DE102007027822A1 - Inductive sensor arrangement and method for influencing the measurement behavior of a measuring coil - Google Patents

Abstract

An inductively operating sensor arrangement comprising a measuring coil (2), wherein an oscillator (4) supplies the measuring coil (2) with an alternating voltage, is characterized in that in order to improve the measuring behavior of the sensor arrangements and to reduce the sensitivity to lateral approaches the measuring coil (2) a further coil (3) is arranged and that the further coil (3) with an amplifier (6) is connected, via which the further coil (3) with one of the AC voltage of the oscillator (4, 8) derived voltage (U <SUB> 2 </ SUB>) can be fed. A corresponding method is indicated.

Description

The The invention relates to an inductively operating sensor arrangement a measuring coil, wherein an oscillator supplies the measuring coil with an AC voltage. The invention further relates to a method for influencing the Measuring behavior of a measuring coil, wherein the measuring coil by a Oscillator is supplied with an AC voltage.

Inductive Working sensor arrangements take an important part in measurement technology Significance. They can be used wherever electrical and / or magnetically conductive objects are detected should. Are such objects in the measuring range of an inductive Sensors, they act on the sensor back. The retroactive effect can be used as a measurement signal. Main applications are distance or proximity sensors as well as distance measuring sensors.

It are in principle two different versions of inductive Sensors known. In one embodiment is by a Coil generates an electromagnetic field, which is reflected in a Measuring range of the sensor located conductive object eddy currents induced. These eddy currents affect the impedance of the Coil back (Lenz's rule). This will both the Real as well as the imaginary part of the impedance of the coil depending on the distance of the coil to the object changed. This change is called a measurement signal used and allows conclusions on the distance of the coil to the object.

Another measuring principle uses two separate coils, one coil exciting an electromagnetic field and the second coil detecting the field. A conductive measurement object located in the measurement field of this arrangement influences the coupling factor between the exciter coil and the detection coil. If the excitation and detection coils are located on the same side relative to the measurement object, the coupling between the coils increases. Such a system is for example from the DE 195 23 519 A1 or the JP 57200803 A known. On the other hand, if the measurement object is located between the excitation coil and the detection coil, the measurement object reduces the coupling. The change in the coupling can be detected metrologically and used both for distance and distance measuring sensors.

Problematic in the known sensor arrangements is that the sensors a relative have strong sensitivity to objects that are approach the sensor sideways. This problem is in the Practice with different approaches encountered. After one Approach, the measuring coil to the rear and laterally by a metallic Housing shielded. This measure will the measuring coil only by approaching an object from the front influenced by the sensor's forehead. The problem with this approach is however, that the quality of the coil over one Air coil is reduced because the impedance is already through the shielding is changed. This is the sensitivity to the approach a measuring object reduces, resulting in a smaller usable Measuring range and lower resolution of the sensor compared to an air coil of the same size.

To Another approach known from practice is the coils designed with a magnetic core. Point through the core the coils opposite air coils a higher achievable Goodness and thus greater sensitivity on. Depending on the shape of the core is additionally bundling of the electromagnetic field. A relative insensitivity opposite side approaches offers one Design of the core as a shell core.

adversely Such coils are sensitive to applied magnetic fields react. Modified by additional magnetic fields itself the permeability of the core, which in turn turns up the coil impedance affects. Therefore, these coils can not be used in environments where magnetic interference fields are present (for example, electric motors, solenoids or the like). In addition, the permeability of the core, especially at negative temperatures and temperatures above 100 ° C, strongly dependent on the temperature of the core. The maximum achievable manufacturing tolerances of several percent in the permeability and the mechanical dimensions continue to have a negative impact. Coils with larger diameters (over about 30 mm) can not or hardly realize, since the production the cores are difficult and extremely expensive.

For detecting errors and noise, arrangements are known in which a plurality of coils are arranged one above the other and serve a coil for the detection of an error signal. Such a system is in the DE 33 36 783 A1 shown.

Of the The present invention is therefore based on the object, a sensor arrangement and to design a method of the type mentioned in the beginning and further that the measurement behavior of inductive sensor arrays is improved and in particular a reduction in sensitivity towards lateral approaches is achieved.

According to the invention the above object is solved by the features of claim 1. Thereafter, the sensor in question is Order characterized in that around the measuring coil, a further coil is arranged and that the further coil is connected to an amplifier, via which the further coil can be fed with a voltage derived from the AC voltage of the oscillator voltage.

