JPH0717029Y2 - Magnetic field detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a magnetic field detection circuit for detecting an output voltage corresponding to this magnetic field by using a magnetoresistive element whose resistance changes according to a magnetic field, and particularly to this magnetic field detection. The present invention relates to a magnetic field detection circuit having improved temperature characteristics of the circuit.

With this magnetic field detection circuit, an output voltage corresponding to the position of the magnetic substance can be obtained, and it can be applied, for example, when detecting the position of the valve of the pilot relay used in the electropneumatic positioner.

<Prior Art> A conventional magnetic field detection circuit of this type is shown in FIG. 2 and will be described.

Between the power supply terminal Vcc and the common potential point COM, resistors R ₁ , R ₂ , R ₃ ,
R ₄ is connected in series in sequence. Further, magnetoresistive elements R ₅ and R ₆ are connected in series between the connection point between the resistors R ₁ and R ₂ and the connection point between the resistors R ₃ and R ₄ . This magnetoresistive element
R ₅ and R ₆ are arranged and housed in a single container at a predetermined angle, and when a magnetic field B is applied to the top of the container, the resistance value changes according to the direction of movement of this magnetic field.

The connection point between the magnetoresistive elements R ₅ and R ₆ is the output terminal T ₁ and the resistor R ₂
The connection points between R ₃ and R ₃ are connected to the output terminal T ₂ , respectively.

The output voltage V _o is output between the output terminals T ₁ and T ₂ corresponding to the direction of the magnetic field B. In this case, when the direction of the magnetic field B applied to the magnetoresistive elements R ₅ and R ₆ is reversed, the polarity of the output voltage V _o obtained between the output terminals T ₁ and T ₂ is also reversed accordingly.

<Problems to be solved by the device> However, in the conventional magnetic field detection circuit as described above, since the temperature coefficient of the magnetic detection element used in this magnetic field detection circuit is extremely large, these magnetic field detection elements R ₅ , If there is any difference in the temperature coefficient of R ₆ , there is a problem that the output voltage V _o changes significantly due to temperature changes.

<Means for Solving the Problems> In order to solve the above problems, the present invention provides a pair of first and second magnetoresistive elements whose resistance changes when a magnetic field is applied, and a pair of these magnetoresistive elements. A first variable resistance element having both ends connected between one ends of the first and second magnetoresistive elements;
A first series circuit in which a first resistance, a second variable resistance element, and a second resistance are connected in series between the other ends of the pair of magnetoresistive elements, and a power supply applied to both ends of the series circuit are provided. Then, at the upper limit of the predetermined temperature range, the other end of the first magnetoresistive element and the first
The temperature coefficient of the second series circuit formed by the middle point of the variable resistance element and the temperature coefficient of the third series circuit formed by the other end of the second magnetoresistive element and the middle point of the first variable resistance element are The position of the middle point of the first variable resistor is selected so as to be equal, and the position of the middle point of the second variable resistor is selected so that the offset voltage appearing at each middle point of the first and second variable resistors becomes zero. The output voltage corresponding to the magnetic field is output from each midpoint of the first and second variable resistance elements.

<Operation> The maximum resistance change is exhibited at the upper limit of the predetermined temperature range, and the middle point of the first variable resistance element is selected so that the temperature coefficients of the second series circuit and the third series circuit are equal at this upper limit. Therefore, the change in the output voltage due to the temperature change in the predetermined temperature range can be made small, and the selection causes an offset in the output voltage, which adjusts the position of the middle point of the second variable resistor. It can be removed.

<Example> Next, the Example of this invention is described using drawing.
FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.

The variable resistance element VR ₁ is connected between the magnetoresistive element R ₅ and the magnetoresistive element R _6, and the midpoint thereof is connected to the output terminal T ₁ .

Then, the second series circuit 10 is configured by the combined resistance between the magnetoresistive element R ₅ and the middle point of the variable resistance element VR ₁ , and the second series circuit 10 is formed between the magnetoresistive element R ₆ and the middle point of the variable resistance element VR ₁ . 3rd with synthetic resistance
Each of the series circuits 11 is configured.

