Device and method for the non-destructive magnetic testing of a chain

Abstract

The invention relates to a device (10) and a method for the non-destructive, magnetic testing of a chain (11) with several chain links (12), which is guided by means of a guide device (19) through a magnet arrangement (20) on an axial section (20), wherein a sensor arrangement (24) with a plurality of magnetic field sensors (25) is arranged in the axial section (21). The magnetic field sensors (25) are arranged on a line (26) encircling the chain (11). The device (10) also includes a length measuring device (27) with a measuring wheel (28) or by means of magnetic field sensors in the chain direction (45a), which is configured to detect the path length of the chain relative to the device (10) or vice versa.The device also includes an evaluation unit (30) which is configured to receive the measurement data in the magnetic field sensors, to assign them to a circumferential position and the detected path length with spatial resolution, and to detect defects in the chain (11) in the spatially resolved measurement data.

Description

[0001] The invention relates to devices and methods for the non-destructive, magnetic testing of a chain.

[0002] Chains are used in a wide variety of technical applications, such as in production and industrial plants, as drive chains, and in lifting equipment. During operation, individual chain links can become damaged and / or deformed, for example, longitudinally, causing the chain to stretch, or transversely, causing individual links to bend. Longitudinal or transverse deformation, or damage to the chain links, can render the chain completely unusable and necessitate replacement. Continuing to use deformed or broken chain links can damage components interacting with the chain, such as sprockets, guides, or similar parts. This can lead to the shutdown of entire production lines. Furthermore, in safety-critical applications, this can pose a risk to life and limb.It is therefore desirable to detect changes in the condition of the chain as early as possible during operation.

[0003] In DE 10 2014 225 834 B4 a drive chain length testing system is described which has a measuring device with a horizontal detection sensor and a vertical detection sensor with which elongations of the drive chain can be determined.

[0004] DE 10 2016 015 364 A1 also describes a method for determining geometric characteristics of chain links of a link chain, in which visible edges are optically detected and the geometric characteristics of the chain links are determined from this.

[0005] Optical methods for detecting deformations are prone to errors, especially when the chain is dirty. Furthermore, defects in individual chain links can be concealed if the geometry of the chain links is determined from only a few directions.

[0006] Based on this, the object of the invention is to provide an improved device and an improved method for the non-destructive, magnetic testing of a chain, which in particular makes it possible to test the chain in operation.

[0007] The invention is solved by the device according to claim 1 and the testing method according to claim 15.

[0008] The device according to the invention for the non-destructive, magnetic testing of a chain with several chain links can be arranged, in particular, on an axial section of the chain and moved relative to the chain, or conversely, the chain can be moved relative to the device in the longitudinal direction of the chain. The device according to the invention comprises a magnet arrangement, a sensor arrangement, a length measuring device, and an evaluation unit. The magnet arrangement includes several magnets with which a magnetic field is generated. The generated magnetic field extends, in particular, in the longitudinal direction of the chain. The magnet arrangement can, for example, have a first magnetic area at a first axial position of the axial section and a second magnetic area at a second axial position of the axial section 21, between which the magnetic field is generated. Alternatively, the generated magnetic field can also extend in the transverse direction of the chain.The sensor arrangement comprises a plurality of magnetic field sensors positioned along a line encircling the chain within a sensor area at an axial position of the axial section. This chain-encircling line preferably encloses the chain completely. The line can be adapted to the outer contour of the chain, for example, by having a cross-shaped form. The length measuring device is configured to determine the relative path length between the sensor arrangement and the chain. The evaluation unit is configured to receive measurement data from the magnetic field sensors, spatially assign this data to a circumferential position and the measured path length, and detect defects in the chain within the spatially resolved measurement data.

[0009] This makes it possible to detect defects in individual chain links early in the operation, before individual chain links can break and thus the chain can fail completely.

[0010] A special feature of the present invention is that the magnetic field sensors completely encircle the chain, thereby enabling the detection of magnetic field variations across the entire circumference of the chain. This allows for the detection of defects in individual chain links that would otherwise occur in difficult-to-access locations. Such defects in the chain can include, for example, indentations, deformations of the chain links, cracks in the chain links, and the like.

[0011] To detect defects in the chain links, the evaluation unit is preferably configured to compare the spatially resolved measurement data in the circumferential direction with a reference function, for example by correlating or convolving the reference function with the spatially resolved measurement data. The reference function can be, for example, a rectangular function or the absolute value of a trigonometric function such as a sine or cosine function.

