Method for improved demagnetisation of machines and machine therefor

Abstract

The invention relates to a method for improved demagnetization of a preferably already demagnetized machine (1) with a drive or output (3) and a shaft (2), wherein a magnetism-sensitive sensor (10) can be or is attached to the shaft (2) at a sensor measuring point (12) near a closed measuring line (11) or at a measuring point (11') to check the position of the shaft (2). According to the invention, local demagnetization of the shaft (2) in the region of the measuring line (11) or the measuring point (11'), referred to here as homogenization, is carried out by a rod core choke (20) comprising a ferromagnetic rod (21) wound with an insulated electrical conductor coil (22) and having a front end (23) and a rear end (24) facing away from it. The front end (23) is or is located near the measuring line (11) or the measuring point (11').The measuring point (11') is positioned, preferably on the measuring line (11) opposite the sensor measuring point (12), or in front of the measuring point (11'). The conductor coil (22) is supplied with an alternating current to generate an alternating magnetic field (50) penetrating the shaft (2). The front end surface (23) is either moved along the entire measuring line (11) relative to the shaft (2) by at least one full rotation or held at the measuring point (11'), whereby the alternating magnetic field (50) subsequently decays at the shaft (2). The invention also relates to a device for carrying out this method.

Description

[0001] The invention relates to a method for improved demagnetization of a preferably already demagnetized machine with a drive or output, for example a turbine, and a shaft with a cylindrical surface and an end face, wherein, for checking the position of the shaft, a magnetism-sensitive sensor, for example an induction eddy current sensor, can be or is attached at a sensor measuring point near a closed measuring line on the cylindrical surface or on the end face, or at a measuring point axially on the end face (9) on the shaft. The invention also relates to a machine with which such a method can be carried out. State of the art

[0002] Unwanted magnetism can be very disruptive. For example, shavings can stick to tools, making further work more difficult or even impossible. Furthermore, magnetism generates magnetic fields that can interfere with other devices, especially sensitive measuring instruments.

[0003] Demagnetizing devices are well-known and used in a wide variety of applications. Typically, the component to be demagnetized is exposed to a preferably low-frequency, decaying alternating magnetic field. With a sufficiently strong field, the coercive field strength of the magnetized material is reached; this is also referred to as magnetization. As the alternating magnetic field decays, the structure within the metal solidifies, ideally resulting in no detectable ferromagnetic order, i.e., no magnetism. The decay of the field can be achieved either by removing the conductor exposed to the alternating field from the component or by reducing the current used to generate the alternating field. Another method involves using the component to be demagnetized as an electrical conductor. The current flowing through the component generates a magnetic field within it.

[0004] Swiss patent CH 714207 describes a method for completely demagnetizing a ferromagnetic, elongated component of any length that is accessible from one side along its length, such as railway slides, installed metal beams, or suspension cables. The solutions described include a demagnetizing device with a rod choke or yoke, each with a larger cross-section than that of the component. A prior art coil is also described that completely encircles the component. The component can thus be demagnetized across its entire cross-section and along its entire length. This method requires at least one side of the component to be demagnetized to be completely exposed.

[0005] In US Patent 4811609, a torque sensing device, after generating a disturbing magnetic field, activates a trigger circuit and outputs a drive timing signal to a demagnetization circuit. The demagnetization circuit applies an oscillating current to a demagnetizing coil to generate a periodic, damping, oscillating magnetic field in the rotating magnetic material, the maximum value of which is greater than the coercive force of the rotating magnetic material. Demagnetization is necessary in this method because applying a pulsating magnetic field forces a change in the magnetization state of the rotating element, making accurate measurement of the transmitted torque impossible. The torque sensing device includes a crossed, coil-wound double yoke, which magnetizes the shaft itself during measurement.Furthermore, the rotating magnetic material is often magnetized due to a pulsating, disruptive magnetic field that is irregularly generated by a solenoid valve or a spark plug. Therefore, demagnetization is performed during operation in conjunction with torque measurement and depends on precise timing.

[0006] Both methods described here are designed to ensure complete demagnetization of the component down to the interior of its core.