In procedurally, the above Problem solved by the features of claim 16. Thereafter, the method in question is characterized that a further coil arranged around the measuring coil by means of a Amplifier and / or phase shifter with a voltage which is supplied by the output by the oscillator AC voltage is derived, and that through the further coil the emission characteristic of the sensor arrangement is influenced.

According to the invention First, it has been recognized that the measurement behavior of an inductive Sensor arrangement without encapsulation of the sensor coil and without the Use of magnetic cores can be positively influenced. Instead Suffice comparatively simple measures that intervene less in the behavior of the sensor assembly. To is arranged around the actual measuring coil another coil, which at least partially surrounds the measuring coil. The measuring behavior This extended measuring arrangement can be surprisingly simple Way be improved by that the further coil is supplied with a voltage that feeds from the measuring coil AC voltage is derived. This is done by the oscillator output AC voltage tapped and an amplifier fed to the other coil. By this measure has a change in the impedance of the other coil one very little or no effect on the behavior of the measuring coil. The measuring coil, however, can be independent of the other Be operated coil. The fields of the measuring coil and the others Coil, however, overlap such that an active shielding of the Measuring coil against lateral influences reached becomes. Furthermore, the use of the other coil and leads their special feed to that the measuring field opposite common sensor arrangements much bundled is delivered. This is the local resolution the coil assembly further increased.

To the Increase the flexibility of the application could arranged before or after the amplifier, a phase shifter. As a result, can be fed to the phase angle between the measuring coil AC voltage and the other coil can be influenced, whereby the superposition of the votes by the two coils Fields can be controlled. By choosing the phase position between The two voltages can therefore be the characteristic of the radiated Be affected to a large extent.

Preferably the measuring coil and the further coil are designed such that their winding axes are substantially parallel to each other. Preferably fall the two winding axes substantially together, causing the two coils are formed coaxially. It's essentially that irrelevant, in what way the two coils built up are. Thus, the coils can be formed by a wire winding be. On the other hand, one could be on a carrier applied conductor track to form a coil. This is from practice a number of embodiments known.

there The coils used could be designed as air coils be, d. H. There is no magnetic core located inside the coil. As a result, the sensor arrangement could also be used in environments with magnetic interference fields are used. An influence the core through the interference fields is omitted.

To the Ensure a coordinated overlay the magnetic fields of the measuring coil and the other coil could the two coils may be arranged such that they are in the measuring direction essentially flush.

Of the Amplifier that supplies the supply voltage for the more Coil provides that could be amplified Strengthen both tension (gain greater 1) and optionally attenuate (amplification less than 1). Also an impedance conversion (amplification equal to 1) could be realized. In similar Way, the phase shifter could be different in strength Phase shifts are used. Phase shifts of 0 ° can be realized as well as shifts of nearly 360 °.

Preferably is the amplifier controllable in its gain, whereby the gain depends on the application situation can be adjusted. An optional in addition to the amplifier existing phase shifter could be designed to be controllable. By this configuration is it is possible, especially flexible on the individual magnetic fields and to influence the total field delivered.

The measuring coil and the further coil could be designed such that the field of the further coil amplifies or reduces the field of the measuring coil. For this purpose, a suitable structural design of the coils can be used. On the other hand, by a suitable choice of the amplification factor and the phase position, the superposition of the individual fields can be changed. Fixed Ver Strengthening factors and phase shifts can be used as well as customizable ones.

Of the the measuring coil supplying oscillator could be a voltage deliver at a fixed frequency. In addition, could the voltage have a fixed amplitude. Corresponding oscillators are well known in practice.

alternative the oscillator could be designed to be free-swinging. In this case, the oscillator could be formed by a resonant circuit be, among other things, contains the measuring coil. Thereby would be the frequency emitted by the oscillator change as a function of the impedance of the measuring coil. This embodiment finds, for example, in a detection of Impedance changes application.

The Voltage used to derive the supply voltage for the more coil used could be at different Jobs are tapped. For one thing, the tap could the voltage after a coupling impedance, via the measuring coil is connected to the oscillator. This follows the supply voltage of the other coil of the supply voltage with defined phase position. However, that could lead to the derivation the supply voltage of the other coil also used voltage be tapped immediately after the oscillator.

Preferably the feeding of the amplified and, where appropriate, takes place phase-shifted voltage in the other coil low impedance. there the feed impedance is preferably close to 0 Ω.

