Synchronized multi-node system for monitoring of a machine

Abstract

A configurable state monitoring system (100) for monitoring the operation of a machine (110). The system comprises at least a first and a second wireless sensor node, WSN, (120). The first and second WSN are arranged attached to the machine (110) at a first and second position. Each WSN comprises at least one sensor, an energy providing device, and a processing unit. The system also comprising at least one transceiver (130). The first WSN (120) is configured as a reference sensor node, RSN, the RSN being arranged to provide a reference time and at least one reference measurement to the system. The second WSN (120) is configured as a comparator sensor node, CSN, the CSN being arranged to be synchronized with the RSN and to provide a comparative measurement relative to the reference measurement.

Description

The present disclosure relates to systems and methods for monitoring the operation of machines, particularly heavy-duty machinery such as vibrating screens.BACKGROUNDIn many industries it is desirable to monitor and analyze the operation of machinery in real time in order to detect potential problems, plan maintenance, and avoid interruptions in the production process. Real-time monitoring enables the evaluation of movement patterns and shape deformations. This in turn makes it possible to detect disturbances and deviations in the movement of the machine that can, if allowed to continue, have negative consequences such as decreased productivity, increased energy consumption, or machine breakdown. Such real-time monitoring is particularly important for machines that operate under heavy loads that move during operation and may require measurements to be taken at multiple positions on the machine being monitored.WO2019006506 A1 discloses systems and methods for monitoring the operation of a vibrating screen by correlating measurements from multiple sensor nodes.Still, there is a need for improved systems for monitoring the operation of heavy machinery.SUMMARYIt is an objective of the present disclosure to provide improved monitoring systems for heavy machinery, which, i.a., offer better real-time monitoring and detection of deviations in machine movement. This objective is at least in part obtained by a configurable state monitoring system for monitoring the operation of a machine. The system comprises at least a first and a second wireless sensor node, WSN. The first and second WSN are arranged attached to the machine at a first and second WSN position, with each WSN comprising at least one sensor, an energy providing device, and a processing unit. The system also comprises at least one transceiver. The first WSN is configured as a reference sensor node, RSN, where the RSN is arranged to provide a reference time and at least one reference measurement to the system. At least the second WSN is configured as a comparator sensor node, CSN, the CSN being arranged to be synchronized with the RSN and to provide a comparative measurement relative to the reference measurement.The system is thus arranged to provide synchronized measurements from two or more WSNs placed in different positions on the machine, with all measurements given relative to a reference measurement. In particular, the time synchronization makes it possible to measure how different parts of the machine move relative to each other and to see whether the motion at different points is in phase or out of phase, which is an advantage.Preferably, each WSN comprises a tri-axial accelerometer. This enables the WSN to provide a measurement of an acceleration in each spatial dimension, which in turn can be used to obtain a velocity and a position in each spatial dimension. The reference measurement provided by the RSN may comprise any of a reference acceleration, a reference velocity, and a reference position.According to some examples, the system comprises four or more WSNs. Of these, at least one WSN is configured as a RSN and at least two WSNs are configured as CSNs. Generally, all WSN that are not configured as a RSN will be configured as CSN, so that a system comprising four WSNs in total will have three CSNs, a system with six WSNs will have five CSNs, etc. Advantageously, this provides synchronized measurements from a plurality of points on the machine.As an alternative, at least two WSNs can be configured as a virtual RSN. In this case, the reference time, the reference measurement, and a RSN position are obtained as combinations of a time, a measurement, and a position obtained from each of the two WSNs. The effective position of such a virtual RSN will be at a point between the two physical WSNs. This is an advantage when a reference point between two WSN positions is desired, particularly if the desired reference point is in a position on the machine where it is difficult to place a physical WSN. Preferably, the combinations of the time, the measurement, and the position from each of the two WSNs are obtained as an average according to the least squares method.The system may be arranged to detect a cyclical motion of at least some WSNs. Many types of heavy machinery are configured to perform a desired