[0012] The magnetic areas can contain permanent magnets, such as rare-earth magnets, or electromagnets to generate the magnetic field.

[0013] In particular, the line encircling the chain, on which the magnetic field sensors of the sensor array are arranged, is adapted to a transverse clearance of the chain. This transverse clearance is specifically the sum of the transverse outlines of at least two chain links. Adapting the encircling line to the chain's clearance allows even hard-to-reach areas on the chain links to be reliably detected by the magnetic field sensors, enabling the detection of defects in these areas.

[0014] Preferably, the guide device has several guide surfaces on which the individual chain links are guided. The guide device can be designed as a single piece or in multiple parts. If the guide device is designed as a single piece, it can have at least one guide element on which the multiple guide surfaces are arranged. The guide element can be made of a plastic such as polyamide or the like. Alternatively, the guide device can also have one or more spring-loaded rollers, in which the rolling surfaces of the rollers form the guide surfaces of the guide device.

[0015] Regardless of the specific design of the guide device, it is configured to establish a relative alignment between the sensor assembly and the individual chain links. This alignment of the chain links can then be maintained by the guide device during the testing process.

[0016] If the guide device has at least one guide element, a through-hole can be formed in the guide element, the flanks of which form the guide surfaces for the chain links. Preferably, the contour of the through-hole is adapted to the transversely summed outlines of at least two chain links. It is preferred that the through-hole be cross-shaped. The through-hole may be designed with clearance relative to the contour of the chain.

[0017] The device features, in particular, an openable housing in which a test bore is formed, extending from a first side of the housing to an opposite second side of the housing. Preferably, the magnet arrangement and the sensor arrangement are housed within the housing, thereby protecting them from dirt and other external influences. Preferably, the magnet arrangement and the sensor arrangement are arranged at least partially around the test bore. It is also preferred that the guide device is arranged, at least partially, within the test bore.

[0018] The guide device can have at least one additional guide element by which the chain is guided within the device. For example, the first guide element can be located in one entry area of ​​the test bore and the additional guide element in the other entry area of ​​the test bore. Alternatively, the guide device can also have only one guide element that extends along the entire length of the test bore.

[0019] The sensor arrangement can further comprise at least one measuring coil that extends at least partially (in the circumferential direction) around the chain. The sensor arrangement can also comprise several such measuring coils. The measuring coil can be designed as a single piece or in multiple parts. Furthermore, the one or more measuring coils can be arranged offset from the magnetic field sensors along the longitudinal axis.

[0020] Preferably, the evaluation unit is configured to fuse the measurement data from the magnetic field sensors with the measured path length of the length measuring device and, preferably, with the measurement data from the measuring coil in such a way that at least a three-dimensional measurement image of the measured magnetic field strengths in the circumferential and longitudinal directions of the chain is generated. This allows a complete measurement image of the chain to be generated.

[0021] The evaluation unit is also specifically designed to detect error patterns in the three-dimensional measurement image that indicate a misalignment in the chain. In particular, the evaluation unit is designed to mark these error patterns and place a virtual marker in the measurement data at the detected error pattern location.

[0022] According to a first embodiment, the length measuring device can have at least one measuring wheel configured to roll on the chain links during relative movements between the device and the chain. The measuring wheel can be equipped with an encoder that determines the rolling angle and, based on its known geometry, assigns a distance traveled to this rolling angle. A prerequisite for a clear assignment between the rolling angle and the distance traveled is that the measuring wheel rolls on the chain without slippage. In the first embodiment, the measuring wheel of the length measuring device can be arranged, preferably outside the housing of the device, such that it can roll on the back of the chain links of the alternately oriented chain links, which are aligned in the same direction.Alternatively, the measuring wheel of the length measuring device can be arranged such that it can roll in a groove formed by the alternately aligned chain links in the chain's clearance space in the transverse direction. The radius of the measuring wheel is preferably larger than the lengths of the individual chain links. Preferably, the radius of the measuring wheel is larger than twice the length, and particularly preferably larger than three times the length of the individual chain links. This allows the measuring wheel to roll on the back of the individual chain links without having to follow any depressions formed by the chain links. Alternatively, the measuring wheel can be spring-mounted on the device's housing in such a way that it is pre-tensioned against the chain.

