JP2803091B2 - Magnetic sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor, and more particularly to a magnetic sensor that measures a weak magnetic field of about several gauss.

[Conventional technology]

Conventionally, measurement of a magnetic field has been performed using a Hall element, a magnetoresistive element,
This was done using coils and the like.

[Problems to be solved by the invention]

However, when measuring a weak magnetic field of about several Gauss,
The Hall element and the magnetoresistive element have drawbacks in that their characteristics vary, and that the measurement is difficult due to the temperature dependence of the characteristics. On the other hand, the coil has high sensitivity, but uses an induced current to perform magnetic measurement,
There is a drawback that it can be used only for an AC magnetic field and cannot measure a DC magnetic field.

[Means for solving the problem]

An object of the present invention is to provide a magnetic sensor that solves the above problem. Therefore, in the present invention, the object is achieved by providing a means for converting a DC weak magnetic field into an AC having a constant frequency, and measuring the AC weakened DC weak magnetic field with a coil.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing one embodiment of the present invention. In FIG. 1, a magnetic sensor according to the present invention includes a nonmagnetic, insulating substrate 9, a coil 4 mounted on the substrate 9 and having a magnetic core 5 at the center, a chopper 10 made of a conductor, and a vibrating chopper 10. A piezoelectric element 2 to be driven, a driving circuit 3 for applying a voltage to the piezoelectric element 2, an amplifier 6 connected to the coil 4, and a synchronous detection circuit 7 connected to the amplifier 6 and the driving circuit 3.
It is composed of The chopper 10 also includes a flat vibration part 11, a shaft 12, and a foot 13, and the vibration part 11
Is fixed to the substrate 9 via the foot 13 so that an extension of the shaft 12 passes vertically above the center of the coil 4.

To measure a DC magnetic field with a coil, the number of magnetic fluxes linked to the coil may be changed with time. Therefore, in the present invention, a method of vibrating the chopper near the coil is used. This method will be described in more detail with reference to FIGS. Since the coil 4 has a magnetic core 5 having a high magnetic permeability at the center thereof, the interval between magnetic fluxes interlinking the coil 4 is not constant, as schematically shown in FIG. That is, the magnetic flux density B on the line A in FIG. 2 has a bias represented by a curve as shown in FIG.

On the other hand, when the conductor moves in a magnetic field where the magnetic flux density is not uniform, an eddy current is generated on the conductor surface, and an induced magnetic field is generated by the eddy current (FIG. 4). Since the strength of the induced magnetic field is proportional to the magnetic field strength in the space where the conductor moves, if the conductor is vibrated at a certain cycle, the magnetic field strength changes at the same cycle.

The magnetic sensor shown in FIG. 1 operates as follows. A voltage of a constant frequency is applied from the drive circuit 3 to the piezoelectric element 2 provided on the shaft 12 of the chopper 10. The piezoelectric element 2 expands and contracts due to this voltage, and the vibrating section 11 vibrates accordingly, thereby converting a DC magnetic field into an alternating current. Due to the alternating magnetic field, an induced voltage is generated in the coil 4, amplified by the amplifier 6, and then input to the synchronous detection circuit 7. The synchronous detection circuit 7 outputs a signal detected by using the output voltage of the drive circuit 3 as a synchronization signal. The strength of the magnetic field can be measured from the output signal of the synchronous detection circuit 7.

FIG. 5 is a side view showing another embodiment of the present invention, in which a chopper 10 is mounted below the substrate 9 and perpendicular to the substrate 9. The method of this embodiment will be described in detail with reference to FIGS. 6 (a) and 6 (b). When the chopper 10 is perpendicular to the substrate 9, the magnetic flux does not interlink with the chopper 10 in FIG. 6B, but in other cases, the magnetic flux interlinks the chopper 10. Since the number changes depending on the deflection angle θ of the chopper 10, an eddy current is also generated in the chopper 10. Therefore, in this embodiment, it is not necessary to provide the coil 4 with a magnetic core. Further, by using the same principle, a configuration as shown in FIG. 7 can be adopted. 5 and 7, the chopper 10 is provided below the substrate 9, but the same effect can be obtained by providing the chopper 10 above the coil 4.

FIG. 8 is a view showing still another embodiment of the present invention, in which the vibrating portion 11 of the chopper 10 is made of a magnetic material and the magnetic core 5 of the coil 4 is omitted in the configuration of FIG. As shown in FIGS. 9 (a) and 9 (b), since magnetic flux is collected on the magnetic material, when the chopper vibrates on the coil 4, an induced voltage is generated in the coil. FIG. 10 shows the relationship between the displacement of the chopper vibrating section 11 from the center axis of the coil, the number of magnetic fluxes linked to the coil, and the induced voltage generated by the coil.

〔The invention's effect〕

As described above, the present invention makes it possible to easily measure a weak DC magnetic field using a coil by vibrating a chopper in a magnetic field to be measured and periodically changing the number of magnetic fluxes linked to the coil. The effect is as follows.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, FIG. 2 is a sectional view for explaining the principle of the present invention, FIG. 3 is a view showing a magnetic flux density on a line A in FIG. Is a diagram for explaining the generation of eddy current,
FIGS. 5 and 7 are side views showing another embodiment of the present invention, FIGS. 6 (a) and (b) are diagrams for explaining the principle of FIGS. 5 and 7, and FIG. 9 (a) and 9 (b) show the principle of FIG. 8, and FIG. 10 shows the displacement of the chopper, the number of magnetic fluxes linked to the coil, and the coil electromotive voltage. FIG. In FIG. 1 to FIG. 10, 2 ... piezoelectric element, 3 ... drive circuit, 4 ... coil, 5 ...
... magnetic core, 6 ... amplifier, 7 ... synchronous detection circuit, 9 ... board, 10 ... chopper, 11 ... vibrating part, 12 ... axis, 13 ...
leg.

Claims (3)

(57) [Claims] A magnetic sensor for measuring the strength of a magnetic field around a coil from the magnitude of an induced voltage generated in the coil.
A magnetic sensor, comprising: a chopper that moves at a constant frequency with respect to a magnetic field around the coil so as to change the number of magnetic fluxes linked to the coil at a constant frequency. 2. The magnetic sensor according to claim 1, wherein said chopper includes a conductor piece. 3. The magnetic sensor according to claim 1, wherein said chopper includes a magnetic material piece.