FR2477702A1 - INDUCTIVE DISPLACEMENT INDICATOR - Google Patents

Abstract

INDUCTIVE DISPLACEMENT SENSOR INCLUDING AN INDUCTIVE WINDING, A DETECTOR WINDING AND A FERROMAGNETIC CORE, THE INDUCING WINDING BEING SUPPLIED WITH A PERIODIC VOLTAGE SIGNAL AND THE RESPONSE SIGNAL PRODUCED IN THE DETECTOR WINDING BEING REPRESENTATIVE OF THE PATH. THE FERROMAGNETIC CORE IS A BISTABLE MAGNETIC ELEMENT 1 ON EACH OTHER WHICH ARE PROVIDED FOR MEANS 6, 7 TO PRODUCE A MAGNETIC FIELD 5, INVARIABLE OVER TIME, WHICH PRESENTS AT THE LEVEL OF THE BISTABLE MAGNETIC ELEMENT 1 A GRADIENT OF L 'MAGNETIC FIELD INTENSITY, THE MAGNETIC ELEMENT 1 AND THE MEANS 6, 7 THAT CAN BE THE OBJECT OF A RELATIVE DISPLACEMENT WHOSE DIRECTION HAS A PARALLEL COMPONENT TO THE GRADIENT OF THE MAGNETIC FIELD INTENSITY AT THE MAGNETIC ELEMENT LEVEL 1. THE SENSOR FOLLOWING THE INVENTION CAN BE USED IN PARTICULAR FOR MEASURING THE JOURNEY CARRIED OUT BY A TEST.

Description

The present invention is based on an indicator or inductive sensor of

  displacement comprising an electric winding inductor or exciter, a detector electric winding

  and a ferromagnetic core coupling the inductive winding

  and the magnetic detector winding, the inductor winding being fed with a periodic voltage electrical signal and the electrical response signal produced in the detector winding being representative of the path to be measured. By winding

  inductor means a winding which is

  with a periodic voltage signal of

  aunt. This voltage signal is used to provoke

  in a second winding, namely winding detected

  an electrical response signal, the coupling of the two windings varying, in a manner fixed in advance, according to the path to be measured so that the nature

  of the response signal, produced in the winding detected

  depends on the path taken by a specimen or test body, ie the position of such a test

test tube at a given moment.

  It is known, in the case of a displacement sensor,

  inductive, to make the transformer coupling of the inductor winding (primary transformer)

  and the detector winding (secondary of the transforma-

  vary according to a route, making

  the position of the ferromagnetic core, by which

  the two windings are coupled together, or in

  making the transformer coupling to be reinforced or weakened by the fact that ferromagnetic parts are brought closer to or distant from the otherwise invariable assembly formed of the windings and a coupling core

  these between them. The test tube, of which it is

  watch the move or the position, can constitute

  itself the ferromagnetic core or be a ferro-

  separated romagnetic acting on the windings or be connected to such a piece by means of drive members, so that in any case the variation of the position of the specimen is 2 - bound in a cause-and-effect relationship to a variation of

coupling of the two windings.

  In known inductive displacement sensors

  the inductor winding is fed with a current of

  constant amplitude and amplitude of the signal

  AC voltage produced in the winding detected

  as an answer is representative of the posi-

  tion, or change of position, of the specimen

  vigil. The response signal is therefore an alternating voltage

  native amplitude modulated. This is why the evaluation circuit following the detector winding must

  be adjusted in a very precise way so that the ampli-

  the response signal is transmitted in a manner that is perfectly consistent with the measurement value and is not

distorted.

  The object of the present invention is to create an inductive displacement sensor capable of producing a

  response signal that can be evaluated in a simple way.

  in full compliance with the measurement value.

  This object is achieved according to the present invention, for a displacement sensor of the kind described above, by producing the ferromagnetic core in the form of a bistable magnetic element, by providing means to produce a magnetic field, invariable over time,

  which is superimposed on the bistable magnetic element and

  at the level of the latter, a gradient of the intensity

  magnetic field, and allowing the magnetic element

  bistable tick and the means of producing a magnetic field

  to move relative to each other, the

  direction of relative displacement-presenting a

  parallel to the magnetic field intensity gradient

  tick at the level of the bistable magnetic element. On au

  very advantageous features of the present invention.

are described later.