cyclical motion as a part of normal operation. This is for example the case for vibrating screens. WSNs attached to such a machine will follow the same motion. Advantageously, detecting this cyclical motion makes it possible to extract characteristics such as period, stroke length, etc., and to compare the motion at each WSN position to a desired motion of the machine. It is also possible to detect unwanted differences between the movement of a CSN and the RSN.The cyclical motion may follow an orbit characterized by any of a period, an amplitude or stroke length, a slope, and a degree of ellipticity. A momentary position of the WSN along the orbit may be characterized by a phase. The period, stroke length, slope, and degree of ellipticity for each WSN can for example be compared to those of a desired orbit for the machine, which makes it possible to detect discrepancies in the movement of all or part of the machine.According to some examples, the system is arranged to compare the cyclical motion of at least one CSN to the cyclical motion of the RSN. Comparing the cyclical motion comprises determining a phase shift of the CSN relative to the RSN and / or determining a difference in stroke length between the CSN and the RSN.This enables a comparison of the orbits of different WSNs in the system, and particularly a comparison of each CSN relative to the RSN. Advantageously, a comparison of the cyclical motion between the CSNs and the RSN can show whether the motion of different parts of the machine are in phase or out of phase, if the stroke length is the same or different, etc. Often, minimal or zero phase difference between the WSNs will be preferred in order to maintain optimal machine operation. Being able to detect phase differences is therefore an advantage.Optionally, the WSNs comprised in the system are arranged in pairs, each pair being arranged to provide a measurement of a phase difference and / or of a difference in stroke length between the two WSNs in the pair to the system. Two WSNs forming a pair can for example be placed symmetrically on the machine, e.g. on either side of a main body of the machine. The phase difference or difference in stroke length between the two WSNs can then be used to obtain information about the movement of the part of the machine where they are affixed.The monitoring system may also comprise at least one mounting guide arranged attached to the machine in the position of at least one WSN. The mounting guide comprises at least one hole arranged to receive a mounting means.Preferably, a mounting guide is used for each WSN. The mounting guide can be attached to the machine in a preferred WSN position and the WSN can then be attached to the machine through one or more holes in the mounting guide. If the WSN is removed, the mounting guide stays attached to the machine so that the WSN can be replaced in the same position and with the same orientation. Alternatively, if the WSN needs to be replaced, the new WSN can be installed in the same position as the old one.The objective is also achieved at least in part by a method for operating a monitoring system for a machine. The monitoring system comprises at least a first and second wireless sensor node, WSN. The first and second WSNs are arranged attached to the machine at a first and second position. The system also comprises a transceiver. The method comprises configuring the first WSN as a reference sensor node, RSN, the RSN being arranged to provide a reference time and at least one reference measurement to the system. The method further comprises configuring at least the second WSN as a comparator sensor node, CSN, where the CSN is arranged to be synchronized with the RSN and to provide a comparative measurement relative to the reference measurement. The method also comprises synchronizing the CSN with the RSN; measuring, by the RSN, at least one reference measurement; measuring, by the CSN, at least one comparative measurement; and receiving, by the transceiver, data comprising at least the reference measurement and the comparative measurement.Measuring, by the RSN, at least one reference measurement may for example comprise measuring any of a reference acceleration, a reference velocity, and a reference position.Additionally, the method may comprise detecting a cyclical motion of at least some of the WSNs. Detecting a cyclical motion can for example comprise determining an orbit of the WSN characterized by any of a period, an amplitude or stroke length, a slope, and a degree of ellipticity. A momentary position of the WSN along the orbit is characterized by a phase.Optionally, the method comprises comparing the cyclical motion of at least one CSN to the cyclical motion of the RSN. Comparing the cyclical motion may for example comprise determining a phase shift of the CSN relative to the RSN and / or determining a difference in stroke length between the CSN and the RSN.According to some examples, the method also comprises configuring the WSNs comprised in the system as pairs and providing, by each pair, a measurement of a phase difference and / or a difference in stroke length between the two WSNs in the pair.Furthermore, the method may comprise configuring at least two WSNs as a virtual RSN. The reference time, the reference measurement, and a RSN position are then obtained as combinations of a time, a measurement, and a position obtained from each of the two WSNs.The methods disclosed herein are associated with the same advantages as discussed above in connection to the different apparatuses. There is also disclosed herein computer programs, computer program products, and control units associated with the above-mentioned advantages.Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.BRIEF DESCRIPTION OF THE DRAWINGSThe present disclosure will now be described in more detail with reference to the appended drawings, where:Figure 1 schematically illustrates a configurable state monitoring system;Figures 2 A, B, and C illustrate a configurable state monitoring system arranged on a vibrating screen;Figures 3 A and B illustrate elliptic orbits associated with a working machine;Figures 4 A, B, and C illustrate movements of a set of eight wireless sensor nodes along elliptical orbits;Figure 5 schematically illustrates a mounting guide;Figure 6 is a flow chart illustrating methods;Figure 7 schematically illustrates a control unit; andFigure 8 schematically illustrates a computer program product.DETAILED DESCRIPTIONAspects of the present disclosure will now be described more fully with reference to the accompanying drawings. The different devices and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.The following description focuses on the use of the monitoring system of the invention to monitor vibrating screens. However, a person skilled in the art will realize that the systems and methods herein described can be applied also to other types of industrial equipment, such as movable structures suspended from resilient elements. Such structures are for example found in the automotive, aerospace, or ship industries, or other types of industry.Vibrating screens are used to separate granulated materials, such as crushed ores, into fractions according to their particle size and density. A vibrating screen often comprises a large, heavy rigid structure such as a steel structure suspended by elastic machine elements, which in turn are mounted on a rigid support. At least one motion generator, or motor that induces vibration, is used to induce a cyclical motion in parts of the structure. The moving part generally comprise a screen medium arranged to separate particles. A screen medium is typically a mesh comprising a plurality of holes, where the size of the holes is selected in dependence of the size of the particles that the screen is intended to separate. The screen medium may be woven wire cloth, a punch plate, or be made from rubber or other polymer compounds. Many industrial screens comprise a plurality of screen media with different mesh sizes in order to be able to separate granulated materials into multiple grades. Vibrating screens in general are well known in the art.Ideally, the cyclical motion of the moving part of the machine takes place in two dimensions, i.e. on a plane. Here, this plane will be referred to as the plane of movement. The cyclical path traversed by the moving parts is herein referred to as an orbit. An orbit comprises a series of changing positions that form a sequence known as a stroke. When the entire sequence of the stroke has been traversed, the same movements are repeated in the next cycle. The shape of the orbit in the plane of movement can be elliptic, linear, circular, or any other suitable shape.For a vibrating screen to function optimally, the entire moving part of the machine should follow a desired orbit in a uniform manner, leading to a coherent pattern of movement. Here, a desired orbit is an orbit that is selected to produce an optimal result e.g. for the type of vibrating screen, the material being processed, etc. The different characteristics of orbits will be discussed in more detail below.If the moving parts of the vibrating screen do not move in the desired orbit, or do not move in a uniform manner, the productivity of the machine may be decreased, while the energy consumption and risk of machine failure may increase. It is therefore highly desirable to monitor the movement of the machine in real time and to enable early detection of undesirable patterns of movement.Figure 1 is a schematic representation of a configurable state monitoring system 100 for monitoring the operation of a machine 110. The system comprises at least a first and a second wireless sensor node, WSN, 120. The first and second WSN are arranged attached to the machine 110 at a first and second position. Each WSN comprises at least one sensor, an energy providing device, and a processing unit. The system also comprising at least one transceiver 130.In this system, the first WSN 120 is configured as a reference sensor node, RSN. The RSN is arranged to provide a reference time and at least one reference measurement to the system. At least one other WSN 120 is configured as a comparator sensor node, CSN, where the CSN is arranged to be synchronized with the RSN and to provide a comparative measurement relative to the reference measurement.The transceiver 130 is