The Sensor arrangement could be designed on the one hand, that the measuring coil in conjunction with the other coil both for Generating an electromagnetic field is used as well as a detection realized the conductive materials. This will be particular achieved in that the impedance or its change depending on conductive materials in the Measuring range of the sensor arrangement is measured. These are from the Practice different methods known.

on the other hand could the sensor arrangement be designed such that the measuring coil in conjunction with the other coil an electromagnetic Field generated and additionally provided a detection coil is. The detection coil would then be used to detect conductive Serve materials. The coupling factor would be between the measuring coil and the detection coil are determined.

To the Achieving an even better spatial resolution the sensor arrangement could turn over the detection coil have another coil around the detection coil is arranged. This would make the local resolution the sensor arrangement further increased.

At the Operating such a sensor arrangement, for example, the previously described, the radiation characteristic of the sensor array is through Applying a arranged around the measuring coil another coil with one derived from the supply voltage of the measuring coil Voltage controlled. For this purpose, an amplifier and / or a phase shifter is used. It should be ensured be that influencing the characteristics of the other coil minimal or no influence on the supply voltage the measuring coil takes.

to Control of the radiation characteristic of the sensor arrangement is preferably affects the supply voltage of the other coil. The change the supply voltage could be the gain of the amplifier. Additionally or alternatively, that caused by the phase shifter could Phase shift can be influenced. As a result, the radiation characteristic the measuring coil can be influenced in a wide range. Indeed the gain and / or phase shift could also be be fixed. In this way, the emission characteristics Although not changed, but leaves These are in the construction of the system according to the requirements of Use if necessary.

It Now there are different ways of teaching the present Invention in an advantageous manner and further develop. On the one hand on the claim 1 or 16 downstream Claims and on the other hand to the following explanation preferred embodiments of the invention with reference to the Drawing to refer. In conjunction with the explanation of the preferred embodiments of the invention The drawings are also generally preferred embodiments and further developments of the teaching explained.

In show the drawing

1 a section through a usable in the sensor assembly according to the invention measuring coil with another coil and a front view of the sensor assembly,

2 a sensor arrangement according to the invention, in which a tapping of the voltage to be amplified takes place after a coupling impedance,

3 a diagram of a measurement of Ab stands a measuring coil to a measuring object using a sensor arrangement known from practice,

4 a diagram of a distance measurement according to the 3 underlying measurement, however, using a sensor arrangement according to the invention,

5 a sensor arrangement according to the invention, in which a tap of the voltage to be amplified takes place before a coupling impedance,

6 a sensor arrangement according to the invention, in which a tap of the voltage to be amplified takes place immediately after an oscillator,

7 a known from the prior art sensor arrangement with separate exciter and detection coil that detects a massive object to be measured,

8th the sensor arrangement according to 7 , with which a wire mesh is detected as the object to be measured,

9 a distance diagram, which with a sensor arrangement according to 7 or 8th was won,

10 a sensor arrangement according to the invention, which has a separate excitation and detection coil,

11 a distance diagram, which with a sensor arrangement according to the invention according to 10 was won,

12 a Sensoranordnun invention, in which both the excitation and the detection coil have a further coil.

1 shows a sensor arrangement 1 coming from a measuring coil 2 and a coaxially arranged to this another coil 3 consists. The measuring coil 2 and the other coil 3 are formed such that the measuring coil 2 inside the other coil 3 can be accommodated. Here are the measuring coil 2 and the other coil 3 arranged such that the two coils in the measuring direction (in 1 to the right) flush. The two coils 2 . 3 are designed as air coils, with the other coil 3 has more windings than the measuring coil 3 , Such a sensor arrangement 1 is used in the described in connection with the further figures embodiments of the invention.

2 shows a first embodiment of the invention, in which the measuring coil 2 both for generating an electromagnetic field and for detecting conductive materials in the measuring range of the measuring coil 2 is being used. The measuring coil 2 is through an oscillator 4 via a coupling impedance 5 fed with an AC voltage U ₁ . The oscillator 4 For this purpose, an AC voltage U ₁ with fixed frequency and amplitude. As a result, the measuring coil generates 2 an electromagnetic field F ₁ .

