DE102012005344A1 - Contactless position indicator for detecting position of moving object e.g. excavator, has displacement sensor comprising magnetic field enhancement units that generate magnetic field that is superimposed on magnetic field of magnet - Google Patents

Abstract

The indicator has a sensing transformer (100) with an elongate measuring ferromagnetic core (106) and an elongated coil (108). Another split coil (110) is wound in an end region of the core. A drive magnet (104) is movable along a movement path. An electronic module (102) outputs a measuring signal based on position of the magnet. A permanent magnetic linear contactless displacement sensor comprises magnetic field enhancement units e.g. auxiliary permanent magnet, that generate a magnetic field that is superimposed on the magnetic field of magnet.

Description

The present invention relates to a non-contact type position sensor for detecting the position of a moving object, the position sensor comprising a measuring transformer having an elongated ferromagnetic measuring core and a first elongate winding wound on the measuring core. In one end region of the measuring core, a second, split winding is wound over the first winding. Furthermore, a drive magnet is provided which is linearly movable approximately parallel to the first elongate winding. This drive magnet is connected to the object whose position is to be determined in a suitable manner known per se.

With this arrangement, which is also referred to as a measuring transformer, the current linear position of an object connected to the driving magnet can be detected on the travel path determined by the length of the elongate core and the first elongate winding located thereon. The measuring core of such a sensor, which is also referred to as a PLCD displacement sensor (Permanent Magnetic Linear Contactless Displacement Sensor), is preferably made of a soft magnetic material. The drive magnet, which is approximated to the sensor, leads to a local magnetic saturation of this measuring core and thus to a virtual division of the core. If the elongated primary coil is occupied by a suitable alternating current, a voltage dependent on the position of the saturated region is induced in the evaluation coils of the second divided winding. Thus, the length of the virtual parts of the core and thus the position of the saturated area can be determined. An example of such a measuring transformer is in the German patent specification DE 4425903 C2 explained. A general physical description of this measurement principle is, for example, the article Erb O. et al .: "PLCD, a Novel Magnetic Displacement Sensor, Sensors and Actuators A, 25-27 (1991) pp. 272-282 , refer to.

1 shows a schematic representation of a PLCD displacement sensor, as it is available for example from Tyco Electronics AMP GmbH and can be used with suitable modifications according to the present invention (see the publication "PLCD Displacement Sensors for Industrial Applications", Tyco Electronics AMP GmbH, 2001, Internet: http://www.tycoelectronics.ch/_includes/pdf/ste/catalogs/1308198_0401_g_Sensoren-PLCD.pdf ).

How out 1 As can be seen, the supply of the PLCD measuring transformer takes place 100 with a suitable alternating current, and the processing, evaluation and conversion of the signals by an electronic module 102 , which can either be arranged externally or integrated in the sensor. The electronics module 102 gives as measuring signal as a function of the position x of the control magnet 104 a trace, as in the upper part of the 1 shown off.

How out 1 it can be seen that is from the electronic circuit 102 signal supplied within the measuring range linearly from the location x of the control magnet 104 dependent. In principle, the principle of the PLCD sensor can also be transferred to arrangements in which the sensor is not designed to be rectilinear but curved. Such a sensor is suitable for example for the measurement of rotary actuators. Although all embodiments are therefore directed to a linear PLCD displacement sensor, it will be clear to a person skilled in the art that the principles according to the invention can also be applied to a rotary PLCD sensor, as described, for example, in US Pat. In the publication "PLCD Displacement Sensors for Industrial Applications", Tyco Electronics AMP GmbH, 2001, Internet: http://www.tycoelectronics.ch/_includes/pdf/ste/catalogs/1308198_0401_g_Sensoren-PLCD.pdf , is shown.

An essential aspect of the PLCD principle is the mechanical connection freedom between the drive magnet and the sensor element. As a result, the control of the sensor is also possible through partitions, as long as they consist of non-magnetizable materials. One application that demonstrates the benefits of this capability is the detection of a piston position in hydraulic or pneumatic systems. In these applications, a permanent magnet is mounted on the piston, which drives the PLCD measuring transformer through the cylinder wall.