arranged to send and receive wireless communications using electromagnetic waves, particularly in the radio frequency spectrum. The transceiver 130 in the present system is configured to maintain a wireless connection to at least one WSN 120 in the system. It is also configured to receive measurement data from the WSN 120 over the wireless connection, and to transmit data to the WSN 120. The wireless connection may use e.g. Wi-Fi, 4G, or 5G. It may also use a radio protocol such as Bluetooth Low Energy (BLE), or other wireless communication means.Figure 1 shows a system comprising one transceiver 130. However, a system 100 may also comprise two or more transceivers. The number of transceivers 130 may for example be selected depending on the environment around the machine 110, the shape and size of the machine 110, and the number of WSN 120 in the system.The transceiver 130 may also be arranged to send data to one or more external units 140, and to receive data from the one or more external units 140. This may be accomplished over a wired connection such as an ethernet or CAN connection, or over a wireless connection using e.g. Wi-Fi, 4G, or 5G. The external devices 140 may comprise a data storage device, a local or online server, a mobile device such as a smartphone, or any other suitable device.According to some alternatives, the system also comprises a gateway. A gateway is a device arranged to receive data from the transceiver 130 and distribute it to the one or more external units 140. In a system 100 comprising multiple transceivers, the gateway will receive data from all transceivers 130. In some cases, the gateway and transceiver 130 may be combined into a single unit, especially if the system 100 comprises only one transceiver 130.The system 100 may also comprise one or more display means. A display means can be a stationarily mounted screen, a dashboard, a mobile device, or any other suitable device. The display means may be arranged to display measurement data from WSNs 120, preferably in real time.With reference also to Figure 7, the system 100 also comprises control units 700. In addition to the control unit comprised in each WSN 120, there may also be one or more additional control units. Such additional control units may e.g. be arranged near the transceiver, or alternatively incorporated into the same unit as the transceiver. Control units will be discussed in more detail below.The wireless sensor nodes (WSN) 120 are arranged to collect measurement data relating to the movement of the machine 110. Preferably, each WSN comprises a triaxial accelerometer. According to some examples, the WSNs may also comprise sensors arranged to measure angular velocity and orientation, such as gyroscopes and magnetometers respectively. In some cases, the WSNs may also be equipped with other sensors such as temperature sensors or humidity sensors.Each WSN 120 also comprises an energy provision device. According to a preferred alternative, the energy provision device is an energy harvesting device. According to another alternative, the energy provision device is an energy storage device such as a battery.The WSNs 120 also each comprise a control unit arranged to control operation of the sensors as well as to transmit sensor data to the transceiver 130 and control synchronization of the WSN with other WSNs.The WSNs 120 are attached to the machine 110 using attachment means. The attachment means may for example be a magnetic mount, a bracket, a quick-release plate, or any other suitable attachment means.One of the WSNs 120 is set up to be the reference sensor node (RSN), providing a reference time for synchronization with the other WSNs and at least one reference measurement. According to aspects, the reference measurement provided by the RSN comprises any of a reference acceleration, a reference velocity, and a reference position. Preferably, the reference measurement comprises all three of a reference acceleration, a reference velocity, and a reference position.The other WSNs 120 in the system 100 are configured to act as comparator sensor nodes (CSN). If the system comprises more than two WSNs 120, there will be one RSN and multiple CSNs. According to some alternatives, the system 100 comprises four or more WSN 120, wherein one WSN 120 is configured as a RSN and at least two WSNs 120 are configured as CSN. For example, the system 100 may comprise six WSNs 120, of which one is the RSN and five are CSNs, or the system 100 may comprise eight WSNs 120 of which seven are configured as CSNs.Each CSN is arranged to be synchronized with the RSN via the system 100. This is accomplished by synchronizing an internal clock of the CSN control unit to the reference time provided by the RSN. This is accomplished over a wireless connection, for example using a wireless radio protocol such as Bluetooth Low Energy (BLE). The reference time is preferably provided with a resolution of 1 ms or less.Each CSN also provides at least one comparative measurement, that is, a measurement relative to a reference measurement provided by the RSN. As an example, the comparative measurement can be a measurement of any of the acceleration, velocity, and position of the