FR2477724A1 - MAGNETIC PROXIMITY DETECTOR - Google Patents

Abstract

MAGNETIC PROXIMITY DETECTOR INCLUDING A BISTABLE MAGNETIC ELEMENT, MEANS FOR PRODUCING A CONTINUOUS MAGNETIC FIELD WHOSE ACTION ON THE BISTABLE MAGNETIC ELEMENT VARIES DEPENDING ON THE DISTANCE FROM THE OBJECT TO MONITOR TO THE PROXIMITY DETECTOR, AND A TORQUE SENSOR WINDING MAGNETICALLY WITH BISTABLE MAGNETIC ELEMENT. TO THE BISTABLE MAGNETIC ELEMENT 1 IS ALSO MAGNETICALLY TORQUE AN INDUCTIVE WINDING 3 WHICH IS SUPPLIED WITH A PERIODIC ELECTRIC SIGNAL WHOSE POLARITY AND POWER DURING EACH PERIOD ARE SUCH AS THE INTENSITY OF THE MAGNETIC FIELD PRODUCED BY THE PERIODIC SIGNAL IN THE INDUCER WINDING 3 CAN, AT THE LEVEL OF THE BISTABLE MAGNETIC ELEMENT 1, CHANGE THE DIRECTION OF MAGNETATION OF THE SAME. THE INVENTION IS APPLICABLE FOR EXAMPLE TO THE CONTROL OF THE DRIVING OF MACHINE ORGANS.

Description

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  The present invention relates to a proximity detector

  unit comprising a bistable magnetic element and means for producing a continuous magnetic field, which acts on the bistable magnetic element to a varying degree depending on the distance from the object to be monitored to the proximity sensor, and a winding electrical sensor which is magnetically coupled to the bistable magnetic element and wherein,

  when the distance from the object to be monitored to the detection

  proximity switch passes through a critical value set in advance, an electrical impulse is induced as a result of a

  abrupt change of the sense of magnetization in the magnetic element

tick bistable.

  In the known proximity detector a wire of the type called

  Wiegand is used as a bistable magnetic element.

  As magnetic bistable elements, also

  called bistable magnetic switching cores, it

  Wiegand-type yarns whose constitution and manufacture are described in German Published Patent Application No. 2 143 326 have just been used. Wiegand yarns are, in their composition, homogeneous ferromagnetic yarns (for example in one form). alloy of iron and nickel, preferably 48% iron and 52% nickel, or an alloy of iron and cobalt, or an alloy of iron with cobalt and nickel, or a cobalt alloy with iron and vanadium, preferably 52% cobalt, 38% iron and 10% vanadium), which as a result of a special mechanical and thermal treatment have a soft magnetic core and a magnetic envelope

  lasts, that is to say that the envelope has a coercive force

  higher than the kernel. Wiegand yarns typically have a length of 5 to 50 mm, preferably 20 to mm. If a Wiegand wire, in which the magnetization direction of the soft magnetic core corresponds to the magnetization direction of

  the hard magnetic envelope is placed in a magnetic field

  than the direction of which corresponds to the direction of

  the axis of the wire but whose meaning is opposed to the sense of magneto-

  Wiegand wire, then the direction of magnetization of the soft core of the Wiegand wire is reversed when a field strength of about 16 A / cm is exceeded. This inversion is

  also called reset. In case of a new

  reversal of the direction of the external magnetic field the direction of magnetization of the core is reversed again as soon as the intensity of the external magnetic field exceeds a critical value, of

  so that the core and the envelope are again

  paralleled. This inversion of the sense of magnetization

  occurs very rapidly and is accompanied by a strong vari-

  corresponding magnetic flux per unit of time

  (Wiegand effect). This variation in magnetic flux may

  draw a short and very strong voltage pulse (Wiegand pulse) into an induction coil (depending on the number of turns and the load resistance of the coil)

  induction reach up to about 12 volts).

  when the nucleus is returned to its original state,

  pulsation is also produced in an induction coil but this pulse has, compared to the case of the passage of the direction of magnetization antiparallel to that parallel, a

  significantly lower amplitude and opposite sign.