  As bistable magnetic elements,

  bistable magnetic switching cores, it is appropriate in particular to use wires of the type known as

  Wiegand whose constitution and manufacture are de-

  German Patent Application Publication No. 2,143,326. Wiegand yarns are, in their composition, homogeneous ferromagnetic yarns (for example, an alloy of iron and nickel, preferably 48% of iron and 52% of iron). nickel, or an alloy of iron and cobalt, or an iron alloy with cobalt and nickel, or an alloy of cobalt with iron and vanadium,

  preferably 52% cobalt, 38% iron and 10% vanadium.

  dium), which as a result of mechanical and thermal treatment

  that special have a soft magnetic core and a hard magnetic shell, that is to say that the envelope

  has a coercive force superior to that of the nucleus.

  Wiegand yarns typically have a length of 50 mm, preferably 20 to 30 mm. If a wire Wiegand, in which the magnetization sense of the magnetic core

  soft corresponds to the magnetization direction of the envelope

  gnetic, is placed in an external magnetic field

  whose direction corresponds to the direction of

  the axis of the wire but whose meaning is opposed to the meaning of

  Wiegand wire, then the sense of magnetization of the soft core of the Wiegand wire is reversed in case of

  exceeding a field strength of about 16 A / cm.

  This inversion is also called resetting. In case of a new reversal of the direction of the field

  external magnetic sense of magnetization of the nucleus

  again as soon as the intensity of the external magnetic field exceeds a critical value, so that the

  core and envelope are again magnetized by

  rallèlement. This inversion of the sense of magnetization is

  very quickly and is accompanied by a strong vari-

  corresponding magnetic flux per unit of time (Wiegand effect). This variation of the magnetic flux can

  induce in an induction coil an impulse of

  short and very strong Wiegand pulse (depending on the number of turns and the resistance of

  charge of the induction coil reach up to about

12 volts). -

  When returning the nucleus to its initial state, a pulse is also produced in an induction coil, but this pulse has, compared to the case of the passage of the direction of magnetization parallel to parallel parallel, a substantially greater amplitude. weak and of opposite sign. If one chooses as external magnetic field

  an alternating field, capable of reversing the magnetism first

  tation of the core and then that of the envelope and bring them each to the state of magnetic saturation, then

  it occurs as a result of the change in the sense of magnetism

  of the soft magnetic core, Wiegand pulses alternatively having a positive polarity and a negative polarity and then we can speak of an excitation

  symmetrical wire Wiegand. For this, intensities

  field strengths from about - (80 to 120 A / cm) to + (80 to 120 A / cm). The inversion of the magnetization of the envelope is

  also produced abruptly and also leads to an im-

  impulse in the induction coil but this impulse

  is much lower than that induced during the

  version of the core magnetization and is not exploited

in most of the cases.

  If, on the other hand, we choose a magnetic field

  If a field is able to reverse only the magnetization direction of the soft nucleus and not the hard envelope, then the strong Wiegand pulses occur with the same polarity and then we can speak of an excitation. asymmetrical Wiegand wire. For this it is necessary in a sense a field intensity of

  minus 16 A / cm (to bring the Wiegand wire back to

  tial) and in the opposite direction a field intensity

from about 80 to 120 A / cm.

  It is characteristic of the Wiegand effect that the pulses produced by this effect are, as for

  their amplitude and width, to a large extent inde-

  pendants of the speed of variation of the magnetic field

  outside and have a high signal-to-noise ratio.

  In the context of the invention, it is also possible to use differently designed bistable magnetic elements, provided that they comprise two regions which are magnetically coupled to one another and which have a magnetic hardness (strength with respect to each other). coercitive) and may, similarly to Wiegand wires, be used for pulse generation by rapid, induced inversion of the magnetization of the soft magnetic region. So, it is described for example,

  in German Patent No. 2,514,131 a core of switching

  a bistable magnetic core in the form of a wire which consists of a hard magnetic core (for example nickel-cobalt), an electrically conductive intermediate layer (for example made of copper) deposited on the core and a soft magnetic layer (for example nickel-iron) deposited on the intermediate layer. A

  Another variant further comprises a core formed of a

  inner duct devoid of permeance (for example beryllium-copper) on which the layer is deposited

  hard magnet on which is then deposited the

  intermediate layer which is finally covered with the layer

  soft magnetic. This magnetic switching core bis-

  known table, however, generates switching impulses

  smaller than those generated by a Wiegand wire.