The achievable drive distances are essentially determined by the size and strength of the drive magnet. For a drive distance of approx. 15 mm, a magnet volume of approx. 1 cm ³ must be used when using inexpensive materials such as hard ferrite. In principle, the driving magnetic field in the first order does not enter the measuring signal as long as the field strength is only large enough to reach the core in the saturation region 112 to completely saturate. Due to the principle, mounting tolerances and fluctuations of the air gap between sensor and magnet are only slightly or not at all in the characteristic curve of the sensor, as long as the driving distance is maintained within a certain working range around the optimum driving distance around.

Since magnet prices have risen dramatically in recent years, the driving magnet of a PLCD sensor is a significant cost factor. Since the fall of 2010, rare earth prices have been in a constant upward trend, with mid-2011 causing a price explosion up to 600%. Neodymium is one of 17 elements of the rare earths and is needed, for example, for the production of the magnetic material neodymium-iron-boron (NdFeB).

The object of the present invention is to provide a PLCD sensor with a smaller drive magnet, wherein the sensor nevertheless provides a reliable and reproducible output signal.

This object is solved by the subject matter of the independent claim. Advantageous developments of the present invention are the subject of the dependent claims.

The present invention is based on the idea that a uniform magnetic bias of the measuring core in the direction of saturation reduces the distance to complete saturation at the virtual sub-point of the measuring core and thus enables the use of substantially smaller driving magnets.

Thus, the PLCD sensor according to the invention combines the advantages of a continuous non-contact linear or rotary displacement measurement with cost-effective manufacturability and low installation size.

The main fields of application are in the field of special vehicles, such as forklifts and excavators, the measurement of piston positions in cylinders or the valve position in hydraulics, pneumatics and electric drives, in mechanical and plant engineering, in the level and flow measurement, in automation technology, eg. As for actuators and part-turn actuators, in conveyor and storage technology, as well as in building and security technology.

The magnetic DC component according to the invention, which magnetically biases the measuring core, can be introduced into the magnetic circuit in various ways. On the one hand, an auxiliary permanent magnet can be provided which effects the magnetic field amplification according to the invention. This solution has the advantage that it can be implemented in a comparatively simple manner without changing the software components and the electronic module.

Alternatively, the magnetic DC component can also be impressed by supplying a direct current or a DC voltage in addition to the feeding AC voltage. This solution has the advantage that no additional, again cost-causing permanent magnets must be provided. The electrically generated direct magnetic field can be generated either with one of the already existing windings or with the help of an additional third winding, which is provided on the measuring transformer or an optional existing return core. Such a return core may generally be provided to guide a portion of the magnetic field outside the measuring core and thereby reduce losses.

Both for the at least one auxiliary permanent magnet as well as for the third winding, there are various possibilities of the mechanical arrangement. In principle, these components acting as a magnetic field amplification unit can be installed everywhere in the closed magnetic circuit of the sensor, and all possibilities of the described magnetic field amplification can be arbitrarily combined and modified in a suitable manner.

Another aspect of the present invention results from the fact that the impressed additional magnetic field not only contributes in magnitude to the saturation of the measuring core, but also interacts vectorially with the magnetic field of the driving magnet.

It can be shown that by an arrangement of the drive magnet in such a way that the polarization axis of the drive magnet is not aligned parallel to the longitudinal axis of the measuring core, but forms an angle therewith, the measuring range of the sensor according to the invention is geometrically shifted. By such an offset can be achieved that the displacement sensor displays a center position, while the control magnet is arranged geometrically off-center with respect to the measuring core. This predetermined offset between the displayed and the actual x-value by a certain Offset value can be used for compensation in an advantageous manner, if due to installation conditions an exact match between the center position of the measuring transformer and the zero position of the control magnet can not be realized.

In particular, the polarization of the drive magnet may be directed so that the polarization axis is perpendicular to the longitudinal axis of the measuring core. It is basically irrelevant whether the north-south orientation is such that the north pole is arranged at the measuring core near or at the measuring core distant end of the driving magnet.

