FR2477720A1 - SENSOR OF CONTINUOUS CURRENT LIMIT VALUE - Google Patents

Abstract

CONTINUOUS CURRENT LIMIT VALUE SENSOR WHOSE SIGNAL INPUTS AND SIGNAL OUTPUTS ARE SEPARATED FROM EACH OTHER FROM THE POINT OF VIEW OF THE ELECTRIC CONDUCTION AND IN WHICH THE DIRECT CURRENT TO BE CONTROLLED SUPPLIES A MEASURING WINDING AND THE MAGNETIC FLOW PRODUCED, BY THE DIRECT CURRENT TO BE CONTROLLED, IN A FERROMAGNETIC CORE TORQUE TO THE MEASURING WINDING IS COMPARED WITH A DETERMINED FLOW AND AN OUTPUT SIGNAL IS PRODUCED ACCORDING TO THE VALUE OF THE RESULTING FLOW. THE FERROMAGNETIC CORE IS A BISTABLE MAGNETIC ELEMENT 1 TO WHICH IS MAGNETICALLY COUPLED, AS AN ADDITIONAL ELECTRIC WINDING, A DETECTOR WINDING 5. THE INVENTION IS APPLICABLE TO THE CONTROL OF THE INTENSITY OF DIRECT CURRENTS.

Description

The present invention relates to a sensor or indi-

  DC limit value whose signal inputs and signal outputs are separated by

  each other from the point of view of electrical conduction

  and in which the direct current to be monitored supplies an electrical winding (measuring winding) and the magnetic flux produced by the current to be monitored in a ferromagnetic core coupled to the measuring winding is compared to a determined flux and a signal from

  output is generated based on the value of the resulting flow.

  As. It is known to control continuous currents,

  the respect of limit values, by comparing the

  continuously monitor at a continuous current of a

  determined voltage (reference current) and

  a signal when the difference between these two

  rants exceeds a value fixed in advance. In this respect it is in many applications necessary to separate from one another the current to be measured and the reference current from the point of view of the electrical conduction. To this end

  the two currents can be passed through two windings

  separated from the point of view of electrical conduction

  that are coupled together by a ferromagnetic nucleus

  gnétique. So these are not directly the currents

  continuous but the magnetic fluxes produced by these

  in the ferromagnetic core which are compared with each other. An instrument capable of being used for this purpose is a moving frame apparatus whose output signal is a function of the torque or the angle of rotation of the frame

  mobile, which torque or angle of rotation is

  the difference between the magnetic fluxes and, consequently, between the corresponding currents to be compared. The comparison signal thus obtained can be read or, in a known manner, be converted into a suitable electrical signal.

  to be automatically processed as a value of

safe.

  In current limit value sensors

  In spite of the fact that the separation of the two currents from the point of view of electric conduction can only be obtained

  at considerable expense in electrical equipment

  tromécanique. For example, the ferromagnetic nucleus

  necessary to compare the flows of the two coils

  should be closed, for example by means of a cul-

  laminated iron, so as to obtain a magnetic circuit. Additional expenses are required if, as is usually the case, the insulation between the input and the output of the limit value sensor must have a high dielectric strength; dielectric strength is usually controlled by the application

  a test voltage of 2.5 kV or more.

  However, the object of the present invention is to create a DC current limit sensor or indicator whose signal inputs and signal outputs are separated from each other from the point of view of electrical conduction and which, while being a simple and compact construction, present between the input and the signal output a high dielectric strength, without this requiring special measures, and

  delivers a digital output signal directly

sand.

  This object is achieved according to the invention by means of a

  DC current limiting value of the kind described

  above, but in which the nucleus is a magnetically

  bistable tick to which is coupled magnetically, in

  as an additional electrical winding, a winding

detector.

  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-

  written in the published German Patent Application No.