[0023] According to a second embodiment, the length measuring device can be implemented with a plurality of sensors, preferably arranged in the chain direction. The plurality of sensors can extend along at least a portion, for example at least 25%, 40%, 50%, 60%, or 70%, of the length of the axial section. The sensors can be designed as magnetic field sensors with which the relative movement between the device and the chain can be determined. The plurality of magnetic field sensors, together with the sensor arrangement, can form a sensor unit or separate sensor units. The evaluation unit can include a length measuring module configured to determine the relative movement between the device and the chain from the data of the additional (magnetic field) sensors.Furthermore, the additional sensors can also be designed as optical sensors, which are configured to determine the relative movement between the device and the individual chain links.

[0024] The device can also include a storage unit and a communication interface configured to temporarily store the measurement data from the sensor arrangement and the longitudinal measuring device as needed and to send this data to the evaluation unit. In this embodiment, the evaluation unit is located within the device housing. Alternatively, the evaluation unit can be located within the device housing. In this embodiment, the evaluation unit can have a communication interface configured to connect to other user devices in order to transmit the processed and evaluated measurement data to these devices.

[0025] Furthermore, the problem is solved by a method for the non-destructive, magnetic testing of a chain. The method according to the invention comprises: - Arranging the chain to be tested in an axial section in which a magnetic field is formed such that the chain is located lengthwise in the formed magnetic field; - Measuring the magnetic field strength on a line encircling the chain, arranged perpendicular to the longitudinally formed magnetic field; - Determining the relative path length between the sensor array and the chain; - Assigning the measurement data from the magnetic field sensors to a circumferential position and the recorded path length, preferably creating an associated, spatially resolved measurement image; as well as - Detecting defects in the chain within the associated measurement data.

[0026] The features and advantages described in connection with the device according to the invention are applicable accordingly to the method according to the invention.

[0027] Further details of advantageous embodiments or specific aspects of the invention will become apparent from the drawings, the description, and the dependent claims. These show: Fig. 1 An example of the device according to the invention; Fig. 2 An example of the magnet arrangement and the sensor arrangement of the test device; Fig. 3A An example of the guidance system and sensor arrangement; Fig. 3B Another example of the guide device with the sensor arrangement; Fig. 4 A schematic view of the signal processing of the device according to the invention; Fig. 5A-5E Examples of defects in a chain.

[0028] Fig. Figure 1 shows an example of a device 10 according to the invention for the non-destructive testing of a chain 11 with a plurality of chain links 12. The device 10 has a housing 13 which is designed to be opened. For opening the housing 13, it has an upper housing shell 14 and a lower housing shell 15. The housing 13 also has a first side 16 and a second side 17 opposite the first side 16, wherein a test bore 18 extends from the first side 16 to the second side 17. The chain 11 to be tested is arranged within the test bore 18 during the test. In the Fig. In the example shown, a guide device 19 is also arranged within the test bore 18, which is configured to guide the chain links 12 of the chain 11 within the device 10 during the test procedure of the chain 11. The device 10 also has a magnet arrangement 20, which is arranged such that a magnetic field 22 is arranged in an axial section 21 in the longitudinal direction of the chain 11.

[0029] The device 10 or the chain 11 can be moved relative to each other along a longitudinal direction 45a of the chain 11, which in Fig. 1 is represented by the arrows 23. A transverse direction 45b of the chain 11 is defined transverse to the longitudinal direction 45a. In the axial section 21, a sensor arrangement 24 with a plurality of magnetic field sensors 25 is also arranged on a line 26 encircling the chain 11.

[0030] If the length measuring device is designed by a plurality of magnetic field sensors 53, these are arranged in the longitudinal direction 45a of the chain 11, as shown in Fig. Figure 1 shows the arrangement as shown in dashed lines. The arrangement can, together with the sensor arrangement 24, form a T-shaped arrangement (as shown) in the side projection. Alternatively, the arrangement can also form an L-shaped arrangement in the side projection or comprise two or more ring-shaped magnetic field sonars. In this case, it is no longer necessary for the device 10 to have an additional length measuring device 27 outside the housing 13. Rather, the length measuring device 27 is already implemented inside the housing 13 in the form of the additional plurality of magnetic field sensors 53. The details of the sensor arrangement 24 are described below with reference to the Fig. 2, Fig. 3A and Fig. 3B described in detail.