Because the measuring core is magnetically biased, the operating point of the sensor arrangement shifts in an induction / field strength characteristic in the direction of complete saturation, and with correspondingly high amplitudes of the alternating signal, the positive half-wave can lead to the linear region already being left , Therefore, it can be advantageously provided to evaluate only the negative half-wave of the alternating signal. In this case, the "negative" half-wave denotes that half-wave which counteracts the impressed magnetic flux of the magnetic field amplification unit.

For a better understanding of the present invention, this will be explained in more detail with reference to the embodiments illustrated in the following figures. The same parts are provided with the same reference numerals and the same component names. Furthermore, individual features or combinations of features from the embodiments shown and described can in themselves represent independent inventive or inventive solutions.

Show it:

1 a schematic diagram of a PLCD sensor;

2 a schematic representation of a B / H characteristic for a PLCD sensor;

3 a schematic representation of the magnetic field of a drive magnet over a measuring core of a PLCD sensor;

4 a schematic representation of the magnetic field strength as a function of location in the measuring core;

5 a magnetic equivalent circuit of a PLCD sensor;

6 a magnetic equivalent circuit of a reverse PLCD sensor;

7 a schematic electrical equivalent circuit diagram of a PLCD transformer;

8th a schematic representation of a first embodiment of a PLCD sensor with auxiliary magnets;

9 a second embodiment of a PLCD sensor with auxiliary magnets;

10 a third embodiment of a PLCD sensor with auxiliary magnets;

11 a fourth embodiment of a PLCD sensor with auxiliary magnets;

12 a schematic representation of the time course of a supply voltage with imprinted DC component;

13 a first embodiment of a PLCD sensor with electrically impressed DC magnetic field;

14 a second embodiment of the PLCD sensor with electrically impressed DC field;

15 schematic representation of the characteristic curve induction / field strength and explanation of the operating point of a PLCD sensor;

16 a schematic representation of a PLCD sensor with erected control magnet;

17 a schematic representation of the course of the magnetic flux density as a function of the location x;

18 a schematic representation of the arrangement 16 with driven by 180 ° drive magnet;

19 a schematic representation of the magnetic field of a first magnet;

20 a schematic representation of the magnetic field of a second magnet;

21 Comparison of the magnetic field lines for the magnets 19 and 20 ;

22 a schematic representation of a built-in PLCD sensor with shifted zero point.

With reference to the 1 and 2 The following is the general principle of a Weggebers 100 based on the principle of a PLCD (Permanent Magnetic Linear Contactless Displacement) sensor.

As already mentioned, the measuring effect of the in 1 shown PLCD sensor 100 on that in the measuring core 106 within the elongated first winding 108 in a measuring range between x = 0 mm and x = x _max mm due to the action of the control magnet 104 locally a saturation region 112 is produced.

It is understood, as is well known, under a saturation magnetization that magnetization in which in a ferromagnetic material, an increase in the external magnetic field strength H causes no increase in the magnetization of the substance more. This has thus reached the constant material-specific saturation value. If, in the case of a material, the magnetic flux density B is plotted with respect to the externally applied magnetic field strength H in a characteristic curve, the characteristic also drawn as a magnetization curve is obtained 2 is shown. The flattening of the slope clearly indicates the beginning of the saturation magnetization.

In order to keep losses as low as possible, can still be a return core 114 be provided, which closes the magnetic circuit of the measuring transformer. The drive magnet 104 operates in a local area 112 of the measuring core saturation. As a result, the transformer is virtually separated into two individual transformers. This is schematically in 3 shown.

According to the invention is now in the working range between 0 mm and x _max mm within the measuring core 106 generates a DC magnetic field (or DC magnetic flux) that is applied permanently or during operation of the sensor. This magnetic field (or magnetic flux) must be relative to the field generated by the drive permanent magnet 104 is embossed in the core material, to be rectified.

