DE3232306C1 - Method and circuit arrangement for magnetic excitation of Wiegand sensors - Google Patents

Description

the induction winding was up to approx. 12 volts) Induce voltage impulse (Wiegand impulse).

A pulse is also generated in the sensor winding when the core is reset, but with it significantly lower amplitude and with the opposite sign than in the case of the flip over of the antiparallel in the parallel direction of magnetization. If the Wiegand wire is in a magnetic field, its Direction is reversed from time to time and which is so strong that it first has the core and then the Magnetize the jacket and bring it up to magnetic saturation, so Wiegand impulses occur alternately due to the flipping of the magnetization direction of the soft magnetic core with positive and negative polarity and one speaks of symmetrical excitation of the Wiegand wire. Field strengths of approx. - (80 to 120 A / cm) to + (80 to 120 A / cm) are required for this. The magnetization reversal of the jacket is also erratic and also leads to a pulse in the sensor winding, however, the momentum is much smaller than the momentum induced when the core is flipped over.

However, if one chooses an external magnetic field that is only capable of the soft core, not but to reverse the hard jacket in its direction of magnetization, then the high Wiegand impulses occur only with constant polarity and one speaks of asymmetrical excitation of the Wiegand wire. This requires a field strength of at least 16 A / cm in one direction (for the reset of the Wiegand wire) and in the opposite direction a field strength of approx. 80 to 120 A / cm (for the saturation of the Wiegand wire).

An arrangement of a Wiegand wire and one assigned to it, because of the optimal coupling mostly surrounding electrical winding is hereinafter referred to as Wiegand sensor. Wiegand sensors with symmetrical excitation then deliver Wiegand pulses with high and stable amplitudes, if the hysteresis loop of the Wiegand wire is as far as possible in both directions up to the range of Saturation is passed through. In the case of asymmetrical excitation, which is more important in practice, deliver Wiegand sensors then have particularly high and stable Wiegand pulses when the hysteresis loop of the Wiegand wire is traversed in one field direction as far as possible into the saturation area, whereas in the opposite field direction only a field strength is required which the Wiegand wire with security magnetically resets like this (i.e. at least 16 A / cm, preferably about 20 A / cm); the restoring field strength should, however, expediently should not be chosen higher than approx. 25 A / cm, because above this field strength value already in places a magnetic reversal of the hard magnetic sheath of the Wiegand wire can occur - with others In other words: One arrives at the transition area between asymmetrical and symmetrical excitation, in which compared with purely asymmetrical excitation the Wiegand impulses with lesser and before all strongly fluctuating amplitudes occur.

In the technical applications of Wiegand sensors one tries mostly to excite the Make Wiegand sensors by permanent magnets, their position relative to the Wiegand sensor is temporally variable or whose magnetic fields are caused by ferromagnetic ones that are temporally variable in their position Components are strengthened or weakened at the location of the Wiegand sensor and thereby at the location of the Wiegand sensor generate the field strength swing necessary for its excitation.

Because of the inevitable air gaps between the poles of the permanent magnets and the Wiegand wire However, the required saturation field strengths are often not achieved at the desired level, and as a result the quality of the Wiegand impulses suffers.

The invention is based on the object, while maintaining the principle of ignition of the Wiegand pulses by means of permanent magnets the amplitude of the Wiegand impulses and their evenness to improve. This object is achieved by a method with those specified in claim 1 Features and by a circuit arrangement with those specified in the independent claim 6 Features. Advantageous further developments of the invention are the subject of the respective subclaims. The invention no longer uses a permanent magnet to saturate the Wiegand wire, soib which generates the saturating magnetic field by electrical means directly in the existing sensor winding, which can basically be placed next to the Wiegand wire if at the same time for a close magnetic coupling between the two is taken care of, but if possible, the Wiegand wire intended to surround it. To ensure that the Wiegand sensor after the ignition of a Wiegand pulse can be ignited again as quickly as possible, the invention provides for the current pulse, which generates the saturation magnetic field through 'the Wiegand impulse itself, especially triggered by its leading edge. The length and amplitude of the current pulse is chosen so that the Wiegand wire is magnetically saturated with certainty.

If the leading edge of the Wiegand pulse is used without delay to trigger the current pulse, then this causes the occurrence of a pulse in the sensor winding, the leading edge of which is initially the for a Wiegand impulse has a characteristic shape; from the time of triggering on, however, the Pulse height and length i. w. determined by the electronic circuit triggered by the Wiegand pulse. An essential feature of the invention is thus the occurring Wiegand pulses in a predetermined manner to electronically transform and amplify and thus to generate a defined saturation magnetic field in to use the sensor winding. In principle it would be possible, but it would be a worsened embodiment the invention to generate the saturation magnetic field with a separate second winding.