  2 143 326. Wiegand sons are, in their composition,

  homogeneous ferromagnetic wires (for example, an alloy of iron and nickel, preferably 48% of

  iron and 52% nickel, or an alloy of iron and co-

  balt, or an iron alloy with cobalt and nickel,

  or cobalt alloy with iron and

  N-3, preferably 52% cobalt, 38% iron and

  % of vanadium), which as a result of mechanical treatment

  and special thermal possess a soft magnetic core and a hard magnetic shell, that is to say that the envelope has a coercive force greater than that of the core. Wiegand threads are typically

  a length of 5 to 50 mm, preferably 20 to 30 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 an external magnetic field whose direction corresponds to the direction of the axis of the wire but whose meaning is opposed to the sense of magnetization of the wire Wiegand, then the meaning

  magnetization of the soft core of the Wiegand wire is found

  paid in case of exceeding a field strength of about 16 A / cm. This inversion is also called resetting. In case of a new inversion

  the meaning of the external magnetic field the sense of magnetism

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

  so that the core and the envelope are found again

  calf magnetized parallel. This reversal of meaning

  magnetization takes place very rapidly and is accompanied by

  a large corresponding variation in the magnetic flux

  tick per unit time (Wiegand effect). This variation

  magnetic flux can induce in a induction coil a short and very strong voltage pulse (pulse Wiegand) (depending on the number of

  turns and the load resistance of the ignition coil

  duction reach up to about 12 volts).

  When returning the kernel to its initial state a

  impulse is also produced in a coil of in-

  duction but this pulse has, compared to the case of the passage of the sense of magnetization antiparallel to that parallel, a significantly lower amplitude

and of opposite sign.

  If one chooses as external magnetic field

  an alternating field, capable of reversing the magnetism first

  Then, as a result of the change in the magnetization direction of the soft magnetic core, Wiegand pulses are alternately present, and then each of them is in the state of magnetic saturation. positive polarity and negative polarity, and we can then speak of a symmetrical excitation of the Wiegand wire. For this, field strengths of about - (80 to 120 A / cm) to + (80 to 120 A / cm) are required. Inversion of magnetization

  of the envelope also occurs abruptly and

  also induces a pulse in the induction coil, but this pulse is much weaker than that induced during the inversion of the magnetization of the nucleus

  and is not exploited in most cases.

  If, on the other hand, one chooses as a magnetic field

  that a field capable of reversing only the magnetization direction of the soft core and not that of the hard shell, then the strong Wiegand pulses only occur with the same polarity and

  then talk about an asymmetrical excitation of the wire Wiegand.

  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 a field strength.

from about 80 to 120 A / cm.

  It is characteristic of the Wiegand effect that the impulses produced by this effect are, as far as their

  amplitude and width, to a large extent

  the speed of change of the external magnetic field

  and have a high signal-to-noise ratio.

  In the context of the invention can also be used bistable magnetic elements designed differently, provided that they include two

  magnetically coupled regions and present

  a magnetic hardness (coercive force) different from one another and can, in a manner similar to Wiegand wires, be used for generating

  of pulses by rapid inversion, induced,

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

  written for example in German Patent No. 2,514,131 a bistable magnetic switching core presented

  in the form of a thread which consists of a core material

  gnetic material (eg nickel-cobalt),

  intermediary conductor of electricity (eg

  copper) deposited on the core and a layer of

  soft gnetic (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 which

  is then deposited the intermediate layer which is

  end covered with the soft magnetic layer. This core

  known bistable magnetic switching generates

  times smaller switching pulses than

generated by a Wiegand thread.

  The free value sensor can be operated

  mite of direct current according to the invention,

  very, under conditions of asymmetric excitation of the bistable magnetic element. In the normal state the element

  magnetic bistable must then be magnetized antiparallel

  Similarly, that is, the magnetization direction of the hard magnetic region is opposite to that of the soft magnetic region. If now the DC current to be tested exceeds a determined upper limit value

  or falls below a lower limit value de-

  completed, then the resulting magnetic field reaches, at the level of the bistable magnetic element, in the direction

  opposite to the momentary magnetization of the ma-

  soft gnetic, a value sufficient to reverse the magnetization direction of the soft magnetic region of

  the bistable magnetic element so as to obtain the origin

  parallel entation. This inversion of the sense of magnetism

  occurs abruptly for a field strength

  determined, which depends on the properties of the element

  bistable genetics, and leads to the generation of a

  strong voltage pulse in the detector winding.

