FR2532493A1 - METHOD AND MOUNTING FOR MAGNETICALLY EXCITING WIEGAND DETECTORS - Google Patents

Abstract

A PROCESS FOR MAGNETICALLY SATURIZING WIEGAND 4 DETECTORS, STARTED BY PERMANENT MAGNETS, USING AN ELECTRONIC ASSEMBLY 8 WHICH IS TRIGGERED BY WIEGAND PULSES AND SENT IN THE DETECTOR WINDING 7 OF THE WIEGAND 4 DETECTOR, IS DESCRIBED. ESTABLISH A MAGNETIC FIELD OF SATURATION.

Description

Method and assembly for magnetically exciting Wiegand detectors.

  The invention starts from a method for magnetically exciting Wiegand detectors constituted by a Wiegand wire and an associated induction winding: (detector winding), in

  which the Wiegand pulses appearing in the coils-

  the detector are started by acting on the Wiegand wire by means of at least one permanent magnet The influence of

  permanent magnets on Wiegand detectors is charac-

  stic for the multiplicity of their uses, for example to control the position of moving machine parts,

  in proximity switches, tachometers, sensors

  linear sensors, angular sensors, etc. Wiegand wires are, as regards their composition, homogeneous ferromagnetic wires (for example in an alloy of iron and nickel, preferably 48% of iron and 52% of nickel, or in an alloy of iron and cobalt, or in an iron alloy

  with cobalt and nickel, or a co-alloy

  balt with iron and vanadium, preferably 52% cobalt,

  38% iron and 10% vanadium), which as a result of

  The mechanical and thermal special have a magnetic core.

  soft tick and a hard magnetic envelope, that is to say that the envelope has a coercive force greater than that of the core Wiegand wires typically have a length of 10 to 50 mm, preferably from 20 to 30 mm If a Wiegand yarn,

  in which the direction of magnetization of the soft magnetic core

  corresponds to the direction of magnetization of the hard magnetic envelope, is placed in an external magnetic field whose direction corresponds to the direction of the axis of the wire> but whose direction is opposite to the direction of magnetization of the Wiegand wire, then the direction of magnetization of the soft core of the Wiegand wire is reversed if a field strength of about 16 A / cm is exceeded. This inversion is also called return to the initial state In the event of a new inversion of the direction of the external magnetic field, the direction of magnetization of the

  nucleus reverses again as soon as the intensity of the ma-

  external genetics exceeds a critical value (called in-

  priming field density), so that the nucleus and

  the envelope is again magnetized in parallel.

  This reversal of the direction of magnetization takes place very quickly-

  ment and is accompanied by a strong corresponding variation in the magnetic flux per unit of time (Wiegand effect), This variation in the magnetic flux can induce in a short induction coil, called detector winding, a voltage pulse (Wiegand pulse) and very strong (possibly based on the number of turns and the load resistance

  of the induction coil reach up to approximately 12 volts).

  When the core returns to its initial state, a pulse is also produced in the detector winding, but this pulse presents, compared to the case of the transition from the antiparallel direction of magnetization to that parallel,

  significantly lower amplitude and the opposite sign.

  If the Wiegand wire is in a magnetic field whose direction is reversed from time to time and which is sufficiently intense to be able to reverse first the magnetization of the nucleus; and then that of the envelope and the to bring

  each in a state of magnetic saturation, then it

  due to the change in the direction of magnetization of the nucleus

  soft magnetic, Wiegand pulses presenting alternative-.

  lie a positive polarity and a negative polarity and we

  can then speak of a symmetrical excitation of the Wiegand wire.

  This requires field strengths of approximately

  - (80 to 120 A / cm) to + (80 to 120 A / cm) The inversion of the magnet-

  envelope envelope also occurs abruptly

2,5249.

  and also leads to a pulse in the detector winding,

  but this impulse is much weaker than that in-

  pick when reversing the magnetization of the nucleus.