The position of the middle point of the variable resistance element VR ₁ is selected so that the temperature coefficients of the second series circuit 10 and the third series circuit 11 are equal to each other, for example, at the upper limit T _c of the operating temperature range.

Further, a variable resistance element VR ₂ is connected between the resistance R ₂ and the resistance R _3, and its midpoint is connected to the output terminal T ₂ .

The resistor R ₂ , the variable resistance element VR ₂ and the resistor R ₃ form a first series circuit 12.

In this case, since the temperature coefficients of the second and third series circuits are matched by the variable resistance element VR ₁ , the bridge balance is lost, and an offset voltage is generated between the output terminals T ₁ and T ₂ . Therefore, the offset voltage is removed by selecting the position of the middle point by the variable resistance element VR ₂ .

Next, the operation of the magnetic field detection circuit shown in FIG. 1 configured as above will be described.

Now, from room temperature to the upper limit _{Tc of the} operating temperature range, for example, 20 ° C
To 80 ° C, the resistance change amount based on the temperature coefficient of the magnetoresistive element R ₅ is ΔR ₅ , the resistance change amount of the magnetoresistive element R ₆ is ΔR ₆ , and the variable resistance element VR ₁ 2 The resistance value of the series circuit 10 side is VRX, and the resistance value of the third series circuit 11 side is VR
If (1-X), the temperature coefficient of the second series circuit 10 and the third
When the temperature coefficient of the series circuit 11 matches, the position X of the middle point of the variable resistance element is [(R ₅ + ΔR ₅ ) + VR · x] / [R ₅ + VR · x] = [(R ₆ + ΔR ₆ ). + VR (1-x)] / [R 6 + VR (1-x)] is given by ... (1). Solving this, x becomes x = [ΔR ₅ · R ₆ −R ₅ · ΔR ₆ + ΔR ₅ · VR] / [(ΔR ₆ + ΔR ₅ ) VR] …… (2).

Here, for example, R ₅ = R ₆ = 3KΩ, ΔR ₅ = 610Ω, ΔR ₆ = 6
If 00Ω and VR = 100Ω, this is substituted into the equation (2) and X = 0.752 is obtained. Therefore, the position of the midpoint of the variable resistance element VR ₁ may be selected in this way.

<Advantages of the Invention> As described above in detail with the embodiments, according to the present invention, the first variable so that the temperature coefficients of the second series circuit and the third series circuit become equal at the upper limit of the predetermined temperature range. Since the position of the middle point of the resistance element is selected, the temperature change in this temperature range can be reduced to a practically sufficient level with an inexpensive configuration, and the offset voltage generated due to this can be removed by the second variable resistance element. You can do it.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the configuration of one embodiment of the present invention, and FIG. 2 is a circuit diagram showing the configuration of a conventional magnetic field detection circuit. 10 …… Second series circuit, 11 …… Third series circuit, 12 …… First
Series circuit, R _{1 to} R ₄ ...... Resistance, R ₅ , R ₆ ...... Magnetic resistance element,
B ... magnetic field.

Claims (1)

[Scope of utility model registration request] 1. A pair of first and second magnetoresistive elements whose resistance changes when a magnetic field is applied, and one end of each of the pair of first and second magnetoresistive elements. A first variable resistance element, a first series circuit in which a first resistance, a second variable resistance element, and a second resistance are connected in series between the other ends of the pair of magnetoresistive elements, and the series circuit. And a power source applied to both ends of the second series circuit, the temperature coefficient of the second series circuit formed by the other end of the first magnetoresistive element and the midpoint of the first variable resistance element at the upper limit of a predetermined temperature range. And the position of the middle point of the first variable resistance is selected so that the temperature coefficient of the third series circuit formed by the other end of the second magnetoresistive element and the middle point of the first variable resistance element becomes equal. And so that the offset voltage appearing at each midpoint of the first and second variable resistors becomes zero. Said second selected position of the middle point of the variable resistor, wherein the output voltage corresponding to the magnetic field first, the magnetic field detection circuit, characterized in that so as to output from the midpoint of the second variable resistive element.