sensing element 20. A thermosensitive sensor 14 is provided in a bore extending parallel to the longitudinal axis of the housing 4. The thermosensitive sensor 14 is electrically connected to the PCB 12 by means of legs 18. A connection ring 13 is sandwiched between a cork plate 100 and an inner support structure of the housing 4. The connection ring 13 is electrically connected to the PCB 12 and to the sensing element 20. The bottom portion of that part of the hollow inner portion 26 of the housing 4 that is arranged above the cork plate 100 is filled with a first filler material (e.g. a resin). Similarly, the top portion of that part of the hollow inner portion 26 of the housing 4 that is arranged above the cork plate 100 is filled with a second filler material (e.g. a resin) ensuring that mechanical vibrations can be transferred from the pump through the housing 4 to the vibration sensing element 16 in an effective manner. Even though not shown, the housing 4 may comprise two sections to be assembled. Hereby, it is possible to ease the mounting of the sensing element 20.
[0167] The ultrasonic sensor of the sensing element 20 is configured to be used for dry run detection, whereas the thermosensitive sensor of the sensing element 20 is adapted to measure the temperature of a fluid being in contact with the outside surface of the bottom wall 8. The sensing element 20 is electrically connected to the PCB 12 by means of two legs 18, 18. The sensing element 20 is arranged in an air-filled cavity.
[0168] When FIG. 2A is compared with FIG. 2B, it can be seen that the sensor elements take up less space in FIG. 2B, because the sensing element 20 is a combined sensing element 20 arranged in the same sensor housing member.
[0169] FIG. 2D illustrates a perspective top view of the sensing element 20 shown in FIG. 2C. It can be seen that the connection ring 13 is provided with two opposing electrical connection portions 15, 15 configured to establish electrical connection between the legs 18, 18 connected to the sensing element 20 and to the two legs 17, 17 configured to be electrically connected to the PCB (shown in FIG. 2C).
[0170] FIG. 3 illustrates a schematic, cross-sectional side view of a multistage pump 30 provided with a sensor assembly 2 according to the invention. The pump 30 is a vertically arranged multistage liquid pump 30 comprising three stages arranged in a sleeve 34 that may be made in stainless steel or another suitable material. Each stage comprises an impeller attached to a centrally arranged shaft 50 extending along the longitudinal axis of the sleeve 34. The shaft 50 is rotatably arranged by means of a number of bearings allowing the shaft 50 to be driven by an electric motor (not shown) arranged above the pump head 36 and the motor stool 38 of the pump 30. The shaft 50 may be mechanically connected to the motor by means of a coupling unit (not shown). The pump head 36 is arranged on the top of the sleeve 34, whereas the motor stool 38 is arranged on the top of the pump head 36.
[0171] The pump 30 comprises a pump housing 32 having a flanged inlet port (arranged to the left) and a flanged outlet port (arranged to the right).
[0172] The sensor assembly 2 comprises a display unit 28 being electrically connected to the housing of the sensor assembly 2 by means of an electric cable 27. The electric cable 27 is connected to the housing by means of an electric plug provided in the distal end of the cable 27.
[0173] The display unit 28 comprises a display 29 and a calculation unit 84 configured to carry out calculations on the basis of sensor data received from the sensor elements arranged in the housing of the sensor assembly 2. Calculations may include any processing task. Such processing task may include comparison with stored data or comparison with data that the calculation unit 84 has access to through one or more externally arranged devices (including a server accessible via the internet). The calculation unit 84 may comprise a battery providing electrical power to the calculation unit 84 and to the housing of the sensor assembly 2 via the cable 27. Although not shown, the display unit 28 may be electrically powered through an additional electrical cable. Electrical power may be supplied from the electrical motor coupled to the shaft 50.
[0174] The display unit 28 may comprise a separate user interface (e.g. a keypad). However, in a preferred embodiment according to the invention, the display unit 28 may comprise a touch screen that can display a number of parameters and be used as user interface. The display unit 28 may be a smartphone, a tablet, a PDA or another suitable device.