  If we choose as an external magnetic field an alternating field, able to invert first the magnetization of the nucleus and then that of the envelope and to bring them each to the state of magnetic saturation, then it occurs, as a result of changing the magnetization direction of the soft magnetic core, Wiegand pulses alternately having a positive polarity and a negative polarity and then we can speak of a symmetrical excitation of the wire Wiegand. For this, field strengths of about - (80 to 120 A / cm) to + (80 to 120 A / cm) are required. Inversion of the magnetization of the envelope

  also occurs abruptly and also leads to an impulse

  in the induction coil, but this pulse is much weaker than that induced during the inversion of the magnetization of the core and is not exploited in most

cases.

  If we choose, however, as a magnetic field

  a field capable of reversing only the sense of

  mantation of the soft core and not that of the hard envelope,

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  then the strong Wiegand pulses only occur with the same polarity and we can then speak of an asymmetrical excitation of the Wiegand wire. This requires a field strength of at least 16 A / cm in one direction (to bring the Wiegand wire back to the initial state) and in the opposite direction an inten-

  field strength of about 80 to 120 A / cm.

  It is characteristic of the Iiegand effect that the

  pulses produced by this effect are, in their amplitude and width, to a large extent independent of the rate of change of the external magnetic field and exhibit a

high signal-to-noise ratio.

  In the context of the invention may also be

  used magnetic bistable elements designed differently

  provided that they comprise two regions magnetically coupled to one another and having magnetic hardness (coercive force) different from each other and may, in a manner analogous to Wiegand wires, be used for the generation of pulses by rapid inversion, induced,

  the magnetization of the soft magnetic region. Thus it is de-

  for example, in German Patent No. 2,514,131 a bistable magnetic switching core presented in the form of a wire which consists of a hard magnetic core (eg

  nickel-cobalt example), a conductive intermediate layer

  electricity (eg copper) deposited on the

  core and a soft magnetic layer (eg nickel

  iron) deposited on the intermediate layer. Another variant further comprises a core formed of an inner conductor devoid of permeance (for example beryllium-copper) on

  which is then deposited the hard magnetic layer on the-

  which is then deposited the intermediate layer which is finally covered with the soft magnetic layer. This known bistable magnetic switching core, however, generates lower switching pulses than those generated.

by a Wiegand thread.

  In the known proximity detector the Wiegand wire is surrounded by an electric winding which is intended to receive and transmit the magnetic signal (Wiegand pulse) related to a reversal of the magnetization direction in the

  Wiegand wire, and is therefore called winding detect

  driver or sensor. In the proximity detector known the wire

  Wiegand is normally in the state where the senses of magnetism

  The hard magnetic envelope and the soft magnetic core are antiparallel. If a permanent magnet is now brought to the Wiegand wire from outside, the field at the wire Wiegand is opposite to the magnetization direction of the wire.

  core of the Wiegand wire, then, so long as the strength of the

  permanent mantle is sufficient, the magnetic field of this

  As soon as the distance of the permanent magnet to the Wiegand wire drops below a value fixed in advance, it becomes sufficiently intense at the wire Wiegand that the soft magnetic core of the wire is caused to invert the wire. sense of his magnetization. This passage of the magnetic polarity

  Wiegand wire from antiparallel to parallel

  lel (with respect to the magnetization direction of the Wiegand wire casing) takes place abruptly and generates in the detector winding the characteristic Wiegand pulse. In the case of the known proximity detector, this phenomenon is exploited by bringing a permanent magnet closer to a Wiegand wire provided with a detector winding, by generating a Wiegand pulse in

  the detector winding as soon as the distance of the magnet peria-

  Wiegand goes below the minimum critical value fixed in advance and transmits this impulse

  voltage to an evaluation circuit.

  The known proximity detector has the disadvantage that its output signal is fugitive, that is to say that it is delivered only once, when the distance of the magnet

  permanent over Wiegand becomes lower than the minimum value

  critical, and that it does not persist as long as this distance remains below the critical value. In addition, each time the distance falls below the critical value, it is necessary to reverse the magnetization of the wire again.

