DE4133365A1 - Contactless measurement transmission system for machinery with rotating parts, rollers, drums - using permanent magnet, exploits temp. dependence of field in connection with magnetoresistance bridge circuit containing components having opposite coeffts. - Google Patents

Abstract

The measured value is transmitted from a moving machine part to a stationary receiver by variation of the field of a permanent magnet through the mechanical displacement of an auxiliary Fe core or yoke with temp. compensation by a thermally coupled magnet. The processing circuit includes a magnetoresistive measuring bridge (22) fed from an AC generator (21). An AC amplifier (26) with a tuned filter (27) is connected in one diagonal and DC-compensated by a potentiometer (23) in parallel with the bridge. ADVANTAGE - Measurements of temp., pressure, displacement, speed or acceleration can be transmitted easily and without any consumption of electrical energy.

Description

In technology, there is always a demand moving after the measured value acquisition Machine parts, such as rolls, containers (autoclaves) etc. Temperatures were previously either with thermocouples or similar or measured without contact with pyrometers.

With direct measurement with thermocouples, Pt 100- Resistors or other temperature-dependent components the problem arises in the transmission of measured values from the moving machine part to a fixed station. Slip rings are prone to failure and for thermal voltages of only a few mV not suitable, also brings every transition point a falsification from one metal to another due to additional thermal voltages.

Telemetric transmission of measured values would be an alternative which however has a power supply on it moving assembly. Apart from this, one thing is that telemetry transmitters are expensive anyway Power supply is often not easy to install. It is also necessary to check whether there are telemetry transmitters at the possibly prevailing temperatures there can still work.

Pyrometers are also expensive because they are mostly have expensive lens systems for focusing that Reception sensors expensive depending on the temperature range are and usually a complex evaluation electronics desire. They are also prone to failure neighboring temperature radiators or background radiation. The emission factor also changes with non-homogeneous surface and falsified thus the measurement result.  

It is an object of the invention, a simple other Possibility to specify contactless measurement.

It is known that permanent magnets are partially a considerable temperature dependence in both B and especially in the H field, which on the one hand compensated and on the other hand exploited here shall be.

However, this is not with any permanent magnet possible because other effects are disruptive here to make noticable:

The temperature dependency is divided into one reversible and irreversible change. The former it is important to use, to avoid the latter, especially since this still contains a portion that is due to metallurgical or chemical-structural changes becomes. Through artificial pre-aging of approx. 6 to 10 temperature cycles Turn off effect to a large extent.

The other effect of the irreversible change due to temperature is a thermally induced "self-discharge" of the magnet, which can be simplified in such a way that at higher temperatures the "Weiss areas" become more mobile due to increased vibrations of the crystal lattice. Since with a bar magnet the field lines do not all meet the face perpendicularly, but e.g. If you enter the rod jacket at an angle in advance, the "Weiss districts" can tip over particularly easily, so that the magnetization becomes weaker and weaker over time (see Fig. 1). There are two ways to counter this effect:
1. By choosing the right magnetic material. The larger the coercive force H _C , the more resistant the magnet system is against demagnetization, e.g. B. rare earth magnets, especially samarium-cobalt magnets or neodynium-iron-boron magnets.
2. By artificial aging of the magnets in a slowly decreasing alternating field, the max. must be as large as the highest interference field to be expected. Unstable "Weiss districts" are brought into a stable position by repeated polarity reversal.
3. By choosing the right working point. The working point depends on the geometry of the magnet. With a long magnet with a small air gap it approaches the remanence point B, with a short magnet and a large air gap with the point H _C on the abscissa axis (coercive field strength).

At this point, the requirements contradict each other and the best possible compromise must be found: permanent magnets have their greatest temperature coefficient in the direction of the H field. This is particularly favorable for the sensor in the form of a magnetoresistive sensor that only responds to the H field. At this point of operation, however, the magnet is exposed to the strongest irreversible influences, since the design here is very short and has a large air gap (see Fig. 1). However, it is thermally most stable when the working point is as close as possible to point B (see Fig. 2) of the characteristic. Here, however, the temperature coefficient is approximately 10 times smaller than in the H field. Therefore, as a compromise, an operating point should be chosen that is somewhat above the kink point of the demagnetization characteristic at the highest temperature to be measured. Here the self-demagnetization is still very low and amounts to approx. 0.1% in 10 years. However, this presupposes that the magnets are not operated to the limit of their thermal load capacity, but only about halfway, ie that for a measuring range up to 250 ° C the magnet must have its normal working range up to approx. 500 ° C. Since the max. Working temperature for magnets is 250 ° C is the upper limit of the measuring range.

