EP0606313A1 - Dispositif pour la determination de la force d'un champ magnetique - Google Patents

Dispositif pour la determination de la force d'un champ magnetique

Info

Publication number
EP0606313A1
EP0606313A1 EP92920484A EP92920484A EP0606313A1 EP 0606313 A1 EP0606313 A1 EP 0606313A1 EP 92920484 A EP92920484 A EP 92920484A EP 92920484 A EP92920484 A EP 92920484A EP 0606313 A1 EP0606313 A1 EP 0606313A1
Authority
EP
European Patent Office
Prior art keywords
magnetic field
magnetoresistor
sensor
resistance
electromagnet
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP92920484A
Other languages
German (de)
English (en)
Inventor
Norbert Normann
Gunter Schulze
Ralf Kessler
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Doduco Solutions GmbH
Original Assignee
Doduco GmbH and Co KG Dr Eugen Duerrwaechter
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Doduco GmbH and Co KG Dr Eugen Duerrwaechter filed Critical Doduco GmbH and Co KG Dr Eugen Duerrwaechter
Publication of EP0606313A1 publication Critical patent/EP0606313A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
    • G01R33/09—Magnetoresistive devices

Definitions

  • the invention relates to a device for determining the strength of a magnetic field from a predetermined direction with a magnetic field sensor and with an associated electrical evaluation circuit. 5
  • EP-B-0 263 775 shows a tire pressure monitor in which a bellows is slidably mounted in the rim ring of the wheel and is acted upon from the inside by the tire's air pressure, parallel to the tire
  • the position of the permanent magnet depends on the air pressure.
  • the permanent magnet rotates past a Hall sensor attached to the wheel suspension, which emits a signal which is dependent on the magnetic flux and thus on the position of the permanent magnet and which is fed to an electrical evaluation circuit.
  • the Hall sensor is an active component and therefore requires an energy supply. That is why at least three lines emanate from the Hall sensor.
  • Another disadvantage of the Hall sensors is that they are sensitive to temperature. Their working range is limited to temperatures from -40 to approximately + 120 ° C-150 ° C. In applications on vehicle wheels, however, higher temperatures can occur because the nearby brake discs temporarily radiate considerable heat.
  • the present invention is therefore based on the object of providing a device of the type mentioned at the outset, which does not require more than two supply lines and withstands higher temperatures than a Hall sensor.
  • a fixed arrangement of an electromagnet and an electrical resistor connected in series therewith with a magnetic field-dependent conductivity is used as the magnetic field sensor.
  • magnetoresistor a magnetic field-dependent conductivity
  • Such a magnetic field sensor manages with two supply lines and is suitable for use in temperature ranges from -40 ° C to at least + 200 ° C. It is also advantageous that magnetoresistors have a very low price compared to Hall sensors; the disadvantage with them, however, is that
  • magnetoresistors of a series differ greatly in their basic resistance R_: scattering of the basic resistance by 20% is normal. Therefore, magnetoresistors cannot easily be used for accurate magnetic field measurements,
  • the magnetoresistor is now operated in a manner which nevertheless enables a very precise magnetic field measurement.
  • the magnetoresistor is first coupled to an electromagnet and connected in series with it.
  • the field of the electromagnet is first coupled to an electromagnet and connected in series with it.
  • the magnetoresistor sets the magnetoresistor and shifts its resistance from the basic resistance R_ along the resistance-magnetic flux characteristic to a higher resistance R, which is also referred to below as the operating point of the magnetic field sensor.
  • the evaluation circuit contains a control circuit which regulates the resistance of the magnetoresistor constantly to the value R by controlling the voltage u or the current I of the current source feeding the magnetic field sensor.
  • a control circuit which regulates the resistance of the magnetoresistor constantly to the value R by controlling the voltage u or the current I of the current source feeding the magnetic field sensor.
