DE102007062862A1 - Method for determining position and change of position of measured object, involves arranging magnet in area of influence of sensor, which brings about change in permeability of foil - Google Patents

Abstract

The method involves applying an alternating current to a sensor coil (7) of a sensor (2). A magnet (5) is associated with a measured object (1), in a soft magnetic foil (4), whose permeability changes under the influence of a magnetic field on the basis of the magnetic field strength. The magnet is arranged in the area of influence of the sensor, and brings about a change in the permeability of the foil. The change in the permeability of the foil is used to determine the position and change of position of the measured object relative to the sensor. An independent claim is also included for a sensor arrangement for determining the position and change of position of the measured object.

Description

The The invention relates to a method for determining the position and / or Position change of a measuring object relative to a sensor, wherein the sensor is preferably acted upon by an alternating current Has sensor coil. Furthermore, the invention relates to a corresponding Sensor arrangement.

electromagnetic Sensors are widely used in technology. They become, for example for monitoring the distance between a sensor and a Measuring object, for measuring rotary or valve lift movements, for Determining the position of a piston or detecting conductive Used objects. This non-exhaustive list proves the extensive application possibilities of this sensor type.

At one of the DE 36 10 479 A1 known displacement sensor is used as a measuring object, a permanent magnet which is movable along a soft magnetic core. Around the core, two oppositely applied exciting coils and a secondary coil are wound. Depending on the position of the measurement object with respect to the sensor, a virtual air gap is generated at a location of the soft magnetic core, with the result that the voltage induced in the secondary coil changes with the position of the measurement object. The voltage is proportional to the position of the DUT relative to the sensor.

From the EP 1 158 266 A1 a displacement measuring system is known which comprises an inductive sensor, a transmitter and an evaluation unit. According to one embodiment, a magnet is used as the encoder whose position can vary relative to the sensor. The magnetic field of the magnet brings the soft magnetic material of the sensor into saturation. By this local saturation effect, the inductance of the measuring coil of the sensor, which is coupled to an oscillator whose frequency or amplitude changes is detected changes.

From the DE 203 07 652 U1 is a magnetically actuated transducer with a magnetic field sensor and along a line of movement movable magnets known. Parallel to the line of movement, a rod made of soft magnetic material is arranged, from the front side of the magnetic field sensor is arranged with its sensor direction pointing to the front side. The length of the rod and the width of the magnet determine the measuring range of the transducer.

For the contactless detection of a rotational movement of a pole wheel sensors are used with magnetoelectric transducers. Examples of this are from the US 4,926,122 A . EP 0 729 589 B1 or DE 30 41 041 C2 known. In practice, these transducers are positioned very close to the object to be measured in order to ensure high immunity to interference. At these small distances (often in the order of 1 mm), the sensor, in particular under real operating conditions, can be damaged. It is particularly important in dynamic operation to achieve a reliable detection of the rotational movement with a relatively large base distance.

Other sensors and proximity switches that utilize the saturation effect of high permeability soft magnetic materials are known from US Pat DE 38 03 293 A1 DE 38 03 253 A1 or the DE 36 10 479 A1 known. However, the response distance of such sensors is limited. In order to achieve the larger measuring ranges, the evaluation circuit must have a high amplification factor. However, this leads to large temperature-related errors and high demands on the Einbautolleranzen.

Of the The invention is therefore based on the object of specifying a method with which a position or a position change of a DUT relative to a sensor in both static and be measured in dynamic operation with high resolution can. Furthermore, a corresponding device with as possible simple construction can be specified.

According to the invention the above object by the features of claim 1 solved. Thereafter, the inventive A method characterized in that by a the measurement object associated magnets in a soft magnetic film whose permeability under the influence of a magnetic field depending on the Field strength of the magnetic field changes and that in the Influence range of the sensor is arranged, a change the permeability of the film is caused and that the change in the permeability of the film from their Reaction to the sensor and from this the position and / or Position change of the measurement object relative to the sensor is determined. Identified as determining a position or position change is the determination of an angle, an angle change or a speed measurement.

In terms of the device, the above object is achieved by the features of claim 13. Thereafter, the sensor arrangement according to the invention is characterized in that in the influence of the sensor, a film of soft magnetic material is arranged, wherein the permeability of the film under the influence of a magnetic field as a function of the field strength of the magnetic field changes and that an evaluation circuit is provided by means of the change of the Permeability of the film determined from their retroactive effect on the sensor and is closed to the position and / or position change of the measurement object relative to the sensor. Again, it should be noted that the determination of a position or position change is equated the determination of an angle, an angle change or a speed measurement.

A alternative embodiment of an inventive Sensor assembly that solves the above problem is claimed with the independent claim 25. After that is the sensor arrangement according to the invention characterized in that in the sphere of influence of the sensor a film of soft magnetic material is arranged, wherein the permeability of the film under the influence of a magnetic field changes depending on the field strength of the magnetic field and wherein a movement of the measurement object is substantially in directions takes place parallel to an extension direction of the film and that the change in the permeability of the film from their Reaction to the sensor and from this the position and / or Position change of the measurement object relative to the sensor is closed. Again, it should be noted that the determination of a Position or position change is equal to the Determination of an angle, an angle change or a Speed measurement.

In inventive way is first been recognized that a property of soft magnetic materials can be used for a highly accurate position measurement. Under the influence of an external magnetic field changed the permeability of soft magnetic materials in Dependence of the existing field strength.

These Property can be used in a sensor arrangement. For this purpose, a measurement object whose position is detected relative to the sensor to be assigned to a magnet. Rising through this magnet when approaching the DUT to the sensor or when approaching of the sensor to the test object the magnetic field strength in Area of the soft magnetic material. This decreases its permeability, which affects the properties of a near the soft magnetic Material arranged measuring element affects and over a suitable, connected to the measuring element evaluation circuit a value for the position or position change of the DUT can be assigned. Suitable measuring elements are For example, magnetic field sensors such. B. Hall sensors, AMR and GMR sensors, or inductive sensors such. B. coils of an inductive sensor or an eddy current sensor or any other measuring element, the sensitive to changes in permeability.