[0175] The housing of the sensor assembly 2 is inserted into a threaded bore provided in the pump head 36. The distal portion of the housing of the sensor assembly 2 protrudes into an inner space 40 of the pump head 36. Accordingly, there is access to the inner space 40 that will be filled with the liquid being pumped by the pump 30 under normal operation. Since the housing of the sensor assembly 2 is screwed into a threaded bore provided in a mechanical structure of the pump 30, vibration signals originating from the motor bearing and from cavitation can reach the sensing elements inside the housing of the sensor assembly 2 as the vibration signals travel along the mechanical structures of the pump housing 32, the sleeve 34, the pump head 36 and the motor stool 38.
[0176] It is possible to provide a processing unit inside the housing. Such processing unit may be capable of carrying out any desirable processing signals received by means of sensing elements provided inside the housing of the sensor assembly 2. Processing may include filtering or carrying out any analysis.
[0177] FIG. 4A illustrates a schematic, perspective, exploded view of the elements of a housing 4 of a sensor assembly 2 according to the invention. The housing 4 comprises an inner hollow portion and an outer threaded portion 6 configured to be screwed into a threaded bore. The proximal end of the housing 4 is provided with an inner thread configured to receive an outer threaded portion 24 of a socket structure comprising an annular portion 42 and an additional threaded portion 44. A PCB 12 is arranged between the socket structure and the housing 4. The PCB 12 comprises an ultrasonic sensor 10 protruding from the end portion of the PCB 12. The ultrasonic sensor 10 is electrically connected to the PCB by means of two legs. The PCB 12 comprises a thermosensitive sensor 14 and a vibration sensing element 16 attached to the PCB 12. Although not shown, the PCB 12 may be provided with connection structures configured to be electrically connected to corresponding connection structures inside the socket structure.
[0178] FIG. 4B illustrates a schematic, perspective, cross-sectional view of the elements of the housing 4 of a sensor assembly 2 shown in FIG. 4A, in an assembled configuration. It can be seen that the ultrasonic sensor 10 abuts the bottom wall 8 and is arranged in the distal end of the housing 4. The PCB 12 extends along the longitudinal axis of the housing 4. The outer threaded portion 24 of the socket structure is screwed into the threaded portion of the hollow inner portion of the housing 4. An O-ring 56 is provided in an annular groove provided next to the outer threaded portion 6 of the housing 4. It can be seen that the annular portion 42 of the socket structure fits an inner annular groove provided at the inner side of the proximal end of the housing 4.
[0179] FIG. 5A illustrates a spectral diagram based on spectral analysis of data from an accelerometer attached to a motor of a pump, wherein the detected level 52 is plotted as function of frequency 54. When a motor bearing has a point damage, the vibration signals and sound originating therefrom will have a periodic structure. Accordingly, the corresponding spectral diagram will have line spectra 60.
[0180] FIG. 5B illustrates a spectral diagram based on spectral analysis of data from a sensor assembly according to the invention provided with an accelerometer used as a vibration sensing element. The spectral diagram which is displaying level 52 as function of frequency 54 shows a line spectra 60 corresponding to the one shown in FIG. 5A. The spectral diagram furthermore comprises a noise component 62.
[0181] FIG. 5C shows a spectral diagram based on spectral analysis of data from a sensor assembly according to the invention provided with a microphone used as a vibration sensing element. The spectral diagram depicts the measured level 52 as function of frequency 54 and illustrates a line spectra 60 corresponding to the one shown in FIG. 5A and FIG. 5B. The spectral diagram also comprises a noise component 62.
[0182] FIG. 6A illustrates a Cepstral diagram based on Cepstral analysis carried out on the basis of data from an accelerometer attached to a motor of a pump, wherein the detected level 52 is plotted as function of quefrency 58. It can be seen that the Cepstral domain signal 64 contains a plurality of spikes that indicate the presence of a motor bearing fault.
[0183] FIG. 6B illustrates a Cepstral diagram based on Cepstral analysis carried out on the basis of data from a sensor assembly according to the invention provided with an accelerometer used as a vibration sensing element, wherein the detected level 52 is plotted as function of quefrency 58. The Cepstral domain signal 64 contains a plurality of spikes that indicate the presence of a motor bearing fault. An envelope 98 is indicated by a dotted line.
[0184] In one embodiment of a method according to the invention, a definition of a motor bearing fault can be made on the basis of the Cepstral diagram. A motor bearing fault may be defined to be present when a portion of the envelope 98 exceeds a predefined threshold level T. FIG. 6B will reveal that the motor bearing is damaged, since the amplitude of the envelope 98 exceeds the predefined threshold level T.