  If we choose, on the other hand, as external magnetic field, a field capable of reversing only the direction of magnetization of the soft core and not that of the hard envelope, then the strong Wïegand pulses occur only with a

  same polarity and we can then speak of an asymmetric excitation

  Wiegand wire gauge For this, a field intensity of at least 16 A / cm is required in one direction (to bring the wire back

  Wiegand in the initial state) and in the opposite direction an in-

  field strength of about 80 to 120 A / cm (for saturation

Wiegand wire).

  A circuit constituted by a Wiegand wire and an associated electrical winding, which surrounds it most of the time to obtain an optimal coupling, will be called hereinafter Wiegand detector The Wl'egand detectors supply, by being symmetrically excited, Wiegand pulses having high and stable amplitudes when the hysteresis cycle of the Wiegand wire is traversed as ldin as possible in both directions as far as the saturation zone In the most important case in practice of asymmetric excitation, the detectors

  Wiegand then provide particular Wiegand pulses-

  high and stable when the hysteresis cycle of the Wiegand wire is traversed as far as possible in one of the directions of the field as far as the saturation zone; on the other hand in the direction of the opposite field, one simply needs a field intensity which returns magnetically to the initial state

  Wiegand wire securely (so at least 16 A / cm, pre-

  ference about 20 A / cm); however, the field strength to return to the initial state should not suitably exceed about 25 A / cm, because above this field strength value, demagnetization may occur in places the hard magnetic envelope of the Wiegand wire; in other words, we arrive in the transition zone between asymmetric excitation and symmetrical excitation, in which, compared to a strictly asymmetric excitation, the Wiegand pulses appear with

  lower amplitudes and above all varying more strongly.

  In the industrial uses of Wiegand detectors, an effort has been made above all to effect the excitation of the Wiegand detectors by permanent magnets, the position of which can be varied over time relative to the Wiegand detector or whose magnetic fields are reinforced or weakened at the location of the Wiegand detector with the aid of ferromagnetic components whose position varies over time and which therefore produce at the location of the Wiegand detector the variation of the field strength necessary for its excitation . Because of the inevitable air gaps between the p 6 the magnets

  permanent and Wiegand wire, it often happens that the in-

  necessary saturation field voltages are not

  and the quality of Wiegand impulses suffers.

  The object of the invention is, while retaining the principle of

  initiation of Wiegand pulses using permanent magnets

  nents, improve the level of pulse amplitude

  Wiegand and their regularity This goal is achieved by a pro-

  assigned in which each Wiegand pulse is used to trigger an electronic circuit which then sends into the detector winding for a predetermined period of time a current of suitably chosen polarity sufficient for the magnetic saturation of the Wiegand wire, as well as through a circuit in which the detector winding is connected to a door circuit, which is triggered by Wiegand pulses and is open for a predetermined period of time, the detector winding being connected by the door circuit to a current source, which sends, when the door circuit is open, a current of appropriately chosen polarity in the detector winding, sufficient for the magnetic saturation of the Wiegand wire, To saturate the Wiegand wire, the invention no longer uses a permanent magnet, but produces the magnetic field of

  saturation by electrical means directly in the

  existing detector bearing, which can in principle be dis-

  placed next to the Wiegand wire if care is taken to ensure at the same time a close magnetic coupling between them, but which, as much as possible must however surround the Wiegand wire To ensure that the Wiegand detector, after the initiation of a Wiegand pulse , becomes as fast as possible

  capable of priming, the invention provides for triggering the im-

  current pulse which produces the magnetic field of satu-

  ration, by the Wiegand impulse itself, notably by its

  anterior flank We choose the duration and the amplitude of the im

  current pulse so that the Wiegand wire is saturated

magnetically safely.

  If the front flank of the pulse is used instantly

  Zion Wiegand to trigger the current pulse, this causes the appearance of a pulse in the detector winding, pulse whose anterior flank first has the characteristic configuration for a Wiegand pulse;

  however, from the moment of triggering the ampli

  tude and pulse duration are determined by the cir-

  electronic Wiegand A pulse triggered

  essential characteristic of the invention is therefore to trans-

  electronically train and amplify the Wiegand pulses that appear and use them

  to produce a saturation magnetic field defined in.

  winding detectors In principle, it would be possible, but it would be a worse embodiment of the invention, to produce the saturation magnetic field

  with a second separate winding.

