JPH0933257A - Magnetic direction sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic direction sensor, which indicates the stabilized characteristics without the effect of the change in surrounding environmental conditions. SOLUTION: A bias coil for applying a bias magnetic field on the magnetoresistance element constituting a magnetic sensor, which constitutes the magnetism detecting directions in the reverse directions and comprises the magnetoresistance element as one unitary body, is constituted. Two AC rectangular-wave voltages in opposite phases to each other at the same level are applied. The output voltage of the magnetic sensor 2 at this time is amplified by an amplifier circuit 5 including a bypass filter. The amplified signal is detected by two synchronous detector circuits. The output of the magnetic sensor 2 is obtained through an operator 3 for the difference in the synchronous detected outputs, which operates the two detected synchronous signals. The magnetic sensors 2 are arranged at angle of 90 degrees to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic azimuth sensor using a magnetoresistive element, and more particularly to a magnetic azimuth sensor capable of obtaining a stable output against changes in ambient temperature and changes with time.

[0002]

2. Description of the Related Art In a magnetic sensor using a conventional magnetoresistive element, a predetermined DC bias magnetic field is applied to the magnetoresistive element pattern of the magnetoresistive element from a direction of 45 degrees. With the output of the magnetoresistive element as a reference, the magnetic amount and magnetic polarity are detected by the magnitude and polarity of the output.

FIG. 6 is a principle diagram showing the magnetic detection operation of a conventional magnetic sensor using a magnetoresistive element. The predetermined DC bias magnetic field is + H1, and the output of the magnetoresistive element at that time is V1. Under this condition, the external magnetic field H2sinωt
Is applied, the magnetic field applied to the magnetoresistive element is
(H1 + H2sinωt), and the magnetic field (H1 + H2)
When the output of the magnetoresistive element is V2, the output of the magnetoresistive element Vout is expressed by the equation (1).

Vout = V1 + (V2-V1) sinωt (1)

Therefore, the initial state (external magnetic field 0 DC magnetic field H
(1 only), the magnetic quantity and magnetic polarity of the external magnetic field can be known from the second term (V2-V1) sinωt of the equation (1).

FIG. 7 is a diagram showing an example of an amplifier circuit for amplifying the output of the magnetoresistive element of the conventional magnetic direction sensor.

Normally, two magnetic fields applied from the outside are an AC magnetic field and a DC magnetic field (geomagnetism belongs to the DC magnetic field). Therefore, it is necessary for the magnetic detection device to have a DC response, and Vout represented by the equation (1) must be DC-amplified.

Since the magnetoresistive element output is usually a very small value, it is usually amplified by a differential amplifier circuit as shown in FIG. Amplification is performed by the dynamic amplifier, the offset voltage (output when the external magnetic field is 0) of the amplifier circuit is set by the variable resistors VR4 and VR5, and the amplification degree is set by the variable resistor VR6.

[0009]

The magnetoresistive elements each have a resistance temperature characteristic, and as a result, the offset output voltage of the magnetoresistive element (the output voltage of the magnetoresistive element when the bias magnetic field is 0) varies depending on the temperature. Change. In addition, the offset output voltage of the magnetoresistive element also changes with time. This change contributes to both the magnetoresistive element outputs V1 and V2 in the equation (1), and if the change amount of the offset output voltage of the magnetoresistive element is ΔV, the magnetoresistive element output Vout is the equation (2). It is represented by.

Vout = (V1 + ΔV) + [(V2 + ΔV) − (V1 + ΔV)] sinωt = (V1 + ΔV) + (V2-V1) sinωt (2) )

As is clear from the equation (2), when the reference voltage in the external magnetic field 0 of the magnetoresistive element has an error, the output Vout of the magnetoresistive element is directly amplified by the amplifier circuit. However, there is a drawback that this appears as an offset output voltage error of the magnetoresistive element. Further, it is difficult to correct the temperature change and the time-dependent change of the offset output voltage of the magnetoresistive element because the changing polarity can be both positive and negative. Therefore, it is difficult to obtain an accurate azimuth with a magnetic azimuth sensor using a magnetoresistive element including a large output error of the offset output voltage.

An object of the present invention is to eliminate an error factor due to a temperature change and a time change of a magnetic sensor composed of a magnetoresistive element, and to show an accurate and stable output characteristic with respect to a change of surrounding environmental conditions. A magnetic orientation sensor is provided.

[0013]

According to the present invention, two magnetic resistance elements having matching characteristics are integrally formed so that their magnetic field detection directions are opposite to each other. A magnetic azimuth sensor that operates is obtained.