[0007] Turbines and similar machines with a drive or output shaft include a shaft that penetrates the shaft and can be supported in various ways within the machine housing. Large machines, especially those with shafts of at least 100 or 200 mm in diameter, are very heavy and place correspondingly high loads on the bearings. Over time, shocks and vibrations cause these bearings to age, resulting in increasing play in the shaft's guidance and creating an imbalance that can lead to damage to the drive or output shaft, or ultimately to the turbine itself.

[0008] For this reason, sensors, such as inductive eddy current sensors, are used to continuously measure the deviation of the shaft's position and / or its vibrations by measuring distances. This allows maintenance work to be carried out in a timely manner before damage occurs to the turbine.

[0009] To prevent the sensor results from being distorted, the turbine or machine must be demagnetized, for which various known demagnetization methods are available. Usually, only a limit value is required, e.g., < 2 or < 8 A / cm, without a more precise definition of the demagnetization method.

[0010] It has been shown that such sensors can sometimes produce faulty readings due to residual magnetism, even after prior demagnetization. This occurs even though the required demagnetization was carried out correctly and the permissible limits for residual magnetism are met.

[0011] The often-required demagnetization of such machines prevents erosion and lightning strikes within the machine or turbine. These are caused, for example, on the turbine blades by the magnetism on the blades, which have a high relative speed around the stator. Moving magnetic fields generate unwanted electrical voltage and current, which can also flow through the moving bearings, causing them to erode. Therefore, demagnetization is at least highly recommended, if not mandatory. Description of the invention

[0012] It is therefore the object of the present invention to disclose a method, as described above, for the improved demagnetization of a preferably already demagnetized machine. The magnetism of this machine is to be modified in such a way that a magnetism-sensitive sensor used in such a machine is not disturbed by the magnetism in the machine and can consequently provide reliable measured values. This relates, for example, to a machine in the form of a turbine, pump, or generator, wherein the sensor used can be an induction eddy current sensor. The method is intended to be particularly applicable to large machines whose shafts have diameters of preferably at least 100 mm or at least 200 mm, or material thicknesses of at least 50 mm or at least 100 mm.

[0013] A further object of the present invention is to describe such a machine with which this method can be carried out.

[0014] The problems are solved by the features of the independent claims in the respective categories. Preferred embodiments can be found in the dependent claims.

[0015] It has been shown that, unlike conventional demagnetization methods, this process only requires local demagnetization at the surface, without penetrating the entire cross-section of the shaft. This localized surface demagnetization is sufficient for the sensitive sensor to function reliably again. Furthermore, it is not necessary to demagnetize the entire length, but only the area of ​​the measuring line along which the sensor takes measurements as the shaft rotates—for example, the entire circumference. This surface-level and localized process is referred to as homogenization.

[0016] The first problem is solved by a local, surface demagnetization of the shaft in the area of ​​the measuring line or point, a process known as homogenization, using a rod-core choke. This choke comprises a ferromagnetic rod wound with an insulated electrical conductor coil, with a front end and a rear end facing away from it. In particular, the diameter of the rod is smaller than the radial thickness of the shaft, for example, at most 50 mm. This ensures that the alternating field generated by the choke does not pass through the shaft. This is also advantageous because it prevents the formation of a field that could interfere with the measuring sensor.

[0017] The front end face is positioned near the measuring line or near the measuring point, preferably at or opposite the sensor measuring point, and the conductor coil is energized with an alternating current to generate an alternating magnetic field penetrating the shaft. The front end face is moved along the entire measuring line relative to the shaft by at least one full rotation or held at the measuring point. The alternating magnetic field is then allowed to decay at the shaft, either by removing the rod-core choke from the shaft or by allowing the applied alternating current in the conductor coil to decay.

[0018] The second problem is solved by a device for carrying out local, surface demagnetization, a so-called homogenization, to generate an alternating magnetic field penetrating the shaft. This device comprises a machine with a drive or output shaft and a shaft, and a closed measuring line or measuring point on the shaft where a magnetism-sensitive sensor can be or is attached. According to the invention, this device comprises a rod-core choke, which has a ferromagnetic rod wound with an insulated electrical conductor coil, with a front end and a rear end facing away from it. The front end is arranged close to the shaft at the measuring line or measuring point.The electrical conductor coil can be connected to, or is connected to, an alternating current source to apply an alternating current while the shaft is rotating or stationary. In particular, the diameter of the rod is smaller than the radial material thickness of the shaft.

