FR2793035A1 - METHOD AND DEVICE FOR DETERMINING THE AMPLITUDE AND / OR DIRECTION OF A MAGNETIC FIELD - Google Patents

Abstract

Method for determining the amplitude and / or direction of a magnetic field. A first magnetic field is applied to at least one magnetoresistive sensor, in particular a GMR sensor element with a first magnetic field to be defined. A time-varying compensating magnetic field is applied to this magnetoresistive sensor. The instant of at least one extremum of one of the sensor signals dependent on the magnetic field to be defined and on the compensation field is determined as a function of the signal from the magnetoresistive sensor. The amplitude and / or the direction of the magnetic field to be defined is determined from the amplitude and / or the direction of the compensating magnetic field at at least one instant.

Description

I The present invention relates to a method and a device for

  determine amplitude and / or direction

of a magnetic field.

  Devices are known for carrying out a

  non-contact angle of rotation detection for example according to document DE-OS 195 43 562. In such devices, there is a magnet carried by a rotating shaft and whose angular position is to be determined. The magnetic field which varies with the angle of rotation of the shaft is measured using two sensor elements or more simply sensors. These sensors are for example two Hall effect sensors rotated relative to each other by an angle of 90; we can also have two magnetoresistive sensors offset by 45. The sensors

  or sensor elements are supplied by voltage signals

  alternative phase appropriately out of phase. The combination

  sound of the output signals from the sensors gives a

  signal profile representative of the angular position.

  It is also known to use magnetic field sensors to determine the magnetic fields whose direction is static and the amplitude varies however

with time.

  As sensors, we know next to the sensors mentioned above also GMR sensors, that is to say

  giant magnetoresistive sensors ("giant magneto-

  resistance "GMR) which, compared to usual sensors

  AMR (anisotropic magnetoresistance) have a variation in re-

  high resistance depending on the magnetic field. In general

  ral, this variation of resistance depending on the field

  magnetic in such GMR sensors must however be ex-

  used in relatively expensive bridge assemblies, because the sensor signals generated depend on the voltage of

  operation and temperature. The mounting of such cap-

  GMR or resistance in a bridge installation is, as indicated, complicated and only allows gradient measurements of the magnetic field if the different sensor elements are brought together in space. The magnetic protection of

  two GMR resistors in two bridges is also an opera-

  complicated and in the case of thin conductive layers

  these magnetic, this solution creates difficulties with the

  field saturation of these layers, but then we can perform

  kill absolute field measurements. The dependence of the

  characteristic curve of the sensor as a function of the temperature

  ture is only compensated in the equilibrium state of the bridge,

  so an electronic operating circuit is needed

  (also due to the weak signal strength of the sensor). The object of the present invention is to enable an amplitude to be determined as simply as possible.

  and / or a magnetic field direction.

  To this end, the invention relates to a method of the type described above, characterized in that: - at least one magnetoresistive sensor, in particular a GMR sensor element, is subjected to a first magnetic field to be determined, - at least one this magnetoresistive sensor with a time-varying magnetic compensation field,

  - at least one extremum of a si is determined at a time

  general dependent on the total magnetic field composed of the field

  magnetic to be determined and the compensation field, if-

  general from the magnetoresistive sensor, and

  - the amplitude and / or direction of the ma- field is determined

  genetic to be defined from the base of the amplitude and / or direction of the compensation field at least

a moment.

  The invention also relates to a device for implementing the method, comprising: means for applying a first magnetic field to be defined to at least one magnetoresistive sensor element, in particular a GMR sensor element,

  means for acting on at least this magnetoresistive sensor;

  tif with a time-varying magnetic compensation field,

  means for determining at least one instant of an extreme

  mum of the derivative as a function of time of a magnetic field

  that global composed of the magnetic field to be defined and the compensation field, and - means for determining the amplitude and / or the direction

  of the magnetic field to be defined from the compres-

  the amplitude and / or direction of the compensating field

tion at least a moment.