Advantages of the invention are that for the Generation of the saturation field strength, the strong permanent magnets customary up to now are no longer required, which had to be arranged in compliance with narrow air gaps and thereby created installation and application problems. On the other hand, by electrical means the necessary saturation field strengths can be generated without problems and special installation problems do not occur, because the Both leads to the sensor winding can be used, which are used to transmit the Wiegand pulses are required anyway for a receiving circuit. When arranging the sensor winding on the Wiegand ^ Wire has the great advantage that the Wiegand wire is strictly homogeneous to its axis parallel magnetic field is saturated. This will

the magnetic structure of the Wiegand wire and with it the height and shape of the Wiegand impulses influenced. Such a beneficial effect cannot be achieved by means of permanent magnets.

In the typical practical applications of Wiegand wire with excitation by permanent magnets the Wiegand wire is exposed to different magnetic fields because the magnets themselves relative to the Wiegand wire or the magnets are moved by moving ferromagnetic objects (e.g. machine parts) can be influenced. This is how long the exposure time to the saturation magnetic field is speed-dependent, its amplitude may also vary under certain circumstances. Both have an undesirable effect on the shape and amplitude of the Wiegand pulses; however, both will avoided by the invention.

The most important mode of operation of Wiegand sensors is that with asymmetrical excitation. Here has the Invention has the advantage that the high saturation field strength (preferably approx. 100 A / cm) is no longer permanently magnetic must be generated. For the magnetic reset and for the ignition of the Wiegand wire a field strength increase at the location of the Wiegand wire of no more than ± 20 A / cm is required. this can be realized without major problems with permanent magnets. With symmetrical excitation is for Take care that the saturation alternates in one and in the other direction of the Wiegand wire takes place and accordingly the sensor winding alternately in one and in the other direction is traversed by the current which builds up the saturation magnetic field. This can be done through a easy switching, ζ. B. by means of a bistable circuit controlled by the Wiegand pulses take place. For the ignition of the Wiegand wire, which is still necessary with symmetrical excitation, am is required Place the Wiegand wire a field strength increase of no more than ± 20 A / cm, what with permanent magnets can be done without difficulty.

An advantageous development of the invention with regard to asymmetrically excited Wiegand sensors is characterized by the fact that not only the saturation magnetic field, but also the opposite directed restoring magnetic field by temporarily feeding in a corresponding current, preferably a constant current is generated in the sensor winding. The reset magnetic field is built up between the periods of time in which the saturation magnetic field exists, and that throughout Duration between two such periods of time to avoid unintentional misfires in view of the low, i. d. As a rule, avoid an ignition field strength that is significantly below 10 A / cm. The ignition field strength is achieved in this development in that the restoring magnetic field is an oppositely directed stronger magnetic field of a permanent magnet superimposed, z. B. in such a way that the restoring magnetic field at the location of the Wiegand wire constantly assumes a strength of -20 A / cm, while the permanent magnet for the ignition of the Wiegand wire at its location when it comes closest to the Wiegand wire Magnetic field of strength +40 A / cm generated, so that when both fields are superimposed, one is safe for ignition sufficient resulting field strength of +20 A / cm remains.

The advantage of this development of the invention is, on the one hand, that only one permanent magnet is required or a permanent magnetic field of constant polarity is required to operate the Wiegand wire is, the strength of this magnetic field need not exceed 40 A / cm and therefore without significant Problems is realizable. Another advantage is that the value of the restoring field strength at the location of the Wiegand wire can be adjusted much more precisely and reproducibly in an electrical manner than with permanent magnets. Therefore, it can be ensured that the restoring field strength in one remains relatively narrow range between about 18 A / cm and 25 A / cm. The reset is below 18 A / cm of the Wiegand wire i. d. Usually inadequate and results in lower Wiegand impulses. Above 25 A / cm already set magnetic reorientations in some areas of the hard magnetic jacket of the Wiegand wire, d. H. one arrives at a transition area from the asymmetrical to the symmetrical Excitation, which also results in lower and less well-shaped Wiegand impulses. As a result of the further development of the invention, these disadvantages can be avoided. Favorably on the shape of the Wiegand impulse also has the effect that as in the case of the electrically generated saturation field also in the In the event of the magnetic restoring field generated in the sensor winding, the Wiegand wire turns itself into a severe homogeneous magnetic field parallel to its longitudinal axis.