To feed the other coil 3 with one of the supply voltage U _{1 of} the measuring coil 2 derived voltage U ₂ , the voltage U ₁ after the coupling impedance 5 tapped and an amplifier 6 supplied with adjustable gain. An amplifier 6 downstream phase shifter 7 can influence the phase position. This can cause an adjustable phase shift (under certain circumstances also equal to zero). The voltage U ₂ thus generated becomes low impedance (feed impedance as close as possible to 0 Ω) into the further coil 3 fed. As a result, this generates an electromagnetic field F ₂ , which is the field F _{1 of} the measuring coil 2 superimposed. Depending on the amplitude and phase position, gains or reductions in the field strength result in the field area. The fields F ₁ and F ₂ automatically have the same frequency.

The amplitude and phase relationship of the voltages U ₁ and U ₂ at the two coils 2 . 3 remains constant when approaching a DUT, since the voltage U ₂ at the other coil 3 directly from the voltage U ₁ at the measuring coil 2 derives. As soon as the field F _{1 is changed} by a conductive object in its measuring range, the field F ₂ changes accordingly. A conductive object, which is largely only in the field region F ₂ , but has no or only a small effect on the impedance - and thus on the measurement signal - the measuring coil 2 , The field of the other coil 3 shields the measuring coil 2 thus by overlay against lateral influences. The shielding effect and the field concentration of the field F ₁ can be adjusted by adjusting the amplitude and the phase position of the voltage U ₂ for the further coil 3 to be influenced. The quality of the measuring coil 2 is not reduced, as for example with a metal-shielded sensor, and thus results in the same coil diameter of the measuring coil 2 the same detection distance as an unshielded standard measuring coil. With suitable values of the coils and suitable settings of the amplitude and phase relationships, a significantly better spatial resolution of the measurement can be achieved.

As an example of the effectiveness of the sensor arrangement according to the invention 1 achievable field focusing are the 3 and 4 considered. Both figures each show diagrams of distance measurements in which an inductive sensor has been moved past a metal lid located on a container. The lid points due to a negative pressure in the container a deflection. The 3 and 4 each show a series of measurements carried out with different basic distances. The ordinate of the diagrams shows the distance of the measuring coil to the cover, while the abscissa represents the displacement of the sensor.

3 shows a distance diagram of a measurement that was taken with a known from practice sensor array with only a simple measuring coil. The deflection of the lid is not visible even at a close basic distance. The signal is much wider than the cover diameter due to the wide field of view.

The distance diagrams in 4 on the other hand are with a sensor arrangement according to the invention 1 won. It can be clearly seen that a considerable improvement of the spatial resolution can be achieved even with a relatively large measuring distance. In addition, the width in the diagram corresponds much better to the actual diameter of the lid.

Another embodiment is in 5 shown. The circuit essentially corresponds to that 2 , However, the tap is for the derivation of the supply voltage U ₂ for the other coil 3 immediately after the oscillator 4 even before the coupling impedance 5 ,

The measuring coil 2 is in turn by an oscillator 4 via a coupling impedance 5 fed with a fixed frequency and amplitude. The through the oscillator 4 discharged AC voltage is via an amplifier 6 tapped with adjustable gain and with (or without) phase shift via a phase shifter 7 low impedance (feed impedance as close as possible to 0 Ω) into the further coil 3 fed. As a result, a second electromagnetic field F _{2 is} generated, which is superimposed on the field F ₁ automatically with the same frequency. The amplitude and phase relationship of the voltages at the two coils remains when approaching a measuring object to the measuring coil 2 - In contrast to the first embodiment - but not constant. The voltage U ₂ at the other coil 3 is by tapping directly after the oscillator 4 constant and does not change when the impedance of the measuring coil changes.

A conductive object, which is largely only in the field region F ₂ , has no or only a small influence on the impedance of the coil and thus on the measurement signal. The field of the other coil 3 shields the measuring coil 2 By overlaying the fields against lateral influences largely from. The shielding effect can be influenced by the adjustment of the amplitude and the phase position and thus the strength of the field F ₂ . Thus, a bundling of the field F ₁ results as in the first embodiment, however, with different effects on the phase and the amplitude at the measuring coil 2 ,

6 shows a third embodiment of the invention. Again, the circuit diagram largely corresponds to the circuit diagram according to 2 , The oscillator is in this embodiment, however, as a free-running oscillator 8th educated. This can be formed for example by a resonant circuit, which is out of the measuring coil 2 and a non-illustrated parallel-connected capacitor. As a result, not only the impedance of the measuring coil changes as a conductive object approaches 2 , but also the frequency of the exciting alternating voltage.