  At the level of the bistable magnetic element are superposed the invariable magnetic field over time

  and the periodic magnetic field, produced by the winding

  inductor, to form an alternating magnetic field

  periodic native that brings the bistable magnetic element

  to periodically change magnetic polarity, that is,

  that is, to reverse the magnetization direction of its ma-

  sweet genetics and possibly its hard magnetic region. The periodic change of the magnetic polarity of the bistable magnetic element takes place abruptly

  and leads to the generation of a typical train of impulse

  characteristics in the detector winding. The moment of onset of these pulses depends on the interaction of the invariable magnetic field over time and the field

  periodical magnet since, to trigger the impulse

  the resulting alternating magnetic field must, at the level of the bistable magnetic element, exceed in both directions the threshold values determined by the

  properties of the bistable magnetic element. As a result

  when the intensity of the alternating magnetic field

  resultant, the phase position of the pulses pro-

  of the phase of the periodic excitation voltage signal, also varies. The response signal of the displacement sensor according to the invention is therefore a

  pulse train modulated in phase and at a constant amplitude

  which can then, in a downstream evaluation circuit, be processed additionally, both in digital form and in analogue form, in

  perfect-compliance with the measured value.

  For a given amplitude of the magnetic field, periodically variable as a function of time, product

  by the inductor winding at the magnetic element

  bistable tick the field of action of the displacement sensor

  is limited in space to values of intensi-

  invariable magnetic field in time that are.

  less than the field strength necessary to restore the bistable magnetic element to its state

  in the case of asymmetric excitation) or for

  the magnetization of the hard magnetic region of the

  bistable magnetic resonance (in case of symmetrical excitation),

  the amplitude of the magnetic field produced by the winding

  inductive, since in this case only the resulting magnetic field is able to invert by magnetic means the polarity of the bistable magnetic element

  after each sign change. By handing over

  bistable magnetic resistor in its initial state

  tending to reverse the magnetization direction of the soft magnetic region so as to pass it parallel to the antiparallel orientation with respect to the magnetization direction of the hard magnetic region. Evaluation of the response signal is obviously particularly simple if there is as much as possible a linear relationship between the phase position of the response pulses and the change of position of the specimen. This is why it is advantageous that the gradient of the invariable magnetic field over time is as constant as possible and that the voltage signal

  brought to the inductor winding present during each

  that period as much as possible a linear pace in

  function of time. Means to linearize the distribution

  bution, in space, of the invariable magnetic field

  in time are part of the prior art.

  The time-invariant magnetic field can best be obtained by means of permanent magnets, although electromagnets can in principle also be

be used for this purpose.

  In order to obtain a field of action as wide as possible of the displacement sensor and in order to facilitate the linearization of the invariable magnetic field over time it is advisable to provide, as a field

  invariable magnetic field over time, a field that presents

  a zero crossing (change of sign) of the inten-

  magnetic field, this zero crossing of the inten-

  field of view being preferably in the middle of the

  field of action, in space, of the displacement sensor.

  This advantage can not, however, be fully

  did that if at the same time the periodic magnetic field of the inductive winding is an alternating field, both the magnetic field invariable in time and the field

  alternatively, preferably symmetrically

  triply with respect to their respective zero crossing.

  Here too, the field of action, in space, of

  displacement sensor is limited to values of the in-

  magnitude of the invariable magnetic field over time which

  are sufficiently smaller than the amplitude of the magnetic field

  alternative genetics so that a reversal of the sense of

  may still take place after each change

  sign. Since a certain difference must therefore be respected in any case between the intensity of the invariable magnetic field in time and the amplitude of the alternating magnetic field, good results can be obtained by using, as a voltage signal - 8 exciter to create the alternating magnetic field, a sinusoidal alternating voltage since this is already largely linear as a function of time in a large range on both sides of zero crossings. In the marginal areas of the field of action, that is to say when using the magnetic field of

  inductor winding in the vicinity of the maximum values

  As transients of the magnetic field intensity, a correction of linearity defect can be made to the response signal by appropriate measurements in terms of mounting. This linearity defect correction does not need to be performed if you use it from the start

  a sawtooth-shaped voltage signal for the power supply

  mentation of the inductor winding.