In terms of circuit technology, the invention is best implemented by means of a preferably monostable gate circuit, which is triggered by the Wiegand pulses, opens for a predetermined time and thereby the sensor winding connects to a current source which supplies the current for the saturation magnetic field.

During the time periods in which the gate circuit is closed, a constant current can be used if necessary with opposite polarity using the same power source or a separate power source are fed into the sensor winding to generate a reset magnetic field.

Embodiments of the invention are shown in simplified form in the drawings.

F i g. 1 shows the arrangement of a Wiegand sensor for monitoring a rotating part in plan view.

F i g. 2 shows the arrangement from FIG. 1 in side view.

F i g. 3 shows a block diagram of the circuit diagram in FIG. 1 and 2 circuit used.
F i g. 4 is a more detailed circuit diagram of FIG

so circuit according to FIG. 3.

Figures 5a-c are functional diagrams for illustration the course of the procedure.

Fig. 6 shows a block diagram of an extended circuit, which also the electrical generation of the Reset magnetic field allows, and

F i g. 7 shows diagrammatically similar to FIG. 5a shows the temporal course of the acting on the Wiegand wire Magnetic fields when using the circuit according to FIG. 6th

The arrangement in FIG. 1 and 2 shows a rotating disc 1, on which the edge parallel to A bar magnet 2 is attached to the axis of rotation of the disc 1. A stationary carrier 3 is located next to the pane 1 arranged on which side by side a Wiegand sensor 4 and another bar magnet 5, both with their Axis running parallel to the axis of rotation of the disc, are arranged. The Wiegand sensor 4, consisting of a Wiegand wire 6 and one surrounding it

7 8;

Sensor winding 7, lies between the disk 1 and the other comparator input applied second reference Bar magnets 5. The sensor winding 7 is energized by the Wiegand pulse voltage whtkder

an electronic circuit 8 connected. The two outputs of the comparison circuit to potential »0«

Magnets 2 and 5 have opposite magnetization switched. As a result, the base of the transistor is preserved

directions on. 5 7! a different potential, the transistor 71 becomes conductive

The constant on the Wiegand sensor 4 and feeds a constant current into the sensor winding 7

Acting bar magnet 5 is used for the magnetic one, the height of which is adjustable by selecting the appropriate return of the Wiegand wire 6 and generated at variable series resistance R _v =. Ber

whose place a predominantly to Wiegand wire 6 constant current is so long in the sensor winding

parallel running magnetic field with a strength of approx

-20 A / cm. The sensor winding 7 connected to the disk 1 and connected to the input of the comparative

Bar magnet 2 is used to ignite the Wiegand pulse circuit 22 below that at the other comparator input

This occurs when the bar magnet 2 has dropped to the pending reference voltage, because

Wiegand sensor 4 closely approximates. At the closest approach, the output of the comparison circuit 22

tion (as shown in Fig. 1 and 2) generated the 15 again switched to the potential + Ub , so that the

Bar magnet 2 at the location of the Wiegand wire 6, a transistor 71 blocks again. Lender 22 is like that

predominantly to its axis parallel magnetic field with built up that at its output alternatively only the

a strength of approx. + 40 A / cm, so that the resulting potentials "0" and "Ub" can be. The time,

The magnetic field at the location of the Wiegand wire 6 during which the transistor 71 is conductive is generated by the

Field strength of about +20 A / cm produces, which determines the 20 time constant of the Ci - A ₁ - ^ element.

Ignition is certainly sufficient. As a result of the influence F i g. 5 shows in matching time allocation

Through the two bar magnets 2 and 5, the voltage learns three time diagrams of the course of the üur / ch

Wiegand wire 6 with one revolution of the disc 1 the bar magnets 2 and 5 on the Wiegand wire

a field strength increase of approx. -20 A / cm to +20 A / cm, called field strength (Fig. 5a), from the potential at the output

what kind of ignition and resetting of the Wiegand-Sen- 25 of the comparison circuit 22 (Fig. 5b) and from the voltage

sors 4 is sufficient, but not for its saturation, which according to the voltage curve at the ends of the sensor winding 7

the ignition must take place in any case. This for the (Fig.5c). The latter shows after the ignition of the

Saturation required magnetic field is first the typical according to the Wiegand impulse at Z.