CSN compared to those of the RSN.According to some alternatives, two WSNs 120 may be configured as a virtual RSN. In this case, the reference time, the reference measurement, and a position of the RSN are obtained as combinations of a time, a measurement, and a position obtained from each of the two WSNs 120.The virtual RSN will function as if it occupies a position between the two physical WSNs 120, such as a position at the midpoint of a straight line between the two WSNs 120. The reference time provided by the virtual RSN will be a combination of the internal time of the two WSNs 120, and reference measurements such as a reference acceleration or reference velocity will likewise be obtained as a combination of values provided by the two WSNs 120. Preferably, the combinations of the time, the measurement, and the position from each of the two WSNs 120 is calculated as an average according to the least squares method. Advantageously, a virtual RSN can function as if it occupies a position where it is difficult to place a physical WSN 120.Figures 2A-C show an example use of the system 100 where the machine 110 is a vibrating screen. Figure 2A shows a side view of the vibrating screen with a first WSN 120-1 and a second wireless sensor node 120-3 arranged at a first and second position on the vibrating screen. The first WSN 120-1 is configured as the RSN, while the second WSN 120-3 is configured as a CSN.Figure 2B instead shows a front view of the vibrating screen, with two WSN 120 arranged on either side of the main body of the machine. This figure also shows a transceiver 130. The transceiver 130 may also be configured to act as a gateway as described above.Figure 2C is a perspective drawing of the vibrating screen with the position of four WSN 120-1, 120-2, 120-3, 120-4 indicated. The WSN 120-1 located in the front right corner of the machine is configured as the RSN, while the remaining three WSN are configured as CSN. Note that in this case, the plane of motion of the machine is the x-y plane. This means that the orbit of the machine should preferably be entirely in the x-y plane, while movement in the z direction should be minimized.Preferably, the WSNs 120 should be arranged symmetrically on the machine 110 in the manner shown e.g. in Figure 2C. The vibrating screen in the figure is arranged to move in the x-y plane, and the WSNs are arranged symmetrically around a line extending parallel to the x axis and extending along the middle of the machine in the z direction. That is, for each WSN on one side of the machine there is a second WSN with approximately the same position in x and y, but a different position in the z direction.As mentioned above, part of the structure of a vibrating screen exhibits a cyclical motion that ideally follows a desired orbit. Monitoring how well different parts of the structure follow the desired orbit during operation is a main purpose of the system 100. According to some alternatives, the system 100 is therefore arranged to detect a cyclical motion of the WSNs 120.Deviations from the desired orbit may lead to the cyclical motion of different WSNs 120 being different, that is, the actual orbit of each WSN may be different from that of other WSNs and from the desired orbit. The system 100 may therefore detect an orbit for each WSN, where the orbit is characterized by any of a period, i.e. the time it takes to complete a stroke of the machine, an amplitude or stroke length, a slope, and a degree of ellipticity, and where a momentary position of the WSN 120 along the orbit is characterized by a phase.Figures 3A and 3B illustrate example orbits Oe for the case of elliptical motion of a WSN 120 arranged on a vibrating screen. In Figure 3A, the black dot indicates a momentary position of the sensor node, while the orbit represents its motion in two dimensions during operation of the vibrating screen. The amplitude measured between the turning points of the orbit Oe, i.e. the turning point amplitude, is also indicated as the stroke length. The slope would, in this case, refer to the angle between the longer semi-axis of the ellipse and the horizontal plane. In general the slope of the orbit should be parallel to the direction of movement of the machine 110.In order to detect differences in the orbit of different WSNs, the system 100 is arranged to compare the cyclical motion of at least one CSN to the cyclical motion of the RSN. Comparing the cyclical motion may comprise determining a phase shift of the CSN relative to the RSN and / or determining a difference in stroke length between the CSN and the RSN.The phase shift can advantageously be expressed as a dimensionless number referred to as the degree of phase shift (DoPS). DoPS can take on values between -1 and 1. A DoPS of 0 indicates that the CSN and the RSN are perfectly in phase, while a DoPS of 1 indicates that the CSN is completely in antiphase and ahead of the RSN, and DoPS = -1 indicates that the CSN is completely in antiphase and behind the RSN. This is illustrated in Figure 3B, which shows three example orbits Oe with the black circle indicating the point of the orbit occupied by one comparator sensor node (CSN) when the reference sensor