In principle, the working point of the magnet must be above the break point for two reasons:
1. To keep the irreversible losses low, which is particularly important if he is operated a lot in the high temperature range.
2. To keep the non-linearity of the temperature curve within limits. This can be seen clearly from the demagnetization curve ( Fig. 3) when considering the various working curves and is shown separately in Figs. 4 and 5 for the B and H fields.

As can be seen from the characteristic curves in Fig. 4 and furthermore, the temperature effect for both the B and H fields above the break point is relatively weak compared to the total field strength, which would mean a high compensation of the basic field strength with a high amplification at the same time of the useful signal.

A much higher temperature dependency and thus better measurability is obtained when choosing the working point below the kink, e.g. B. with a length / diameter ratio of 0.25 according to Fig. 3. Here, however, the demagnetization of the magnet must be observed. Modern samarium-cobalt magnets also have an astonishing stability in this area, but they have to be taken into account on a case-by-case basis. B. once a year, which is easily possible due to the microprocessor that is required anyway, as will be shown later.

In addition to temperature detection, a magnet can also be used as a sensor for other measured variables: all measured values can be used for this purpose, which by their nature can cause the magnet's iron yoke to shift, and thus a change in field, in particular:
Path, force, pressure, speed, acceleration etc.

In order to change the way of the Eisenjoches regardless of the temperature, two measurements are to be taken two identical magnets necessary, one for temperature detection, the second to record the yoke change. In addition to the temperature measurement also compensation for the influence of temperature the yoke change measurement. Are located both magnets on one on one another Sensor moving body, e.g. B. on one rotating disc or wheel, so both can Evaluate magnetic field strengths with a sensor so that also changes in temperature or aging of the Sensor fall out.

When using two identical magnets for the Temperature and the yoke change can be measured Field for the yoke movement only ever smaller than with temperature measurement. So it is from a microprocessor recognizable, in addition is forward / backward detection is possible. Several measured values can be transmitted in that correspondingly several of these units in a row are switched, with a temperature sensing magnet must always be there as a reference. With everyone Passing the magnets past the sensor becomes a measured value transmitted without a power supply the moving machine part got to. One can also be used with several measuring magnets Continue to perform forward / backward detection with a clever asymmetrical arrangement of the temperature measuring magnet, if necessary, two or more use this as coding.

The acquisition and transmission of measurands that do not Can cause displacement of the iron yoke achieve themselves by doing something that is known per se and a tracking system suitable for this purpose, e.g. B. with a small motor or other suitable Device is used, the mechanical  Changes in the Eisenjoch effect. Can be disadvantageous here, however, a necessary energy supply for the after-run system. The Eisenjoch not necessarily made of iron, but can also, for example, a magnetic liquid be or a reversible structural change that causes a change in the magnetic field. Can too instead of the after-run system, a current-carrying one Coil are used, whose current is proportional to the measured value is.

All known magnetic field sensors are suitable as magnetic field sensors in different ways: coils with appropriate evaluation, as z. B. in the Font DT 22 19 780 B2 is described, according to Art the "Förster probe", based on the principle of the magnetic amplifier or similar principles. These are all applicable, but do not meet the expectations modern sensor technology because it is too big in itself are. Semiconductor components such as magnetic diodes or Hall sensors, as an analog component, have the disadvantage that as a semiconductor it is itself temperature dependent are and a correspondingly complex compensation circuit require. Favorable for this application is a magnetoresistive sensor as a bridge circuit, possibly as a half-bridge, since it is independent of temperature at high common mode field strengths very much is sensitive. Therefore, he is only in the considered further, although all other sensors mentioned can also be used can and do not affect the principle of the invention.

Thus, according to the task, a simple procedure is specified after being touchless in some cases and mostly without energy supply measured values of one moving machine part on a fixed part (Scaffolding, frame, bearing block or similar) transferred.

Fig. 1 shows the field line course of the known bar magnet 1 . The indicated field lines 2 are intended to make it clear once again that the field lines 2 emerge not only at the pole faces 3 (north pole) and 4 (south pole), but also at the ends of the rod beforehand, and not perpendicular to the surfaces of the magnet , but in the way indicated. This makes it clear that Weisssche districts, which are furthest to the center of the rod, fall into an undirected state due to vibrations of the crystal structure at higher temperatures during cooling and thus weaken the magnets and thus cause slow demagnetization at every temperature cycle.