  The displacement sensor can be operated

  according to the invention under excitation conditions

  the asymmetric element of the bistable magnetic element and this

  especially when the magnetic field periodically varies

  The inductive winding produced by the inductive winding is a pulsating DC field that the invariable magnetic field in time contradicts so that the resulting magnetic field is an alternating field. For a given amplitude of the pulsating DC field, the field of action of the displacement sensor is a function of the intensity of the invariable magnetic field in the

  time at the bistable magnetic element. Linen-

  the invariable field strength in time must at least be sufficient for the resultant alternating field at the bistable magnetic element to be

  meaning (the negative sense), at least quite intense for

  see returning the bistable magnetic element to its initial state, that is to say to be able to change the magnetization of the soft magnetic region of the bistable magnetic element so that its direction of magnetization is no longer parallel but antiparallel to the magnetization direction of the hard magnetic region, and the intensity of the invariable field over time must, at

  level of the bistable magnetic element, become

  9 high enough for the resulting field strength

  still allow the magnetic element

  table again from antiparallel magnetization to magnetism

  of its regions, change during the

  which a strong characteristic impulse is produced in the detector winding. When using a Wiegand wire as a bistable magnetic element

  for the delivery of the latter to the initial state,

  a field strength resulting from about -16 A / cm, whereas to reverse the magnetization so as to obtain the parallel orientation into the saturation range typically a field strength of about 80 to 120 A / cm. If the indicated minimum of the intensity of the invariable magnetic field in time is not reached, the bistable magnetic element can no longer be brought back to its initial state by magnetic means. If the intensity of the invariable field in time exceeds the maximum indicated, the magnetization of the bistable magnetic element can no longer be reversed, despite its reset, by magnetic means, so as to obtain the orientation parallel; in both cases the characteristic pulses are lacking. If, however, the intensity of the invariable magnetic field in time increases, beyond the maximum indicated, it may happen that the resulting magnetic field becomes so

  intense in the opposite direction that the magnetization of the re-

  The hard magnetic element of the bistable magnetic element is inverted and the bistable magnetic element is again subjected to asymmetric excitation, which nevertheless leads to pulses of opposite polarity.

in the detector winding.

  However, the displacement sensor should preferably be operated so that

  the bistable magnetic element is excited symmetrically.

  In this respect, an advantageous embodiment of

  the invention consists in that the magnetic field

  in time is established so as to present, within the field of action, in space, the sensor

- 10 -

  of displacement a zero crossing (change of sign) of its magnetic field strength and in that the field

  magnetic, periodically variable in time,

  duit by the inductor winding is an alternating field.

  In this case, it is furthermore advantageous that the zero crossing of the invariable magnetic field in time is approximately in the middle of an intensity interval.

  constant gradient field, in space, of the inten-

  field of view, and that the alternating field produced by the inductor winding at the bistable magnetic element is symmetrical with respect to periodic zero crossings (sign changes) of its field strength. According to another advantageous characteristic of the invention, the inductor winding is supplied with a sinusoidal alternating voltage. Next one more

  Another advantageous characteristic of the invention is the

  The inductor is supplied with an alternating

  sawtooth, the two sides of each tooth having the same slope. In the case of symmetrical excitation and for a given positive and negative amplitude of the alternating magnetic field, the field of action of the displacement sensor is limited by the fact that at the level of

  the bistable magnetic element the amplitudes of the inten-

  sity of the resulting alternating magnetic field are suf-

  in both directions to reverse the magnetization direction not only of the soft magnetic region but also of the hard magnetic region. Yes

  this condition is respected, we get in the hoist-

  Detecting a pulse train with alternating signs, the position of the pulses with respect to the phase of the exciter voltage signal being representative of the position, or the change of position, of the test piece being monitored. If the indicated condition is not respected, but the bistable magnetic element is brought into a

  zone with the highest intensity of the invariant magnetic

  time, then the symmetric excitation of

  the bistable magnetic element first becomes an exciter

  asymmetric tapping of the bistable magnetic element so that pulses of one polarity do not occur

  more in the detector winding, the polarity of the pulses

  which continue to occur depending on the direction in which the field of action of symmetric excitation

is exceeded.