In general, the following relationship applies for the specified working range between 0 mm and x _max mm for the individual transformers:

Furthermore: Θ _pri1 ~ n _pri1 (5) Θ _pri2 ~ n _pri2 ; (6) = _IN = Θ _pri1 + Θ _pri2 (7)

n_pri:

Gesamtanzahl der Windungen der Primärwicklung

n_pri1:

Anzahl der Windungen, welche in Transformator 1 wirksam sind

n_pri2:

Anzahl der Windungen, welche in Transformator 2 wirksam sind

ü₁:

Übersetzungsverhältnis Transformator 1

ü₂:

Übersetzungsverhältnis Transformator 2

Θ_pri1:

eingeprägte Magnetische Spannung in Transformator 1

The following terms apply:

n _pri :

Total number of turns of the primary winding

_npri1 :

Number of turns, which are effective in transformer 1

n _pri2 :

Number of turns, which are effective in transformer 2

ü ₁ :

Gear ratio transformer 1

ü ₂ :

Gear ratio transformer 2

Θ _pri1 :

imprinted magnetic voltage in transformer 1

The 5 and 6 show magnetic equivalent circuits of the arrangement 1 which apply at any operating point x. In this case Θ _PM denotes the magnetic tension caused by the control magnet 104 is produced. This is inversely proportional depending on the distance between the drive magnet 104 and the measuring core 106 , Furthermore, R _{mpri1 means} the magnetic resistance of the primary winding of transformer 1 and R _mpri2 the magnetic resistance of the primary winding of transformer 2 , Similarly, R _{msec1 denotes} the magnetic resistance of the secondary winding of the transformer 1 and R _msec2 the magnetic resistance of the secondary winding of transformer 2. R _{m_saturation} denotes the magnetic resistance of the saturated core region 112 and R _{m_air} denotes the magnetic resistance of the air gap, if appropriate, between the measuring core 106 and an optional inference core 115 , R _{m_air_to_PM} designates the magnetic resistance of the air gap between the drive magnet 104 and the measuring core 106 ,

The magnetic resistance of the core material per se can be neglected because it is smaller by orders of magnitude than the other magnetic resistances and only the magnetic resistance of the saturated core region R _{m_saturation} has to be considered.

und der magnetische Widerstand im Luftspalt kann angegeben werden durchGenerally, the magnetic resistance of a solenoid is defined by

and the magnetic resistance in the air gap can be indicated by

Furthermore, R _{m_air} , R _{m_air_to_PM} and R _{m_saturation} are much larger than R _{m_pri1} , R _{m_pri2} , R _{m_sek1} and R _{m_sek2} . That I μ = dB / dH With the working point, the following applies: μ _r = dB / dH / μ ₀ (10)

ergibt sich, dass R_{m_saturation} dann ansteigt, wenn die Flussdichte bzw. Feldstärke an diesem Punkt erhöht wird (s. 2). Der magnetische Fluss Φ berechnet sich zu

There

shows that R _{m_saturation} increases when the flux density or field strength is increased at this point (s. 2 ). The magnetic flux Φ is calculated to

5 shows in particular the magnetic equivalent circuit diagram of a PLCD sensor, in which an alternating voltage or an alternating current is fed into the primary winding, which generates an alternating field or an alternating flux in the measuring core. The relationships (5) - (7) above apply, where Θ _{pri1 denotes} the impressed magnetic voltage in the transformer 1 and Θ _{pri2 denotes} the impressed magnetic voltage in the transformer 2.

Analog shows 6 the magnetic equivalent circuit of a so-called "reverse PLCD sensor", in which in the second winding 110 an alternating voltage or an alternating current is fed, whereby in the measuring core 106 In turn, an alternating field or an alternating flux is generated. Where Θ _{sec1 is} the impressed magnetic voltage in transformer 1 and Θ _{sec2 is} the impressed magnetic voltage in transformer 2. The following applies: Θ _IN = Θ _sec1 + Θ _sec2 (12)

For an electrical view, as in 7 is shown schematically, one needs the following dependencies between voltage and flux density: U _eff = √ 2 · Π · B · A · f · n, (13) ie U ~ B · n.

