FI79192B - SENSOR FOER MAETNING AV FOERAENDRINGAR I MAGNETFAELT. - Google Patents

Description

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The present invention relates to a sensor for measuring a change in a magnetic field, e.g. by indicating a distance to a magnetically conductive object or a distance between magnetically conductive objects.

It is already known to determine the distance to a magnetically conductive object by measuring the change in the magnetic field.

DE-A-21 02 058, for example, discloses a nozzle with a ferromagnetic conductor in its sheath. An annular magnet is placed in the nozzle, which generates a magnetic field which flows from the north pole of the magnet through a conductor, a pole shoe and a focusing point with a measuring element back to its south pole. The measuring element thus provides a direct measurement of the distance between the conductor and the pole piece. The disadvantage of this direct measurement form is that the measuring element must be located on a magnetic track and that such a position is not always possible, e.g. due to lack of space or because the measuring element may be damaged.

For example, DE application publication 14 73 854 also discloses continuous monitoring of the distance to the drive shaft by means of Hall generators with a large axial clearance. According to this publication, the shaft is provided with magnetic bands spaced apart from each other and having opposite polarities. At a certain distance from the shaft is the Hall generator. The hall generator thus directly measures the magnetic field between the magnetic bands and thus senses the axial clearance. In this construction, the shaft must be made of a non-magnetic material.

2,719,192 SE 30-211 discloses an apparatus used in a disc refiner to measure the distance between discs. This device uses magnets and coils located on the circumferences of the discs, and the magnetic field between them indicates the distance between the magnet and the coil and thus the distance between the discs. Thus, the distance between the discs is measured at their perimeters, but not the air gap between the refiner segments. Since the coils provide a pulsating output signal, it has been considered necessary to use an expensive oscilloscope to read the output signal. This known device is also an example of direct sensing of a magnetic field, the magnitude of which depends on the distance. The possible wear of the magnet therefore affects the measured distance.

Another known distance measurement method is disclosed in SE patent 359 644. This method uses a direct measurement of the magnetic field between the objects in question and a comparative measurement in a second magnetic circuit. A disadvantage of this method is also, in principle, that the measuring sensor must be placed directly in the field between the objects between which the distance is to be determined.

According to U.S. Patent 3,849,724, two signals are used to determine the distance between two magnetic objects. Here again, it is preferred that at least one sensor is located in the main magnetic field, but that the second sensor is also located in the leakage magnetic field. The disadvantage of this type of measurement method is the same as in all the other methods mentioned above, and the method also requires complicated electronic equipment.

SE patent application 7 612 348-7 discloses a method for indicating the position of moving parts by means of a Hall generator. This known method uses two permanent magnets and a Hall generator interposed between the magnets. The disadvantage of this known method is that it 3 79192 cannot be used to measure the distance to an object or to measure the distance between two objects. It also requires two permanent magnets in the symmetry fields where the Hall generator must be located. Similar symmetry arrangements with two cooking magnets are also used in other contexts as signal sensors, see eeim, article "Contacting Sig-nalgeber mit beriihrungsloser Betätigung durch Eisentei1e", by H.J. Lippmann, pages 367-372 in ETZ-A Θ3 (1962): 11. The signal sensor shown in this latter publication can only be used if the object is approaching the signal sensor and not to measure the distance to the object or the distance between two objects. It also uses two permanent magnets.

The main object of the present invention is to provide a simple and uncomplicated sensor for determining the distance to a magnetically conductive object or for determining the distance between two magnetically conductive objects by avoiding complicated electronics.

Another object of the invention is to provide a sensor which does not require a field sensor placed in the main magnetic field and which can participate in the wear, e.g. between grinding discs, without significantly changing the measurement result.

The present sensor for measuring the distance to a magnetically conductive object is characterized by what is described in more detail in the characterizing part of claim 1.

Other preferred embodiments of the invention are set out in the dependent claims.

The following invention will be described in more detail by means of an exemplary embodiment with reference to the drawing, in which: Figures 1a and Ib show the principle of a sensor structure with a magnetic object close to and far from the sensor, Figures 2 and 3 show different alternative embodiments of the sensor of Figure 1; , Fig. 4 shows in principle a sensor solution used and placed outside the discs between which the air space is to be determined, Figs. 5 and 6 show alternative sensor forms, Fig. 7 shows an embodiment of the invention, Fig. 8 shows the embodiment of Fig. 7 with the magnet in a different position, and Figs. show the measurement sensitivity curves of the arrangements of Figures 7 and 8.

According to Fig. 1, a magnetically conductive object to which the distance is to be determined, for example, is denoted by reference numeral 1. A permanent magnet 2 is placed between two magnetically conductive metal bodies or cores 3, 4 which control the magnetic flux of the magnet 2. The field of the magnet 2 must be adapted to the magnetic conductivity of the leak-guiding metal pieces 3, 4. The magnet 2 generates two magnetic fields, one of which passes from the north pole of the magnet 2, denoted N, through the metal body 3, the air gap 9, the object 1, the air gap 10 and the second metal body 4 to the south pole S of the magnet 2. through the air gap 11 and the second metal piece 4 to the south pole S of the magnet 2. An Hall generator or other device for sensing the magnitude of the magnetic field is placed in the air gap 11. The hall generator 5 or other device can in principle be located in any other field, but the preferred location is shown in Figure 1. The wires not shown pass from the Hall generator to some sort of pointer and / or processing unit to indicate a field change in the air gap 11.

When the sensor according to Fig. 1b is placed close to the magnetically conductive object 1, as shown in Fig. 1a, the two magnetic fields change relative to each other so that the field passing through the Hall generator 5 decreases to an extent dependent on the size of the gaps 9 and 10, te. the distance between the object 1 and the ends of the metal pieces 3 and 4.