  This voltage pulse can be used to multiply

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  many ways, for example to stop the device

  wherein the current limit value sensor continues

  naked is incorporated. When, after verification of the

  Once again, it is switched on again and the

  continuous control is again within its nominal range, the resulting magnetic field is directed in the opposite direction to that in which it was

  directed at the onset of the characteristic impulse

  that he is able to bring back the

  Gentle gnetic magnetic element magnetic bistable again, in the state where the magnetizations of the soft and hard magnetic regions are opposite. In the case of Wiegand wires this requires a field strength

about - 16 A / cm.

  While a limit value sensor that does not

  only one impulse when the limit value

  the end is exceeded, can only be used to stop the device concerned or take similar safety measures, it is provided according to a variant of the invention to superpose the determined reference flow, which represents the nominal value of direct current, a flux component varying periodically in the

  time, so that the resulting flow obtained in defini-

  It varies, too, periodically in time. This

  has the advantage that if the value

  determined the magnetic bistable element is excited periodically asymmetrically, that is to say that after exceeding the limit value determined intensity

  the resulting magnetic field oscillates at the level of the

  bistable magnetic layer, between two sign values

  contrary, one of which is sufficiently high for

  see bringing back the bistable magnetic element by way of

  gnetic to its previous state and whose other value is sufficiently high to be able, conversely, to make

  to pass the bistable magnetic element

  tion of its two regions, the characteristic impetus

  corresponding risk being generated each time in

the detector winding.

  -7- After crossing the limit value we get

  therefore at the output of the sensor, as a signal of

  a periodic pulse train which, depending on the choice of superimposed magnetic fields, occurs either as long as the DC current to be controlled is in the range of allowable values,

  when it is situated in the field of inappropriate values

  communicable. The presence or absence of the pulse train therefore indicates which side of the limit value is

the direct current to be controlled.

  The measures that must be taken to obtain that the magnetic fields, that is to say their flux, are such that the bistable magnetic element is excited, so as to produce pulses, is

  - side of the limit value, either on the other side of the

  their limit are universally known to those

in this area.

  The reference flow set in advance may also

  that the periodically varying flux that allows the exci-

  Periodically, the bistable magnetic element is produced in principle by permanent magnets, the reference flow being produced for example by a magnet bar mounted next to the bistable magnetic element and the variable flow can be produced for example by a magnet arranged next to the bistable magnetic element and rotating at a determined speed. Preferably,

  both the reference flow and the periodic variant flow-

  however, are produced by two windings

  where one (the reference winding) is

  run by the reference current and the other (roll up

  to the previous state) by an alternating current

  native or a pulsating DC current, either by a

  common bearing which is traversed by a pulsating direct current or an alternating current and which fulfills both the function of the reference winding and the

  of the rewinding winding.

  In case of asymmetric excitation of Wiegand wires the amplitude of variation of the alternating magnetic field

  fixed in advance must, at the level of the Wiegand wire, be

  less than about 100 to 140 A / cm and in case of symmetrical excitation of Wiegand wires it must be greater than about 160 to 240 A / cm. In the latter case there is the possibility of setting two limit values, the first of which

  constitutes the transition threshold for the absence of excitatory

  asymmetric excitation and the second constitutes the transition threshold of asymmetric excitation at

  the symmetrical excitation of the bistable magnetic element.

  The corresponding output signals of the DC limit value sensor are as follows

  a) absence of pulses in the winding detected

tor,

  (b) unipolar pulse train in the winding

  detector, (c) pulse train of alternating polarities in

the detector winding.

  The field of asymmetric excitation can be

  used, for example, to produce a warning signal.

  previously determined that indicates that the DC current to be controlled has approached its limit value (which in this case is defined by the transition threshold

to symmetrical excitation).