Fig. 2 recalls the known hysteresis curve of a magnet and shows Quadrant II, which is only shown in the following curves. An initially non-magnetized ferromagnetic material initially follows the new curve 5 when introduced into a constant magnetic field until the magnet is saturated. When the external field H slowly decreases, the induction B also decreases according to the demagnetization curve 6 . If the external field disappears, the remanence B remains and only when the polarity is reversed does the magnet discharge and polarize in accordance with. Curve 6 around. A renewed weakening and subsequent polarity reversal then takes place according to. Characteristic curve 7 .

Fig. 3 shows the characteristics of an industrially manufactured neodynium-iron-boron magnet in the 2nd quadrant of the characteristic field with the temperature as a parameter. As expected, at the highest temperatures of 140 ° C (curve 12 ) the B-field and the H-field are the smallest due to the higher lattice mobility and the largest at curve 8 (-20 ° C). Curves 9 , 10 , 11 are intermediate values at + 20 ° C, + 60 ° C and + 100 ° C.

The working lines 13 are drawn in the L / D ratios from 0.1 (very flat straight line) to 4.0 (steepest straight line). If one follows the intersection points with the individual temperature curves on the respective working straight lines, it is found that in the region of the operating points greater than 2.0 and less than 0.25 the distances to the individual temperature curves are relatively constant, while in the region of greater than 0.25 up to approx. 1.5 the distances are very different due to the kinks in the temperature characteristics, ie, in the area of the working line from 0.25 to 1.5, the induction or field strength as a function of the temperature are purposefully strongly non-linear.

This behavior is shown in Fig. 4 for induction B: curve 14 corresponds to the working line for L / D = 4.0. Although it is sufficiently linear, the change with temperature is relatively small. Curve 15 corresponds to the L / D ratio 0.75 and runs through the break points of the B / H characteristic curves. Accordingly, the B / T characteristic has a kink area that is at least more difficult for the evaluation. Curve 16 applies to the straight 0.25. It is again somewhat linear with a good stroke of the induction over the temperature, but again with the disadvantage that it is actually in the forbidden range in which the self-demagnetization is greatest.

Fig. 5 corresponds to Fig. 4, but the H field is shown instead of the B field. Curve 17 applies to the working straight line 0.25, curve 18 for the working straight line 0.75, 19 for 2.0 and 20 for 4.0. Because of the small change above the temperature, the operating point 4.0 is of little use, curves 18 and 19 can be used in restricted areas and curve 17 can be used over the entire temperature range, provided that the magnet can still work with sufficient stability in the forbidden area .

Fig. 6 shows a possible and advantageous design of an evaluation circuit with a magnetoresistive measuring bridge, although, as already mentioned on page 6, lines 12 to 31, other circuits can be used.

The magnetoresistive bridge circuit 22 is fed by an AC voltage generator 21 . In this case, an AC voltage is taken from the bridge diagonal of the sensor 22 , which changes when it is introduced into a magnetic field. This change is caused by the fact that two resistors present in pairs react in opposite directions to the magnetic field, e.g. B. the resistors 24 are larger in the magnetic field, the resistors 25 correspondingly smaller. The different behavior is shown by different hatching. The AC voltage drawn diagonally at the bridge is fed to an AC voltage amplifier which is known per se and which can additionally be provided with a filter 27 which is matched to the generator frequency, so that only this frequency is passed and effectively suppresses other interference voltages. Since the sensor 22 is exposed to a strong DC field by the magnet, the change of which, however, is of interest for the measurement, this DC field is compensated for by an additional connection of an AC voltage, which can be set with the potentiometer 23 . This potentiometer 23 is supplied with voltage parallel to the sensor bridge 22 , so that voltage changes of the AC voltage generator have little effect. The use of AC voltage for the supply of the bridge circuit has the parts known per se that the temperature drift of the amplifier circuit and falsifying thermal voltages that can arise at the various contact points are ineffective. So this amplifier can be made relatively simple. For further processing of the AC voltage signal, it is generally necessary to rectify it (rectifier 28 ).