According to the invention Furthermore, it has been recognized that an improvement in sensitivity the sensor arrangement can be achieved in that the soft magnetic Material is formed only as a thin film. In order to the emergence of volume effects is largely avoided resulting in changes in permeability lower field strengths are necessary and shorter Time can expire. This has a favorable effect on the sensitivity and dynamics of the sensor array. Conversely leads this is because the magnetic field of the magnet associated with the measurement object In a relatively wide measuring range influence on the permeability the film takes.

at Movements between the measuring object and the sensor in directions in the Run substantially parallel to an extension direction of the film arise in the film, a region of high permeability, an area reduced permeability and a transition region between the two areas. Depending on the distance between sensor and measuring object, the transition area be moved along the slide. This will over a comparatively large measuring range across a high Influencing the measuring element causes.

From particular advantage is a sensor arrangement configured in this way, in which the magnetic field direction of the magnet of the measurement object along an axis of "heavy" magnetization of the film is. In this Case, the magnetic field of the magnet has a coupling only smaller Surface of the front side of the foil. Also advantageous is when the unsaturated region of the film is used effectively can be.

The Resolution and accuracy of the invention Sensor arrangements is dependent on the electromagnetic and mechanical properties of the film. It can, for example Films of M-metal, Vitrovac or ferrite can be used.

Advantageous is a combination of high mechanical strength and very Good electromagnetic properties, for example, through achieved the use of a film of nanocrystalline material. Among the very good electromagnetic properties include a high magnetic permeability (for example μ = 50,000 ... 500,000), a relatively small electrical conductivity and small losses in large temperature and frequency ranges.

The described effects can be inventively by use the embodiments described below. Goal of this Embodiments is to use a sensor with the largest possible Detection range to create and the highest possible sensitivity to reach the sensor.

According to the invention a film of soft magnetic material used, whose permeability change affects a sensor coil.

The change the permeability produces a detectable reaction on the coil, usually in a change of impedance the coil precipitates. The impedance or the impedance change The coil can be measured in the usual way by the sensor coil is supplied with alternating current, for example.

It However, it should be emphasized that the permeability change also with other inductive or magnetic field-sensitive measuring elements can be detected.

In Framework of an advantageous embodiment is in the vicinity the soft magnetic film in addition to the one with AC acted upon sensor coil a compensation coil arranged, which is energized with DC. This can - depending on Training and arrangement of the coil - the permeability influenced in a more or less large area of the film become. This can be used to target particularly cheap Conditions for the detection of the DUT arise allow. Is the measurement object in a relatively large Distance, so the magnetic field of the measuring object is assigned Magnets only slight influence on the film, since the sensitivity of the sensor arrangement in an unfavorable Area is located. By applying the compensation coil with a direct current can cause a shift in the sensitivity characteristic achieved and the sensitivity at a certain part of the measuring range be increased specifically. On the other hand, the Field strength have already assumed too high values when For example, the measurement object is very close to the sensor. By the compensation coil can then target the field strength be reduced, so that the sensor assembly back in one is more favorable operating condition. This way you can depending on polarity and strength of DC, the measurement range is greatly extended and the sensitivity over the measuring range can be improved. Furthermore, by Setting the magnetic field of the compensation coil Installation tolerances or slowly changing disturbances, such as temperature drift or aging, be compensated or corrected.

Both Embodiments can also be realized simultaneously, whereby the positive effects of both embodiments add up.

at the embodiment with a Gleichstromerregten compensation coil Advantageously, the DC current is adjustable. This can happen relate only to the strength of the direct current, on the other hand, its polarity could also be changed become. By adjusting the strength of the DC current leaves the degree of influencing the permeability change the soft magnetic film. A change the polarity causes the resulting magnetic field, resulting from the magnetic fields of the sensor coil, the compensation coil and the magnet of the DUT, increases or decreases becomes. This can be particularly extensive on the permeability The film influencing the magnetic field are acted upon. It could the direct current can be adjusted so that a substantially constant magnetic field of the sensor coil adjusts.

In Advantageously, the sensor, in particular before the first Commissioning, subjected to a calibration. These are preferably the following steps are performed. In a first step the measured object is relative to at a plurality of positions h positioned the sensor. The individual positions have h a step size δh. Preferably, the individual Positions arranged so that they are essentially on a common line.

At each of the positions h, an alternating current is fed to the sensor coil. As a result, the sensor coil generates an electromagnetic alternating field, which is influenced by the soft magnetic film. For each of the positions h, the impedance Z and / or the relative impedance change ΔZ / Z of the coil is determined. For this purpose, various methods are known in practice. From the values thus determined, a characteristic curve is determined which describes a relationship between the relative sensitivity S of the sensor coil and the position h of the test object relative to the sensor coil. The relative sensitivity S is given by

From this characteristic, a position h _{0 is} determined at which the relative sensitivity S assumes a maximum value. The value Z _{0 of} the complex impedance corresponding to this position h ₀ is stored in a non-volatile memory. With these steps, the characteristic curve of the sensor was determined.

In the next steps the dependence of the measurement results on the strength of the direct current is determined. For this purpose, a direct current is first fed into the compensation coil. Again, the measurement object is placed at different positions h and the impedance Z and / or relative impedance change ΔZ / Z of the coil at each position h is determined. The superposition of the magnetic fields of the sensor coil, the Kom, acts on the foil compensation coil and the magnet of the DUT. In a next step, the strength of the direct current in the measuring range ± Δh is varied. This is repeated until a predetermined and stored reference value of the impedance is reached. From the values thus determined, the dependence of the direct current on the change in position of the DUT is determined. It has been shown that in the measuring range ± Δh results in a substantially linear relationship between the position h and the DC current through the compensation coil. Therefore, in many applications it may be sufficient to determine and store only the proportionality factor between position change and direct current.