  Wiegand so as to bring him to the state -presenting the meanings of

  antiparallel therapy so that in a new

  Finally, a new Wiegand pulse can be triggered.

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  There are, of course, proximity detectors that pro-

  continuously provide a signal, as long as the distance involved is less than a critical distance fixed in advance, namely for example inductive or capacitive proximity sensors or proximity sensors equipped with a Hall generator or semiconductors with variable resistance

  by magnetic means, but these different detectors

  have serious drawbacks. Since semiconductors sensitive to magnetic fields are used, they can only be used in a very limited temperature range, whereas proximity detectors equipped with a Wiegand wire are perfectly insensitive to

  external influences. Other detectors have the disadvantage

  deny the need for an electronic circuit at the measuring

relatively expensive asset.

  The object of the invention is to create a proximity detector

  robustness using a bistable magnetic element

  effectively insensitive to external influences and capable of

  generate a non-fugitive electrical output signal, i.e.

  say that it remains as long as the distance involved is

  less than a critical distance established in advance.

  This object is achieved according to the invention by providing a

  proximity switch in which is magnetically coupled

  to the bistable magnetic element an electric winding

  that additional (winding inductor) which is fed with

  a periodic electrical signal whose polarity and power

  are during each period such as the intensity

  of the magnetic field produced by the periodic electric

  that in the inductor winding is capable at the level of the bistable magnetic element to reverse the magnetization direction of the bistable magnetic element. Other features

  Advantages of the invention are described below.

  when, because the distance becomes less than the critical threshold, the change thus brought to the action of the continuous magnetic field on the bistable magnetic element causes the inversion of the magnetization direction of the latter, this change can in this way be canceled periodically by

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  the magnetic field produced periodically by the inductor winding and acting in the opposite direction. Therefore, two cases can be distinguished as to the signals. On one side of the threshold critical distance the detector winding does not receive pulses indicative of a change in the sense of magnetization of the bistable magnetic element because at the magnetic field there is no magnetic field. presenting the

  direction and strength necessary to achieve such a change

  is lying. On the other side of the critical distance forming threshold

  exists at the level of the bistable magnetic element an inten-

  sufficient field strength to reverse the magnetism

  tion of the bistable magnetic element and thus generate in

  the winding detects a voltage pulse correspon-

  dante. However, on this other side of the critical distance threshold inversion of the direction of magnetization of the element

  bistable magnetic is periodically canceled by superimposed

  periodic magnetic field to the conti-

  naked, so that in the winding detector is produced a periodic pulse train as long as the object to be monitored is on this other side of the critical distance

threshold.

  In this respect, the arrangement can be chosen either

  that the pulse train appears when the distance

  the boundary passes below the critical threshold, so that it appears when the distance becomes greater than the critical threshold. In the first case, it is possible for example to mount the bistable magnetic element and a permanent magnet fixed and to connect to the object to be monitored a ferromagnetic part, for example a metal pallet which, when approaching the permanent magnet,

  weakens the field of the latter at the magnetically

  tick bistable. As long as the pallet is far away, the field of the permanent magnet at the level of the magnetic element

  bistable overrides the magnetic field produced periodically-

  The magnetic field of the bistable magnetic element has a periodic oscillating continuous field which is unable to change the direction of the magnetization of the bistable magnetic element. As

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  the ferromagnetic pallet approaches, the field of the permanent magnet at the level of the bistable magnetic element is gradually weakened so that finally the field

  periodical magnetic force prevails over the field of the magnet

  nent. When the distance concerned becomes less than a critical threshold, the periodic field of the inductor winding periodically becomes sufficiently greater than the opposite field

  of the permanent magnet so that the sense of magnetization of the element

  Bistable magnetic medium changes periodically.