According to the present invention, the magnetic sensor is
A magnetic azimuth sensor is obtained, which is characterized by being arranged at an angle of 90 degrees with respect to each other in the X direction and the Y direction.

Further, according to the present invention, in the above magnetic sensor, a bias coil is wound around the magnetic sensor in each direction,
A rectangular-wave AC current is applied to the bias coil, a rectangular-wave AC magnetic field is applied, and each maximum value in the positive and negative directions of the rectangular-wave AC magnetic field is applied up to the characteristic point of the maximum inclination of the magnetic characteristics of the magnetoresistive element. A magnetic azimuth sensor characterized by the above is obtained.

Further, according to the present invention, there can be obtained the above magnetic azimuth sensor including an amplifier having two input terminals for amplifying two output signals of the magnetoresistive elements constituting each of the magnetic sensors.

In the present invention, two magnetoresistive elements having matching characteristics are constructed so that their magnetic field detection directions are opposite to each other, and the two magnetic sensors are respectively 90 degrees in the X and Y directions. In the magnetic azimuth sensor arranged at an angle of, a bias coil is wound around the two magnetic sensors, a rectangular-wave alternating current is applied to the bias coils, and a rectangular-wave alternating magnetic field is applied. Each maximum value of the AC magnetic field in the positive and negative directions is applied up to the characteristic point of the maximum inclination of the magnetic characteristics of the sensor, and the output voltage of the two magnetoresistive elements that compose the magnetic sensor has two input terminals each including a high-pass filter. Amplification by the amplifier circuit, the output is detected by the two synchronous detection circuits, the difference between the two detected synchronous signals is obtained, the error of the output of the two magnetic sensors is eliminated, and the correct azimuth is obtained. It is possible to obtain the degree in magnetic direction sensor. With this configuration, it is possible to obtain a magnetic azimuth sensor that exhibits accurate and stable output characteristics, which is not affected by changes in surrounding environmental conditions such as temperature drift and temporal change of the offset output voltage of the magnetoresistive element.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows the magnetic sensor according to the present invention as X.
It is a principle view of the magnetic direction sensor which used two directions, a direction and a Y direction. As shown in FIGS. 2 (a) and 2 (b), the two magnetic sensors a and b detect two magnetic resistance elements 2a and 2b whose characteristics are matched in the X direction and the Y direction by detecting their magnetic fields. The directions [indicated by arrows in FIG. 2B] are arranged so as to be opposite to each other, and are arranged at an angle of 90 degrees in the X direction and the Y direction. When the output of the magnetic sensor a is Va and the output of the magnetic sensor b is Vb, the angle of the magnetic azimuth sensor c with respect to the magnetic direction is expressed by equation (3).

Θ = tan ⁻¹ (Vb / Va) (3)

Therefore, by substituting the outputs of the magnetic sensors a and b into the equation (3), the magnetic orientation becomes clear. θ is an angle with an external magnetic field (for example, a horizontal component of the earth's magnetism).

FIG. 3 is a principle diagram showing the magnetic detection operation when the external magnetic field is zero in the magnetic sensor in the magnetic direction sensor of the present invention. Since the magnetic field detection directions are composed of two magnetoresistive elements that are opposite to each other, the characteristic curves are left and right with respect to the Vout axis. A bias coil is wound around the magnetic sensors a and b in each direction, a rectangular alternating current is passed through the bias coil, and a rectangular wave alternating magnetic field is applied. For the magnetoresistive element,
An AC rectangular wave bias magnetic field of −H1 is applied from the magnetic field amount H1. Therefore, the maximum value in the positive and negative directions of the rectangular-wave AC magnetic field is set so as to be applied at the characteristic point of the maximum inclination of the magnetic characteristic of the magnetoresistive element (the characteristic point that becomes the output V1). The output voltage characteristic of the magnetoresistive element with respect to the magnetic field is shown in FIG.
It has a symmetrical shape with respect to the t-axis, and the same output voltage of the magnetoresistive element can be obtained when the positive and negative magnetic fields are the same.

Therefore, the AC rectangular wave bias magnetic field is + H1.
The output of the magnetoresistive element is Vout1, and the output of the magnetoresistive element when the AC rectangular wave bias magnetic field is -H1 is Vout2.
When the external magnetic field is 0, the output voltage V1 of the magnetoresistive element corresponding to the bias magnetic field H1 is obtained as the output voltage V1 of the magnetoresistive element in the case of FIG. It is expressed by equation (5).