Invention by means of the circuit 8 on the electrical rise of a Wiegand pulse. At Erj-eicnen the

Paths generated in the sensor winding 7. The block 30 reference voltage Ur, however, becomes the transistor Tt

The circuit diagram of the circuit 8 in FIG. 3 shows a conductive and the further rise and course: the

Comparison circuit 9, one input of which is a voltage in the sensor winding through the

Reference voltage U _{R is} supplied and its connected electronic circuit 8 is determined. The;

other input connected to the sensor winding 7 circulation time T of the disc 1 and the through the

is. If and as long as the time constant of the Q - /? I - /? _2- member certain Zetf

transmitted tp originating from a Wiegand pulse during which transistor 71 is conductive

Pulse voltage is higher than the reference voltage Ur, shown. Only partially drawn in with dashed lines

is followed by one of the comparison circuit 9 which is followed by the circuit for the duration t _p

activated pulse circuit 10 emitted a control pulse, caused saturation field strength in the sensor winding

for the duration of this pulse a switch 11 40 ment 7, which is the permanent magnetic field in

closes, through which the sensor winding 7 with a F i g. 5a superimposed.

Constant current source 12 is connected to the one for Fi g. 6 shows a block diagram of an expanded

Saturation of the Wiegand wire 6 sufficient current circuit 8, which differs from the block diagram of the

feeds into the sensor winding 7. F i g. 3 only differs in that in addition to the

An embodiment for a monostable switching 45 constant current source 12 yet another opposite

according to FIG. 3 shows FIG. 4. The sensor winding 7 polarized constant current source 15 is provided, which

is via a differentiator Q — R \ - R2 with the one during the times in which the constant current source

The input of a comparison circuit 22 is connected, the 12 of which is not connected to the sensor winding 7,

other input a constant reference voltage is in turn connected to the sensor winding 7 and in

receives, which feeds a current through one of the resistors R3 50, which is a back-up

on the one hand and /? 4 and R2 on the other hand existing development of the Wiegand wire 6 sufficient magnetic field

Voltage divider of the voltage + Ub of a con with a strength of approx. 20 A / cm inside the

constant voltage source is derived. The output of the sensor winding 7 is generated. For this purpose is the

Comparison circuit 22 is replaced by one via two on-off switches 11 from FIG. 3 located in series

a voltage divider forming resistors R ₅ and Re 55 changeover switch 14. By the constant current source 15 is

placed on Ub . Between R5 and Re , the control voltage is the bar magnet 5 in FIG. 1 and 2 replaced. As the only one

Voltage for a transistor 71 is tapped, the emitter permanent magnet of which is still the one for the ignition def

is connected to Ub and whose collector requires a Wiegand pulse (e.g. bar magnet 2 in Fig. 1

Series resistor Rv connected to the sensor winding 7 and 2). ^{! :}

the other end of which is connected to earth. The comparison 60 Fig. 7 is a representation similar to Fig.5a and shows

Circuit 22 is constructed so that in the idle state, i. i. the temporal course of the various on the

in the absence of a Wiegand: impulse, their output Wiegand wire 6 with acting magnetic fields

is at the potential + Ub , so that the transistor 71 using a circuit arrangement according to FIG. 6th

Is blocked. If a Wiegand- In F i g. 7 is shown in dashed lines, the field strength

If the pulse is ignited, it passes through the differential ^{65 of} the reset field (approx. -20 A / cm), which exists up to

ornamental link C1 - Ä1 - Ä2. whose time constant i. w. through at the time of the ignition of the Wiegand pulse

C \ and R \, is determined to one input of the (point Z) and is rebuilt when the

Comparison circuit 22. When the saturation magnetic field (approx. +100 A / cm) is exceeded, it decays. That

from permanent magnets (ζ. B. bar magnet 2 in Fig. 1 and 2) the magnetic field temporarily generated at the location of the Wiegand wire 6 is shown in dotted lines. It temporarily compensates for the reset field and, with a resulting field strength of approx. 1 + 8 A / cm the ignition of the Wiegand pulse. With the ignition at Z, the feed-in of the current from the

10

Constant current source 12 in the sensor winding, for a short period of time tp, during which the constant current source 15 is separated from the sensor winding. The overall resulting field strength at the location of the Wiegand wire 6 is given by the solid curve.