  In the context of the invention there is also provided a more complex direct current limit value sensor which, fulfilling the functions of two separate limit value sensors, produces a characteristic output signal in case of crossing.

  of a lower limit value than in the case of crossing

  of an upper limit value of the direct current

  to control. In this respect there are different possibilities

  the construction and operation of this limit value sensor. In

  a first variant of it the two elements

  Bistable genetics are mounted in such a way that their

  hard magnetic regions are magnetized in the opposite direction

  milking one with respect to the other. Magnetic fields

  created ions act on the two magnetic elements

  bistable in the opposite direction since their magnetic regions

  hard spots are polarized in opposite directions, one

  port to another. Therefore, if the two elements

  binary signals are influenced by an alternating magnetic field with an amplitude of variation

  sufficient and superimposed on the field of the conti-

  ness to be controlled, then the resultant magnetic field thus obtained will, in case of variation of the direct current controlled in one direction, a value allowing one of the

  bistable magnetic elements to be excited asymmetrically

  only when there is a variation in the direct current

  in the other direction the resulting magnetic field reaches

  at a given time a value allowing asymmetric excitation of the other bistable magnetic element. In

  these conditions a train of impulses is each time in-

  in the common sensor winding but the pulses

  For both limit values there are

  different ways so that an evaluation circuit of im-

  pulses, provided at the output of the limit value sensor.

  can determine which of the two values

  limits that which has been crossed. In the case of winding

  separate detectors the pulses do not appear

  whenever in the corresponding winding detector

  to the bistable magnetic element that has

magnetization version.

  If only one common state reset winding is used to establish the magnetic field

  alternative and that only a

  As a common reference for transforming a reference current into a reference field, the choice of the position of the two limit values is naturally limited. That is why it is better to associate

  each bistable magnetic element has its own winding

  reference windings, these reference windings being supplied with different DC currents

  of reference currents while the winding of

  common and therefore unique state of the art is

- 10 -

  with an alternating current or a pulsating direct current, or to associate with each magnetic element

  bistable its own winding up to the ante-state

  these rewinding windings being fed with different pulsating DC currents while the common reference winding

  and therefore unique is fed with the reference current.

  It is then possible, for given numbers of turns of the windings, to select the value and the difference between the two limit values freely by a choice.

  appropriate reference currents and currents.

  ternative or pulsating continuous currents.

  We can, however, give up the idea of

  common reference or rewinding

  the common prior state for the field component al-

  ternative and instead use two coils

  respectively to the bistable magnetic elements

  and who are each fed both with a current of

  only with an AC component and thus serve as a reference winding and at the same time

  rewinding winding.

  If, on the other hand, the two bistable magnetic elements are mounted in such a way that their hard magnetic regions act in the same direction, then they

  are influenced in the same direction by the field of

  measuring bearing and another common winding possibly present. In order that, nevertheless, at the level of an upper limit value for one of the bistable magnetic elements and at a lower limit value for the other bistable magnetic element the threshold of the asymmetric excitation can be crossed, one of the Bistable magnetic elements in this case must further be subjected to a continuous magnetic field which is opposite to the continuous magnetic field to which the other bistable magnetic element is further subjected for limit value setting purposes. This can be done,

  on the one hand, by associating with each of the two

  bistable genetics a separate reference winding

- 11 -

  which is supplied with a reference current such that the fields thus created at the level of the bistable magnetic element are opposed, whereas a common winding is supplied with an alternating current or a pulsating direct current. In this respect, the meaning of the magnetic fields thus created can be fixed both by the choice of the sign of the reference current and by the choice of meaning.

  winding (winding right or left).

  However, we can also

  the rewinding winding up to the common prior state and

  to each of the two continuous currents, which feeds

  the two associated reference windings

  to the bistable magnetic elements, its own alternating current component. If these components of alternating current have the same frequency, it is necessary

  provide for each bistable magnetic element a

* Separate detector bearing to be able to recognize the one of the two bistable magnetic elements which produces

  the impulses. If, on the other hand, the

  alternating current have different frequencies,

  then the pulse frequencies make it possible to recognize

  the bistable magnetic element from where the pulses come from and therefore we do not absolutely need to

two windingsdetectors.

  In order to obtain such an efficient magnetic coupling

  as much as possible, which avoids to a large extent

  dispersion losses, the different windings in

  turn the bistable magnetic elements preferably

  directly. In order to obtain particular signals

  pronounced and free from disturbances it is particularly advisable to use as elements

  magnetic bistable wires Wiegand.