  According to the invention, it is possible to determine

  the amplitude and / or direction of a magnetic field in pro-

  yielding in a simple way. By determining the amplitude and / or the direction of a compensation field whose amplitude and / or direction vary over time, at the instant of an extremum of the resistance signal of the sensor, i.e. say for example at the time of total compensation of the magnetic field to be determined (reciprocal compensation of the magnetic fields),

  we can avoid both the absolute value of the resistance

  tance of the sensor (which depends for example on the temperature) and the absolute value of the effect of the sensor or the form of its function or its characteristic curve do not influence the

  measurement accuracy. If, for example, we use the

  You can come and go from the compensation field, you can

  also compensate for the hysteresis of the sensor. Like the big-

  deur to be measured (resistance of the sensor at the time of comp

  total thinking of the total magnetic field) is transformed

  in a time, we can simply represent numerically

  this quantity using a counter.

  According to a preferred embodiment of the pro-

  yielded from the invention, at least a moment from the extremum of the

  resistance of the magnetoresistive sensor is defined in

  noticing an algebraic sign change thanks to the

  signal as a function of time. Differentiating elements-

  ters that can determine a change of algebraic sign of a derivative as a function of time are simple and

cheap.

  Advantageously, to determine the change-

  algebraic sign, we use a differentiator

  saturated, the output signal of which jumps when

  finds an extremum in the resistance of the magnetorean sensor

  sistive, from a first level to a second level. The moment of

  change of algebraic sign of the derivative of the resis-

  both of the magnetoresistive sensor is very precisely defined.

  According to another preferential development of the pro-

  yielded from the invention, the current form used to create the compensation field is generated using a counter

  and a digital / analog converter cooperated

  rant with this counter. Such components are simple and few

  expensive; in practice, they have proven to be robust and reliable.

  wheat. Advantageously, the compensation field applied to at least one instant is carried out by observing the counting state of the digital counter at this instant. Such a counting state is observed in a simple and safe manner and can be recorded in a memory; this information is

  then available as a measure of the amplitude of the field of com-

  thinking and so the magnetic field to be determined, directed

in the opposite direction.

  It is also possible to execute the compensation field applied at least one instant by observing the surface under a rectangular voltage at the output of the differentiating element. Such analog determination

  of the compensation field is advantageous for certain

  kills. In case we want to determine the amplitude of a

  magnetic field of known direction, it is advantageous to generate-

  at the location of the magnetoresistive sensor, a com-

  thought variable in time, directed opposite the magnetic field to be determined. This can be done for example using a coil wound around the sensor or using

  of a conductor which crosses the sensor at right angles to

  port to the field to be determined. In addition, it is possible to

  read the sensor so that it compensates at zero, by itself the

magnetic field to be defined.

  To determine a known amplitude in a di-

  rection of a magnetic field, a magnetic field advantageously rotating at the location of the sensor, field of which

  the amplitude corresponds to that of the magnetic field to be defined.

  In this case, it is also sufficient to generate a rotating, unmodulated magnetic field which produces, for example at intervals of 180, a change in the deduced sensor function, assuming that we are in the part of the characteristic curve of the sensor depending on the intensity of the field. It should be noted that the magnetic rotating field or the compensation field does not have

  necessarily the same amplitude as that of the field to be determined-

  undermine, because even for fields of different amplitudes, the extremes of the sensor signal that occur allow

  deduce the desired information.

  To determine both the amplitude and the di-

  rection of a magnetic field, it is planned to generate at the location of the magnetoresistive sensor, a rotating magnetic field, amplitude modulated. Such a magnetic field is

  creates for example using two sinusoidal currents circu-

  lant in orthogonal directions. The vector resulting from a magnetic field thus generated thus passes as for example in the case of a fast rotation and a slow modulation, on a spiral, from a zero value to a maximum value. The operating criterion corresponds in principle to what has already been described; the angle to be defined is calculated from the instantaneous values of the sinusoidal currents

  (i.e. sinusoidal currents at the time of the sup-

  total pressure of the resulting magnetic field and we calculate

  the field from the amplitude of the sum vector.