These circuits known per se can be selected differently depending on the accuracy to be achieved. The rectified signal can either go directly for further processing via output 32 or be linearized beforehand and then go to output 31 . The linearization is preferably done via an analog-to-digital converter 29 and a microprocessor or via a linear re known in abundance, or also by one of the newer freely programmable logic circuits in a known manner. If the circuit acc. Fig. 6 used, the existing microprocessor can automatically compensate the DC field at a defined temperature by replacing the variable voltage tap of the potentiometer 23 by a digital / analog converter and the processor readjusted until the adjustment to zero or one other defined value has occurred.

The possibility shown on page -4-, line 31 to page -6-, line 10, to transmit further measurement signals of distances, pressure, acceleration or similar is shown in Fig. 7 as a function of the H field with the L / D ratio (change in path or shear) is shown. The H field change is also dependent on the temperature as a parameter. Curve 33 shows the course at -20 ° C, curves 34 , 35 , 36 and 37 respectively increase by + 40 ° C to + 140 ° C. From the curves it can be seen that only the range from 1.5 to 4.0 is suitable for this task: Below 1.5 the temperature influence is too high, above 4.0 the change in rim thickness is too small, but the stroke is possible here large enough to carry out measurements by changing the shear in a sufficiently large area.

Figs. 8.1 to 8.4 show basic arrangements with which a movement measurement is possible. Fig. 8.1 and Fig. 8.3 are arrangements for a straight movement, the arrangement Fig. 8.2 and Fig. 8.4 for a rotary movement.

Fig. 8,1 consists of a magnet 43 and a ferromagnetic rod 39 behind it. When this rod 39 is moved in the direction of arrow 42 , the shear line of the magnet changes in the characteristic field. This change is recorded by the sensor 22 . For the practical implementation of the arrangement, it is advantageous to support the ferromagnetic rod with a spring against the magnet so that the rod is not attracted to the magnet and the measurement is falsified. It is necessary to use a spring with a progressive characteristic curve (e.g. due to different pitch in a spiral spring) that counteracts the forces of attraction in every position. The arrangement can be mechanically held z. B. by a pot 40 with a collar for receiving the coil spring 41 and an outer shell 38 , on the bottom of which the magnet 43 is attached.

Fig. 8.2 shows a rotating bar magnet 43 in two positions, which changes the field due to the rotation (see also Fig. 9 upper right curve), which in turn is picked up by sensor 22 .

Figures 8.3 and 8.4 show two examples in which the sensor is arranged in a variable air gap in an approximately closed magnetic circuit. The magnet lies in series with an iron yoke 44 and a ferromagnetic (iron) pipe piece 45 , into which a further arrangement 47 is guided, which move in accordance with the pipe. the arrow direction 48 leaves and thus causes the change in the air gap.

Fig. 8,4 shows a similar arrangement in which the field is changed by a rotary movement. The iron yoke 44 is provided with an axis 49 about which the part 50 rotates in the direction of the arrows 51 . The field change is again detected by sensor 22 .

These are just a few basic examples of the change in the magnetic field depending on the space possibility in a specific application under can be different. Therefore, another arrangement do not touch the basic idea of this teaching, e.g. B. by swapping the yoke and magnet or the like.

In Examples 8, a second magnet of similar design in the vicinity and thermally coupled is necessary to compensate for the influence of temperature in any case. An example of this is shown in Fig. 10, in which the temperature measuring magnet 55 and an arrangement 56 for measuring a mechanical quantity are mounted on a wheel (shown here as an arc). The arrangement 56 corresponds to the figure 8.1. The measurement is again taken with the fixed sensor 22 . The diagram below shows the schematic signal curve for the temperature value 57 and the mechanical measured value 58 . With the same magnets for temperature and mechanical size, the temperature value according to Fig. 3 or Fig. 7 are the largest, because when adding an additional iron core, the shear line becomes steeper and the H field becomes weaker. This makes forward / backward detection easy.

An interference field influence 59 can easily be found out and deducted from the processor if the interference field was present for most of the revolution and was stored by the processor during this time.

Fig. 9 shows another way to use two different magnetized disks 52 and 53 for accurate rotation angle determination according to the type of resolver. The accuracy of the simple sinusoidal curve during a revolution with the magnet 52 can be increased by superimposing it with a disk 53 which has been magnetized more than once, as was previously used for resolvers. (Today mostly replaced by digital detectors.) When storing the maxima of the field strength of one of the two magnets, u. U. to be dispensed with another Tempe raturmeßmagneten.

The measured value is recorded again with the sensor 22 . The more magnetic circuits are arranged on the disk 53 , the greater accuracy can be achieved with the arrangement.