For a dc field also applies: B = μ _r · μ ₀ · H = μ _r · μ ₀ · I · n / 1 (14)

According to the invention, the core material of the measuring core is now 106 magnetically biased by a direct component superimposed on the alternating field. This can be achieved by introducing an auxiliary permanent magnet into the magnetic circuit of the transformer. Various possible arrangements with an auxiliary permanent magnet are described below with reference to FIGS 8th to 11 be explained in more detail.

According to a first embodiment, the in 8th are shown are two auxiliary permanent magnets 116 outside the measuring core 106 and the inference core 114 arranged. In the polarization of the auxiliary magnets 116 Care must be taken that these are in the same direction as the field of the control magnet 104 acts. On the other hand, it must also be ensured that the DC component generated does not already lead to saturation of the core without the action of the control magnet. In general, of course, only a single auxiliary magnet is sufficient 116 to generate the corresponding magnetic bias.

In the 8th shown arrangement outside the two cores 106 and 114 has the advantage that retrofitting existing sensor arrangements is easily possible.

A more compact design can be achieved if, as in 9 shown the auxiliary magnets 116 in the measuring core 106 and / or the inference core 114 be embedded.

10 shows an embodiment in which two auxiliary magnets 116 within the array measuring core 106 and conclusion core 114 are installed, the auxiliary magnets the measuring core 106 and / or the Inference core 114 can also touch directly. For this, as in 11 shown, the measuring core 106 and / or the inference core 114 also over the second windings 110 be lengthened accordingly.

In all arrangements shown in accordance with 8th to 11 becomes the total saturation of the measuring core 106 permanently raised so far that a much smaller driving magnet 104 is sufficient for the required virtual graduation of the measuring transformer 100 to reach in two transformers. Although for this magnetic bias additional auxiliary magnets 116 are needed, but overall the cost savings over the known solution with a single larger driving magnet 104 significant.

It should also be noted that all embodiments according to the 8th to 11 can also be used in any combination.

Alternatively or in addition to the magnetic bias by means of one or more permanent magnets 116 the required magnetic DC component can also be wholly or partially impressed by electrical means into the measuring arrangement. If you look at 12 , in which the time course of an alternating voltage or an alternating current with additional DC component is shown, together with the relationship, according to which the B field generated in a coil is directly proportional to the effective value of the generating voltage, it is clear that also by feeding a additional electrical DC component, a corresponding magnetic offset can be achieved. For such a superimposition of the alternating component with a DC offset or a DC offset, a corresponding electronic circuit must be implemented, to which the PLCD unit is connected. The circuit can be designed so that the DC component is superimposed directly with the AC component. This can be z. B. be realized by means of an operational amplifier circuit or a transistor amplifier circuit. By feeding the DC component in the acting as a primary winding first winding 108 of the 1 Therefore, according to the invention a corresponding superimposed magnetic bias can be achieved. This solution represents the simplest alternative aparativ and can be easily used for existing PLCD sensor units with appropriate design of the control electronics.

For a reverse PLCD, its equivalent circuit in 6 is shown in reverse, that the additional offset voltage is fed into the second windings.

Another possibility, a magnetic DC component in the measuring core 106 to memorize is to provide a dedicated third winding which acts as an auxiliary electric magnet and subsequently as a tertiary winding 118 referred to as. The tertiary winding 118 can, for example, via the measuring core 106 be wrapped. This embodiment is in 13 shown. A DC current I _G through the third coil 118 generates the schematically illustrated magnetic constant field B _G , which is superimposed additively to the field, by the driving magnet 104 is caused.

Alternatively or in addition to that on the measuring core 106 provided tertiary coil 118 Such a tertiary coil can also be connected to the magnetic core 114 be provided, as in 14 is shown. In any case, for the impressing of the direct current I _G by the tertiary coil, a corresponding electronic circuit must be implemented, to which the tertiary coil 118 is connected. The circuit can be designed extremely simple, for example, a voltage at the input of the tertiary coil 118 can be specified, with a series resistor may optionally be provided, or the current can be fed by means of a power source.