  The invention makes it possible in a simple and economical way

  than to realize a current limit value sensor

  continuous, reliable and compact, whose inputs and outputs

  are separated from each other from the point of view of electrical conduction and whose insulation has a particularly high dielectric strength. The

- 12 -

  sensor output signal is digital and is

  killed by impulses of width and amplitude

  aunts that are directly exploitable.

  Another advantage of the invention resides in that in the vicinity of the limit value can furthermore be obtained an analog output signal by means of a phase detector. This is because the phase position of the pulses produced with respect to the phase of the AC component used depends,

  as explained below, the intensity of the

the resulting DC current.

  Below are examples of realizations

  The invention is illustrated schematically in the accompanying drawings, in which: FIG. 1 shows an assembly comprising a Wiegand wire; FIG. 2 shows, in graphical form, a magnetic field produced in the circuit of FIG. 1 in the state of absence of excitation; - Figure 3 shows, in graphical form, a magnetic field produced in the assembly of Figure 1 in case of asymmetric excitation; and - Figure 4 shows a mounting allowing

  to control two DC limit values.

  FIG. 1 shows a Wiegand wire 1 which carries four windings 2 to 5. The current to be controlled Ix feeds a measurement winding 4 and produces in the wire Wiegand 1 the magnetic field of intensity H x. The reference current Is, which is to be compared

  the current to be controlled, feeds a winding of

  3 and created in wire Wiegand 1 a magnetic field

  intensity tick H s. To these two magnetic fields con-

  tinus is superimposed a pulsating magnetic field by leading to a winding 1, intended to bring back the wire

  Wiegand in its initial state, a pulsating DC current

  re, that is to say for example an alternating current if-

  nusoldal I1 rectified by double straightening

  alternation and which leads to a pulsating magnetic field

- 13 -

  H1 whose evolution over time is represented

in Figure 2.

  Finally, the sensor further comprises a detector winding 5 mounted on the Wiegand wire 1 and in which the Wiegand pulses are induced. If Hx = H., ie the resulting magnetic field created by currents Ix and Is is exactly

  zero: Hxw = H - Hs =, then the resulting magnetic field

  so obtained in total H Hw + H1 has the appearance shown in Figure 2. In

  the detector winding If there is no impulse

  because the resulting magnetic field H does not present

  you do not go through zero so that the process

  The reset logic necessary for asymmetric excitation of the Wiegand 1 wire can not take place. This reset can indeed take place only from the instant Hxw <- 16 A / cm because it takes a field strength of about -16 A / cm

  to return the Wiegand 1 wire to its original state. If this

  the field intensity is reached, then the field

  sultant has the appearance illustrated in Figure 3 and a pulse. Wiegand 6 is produced in the detector winding during each period of the pulsating DC current. The threshold value that the current Ix must not exceed is therefore determined, in the example represented, by the sum of the reference field Hs (Is )

  and the reset field of -16 A / cm.

  In the example illustrated in FIG. 4, two Wiegand wires 1 and 1 'extend parallel to each other but overlap only partially in the longitudinal direction. The hard magnetic regions (envelopes) of Wiegand wires are antiparallel magnetized one

compared to each other.

  DC, which serves as the reference current,

  Is (nominal value), feeds a winding of

- 14 -

  reference 3, and the intensity control current I

  (effective value) supplies a measuring winding 4.

  The measuring winding 4 and the reference winding 3 are both arranged to be traversed by the two Wiegand wires 1 and i 'over the entire length of the windings. At their ends not overlapping,

  the two Wiegand wires 1 and 1 'each comprise a

  bearing 7; 8 respectively powered with a current

  continuous pulsating I he; Il., In order to produce

  opposing pulsating magnetic field posers, as well as

  a detector winding 9; 10 in which the

Wiegand impulses are produced.

  Each of the two Wiegand wires 1 and 1 'can in itself, with the four windings 3, 4, 7 and 9; 3, 4, 8 and 10 respectively associated therewith be considered to be identical to wire Wiegand 1 of FIG.

  with its four windings 2 to 5.