[0031] In Fig. Figure 1 also shows a length measuring device 27, which is set up to determine the relative path length between the device 10 and the chain 11. The in Fig. The length measuring device shown in Figure 1 has a measuring wheel 28 which is rotatably mounted about an axis and pivotably attached to the housing 13 by means of an arm 29. The measuring wheel 28 can be spring-loaded against the chain 11 via the arm 29.

[0032] Furthermore, the device 10 has an evaluation unit 30 which is configured to receive measurement data 31 from the magnetic field sensors 25 and the length measuring device 27, to assign these to a circumferential position 32 and a recorded path length 33 with spatial resolution and to detect defects 34 in the spatially resolved measurement data.

[0033] Furthermore, the device 10 has a communication interface 35, which is configured to communicate with user terminals, for example, to communicate detected defects 34 or the spatially resolved measurement data to the user terminal 36. The device 10 may also have a storage device 37, which may be configured to temporarily store measurement data from the sensors 25, 27 and / or the evaluation unit 30.

[0034] In Fig. Figure 2 illustrates the magnet arrangement 20 together with the sensor arrangement 24 and the chain 11 to be tested. The magnet arrangement 20 has a first magnet section 38 at a first axial position 39 and a second magnet section 40 at a second axial position 41 of the axial section 21. The first magnet section 38 and the second magnet section 40 are connected to each other via a yoke 42. In particular, the first magnet section 38 has permanent magnets that are polarized in the opposite direction to the permanent magnets of the second magnet section 40. Fig. The negative poles are labelled N and the positive poles S. The field lines of the magnetic field 22 formed between the first magnetic region 38 and the second magnetic region 40 are shown in Fig. 2 is shown as a dashed line. The magnetic field 22 extends longitudinally to the chain 11. Unlike in Fig. As shown in Figure 2, the first magnetic area 38 and the second magnetic area 40 can also contain electromagnets, between which the magnetic field 22 is constructed accordingly.

[0035] The sensor arrangement 24 comprises a plurality of magnetic field sensors 25, which are arranged in a sensor area 43 at a third axial position 44 located between the first and second axial positions 39, 41 on a line 26 encircling the chain. The magnetic field sensors 25 are, for example, designed as Hall sensors.

[0036] In Fig. 2 is further shown as a length measuring device 27, which is realized by the multitude of magnetic field sensors 53, from whose data the relative path length between the device 10 and the chain 11 can be determined.

[0037] Fig. Figure 3A shows an example cross-section of the sensor arrangement 24. The magnetic field sensors 25 are located in the Fig. In the example shown in Figure 3A, the magnetic field sensors 25 are arranged on a circular line 26 around the chain 11. The magnetic field sensors 25 are arranged equidistant from each other on the line 26.

[0038] In Fig. Figure 3A also shows an example of the guide device 19. In the example shown here, the guide device 19 has a guide element 46 in which a cross-shaped through-hole 47 is formed. The individual chain links 12 of the chain 11 are guided in the cross-shaped through-hole 47. The flanks of the through-hole 47 form guide surfaces 48 for the individual chain links 12. The dimensions of the through-hole 47 are adapted to the dimensions of the chain links, with the through-hole having a clearance fit with the chain 11.

[0039] The guide element 46 can be interchangeably connected to the test device 10. In particular, the test device 10 can have many different elements 46, each adapted to different chains 11.

[0040] Fig. Figure 3B shows another example of the sensor arrangement 24 together with the guide device 19. For the in Fig. The example shown in 3B applies in relation to the above. Fig. 3 said with reference to the reference marks accordingly. The in Fig. The example shown in 3B differs from the one in Fig. 3A shows the following difference: the sensor arrangement 24 has more magnetic field sensors 25 than the one shown in 3A. Fig. Example 3A is shown. On the other hand, the two examples differ in that these magnetic field sensors are 25 in Fig. 3B are not arranged on a circular circumferential line 26, but on a line 26 adapted to the cross-sectional contour of the chain 11. The in Fig. Line 26 shown in 3B is not circular.