[0019] Homogenization is typically performed during a service check or when the sensor detects critical values. If critical values ​​are measured again after homogenization, they are definitely due to a positional deviation. Otherwise, the initial measurement can be identified as a faulty measurement caused by interfering magnetization on the shaft.

[0020] Homogenization can be performed manually using a throttle if required. Alternatively, it can be permanently mounted and operated with the shaft rotating.

[0021] Furthermore, a complete demagnetization of the entire machine, including the shaft, can be carried out from time to time, although very rarely. This complete demagnetization is performed according to the prior art and is not, in itself, the subject of the invention. However, the invention also claims a method in which two demagnetizations must be carried out: a complete demagnetization, which is rarely performed, and a partial demagnetization of the surface, or homogenization, which is performed more frequently.

[0022] It has been found that even after demagnetization, domains can be present in the shaft of such machines. These are small magnetized regions within the structure of a ferromagnetic material, in which the magnetic moments of the atoms are aligned parallel to each other. The harder these inclusions are mechanically, the greater their magnetic coercivity. The direction of magnetization is determined by the crystal lattice of the material. Adjacent domains always differ in their magnetization direction, so they cancel each other out. Therefore, the total magnetization is close to zero. However, this only applies to regions that are far away, relative to the size of the domains. In close proximity, the domains can lead to magnetically distinct zones on the surface of the shaft.

[0023] Therefore, the local magnetizations of the domains are sufficient to interfere with a sensor that is sensitive to magnetism.

[0024] For this reason, according to the invention, in a demagnetization process, and optionally in a second process, the structure is locally homogenized near a measuring point such that these domains are reduced in size to such an extent that they no longer cause interference at the sensor. The use of a rod-core choke has proven advantageous. The alternating electromagnetic field should penetrate at least 15-30 mm into the ferromagnetic structure of the wave. However, complete penetration is not achieved. Furthermore, the area on both sides of the measuring line or around the measuring point can also be homogenized, preferably with a respective offset of up to 15-30 mm.

[0025] Since the domains recombine and merge over time, it is advisable to repeat such homogenization processes periodically. For this reason, it can be advantageous to install such a rod-core choke in the machine to perform homogenization routinely, e.g., once a month.

[0026] The rod-core choke is positioned as far away as possible from the sensor to prevent its measurement from being disturbed by the alternating magnetic field during homogenization. Additionally, a shield can be placed between the sensor and the rod-core choke.

[0027] Alternatively, the sensor can be temporarily removed for homogenization. To do this, and to save space, the sensor can be inserted into a central recess in the ferromagnetic rod and removed again for homogenization.

[0028] It is noteworthy that the wave is homogenized only locally within the area of ​​the measurement line or point, while the rest of the wave, after any initial demagnetization, undergoes no further homogenization, as this homogenization is performed only locally. The described local homogenization is therefore a very successful, simple, reliable, and cost-effective method for solving the aforementioned problem. Furthermore, the locally available mains frequency of 50 or 60 Hz can be used to generate the alternating field in the coil, which simplifies its application.

[0029] It is important to ensure that the front end face is always spaced away from the shaft. This can be achieved using a non-metallic spacer, such as a plastic part, attached to the front end face. This spacer can have the contour of the shaft on its front side.

[0030] The inventive method and the corresponding device make it possible to solve the problem of monitoring a shaft in a safe and simple way in a very simple manner. Brief description of the drawings

[0031] The invention is illustrated in the following drawings and explained in more detail with the aid of the reference numerals explained later. The drawings show: Fig. 1 A schematic cross-sectional view of a machine according to the invention, suitable for carrying out the method according to the invention; Fig. 2 A schematic side view of a rod core choke; Fig. 3 Schematic views of the shaft with a rod core choke arranged at the end face; (a) on a measuring line; (b) axially at a measuring point; Fig. 4 A schematic side view of a machine during the execution of a first magnetization. Ways to implement the invention

[0032] In Fig. 1Figure 1 is an example of a machine 1 suitable for performing local demagnetization, here called homogenization. This machine 1 comprises a drive or output 3, which can be configured as a turbine, pump, generator, or the like, and is penetrated by a rotating shaft 2. The process is particularly suitable for large machines with shafts that are at least 100 mm or at least 200 mm in diameter. In the case of hollow shafts, the material thickness is at least 50 mm.