15 shows the operating point in a characteristic curve in which the induction is indicated as a function of the field strength. A first possibility for the position of the operating point is with the reference numeral 120 specified. Here, the operating point is such that the maximum magnetic field strength which occurs in the PLCD sensor is in the end region of the linear region of the characteristic curve 122 lies. This is the threshold 124 the end of the linear range. The saturation of the core material is through the limit 126 symbolizes.

It can be seen that at field strengths exceeding the range 124 go out, non-linearities occur, which can limit the measurement accuracy. If, according to an advantageous development of the present invention, only the negative half-wave of the fed-in alternating signal is evaluated, the operating point of the transformer can still increase in the direction of saturation 126 be shifted so that the zero crossing of the alternating signal can be moved to the end of the linear range. This is through the second operating point 128 symbolizes.

The corresponding shift of the operating point is done, as described above, by the corresponding change of the DC field B _G. By definition, the negative half-wave is that half-wave which counteracts the impressed flow B _G. If the supplied alternating signal is given by a sine voltage or a sine current, it is known in which operating point the system is located. With the help of a microcomputer, digital signal processor and / or microcontroller can be specified to use only the negative half-waves of the measurement signals of the secondary coils for the calculation of the sensor output signal and thus a position signal.

Possibilities have been outlined above of how to impress a DC magnetic field which results in the driving magnet required to produce the saturation 104 can be downsized. Depending on the specific implementation, ie the use of auxiliary magnets 116 , Overlaying the AC voltage fed with a DC component, or the impressing of a DC component via a third coil 118 , additional costs are generated. The cost savings through the miniaturized drive magnet 104 however, significantly exceeds these additional costs.

The additionally imprinted DC magnetic field B _G interacts with the measuring transformer but not only in such a way that the saturation of the measuring core 106 is achieved at lower driving magnetic field strengths, but it is also the field lines of the driving magnet vectorially additive superimposed. As a result, the maximum field strength on the x-axis is shifted so that an offset can be generated between the measured center of the magnet and an actual center position in the event that the magnet 104 is no longer aligned so that a polarization axis runs along the core axis, but forms an angle with it.

In particular, the drive magnet 104 transverse to the longitudinal axis of the measuring core 106 be aligned, as in 16 is shown. In 16 the variant turns off 13 used in which a tertiary winding 118 at the measuring core 106 is provided to generate the corresponding DC field B _G. Of course, all other possibilities according to the present invention can also be used to produce a corresponding DC component B _G.

As from the synopsis with 17 recognizable results from the superposition of the magnetic field of the driving magnet 104 and the DC field B _G a difference x _offset between the actual position 130 of the driving magnet and the indicated position 132 of the magnet 104 ,

This is also valid in the case of the north-south direction of the driving magnet 104 is reversed, as in 18 is shown. Analogous to the arrangement 16 and 17 Here is the displayed position 132 geometrically shifted in the direction of higher x-values.

The type of displacement caused by superposition of the two magnetic fields of the magnet 104 and the DC field B _G comes naturally depends on the course of the field lines and thus of the shape of the driving magnet 104 from. The 19 and 20 show two different control magnets 104 , both of which have the same extent in the x-direction. For immediate comparison, both magnets are in 21 drawn over each other. The position of the measuring core 106 as well as the impressed direct flow B _G is schematically on the left side of 21 indicated.

It could be shown that in this way an offset of the measuring range by up to 21 mm is possible. The advantage of this special measuring range shift is shown in the illustration of the 22 clear. Here is a PLCD sensor 100 in a housing or other application part 134 installed so that the desired measuring range 136 not with the actual physical position of the sensor 100 matches. Rather, there is a geometric offset x _offset , the by the inventive arrangements according to 16 and 18 can be compensated magnetically. Thus, based on a magnetic bias, by providing a drive magnet which is rotated by 90 ° in the optimum case 104 , a shifted measuring range can be generated which is able to easily compensate for certain disadvantageous installation situations. LIST OF REFERENCE NUMBERS numeral description 100 measuring transformer 102 electronic module 104 Ansteuermagnet 106 measuring core 108 first winding 110 second winding 112 saturated area 114 Inference core 116 Auxiliary permanent magnet 118 tertiary winding 120 first working point 122 curve 124 End of the linear range 126 Saturation of the core material 128 second operating point 130 actual position of the magnet 104 132 indicated position of the magnet 104 134 casing 136 desired measuring range