  • current and voltage are continuously measured at the magnetic field sensor and the resistance R is determined therefrom by means of a dividing device. From the deviation of the determined resistance from the working point a manipulated variable is derived which controls the current flow through the magnetic field sensor so that its self-generated magnetic field compensates for the influence of the external magnetic field on the magnetoresistor and thereby its resistance to the operating point R ⁇ . leads back.
  • the circuit which picks up this signal can either bring it to further processing in the evaluation circuit or display it.
  • a temperature drift of the magnetic field sensor can be compensated for by providing a reference magnet which generates a magnetic field of known strength and orientation at the location of the magnetic field sensor. From time to time, the magnetic field sensor is exposed to the known magnetic field of the reference magnet instead of the magnetic field to be determined. If it is established that the signal supplied by the tapping circuit and proportional to the manipulated variable, which signal originates from the influence of the reference magnet, is of a normal value, e.g. determined at a temperature of 20 ° C, then the next time the unknown magnetic field is determined, the signal proportional to the manipulated variable is compensated by the drift previously determined by means of the reference magnet and the temperature influence is thereby compensated. Other influences falsifying the measurement result, e.g. an aging can be compensated in this way.
  • an air coil can be used as an electromagnet.
  • the magnetoresistor could also be connected to a non-magnetic, e.g. Attach ceramic core that is sufficiently heat-resistant and can also serve as a support for the coil.
  • a field plate magnetic sensor is preferably used as the magnetoresistor, in particular one whose magnetic field sensitive material contains a semiconductor based on indium antimonide / nickel anti onide.
  • the device according to the invention is preferably used in a tire pressure monitor as described in EP-B-0 263 775: the magnetic field sensor is fixed in place on part of the wheel suspension and is oriented parallel to the wheel axle. On the rim ring of the wheel there is a permanent magnet at the end of a bellows which is acted upon by the tire pressure on the inside. The bellows and the permanent magnet are oriented parallel to the wheel axis, so that the distance of the permanent magnet from the magnetic field sensor, if it rotates past it, depends on the tire pressure. Two lines lead from the magnetic field sensor into the interior of the vehicle to the evaluation circuit, which is preferably located in the area of the dashboard. A reference magnet provided for the temperature compensation is fixed in place on the rim ring, namely at such a distance from the magnet on the bellows that its fields practically do not influence one another; in front-
  • the reference magnet is preferably located at a position of the rim ring diametrically opposite the bellows.
  • a magnetic field sensor can also be used
  • Nuclear coil can also be used to detect soft magnetic materials.
  • a sensor itself generates a magnetic field and has a magnetic circuit, the permeability U of which determines the proportionality factor between the coil current I and the generated magnetic field. Since this ⁇ . is increased by the presence of soft magnetic material near the sensor, the control loop reacts to this material by lowering the current I.
  • Figure 1 is a block diagram of an apparatus for
  • FIG. 2 shows the structure of the magnetic field sensor in detail
  • Figure 3 shows a typical example of the course of the characteristic of the magnetic field sensor, which shows the change in resistance depending on the magnetic
  • Figure 4 shows the arrangement of the magnetic field sensor on a wheel suspension
  • FIG. 5 shows in detail the interaction of the magnetic field sensor with a pressure sensor on the vehicle wheel.
  • the device shown in FIG. 1 consists of a magnetic field sensor 1 and an evaluation circuit 2 connected to it.
  • the magnetic field sensor consists of an electromagnet 3 and a magnetoresistor 4, in particular a field plate magnetic sensor, the resistance R of which is square of the amount of the magnetic flux B (FIG. 3) changes.
  • the electromagnet 3 consists of a cylindrical coil 6 on a rod-shaped core 5, at one end of which the magneto-resistor 4 is attached.
  • the evaluation circuit 2 contains a controllable current source 7, which feeds a current I into the magnetic field sensor 1, through which a magnetic force flow B is generated at the location of the magnetoresistor 4, so that the resistance R of the magnetoresistor via the basic resistance R Q , that exists in the absence of a magnetic field increases.