[0033] The shaft 2 is usually supported on at least two bearings 4, with both the bearings 4 and a housing above the input or output 3 being supported on supports 5 on a solid base 6.

[0034] To check the quality of the bearings 4 of shaft 2, a sensor 10 is installed at a sensor measuring point 12. During operation, this sensor measures either the deviation of the shaft 2's position from its rest position or its vibrations. Such sensors 10 can be, in particular, induction eddy current sensors 10 or others that are sensitive to magnetism. The sensor measuring point 12 is located close to the shaft 2, so that the measuring points on the shaft 2 form a closed measuring line 11 when the shaft 2 rotates. This line is located either on a lateral surface 8 of the shaft 2, as shown in [reference missing]. Figs. 1 and 2 shown, or on an end face 9 of the shaft 2, as in Fig. 3a The sensor 10 is not needed for homogenization; it can be used later. It is sufficient if the location of the measuring line 11 is known, with the sensor measuring point 12 being close to this measuring line 11.

[0035] Alternatively, the sensor 10 can be arranged axially on the end face 9. In this case, rotation does not create a measuring line, but rather a measuring point 11', as shown in Fig. 3b depicted.

[0036] The device according to the invention comprises, in addition to the machine 1 with the shaft 2, a rod core choke 20, which is also in Fig. 2 The rod core choke 20 has a ferromagnetic rod 21 wound with an insulated electrical conductor coil 22, with a front end 23 and a rear end 24 facing away from it. The front end 23 is arranged close to the shaft 2 at the measuring line 11 or at the measuring point 11', preferably at or opposite the sensor measuring point 12. The diameter of the rod 21 is particularly smaller than the diameter of the shaft 8.

[0037] For operation, the electrical conductor coil 22 can be connected to or is connected to an alternating current source 30 to apply an alternating current while the shaft 2 is rotating or stationary. This generates an alternating magnetic field 50 penetrating the shaft 2, which in Fig. 2 is marked with an area 51.

[0038] Preferably, the rod core choke 20 is mounted on a guide 26 which allows linear movement on both sides of the measuring line 11 on the shaft 2, as shown in Fig. 2 and in Fig. 3a as indicated by arrows. By shifting the guide 26, the rod core choke 20 can homogenize the shaft 2 over a larger area 51' on both sides of the measuring line 11. This increases the size of the homogenized area, as shown in Fig. 2The area marked under the arrow on shaft 2 is homogenized during rotation, with a penetration depth of approximately 15-30 mm and a total width of approximately 30-60 mm. The remaining domains outside this homogenized ring area around measuring line 11 no longer influence a sensor 10 at sensor measuring point 12, as they are too far away.

[0039] In the case of a measuring point 11', a guide 26 can be arranged such that a continuous offset of the rod core choke 20 of preferably 15-30 mm from the measuring point 11' is achieved, whereby the area around the measuring point 11' is homogenized by rotating the shaft 2. Alternatively, a circular or spiral guide 26 can be arranged which homogenizes the rod core choke 20 in the vicinity of the measuring point 11' when the shaft 2 is stationary. The arrows in Fig. 3b symbolize this possible offset.

[0040] In a preferred embodiment, the alternating current source 30 for the alternating field in the electrical conductor coil 22 of the rod core choke 20 has a frequency of 10-100 Hz, preferably 40-60 Hz, in particular mains frequency, depending on the region approximately 50 or 60 Hz. This makes it possible to operate the rod core choke 20 directly with mains voltage and without a power supply.

[0041] Additionally, the electrical conductor coil 22 or an auxiliary coil 25 around the ferromagnetic rod 21 of the rod-core choke 20 can be connected to, or be connectable to, a DC current source 31. An additional DC current can effect further adjustment of the desired sensor signal.

[0042] The electrical conductor coil 22 on the ferromagnetic rod 21 can be positioned closer to the front end face 23 than to the rear end face 24, as shown in Fig. 2This is shown. As a result, an alternating magnetic field 50 is formed in the area of ​​the front end surface 23, the field lines of which penetrate more strongly and further into the wave 2 and only later veer off laterally than at the rear end surface 24. Therefore, the penetration depth can be increased in this way.