  It is advisable to linearize the field of

  symmetrical excitation of the bistable magnetic element. In the event of crossing the threshold marking the transition from the symmetrical to the asymmetrical excitation,

  the evaluation circuit to connect to the winding detec--

  Advantageously, it can be produced in such a way that it delivers a warning signal which indicates that the linear field of action of the displacement sensor is exceeded and the direction in which it is exceeded.

occurs.

  Whether the bistatic magnetic element

  ble is at rest and the invariable magnetic field in time moves or conversely, is unimportant

  for the operating principle of the displacement sensor

  cement; both cases are possible. The displacement of the

  invariable magnetic field over time can be obtained

  naked by moving the magnets producing this field but can also be obtained, in the case of fixed magnets,

  by moving ferromagnetic conductive elements.

  The inductor winding and the winding detect

  may in principle be arranged next to the

  bistable magnetic element if this makes it possible to achieve sufficient magnetic coupling with the bistable magnetic element. However, both the inductor winding and the detector winding are preferably directly placed around the bistable magnetic element. In order to obtain signals with a good performance it is in

  It is also advantageous to use as a magnetically

that bistable a wire Wiegand.

  In addition, it is advantageous for the two superimposed magnetic fields to have, at the level of the bistable magnetic element, field lines extending in parallel, preferably parallel to 12 -

  the longitudinal axis of the bistable magnetic element.

  Displacement sensors usually transform

  linear movements, that is to say changes in

  linearly performed positional gears into an output signal. In this case, it is also possible to use the displacement sensor as a sensor

  angle of rotation. This assumes that the magnetic field

  that invariable in the present time, in an interval

  azimuthal angle, a gradient of the inten-

  field of view in the azimuthal direction, which gradient should be analogous to the case of a

  linear displacement, preferably constant in the

  corresponding azimuthal angular range (field of action),

  and linked to a zero crossing of field strength.

  Two exemplary embodiments of the invention are described below and shown very schematically in the accompanying drawings in which: FIG. 1 represents, in principle, the

  construction of a displacement sensor according to the in-

  vention; FIG. 2 represents the shape of a magnetic field, invariable in time, which is suitable for the displacement sensor; - Za Figure 3 illustrates the phase position of

* response pulses in the case where the winding in-

  driver is excited with a sinusoidal alternating

  dale and Wiegand wire is disposed at the zero crossing of the invariable magnetic field in time; - Za Figure 4 is a representation similar to that of Figure 3, the Wiegand wire has been moved

  outside the zero crossing of the invasive magnetic field

  reliable in time; and FIGS. 5 and 6 are representations similar to those of FIGS. 3 and 4 with however the difference that an alternating voltage in the form of

  sawtooth is used for the excitation of the hoist

inductor.

  The displacement sensor shown on the

- 13 -

  FIG. 1 is constituted by a Wiegand wire 1 forming

  bistable magnetic field, an inductor winding 3 connected to an AC voltage source 4 and which, like a detector winding 2, directly surrounds the Wiegand wire, an evaluation circuit 8 following the detector winding 2 and which determines the nature

  and the phase position of the voltage pulses pro-

  picked up in the detector winding 2, as well as by two magnetized bars 6 and 7 which extend parallel to the

  wire Wiegand 1 on either side of it and present

  antiparallel magnetization senses, one

  port to another, so that the magnetic field 5 which

  between the two magnets 6 and 7 is a step

  wise by zero, that is, an inversion occurs

  direction of the magnetic flux. Provided that

  two magnets 6 and 7 have the same intensity of

  the magnetic field 5 is not deformed.

  by external influences, this passage by zero

  of the magnetic field strength is central-

  between the two magnets-: 6 and 7. The speed of the HM (s) intensity of such a magnetic field is represented on

  Figure 2 where s denotes the distance between the two

mants 6 and 7 along a line.