Claims (42)

1. Measured value transmission system for the contactless transmission of measured variables from a moving machine part to a fixed receiver without energy supply to the moving part, characterized in that a magnet is used to detect the measured variable, the change in the magnetic field by the measured variable is used to transmit measured values . 2. Measurement value transmission system according to claim 1, characterized characterized that all those as measured variables are suitable, the mechanical displacement an additional iron core (yokes) NEN, especially pressure, paths, speed, loading acceleration or the like or the back to these sizes can be performed. 3. Measurement value transmission system according to claim 1 and 2, because characterized in that to compensate for the tem temperature influence a second thermally coupled Magnet is used which influences the field change due to the measured variable is not exposed. 4. Measurement value transmission system according to one of the claims 1 to 3, characterized in that the detection the temperature to compensate for the other measurand ß itself is used as a measurand. 5. Measurement value transmission system according to one of the claims 1 to 4, characterized in that the temperature even as the sole measurand with only one magnet ten is transmitted.   6. Measurement value transmission system according to one of the claims 1 to 5, characterized in that for the Erfas solution for each individual measured variable, a separate Em pfangsystem is established. 7. Measurement value transmission system according to one of the claims 1 to 6, characterized in that the individual Measured variables in succession from a single measured value recording system recorded and until the next Measured value is cached when the individual Measuring magnets due to the movement of the measured Machine part ge past the recording system leads. 8. Measurement value transmission system according to one of the claims 1 to 7, characterized in that for the on taking the magnetic field all known magnetic field Measuring methods can be used, such as or coils through which alternating current flows, so-called "foresters probes ", Hall sensors, magnetic diodes or transis gates or resistors dependent on the magnetic field. 9. Measurement value transmission system according to one of the claims 1 to 8, characterized in that the magnetic field preferably a resistance measuring bridge from two oppositely acting opposites Stand materials is used, so that by a external magnetic field a change in the bridge slide gonal voltage is caused because these measuring bridges only influenced by the strongly temperature-dependent H field to be flowed. 10. Measurement value transmission system according to one of claims 1 to 9, characterized in that the voltage on of the bridge diagonals a DC voltage difference amplifier is supplied and the measuring bridge corresponds is operated with DC voltage or current.   11. Measurement value transmission system according to one of the claims 1 to 9, characterized in that this measuring bridge is operated with AC voltage greater than 50 Hz. 12. Feeding the sensor bridge according to claim 11, there characterized in that the change used voltage is not a multiple of the usual network frequencies zen of 50, 60 or 16² / ₃ Hz (web frequency) for Avoid interference. 13. Magnetic field measuring bridge according to claim 11 and 12, there characterized in that when feeding the measuring bridge to avoid falsification of the measurement result due to drift of the subsequent amplifier or additional thermal voltage at the contact point len for the measurement processing a known per se AC amplifier is used. 14. Magnetic field measuring bridge with subsequent AC voltage amplifier according to claim 13, characterized in that this amplifier for suppressing interference signals from the outside (interference, etc.) is provided with an additional filter which is tuned to the frequency of the generator feeding the measuring bridge ( see Fig. 6 and p. 9, line 22 ff.). 15. Magnetic field measuring bridge with subsequent voltage preparation, characterized in that the on prepared voltage via an analog / digital converter processed by a microprocessor, to make a characteristic curve correction. 16. Magnetic field measuring bridge according to claim 16, that the off evaluation instead of with a microprocessor programmable logic modules (Asics, PALs or similar) can be done.   17. Magnetic field measuring bridge according to claim 15 and 16, there characterized in that the linearization of the Output signal also with one of the known analog gene linearization circuits can take place. 18. Magnetic field measuring bridge evaluation according to one of the An sayings 9 to 16, characterized in that for Compensation of the DC magnetic component Compensation voltage switched to the amplifier becomes. 19. Compensation of the magnetic DC component of the evaluation circuit according to claim 17, characterized in that to avoid interference from fluctuations in the supply voltage for the measuring bridge, the compensation voltage is derived from this in known manner (see Fig. 6). 20. Setting the compensation voltage according to claim 17 and 18, characterized in that the setting according to a tentiometer connected to the supply voltage Po tentiometer. Fig. 6 is made. 21. Automatic adjustment of the compensation voltage according to one of claims 17 to 19, characterized records that this setting from that to Lineari provided microprocessor is made. 22. Automatic adjustment of the compensation voltage according to claim 20, characterized in that instead of the potentiometer a digital / analog converter ver is applied to the automatic compensation is controlled by the microprocessor. 