For this purpose 3 sheets of drawings

Claims (8)

ι 2 claims: (9, 10) and the power source (12) on the other hand, a switch controlled by the Wiegand pulses 1. A method for magnetic excitation from is provided, which after each saturation current one Wiegand wire and a pulse assigned to it, the connection polarity of the sensor winding (7) Induction winding (sensor winding) existing 5 reverses. Wiegand sensors, in which the in the sensor 9. Circuit arrangement according to claim 6 or 7 Wiegand impulses occurring in the winding through the asymmetrical excitation of Wiegand sensor Influencing the Wiegand wire by means of a few, characterized in that for generating the at least one permanent magnet are ignited, restoring field strength for the Wiegand wire (6) a characterized in that each io connected to the sensor winding (7) feed switch Wiegand pulse for triggering electronics (15) is provided, which within the see circuit is used, which then for time periods in which the gate circuit (9, 10) a predetermined period of time one is closed to the magneti-, a current of the opposite see saturation of the Wiegand wire sufficient - polarity feeds into the sensor winding (7), the current of appropriately preselected polarity 15 10. Circuit arrangement according to claim 9, there- feeds into the sensor winding. characterized in that the connection of the 2. The method according to claim 1, characterized in that the feed circuit (15) for resetting the shows that the front flank of the Wiegand-Im-Wiegand wire (6) through the gate circuit (9,10) pulses to trigger the electronic circuit is controlled. is used. 20th 3. The method according to claim 1 or 2, characterized characterized in that the electronic circuit after it has been triggered, the current immediately flows into the Feeds sensor winding. The invention is based on a method with the 4. The method according to any one of the preceding 25 feature claims specified in the preamble of claim 1 for asymmetrical excitation of len (DE-OS 30 08 562, DE-PS 30 14 783). The permanent Wiegand sensors, characterized in that the magnetic influence of Wiegand sensors is between the time periods in which the sensor is characteristic for the majority of their applications, winding to saturate the Wiegand wire z. B. for position monitoring of moving machine current a preselected polarity fed in 30 divide, for proximity switches, for tachometers, is, the sensor winding a current from opposite - with displacement sensors, with angle sensors and others. m. Set polarity is fed, the strength of which Wiegand wires are in their 'composition for the magnetic resetting of the Wiegand wire - homogeneous, ferromagnetic wires (e.g. from a tes is sufficient, and that the at least one alloy of iron and nickel, preferably 48% Permanent magnet exclusively to ignite the 35 iron and 52% nickel, or from an alloy of Wiegand impulse is used. Iron and cobalt, or an alloy of iron 5. The method according to claim thereby marked with cobalt and nickel, or from an alloy of draws that the current to the magnetic return cobalt with iron and vanadium, preferably 52% development of the Wiegand wire throughout the cobalt, 38% iron and 10% vanadium), which as a result Length of time between two consecutive 40 of a particular mechanical, and thermal Periods of time is fed, in which the sensor treatment a soft magnetic core and a winding have a current to saturate the Wiegand magnetically hard jacket, d. H. the coat Wire is fed. has a higher coercive force than the core. 6. Circuit arrangement for the magnetic excitation Wiegand wires typically have a length of 10 to gung from a Wiegand wire and one 45 to 50 mm, preferably from 20 to 30 mm. If you bring the associated induction winding (sensor winding) a Wiegand wire, in which the magnetization direction existing Wiegand sensors, in which the Wiegand impulses occurring in the direction of the soft magnetic core with the magnetization of the sensor winding correspond to the direction of the hard magnetic jacket by influencing the Wiegand wire by means of an external one Magnetic field, the direction of which coincides with the direction of the wire axis when ignited with at least one permanent magnet, characterized in that the sensor magnetization direction of the Wiegand wire but winding (7) with a gate circuit (9, 10) is opposite, then at Exceeding one is connected, which is triggered by the Wiegand pulse field strength of about 16 A / cm the Magnetisierungsrichgetriggered and for a predetermined period of time device of the soft core of the Wiegand wire is opened, and that the sensor winding (7) about 55 turns. This reversal is also referred to as resetting the gate circuit (9, 10) with a current source (12). When the direction of the outer magnetic field is reversed again, the direction of magnetization (9,10) in the sensor winding is reversed when the magnetic field is open referred to as the ignition field current of the corresponding preselected polarity ⁶ O strength) again, so that the core and the feeds. Sheath are magnetized again in parallel. These 7. Circuit arrangement according to claim 6, thereby reversing the direction of magnetization takes place very much characterized in that the gate circuit (9, 10) has a fast and goes with a correspondingly strong monostable circuit (monoflop) is. Change in the magnetic flux per time 8. Circuit arrangement according to claim 6 or 7 ⁶ 5 means together (Wiegand effect). This change in the symmetrical excitation of Wiegand-Senso force flow can be in an induction winding, which is called ren, characterized in that between the sensor winding, a short and very sensor winding (7) on the one hand and the gate circuit high (depending on the number of turns and load resistance -