Advantageous is when the predetermined target value of the complex impedance at a The basic distance between the test object and the sensor is determined in which the position changes the object to maximum impedance changes of the coil system leads.

in the Generally, to determine the retroactivity of the change the permeability of the film to the coil their impedance or change measured. However, it should be noted that the measurement of permeability in principle to others Way could be determined. The measurement of the impedance can be done directly or indirectly. For example, when impressed a known current, the voltage drop across the coil measured and by dividing the voltage by the current the impedance be determined. However, the impedance could also be through a parallel switched capacity to a free-running Oscillator be extended, for example, via a PLL (Phase Locked Loop) circuit is controlled. From the output signal the PLL circuit can be closed to the impedance of the sensor coil become.

From the complex impedance Z of the sensor coil, the real part Re {Z} and the imaginary part Im {Z} can be determined. The determination of the real and imaginary part can be analog or digital. Corresponding methods are well known in practice. In addition, the quotient D could be formed from the real part Re {Z} and the imaginary part Im {Z}, where the quotient D holds: D = Re {Z} / In {Z}.

To A preferred embodiment of the invention is the Size of direct current through the compensation coil in a tracking control by means of a closed loop set. The quotient D can be used as a setpoint for serve the control loop, where D could be kept constant. From the imaginary part Im {Z} could be the position or position change of the measurement object relative to the sensor be determined. Additionally or alternatively could the strength of the DC current through the compensation coil then be used for position determination.

Preferably, the regulation takes place in such a way that a maximum relative sensitivity S of the sensor over the entire measuring range or at least a part thereof is kept constant. For this purpose, the information obtained from a calibration could be used. Maximum sensitivity is at the position h ₀ , which can be shifted by selecting a DC current through the compensation coil.

alternative to a scheme, the DC could be set manually become. Especially with movements of the DUT with high dynamics The scheme might not be fast enough to change react. A manual adjustment of the direct current leaves to realize themselves in different ways. So could the strength of the direct current over, for example Keys or a keyboard can be entered. Alternatively or in addition could be analog or digital rotary or slider Find use.

at the sensor arrangement, which has a Gleichstromerregte compensation coil the magnetic fields of the sensor coil, the compensation coil and the magnet of the DUT to a superimpose the resulting magnetic field. Here are the Directions and polarity of the individual magnetic fields in the Generally be different. The magnetic field of the sensor coil is due to the supply of an alternating current an alternating field and thus changes with twice the frequency of the alternating current his polarity. The magnetic field of the compensation coil becomes relative depending on the position of the measuring object to the sensor via a control or manually adjusted. In this case, the polarity of the compensation coil exciting DC are chosen such that the static Field component of the magnetic field is increased or decreased. This will depend on which direction the resulting Magnetic field should be shifted to the best possible or even ideal conditions for measuring the positions. The magnetic field the magnet associated with the measurement object generally becomes one be inhomogeneous magnetic field and the distance between sensor and the object to be measured.

The sensor coil and the compensation coil could be galvanically isolated from each other. As a result, the two coils can be acted upon completely independently of each other with currents. It should be noted, however, that the two coils also combined into a single coil could be summarized or one of the two coils can be configured by a Zwischenabgriff as a section of the other coil. When configured by a single coil, a shifted by a Gleitstromanteil alternating current was fed into the coil. The offset could be adjusted by means of a control loop or manually as well as in galvanically separated embodiment of the two coils.

at the magnet of the test object is preferably a Permanent magnets. As a result, the measurement object can be independent be used by any other energy supply. Indeed The magnet could also be formed by an electromagnet be. This could further influence the measurement become. For example, if the measurement object is comparatively close at the sensor, so could by reducing the excitation current the magnetic field of the magnet can be reduced. Likewise could at a large distance between the object to be measured and the sensor increases the excitation current become. Both embodiments of the magnet could also be applied in combination.

In a possible embodiment of the evaluation circuit for the sensor, the film is capacitively coupled to the sensor coil. In this embodiment, the foil has an electrical contact which is connected to an oscillator. The other pole of the oscillator is connected to one of the terminals of the sensor coil. In this way, the energy would be capacitively coupled into the sensor coil. The two terminals of the sensor coil are connected to the inputs of an amplifier, which amplifies the voltage drop across the sensor coil. The amplifier is part of the evaluation circuit, by means of which the change in the permeability of the film is determined. The voltage drop across the coil is amplified by the amplifier and output as amplified signal U ₂ . This signal U ₂ is proportional to the relative impedance change ΔZ / Z.

As an alternative to this embodiment, the oscillator could be connected directly to the sensor coil. The alternating current would therefore be coupled directly into the coil. The film could then be connected to ground, for example. In this embodiment too, the voltage drop across the sensor coil would be amplified and a signal U ₂ proportional to the relative impedance change ΔZ / Z would be output.

In both cases, an electronic arrangement could be provided which forms two orthogonal voltage components from the voltage signal U ₂ . The two components are then proportional to the real part Re {Z} or imaginary part Im {Z} of the complex impedance Z of the sensor coil. The electronic device would output voltage signals U ₃ and U ₄ representing the two orthogonal voltage components. The signal U ₄ could be used to synchronize the oscillator, while the signal U _{3 is used} to control the voltage source, which feeds the compensation coil with a sliding current. The electronic device could be implemented by a variety of arrangements known in the art. Preferably, the analysis of the amplified voltage is digital. The electronic device would then comprise an A / D converter, a processor and a memory. For galvanic isolation of the electronic device from the power source, an optocoupler could additionally be provided, via which the control information is transferred galvanically decoupled to the power source.

at the embodiment of the sensor arrangement without compensation coil and with limited direction of movement of the measurement object Directions that are substantially parallel to an expansion direction the film is done, the magnet could also be through a Permanent magnets or an electromagnet can be realized. at Design by an electromagnet could turn on the measurement behavior of the sensor - as previously described - influence be taken.

