JPS585683A - magnetic detection element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic sensing element, particularly a fluxgate type magnetic sensing element.

Up to now, fluxgate-type magnetic detectors have often been used to detect minute magnetism in the earth's magnetism. Figure 1 shows the basic circuit of the open core type flux gate.

Looking at Figure 1, ca and cb are the core, 1 is the excitation chamber-source,
Wl a and -Wl b are excitation coils that receive an excitation signal from the excitation power source 1 and excite the cores ca and cb.

W2 a - W2 b are signal detection coils, 2 is an amplifier circuit that amplifies the signal detected by the signal detection coil/l/W2 a - W 2b, and 5 is a canceler that generates a signal to cancel the base component of the earth's magnetic field. Power supplies, w3a-w3b are cancellation coils.

Earth's magnetism generally has a base component H and a minute magnetism ΔH as shown in FIG. 2, so by the circuit shown in FIG.
-W5 b cancels out the micromagnetic signal detection coil/
Detection is performed using L/W 2 a - W 2 b.

By the way, the conventional core and coil components used in the basic circuit shown in FIG. 1 are as shown in FIG. As shown in FIG. 3(b), the magnetic field becomes smaller at the ends, and a uniform magnetic field cannot be obtained, making it impossible to uniformly magnetize the core 4. Also, synthetic resin such as plastic is used as the material for the bobbin, but since plastic has a large thermal i coefficient, the size of the bobbin changes depending on the temperature. Generally, the strength H of the magnetic field generated in a coil when a current is passed through the coil is determined by the number of turns of the coil being N and the current being 1. If the coil length is L, then H■
It is expressed as NI/L and is inversely proportional to the coil length. Therefore, when the length of the grain pin changes due to thermal expansion, L also changes, so 1
On the contrary, the generated magnetic field H changes to become smaller. Therefore, cancellation of the pace magnetic field H becomes unstable when ΔH is small compared to H, and it is difficult to detect a very small ΔH.

An object of the present invention is to eliminate the drawbacks of the conventional magnetic detection elements described above and to provide a magnetic detection element capable of stably detecting even minute magnetism.

In order to achieve the above object, the magnetic sensing element of the present invention has the winding width of the coil longer than the length of the open core, and the bobbin is made of a material with a small coefficient of thermal expansion. ing.

The present invention will be further explained in detail below with reference to embodiments shown in the drawings.

FIG. 4 shows a coil device according to an embodiment of the present invention (
-) is a sectional view of the coil device, and (b) is a characteristic diagram showing the distribution of the magnetic field.

In FIG. 4(a), there is no difference from that in FIG. 3(a) in that a carp/1/9 is wound around an open core 7 via a bobbin 8. However, by adjusting the winding width of the coil 9, the distribution of the magnetic field strength H on the central axis of the coil becomes as shown in FIG. 4(b).

A uniform magnetic field strength can be obtained at least within the length range of the open core 7. Therefore, since the core can be magnetized uniformly, noise caused by not being able to magnetize uniformly can be significantly reduced. Also, even if the positions of coil lv9 and core 7 are slightly shifted, the strength of the magnetic field applied to core 7 will hardly change.
There is no need to strictly fix the positional relationship of l/9.

Furthermore, the bobbin 8 is made of a material with a small coefficient of thermal expansion, such as ceramic or quartz. As a result, changes in the generated magnetic field due to temperature changes are improved by more than two orders of magnitude compared to the conventional system, and even extremely small ΔH can be detected.

In the above embodiment, the coil is formed by winding a conductive wire on a bobbin, but the conductor 11 may be spirally deposited directly on the bobbin 10 as shown in FIG. Stability is further enhanced because there is less mechanical movement of the coil windings.

Further, other conductive wires may be wound over the coil formed by depositing the conductor 11 on the bobbin 10 shown in FIG. 5, or bobbins of various diameters may be combined.

The magnetic detection element may be constructed by stacking a required number of bobbins.

As described above, according to the magnetic detection element of the present invention.

The winding width of the coil that makes up the magnetic sensing element is longer than the length of the open core, and the bobbin is made of a material with a small coefficient of thermal expansion.

When detecting variations in geomagnetism, the base component of geomagnetism can be canceled out with high stability, and the core can be magnetized uniformly, so core noise can also be reduced.

Furthermore, there is an effect that instability caused by mechanical positional deviation between the core and the coil can be reduced and eliminated.

[Brief explanation of the drawing]

Figure 1 is a circuit connection diagram showing the basic circuit of an open-core fluxgate, Figure 2 is a characteristic diagram showing the base component H and minute change ΔH'' of the earth's magnetic field, and Figure 3 is a coil of a conventional magnetic detection element. A cross-sectional view of the device (a) U-coy/l/device;
(b) is a diagram showing the distribution of magnetic field strength. FIG. 4 shows a coil lv'lj device for a magnetic detection element showing one embodiment of the present invention, and (a) is a cross-sectional view of the coil device. (b) is a diagram showing the distribution of magnetic field strength, and FIG. 5 shows a coil device according to another embodiment of the present invention. 1...Excitation power supply, 2...Amplification circuit. 5...Cancelling power supply, Wla-Wlb... Excitation coil p. W2 a - W2 bH" detection carp /L/. W'5a, w5 b-cancellation coil. 4, 7...core, 5, 8, 10...bobbin. 6, 9, 11... carp μ Patent applicant Shimadzu Corporation Representative Patent attorney Shigeru Nakamura Nobu No. 1 Figure 11 Figure 2

Claims (2)

[Claims] (1) In a magnetic sensing element composed of an element in which a coil is wound around a core via a bobbin, the winding width of the coil is made longer than the length of the core, and the bobbin has a thermal expansion coefficient. A magnetic detection element characterized in that it is made of a material with a small size. (2) The magnetic sensing element according to claim 1, wherein the coil is a conductor deposited directly on the bobbin in a spiral shape.