  The present invention will be described below in more detail with the aid of the appended drawings, in which: - Figure 1 is a diagram of an arrangement for applying a compensating magnetic field to a GMR sensor, - Figure 2 shows the characteristic curve of a sensor resistance signal as a function of the total magnetic field,

  - Figure 3 shows the curve of the signal supplied by an element

  differentiating limiter with the signal of FIG. 2 as input signal,

  - Figure 4 is an exploded perspective view of an element

  GMR sensor ment with current conductors to generate a rotating magnetic field, - Figure 5 shows the characteristic curve of a resistance sensor signal in the case of a compensating rotating field, of constant amplitude, - Figure 6 shows the output signal from the sensor of a differentiator which receives the signal according to Figure 5

as an input signal.

  Figure 1 shows a GMR sensor element 1 with insulation 2 applied to a substrate 3. The insulation

  2 is provided with an electrical conductor 4 as a control strip

  field thinking. The GMR sensor element 1 is subjected to the action of a certain magnetic field M shown diagrammatically by three

  parallel arrows. By passing a corresponding current

  dant through the field compensation band 4, we generate

  a compensating magnetic field whose direction is op-

  posed to that of the magnetic field M to be determined.

  The passage of current through the band of com-

  field thinking 4 is controlled using a converter

  digital / analog 7 subjected to the action of a digital counter

  rique 6. The digital counter 6 is itself clocked by a clock 8. The current is counted using the cadence frequency generated by the clock in the digital counter to be converted by the digital / analog converter 7 into

  a time-varying analog current. The magnetic field

  tick (compensation field) generated around the field compensation band 4 is thus variable according to the current

  variable over time, also in minimum and maximum

  mum. This means that by an appropriate choice of the maximum or minimum current through the field compensation band 4, it is guaranteed that at a precisely determined instant, the magnetic compensation field generated by the passage of current through the field band field compensation 4 fully compensates for the magnetic field to be measured,

  that is, we obtain a total magnetic field

  sultant H equal to zero. At this instant (total magnetic field H resulting equal to zero), the value of the resistor R sensor

  of the GMR sensor element is maximum as is

  shown schematically in Figure 2.

  To determine this instant, we transmit the

  general of Rsensor resistance, or a signal associated with the Rsensor resistance signal of the GMR 1 sensor or the

  GMR sensor, for example intensity or voltage values

  proportional to the resistance signal, to an element

  differentiator 5 which, when the resistance signal has

  dye the maximum, jump from level H to level L like this-

  1a is shown diagrammatically in FIG. 3. The instant of the change of algebraic sign is transmitted to a trigger element 9 by a corresponding signal noting the state of the digital counter at this determined instant and recording it in a digital memory. As the counting state of the digital counter is unequivocally associated with a current passing through the field compensation band 4,

  which itself corresponds to a compensation field of a certain

  high amplitude, the magnetic field is thus defined at

  rer whose amplitude corresponds to that of the field of

  compensation, but whose meaning is opposite.

  In the case of a combined 360 angle sensor

  and field strength, two sinuous currents must be modulated

  solids phase shifted by 90 to create a compensation field.

  A combination of two compensation field bands 4a,

  4b perpendicular to each other for this purpose is shown

  shown in Figure 4. The exploded perspective view of the figure

  gure 4 lets appear between the bands of compensation field 4a, 4b, a GMR element 1, in the form of meanders

  as well as the insulation 2 surrounding this element. By a modu-

  appropriate relationship of the currents flowing in the bands of

  field compensation 4a, 4b, a compensation field is generated

  variable amplitude and direction. The exploitation of

  compensation field or the total field resulting from the com-

  pairing with the magnetic field to be measured is done so

  analogous using the procedure described in Figure 1.

  To determine only the angle of a ma-

  external genetics to be defined, a rotating magnetic field, not modulated, which produces at intervals of 180,

  a change of algebraic sign of the resistance function

  tance deducted from the sensor. It is not necessary for this that the amplitude of the rotating magnetic field corresponds to

  the amplitude of the external magnetic field that we want to

  finish. This will be described in more detail using FIGS. 5 and 6. In FIG. 5, it is assumed that El and E2

  represent the maximum and minimum values of the resistance

  GMR sensor tance, values that occur when the

  compensation field does not exactly match in ampli

  study those of the field to be measured. The working range of the cap-

  The GMR (or sensor element) is represented by a curve drawn in thick lines between the points El and E2. We recognize for example that there can be no deletion