23. Automatic compensation setting using the Microprocessor according to claim 21, characterized records that this compensation value digitally zero voltage-safe through EEPROMs, battery-backed RAMs, relay relays or similar is saved.   24. Measurement value transmission system according to one of the claims 1 to 9, characterized in that as temperature sensor is chosen a magnet that is one possible has low magnetic self-demagnetization. 25. Magnet with low self-demagnetization according to An Proverb 24, characterized in that it is possible has the highest possible coercive force. 26. Magnet according to claim 24 and 25, characterized net that he is preferably from samarium-cobalt alloy or neodynium-iron-boron compounds ht that these properties acc. Claim 24 and Own 25. 27. Magnet according to one of claims 24 to 26, characterized in that the shear line in the Ent magnetization characteristic field of the II. Quadrant is placed so that the shear line in the whole temperature range of interest in order to obtain a linear characteristic is obtained so that it does not run through the kink of the demagnetization curve in this area, ie in Fig. 3 for shear lines (work lines) greater than 2.0 or less than 0.25. 28. Magnet for transmission of measured values according to one of the claims 1 to 9 and 24 to 27, characterized in that the working point to avoid self-ent magnetization above the kink of the demagneti sation curve is laid. 29. Magnet for transmission of measured values according to one of the claims 1 to 9 and 24 to 28, characterized in that to achieve an age-free transmission of the measured values the magnets according to one of the known Method of stabilization either by a mag netic alternating field or more by driving through rer (up to 6) temperature cycles is stabilized.   30. Magnet for transmission of measured values according to one of the claims che 1 to 9 and 24 to 29, characterized in that for measurements on a work line smaller 0.25 a magnet with extremely low self-demagnetization tization, preferably neodynium-iron-boron magnets be used. 31. Measured value acquisition with magnets, characterized in that the measured value causes a change in the working device (shear), in particular by shifting an additional iron core (yoke) according to. Fig. 7. 32. Measured value acquisition with magnets according to claim 31, characterized in that for this purpose the characteristic curve according to Fig. 7 is preferably used in the range from 1.5 to 4.0 of the working straight line, so that the temperature influence is as small as possible and largely linear. 33. Measured value acquisition with magnets according to one of the preceding claims, characterized in that the additional iron core with a spring ( 41 ) with per gressive characteristic according. Fig. 8.1 is equipped, which counteracts the attractive forces of the magnet on the iron core. 34. Measured value acquisition with magnets acc. Fig. 8.1, characterized in that this arrangement is preferably used for measuring pressure, acceleration and smaller displacement measurements. 35. Measured value acquisition with magnets according to one of the preceding claims, characterized in that the sensor gem. Fig. 8,3 is in a changeable air gap of an iron yoke. 36. Measurement value acquisition with magnets according to claim 33 to 35, characterized in that the change in the air gap according to a rotary movement of the iron yoke. Fig. 8.4 can be done. 37. Measured value acquisition with magnets according to claim 33 to 36, characterized in that the change in Air gap through a magnetic liquid follows. 38. Measured value acquisition with magnets according to one of the preceding claims, characterized in that the magnet itself is rotated relative to the sensor to change the magnetic field by the measurement size (according to Fig. 8.2 and / or 9). 39. Measured value acquisition with magnets according to claim 37, characterized in that in order to increase the accuracy, a second magnetic wheel with several magnets according to. Fig. 9 below is used, the output signal is in turn a sine curve with accordingly the number of poles higher frequency, which is superimposed on the basic arrangement with a magnet per revolution, so that with larger output ampli tude an exact assignment is possible at any time. 40. Measured value acquisition with magnets according to one of the preceding claims, characterized in that according to an arrangement. Fig. 10 with the measuring magnet and the temperature measuring and compensation magnet in the meantime a possibly existing magnetic interference field ( 59 ) measured and can be deducted by the evaluation processor, so that interference fields have no influence on the measurement as long as it is long enough compared to the actual measuring points. 41. Measured value acquisition with magnets according to Fig. 10, characterized in that from the order of the measured values ( 57 ) and ( 58 ), which are of different sizes in a characteristic manner, the direction of rotation can be determined in a manner known per se. 42. Measurement value acquisition with magnets according to Fig. 10, characterized in that the magnets can not only be attached to the inside of a wheel as in Fig. 10, but also naturally on the outside, just as with translational movements in a line.