node (RSN) is at its uppermost turning point. The orbit to the left in the figure illustrates that the CSN is ahead of the RSN in the orbit, with a DoPS of 0.15. The orbit to the right illustrates a CSN that is behind the RSN in the orbit with a DoPS of -0.15, while the middle orbit illustrates a CSN that is in phase with the RSN and has a DoPS of 0.In a system with multiple CSN, the DoPS for each CSN may be collected into a phase comparison matrix (PCM). Advantageously, the PCM can be recorded at predetermined time intervals and saved in a computer-readable memory within the system 100. In particular, the PCM for a predetermined number of timesteps may be stored in a ring buffer that is continually updated. The PCM data saved in the ring buffer can then at any point in time be used to represent the movement pattern of the machine.According to some examples, the PCM may also comprise the reference time, the position of the RSN in x, y, and z, and the position of each CSN in x, y, and z. The movement of the machine 110 can then be evaluated based on that the positions of each CSN should follow that of the RSN, while the DoPS for each CSN should be minimized.Figures 4A, B, and C show orbits Oe(1) to Oe(8) of a set of eight WSN. The black xsymbols indicate the momentary position of each WSN in its orbit, and help lines are drawn between the momentary positions of neighboring WSN in order to illustrate the movement of the machine as a whole. In Figure 4A, all WSN are in phase and reach the lower turning points of the orbits simultaneously, that is, DoSP for all CSN is 0. In Figure 4B, all WSN are also in phase and are shown at the upper turning point, still with DoSP of 0 for all CSN. Figure 4C shows a worst-case scenario wherein all neighboring WSN are in phase opposition, DoSP being either -1 or 1 for all CSN. This state would lead to undesirable deformations of the machine being monitored.In addition to measuring the phase comparison matrix mentioned above, it is also possible to construct an amplitude comparator matrix (ACM). Instead of the DoSP, this matrix would contain the relative turning point amplitude for each CSN, calculated as a ratio of the turning point amplitude or stroke length of each CSN to that of the RSN.According to another alternative, the WSNs 120 comprised in the system 100 are arranged in pairs, each pair being arranged to provide a measurement of the phase difference and / or the difference in stroke length between the two WSNs 120 in the pair to the system 100. Preferably, the WSNs in a pair are placed in symmetrical positions on either side of the machine 110. Referring again to Figure 2C, the WSNs 120-1 and 120-2 may then form a first pair, while the WSNs 120-3 and 120-4 form a second pair.For any herein described alternative or exemplary embodiment of the system, the measured data can be used to evaluate the movement of the machine 110 in real time. To this end, it may be displayed in such a way that it is visible to a person operating the machine. It may for example be displayed using a display means such as a dashboard, screen, or mobile device as previously discussed. This enables the operator to adjust operational parameters of the machine 110 and take action when a deviation is detected. Automated analysis of the measurement data may also be used to trigger an alarm to alert the operator to an undesirable movement pattern.The monitoring system 100 may also comprise at least one mounting guide 500 as illustrated in Figure 5. The mounting guide is arranged to be attached to the machine 110 in the position of at least one WSN 120. The mounting guide also comprises at lest one hole 510 arranged to receive a mounting means. Preferably, one mounting guide 500 is used for each WSN 120, and the mounting guides are placed on the machine 110 in the positions where WSNs should be attached.As mentioned above, the holes 510 allow for a mounting means attached to the WSN to connect to the machine through the mounting guide. Optionally, the mounting guide 500 comprises direction indicators 520 which show the intended orientation of the mounting guide. The mounting guide preferably comprises a rubber material such as ethylene propylene diene monomer rubber (EPDM). The side of the mounting guide 500 that is in contact with the surface of the machine is preferably coated with an adhesive.Advantageously, the mounting guide 500 reduces the risk that the WSN 120 moves on the surface of the machine due to the vibrations experienced in operation, i.e., the mounting guides 500 provide an anti-slip functionality. This is especially relevant for WSNs 120 equipped with magnetic mounts, which are not bolted to the machine. The mounting guides 500 also assist in the correct alignment of the WSN 120 and ensure that the WSN 120 can be returned to the same position on the machine after being removed, or that a new WSN 120 replacing an old one can be installed in the same position.With reference to Figure 6, there is also herein disclosed a method for operating a monitoring system 100 for a machine 110. The monitoring system comprises at least a first and second wireless sensor node, WSN, with the first and second WSNs being arranged