Magneto-resistive angle sensing device with a temperature-stable

Details Magneto-resistive angle sensing device with a temperature-stable Magneto-resistive angle sensing device with a temperature-stable

1998-05-14

2000-08-15

Patidar, Jay

Electricity: measuring and testing

Magnetic

Displacement

32420712, 324202, 32420725, G01B 714, G01R 3306, G01D 518

Patent

active

061041874

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to magneto-resistive sensing devices for position measurement and, more particularly, to a contactless magneto-resistive angular position sensing device with a temperature-stable zero point that produces an output signal according to its angular position in an applied magnetic field.
2. Prior Art
It is known to use magneto-resistive sensors for contactless detection of changes in state, for instance for measuring an angular position of a rotatably mounted part. Such magneto-resistive sensors typically include magnet-field-dependent resistors which are connected in a bridge, and through which a control current that is fed to a bridge diagonal flows.
When such a magneto-resistive sensor is influenced by a magnetic field, a voltage is established at the other bridge diagonal, the magnitude of the voltage depending on the magnetic field or on the direction of the magnetic field referred to the sensor. The relationship between the bridge voltage and the magnetic field direction is utilized in a contactless AMR (Anisotropic Magneto Resistance) angle encoder for detecting measurement values. If precise measurement is to be possible at all, a zero point must first be defined, or a calibration of the sensor must be performed.
From Published, Non-Examined German Patent Application DE-OS 43 364 82, a method for calibrating a magneto-resistive sensor is known with which the offset error can be compensated for. To that end, the magneto-resistive sensor, which is constructed as a bridge circuit, is acted upon by a homogeneous magnetic field oriented in a definite way, and a definite control current is applied to the current contacts of the bridge circuit. The voltage that is then established at the other contacts is measured on an ongoing basis. The magneto-resistive sensor is processed with the aid of a laser until such time as the offset voltage when the magnetic field is applied becomes equal to zero.


SUMMARY OF THE INVENTION

Since magneto-resistive sensors typically furnish a temperature dependent output voltage, it is the object of the present invention to provide a magneto-resistive angle sensing device with a temperature-stable zero point, or to subject a conventional magneto-resistive sensing device to a calibration method that assures that a maximum temperature stability at the zero point is attained.
According to the invention the contactless magneto-resistive angle sensing device comprises means for producing a magnetic field; two sensor components arranged in the magnetic field at a predetermined fixed angle relative to each other, wherein each sensor component includes a plurality of magneto-resistive resistors connected in a respective bridge, each bridge includes input terminals for a respective input voltage and output terminals for a respective output signal, the input terminals are arranged diagonally across from each other in each bridge along one bridge diagonal thereof and the output terminals are arranged diagonally across from each other along another bridge diagonal; controllable power supply means for providing the respective input voltages to heat and maintain the sensor components at different temperatures; and evaluation means connected with the sensor components to receive and analyze the output signals from the sensor components in response to the magnetic field and input voltage. The evaluation means analyzes the output signals in a preferably rotating magnetic field as a function of field angle and sensor component temperature to determine a reference angle or angles at which the output signals of the angle sensing device have a minimum temperature dependence and stores the reference angle or angles as a zero point for subsequent angular measurements.
The method according to the invention has the advantage that a conventional magneto-resistive sensor compound can be used and that nevertheless a temperature-stable zero point can be established without having to change the basic construction of the magne

REFERENCES:
patent: 5351003 (1994-09-01), Bauer et al.
Kwiatkowski et al., "The permalloy magnetoresistive sensors-properties and application", The Journal of Physics 19, pp. 502-515, Jul. 1986.
Eijkel et al., "A Thin-film Magnetoresistive Angle Detector", Sensors and Actuators, A21-A23, pp. 795-798, Mar. 1990.

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