[0185] FIG. 6C illustrates a Cepstral diagram based on Cepstral analysis carried out on the basis of data from a sensor assembly according to the invention provided with a microphone used as a vibration sensing element, wherein the detected level 52 is plotted as function of quefrency 58. It can be seen that the Cepstral domain signal 64 contains a plurality of spikes indicating the presence of a motor bearing fault. An envelope 98 is indicated by a dotted line.
[0186] When using the method referred to with reference to FIG. 6B, it can be concluded that a motor bearing fault is present because the envelope 98 exceeds a predefined threshold level T.
[0187] When comparing FIG. 6B and FIG. 6C, it can be seen that the spikes occur at the same quefrencies 58. Therefore, it is reasonable to conclude that vibration measurements maybe carried out by either an accelerometer or a microphone.
[0188] FIG. 7A illustrates a spectral diagram based on spectral analysis of data from an accelerometer attached to a motor of a pump, during cavitation and under normal operation, wherein the detected level 52 is plotted as function of frequency 54. The spectral diagram contains a cavitation signal 66 based on spectral analysis of data during cavitation. The spectral diagram also contains a normal operation signal 68 based on spectral analysis of data during normal operation.
[0189] It can be seen that the spectral diagram reveals that there is a relatively high level increase in the frequency band II during cavitation. There seems to be a level increase in the lower frequency band I, however, the relative increase is larger in the higher frequency band II. Therefore, in one embodiment of the method according to the invention, cavitation is defined to be present when the spectral level 52 increases in a predefined frequency band II. The predefined frequency band II may lie within the range 10-20 kHz. In one embodiment of the method according to the invention, cavitation is defined to be present when the spectral level 52 increases in the frequency 15-20 kHz.
[0190] FIG. 7B illustrates a spectral diagram based on spectral analysis of data from a sensor assembly according to the invention provided with an accelerometer used as a vibration sensing element, during cavitation and under normal operation, wherein the detected level 52 is plotted as function of frequency 54.
[0191] The spectral diagram contains a cavitation signal 66 based on spectral analysis of data during cavitation and a normal operation signal 68 based on spectral analysis of data during normal operation.
[0192] The spectral diagram shows that there is a relatively high level increase in the frequency band II during cavitation. Even though there is a level increase in the lower frequency band I, it can be seen that the relative increase is larger in the higher frequency band II. Accordingly, in a preferred embodiment of the method according to the invention, cavitation is defined to be present when the spectral level 52 increases in a predefined frequencyband II e.g. within the range 10-20 kHz. Thus, in one embodiment of the method according to the invention, cavitation is defined to be present when the spectral level 52 increases in the frequency 15-20 kHz.
[0193] FIG. 8A illustrates a schematic, side view of the elements of a sensor assembly 2 according to the invention, wherein the sensor housing 4 is arranged in a bore of a vertically arranged multistage pump 30 provided with an electric motor 70. The sensor assembly 2 comprises a sensor housing 4 provided with a communication unit configured to communicate wirelessly with an external receiving unit 72 provided with a display 29 and a calculation unit 84. The receiving unit 72 may, however, also be configured to transmit wireless signals, whereas the communication unit in the sensor housing 4 of the sensor assembly 2 may be adapted to receive signals from the external receiving unit 72. Such signals may be a stop signal in case of a critical fault (e.g. a cavitation or a critical motor bearing fault). The receiving unit 72 may be a tablet, a smartphone or another suitable external device.
[0194] The communication unit 84 may comprise a processing unit and a storage for storing one or more software programs to carry out any desirable processing. The display unit 29 may be of any suitable type, including a touch screen that may be used to display one or more parameters and as a user interface. The processing unit may preferably be capable of processing data received from the sensing elements in the housing 4 in real time.
[0195] FIG. 8B illustrates a schematic, side view of the elements of another sensor assembly 2 according to the invention, wherein the housing 4 is arranged in a bore of a multistage pump 30 and wherein the sensor assembly 2 is configured to communicate with a cloud-based server indicated as a calculation unit 84 accessible via the Internet 74.