  If the inductor winding 3 is powered with

  a sinusoidal alternating voltage, the inductive winding

  3 produces an approximately sinusoidal magnetic field in time, which field varies, at the Wiegand wire, according to the formula (I) Hws = Hws. sin ut

  or Hws represents the intensity of the alternating magnetic field

  native at wire level Wiegand 1, Hws the amplitude of this

  field, t the time and w the pulsation of the

  exciter alternative. If, at wire Wiegand 1, the alternating magnetic field Hws acts alone

  and that the amplitude of the latter is greater than

  HS field strength (FIG. 3) required to invert the magnetization of the Wiegand wire 1 symmetrically

- 14 -

(II) ilws> Hs

  (HS being in the case of Wiegand wires included in the

  range from + (80 to 120) A / cm), then it occurs, for

  a determined field strength Hp less than

  field strength Hs, Wiegand pulses 9, pronounced

  and features that are shown in Figure 3.

  For the field strength Hp the magnetization of the master nucleus

  The gentle genetics of the Wiegand 1 thread are reversed in such a way that

  be from antiparallel to parallel orientation.

  For the field strength Hs is then reversed the magnetization direction of the hard magnetic envelope Wiegand wire. This causes in the detector winding 2 also a pulse which is however much weaker than the pulse 9 occurring for the intensity

  Hp field and is no longer considered below.

  under. This impulse can be suppressed by a simple

discriminator circuit.

  Wiegand pulses 9 occur in the ab-

  sence of the field 5 (HM = 0) in the phase positions O t1 and Xo t1 + e. This corresponds to the case where the wire Wiegand 1 is located exactly at the zero crossing of the

magnetic field 5 (HM = 0).

  If now the wire Wiegand 1 is moved in the magnetic field 5 along the double arrow 10 in the direction of one or other of the magnets 6 and 7, then it is superimposed on the alternating field Hws = Hws. sin X t a continuous field HM (s) so that the alternating magnetic field HWS is "raised" or "lowered" depending on whether the wire Wiegand is moved towards one or the other of the magnets 6 and 7 The modified conditions thus obtained can be read in FIG. 4 which indicates the shape of the magnetic field resulting in time:

(III) H = HWS HM

  Wiegand 9 pulses now occur

  in phase positions w t2 and w t3 which, with respect to

  port to the starting positions w t1 and w t1 + to, are

  offset in the direction of the maximum value of

- 15 -

  the field strength, which value is located between these starting positions at the phase position w / 2. As long as HW << Hws, the change of the phase position of the Wiegand pulses 9 takes place in the interval where the field strength HWs or HWS-HM varies linearly.

depending on the phase m t.

  If it is desired to obtain, throughout the phase range, a linear relation between the phase position

  Wiegand pulses 9 and the magnetic field HM inva-

  in time, this can be done by using

  an alternating sawtooth voltage for the power supply

  of the inductor winding 3. The magnetic field

  Hsz of the inductor winding 3 then also

  at approximately sawtooth (Figure 5). As long as the wire Wiegand 1 is at the zero crossing of the field S (HM = 0), invariable in

  the time, the Wiegand pulses 9 present the posi-

  phase m t4 and m t4 + w (Figure 5). If a field

  HM is superimposed on the Hsz alternating field by

  As a result of a displacement of the wire Wiegand 1 along the double arrow 10, then the phase positions of the Wiegand pulses 9 move towards the values X t5 and <t6 which are shifted with respect to the initial phase positions w t4 and t4 + w in the direction of value

  maximum, located in the phase 4/2 position, of the

  field strength, this displacement of the phase positions being proportional to the intensity of the HM field: (IV) w (t - t4) = K1. HM (V) w (t4 + e - t6) = K2. HM o the constants K1 and K2 depend on the slope of the two sides of each saw tooth of the magnetic field

  alternative. If, as is the case in the example

  the two flanks have similar slopes,

  then K1 = K2 and the impulses Wiegand 9 of the two pol-

  have the same phase shift which varies linearly

  depending on the intensity of the HM field.

  If we further linearize the distribution

- 16 -

  localization of the magnetic field HM so that: (VI) HM = K3. s

  o K is a constant, so the phase shift of the impulses

  Wiegand 9 also varies linearly as a function of the displacement A s in the magnetic field 5. The excitation of the wire Wiegand 1 is symmetrical as long as: (VII) HM <IWS - HS (FIG. 3) or (VIII) HM <HSZ- Hs (Figure 5) If these values are exceeded, the excitation becomes asymmetric so that a Wiegand pulse

  out of two is suppressed and the impulses remain

  aunts therefore have only one polarity.