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 4425903 C2 [0002]

Cited non-patent literature

• Erb O. et al .: "PLCD, a Novel Magnetic Displacement Sensor, Sensors and Actuators A, 25-27 (1991) pp. 272 to 282 [0002]
• "PLCD Displacement Sensors for Industrial Applications", Tyco Electronics AMP GmbH, 2001, Internet: http://www.tycoelectronics.ch/_includes/pdf/ste/catalogs/1308198_0401_g_Sensoren-PLCD.pdf [0003]
• "PLCD Displacement Sensors for Industrial Applications", Tyco Electronics AMP GmbH, 2001, Internet: http://www.tycoelectronics.ch/_includes/pdf/ste/catalogs/1308198_0401_g_Sensoren-PLCD.pdf [0005]

Claims (13)

A contactless position sensor for detecting the position of a moving object, the position sensor comprising: a measuring transformer ( 100 ) with an elongated ferromagnetic measuring core ( 106 ) and a first, elongate winding ( 108 ), which on the measuring core ( 106 ), with a second, split winding ( 110 ), which in an end region of the measuring core ( 106 ) over the first winding ( 108 ) is wound, as well as with a drive magnet ( 104 ), which along a travel path along a longitudinal axis of the measuring core ( 106 ) is movable, a control and evaluation circuit ( 102 ) for driving the windings ( 108 . 110 ) and for outputting a measurement signal as a function of the position of the drive magnet ( 104 ), wherein the displacement sensor further comprises a magnetic field amplification unit ( 116 ; 118 ) which generates a magnetic field (B _G ) which corresponds to the magnetic field of the control magnet ( 104 ) is superimposed. A non-contact encoder according to claim 1, wherein the magnetic field amplifying unit comprises at least one auxiliary permanent magnet ( 116 ). A non-contact encoder according to claim 2, wherein at least one auxiliary permanent magnet ( 116 ) in the measuring core ( 106 ) is embedded. A non-contact encoder according to claim 2 or 3, wherein at least one auxiliary permanent magnet ( 116 ) in the magnetic circuit outside the measuring core ( 116 ) is arranged. Contactless encoder according to one of the preceding claims, further comprising a return core ( 114 ) for guiding at least part of the magnetic field outside the measuring core ( 106 ). A non-contact encoder according to claim 5, wherein at least one auxiliary permanent magnet ( 116 ) in the inference core ( 114 ) is embedded. Contactless position sensor according to one of the preceding claims, wherein the magnetic field amplification unit comprises a DC power source for generating by means of a winding the magnetic field (B _G ) which corresponds to the magnetic field of the control magnet ( 104 ) is superimposed. A non-contact encoder according to claim 7, wherein the DC power source is connected to the first ( 108 ) or the second ( 110 ) Winding is connected to generate the superimposed magnetic field (B _G ). A non-contact encoder according to claim 7, wherein the DC power source is provided with an additional third winding ( 118 ) to generate the superimposed magnetic field (B _G ). A non-contact encoder according to claim 9, wherein the third winding ( 118 ) on the measuring core ( 106 ) and / or a return core ( 114 ) is arranged. Contactless position sensor according to one of the preceding claims, wherein the control magnet ( 104 ) is oriented so that its polarization axis is at an angle of more than 0 ° with the longitudinal axis of the measuring core ( 106 ). Contactless position sensor according to claim 11, wherein the polarization of the drive magnet ( 104 ) is directed so that the polarization axis is perpendicular to the longitudinal axis of the measuring core. Contactless position sensor according to one of the preceding claims, wherein the drive and evaluation circuit ( 102 ), only the negative half wave of the measurement signals of the measuring transformer ( 100 ).

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