[0196] The housing 4 is electrically connected to an intermediate box 78 attached to a control box fixed to the motor housing of the motor 70 by means of an electrical cable 27. Accordingly, the sensors in the housing 4 can be powered through the cable 27, and sensor signals received by the sensors can be transferred to the intermediate box 78. It is possible to have a processing unit inside the intermediate box 78 so that the vital calculation can be carried out without any external device. If this is the case, communication with the receiving unit 72 (e.g. a smartphone) and the calculation unit 84 via the Internet 74 may be carried out in order to exchange data or carry out comparisons.
[0197] A communication unit configured to wirelessly communicate via the Internet 74 (e.g. to a calculation unit 84 being part of a server or to a receiving unit 72 having a display and a calculation unit 84) is arranged in the intermediate box 78.
[0198] Accordingly, calculations and processing may be carried out in either the calculation unit 84 accessible through the Internet 74 or in the calculation unit 84 arranged to wirelessly communicate with the intermediate box 78.
[0199] The receiving unit 72 and the internet-based calculation unit 84 are capable of communicating with each other.
[0200] FIG. 8C illustrates a schematic, side view of the elements of a further sensor assembly 2 according to the invention, wherein the housing 4 is arranged in a bore of a multistage pump 30 and wherein the sensor assembly 2 is configured to communicate with a cloud-based server 84 constituting a calculation unit 84.
[0201] The housing 4 is provided with a number of sensors and a communication unit configured to wirelessly communicate with the cloud-based server 84 constituting the calculation unit 84 and with a calculation unit 84 of a receiving unit 72 (e.g. a smartphone, a tablet or a PDA). The receiving unit 72 comprises a display 29 and a calculation unit 84. The housing 4 may comprise a battery for providing electric power to the sensor elements and the communication unit. Alternatively, electric power may be supplied to the housing 4 via an electric cable (not shown) or via an energy harvesting unit (e.g. a thermoelectric generator).
[0202] The method according to the invention may be carried out by using a sensor assembly 2 like the one shown in FIG. 8C. A Cepstral analysis may be carried out in the calculation unit 84 accessible via the Internet 74 or in the calculation unit of the receiving unit 72. It is possible to carry out calculations simultaneously in several locations (e.g. in the calculation unit 84 accessible via the Internet 74 and in the calculation unit of the receiving unit 72). It is possible to exchange data between the calculation unit 84 accessible via the Internet 74 and the receiving unit 72 and to store data in a server accessible via the Internet 74 or in the receiving unit 72. Data may be distributed to other external devices from either the calculation unit 84 accessible via the Internet 74 or the receiving unit 72. It is possible to update software stored on the calculation unit 84 accessible via the Internet 74 or the receiving unit 72 from a centrally arranged server. Hereby, it is possible to ensure that all calculation units 84 are provided with updated software.
[0203] FIG. 8D illustrates a schematic, side view of the elements of a sensor assembly 2 according to the invention, wherein the housing 4 is arranged in a bore of a multistage pump 30, and wherein the sensor assembly 2 comprises a display device 76 attached to the housing 4. The user may apply the display device 76 to read parameters (e.g. bearing faults, cavitation, unbalances, dry run, temperature and rotational speed) displayed thereon. The display device 76 may be applied as a user interface and as a calculation unit. Accordingly, all required calculations may be carried out by using the display device 76.
[0204] The display device 76 and the housing 4 may be powered by the motor 70 via an electric cable (not shown) or by a battery arranged in the display device 76.
[0205] FIG. 9A illustrates a schematic, perspective, cross-sectional view of the elements of a housing 4 of a sensor assembly 2 corresponding to the one shown in FIG. 4B. An ultrasonic sensor 10 is brought into contact with the bottom wall 8 arranged in the distal end of the housing 4. A thermosensitive sensor 14 and vibration sensing element 14 are electrically connected to the PCB 12 extending along the longitudinal axis of the housing 4. The ultrasonic sensor 10 is electrically connected to the PCB 12 by means of two legs 18, 18. An O-ring 56 is arranged next to an outer threaded portion 6 of the housing 4 for sealing against the bore into which the housing has to be inserted. The proximal end of the housing 4 is provided with an inner thread that has received the outer threaded portion 24 of a socket structure comprising an annular portion 42 and an additional threaded portion 44. Three parallel connection structures extend through the socket structure. Even though it is not shown in FIG. 9A, additional connection elements may electrically connect the PCB 12 and the connection structures extending through the socket structure.