Also in this type of embodiment could be a calibration the sensor arrangement are performed. For that would the previously described steps for determining the characteristic of the Sensors are carried out accordingly.

The design of the evaluation circuit would be done in a similar manner as in the embodiment with compensation coil. An oscillator could feed a voltage signal directly into a contact of the foil. The voltage could then be capacitively coupled into the sensor coil. The voltage generated at the coil could in turn be amplified by an amplifier and fed to an electronic device for determining the real and the imaginary part. From a the imaginary part proportional voltage signal U ₄ , a synchronization of the oscillator could be brought about.

As well the oscillator could be connected directly to the sensor coil and the voltage drop across the coil over amplify an amplifier. Again could the amplified signal is fed to an electronic device, from the amplified signal the real and the imaginary part to extract.

In both embodiments of the sensor arrangement according to the invention - that is, the sensor order with or without compensation coil - the sensor could be formed in different ways. Thus, the sensor could be applied in a round or in some other way three-dimensionally pronounced carrier. On this carrier, the sensor coil, the film and possibly the compensation coil could be wound, glued or applied in any other way.

In an alternative embodiment, the sensor could be flat be designed. The sensor is preferably on a plan Carrier applied. However, the carrier could also curved and adapted to special working environments be. After appropriate calibration measures can Such sensors are used easily.

wobei ω = 2πf mit f als Frequenz des Wechselfeldes gilt und σ die Leitfähigkeit und μ die Permeabilität der Folie sind. Wie zu erkennen ist, ist δ umgekehrt proportional zu der Wurzel aus der Permeabilität μ der Folie. Sinkt also bedingt durch ein äußeres Magnetfeld die Permeabilität der Folie, so steigt die Eindringtiefe des elektromagnetischen Felds in die Folie. Ist die Dicke der Folie geeignet dimensioniert, so dringt das elektromagnetische Feld in Bereichen mit niedriger Permeabilität durch die Folie hindurch. Dieser Effekt kann weiter zu einer Erhöhung der Empfindlichkeit genutzt werden. Es könnte nämlich auf der der Sensorspule abgewandten Seite nahe der Folie eine leitfähige Fläche angeordnet sein. Dabei weist diese leitfähige Fläche vorzugsweise eine im Vergleich zu der weichmagnetischen Folie wesentlich höhere Leitfähigkeit auf. Dadurch würden in der leitfähigen Fläche in höherem Maße Wirbelströme induziert als in der weichmagnetischen Folie.For a further improvement of the sensitivity of the sensor arrangement, the thickness of the film could be adapted to the penetration depth of the electromagnetic field generated by the sensor coil. In this case, the electromagnetic field generated by the sensor coil is preferably high-frequency. For the penetration depth δ into a conductive material, the following applies:

where ω = 2πf where f is the frequency of the alternating field and σ is the conductivity and μ is the permeability of the film. As can be seen, δ is inversely proportional to the root of the permeability μ of the film. Thus, if the permeability of the film decreases due to an external magnetic field, the penetration depth of the electromagnetic field in the film increases. When the thickness of the film is properly sized, the electromagnetic field penetrates through the film in areas of low permeability. This effect can be further used to increase the sensitivity. It could namely be arranged on the sensor coil side facing away from the film, a conductive surface. In this case, this conductive surface preferably has a much higher conductivity compared to the soft magnetic film. As a result, eddy currents would be induced to a greater extent in the conductive surface than in the soft magnetic film.

Especially when restricting the movement of the measuring object in directions becomes substantially parallel to an extension direction of the film ensures that the soft magnetic film lies behind it conductive area depending on Position of the DUT releases. Depending on the position of the DUT would be a different width zone with reduced Permeability of the soft magnetic film for the electromagnetic field of the sensor coil become permeable to let. (This can be clearly presented in such a way that the Foil similar to a blind a different sized part a window opening releases.) This would depending on the position of the DUT in different strong measure eddy currents in the conductive Surface induced. These cause a stronger influence the impedance of the sensor coil than that in the soft magnetic film induced eddy currents, which in turn has a positive effect the sensitivity of the sensor arrangement affects.

In Advantageously, the sensor coil with an alternating current fed at high frequency. Thus, the dynamics of the sensor is very high. Due to the high frequency, although the penetration depth of the eddy currents low in conductive materials, but what for thin films (for example, 20 microns) is sufficient. It can be seen that a volume effect is not necessary or even not wanted: With a voluminous Soft magnetic material, the eddy current would also just flow in a thin layer, so that the Measuring effect in relation to the volume is low.

As previously described, the zone is the permeability change depending on the magnetic field strength. Depending on the magnet the sensor can determine its position at a relatively long distance (eg 30 ... 50 mm) with very high resolution (a few μm) measure, by a suitable arrangement, the zone of highest sensitivity just placed so that the operating point at the given Base distance of the magnet is relative to the sensor. In a suitable embodiment of the magnetic circuit is a so-called redundancy factor of more typical Size 3 achievable. It means that the distance of the movement of the object to be measured increases by a factor of 3 is considered the change in the distribution of permeability in the slide. The length of the film is thus around the redundancy factor shortened compared to the track of movement. This is particularly advantageous because a short and compact Design of such sensors is possible.

The previously described embodiments of the sensors can Also be realized in such a way that the film and the magnet fixed are and only the coil is moved.