The AC voltage at the measuring coil 2 , which generates the electromagnetic field F ₁ , is via an amplifier 6 tapped with adjustable gain, and with (or without) phase shift via a phase shifter 7 in the other coil 3 Low impedance fed (feed impedance as close as possible 0 Ω). Thus, a second electromagnetic field F _{2 is} generated, which is superimposed on the field F ₁ automatically with the same frequency. The amplitude and phase relationship of the voltages across the two coils 2 . 3 remains constant, since the voltage U ₂ at the other coil 3 directly from the voltage U ₁ at the measuring coil 2 derives. As soon as the field F _{1 is changed} by a conductive object in its measuring range, the field F ₂ changes accordingly. However, a conductive object, which is largely only in the field region F ₂ , has no or only a small influence on the impedance of the measuring coil 2 and thus to the measurement signal. The field of the other coil 3 shields the measuring coil 2 by overlay against lateral influences. The shielding effect and the field concentration of the field F ₁ can be achieved by adjusting the amplitude and the phase position at the other coil 3 and thus the field F _{2 are} affected.

The 7 to 12 refer to a system with separate excitation and detection coil. The show 7 to 9 the conditions that show up in a system known from practice. A free-running oscillator 8th Among other things, a measuring coil 9 contains, feeds the measuring coil 9 with an alternating voltage U ₁ . This generates the measuring coil 9 an electromagnetic field F ₃ , which is in the direction of a detection coil 10 is emitted. The distance between the excitation and the detection coil can be a multiple of the coil diameter, wherein the diameter of the two coils 9 . 10 are the same size. However, the coils can also be different Have diameter.

A measurement object 11 will be between the two coils 9 . 10 emotional. Depending on the position x of the DUT 11 the coupling between the exciter and the detection coil is changed. Therefore, that is through the detection coil 10 generated voltage U _e of the position x dependent. In another application, this effect can be used, for example, to make a statement about the dimensions of a small or a narrow object (for example, a wire).

8th essentially corresponds to the 7 , However, shows 8th not a massive measuring object, but a measuring object consisting of individual wires lying close to each other 12 ,

9 shows a diagram showing the voltage U _e in the detection coil 10 depending on the position x of the DUT 11 . 12 reproduces. This results in both the massive measurement object 11 as well as the made of wires measuring object 12 the same diagrams. The individual wires can not be detected separately because of the very wide measuring field in the arrangement known from practice. For this purpose, the spatial resolution of the system is too low.

The 10 to 12 refer to a sensor arrangement according to the invention. In 10 a fourth embodiment of the invention is shown in which the exciter coil next to a measuring coil 2 another coil 3 having. The measuring coil 2 is from an oscillator 4 supplied with an AC voltage with fixed frequency and amplitude. The measuring coil 2 thereby emits an electromagnetic field F ₃ . The further coil is fed with a voltage, which is amplified by means of an amplifier 6 with adjustable gain and a phase shifter 7 with adjustable phase shift from the supply voltage of the measuring coil 2 is derived. The further coil 3 thereby generates an electromagnetic field F ₄ , which is superimposed on the field F ₃ . These superimposed fields become an opposite simple detection coil 10 radiated, which generates a voltage U _e as a result of the alternating field. The distance between the field coil arrangement (formed by the measuring coil 2 and the other coil 3 ) and the detection coil 10 can be a multiple of the coil diameter of the measuring coil 2 or the detection coil 10 be.

Between the exciting coil assembly and the detection coil 10 in turn becomes a measuring object consisting of individual wires lying close to each other 12 moved past. The measurement object 12 affects the coupling between the exciting coil assembly and the detection coil 10 , By suitable choice of the coil dimensions and the amplitude and phase relationships of the voltages on the excitation coil arrangement, the voltage U _{e can} be adjusted so that the spatial resolution of the arrangement is substantially better than with an exciter coil.

11 shows the course of the voltage U _e , which occurs when the measurement object 12 in the x-direction, that is, substantially perpendicular to the coil axes, is moved. It becomes clear that the individual wires of the test object 12 are well differentiated from each other and thus even their distance to each other can be determined. The spatial resolution is thus significantly improved in comparison to the arrangement known from practice.

A still further improvement is provided by an arrangement which also includes a detection coil 13 another coil 14 assigned. Such a circuit is in 12 shown. The circuit corresponds (apart from the other coil 14 around the detection coil 13 ) the in 10 illustrated circuit. This results in the detection coil 13 and the other coil 14 different reception voltages, which by suitable combination of the summation by means of an adjustable amplifier and a phase shifter an even better spatial resolution than the circuit according to 10 enable.