  The asymmetric excitation ends when: (VIIa) HM -> HWs - HR or (VIIIa) HM> HWS-HR o HR represents the field strength (about 16 A / cm)

  necessary to return the Wiegand wire to its original state

tial by magnetic means.

  The limit value deduced from relation (VII)

  is shown in Figure 2. From this

  their limit is determined the field of action Shdu sensor

of displacement.

Claims (15)

  1. - Inductive displacement sensor comprising   an electric winding inductor, an electric winding   detector and a ferromagnetic core coupling the inductor winding and the magnetic detector winding, the inductor winding being fed with a periodic voltage electrical signal and the electrical response signal produced in the detector winding being representative of the measuring, characterized in that the ferromagnetic core is a bistable magnetic element (1), in that means (6, 7) are provided for producing a time-invariant magnetic field (5) which is superimposed on the element   magnetic bistable (1) and present at the level of this   ci, a gradient of the magnetic field intensity, and in that the bistable magnetic element (1) and the means   (6, 7) producing a magnetic field can be   relative displacement between them, the direction of the relative displacement having a component parallel to the gradient of the magnetic field intensity at the level of   the bistable magnetic element (1).   2. - Displacement sensor according to the claim   1, characterized in that the means (6, 7) for   the time-invariant magnetic field (5) are made and arranged so that the gradient of this magnetic field (5) is constant in a certain   interval of the distance to be monitored (s).   3. - Displacement sensor according to the claim   1 or 2, characterized in that the periodic voltage electrical signal, feeding the inductor winding (3), varies in each period linearly as a function of time.   4. - Displacement sensor according to the claim   3, characterized in that the voltage signal is in the form of saw teeth, the two sides of each tooth having a similar slope.   5. Displacement sensor according to any one   claims 1 to 4, characterized in that the - 18 -   means (6, 7) for producing the magnetic field (5) inva-   time are constituted by a permanent magnet   or a set of permanent magnets (6, 7).   6. - Displacement sensor according to any one   claims 1 to 5, characterized in that the   Magnetic field (5) invariable over time is   killed in such a way that it presents inside the   field of action (Sh), in the space of the displacement sensor   a zero crossing (change of sign) of its   magnetic field strength and that the magnetic field   gnetic, periodically variable with time,   generated by the inductor winding (3) is a field ternatif.   7. - Displacement sensor according to the claim   6, characterized in that the zero crossing of the time invariant magnetic field (5) is approximately in the middle of a field intensity interval where the field intensity gradient is constant in the field. space, and in that the alternating magnetic field   produced by the inductor winding (3) at the level of the   bistable magnetic element (1) is symmetrical with respect to periodic zero crossings (sign changes) of its field intensity.   8. - Displacement sensor according to the claim   6 or 7, characterized in that the inductive winding   (3) is supplied with a sin- soldale.   9. - Displacement sensor according to the claim   6 or 7, characterized in that the inductive winding   (3) is supplied with a sawtooth alternating voltage, the two sides of each tooth having the same slope.   10. - Displacement sensor according to any one   claims 6 to 9, characterized in that   downstream of the detector winding (2) is mounted an evaluation circuit (8) which, in the absence of pulses (9) of one of two polarities, delivers a signal fixed in advance. - 19 -   11. - Displacement sensor according to any one   claims 1 to 10, characterized in that   the inductor winding (3) is placed directly around   the bistable magnetic element (1).   12. - Displacement sensor according to any one   claims 1 to 11, characterized in that   the winding detector (2) is placed directly around   the bistable magnetic element (1).   13. - Displacement sensor according to any one   conque of claims 1 to 12, characterized in that   the bistable magnetic element (1) is a Wiegand wire.   14. - Displacement sensor according to any one   conque of claims 1 to 13, characterized in that   the periodically variable magnetic field as a function of time and the magnetic field (5) invariable in the   time, at the level of the magnetic element bis-   table (1), field lines extending as far as pos-   parallel to each other.   15. - Use of a displacement sensor   any of claims 1 to 14, in the   which the invariable magnetic field in the present time   a gradient of field strength in azimuth direction   tale, as a rotation angle sensor.