attached to the machine 110 at a first and second position. The system 100 also comprises a transceiver 130. The method comprises configuring S1 the first WSN 120 as a reference sensor node, RSN, where the RSN is arranged to provide a reference time and at least one reference measurement to the system. The method also comprises configuring S2 at least the second WSN 120 as a comparator sensor node, CSN, where the CSN is arranged to be synchronized with the RSN and to provide a comparative measurement relative to the reference measurement. The method further comprises synchronizing S3 the CSN with the RSN, measuring S4, by the RSN, at least one reference measurement, measuring S5, by the CSN, at least one comparative measurement, and receiving S7, by the transceiver 130, data comprising at least the reference measurement and the comparative measurement.According to a preferred alternative, measuring S4, by the RSN, at least one reference measurement comprises measuring any of a reference acceleration, a reference velocity, and a reference position.According to some examples, the method comprises detecting S6 a cyclical motion of the WSNs 120. Furthermore, detecting S6 a cyclical motion may comprise determining S61 an orbit of each of the WSNs 120 characterized by any of a period, an amplitude or stroke length, a slope, and a degree of ellipticity. Here, a momentary position of each WSN 120 along its respective orbit is characterized by a phase.According to some examples, the method may comprise comparing S62 the cyclical motion of at least one CSN to the cyclical motion of the RSN, wherein comparing the cyclical motion comprises determining a phase shift of the CSN relative to the RSN and / or determining a difference in stroke length between the CSN and the RSN.Furthermore, the method may comprise configuring S63 the WSNs 120 comprised in the system as pairs and providing S64, by each pair, a measurement of a phase difference and / or difference in stroke length between the two WSNs 120 in the pair.In this case, the reference time, the reference measurement, and a RSN position are obtained as combinations of a time, a measurement, and a position obtained from each of the two WSNs 120. Preferably, the combinations of the time, the measurement, and the position from each of the two WSNs are obtained as an average according to the least squares method.There is furthermore herein disclosed a computer program comprising program code means 810 for performing the steps of the methods described above when said program is run on a control system comprising one or more control units. Additionally, a computer readable medium 820 is disclosed carrying a computer program comprising program code means 810 for performing the steps of any of the abovementioned methods, when said program product is run on a control system comprising one or more control units. There is also a computer program product 800 comprising such a computer program 810, and a computer readable storage medium 820 on which the computer program is stored.Figure 7 schematically illustrates, in terms of a number of functional units, the general components of a control unit 700. Processing circuitry 710 is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium 730. The processing circuitry 710 may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.Particularly, the processing circuitry 710 is configured to cause the monitoring system 100 to perform a set of operations, or steps, such as the methods discussed in connection to Figure 6, and the discussions above, and also to set operating parameters of the system according to the discussions above. For example, the storage medium 730 may store the set of operations, and the processing circuitry 710 may be configured to retrieve the set of operations from the storage medium 730 to cause the device to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 710 is thereby arranged to execute methods as herein disclosed.The storage medium 730 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. This storage medium may be configured to store one or more sets of configuration settings for the monitoring system 100.The control unit 700 may further comprise an interface 720 for communications with at least one external device. As such the interface 720 may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication.The processing circuitry 710 controls the general operation of the control unit 700, e.g., by sending data and control signals to the interface 720 and the storage medium 730, by receiving data and reports from the interface 720, and by retrieving data and instructions from the storage medium 730.Figure 8 illustrates a computer readable medium 810 carrying a computer program comprising program code means 820 for performing the methods illustrated in Figure 6 and / or for executing the various functions discussed above, when said program product is run on a computer. The computer readable medium and the code means may together form a computer program product 800. This computer program product may comprise one or more sets of configurations for controlling the device 100 discussed above to perform the methods disclosed herein.