[0041] Fig. Figure 4 schematically shows the signal processing of the device 10 according to the invention. The measurement data 31 from the magnetic field sensors 25 and the path lengths 33 from the length measuring device 27 are received by the evaluation unit 30. The evaluation unit 30 can be configured to fuse the received data in such a way that at least a three-dimensional measurement image 52 of the detected magnetic field strength in the circumferential direction 32 and in the longitudinal direction 33 of the chain 11 is generated. The evaluation unit 30 is also configured to detect error patterns 49 in the three-dimensional measurement image 52. In the Fig. In the example shown, several regular patterns 50 are depicted, which result from the eyelets of the individual chain links 12 in connection with the relative motion. Furthermore, in Fig. 4 shows a defect pattern 49, which indicates a crack in a chain link 12. Information about the defect pattern 49 and the defects 34 detected in the measurement data 31, 33 can be virtually marked by the evaluation unit 30. This information, or the raw data underlying the information, can be stored in a storage device 37 and / or transmitted via the communication interface 35, for example, to a user terminal 36 or an external computing device, such as a computer, a server, or cloud, and processed, displayed, or stored there.

[0042] The Fig. 5A, Fig. 5B, Fig. 5C, Fig. 5D and Fig. Figure 5E shows several different examples of defects 34 in a chain link 12 of the chain 11. Fig. 5A has one of the chain links 12 with a notch 34. The notch has in the Fig. The example shown in 5A does not yet have an effect on the chain link length 51. However, it can be detected and recognized at an early stage using the device 10. Fig. 5B shows a defect 34 where a chain link 12 is completely broken. Also in the Fig. In the example shown in 5B, the chain link length 51 of the affected chain link 12 has not yet been increased. Fig. 5C also shows a crack as defect 34, but the chain link length 51 in the example shown here is increased compared to the regular chain link length. Fig. Figure 5D also shows a defect where a chain link 12 is bent. This defect is also characterized by a characteristic defect pattern 49 in measurement figure 52. Fig. Figure 5E also shows an example of chain 11 where individual chain links 12 have elongated. The elongation 34 of the individual chain links 12 is also recognizable as a defect 49 in measurement figure 52.

[0043] The invention relates to a device 10 and a method for the non-destructive, magnetic testing of a chain 11 with several chain links 12, which is guided by means of a guide device 19 through a magnet arrangement 20 on an axial section 21, wherein a sensor arrangement 24 with a plurality of magnetic field sensors 25 is arranged in the axial section 21. The magnetic field sensors 25 are arranged on a line 26 encircling the chain 11. The device 10 also includes a length measuring device 27, which is configured to detect the path length of the chain relative to the device 10 or vice versa, for example via a measuring wheel or via additional magnetic field sensors arranged in the chain direction 45a.The device also has an evaluation unit 30, which is designed to receive the measurement data in the magnetic field sensors, to assign them to a circumferential position and the recorded path length with spatial resolution, and to detect defects in the chain 11 in the spatially resolved measurement data. Reference symbol: 10 Device 11 chain 12 chain links 13 cases 14 upper case shell 15 lower case shell 16 first side of the case 17 second side of the case 18 Test bore 19 Command device (command element) 20 Magnet arrangement 21 Axial section 22 Magnetic field 23 Relative motion between device and chain 24 Sensor arrangement 25 magnetic field sensors Line 26 27 Length measuring device 28 measuring wheel 29 Arm 30 evaluation measurement units 31 measurement data 32 Scope position 33 Path length 34 Missing Item 35 Communication interface 36 User terminal 37 Storage device 38 first magnetic area 39 first axial position 40 second magnetic area 41 second axial position 42 yoke 43 Sensor area 44 third axial position 45a Longitudinal direction of the chain 45b Cross direction of the chain 46 Guide element 47 Through hole 48 guide surfaces 49 defective samples 50 regular pattern 51 chain link length 52 Measurement illustration QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 225 834 B4

[0003] DE 10 2016 015 364 A1

[0004]