  In the second case one can for example provide on the object to be monitored a permanent magnet which, approaching

  of the bistable magnetic element, increases at this level.

  ci the intensity of the magnetic field; or, as above,

  a permanent magnet is mounted fixed and the object to be monitored

  1er is ferromagnetic or provided with a ferromagnetic pallet which, when approaching the proximity detector, reinforces the magnetic field of the permanent magnet at the level of the bistable magnetic element. As long as the object is far away, the magnetic field of the inductor winding predominates periodically

  at the level of the bistable magnetic element and a dolly train

  periodic pulses is produced in the detector winding.

  When, on the other hand, the object approaches the detector of

  proximity so as not to be further apart than

  the field of the permanent magnet becomes, in comparison with the periodic magnetic field opposite the inductor winding, sufficiently intense so that the periodic magnetic field can no longer cancel the inversion induced by the magnetic field. permanent magnet, of the magnetization direction of the bistable magnetic element, so that the pulse train in the detector winding is interrupted when the distance from the object to the proximity detector becomes less than the critical distance forming threshold.

  Therefore, in both cases the presence or ab-

  the presence of a pulse train in the detector winding is a sign that the distance from the object to the proximity detector is greater or less than a distance

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determined threshold.

  According to one embodiment of the invention a

  pulsating continuous magnetic field is produced through

  of the inductor winding. This can be done in

  a series of periodic electrical pulses, for example sawtooth or rectangular pulses, but preferably by supplying it with rectified alternating current by two-phase rectification.

  alternations. In the pulsating continuous magnetic field

  placing at the bistable magnetic element the continuous magnetic field produced for example by a permanent magnet

  and which is opposite to the pulsating magnetic field.

  Two fundamental variants of the proximity switch are then possible. In the case of the first variant the influence of the variable DC magnetic field

  the distance from the object to be monitored is negligible at

  calf of the bistable magnetic element, as long as the object is far away from the proximity detector and is accentuated

  the distance from the object to the proximity sensor decreases.

  As long as this distance is large, the pulsating magnetic field

  therefore predominates, this field being sufficiently

  intense to bring the periodic bistable magnetic element

  in the state of magnetic saturation in which the hard and soft magnetic regions of the bistable magnetic element are magnetized in parallel. At the level of the minimuqis of the pulsating magnetic field, the resulting magnetic field changes periodically with sign due to the influence of the opposite continuous field, but in this interval at opposite sign the resulting magnetic field is still too weak, as long as the object is far from the proximity switch, so that

  the sense of magnetization of the soft magnetic region of the

  Bistable magnetic element is reversed so as to be opposite to the magnetization direction of the hard magnetic region (this passage of the parallel magnetization to the antiparallel magnetization is hereinafter referred to as the "reset" of the magnetic element

  bistable). When the object approaches the proximity detector

  mity, the resulting alternating magnetic field

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  a critical distance fixed in advance, at the level of the minimums of the pulsating magnetic field, an intensity sufficient to

  bring the bistable magnetic element back to its original state.

  When the following sign change in the magnetic field results

  the intensity of the field increases again in the opposite direction sufficiently that the magnetization of the soft magnetic region changes sharply again by producing a characteristic pulse in the detector winding and the bistable magnetic element is again brought in the state of magnetic saturation. As long as the distance from the object to the proximity detector remains below the critical distance, the bistable magnetic element is excited asymmetrically.

  and it is generated in each period a strong impulse

  (when the bistatic magnetic element is

  ble to its initial state it is also generated a pulse

  which, however, has a much smaller amplitude).

  In the case of the second variant of the proximity detector the influence exerted by the magnetic field, coupled

  to the object to be monitored, at the level of the magnetic element bis-

  The table does not become stronger, as it does for the first variant, but weakens as the distance from the object to the proximity detector decreases. It has already been explained how this could happen. As long as the object is far away, the magnetic field depending on the distance of the object must then prevail sufficiently on the field

  pulsating magnetic field produced by the inductive winding

  for the resulting magnetic field to be a field con-

  pulsating tinu of inverse polarity. At this state there is no characteristic pulse train in the detector winding. When the distance from the object to the detector of

  proximity decreases, the influence of the non-pulsating magnetic field

  at the level of the bistable magnetic element decreases and the

  resulting magnetic field becomes, instead of a pulsating field

  continuous field, an alternating pulsating field which, starting from

  of a critical distance forming a threshold, is able to

  the bistable magnetic element to its initial state and, after the next sign change, during the same period to bring it back to the state of magnetic saturation

  abruptly changing the magnetization direction of the ma-

  sweet gnetic of the bistable magnetic element so that,

  as in the case of the first variant, a train of

  is produced in the detector winding by excitation

  asymmetrical bistable magnetic element.