Vout1 (AC rectangular wave bias magnetic field + H1) = V1 (4)

Vout2 (AC rectangular wave bias magnetic field −H1) = V1 (5)

Since the magnetic field detection directions of the two magnetoresistive elements are opposite to each other, the output Vout3 is represented by the equation (6).

Vout3 = Vout1-Vout2 (6)

Therefore, in the case of FIG. 3 (state of 0 external magnetic field)
Vout3 of

Vout3 = 0 (7)

Further, when the output of the magnetoresistive element changes from V1 to V1 + ΔV due to changes in the external environment, V
out3 is

Vout3 = (V1 + ΔV) − (V1 + ΔV) = 0 (8)

As is apparent from the equations (7) and (8), Vout3 in the state where the external magnetic field is 0 is an output irrelevant to changes in the external environment.

FIG. 4 is a principle diagram showing a magnetic detection operation when an external magnetic field H2 is applied to the magnetic sensor of the magnetic azimuth sensor of the present invention. The external magnetic field H2 applied to the state of FIG. 3 changes the amount of magnetic field applied to the magnetoresistive element, and the magnetic field applied to the magnetoresistive element at the time of AC rectangular wave bias magnetic field + H1 is (H1 + H2) The magnetic field applied to the magnetoresistive element during the bias magnetic field −H1 is (−H1 + H2). If the output voltage of the magnetoresistive element when the magnetic field (H1 + H2) is V2 and the output voltage of the magnetoresistive element when the magnetic field (-H1 + H2) is V3, Vout1
And Vout2 are expressed by equations (9) and (10).

Vout1 = V1 + (V2-V1) (9)

Vout2 = V1 + (V3-V1) (10)

That is, the output of the magnetoresistive element changes with V1 (the output voltage of the magnetoresistive element when the external magnetic field is 0) as the center both in the magnetic field (H1 + H2) and in the magnetic field (-H1 + H2). Will be configured.

By the way, since the magnetic amount and magnetic polarity of the external magnetic field are expressed by the equation (6), Vout in the case of FIG.
3 is

Vout3 = V2-V3 (11)

Furthermore, Vo when V2 changes to V2 + ΔV and V3 changes to V3 + ΔV due to changes in the external environment.
ut3 is

Vout3 = (V2 + ΔV)-(V3 + ΔV) = V2-V3 (12)

As is clear from the equations (11) and (12), Vout3 at the time of the external magnetic field H2 is an output irrelevant to changes in the external environment.

Therefore, the output Vout of the magnetic sensor is always
If 3 is measured, it is possible to perform magnetic detection that does not affect changes in the external environment such as changes in temperature and changes over time.

FIG. 5 is a diagram showing an embodiment of an amplifier circuit for amplifying the output of the magnetoresistive element of the magnetic sensor of the present invention. The output of the magnetoresistive element is made up of a resistor R1, a resistor R2 and an operational amplifier 9. A high-pass filter including a capacitor C1 and a resistor R3, which is first-stage amplified by a direct current amplifier circuit and is connected to the output terminal of the operational amplifier 9, is used for direct current change such as temperature change and temporal change of the offset voltage of the operational amplifier 9 and the offset voltage of the magnetoresistive element. Amplified voltage component is removed, and variable resistors VR3 and R4
Is a two-stage amplifier circuit that amplifies with a common-mode amplifier circuit composed of an operational amplifier 10. If the cutoff frequency of the high-pass filter composed of the capacitor C1 and the resistor R3 is set to be considerably smaller than the frequency of the AC rectangular wave bias magnetic field, the amplifier output becomes a rectangular wave output, and the output of the magnetoresistive element can be amplified. . The variable resistors VR1 and VR2 are adjusting resistors for arbitrarily setting the offset voltage of the circuit, and the variable resistor VR3 is for arbitrarily setting the amplification degree of the output amplifier circuit of the magnetoresistive element. It is a resistance for adjustment.

FIG. 1 is a diagram showing a circuit block of the magnetic sensor of the present invention. Two AC rectangular wave voltage generators (A, B) 1 applied to two bias coils of the magnetic sensor 2.
90 degree phase and 270
A-wave 90-degree phase modulator 3 that outputs a signal at the time of phase and A
There is a wave 270-degree phase modulator 4, and the output of the amplifier circuit 5 for amplifying the output of the magnetic sensor 2 is synchronously detected by the signals from the two modulators. A wave 90-degree phase synchronous detector 6 and A wave The configuration is such that the output of the magnetic sensor is obtained through the synchronous detection output difference calculator 8 that calculates the difference between the output signals of the two synchronous detectors of the 270-degree phase synchronous detector 7.