Finally be particularly emphasized that previously purely arbitrary selected embodiments for discussion only serve the teaching of the invention, but these not limited to the embodiments.

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 19523519 A1 [0004]
• - JP 57200803 A [0004]
• - DE 3336783 A1 [0008]

Claims (18)

Inductive sensor arrangement with a measuring coil ( 2 ), where an oscillator ( 4 . 8th ) the measuring coil ( 2 ) supplied with an alternating voltage, characterized in that around the measuring coil ( 2 ) another coil ( 3 ) and that the further coil ( 3 ) with an amplifier ( 6 ), over which the further coil ( 3 ) with one of the AC voltage of the oscillator ( 4 . 8th ) derived voltage (U ₂ ) can be fed. Sensor arrangement according to claim 1, characterized in that before or after the amplifier ( 6 ) a phase shifter ( 7 ) is provided. Sensor arrangement according to claim 1 or 2, characterized in that the measuring coil ( 2 ) and the other coil ( 3 ) are formed substantially coaxially. Sensor arrangement according to one of claims 1 to 3, characterized in that the coils ( 2 . 3 ) are designed as air coils. Sensor arrangement according to one of claims 1 to 4, characterized in that the measuring coil ( 2 ) and the other coil ( 3 ) terminate substantially flush in the direction of measurement. Sensor arrangement according to one of claims 1 to 5, characterized in that the amplifier ( 6 ) and / or the phase shifter ( 7 ) are controllable. Sensor arrangement according to one of claims 1 to 6, characterized in that the field (F ₂ , F ₄ ) of the further coil ( 3 ) the field (F ₁ , F ₃ ) of the measuring coil ( 2 ) increases or decreases. Sensor arrangement according to one of claims 1 to 7, characterized in that the oscillator ( 4 ) outputs a voltage with a fixed frequency. Sensor arrangement according to one of claims 1 to 7, characterized in that the measuring coil ( 2 ) Part of a freely oscillating oscillator ( 8th ) whose frequency depends on the impedance of the measuring coil ( 2 ) changes. Sensor arrangement according to one of claims 1 to 9, characterized in that the tap for deriving the supply voltage (U ₂ ) for the further coil ( 3 ) used voltage after a coupling impedance ( 5 ), via which the measuring coil ( 2 ) with the oscillator ( 4 ) connected is. Sensor arrangement according to one of claims 1 to 9, characterized in that the tap for deriving the supply voltage (U ₂ ) for the further coil ( 3 ) used voltage immediately after the oscillator ( 4 . 8th ) he follows. Sensor arrangement according to one of claims 1 to 11, characterized in that the supply of the amplified and / or phase-shifted voltage (U ₂ ) in the further coil ( 3 ) takes place with low impedance. Sensor arrangement according to one of claims 1 to 12, characterized in that the measuring coil ( 2 ) serves both to generate an electromagnetic field (F ₂ ) and to detect conductive materials. Sensor arrangement according to one of claims 1 to 13, characterized in that the measuring coil ( 2 ) generates an electromagnetic field (F ₃ ) and a detection coil ( 10 . 13 ) for the detection of conductive materials ( 11 . 12 ) serves. Sensor arrangement according to claim 14, characterized in that around the detection coil ( 13 ) as well as another coil ( 14 ) is arranged. Method for influencing the measuring behavior of a measuring coil ( 2 ), in particular using a sensor arrangement according to one of claims 1 to 15, wherein the measuring coil ( 2 ) by an oscillator ( 4 . 8th ) is acted upon by an alternating voltage, characterized in that one around the measuring coil ( 2 ) arranged further coil ( 3 ) by means of an amplifier ( 6 ) and / or phase shifter ( 7 ) is subjected to a voltage that is different from that provided by the oscillator ( 4 . 8th ) is discharged, and that by the further coil ( 3 ) the radiation characteristic of the sensor arrangement ( 1 ) being affected. A method according to claim 16, characterized in that for controlling the emission characteristic of the sensor arrangement ( 1 ) the supply voltage of the other coil ( 3 ) is changed. Method according to Claim 16 or 17, characterized in that the change in the supply voltage is achieved by changing the amplification factor of the amplifier ( 6 ) and / or the phase difference of the phase shifter ( 7 ) is carried out.