  The advantages of the invention consist in that one no longer has

  need to produce the saturation field strength of the

  usual strong permanent magnets that I had to be available

  sés by respecting narrow air gaps and thus created problems of assembly and use On the other hand, one can

  electrically produce them without problems

  saturation field voltages required * and there is no

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  particular mounting problems because, to bring the current which produces the saturation magnetic field, we

  can use the two pipes arriving at the winding-

  ment detector which are in any case necessary to transmit the Wiegand pulses to a receiving circuit. By placing the detector winding on the Wiegand wire, we have the great advantage that the Wiegand wire is saturated in a

  strictly homogeneous magnetic field parallel to its axis.

  This has a favorable impact on the magnetic structure of the Wiegand wire and with it on the amplitude and the shape of the Wiegand pulses. Such a favorable effect cannot be

  obtained by means of permanent magnets.

  In typical practical uses of the Wiegand wire by excitation with permanent magnets, the Wiegand wire is exposed to different magnetic fields by the fact that the magnets themselves are moved relative to the Wiegand wire, or that the magnets are influenced by objects

  ferromagnetic in motion (eg machine parts).

  In this way, the duration of action of the magnetic field of its-

  turation depends on the speed and in some cases its ampli

  tude also varies These two factors have a detrimental effect on the shape and amplitude of the Wiegand pulses;

  the invention avoids these two drawbacks.

  The most important operating mode of the Wiegand detectors is that with asymmetric excitation The invention has here the advantage that there is no longer any need to produce by permanent magnets the high intensity of saturation field (preferably about 100 A / cm) For the magnetic return to the initial state and for the priming of the Wiegand wire, there is no need for a variation of the field strength of more than + 20 A / cm at the location Wiegand wire This can be

  realized without big problems with permanent magnets.

  For symmetrical excitation, it must be ensured that the saturation takes place in one direction and the other of the Wiegand wire and that consequently the detector winding is crossed alternately in one direction and in the other by the s 2532493 current which establishes the magnetic saturation field This can be done by simple switching, for example at

  by means of a bistable assembly triggered by one of the

  Wiegand pulses For the priming of the Wiegand wire which is still necessary in the event of symmetrical excitation, one needs at the place of the Wiegand wire a variation of the field intensity

  at most + 20 A / cm, which can be achieved without difficulty

tees with permanent magnets.

  An advantageous development of the invention with regard to

  asymmetrically excited Wiegand detectors are characterized

  made by the fact that not only does the magnetic field

  saturation tick, but also the magnetic field returning to the initial state oriented in the opposite direction by intermittently sending an appropriate current preferably a

  constant current in the detector winding, The magnetic field

  return to initial state tick is established between laps

  of time in which the magnetic field of satura-

  tion, namely throughout the duration between two: of these periods of time to avoid accidental ignition faults, having regard to the low intensity of the ignition field generally clearly less than 10 A / cm In this development, we reach the initiation field intensity by the fact that a stronger magnetic field oriented in the opposite direction is superimposed on the magnetic field returning to the initial state, for example by the fact that the magnetic field returning to the state initial constantly takes the intensity 20 A / cm at the place of the Wiegand wire, while the permanent magnet produced for

  the initiation of the Wiegand wire at the place of the latter, using

  using a maximum of Wiegand wire, a magnetic field with an intensity of + 40 A / cm so that, when superimposed

  of the two fields, there remains a field strength resulting

  aunt of + 20 A / cm which is reliably sufficient for damping

  pledge. The advantage of this development consists, on the one hand, in that one only needs a single permanent magnet, or a permanent magnetic field of constant polarity, to make

  operate the Wiegand wire; the intensity of this magnetic field

  tick does not need to exceed 40 A / cm and can be, for this reason, carried out without significant problems Another advantage is that one can regulate by electric means the value of the field of return to the initial state at l location of the Wiegand wire and reproduce it with much more precision than with permanent magnets We can thus have

  assurance that the intensity of the field returning to the initial state

  tial remains in a relatively narrow range between 18 A / cm and 25 A / cm approximately Below 18 A / cm the return to the initial state of the Wiegand wire is, in general, insufficient and the result is weaker Wiegand pulses Au top of