[0043] Preferably, a power element 32 is connected between the AC power source 30 and, optionally, the DC power source 31 and the electrical conductor coil 22, which can generate the decay of the alternating current and thus also of the alternating magnetic field 50. This is advantageous if the rod core choke 20 is not manually guided and is installed, since it cannot then be easily removed from the shaft 2.

[0044] In a particularly preferred device, the rod core choke 20 is arranged in the region of a bearing 4. In particular, if the bearing 4 has a bearing shell, e.g. made of bronze or another non-magnetic material, homogenization can be carried out through this shell.

[0045] For the application of the procedure, machine 1 was usually demagnetized as a whole beforehand. Fig. 4 A possible device is described for demagnetizing such a machine 1. For this purpose, a conductor cable 40 is wrapped several times around the machine 1 and connected to an alternating current source 30. A decaying alternating current can be generated using a power unit 32.

[0046] Alternatively, machine 1 can also be moved through a coil carrying an alternating current (not shown), whereby the effect of the alternating field on machine 1 decreases with increasing distance and thus decays. This decay is necessary to prevent any residual magnetism from developing.

[0047] The inventive method, which can be applied with a device described above, is described below. It leads to improved demagnetization of a machine 1, which may already be demagnetized, with a drive or output 3, for example a turbine 3, and a shaft 2 with a circumferential surface 8 and an end face 9.

[0048] To check the position of the shaft 2, a sensor 10 sensitive to magnetism, for example an induction eddy current sensor 10, is attached at a sensor measuring point 12 close to a closed measuring line 11 on the lateral surface 8 or on the end face 9 of the shaft 2, or at a measuring point 11' axially on the end face 9 of the shaft 2.

[0049] According to the invention, a local demagnetization of the shaft 2 in the area of ​​the measuring line 11 or the measuring point 11', here called homogenization, is carried out. This is done by means of a rod core choke 20, as is used in Fig. 2This is shown in more detail below. It comprises a ferromagnetic rod 21 wound with an insulated, electrical conductor coil 22, having a front end 23 and a rear end 24 facing away from it. The diameter of the rod 21 is, in particular, smaller than the diameter of the shaft 1. The front end 23 is or is positioned near the measuring line 11 or the measuring point 11', preferably on the measuring line 11 opposite the sensor measuring point 12, or axially in front of the measuring point 11' on the end face 9. The conductor coil 22 is energized with an alternating current to generate an alternating magnetic field 50 penetrating the shaft 2, wherein the front end 23 is either moved along the entire measuring line 11 relative to the shaft 2 by at least one full revolution or held at the measuring point 11'.Subsequently, the alternating magnetic field 50 at the shaft 2 decays, either by removing the rod core choke 20 from the shaft 2 or by the decay of the applied alternating current in the conductor coil 22.

[0050] This homogenization process breaks up the domains, resulting in a finer magnetic structure with much smaller domains. This reduces the residual magnetism acting on sensor 10 to such an extent that the interference is greatly diminished.

[0051] As described, machine 1 may have already been demagnetized beforehand. This can be done by exposing it to a decaying alternating magnetic field. As in Fig. 4This can be achieved by means of a conductor cable 40, which is wound around the machine 1 and supplied with alternating current, whereby either the alternating current decays or the conductor cable is removed from the machine to generate the decay of the alternating magnetic field. A decay can be generated by a suitable power unit 32.

[0052] Alternatively, to generate the decaying alternating magnetic field, machine 1 can be guided through a coil supplied with alternating current (not shown) and then move away from it.

[0053] In another alternative, machine 1 can be flooded with a pulsed decreasing current in direct current, with each pulse having a reversed current direction and the current decreasing to generate the decaying alternating magnetic field.

[0054] Preferably, the conductor coil 22 of the rod-core choke 20 is supplied with an alternating current of a frequency of 10-100 Hz, preferably 40-60 Hz, in particular with mains frequency, depending on the region approximately 50 or 60 Hz. Thus, it can be plugged directly into the mains and does not require a power supply.