[0206] FIG. 9B illustrates a schematic, perspective, cross-sectional view of the elements of a housing 4 of another sensor assembly 2 basically corresponding to the one shown in FIG. 2B. A PCB 12 is arranged in the hollow inner portion of the housing 4. A vibration sensing element 16 is electrically connected and mechanically attached to the PCB 12. A sensing element 20 comprising a thermosensitive sensor and an ultrasonic sensor is arranged in the distal portion of the hollow inner portion of the housing 4 which is filled with an ultrasound gel 82 in order to achieve a good acoustical connection between the ultrasonic sensor of the sensing element 20 and the wall members being in contact with the fluid, of which the temperatures is being measured.
[0207] The sensing element 20 is brought into contact with the bottom wall 8 in the distal end 46 of the housing 4 in order to minimize the thermal resistance for achieving the most valid temperature measurement conditions by using the thermosensitive sensor and for achieving optimal conditions for providing dry run detection by using the ultrasonic sensor of the sensing element 20.
[0208] The sensing element 20 is electrically connected to the PCB 12 by two legs 18, 18. The housing 4 and the socket structure attached to its proximal end portion have the same shape as shown in FIG. 9A.
[0209] FIG. 10 illustrates a schematic, cross-sectional side view of a multistage pump 30 according to the invention provided. The pump 30 is provided with a sensor assembly 2 according to the invention. The pump 30 corresponds to the vertically arranged multistage liquid pump 30 shown in FIG. 3. The pump 30 has three stages each comprising an impeller attached to a centrally arranged shaft 50 extending along the longitudinal axis of the sleeve 34, into which the stages are arranged. The shaft 50 is rotatably arranged to be driven by an electric motor (not shown) arranged above the pump head 36 and the motor stool 38 of the pump 30. The pump 30 comprises a pump housing 32 having a flanged inlet port (arranged to the left) and a flanged outlet port (arranged to the right).
[0210] The sensor assembly 2 comprises a display unit 28 electrically connected to the housing of the sensor assembly 2 via an electric cable 27. The display unit 28 comprises a display 29 and a calculation unit 84 for carrying out calculations on the basis of sensor data from the sensor elements arranged in the housing of the sensor assembly 2.
[0211] The housing of the sensor assembly 2 is mounted in a threaded bore provided in the pump head 36. Vibration signals V.sub.1 originating from the motor bearing travel along a vibration travel path 86 extending along the motor stool 38 and the pump head 36 and are eventually received by a vibration sensing element in the housing of the sensor assembly 2. Likewise, vibration signals V.sub.2 originating from cavitation travel along a vibration travel path 88 extending along the sleeve 34 and are eventually received by a vibration sensing element in the housing of the sensor assembly 2. The vibration signals V.sub.2 originating from cavitation also travel along another vibration travel path 90 going through the mechanical structures of the stages and the fluid being pumped by the pump 30.
[0212] In order to be able to detect vibration signals V.sub.1, V.sub.2 having sufficiently large amplitude, the housing of the sensor assembly 2 may be mechanically attached to the pump 30 within a zone Z defined by an upper line L.sub.2 and a lower line L.sub.1. It can be seen that the housing of the sensor assembly 2 is mounted in a threaded bore provided in the pump head 36 inside the zone Z. By mounting the housing of the sensor assembly 2 in a threaded bore, it is possible to fasten the housing firmly to the pump 30. Accordingly, the risk of experiencing a self-loosening housing is minimized.
[0213] FIG. 11A illustrates a schematic view of a sound analysis carried out to categorize sound signals S.sub.1, S.sub.2, S.sub.3 into a plurality of classes/groups G.sub.1, G.sub.2, G.sub.3, G.sub.4, wherein corresponding sensor signals are recorded, and the sound signals are evaluated by using a predefined benchmarking method.