  Therefore, one of the two Wiegand wires 1, 1 'can be excited asymmetrically in case of positive difference H of the magnetic field strengths H and H xw x -s and the other Wiegand wire can be asymmetrically excited in case of difference. Hxw negative, so a train

  of Wiegand pulses is induced in the winding de-

  9 when one of the limit values is reached

  and a Wiegand pulse train is induced in the

  detector bearing 10 when the other limit value is reached.

  In both embodiments the excitatory

  asymmetrical Wiegand wire is possible only if the pulsating magnetic field H1 has an amplitude of variation of at least 100 to 140 A / cm in order to obtain, on the one hand, the field strength 16A / cm necessary to restore the previous state and, on the other hand, the field strength of the order of + 80 to 120 A / cm necessary for the saturation of Wiegand wire in the other direction. In addition to the digital output signal of the limit value sensor, the phase position of the pulses

- 15 -

  Wiegand with respect to the pulsating DC currents I.1, I1, I12 can still be exploited as an analog output signal in the vicinity of the limit value, ie when the asymmetric excitation starts at happen. This is explained below with the aid of FIGS. 2 and 3. The magnetic field H1 linked to the pulsating current I1 is formed by positive sinewave halfwaves which in the phase interval from Y = 0 to v = w satisfy to the equation: (I) H1 = 1. sin wt

  o t is the time, w the angular frequency, or pulsa-

  tion, and H1 the amplitude of the magnetic field H1.

  A Wiegand pulse 6 can be produced only when the pulsating magnetic field H1 is superimposed

  a continuous magnetic field Hxw <- 16A / cm. The impulses

  Wiegand 6 occur, however, for reasons relating to the constituent material of the

  Wiegand, not at the level of the zero crossing of the in-

  the resulting field strength H = H1 + Hxw, but at the envi-

  have a value H = + 10 A / cm, so that the posi-

  phase: (II) fM = wM t satisfies the relation (III) H1 (M) = 10 A / cm = H1. sin M + Hxw or 10 A / cm - Hxw (IV) sin = M xw N1 for Hxw <- 16 A / cm and 0 <M <g90 o

  Since Hxw are supposed to be

  their negative, we can also introduce into the

  equation (IV) the absolute value IHxwl, so that (IV)

becomes: 10 A / cm + IHxw.

(V) sin M = /

-N 1

  This relationship can be used to determine

- 16 - 2477720

  how far a limit value is exceeded. If, however, the magnetic fields are chosen so that in the range of admissible current intensities a pulse train is produced which is interrupted when crossing the limit value, then it is possible to determine from

  the phase position of the pulses, by means of a detec-

  phase, what is the gap still existing between the momentary current intensity I and the limit value x S.

0 0 0 0

0-O - O 0

- 17 -

Claims (18)