  In both variants it is obviously possible to obtain, by choosing a suitable arrangement of the magnetic fields,

  that the characteristic pulses in the winding detect

  are not generated below, but beyond the dis-

  determined critical threshold, that is to say that, when the object is far away, the two magnetic fields are superimposed to form an alternating magnetic field which

  allows the asymmetric excitation of the bistatic magnetic element

  as the object gets closer to the

  proximity sensor the resulting alternating magnetic field

  as it gets closer, by variation of its field component

  continuous, more and more of the state of a magnetic field con-

  tinu whose ability to return the bistable magnetic element to its initial state ends from a determined critical distance, thereby interrupting the pulse train in

the detector winding.

  According to another embodiment of the invention, it is a question of generating the characteristic pulses in the detector winding, not by asymmetric excitation.

  but by symmetrical excitation. The sizing and the

  of the inductor winding and the value of the alternating excitation current, preferably a sinusoidal alternating current, must be chosen in such a way that, in the absence of another magnetic field, the alternating magnetic field resulting from the winding inductor excites the bistable magnetic element symmetrically so as to generate, during each half-wave, in the detector coil a

  characteristic voltage pulse, the impulses presented

  alternatively a different polarity. In the case of the symmetrical excitation the magnetic polarity of the soft magnetic region of the bistable magnetic element is first 1 1 inverted during each half-wave, which leads to a

  strong impulse in the detector and, if the inten-

  Moreover, the magnetic polarity of the hard magnetic region is also inverted during the same half-wave, which causes in the coil-detector a substantially smaller impulse which is generally not

not exploited.

  The symmetrical excitation proximity sensor of the bistable magnetic element can in principle operate in two ways. In the first variant, the continuous magnetic field, the intensity of which at the level of the bistable magnetic element depends on the distance of the object to be monitored, is

  chosen so that its intensity at the level of the element

  Bistable gnetic increases as the distance from the object

  to the proximity sensor decreases. In the alternating magnetic field

  native is then superimposed more and more on a continuous magnetic field. when the distance from the object to the proximity detector becomes less than a first critical distance, the amplitude of the resulting magnetic field oriented in one direction, which is opposite to the direction of the continuous field, is no longer sufficient to be able to change again in this direction the magnetization of

  the hard magnetic region of the bistable magnetic element.

  This has the consequence that the symmetrical excitation becomes an asymmetric excitation of the bistable magnetic element and

  that the impulses of one of the polarities are suppressed

  mées. When the object gets closer to the proximity detector, the resulting magnetic field oriented in one direction, which is opposite to the direction of the continuous field, becomes so weak, when the distance from the object to the proximity detector is brought back within a second (smaller) critical distance, than it is not enough to bring the bistable magnetic element back to its initial state, so that the pulses excited asymmetrically in the winding

detector are also missing.

  In the case of the second variant, the continuous magnetic field whose intensity at the level of the bistable magnetic element depends on the distance from the object to the detector of

  proximity, is chosen in such a way that it decreases

  calf of the bistable magnetic element as the

  tance of the object to the proximity sensor decreases. As long as

  the object is far away, the continuous magnetic field super-

  applying to the magnetic field from the field winding a continuous field component strong enough for the resulting magnetic field at the magnetic element

  bistable is a pulsating continuous field. As the result

  jet approaches the proximity detector the continuous magnetic field component at the bistable magnetic element weakens and the bistable magnetic element changes from the non-excited state, when the distance from the object to the

  proximity sensor becomes less than a first dis-

  critical, first in the state of asymmetric excitation,

  in which an impulse of the same polarity is firstly pro-

  in each period, to finally pass, when the distance from the object to the proximity detector becomes

  less than a second critical distance, in the state of exci-

  symmetrical tapping, in which pulses of alternating polarity are produced in the detector winding, namely

  two pulses per period (one pulse per half wave).