  reciprocal complete magnetic fields and the maximum value

  absolute male of the resistance for which we would have an in-

  total magnetic field density H equal to zero is a

  value which is not reached here. The corresponding angular range

  laying at the interval between points El and E2 is here as shown in Figure 6. In the case of a monotonic rotation of the compensation field, we arrive at a variation of the resistance signal of the element of sensor 1

  between the values El and E2 (back and forth movement). When-

  that we reach point El or point E2, in a similar way to

  which has already been described in relation to FIG. 1, we ar-

  shore to a variation of algebraic sign of the derivative of the si-

  resistance which can be seen again using a differentiator as shown in the

  figure 6. The instants of the different jumps of the signal of the diff-

  ferenciator occur simultaneously with a parallel or antiparallel alignment between the compensation field and the field to be measured. If, for example, the angular movement of the compensation field is controlled digitally, it is similarly possible to detect, store and supply an existing angular signal at the time of a jump in the

  angular signal of the differentiator.

  It should be noted that the currents crossing

  the field compensation bands 4, 4a, 4b in the event of dif-

  difficulty, for example because of a sharp rise in temperature

  erasures, -in GMR elements made as conductors

  in a thin layer, can be pulsed currents.

REV E N D I C A T I ON S

  1) Method for determining the amplitude and / or the direction of a magnetic field, characterized in that: - at least one magnetoresistive sensor (1) is subjected, in particular

  a GMR sensor element, with a first magnetic field

  tick to be determined, - at least this magnetoresistive sensor (1) is subjected to a time-varying magnetic compensation field, - an instant of at least one extremum of a signal is determined

  depending on the total magnetic field composed of the ma-

  genetic to be determined and the compensation field, signal from the magnetoresistive sensor, and

  - the amplitude and / or direction of the ma- field is determined

  genetic to be defined from the base of the amplitude and / or direction of the compensation field at least

a moment.

  2) Method according to claim 1, characterized in that at least this instant is defined by noting a change

  of algebraic sign of the derivative as a function of time if

  general sensor supplied by the magnetoresistive sensor (1).

  3) Method according to claim 2, characterized in that

  to see the change in the algebraic sign of the deviation

  as a function of time, we use a differentiation element

  saturation-controlled timer (5), the output signal of which jumps from a first to a second level when a

  signal extremum of the magnetoresistive sensor (1).

  4) Method according to one of the preceding claims,

  characterized in that a variable current is used which can be used to generate the compensation field using a digital counter (6) and a digital analog converter (7) cooperating with a counter. he

   ) Method according to any one of the preceding claims.

  teeth, characterized in that the compensation field existing at least one instant is determined by determining the counting state of the digital counter

that (6) at least one instant.

  6) Method according to one of claims 3 or 4,

  characterized in that the compensation field applied at least one instant is determined by determining the area of a rectangular tension

  at the exit of the differentiating element (5).

  7) Method according to one of the preceding claims,

characterized in that

  to determine the amplitude of a directional magnetic field

  tion known at the magnetoresistive sensor (1), we manage

  creates a time-varying compensation field of

  opposite direction to that of the magnetic field to be determined.

  8) Method according to one of the preceding claims,

characterized in that

  to determine a direction of a magnetic field of an am-

  known or unknown fullness at the magnetorean sensor

  sistive (1), a rotating magnetic field is generated.

  9) Method according to one of the preceding claims,

characterized in that

  to determine an amplitude and a direction of a ma-

  magnetic at the location of the magnetoresistive sensor (1),

  generates an amplitude modulated rotating magnetic field.

   ) Device for determining an amplitude and / or a di-

  rection of a magnetic field, characterized in that it comprises: - means for applying a first magnetic field to be defined to at least one magnetoresistive sensor element (1), in particular a GMR sensor element, - means (4 , 6, 7) to act on at least this magnetoresistive sensor (1) with a magnetic compensation field

  variable over time, - means for determining at least one instant of an ex-

  mum of the derivative as a function of time of a global magnetic field composed of the magnetic field to be defined and the compensation field, and- means (9) for determining the amplitude and / or the direction of the magnetic field to be defined from the ground up

  including the amplitude and / or the direction of the compensating field at least one instant.