Claims

1. A configurable state monitoring system (100) for monitoring the operation of a machine (110), the system comprisingat least a first and a second wireless sensor node, WSN, (120), the first and second WSN being arranged attached to the machine (110) at a first and second WSN position, each WSN comprising at least one sensor, an energy providing device, and a processing unit,the system also comprising at least one transceiver (130),wherein the first WSN (120) is configured as a reference sensor node, RSN, the RSN being arranged to provide a reference time and at least one reference measurement to the system, andwherein at least the second WSN (120) is configured as a comparator sensor node, CSN, the CSN being arranged to be synchronized with the RSN and to provide a comparative measurement relative to the reference measurement.

2. The state monitoring system (100) according to claim 1, wherein each WSN comprises a tri-axial accelerometer.

3. The state monitoring system (100) according to claim 1 or 2, wherein the reference measurement provided by the RSN comprises any of a reference acceleration, a reference velocity, and a reference position.

4. The monitoring system (100) according to any previous claim, comprising four or more WSNs (120), wherein at least one WSN (120) is configured as a RSN and at least two WSNs (120) are configured as CSN.

5. The monitoring system (100) according to claim 4, wherein at least two WSNs (120) are configured as a virtual RSN, and wherein at least the reference time, the reference measurement, and a RSN position are obtained as combinations of a time, a measurement, and a position obtained from each of the two WSNs (120).

6. The monitoring system (100) according to claim 5, wherein the combinations of the time, the measurement, and the position from each of the two WSNs (120) are obtained as an average according to the least squares method.

7. The monitoring system (100) according to any previous claim, wherein the system (100) is arranged to detect a cyclical motion of at least some WSNs (120).

8. The monitoring system (100) according to claim 7, wherein the cyclical motion follows an orbit characterized by any of a period, an amplitude or stroke length, a slope, and a degree of ellipticity, and where a momentary position of the WSN (120) along the orbit is characterized by a phase.

9. The monitoring system (100) according to claim 7 or 8, wherein the system (100) is arranged to compare the cyclical motion of at least one CSN to the cyclical motion of the RSN, and wherein comparing the cyclical motion comprises determining a phase shift of the CSN relative to the RSN and / or determining a difference in stroke length between the CSN and the RSN.

10. The monitoring system (100) according to any of claims 7 to 9, wherein the WSNs (120) comprised in the system (100) are arranged in pairs, each pair being arranged to provide a measurement of a phase difference and / or of a difference in stroke length between the two WSNs (120) in the pair to the system (100).

11. The monitoring system (100) according to any previous claim, comprising at least one mounting guide (500) arranged attached to the machine (110) in the position of at least one WSN (120), the mounting guide (500) comprising at least one hole (510) arranged to receive a mounting means.

12. A method for operating a monitoring system (100) for a machine (110), the monitoring system comprising at least a first and second wireless sensor node, WSN, (120), the first and second WSNs being arranged attached to the machine (110) at a first and second position, the system (100) also comprising a transceiver (130), the method comprisingconfiguring (S1) the first WSN (120) as a reference sensor node, RSN, the RSN being arranged to provide a reference time and at least one reference measurement to the system,configuring (S2) at least the second WSN (120) as a comparator sensor node, CSN, the CSN being arranged to be synchronized with the RSN and to provide a comparative measurement relative to the reference measurement,synchronizing (S3) the CSN with the RSN,measuring (S4), by the RSN, at least one reference measurement,measuring (S5), by the CSN, at least one comparative measurement, and receiving (S7), by the transceiver (130), data comprising at least the reference measurement and the comparative measurement.

13. The method according to claim 12, wherein measuring (S4), by the RSN, at least one reference measurement comprises measuring any of a reference acceleration, a reference velocity, and a reference position.

14. The method according to claim 12 or 13, further comprising detecting (S6) a cyclical motion of at least some of the WSNs (120).

15. The method according to claim 14, wherein detecting (S6) a cyclical motion comprises determining (S61) an orbit of the WSN (120) characterized by any of a period, an amplitude or stroke length, a slope, and a degree of ellipticity, where a momentary position of the WSN (120) along the orbit is characterized by a phase.

16. The method according to claim 14 or 15, comprising comparing (S62) the cyclical motion of at least one CSN to the cyclical motion of the RSN, wherein comparing the cyclical motion comprises determining a phase shift of the CSN relative to the RSN and / or determining a difference in stroke length between the CSN and the RSN.

17. The method according to any of claims 12 to 16, comprising configuring (S63) the WSNs (120) comprised in the system as pairs and providing (S64), by each pair, a measurement of a phase difference and / or a difference in stroke length between the two WSNs (120) in the pair.

18. The method according to any of claim 12 to 17, comprising configuring at least two WSNs (120) as a virtual RSN, such that the reference time, the reference measurement, and a RSN position are obtained as combinations of a time, a measurement, and a position obtained from each of the two WSNs (120).

19. A computer program comprising program code means (810) for performing the steps of any of claims 12 to 18, when said program is run on a control system comprising one or more control units.

20. A computer readable medium (820) carrying a computer program comprising program code means (810) for performing the steps of any of claims 12 to 18, when said program product is run on a control system comprising one or more control units.

21. A computer program product (800) comprising a computer program (810) according to claim 19, and a computer readable storage medium (820) on which the computer program is stored.