  In both variants the two-phase signal, cor-

  corresponding to the transition from symmetric excitation to excita-

  asymmetrically, on the one hand, and the transition from asymmetric excitation to a non-excited state (absence of pulses),

  on the other hand, can be advantageously used for triggering

  successively two different processes. For example, at the moment when the first critical distance (greater) is reached, reduce the drive of a

  machine at a reduced speed (slow

  where the distance from the object to the proximity

  less than a second (smaller) critical distance, the control mechanism is completely stopped.

  Another advantage of the symmetrical excitation of the detection

  The proximity sensor according to the invention resides in that it makes it possible to distinguish which of two directions is that in which an object approaches the proximity detector.

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  or which of two different objects is closer to the proximity detector. This goal can be achieved

  establishing for both directions or for both

  throws continuous magnetic fields of opposite polarity superimposed on the alternating magnetic field of the inductor winding. For this purpose two objects, which are close to the proximity detector, can for example each carry a permanent magnet, thus making it possible to establish at the level of

  the bistable magnetic element of the fields of opposite polarity.

  If one of the objects gets too close to the proximity switch,

  then it appears in the winding detectors in the inter-

  transitional value of asymmetric excitation, impulse

  polarity but, in case of approaching the other object, pulses of the opposite polarity, so that during the asymmetric excitation the polarity of the pulses

* can be used to distinguish the objects.

  At the detector winding can advantageously be connected a phase detector which determines the phase position

  pulses generated in the detector winding by

  to the phase of the periodic excitation current in the

  inductor bearing. If we take for example as a point of

  the case of symmetrical excitation of the magnetic element

  that bistable and a continuous magnetic field is superimposed on the alternating field with increasing intensitybe as the object to be monitored approaches the critical distance threshold, then the pulses thus produced, when the alternating field is finds in its phase during which it is oriented in the opposite direction of the continuous field,

  move more and more towards the highest point of the cou-

  excitation in this phase interval until,

  finally, the change in the magnetization of the magnetic region

  tick in the corresponding direction can no longer be

  to the culminating point, whereas in the case where the object

  gets closer to the proximity sensor the more

  Bistable magnetic resonance can only be excited asymmetrically and the pulses of one of the polarities are suppressed in the detector winding. The variation of the phase position of the pulses thus allows

  to deduce to what extent the object to be monitored is still distant

  of its critical distance, forming a threshold, with respect to the proximity detector. Thus, a machine member can already be slowed down, by appropriate measures, sufficiently before this threshold critical distance is reached.

  Permanent magnets or sets of magnets

  manents advantageously serve as means for producing continuous magnetic fields, although electromagnets

  can in principle also be used for this purpose.

  Advantageously, the bistable magnetic element is fixedly mounted,

  while permanent magnets and ferromagnetic elements

  influencing these permanent magnets are mobile and

  linked to the object to be controlled remotely. In principle, however, it is also possible to reverse this provision by

  rendering, on the contrary, the mobile bistable magnetic element.

  In order to obtain signals with high efficiency it is preferable to use as bistable magnetic element a

  Wiegand wire and arrange the detector winding and the winding

  inductor around the bistable magnetic element.