In a further advantageous embodiment, the magnet can be firmly connected to the sensor. In order to obtain a magnetic field which varies from the position of the measurement object at the location of the sensor coil, the measurement object must be made of a material which influences magnetic fields. This may be, for example, a ferromagnetic material. By a change in position of the ferromagnetic object to be measured relative to the sensor and the magnet connected to the sensor, the magnetic field lines are influenced and thus also a Changing the distribution of permeability causes in the film.

It Now there are different ways of teaching the present Invention in an advantageous manner and further develop. On the one hand to the claims 1, 13th and 25 each subordinate claims and on the other hand to the following explanation of preferred embodiments of the invention with reference to the drawing. Combined with the explanation of the preferred embodiments The invention with reference to the drawings are also generally preferred Embodiments and developments of the teaching explained. In the drawing show

1 1 a schematic representation of a device according to the invention for detecting the position and / or position changes of a measurement object,

2 a diagram shows the relationship between a magnetic field distribution along a soft magnetic film and the position h of the measurement object,

3 2 is a diagram with an exemplary profile of the relative sensitivity S as a function of the position h of the measuring object relative to the sensor,

4 a diagram with a profile of the direct current I_ as a function of the position h of a measured object,

5 A first embodiment of a sensor arrangement according to the invention with a compensation coil,

6 A second embodiment of a sensor arrangement according to the invention with a compensation coil,

7 A third embodiment of a sensor arrangement according to the invention with a compensation coil and a permanently installed permanent magnet and

8th a circuit diagram of a controllable current source for driving the DC coil.

at The individual figures are for the same or similar Components same reference numerals used.

1 shows a schematic diagram of a block diagram of a sensor arrangement according to the invention 1 for detecting the position h and / or position change of a measuring object 2 relative to an electromagnetic sensor 3 , The measurement object 2 is a magnet 4 assigned in the form of a permanent magnet, in the illustrated embodiment of the measuring object 2 is enclosed to almost all sides. The sensor 3 has a coil system 5 on that from a sensor coil 6 and a compensation coil 7 consists. In the sphere of influence of the coil system 5 is a foil 8th made of soft magnetic material. The sensor coil 6 has two connections K ₁ and K ₂ . The connection K ₁ is with the synchronizable oscillator 10 connected, the terminal K ₂ is connected to the input of an evaluation circuit 11 and the electrical contact 9 connected to the film. The oscillator 10 feeds the sensor coil 6 with an alternating voltage of fixed frequency and amplitude. This is done by the sensor coil 6 generates an alternating electromagnetic field, which in the film 8th Eddy currents induced. The electromagnetic properties, such as the electrical conductivity σ and the magnetic permeability μ of the material of the film, influence this 8th , the character and the retroactivity of the eddy currents on the alternating field. By a change in distance between the measurement object 2 and the sensor 3 the magnetic permeability μ of the film changes 8th , what to change the alternating field in the coil system 5 leads. As a result, the complex impedance Z of the sensor coil changes 6 , with the help of an evaluation circuit 11 is measured. The voltage drop between the terminals K ₁ and K ₂ is provided by a differential amplifier 12 amplified, the voltage U ₂ at the output of the amplifier 12 proportional to the impedance Z of the sensor coil 6 is. To the voltage U ₂ are by an electronic device 13 two orthogonal components U ₃ and U ₄ determined.

The voltage U ₃ is used to control a controllable voltage source 14 used the compensation coil 7 of the coil system 5 fed with a direct current I_. This is done by the compensation coil 7 generates a constant magnetic field which, together with the magnetic field of the permanent magnet 4 and the alternating field of the sensor coil 6 forms a resulting magnetic field. The magnitude of the DC current I_ is across the voltage drop across a stable resistor 15 using an integrator 16 measured. The signal at the output "out1" of the integrator 16 is used to determine the distance changes between the measurement object 2 and the sensor 3 used.

The controllable voltage source 14 can be formed in different ways. It can be used a D / A converter or a digital potentiometer, which are controlled by the signal U ₃ . One possible embodiment is in 8th and will be described in more detail below.

The second voltage component U ₄ , which is generated by the electronic arrangement of the voltage U ₂ , is used to synchronize the oscillator 10 used. As a result, the output by the oscillator voltage U ₁ and the voltage U _{4 are} synchronous.

The sensor arrangement 1 could be used in a closed loop, where the signal U _{3 is} a steep amount, which is the difference between a setpoint in the memory of the electronic device 13 and the voltage U _{2 is} determined. In another variant of the control loop, the signal U _{3 is} interrupted and the voltage source 14 manually, for example via a keyboard, controlled to reach a certain value of the DC I_. The output becomes "out2" of the electronic device 13 generated.

Based on 2 (A) , (B), (C), the relationship between the magnetic field distribution along the film 8th and the position h of the magnet 4 be explained. The foil 8th consists of a nanocrystalline material and is on a support 17 , which consists for example of ceramic, applied. At this 2 The significance of the redundancy factor can also be recognized: When the position of the measurement object changes from the distance h ₁ to h ₄ , the distribution of the permeability in the film changes only by the distance from a-b to g-h. This distance is shortened by the redundancy factor with respect to the distance traveled h of the object to be measured, the redundancy factor having the value 3, for example.

2 (A) shows an arrangement consisting of a on a support 17 applied film 8th exists and with the the distribution of the through a permanent magnet 4 generated magnetic field along the film 8th can be determined indirectly. A measuring coil 18 with a width Δ = 3 mm is single-layer around the carrier 17 and the film 8 around. Here is the measuring coil 18 configured such that they are in the longitudinal direction of the film 8th is displaceable.