  A / cm, there are changes in orientation magnetically

  tick in partial zones of the hard magnetic envelope of the Wiegand wire, that is to say that one arrives in a transition zone between the asymmetric excitation and the excitation

  symmetrical, which also results in impulses

  Wiegand sions weaker and of less good configuration

  The development of the invention makes it possible to avoid these inconveniences.

  vénients Furthermore, the fact that, as in the case of an electrically produced saturation field, the Wiegand wire is in a strictly homogeneous magnetic field by parallel to its longitudinal axis, also in the case of the magnetic field returning to the 'initial state produced in the detector winding, has a favorable impact on the shape of the Wiegand pulse' l Technically, as regards the assemblies, the invention is best carried out by means of a circuit of door, preferably monostable, which is triggered by Viegand pulses, opens for a predetermined period and therefore connects the detector winding to a current source which supplies the current for the magnetic field of

  saturation During the periods of time in which the

  door fired is closed, a constant current of opposite polarity using the same current source or a separate source can be sent into the detector winding to

  produce a magnetic field returning to the initial state.

  The invention will be clearly understood on reading the description

  detailed, given below by way of example only, of embodiments shown schematically in the drawing, in which: FIG. 1 represents the mounting of a Wîegand detector for monitoring a rotating part, seen from above; Fig 2 shows the mounting of the freeze 1 in side view; fig 3 is a block diagram of: assembly used in fig. 1 and 2; fig 4 is a detailed diagram of the connections of the assembly of fig 3;

  fig 5 a c are functional diagrams for illus-

  trate the process; FIG. 6 represents a block diagram of an enlarged assembly which also allows the electrical production of the magnetic field back to the initial state; and fig 7 represents on diagrams similar to fig 5 has the shape in time of the magnetic fields acting on the

  Wiegand wire, using the assembly according to fig 6.

  The assembly of Figs 1 and 2 shows a rotary disc 1 on the edge of which is fixed, parallel to the axis of rotation of the disc 1, a magnetic bar 2 Next to the disc l is placed a fixed support 3 on which are arranged l 'next

  on the other a Wiegand 4 detector and another magnetic bar

  tick 5, with their two axes parallel to the axis of rotation

  of the disc The Wiegand 4 detector, consisting of a Wie-

  gand 6 and a detector winding 7 surrounding it, is placed

  between the disc 1 and the second magnetic bar 5 The

  detector bearing 7 is connected to an electronic assembly 8.

  The two magnets 2 and 5 have opposite directions of magnetization.

  The magnetic bar 5 acting constantly on the Wiegand detector 4 serves for the magnetic return to the initial state of the Wiegand wire 6 and produces at the location of the wire a magnetic field mainly parallel to the Wiegand wire 6 of an intensity of approximately 20 A / cm The magnetic bar 2 driven with the disc 1 is used to start the pulse

  Wiegand which takes place when the magnetic bar 2 approaches

  che very close to the Wiegand 4 detector When approaching

  maximum (as shown in Figures 1 and 2), the bar-

  magnetic grid 2 produced at the Wiegand wire 6 un

  magnetic field mainly parallel to its axis

  ci and an intensity of about 40 A / cm, so that the chanp magné-

  resulting tick at the location of the wire Wiegand 6 has a field intensity of approximately + 20 A / cm, which is reliably sufficient for priming Due to the effect of the two magnetic bars 2 and 5, the wire Wiegand undergoes during a rotation of the disc 1 a variation of the field strength from about 20 A / cm to + 20 A / cm, which is sufficient for the initiation and the return to the initial state of the Wiegand detector 4, but not for its saturation which must, in any case, take place after priming Ce

  magnetic field necessary for saturation is produced, according to the invention

  tion, by means of mounting 8 by electrical means in the winding

  detector 7 The block diagram of assembly 8 in Figure 3 shows

  be a comparison circuit 9 at one of the inputs from which a reference voltage UR is brought and the other input of which is connected to the winding 7 When, and as long as the pulse voltage transmitted by the detector winding

  and coming from a Wiegand pulse is greater than the ten-

  reference path U Rd a pulse circuit 10 mounted following the comparison circuit 9 sends a control pulse which, for the duration of this pulse, closes a

  switch 11 by which the detector winding 7 is re-

  linked to a constant current source 12 which sends into the

  detector bearing 7 sufficient current for saturation

Wiegand 6.