  Exemplary embodiments of the proximity sensor according to the invention are explained below and shown very schematically in the accompanying drawings in which:

  FIG. 1 shows a proximity detector comprising

  a Wiegand wire; FIG. 2 represents, in graphical form, the operating mode of the proximity detector of FIG. 1, in the case of symmetrical excitation in a first switching state; FIG. 3 is a graph, similar to that of FIG. 2, illustrating a second switching state; FIG. 4 is a graph, similar to that of FIG. 2, illustrating a third switching state; FIG. 5 shows the proximity detector of the

  Figure 1 in case of operation under conditions of exci-

  asymmetrical tation; - Figure 6 is a graph, similar to that of the

  FIG. 2, illustrating one of the switching states of the detection

  proximity switch of FIG. 5; and FIG. 7 is a graph, similar to that of FIG. 6, showing the other switching state of the proximity detector of FIG. 5. According to FIG. 1 a detector winding 2 and an inductor winding 3 are wound on a Wiegand wire 1. A

  magnet bar 4 is mechanically connected to an object to be

  ensure. The magnetic bar is arranged parallel to the Wdiegand wire 1 and can be moved parallel to itself so that it can be brought closer to the wire Wiegand 1 and thus strengthen the continuous field, coming from the bar, at the wire

  Wiegand 1. The inductor winding 3 is powered by a

  sinusoidal alternating current 1e with angular frequency w - Ie = Io * sin t

  where t represents the time and I represents the amplitude of the

rant of excitement.

  It is thus produced at the Wiegand wire 1 an alternating magnetic field which also varies sinusoidally: Xe = H. sinwt

  o H represents the intensity of the magnetic field.

  As long as the magnet bar 4 is far away, practically

  no continuous field is superimposed on the alternating field.

  tif He (Figure 2). At the moment when the field strengths H a and

  - they are affected each time, under conditions

  a symmetric excitation, a strong impulse Wiegand 5

  in the detector winding 2. The Wiegand pulses 5 pre-

  - feel different signs alternately (Figure 2); these pulses come from the fact that the magnetically soft core of wire Wiegand 1 sees its sense of magnetization becoming

  abruptly antiparallel to the magnetic envelope

  that lasts. For an even higher field strength s or - H. the envelope also changes polarity and its direction of magnetization becomes parallel to that of the core of the Wiegand wire. This causes in the detector winding 2 a

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  weaker pulse 6 which in general is not exploited.

  When the magnet bar 4 gets closer to the Wdiegand wire

  1, a continuous magnetic field H is superimposed on the alternating field

  native He. When Hm at wire Wiegand 1 becomes higher

  In the case of Ho - Hs, the field strength H = Ho - Hm is no longer sufficient to reverse the magnetization direction of the envelope.

  magnetic hard wire Wiegand and the symmetric excitation of

  comes an asymmetric excitation in which only Wiegand pulses 5 of the same polarity remain

(Figure 3).

  When Hm at wire Wiegand 1 exceeds the value Ho - HR, o H, represents the field strength necessary to return the core of wire Wiegand 1 to its initial state.

  changing its sense of parallel magnetization to a sense of magnetism

  antiparallel (with respect to the direction of magnetization of the envelope), this field strength being about 16 A / cm, then this delivery Wiegand wire 1 to its initial state is also lacking and it does not occur any more. everything from impulses

Wiegand (Figure 4).

  If it is a question of exciting the wire Wiegand 1 not with alternating current but with a pulsating direct current Ieg (FIG. 5), it is possible for this purpose to connect to the inductor winding 3 a bridge rectifier 7 which is powered from an AC source 8 and rectifies the current

  alternative by full-wave rectification.

  As long as the magnet bar 4 is sufficiently far from the wire Wiegand 1 so that its field at the wire Wiegand 1 is negligible, only the pulsating continuous field Heg acts

  on the wire Wiegand 1 (Figure 6). Since no change

  sign of the Heg magnetic field does not take place, it does not occur

  also does not have Wiegand impulses in the winding

detector 2.