In the embodiment shown in Figure 2, the sensor is mounted on a fixed or possibly rotating grinding disc 15, which is intended, for example, to grind the substance together with the rotating or fixed disc 1. Here, the sensor is embedded in the non-magnetic material 6, and the ends of the magnetically conductive metal pieces 3 and 4 are notched or chamfered at 13, 14 as shown in Fig. 2 so that the resistance of the sensor to magnetic flux is kept substantially constant. the grinding sides of the sensor wear.

The notch or bevel of the metal pieces or cores 3 and 4 affects the magnetic resistance, because if the metal pieces 3 and 4 wear at their ends, the magnetic resistance of these metal pieces decreases as they shorten. This decrease in magnetic resistance is compensated by a corresponding increase in the distance between the ends of the metal pieces 3, 4. Thus, the distance between the ends of the metal pieces 3, 4 increases as their ends wear, as a result of which the magnetic resistance of the magnetic circuit passing from the north pole of the magnet 2 through the metal piece 3, the air gaps, the member 1 and the metal piece 4 to the south pole remains unchanged. in the notched or chamfered area of metal pieces 3 and 4.

Figure 3 shows a second sensor path section in which the "metal body" 3 'belongs as an indivisible part to the refining disc 15', which is also preferably a magnetically conductive member. In addition, the metal body 3 'has an inwardly extending portion 13' for the same reason as the notches or chamfers 13, 14 shown in Fig. 2. The sensor is further provided with a metal body 4, 6 79192 embedded in the non-magnetic material 6 '. Within the surfaces 1 of the disc 15 'and the adjacent surface 1 of the metal body 4', the effective length of the metal body 4 'and the thickness of the disc 15' shorten, but the distance between said ends increases, leaving the magnetic resistance of the sensor substantially unchanged.

Fig. 4 shows an embodiment of the sensor according to Fig. 1, in which the grinding clearance between two mutually rotating discs 7 and Θ must be indicated. It should be noted that the sensor does not need to be mechanically connected or connected to the refining discs 7 and 8 in any way. If the distance between the metal body 4 and the disc 7 and the metal body 3 and the disc 8 is substantially constant, the Hall generator 5 reading will be proportional to the refining segments. 17, 18 for a change in the grinding clearance between opposite surfaces.

In Figs. 5 and 6, the permanent magnet 2 according to the other figures has been replaced by a magnetically conductive body 12, and the magnetically conductive bodies 3 and 4 are placed inside the permanent magnets 19, 20. In this way, e.g. provided that the sensor is less sensitive to the surrounding material, so that the permanent magnets 19, 20 act to some extent as protection against the effects of the surrounding material.

According to Fig. 6, the magnetically conductive body 12 is provided with a winding 16 through which a constant but adjustable direct current can flow to generate a constant auxiliary magnetic field, so that in this way, for example, the effective measuring range of the sensor can be changed. Obviously, the metal body 12 and the coil 16 can be replaced by a permanent magnet if desired. The outer, magnetically conductive shield 25 prevents the surrounding electric fields from interfering with the measurement. In Figure 5, the cover 25 is located separately from the magnets 19 and 20, and in Figure 6, the cover 25 contacts the surface of the magnets 19 and 20.

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Fig. 7 shows a sensor according to the invention, in which the Hall generator 5 is mounted at the end of a magnetically conductive, rod-like member 21, said member being coaxially arranged inside the outer, magnetically conductive member 23. A permanent magnet 22 is positioned between the rod 21 and the outer cylindrical member 23 so that it can slide in the axial direction of said rod and the outer cylindrical member 23. The magnet 22 may have an intermediate fit between the rod 21 and the outer cylindrical member 23 so that it remains in place where it is placed by frictional forces, or it may be fixed in place permanently, for example by means of glue.

The entire sensor arrangement of Figure 7, surrounded by an outer, magnetically conductive member 23, can be fitted as a unit, e.g. in a hole in a disc or the like, so that the surrounding electric fields have very little, if any, effect on the measured values obtained. Figure 7 shows the sensor unit next to the surface 1 to which the distance is to be measured. In Figure 7, the hall generator is shown connected to a pointing device 24, such as a voltmeter.

Fig. 9 shows a measurement curve obtained from the sensor of Fig. 7. In Fig. 9, the horizontal axis shows the distances in mm to one magnetically conductive object or non-magnetically conductive object as measured by a magnetically conductive member placed on the distal side of the object to be measured. The vertical axis represents power in volts from the Hall generator. In addition, it is also possible to measure the thickness of a thin, magnetically conductive plate using such a large magnetic field that the plate does not become saturated, whereby the reduction of the output signal from the Hall generator 24 is an indirect measurement of the plate thickness.

By moving the magnet 22 to a different axial position along the rod 21 and the outer cylindrical member 23, the measurement curve obtained from the Hall generator 8 79192 can be varied. In Figure 8, the magnet 22 is shown in an intermediate position along the length of the rod 21 and the outer cylindrical member 23. Fig. 10 shows a measurement curve obtained from a Hall generator for the embodiment shown in Fig. 8. The different axial positions of the magnet 22 result in differently inclined measurement curves. Depending on the distances to be measured in each case and the desired sensitivities for different distances, the axial position of the magnet can be varied. The magnet can be located in any position between the ends of the magnetically conductive members 21 and 23.

Either the ends of the rod 21 or the outer cylindrical member 23, or both, may be chamfered or notched, as shown in Figures 2 and 3, so that the sensor has a substantially constant magnetic resistance during use of the ends.

Claims (3)

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