When the magnetic sensor is used as a magnetic azimuth sensor, the magnetic sensors are arranged at an angle of 90 degrees with each other and the respective magnetic sensor outputs are substituted into the equation (3) to obtain the azimuth angle. Since the error in the magnetic sensor output can be corrected, the accurate azimuth angle can be obtained.

[0046]

As described above, according to the present invention,
A bias coil is wound around the magnetic sensor in each of the X and Y directions, and a rectangular alternating current is passed through the bias coil.
A magnetic azimuth sensor that applies an alternating magnetic field of a rectangular wave, and two magnetic sensors are arranged at an angle of 90 degrees to each other, and a bias coil for applying a bias magnetic field to a magnetoresistive element is connected to each other. Two alternating rectangular wave voltages of the same level are applied in anti-phase, and the maximum value in the positive and negative directions of the alternating magnetic field of the rectangular wave is applied at the characteristic point of the maximum inclination of the magnetic characteristics of the sensor. The output voltage of the resistance element is amplified by an amplifier circuit including a high-pass filter, and the amplified signal is detected by two synchronous detection circuits. Since there is no error in the magnetic sensor output, an accurate azimuth angle can be obtained, and the output characteristics are accurate and stable against changes in ambient environmental conditions such as temperature drift of the offset output voltage of the magnetic sensor and changes over time. It is possible to provide a magnetic azimuth sensor indicating

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit block of a magnetic bearing sensor of the present invention.

FIG. 2 is a principle diagram of a magnetic azimuth sensor using two magnetic sensors according to the present invention, and an explanatory diagram showing a magnetic sensor in which two magnetic resistance elements are configured so that their magnetic field detection directions are opposite to each other. FIG. 2A is a principle diagram of direction measurement. FIG.
FIG. 6B is a diagram showing a magnetic sensor using magnetic resistance elements whose magnetic field detection directions are opposite to each other.

FIG. 3 is a principle diagram showing a magnetic detection operation when the external magnetic field is zero in the magnetic sensor in the magnetic direction sensor of the present invention.

FIG. 4 is a principle diagram showing a magnetic detection operation when an external magnetic field H2 is applied to the magnetic sensor in the magnetic direction sensor of the present invention.

FIG. 5 is a diagram showing an embodiment of an amplifier circuit for amplifying the output of a magnetoresistive element that constitutes the magnetic sensor of the present invention.

FIG. 6 is a principle diagram showing a magnetic detection operation of a magnetic sensor using a conventional magnetoresistive element.

FIG. 7 is a diagram showing an example of an amplifier circuit that amplifies a magnetoresistive element output of a conventional magnetic sensor.

[Explanation of symbols]

1 AC rectangular wave voltage generator (A, B) 2 Magnetic sensor 2a, 2b Magnetoresistive element 3 A wave 90 degree phase modulator 4 A wave 270 degree phase modulator 5 Amplification circuit 6 A wave 90 degree phase synchronous detector 7 A wave 270 degree phase synchronous detector 8 Synchronous detection output difference calculator 9, 10, 11 Operational amplifier a, b Magnetic sensor c Magnetic direction sensor C1 Capacitor R1, R2, R3, R4, R5, R6, R7 Resistance VR1, VR2 , VR3, VR4, VR5, VR6
Variable resistance

Claims (4)

[Claims] 1. A magnetoresistive element having matching characteristics,
A magnetic azimuth sensor comprising a magnetic sensor integrally configured such that magnetic field detection directions thereof are opposite to each other. 2. Two magnetic bearing sensors according to claim 1,
A magnetic azimuth sensor characterized by being arranged at an angle of 90 degrees in the X direction and the Y direction. 3. The magnetic azimuth sensor according to claim 2, wherein a bias coil is wound around the magnetic sensor in each direction, a rectangular wave alternating current is applied to the bias coil, and a rectangular wave alternating magnetic field is applied. A magnetic azimuth sensor characterized in that each maximum value of a square wave alternating magnetic field in the positive and negative directions is applied up to a characteristic point of a maximum inclination of magnetic characteristics of a magnetoresistive element. 4. A magnetic bearing sensor according to claim 2, comprising an amplifier having two input terminals for amplifying two output signals of the magnetoresistive element constituting each magnetic sensor according to claim 2.