CLAIMS CATI ONS   1. - DC limit value sensor whose signal inputs and signal outputs are   separated from each other from the point of view of   electrical supply and in which the direct current to be controlled feeds an electric winding (measuring winding) and the magnetic flux produced by the   control, in a ferromagnetic core coupled to the   measurement bearing is compared to a given flow and an output signal is generated according to the value of the   resulting stream, characterized in that the core is an element   bistable magnetic element (1, 1 ') to which is coupled by   magnetic path, as an additional electrical winding   a detector winding (5, 9, 10).   2. - DC limit value sensor   according to claim 1, characterized in that a   permanent mantle or a set of permanent magnets is   planned to produce the determined flow.   3. - DC limit value sensor according to claim 1, characterized in that for   produce the determined flow a third   reference winding bearing (3) and   designed to be connected to a DC power source   a continuous current of determined intensity (current reference).   4. - sensor for limiting DC values according to claim 3, characterized in that the determined flow is superimposed a varying flow component   periodically in time and whose range of   is sufficient to allow at least the excitement   asymmetric representation of the bistable magnetic element (1, 1 ').   5. DC dc limit sensor according to claim 4, characterized in that at the determined flux is superimposed a varying flow component.   periodically in time and whose range of   is sufficient to also allow the exci-   symmetrical representation of the bistable magnetic element (1, 1 ').   6. - DC limit value sensor - 18 -   according to claim 4 or 5, characterized in that,   to produce a periodic variant flow component   over time, it is planned next to the manual element   bistable gnetic a permanent magnet rotating at a vi-   determined speed. 7. - DC limit value sensor according to claim 4 or 5, characterized in that,   to produce the periodic variant flux component   over time and overlaying the determined flow,   the reference winding (3) is traversed by a   alternating current or pulsating DC current.   8. - DC limit value sensor according to claim 4 or 5, characterized in that,   to produce the periodic variant flux component   over time and overlaying the determined flow,   it is coupled to the bistable magnetic element (1) a quadruple   third winding winding (2, 7, 8) for the restoration to the previous state and which is traversed by   an alternating current or a pulsating direct current.   9. - DC limit value sensor according to claim 7 or 8, characterized in that there are provided two bistable magnetic elements (1, 1 ') which   both are coupled to the measuring winding (4) and   if both are at the reference winding (3) and each individually at a winding (7, 8) for reset, either each individually   to a reference winding and both to wind it up   reset and, in addition, either to a common sensor winding, or each to its own   winding detector (9, 10) and in that both   bistable magnetic elements (1, 1 ') are arranged   that their hard magnetic regions are magnetized in the opposite way.   A DC current limit sensor according to Claim 7 or 8, characterized in that two bistable magnetic elements (1, 1 ') are provided which are both coupled to the measuring winding (4).   the reference winding (3) and the winding - 19 -   a single common winding, or each to its own detector winding (9, 10) and in that the two bistable magnetic elements (1, 1 ') are arranged so that their magnetic hard regions are magnetized in the opposite way.   11. - DC limit value sensor according to Claim 7, characterized in that two bistable magnetic elements (1, 1 ') are provided which are both coupled to the measuring winding (4) and   addition, each individually to a winding addition-   which is intended to be supplied with pulsating DC currents and serving as both a reference winding and a winding winding, and either to a common detector winding or each to its own detector winding (9, 10), and in that   the two bistable magnetic elements (1, 1 ') are   so that their hard magnetic regions are magnetized in opposite directions.   12. - DC limit value sensor   according to any one of claims 9 to 11,   characterized in that the two bistable magnetic elements   (1, 1 ') are coupled to a common sensor winding.   13. - DC limit value sensor according to claim 8, characterized in that there are provided two bistable magnetic elements which are both coupled to the measuring winding and the winding of   surrender to the previous state, as well as each individual-   reference winding, polarized of such   way that the magnetic fields created by the windings   reference documents are opposed to one another   calf magnetic elements bistable, and in addition either   to a common sensor winding be each individual-   its own detector winding, and that the two bistable magnetic elements are arranged so that their magnetic hard regions are magnetized. in the same sense.   14. - DC limit value sensor - 20 -   according to claim 7, characterized in that it is   provided two bistable magnetic elements which are   both to the measuring winding, as well as each   individually to an additional winding of   born to be powered by pulsating continuous currents   and serving as both reference winding and winding   the two coils   in question being polarized so that the fields   created by them are opposed to one another at the level of the bistable magnetic elements, and furthermore   to a common detector winding, each one at its own   pre winding detector, and in that the two bistable magnetic elements are arranged so that their hard magnetic regions are magnetized in the same meaning.   15. - sensor for limiting DC values according to claim 14, characterized in that the   pulsating DC currents feeding the two coils   ments used as reference windings and at the same time   rewinding winding time present try different frequencies.   16. - DC limit value sensor   according to any one of claims 1 to 15,   characterized in that the different windings (2 to 5,   7 to 10) surround the bistable magnetic elements cor- respondents (1, 1 ').   17. - DC limit value sensor   according to any one of claims 1 to 16,   characterized in that the bistable magnetic elements (1, 1 ') are Wiegand threads.   18. - DC limit value sensor   according to any one of claims 4 to 17,   characterized in that the sensor windings (5, 9, 10) on the one hand, and the windings (2, 7, 8) for   restored to the previous state and covered by a   alternating current, on the other hand, are connected to a phase detector.   Andrê NETTER -Côa1 in Patents of Invenfon;