  An exemplary embodiment of a monostable circuit according to FIG. 3 is shown in FIG. 4 The detector winding 7 is connected by a differentiating element C -R 1-R 2

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  one of the inputs of a comparison circuit 22, the other input of which receives a constant reference voltage which is derived, using a voltage divider constituted by the resistors R 3 on the one hand, and R and R on the other hand,

3 4 2

  of the voltage + UB of a constant voltage source The output

  part of the assembly of comparaisdn 22 is brought to UB via the

  median of two resistors in series R 5 and R 6 constituting a voltage divider Between R 5 and R 6 is taken the control voltage for a transistor T 1, whose emitter is connected

  to U and whose collector is connected by a resistor

  rie Rv to the detector winding 7, the other end of which is grounded The comparison circuit 22 is mounted

  so that in the state of rest, that is to say in the absence

  ce of a Wiegand pulse, its output is at + UB potention so that the transistor T 1 blocks If a Wiegand pulse is initiated in the Wiegand 4 detector, this;

  arrives through the differentiating element C 1-R 1-R 2, whose cons-

  time aunt is essentially determined by C 1 and R 1 i at one of the inputs of the comparison setup 22 When

  the voltage of the Wiegand pulse exceeds the reference voltage

  Since the input is at the other comparator input, the output of the comparison assembly is switched to the potential "'"

  Consequently, the base of transistor T 1 receives another poten-

  tiel, the transistor T 1 becomes conductive and sends into the

  detector bearing 7 a constant current, the intensity of which can be adjusted by choosing a series resistance Rv which can vary appropriately The constant current supplies the detector winding until the voltage at the input of the comparison circuit 22 connected to the coil

  detector 7 has fallen below the reference voltage

  at the other comparison entry, because at this

  At this point, the output of the comparison assembly 22 is again

  calf switched to potential + UB so that transistor T 1 again blocks Comparator 22 is mounted so that there can only be potentials "O" and UB "B at its output alternately which the transistor T 1 is conducting is determined by the time constant of the element C 1-R 1-R 2 o Figure 5 represents, coinciding chronologically, three chronological diagrams of the shape of the field intensity produced by the magnetic bars 2 and 5 on the Wiegand wire (FIG. 5 a), of the potential at the output of the comparison assembly 22 (FIG. 5 b) and of the voltage at the ends of the detector winding 7 (FIG. 5 c) The latter presents, after the initiation of the Wiegand pulse in Z, first the typical rise of a Wiegand pulse However,

  when the reference voltage UR is reached, the transis-

  tor T 1 becomes conductive and following the rise and lighting

  re of the voltage in the detector winding are determined

  born by the connected electronic circuit 8 The response time

  evolution of disk 1 and the time tp determined by the constancy

  time of element C 1-R 1-R 2, during which the transis-

  tor T 1 is conductive are shown in the drawing, We have only worn

  only partially and in dashes the intensity of the saturation field

  tion caused by mounting for the duration tp in the winding

  detector 7, which is superimposed on the magnetic field

permanent in Figure 5 a.

  FIG. 6 represents a block diagram of an enlarged assembly 8, which differs from the block diagram of FIG. 3 only by the fact that, in addition to the constant current source 12, another constant current source 15 is provided. opposite polarity which,

  during the times when the current source is

  as long as 12 is not connected to the detector winding 7, is in turn connected to the detector winding 7 and sends into

  this one a current which produces inside the coil-

  detector 7 a magnetic field with an intensity of approx.

  ron 20 V / cm sufficient for the return to the initial state of the Wiegand wire For this purpose, the on-off switch 11 of FIG. 3 is replaced by a switch 14 The magnetic bar tick 5 in FIGS. 1 and 2 is replaced by the constant current source 15 -We no longer need as the only magnet oers manent that of the one used to initiate the wiez gand pulses (for example the magnetic bar 2 in Figures 1

and 2).