This in 2 B) The diagram reproduced shows the amount of the complex impedance of the measuring coil 18 with displacement of the measuring coil 18 in the x-direction along the slide 8th (Length of the film L = 25 mm, width 5 mm and thickness 0.02 mm). In this case, several impedance curves are shown in the diagram, which are at different positions h of the measurement object 2 relative to the film 8th result. For clarification, the numerical values given are the positions h ₁ = 60 mm, h ₂ = 50 mm, h ₃ = 40 mm and h ₄ = 30 mm. This also illustrates how large the measuring range of such an arrangement can be adjusted.

The diagram in 2 (C) schematically shows the area of the film in which sets a maximum slope of the impedance characteristic and thus a maximum sensitivity of a sensor using the soft magnetic film. The ranges are shown for the positions h ₁ = 60 mm, h ₂ = 50 mm, h ₃ = 40 mm and h ₄ = 30 mm. It can be clearly seen that the regions (a-b), (c-d), (e-f) and (g-h) are proportional to the position h of the permanent magnet 4 move with it.

wobei ΔZ/Z die relativen Impedanzänderung der Sensorspule (7) und δh die Schrittweite zwischen den einzelnen Positionen h sind. Es ist deutlich zu erkennen, dass die relative Empfindlichkeit S an der Position h₀ maximale Werte annimmt. In einem Bereich ± Δh um die Position h₀ herum bleibt die relative Empfindlichkeit S noch auf signifikanten Werten und ist danach erheblich reduziert.In 3 is the relative sensitivity S as a function of the position h of the measurement object 2 shown in more detail. For the sensitivity S of the sensor 3 applies:

where ΔZ / Z is the relative impedance change of the sensor coil ( 7 ) and δh are the step size between the individual positions h. It can be clearly seen that the relative sensitivity S at the position h ₀ assumes maximum values. In a range ± Δh around the position h ₀ , the relative sensitivity S still remains at significant values and is then significantly reduced.

4 shows a diagram of the DC waveforms, depending on the position change ± Δh of a DUT relative to the basic position h ₀ . The diagram shows that between the DC current I_ and the position changes of the permanent magnet ± Δh a linear function could be inserted.

5 shows a first embodiment of a sensor arrangement according to the invention, which consists of a measured object 2 and a sensor 3 consists.

A permanent magnet 4 is in a housing of the measurement object 2 installed so that the magnetic field direction with the axis of movement of the measurement object 2 matches. The sensor 3 is flat and contains a carrier 17 , on the two sides of two planar coils 6 and 7 are arranged.

As a carrier 17 For example, a printed circuit board or a ceramic substrate could be used and the coils 6 and 7 could be prepared inexpensively by known methods, for example by screen printing on the support 17 printed or glued on this.

The carrier 17 with the coils 6 and 7 is with two plates 19 . 20 made of electrically conductive material, preferably aluminum or copper, r covered. The width "Δ" of the coils 6 and 7 is only about 25% of the length "l" of the film 8th which are on one side of the plate 20 is glued on. The sink 6 will with fed high-frequency AC voltage and serves as a measuring coil. The compensation coil 7 consists of several layers and is supplied with direct current.

6 shows a second embodiment of a sensor according to the invention. The sensor 3 consists of a round carrier 17 , which is made of a plastic, for example. A first multilayer coil acting as a compensation coil 7 serves and is fed with DC, is in a groove around the carrier 17 wound.

The measuring coil 6 , which is fed by an oscillator with higher frequency alternating current, is single-layered along the carrier 17 wrapped and includes the compensation coil 7 ,

A slide 8th made of nanocrystalline or amorphous material is inside a tube 21 glued. The pipe 21 consists of a material with high electrical conductivity and also serves as a sensor housing. From the side of the measurement object 2 is the pipe 21 with a lid 23 covered by electrically conductive material, but which for the permanent magnetic field (H =) of the measurement object 2 is permeable. The evaluation electronics 24 is in a housing 25 installed, which for EMC reasons with the pipe 21 and the foil 8th should be connected.

An advantage of this embodiment is that the sensor 3 completely encapsulated and shielded and, for example, directly without additional pressure tube in a pressure chamber, such as a hydraulic or pneumatic cylinder, can be installed.

7 shows a third embodiment of a sensor 3 in which a permanent magnet 4 at a certain, fixed distance D to the coil system 5 of the sensor 3 is arranged and not with the measurement object 2 emotional.

The measurement object 2 consists of a ferromagnetic steel and is at a base distance h to the surface of the sensor 3 arranged and movable.

In a first variant (A) is the permanent magnet 4 on the object to be measured 2 opposite side of the coil system 5 arranged. This arrangement is particularly advantageous when using a sensor 3 small size, for example, a diameter of 10 mm, relatively large measuring ranges, for example 15 mm, are measured with a good linearity.

In a second variant (B) is the permanent magnet 4 between the measuring object 2 and the coil system 5 arranged. This variant can advantageously be used if small changes in position Δh should be measured at a relatively large basic distance h of, for example, 25... 30 mm and the diameter of the sensor is, for example, only 10 mm.

In a third variant is the coil system 5 of the sensor 3 that consists of two coils 6 and 7 exists on a support 17 wrapped concentrically. Between the coils 6 and 7 is a foil 8th made of soft magnetic material, which is the coil 7 includes. The sink 6 serves as a measuring coil whose impedance or the imaginary part Im Z of the impedance depends on the distance h and is measured. The sink 7 is supplied with direct current and serves as a compensation coil. Above it is a pipe 26 from a good electrically conductive material, such as aluminum or copper. Then the case could be 25 inexpensive made of non-conductive material, such as plastic. The DC current could be adjusted (or adjusted) so that when position changes Δh between the sensor 3 and the measurement object 2 the impedance or

in the Z remains constant. In this case, the height of the DC proportional to changes in position Δh. The measurement object could also have a profiled surface, For example, a gear or a flywheel, which with the sensor also Speeds and / or angles can be measured.