  If, however, the magnet 4 is close to the wire Wiegand 1, then the magnetic field Hm of the magnet bar 4 is superimposed on the pulsating continuous field Heg with respect to which it is oriented in the opposite direction. The resulting magnetic field Heg - Hm is an alternating field. As soon as the magnet bar 4 is sufficiently close to the wire Wiegand 1 so that Hm at the wire Wiegand 1 exceeds the value HR, where HR is the field strength (about 16 A / cm) necessary to bring back the wire Wiegand Magnetically in its initial state (as explained above with reference to FIG. 4), the vWiegand wire 1 can be periodically reset to its initial state so that pulses 5 are also periodically produced in the stool. In both embodiments, it is necessary to connect to the terminals 9 and 10 of the e-roll. detector 2 the evaluation circuit. Celldioi can also count a

  phase detector which detects the positioL. the phase of

  Wiegand 5 impulses compared to the phease of the ezero current

alternative ion Ie or continuous gi

RÉNVDICATIMN

  A magnetic proximity detector comprising a bistable magnetic element and means for producing a continuous magnetic field, which acts on the bistable magnetic element to a varying degree depending on the distance of the magnetic field.

  the object to be monitored at the proximity switch, and a winding

  sensor which is magnetically coupled to the magnet element

  bistable tick and in which, at the instant when the distance from the object to be monitored to the proximity sensor passes through a critical value set in advance, an electrical pulse is

  induced by a sudden change in the sense of magnetism

  in the bistable magnetic element, characterized in that the bistable magnetic element (1) is coupled

  an additional electric winding (3) (winding

  inductor) which is fed with a periodic electrical signal whose polarity and power are during each period such that the intensity of the magnetic field produced by the periodic electrical signal in the inductor winding (3) is capable of the bistable magnetic element (1) to change the magnetization direction of the element

magnetic bistable (1).

  2. Proximity detector according to claim 1, characterized in that the inductor winding (3) is connected to

  a current source (7) producing a pulsating direct current

  whose pulsating magnetic field is oriented, at the level of the bistable magnetic element (1), at least with a

  magnetic field component in the opposite direction of the magnetic field

  tick depending on the distance.

  Proximity detector according to Claim 2,

  characterized in that the current source (7) is a redres-

  alternator powered by alternating current.

  4. Proximity detector according to claim 1, characterized in that the inductor winding (3) is connected to

  a source of alternating current, the intensity of the magnetic field

  alternating tick coming from the inductor winding (3) being sufficient to allow this field, in the absence of another magnetic field, to excite the bistable magnetic element (1) 4-

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  symmetrically in order to invert its direction of magnetization.

  5. Proximity detector according to claim 4, characterized in that, to distinguish two objects approaching alternately proximity detector, these objects are connected in such a way as to produce different continuous magnetic fields that these Continuous fields are oriented in opposite directions with respect to each other at the level of the bistable magnetic element and become at this level either more intense or weaker as the distance from the respective object to the

proximity detector increases.

  Proximity detector according to Claim 4,

  characterized in that to distinguish two directions

  in which objects can get closer to the proximity sensor these objects are connected in such a way

  to means of producing continuous magnetic fields different

  that when objects approach the proximity detector in one of the two directions, these continuous fields are oriented, at the level of the bistable magnetic element, in the direction of continuous fields produced when objects

  get closer to the proximity switch in the other direc-

  and that both the fields oriented in one direction and those oriented in the other direction become either weaker or more intense as the distance from the objects to the proximity detector increases. any of the

  Claims 1 to 6, characterized in that the winding

  detector (2) is connected a phase detector by which the position of the voltage pulses produced in the detector winding (2) as a result of the inversion of the magnetization direction in the bistable magnetic element (1) is determined by compared to the phase of the periodic electrical signal supplying

the inductor winding (3).

  8. Proximity detector according to any one of

  Claims 1 to 7, characterized in that to produce the

  magnetic field. permanent magnet is provided (4) or

a set of permanent magnets.

  9. Proximity detector according to claim 8, characterized in that the permanent magnets (4) are fixed mounted and are influenced by ferromagnetic elements whose displacement is related to the movement of the object or objects to be monitored. 10. Proximity detector according to any one of

  Claims 1 to 9, characterized in that the magnetically

  bistable tick (1) is a Wiegand thread.

  11. Proximity detector according to any one of

  Claims 1 to 10, characterized in that the winding

  detector (2) is located on the bistable magnetic element (1).

  12. Proximity detector according to any one of

  Claims 1 to 11, characterized in that the winding

  inductor (3) is on the bistable magnetic element (1).