  • the voltage U of the current source 7 is controlled so that the resistance R assumes a predetermined value R 3, which is referred to here as the operating point (see
  • a divider circuit 8 which, on the one hand, taps the voltage U of the controllable current source 7 and, on the other hand, supplies a measurement signal proportional to the current intensity I.
  • REPLACEMENT LEAF circuit the resistance R of the magnetic field sensor and transmits the result to a microcomputer 9 and to a controller 10.
  • the microcomputer 9 also receives a voltage signal proportional to the current I, digitizes the resistance signal transmitted to it in an analog / digital converter 11 and the signal representing the current value I in an analog / digital converter 14, checks the resistance value and the current value for plausibility and gives the controller 10 a new one if the measuring range is exceeded or undershot via a digital / analog converter 12
  • Working point R des
  • the controller 10 derives a manipulated variable S with which the voltage u of the controllable current source 7 is set such that the magnetic field sensor 1 has the resistance R 3.
  • the resistance of the magnetic field sensor is either greater or less than R, depending on whether the outer magnetic field 13 is rectified or opposed to the magnetic field generated in the magnetic field sensor itself.
  • the changed resistance is determined by the dividing circuit 8, communicated to the controller 10 as the actual value, which then forms a manipulated variable S by comparison with the setpoint value R 3, by means of which the voltage of the controllable current source 7 is changed such that the resistance of the magnetic field sensor again assumes the value R_.
  • the manipulated variable S is proportional to the force flow of the external magnetic field 13 at the location of the magnetoresistor 4. Die
  • the manipulated variable is therefore a further input of the microcomputer
  • REPLACEMENT LEAF 9 supplied, there digitized in an analog / digital converter 14 and evaluated according to a predetermined program. The result of the evaluation can be shown numerically on a display. However, it is also possible to control an analog display, for example a signal lamp 16, via a further digital / analog converter 15, which can indicate that a limit value has been reached.
  • an analog display for example a signal lamp 16, via a further digital / analog converter 15, which can indicate that a limit value has been reached.
  • the magnetic field sensor 1 is exposed from time to time to the known magnetic field of a permanent magnet 17 by approaching the permanent magnet 17 from time to time to the magnetic field sensor 1, one can see from the comparison of the measured force flow that that of the permanent magnet 17 goes out, determine and compensate for a possible temperature drift of the magnetic field sensor with its known, actual power flow.
  • FIG. 4 shows the arrangement of such a magnetic field sensor for monitoring the pressure in pneumatic tires of vehicles.
  • the pneumatic tire 20 sits on the rim 21 of a wheel 22 which is screwed to a hub 23 which is part of a wheel suspension 24.
  • a pressure sensor 25 is installed in the rim 21 parallel to the wheel axis 26, which projects with one end into the air space 27 of the tire and with its other end lies outside the air space 27.
  • the structure of the pressure sensor is shown in detail in FIG. 5. It consists of a tube 28, at the end of which is located in the air space 27, the open end of a bellows 29 is fastened, which inside is subjected to the pressure P in the air space 27.
  • the opposite end of the bellows 29 is closed and carries a permanent magnet 30, the position of which in
  • T Pipe 28 depends on the pressure P.
  • a magnetic field sensor according to the invention is attached to part of the wheel suspension 24, namely to a spring strut 31, on which the magnet 30 moves once with each revolution of the wheel 22.
  • the pressure P can be determined from the measured force flow of the magnet 30 at the location of the magnetic field sensor 1.
  • a permanent magnet 17 is firmly attached as a reference magnet, which enables temperature compensation. Changes in the ambient temperature, but also heat, which is temporarily emitted by the brake disk 32 and heats the magnetic field sensor 1, do not lead to a falsification of the measurement result in this way.