8th shows a schematic circuit of a controllable DC power source for driving the compensation coil of the device according to 1 , The DC power source has an electronically adjustable digital potentiometer 27 on, via a control line 28 is controlled by a tracking control or a keyboard. The digital potentiometer 27 is through two operational amplifiers 29 . 30 fed symmetrically with a DC voltage, wherein between the non-inverting inputs of the operational amplifier 29 . 30 a reference voltage U _Ref is applied. The grinder 31 of the digital potentiometer 27 is connected to the non-inverting input of another operational amplifier 32 connected. Between the output of the operational amplifier 32 and its inverting input is a coil 33 arranged over which a direct current I_ flows. The sink 33 is here through the compensation coil 7 the circuit according to 1 educated. The level of DC I_ is through a resistor 34 depending on the voltage at the output of the operational amplifier 32 determined, in turn, from the position of the grinder 31 depends on the digital potentiometer. The circuit is dimensioned such that at the center position of the grinder 31 the current I_ is equal to zero. Depending on the position of the grinder can be a positive or a negative Electricity will be spent. Depending on the position of the operating point of the sensor, the polarity and the height of the DC current I_ is set such that in the range ± Δh a constant sensitivity of the sensor is achieved.

The above the resistance 34 Falling voltage is via an integrator, which consists of an operational amplifier 35 a resistance 36 and a capacity 37 exists, measured.

After all It should be noted that the embodiments discussed above merely explain the claimed teaching, but these do not limit to the embodiments.

1

sensor arrangement

2

measurement object

3

sensor

4

magnet

5

coil system

6

sensor coil

7

compensating coil

8th

foil

9

el. Contact (foil)

10

oscillator

11

evaluation

12

amplifier

13

electronic arrangement

14

voltage source

15

(Measuring) resistance

16

integrator

17

carrier

18

measuring coil

19

carrier (Round)

20

pipe

21

el. Contact (pipe)

22

casing

23

evaluation

24

carrier (plan)

25

shielding

26

conductive area

27

Digital Potentiometers

28

drive line

29

operational amplifiers

30

operational amplifiers

31

grinder (Pot)

32

operational amplifiers

33

Kitchen sink

34

resistance

35

operational amplifiers

36

resistance

37

capacity

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 3610479 A1 [0003, 0007]
• EP 1158266 A1 [0004]
• - DE 20307652 U1 [0005]
• - US 4926122 A [0006]
• EP 0729589 B1 [0006]
• - DE 3041041 C2 [0006]
• - DE 3803293 A1 [0007]
• - DE 3803253 A1 [0007]

Claims (35)

Method for determining the position and / or position change of a test object relative to a sensor ( 2 ), whereby the sensor ( 2 ) preferably a charged with alternating current sensor coil ( 7 ), characterized in that by a measuring object ( 1 ) associated magnets ( 5 ) in a soft magnetic film ( 4 ) whose permeability changes under the influence of a magnetic field as a function of the field strength of the magnetic field and which in the influence of the sensor ( 2 ), a change in the permeability of the film ( 4 ) and that the change in the permeability of the film ( 4 ) from their reaction to the sensor ( 2 ) and from this the position and / or position change of the measurement object ( 1 ) relative to the sensor ( 2 ) is determined. A method according to claim 1, characterized in that by a DC-excited compensation coil ( 8th ) generates a magnetic field by means of which the permeability of the film ( 4 ) or parts of the film ( 4 ) being affected. A method according to claim 2, characterized in that the direct current is adjusted such that a substantially constant magnetic field of the sensor coil ( 7 ). A method according to claim 1 to 3, characterized in that for calibrating the sensor ( 2 ) the following steps are carried out: positioning the measuring object ( 1 ) at a plurality of positions h relative to the sensor ( 2 ) with a step size δh, feeding an alternating current into the sensor coil ( 7 ), Determining the impedance Z and / or relative impedance change ΔZ / Z of the sensor coil ( 7 ) at each of the positions, determining a characteristic which has a dependence of the relative sensitivity S of the sensor coil ( 7 ) from the position h of the measurement object ( 1 ), wherein