  Figure 7 is a representation similar to Figure 5 a

  and shows the appearance over time of the different ma-

  gnetics acting on the Wiegand 6 wire using an assembly according to Figure 6 Eur Figure 7, there is shown in dashes the intensity of the field back to the initial state (about 20 A / cm) which remains until l moment of initiation of the Wiegand pulse (point Z) and is again established when the saturation magnetic field (approximately

  + 100 A / cm) disappears The magnetic field produced temporarily

  rement at the location of the Wiegand wire 6 by the permanent magnet (for example the magnetic bar 2 in Figures 1 and 2) is shown in dotted lines It temporarily compensates for the

  field to return to the initial state and causes, with an inten-

  resulting field strength of approximately + 8 A / cm, the initiation of the Wiegand pulse At the same time as the initiation in Z

  starts the arrival of the current coming from the source of

  constant rant 12 in the detector winding, i.e. for a short period tp, during which the current source

  constant 15 is cut off from the detector winding

  resulting total field tee at the location of the Wiegand 6 wire

  is represented by the solid line curve.

Claims (9)

Claims   1 Method for magnetically exciting Wie- detectors   gand formed by a Wiegand wire and an information winding   associated duction (detector winding), in which the pulses appearing in the detector winding are initiated by acting on the Wiegand wire by means of at least one permanent magnet, characterized in that each Wiegand pulse is used to trigger an electronic assembly, which then sends into the detector winding, for a predetermined period of time, a current of appropriately chosen polarity, sufficient for the magnetic saturation of the Wiegand wire.   -2 Method according to claim 1, characterized in that   uses the anterior flank of the Wiegand pulse to de- trigger the electronic assembly.   3 Method according to claim 1 or claim 2,   characterized in that after it has been triggered the electric mounting   tronic immediately sends the current in the winding guardian.   4 Process according to any one of the preceding claims.   teeth for asymmetric excitation of Wiegand detectors, characterized in that between the periods in which   the detector winding is supplied with current from a pola-   preselected rite to saturate the Wiegand yarn,   The detector is supplied with a current of opposite polarity.   sée, whose intensity is sufficient for the magnetic return to the initial state of the wiegand wire, and in that the permanent magnet is used exclusively for the initiation of the wiegand pulses. 5 Method according to claim 4, characterized in that the current for the magnetic return to the initial state of the Wiegand wire is sent throughout the duration between two successive periods during which a current is sent in   the detector winding to saturate the wiegand wire.   6 Mounting for magnetic excitation of Wiegand detectors constituted by a Wiegand wire and an associated induction winding (Wiegand detector), in which the pulses   Wiegand appearing in the detector winding are amor-   by acting on the Wiegand wire by means of at least one   permanent magnet, characterized in that the winding detects   tor (7) is connected to a door circuit (9, 10) which is triggered by Wiegand pulses and opens for a predetermined period, and in that the detector winding (7) is connected by the door circuit (9, 10) to a current source (12) which, when the gate circuit (9, 10) is open, sends into the detector winding a current of suitably preselected polarity sufficient to   magnetically saturate the Wiegand wire (6) -   7 assembly according to claim 6, characterized in that the door circuit (9, 10) is a monostable assembly (monoflop).   8 Assembly according to claim 6 or claim 7   for symmetrical excitation of Wiegand detectors,   risé in that there is provided between the detector winding (7), on the one hand and the door circuit (9, 10) and the current source (12), on the other hand, a switch controlled by pulses Wiegand, which after each saturation current pulse, reverses the polarity of the winding terminals detector (7).   9 Assembly according to claim 6 or claim 7 D   for asymmetric excitation of Wiegand detectors, charac-   terized in that it is expected to produce the field strength returning to the initial state for the Wiegand wire (6) a supply assembly (15) connected to the detector winding (7), which at the inside the periods during which the door circuit (9, 10) is closed, sends into the detector winding   (7) a current of opposite polarity.   Assembly according to claim 9, characterized in that the switching on of the supply assembly (15) for the return to the initial state of the Wiegand wire (6) is controlled by the door circuit (9, 10).