Landscapes

  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Measuring Fluid Pressure (AREA)
  • Measuring Magnetic Variables (AREA)

Abstract

Pour la détermination de la force d'un champ magnétique d'orientation prédéterminée sont prévus un détecteur de champ magnétique (1) et un circuit d'évaluation électrique (2) qui y est relié. Le détecteur de champ magnétique (1) est un dispositif fixe constitué d'un électro-aimant (3) et d'une résistance électrique (4) montée en parallèle avec ce premier et ayant une conductivité variable en fonction du champ magnétique (magnétorésistance). Le circuit d'évaluation (2) a une source de courant pilotable (7) alimentant l'électro-aimant (3). La résistance du détecteur de champ magnétique (1) est mesurée et réglée par un circuit de réglage (10) à une valeur constante. Un circuit de prélèvement (14) prélève un signal proportionnel au courant I et l'amène pour traitement ultérieur au circuit d'évaluation (2, 9) ou bien à l'affichage.
EP92920484A 1991-10-04 1992-10-03 Dispositif pour la determination de la force d'un champ magnetique Withdrawn EP0606313A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
DE4133041 1991-10-04
DE4133041 1991-10-04
DE4200156 1992-01-07
DE19924200156 DE4200156A1 (de) 1991-10-04 1992-01-07 Vorrichtung zum bestimmen der staerke eines magnetfeldes
PCT/EP1992/002288 WO1993007505A1 (fr) 1991-10-04 1992-10-03 Dispositif pour la determination de la force d'un champ magnetique

Publications (1)

Publication Number Publication Date
EP0606313A1 true EP0606313A1 (fr) 1994-07-20

Family

ID=25907970

Family Applications (1)

Application Number Title Priority Date Filing Date
EP92920484A Withdrawn EP0606313A1 (fr) 1991-10-04 1992-10-03 Dispositif pour la determination de la force d'un champ magnetique

Country Status (3)

Country Link
EP (1) EP0606313A1 (fr)
DE (1) DE4200156A1 (fr)
WO (1) WO1993007505A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4408511A1 (de) * 1994-03-14 1995-09-21 Duerrwaechter E Dr Doduco Verfahren zum Überwachen des Drucks in Luftreifen

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1297755B (de) * 1963-05-10 1969-06-19 Siemens Ag Magnetfeldmessgeraet mit einer Sonde mit magnetfeldabhaengigem Widerstand
SU485384A2 (ru) * 1973-12-07 1975-09-25 Уфимский авиационный институт им. Орджоникидзе Датчик линейной скорости
CH651151A5 (de) * 1979-11-27 1985-08-30 Landis & Gyr Ag Messwandler zum messen eines insbesondere von einem messstrom erzeugten magnetfeldes.
JPS58218652A (ja) * 1982-06-14 1983-12-19 Nippon Denso Co Ltd 回転検出装置
ATE65967T1 (de) * 1986-10-08 1991-08-15 Alligator Ventilfab Gmbh Vorrichtung und verfahren zum ueberwachen des luftdruckes eines fahrzeugreifens.
EP0316493B1 (fr) * 1987-11-18 1990-06-20 Equipement Industriel Normand France Dispositif de contrôle du bon fonctionnement électrique et/ou mécanique d'éléments indicateurs de type électromagnétique
DE3739111A1 (de) * 1987-11-19 1989-06-01 Standard Elektrik Lorenz Ag Magnetfelddetektor, verfahren und schaltungsanordnung zur erzeugung eines elektrischen signals mit dem magnetfelddetektor
EP0406024B1 (fr) * 1989-06-30 1994-09-14 SHARP Corporation Procédé et dispositif pour détecter un champ magnétique au moyen d'une propriété magnétorésistive d'un matériau supraconducteur

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9307505A1 *

Also Published As

Publication number Publication date
DE4200156A1 (de) 1993-04-08
WO1993007505A1 (fr) 1993-04-15

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