[0055] Preferably, the rod-core choke 20 circles the measuring line 11 several times, also moving perpendicular to the measuring line 11, in order to homogenize the shaft 2 on both sides of the measuring line 11. A distance of 15-30 mm on each side of the measuring line 11 is generally sufficient.

[0056] The rod-core choke 20 can be held by hand by a user for homogenization. It can be guided around the shaft 2, or the shaft 2 can rotate for this purpose. The rod-core choke 20 can then be removed from the shaft 2 to allow the alternating magnetic field to decay slowly.

[0057] Alternatively, the rod-core choke 20 can be fixedly or slidably mounted near the measuring line 11 on the outer surface 8 or on the end face 9 of the shaft 2, preferably opposite the sensor measuring point 12, and the shaft 2 can rotate during homogenization. In this case, a power unit 32 can be attached to generate the decaying alternating current. The power unit 32 reduces the current flow in the rod-core choke 20 so that no residual magnetism develops in the shaft 2.

[0058] In particular, the rod core choke 20 can be mounted in a guide 26 that allows movement transverse to the measuring line 11. To homogenize the shaft 2, it is moved axially so that it can be displaced on both sides of the measuring line 11. This increases the homogenized area around the measuring line 11.

[0059] It is also possible to operate the rod core choke 20 permanently during the operation of the machine 1 in order to always generate homogenization through the generated alternating magnetic field 50.

[0060] In an alternative embodiment, the rod core choke 20 is arranged axially at the end face of the shaft 2 at measuring point 11', as shown in Fig. 3b The ferromagnetic rod 21 preferably has a central recess 27 for the removable reception of the sensor 10. For homogenization, the sensor 10 is removed from the recess 27 to prevent damage from the alternating magnetic field 50. Following homogenization by the rod core choke 20, the sensor 10 is reinserted into the central recess 27 to monitor the position of the shaft 2. In this way, the rod core choke 20 can remain permanently mounted on the machine 1, even during operation and during measurements by the sensor 10.

[0061] In a preferred method, the conductor coil 22 of the rod core choke 20 or an additional conductor coil 25 around the ferromagnetic rod 21 is additionally supplied with a direct current. This allows for further adjustment of a desired sensor signal.

[0062] Preferably, in this method, the electrical conductor coil 22 is mounted on the ferromagnetic rod 21 closer to the front end 23 than to the rear end face 24. This allows homogenization to be achieved deeper behind the surface of the shaft 2 with the same power of the applied alternating current. Reference symbol list

[0063] 1 Machine 2 Shaft 3 Input or output, for example turbine, pump, generator 4 Bearing 5 Supports 6 Base 7 Axis of the shaft 8 Shaft surface 9 Shaft end face 10 Sensor, e.g. induction eddy current sensor 11 Measuring line 11' Measuring point 12 Sensor measuring point 20 Rod core choke 21 Ferromagnetic rod 22 Electrical conductor coil 23 Front end face 24 Rear end face 25 Auxiliary coil 26 Guide 27 Central recess 30 AC power source 31 DC power source 32 Power section for decaying AC current 40 Conductor cable 50 Alternating magnetic field 51 Homogenized area on the shaft surface 51' Enlarged homogenized area on the shaft surface

Claims

1. Method for improved demagnetization of a preferably already demagnetized machine (1) with a drive or output (3), for example a turbine (3), and a shaft (2) with a cylindrical surface (8) and an end face (9), wherein, for checking the position of the shaft (2), a sensor sensitive to magnetism (10), for example an induction eddy current sensor (10), can be or is attached at a sensor measuring point (12) near a closed measuring line (11) on the cylindrical surface (8) or on the end face (9) of the shaft (2), or at a measuring point (11') axially on the end face (9) of the shaft (2), characterized bya local demagnetization of the shaft (2) in the region of the measuring line (11) or the measuring point (11'), here called homogenization, by a rod core choke (20), comprising a ferromagnetic rod (21) wound with an insulated, electrical conductor coil (22) having a front end surface (23) and a rear end surface (24) facing away from it, wherein the diameter of the rod (21) is in particular smaller than the radial material thickness of the shaft (2) a. wherein the front end surface (23) is positioned or is positioned near the measuring line (11) or the measuring point (11'), preferably on the measuring line (11) opposite the sensor measuring point (12), or axially in front of the measuring point (11') on the end face (9), and wherein the conductor coil (22) is supplied with an alternating current to generate an alternating magnetic field (50) penetrating the shaft (2), b.wherein the front end surface (23) is moved along the entire measuring line (11) relative to the shaft (2) by at least one full revolution or is held at the measuring point (11'), c. and wherein the alternating magnetic field (50) on the shaft (2) subsequently decays, either by removing the rod core choke (20) from the shaft (2) or by decaying the applied alternating current in the conductor coil (22).