[0214] In order to categorize sound signals S.sub.1, S.sub.2, S.sub.3 into a plurality of predefined classes/groups G.sub.1, G.sub.2, G.sub.3, G.sub.4 trained service staff 92 having experience with motor bearing faults are presented for the sound signals S.sub.1, S.sub.2, S.sub.3. These trained staff put every sound signals S.sub.1, S.sub.2, S.sub.3 into one of the predefined classes/groups G.sub.1, G.sub.2, G.sub.3, G.sub.4 on the basis of their experience. The classes/groups G.sub.1, G.sub.2, G.sub.3, G.sub.4 may be:
[0215] G.sub.1: the bearing is not damaged;
[0216] G.sub.2: the bearing is slightly damaged; but can be used for some time;
[0217] G.sub.3: the bearing is moderately damaged and should be replaced;
[0218] G.sub.4: the bearing is completely damaged and must immediately be replaced.
[0219] Instead of using trained service staff 92 to categorize the sound signals S.sub.1, S.sub.2, S.sub.3 into one of the predefined classes/groups G.sub.1, G.sub.2, G.sub.3, G.sub.4, it is possible to apply an algorithm. The algorithm may be defined by theoretic considerations. The algorithm may be defined on the basis of data collected by trained service staff and be built by using an artificial neural network or a fuzzy network.
[0220] FIG. 11B illustrates a schematic view of a method comprising the step of applying a data table/feature matrix 96 comprising pre-recorded signals or signal patterns (A.sub.11, A.sub.12, . . . , A.sub.1n), (A.sub.21, A.sub.22, . . . , A.sub.2n), . . . , (A.sub.m1, A.sub.m2, . . . , A.sub.mn) associated with known pump error types and comparing sensor signals V.sub.3 with pre-recorded signals or signal patterns (A.sub.11, A.sub.12, . . . , A.sub.1n), (A.sub.21, A.sub.22, . . . , A.sub.2n), . . . , (A.sub.m1, A.sub.m2, . . . , A.sub.mn) in order to associate the sensor signals V.sub.3 with a known sensor error type.
[0221] A sensor signal V.sub.3 is detected e.g. by using a sensor assembly according to the invention. Hereafter, a feature extractor 94 is used to extract features from the sensor signal V.sub.3, hereby generating a feature vector C. The next step is to use the feature matrix 96 to identify the signal patterns (A.sub.11, A.sub.12, . . . , A.sub.1n), (A.sub.21, A.sub.22, . . . , A.sub.2n) , . . . , (A.sub.m1, A.sub.m2, . . . , A.sub.mn) that is closest to the feature vector C in order to categorize the signal V.sub.3 into one of the predefined classes/groups G.sub.1, G.sub.2, G.sub.3, G.sub.4 as it will be explained with reference to FIG. 12A and FIG. 12B.
[0222] FIG. 12A illustrates a schematic view of the process of associating a detected sensor signal P=(C.sub.1, C.sub.2, C.sub.3, C.sub.i, C.sub.i+i, C.sub.n) with a known sensor error type by using a method according to the invention. By using the feature matrix shown in FIG. 11B, one can find that the point P.sub.i is the point from the feature matrix positioned closest to the point P (in the n-dimensional space). Accordingly, this point P.sub.i is selected, and the categorization G.sub.4 of P.sub.i is associated to the point P.
[0223] In FIG. 12A, the n-dimensional space is separated into four areas G.sub.1, G.sub.2, G.sub.3, G.sub.4 corresponding to the four classes/groups G.sub.1, G.sub.2, G.sub.3, G.sub.4 explained with reference to FIG. 11A and FIG. 11B. The first group G.sub.1 is indicated with squares, the second group G.sub.2 is indicated with stars, the third group G.sub.3 is indicated with triangles, whereas the fourth group G.sub.4 is indicated with circles.
[0224] FIG. 12B illustrates a close-up view of the process illustrated in FIG. 12A, in which the point of the feature matrix being positioned closets to P is identified. It can be seen that the distance D.sub.min between P and P.sub.i is smaller than the distance D.sub.k between P and Pk and the distance D.sub.j between P and P.sub.j.
[0225] Instead of selecting a single point P.sub.i, to categorize the point P, it is possible to select a predefined number (e.g. two, three, four, five or more) of points being located in the shortest distance to the point P. In one embodiment according to the method of the invention, the three points P.sub.i, P.sub.n, P.sub.m located with the shortest distance to P, are selected, and the average category is calculated. In FIG. 12A and FIG. 12B, all three points P.sub.i, P.sub.n, P.sub.m have the category G.sub.4 having the value 4. Accordingly, the category of the point P is set to (4+4+4)=4.
[0226] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