Claims

[1] Device (10) for magnetic testing of a chain (11) with several chain links (12), wherein the device (10) can be arranged on an axial section (21) of the chain (11) and is movable relative to the chain (11) or conversely the chain (11) is movable relative to the device (10) in the longitudinal direction (45a) of the chain (11), comprising: - a magnetic arrangement with several magnets which are configured to form a magnetic field (22) in an axial section (21), preferably in the longitudinal direction (45a); - a guidance device (19) for guiding the chain (11); - a sensor arrangement (24) with a plurality of magnetic field sensors (25) arranged in a sensor area (43) at a third axial position (44) of the axial section (21) located between the first and second axial positions (41) on a line (26) encircling the chain (11); - a length measuring device (27) configured to determine the relative path length (33) between the sensor arrangement (24) and the chain (11); and - an evaluation unit (30) which is set up to, to receive measurement data (31) from the magnetic field sensors (25), to assign these to a circumferential position (32) and the detected path length (33) with spatial resolution, and to detect defects (34) in the chain (11) in the spatially resolved measurement data (31). [2] Device (10) according to claim 1, characterized by , that the line (26) encircling the chain (11), on which the magnetic field sensors (25) of the sensor arrangement are arranged, is adapted to a light space of the chain (11) in the transverse direction (45b) of the chain (11). [3] Device (10) according to claim 1 or 2, characterized by , that the guide device (19) has several guide surfaces (48) on which the chain links (12) of the chain (11) are guided. [4] Device (10) according to any of the preceding claims, characterized by , that the guide device (19) has at least one guide element (19) wherein a through hole (47) is formed in the guide element (19) the flanks of which form the guide surfaces (48) for the chain links (12) of the chain (11). [5] Device (10) according to claim 4, characterized by , that a contour of the through-hole (47) is adapted to the transversely summed outlines of at least two chain links (12). [6] Device (10) according to any of the preceding claims, characterized by , that the device (10) has an openable housing (13) in which a test passage bore (18) is formed, which extends from a first side (16) of the housing (13) to an opposite, second side (17) of the housing (13). [7] Device (10) according to claim 6, characterized by, that the magnet arrangement (20) and the sensor arrangement (24) are housed in the housing (13) and are arranged at least partially around the test passage bore (18), wherein the guide device (19) is preferably arranged at least partially in the test passage bore (18). [8] Device (10) according to any of the preceding claims, characterized by , that the evaluation unit is set up to fuse the measurement data (31) of the magnetic field sensors (25) with the recorded path length (33) of the length measuring device (27) in such a way that at least a three-dimensional measurement image of the recorded magnetic field strength in the circumferential direction and in the longitudinal direction of the chain (11) can be generated. [9] Device (10) according to any of the preceding claims, characterized by , that the evaluation unit (30) is set up to detect error patterns (49) in the three-dimensional measurement image (52) that indicate a defect (49) in the chain (11). [10] Device (10) according to any of the preceding claims, characterized by , that the length measuring device (27) has at least one measuring wheel (28) or magnetic field sensors (53) in the chain direction (45a) which is designed to roll or detect on the chain links (12) of the chain (11) during relative movements between the device (10) and the chain (11). [11] Device (10 according to claim 10, characterized by , that the measuring wheel (28) of the length measuring device (27) can be arranged outside the housing (13) of the device (10) in such a way that the measuring wheel (28) can roll onto the chain link back (12) of the chain links (12) which are aligned in the same direction. [12] Device (10) according to claim 10, characterized by, that the measuring wheel (28) of the length measuring device (27) can be arranged such that the measuring wheel (28) can roll in a groove formed by the alternately aligned chain links (12) in the clearance space of the chain in the transverse direction. [13] Device (10) according to any one of claims 1 to 12, characterized by , that the radius of the measuring wheel (28) is greater than the length of the individual chain links (12). [14] Device (10) according to any of the preceding claims, characterized by , that the device (10) also has a storage unit (37) and a communication interface (35) which are configured to temporarily store the measurement data (31) of the sensor arrangement (24) and the length measuring device (27) as required and to send this data to the evaluation unit (30). [15] Method for magnetic testing of a chain (11), comprising: - Arranging the chain (11) to be tested in an axial section (21) in which a magnetic field (22) is formed, wherein the chain (11) preferably extends longitudinally in the formed magnetic field; - Detecting the magnetic field strength with a plurality of magnetic field sensors (25) of a sensor arrangement (24) in a sensor area (43) at a third axial position (44) of the axial section (21) arranged between the first and second axial positions (41) on a line (26) encircling the chain (11); - Determining the relative path length (33) between the sensor arrangement (24) and the chain (11); - Assigning the measurement data (31) of the magnetic field sensors (25) to a circumferential position (32) and the detected path length (33) and preferably creating an associated, spatially resolved measurement image (52); as well as - Detecting defects (48) in the chain (11) in the associated measurement data (31).

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