2. Method according to claim 1, characterized by the fact that the entire machine (1) is demagnetized beforehand and thereby exposed to a decaying alternating magnetic field.

3. Method according to any one of the preceding claims, characterized by the fact that the conductor coil (22) of the rod core choke (20) is supplied with an alternating current of a frequency of 10-100 Hz, preferably 40-60 Hz, in particular mains frequency, depending on the region approximately 50 or 60 Hz.

4. Method according to any one of the preceding claims, characterized by the fact thatthe rod core choke (20) is positioned at the measuring line (11) and is moved around it several times, preferably also transversely to the measuring line (11) on the surface of the shaft (2) in order to homogenize the shaft (2) on both sides of the measuring line (11).

5. Method according to any one of the preceding claims, characterized by the fact that The rod core choke (20) is guided manually by a user for homogenization.

6. Method according to any one of the preceding claims, characterized by the fact that the rod core choke (20) is fixedly or movably attached close to the measuring line (11) on the outer surface (8) or on the end face (9) of the shaft (2), preferably opposite the sensor measuring point (12), and the shaft (2) rotates during homogenization.

7. Method according to claim 6, characterized by the fact that the rod core choke (20) permanently generates the alternating magnetic field (50) while the machine (1) is in operation.

8. Method according to any one of claims 1 to 5, characterized by the fact that the rod core choke (20) is arranged axially on the end face of the shaft (2) at the measuring point (11').

9. Method according to claim 8, characterized by the fact that the ferromagnetic rod (21) has a central recess (27) for the removable reception of the sensor (10).

10. Method according to claim 9, characterized by the fact that Following homogenization by the rod core choke (20), a sensor (10), in particular an induction eddy current sensor, is inserted into the central recess (27) to monitor the position of the shaft (2).

11. Device for carrying out local demagnetization, here called homogenization, according to one of the preceding claims, comprising a machine (1) with a drive or output (3), for example a turbine (3), and a shaft (2) with a sensor measuring point (12) at a closed measuring line (11) on the lateral surface (8) or on the end face (9) of the shaft (2) or a measuring point (11') axially on the end face (9) of the shaft (2), in which a magnetism-sensitive sensor (10) can be or is attached, characterized bya rod core choke (20) comprising a ferromagnetic rod (21) wound with an insulated, electrical conductor coil (22) having a front end surface (23) and a rear end surface (24) facing away from it, wherein the diameter of the rod (21) is in particular smaller than the radial material thickness of the shaft (2), wherein the front end surface (23) is arranged close to the shaft (2) at the measuring line (11), preferably opposite the sensor measuring point (12), or at the measuring point (11'), and wherein the electrical conductor coil (22) can be connected to or is connected to an alternating current source (30) for applying an alternating current while the shaft (2) is rotating or while it is stationary, in order to generate an alternating magnetic field (50) penetrating the shaft (2).

12. Device according to claim 11, characterized by the fact thatthe rod core choke (20) is axially attached to the end face (9) of the shaft (2) at the measuring point (11') and the ferromagnetic rod (21) has a central recess (27) for the removable reception of the sensor (10).

13. Device according to claim 11, characterized by the fact that The alternating current in the electrical conductor coil (22) of the rod core choke (20) has a frequency of 10-100 Hz, preferably 40-60 Hz, in particular mains frequency, depending on the region approximately 50 or 60 Hz.

14. Device according to one of claims 11 to 13, characterized by the fact that the electrical conductor coil (22) or an additional coil (25) around the ferromagnetic rod (21) of the rod core choke (20) is additionally connected or connectable to a DC power source (31).

15. Device according to one of claims 11 to 14, characterized by the fact that the rod core choke (20) is arranged in the area of ​​a bearing (4) which supports the shaft (2).

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