Determining a position h ₀ in the characteristic curve in which the relative sensitivity S assumes maximum values, storing the value of the complex impedance Z ₀ , which corresponds to the position h ₀ , into a nonvolatile memory, injecting a direct current into the compensation coil ( 8th ) Determining the impedance Z and / or relative impedance change ΔZ / Z of the sensor coil ( 7 ) at each position h, with the film ( 4 ) the magnetic fields of the sensor coil ( 7 ), the compensation coil ( 8th ) and the magnet ( 5 ), changing the direct current in the measuring range ± Δh until a stored reference value of the impedance is reached, determining the dependence of the direct current on the position change of the test object ( 1 ). Method according to one of claims 1 to 4, characterized in that for the detection of the change in the permeability of the film ( 4 ) caused reaction on the sensor coil ( 7 ) a determination of the impedance or its change is performed. Method according to Claim 5, characterized in that the real part Re {Z} and the imaginary part Im {Z} of the complex impedance of the sensor coil ( 7 ) and the quotient D = Re {Z} / Im {Z}. Method according to one of claims 1 to 6, characterized in that the size of the direct current through the compensation coil ( 8th ) is adjusted in a tracking control by a closed loop. Method according to claim 7, characterized in that that the quotient D is used as setpoint for the control loop becomes. A method according to claim 7 or 8, characterized in that the imaginary part Im {Z} for determining the change in position between the measurement object ( 1 ) and the sensor ( 2 ), where D is kept constant. Method according to claim 7 or 8, characterized in that the intensity of the direct current flowing through the compensation coil ( 8th ) flows, is used for position determination. Method according to one of claims 7 to 10, characterized in that by the control a maximum relative sensitivity S of the sensor ( 2 ) is kept constant over the entire measuring range or a part thereof. Method according to one of claims 1 to 6, characterized in that the direct current set manually becomes. Sensor arrangement for determining the position and / or position change of a test object ( 1 ) relative to a sensor ( 2 ), wherein the measurement object ( 1 ) preferably a magnet ( 5 ) and wherein the sensor ( 2 ) preferably a charged with alternating current sensor coil ( 7 ), in particular for the application of a method according to one of claims 1 to 12, characterized in that in the sphere of influence of the sensor ( 2 ) a film ( 4 ) made of soft magnetic material is arranged, wherein the permeability of the film ( 4 ) changes under the influence of a magnetic field as a function of the field strength of the magnetic field and that an evaluation circuit ( 10 ) by means of which the change in the permeability of the film ( 4 ) from their reaction to the sensor ( 2 ) and the position and / or position change of the measurement object ( 1 ) relative to the sensor ( 2 ) is closed. Sensor arrangement according to claim 13, characterized in that a DC coil excited by direct current ( 8th ) is provided, with which the permeability of the film ( 4 ) or part of the film ( 4 ) being affected. Sensor arrangement according to claim 14, characterized in that the magnetic fields of the sensor coil ( 7 ), the compensation coil ( 8th ) and the magnet ( 5 ) superimpose to a resulting magnetic field. Sensor arrangement according to claim 14 or 15, characterized in that the sensor coil ( 7 ) from the compensation coil ( 8th ) is galvanically isolated. Sensor arrangement according to one of the claims 13 to 16, characterized in that the direct current in its Strength is adjustable. Sensor arrangement according to one of claims 13 to 17, characterized in that the magnet ( 5 ) comprises a permanent magnet and / or an electromagnet. Sensor arrangement according to one of claims 13 to 18, characterized in that the film ( 4 ) Capacitive with the sensor coil ( 7 ) and an electrical contact ( 6 ). Sensor arrangement according to claim 19, characterized in that an oscillator ( 14 ) between the contact ( 6 ) of the film ( 4 ) and a connection ( 17 ) of the sensor coil ( 7 ) connected. Sensor arrangement according to claim 19 or 20, characterized in that a second connection ( 18 ) of the sensor coil ( 7 ) with an input of an amplifier ( 11 ) of the evaluation circuit ( 10 ), one through the amplifier ( 11 ) signal U ₂ proportional to the relative impedance change ΔZ / Z of the sensor coil ( 7 ). Sensor arrangement according to claim 21, characterized in that an electronic arrangement ( 12 ) is provided for determining two orthogonal components of the voltage U ₂ , one of the two components being proportional to the real part Re {Z} and the other being proportional to the imaginary part Im {Z} of the complex impedance Z of the sensor coil ( 7 ) are. Sensor arrangement according to claim 22, characterized in that the electronic arrangement ( 12 ) Generates signals U ₃ and U ₄ , wherein by the signal U _{4 of} the oscillator ( 14 ) is synchronized and the signal U ₃ for controlling the voltage source ( 13 ) is used. Sensor arrangement according to claim 22 or 23, characterized in that the electronic arrangement ( 12 ) contains an A / D converter, a processor and a memory and by an optocoupler with the input of the voltage source ( 13 ) connected is. Sensor arrangement for determining the position and / or position change of a test object ( 1 ) relative to a sensor ( 2 ), wherein the measurement object ( 1 ) preferably a magnet ( 5 ) and wherein sensor ( 2 ) preferably a charged with alternating current sensor coil ( 7 ), characterized in that in the sphere of influence of the sensor ( 2 ) a film ( 4 ) is arranged from soft magnetic material, wherein the permeability of the film ( 4 ) changes under the influence of a magnetic field as a function of the field strength of the magnetic field and wherein a movement of the measurement object ( 1 ) substantially in directions parallel to an extension direction of the film ( 4 ) and that the change in the permeability of the film ( 4 ) from their reaction to the sensor ( 2 ) and from this the position and / or position change of the measurement object ( 1 ) relative to the sensor ( 2 ) is closed. Sensor arrangement according to claim 25, characterized in that an evaluation circuit ( 10 ) by means of which the change in the permeability of the film ( 4 ) from their reaction to the sensor coil ( 7 ) is determined. Sensor arrangement according to claim 26, characterized in that the magnet ( 5 ) comprises a permanent magnet and / or an electromagnet. Sensor arrangement according to claim 26 or 27, characterized in that the film ( 4 ) Capacitive with the sensor coil ( 7 ) and an electrical contact ( 6 ). Sensor arrangement according to claim 28, characterized in that an oscillator ( 14 ) between the contact ( 6 ) of the film ( 4 ) and a connection ( 17 ) of the sensor coil ( 7 ) connected. Sensor arrangement according to claim 28 or 29, characterized in that a second connection ( 18 ) of the sensor coil ( 7 ) with an amplifier ( 11 ) the evaluation circuit ( 10 ), wherein a signal U ₂ at the output of the amplifier ( 11 ) proportional to the impedance change ΔZ / Z of the sensor coil ( 7 ). Sensor arrangement according to one of claims 13 to 30, characterized in that the sensor ( 17 ) on a round carrier ( 21 ) is applied. Sensor arrangement according to one of claims 13 to 30, characterized in that the sensor ( 34 ) is flat and applied to a preferably planar carrier. Sensor arrangement according to one of claims 13 to 32, characterized in that due to the change in the permeability of the film, the penetration depth of the through the sensor coil ( 7 ) increased electromagnetic field and that the film ( 4 ) is dimensioned in thickness such that the electromagnetic field in areas of low permeability through the film ( 4 ) can pass through. Sensor arrangement according to one of claims 13 to 33, characterized in that a conductive surface (13) is provided, which is close to the film ( 4 ) and on the sensor coil ( 7 ) facing away from the side. Sensor arrangement according to claim 33 or 34, characterized in that through the film ( 4 ) inducing electromagnetic field in the conductive surface induces eddy currents.