JPH0155427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a magnetic sensing element, particularly a flux gate type magnetic sensing element.

(b) Conventional technology Until now, flux gate type magnetic detectors have been often used to detect minute magnetism in the earth's magnetism. Figure 1 shows the basic circuit of the open-core flux gate.

In Figure 1, C _a and C _b are cores, 1 is an excitation power source, W1a and W1b are excitation coils that receive excitation signals from excitation power source 1 and excite cores C _a and C _b , and W2
a and W2b are signal detection coils, 2 is an amplifier circuit that amplifies the signals detected by the signal detection coils W2a and W2b, 3 is a cancellation power supply that generates a signal to cancel the base component of the earth's magnetic field, and W3a and W3b are cancellations. It is a coil.

Earth's magnetism generally has a base component H and a minute magnetism ΔH as shown in FIG. 2, so the base component H is canceled by the canceling power supply 3 and canceling coils W3a and W3b using the circuit shown in FIG. At the same time, minute magnetism is detected by signal detection coils W2a and W2b.

(c) Problems to be Solved by the Invention The conventional core and coil components used in the basic circuit shown in FIG. 1 are as shown in FIG. The winding width of the coil and the length of the core 4 were either approximately the same or shorter. Therefore, as shown in FIG. 3b, the strength distribution of the magnetic field on the central axis of the coil becomes smaller at the ends, and a uniform magnetic field cannot be obtained, making it impossible to uniformly magnetize the core 4. Furthermore, synthetic resin such as plastic is used as the material for the bobbin, but since plastic has a large coefficient of thermal expansion, the size of the bobbin changes depending on the temperature. In general, the strength of the magnetic field H generated in a coil when current is passed through it is expressed as H∞NI/L, where N is the number of turns in the coil, I is the current, and L is the length of the coil, and is inversely proportional to the length of the coil. do. Therefore, when the bobbin length changes due to thermal expansion, L also changes, so the generated magnetic field H changes to become smaller. Therefore, the cancellation of the base magnetic field H also becomes unstable when ΔH is small compared to H, making it difficult to detect a very small ΔH.

SUMMARY OF THE INVENTION 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.

(d) Means and Effects for Solving the Problems In the magnetic sensing element of the present invention, the winding width of the coil of the bobbin is at least 1.2 times longer than the length of the core, and the bobbin has a small coefficient of thermal expansion. It is made up of materials.

In this magnetic sensing element, the winding width of the coil is at least 1.2 times longer than the length of the core, so the magnetic field distribution in the axial direction of the coil is uniform. Furthermore, since the bobbin is made of a material with a small coefficient of thermal expansion, the magnetic field distribution is less likely to change depending on temperature.

(E) Examples The present invention will be explained in more detail below with reference to Examples.

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

In Fig. 4a, the bobbin 8 is attached to the open core 7.
Figure 3a shows that the coil 9 is wound through the
It's no different from the one. However, a feature is that the winding width of the coil 9 is made sufficiently longer than the length of the open core 7. It is desirable that the winding width of the coil 9 is at least 1.2 times the length of the core 7 in order to achieve the effect. With this configuration, the distribution of the magnetic field strength H on the central axis of the coil becomes as shown in FIG. 4b, and a uniform magnetic field strength can be obtained at least within the length range of the open core 7. Can be done. 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 9 and core 7 are slightly shifted, core 7
Since the strength of the magnetic field applied to the core 7 and the coil 9 hardly changes, there is no need to strictly fix the positional relationship between the core 7 and the coil 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 conventional systems, 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.

(F) Effects of the Invention According to the magnetic sensing element of the present invention, the winding width of the coil constituting the magnetic sensing element is at least 1.2 times longer than the length of the open core, and the bobbin is also made of a material having a small coefficient of thermal expansion. Since it is made of materials,
When detecting changes in geomagnetism, the base component of geomagnetism can be canceled 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 drawings]

Figure 1 is a circuit connection diagram showing the basic circuit of an open-core flux gate, 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 device of a conventional magnetic detection element. 4 is a cross-sectional view of the coil device, b is a diagram showing the distribution of magnetic field strength, FIG. 4 is a coil device of a magnetic detection element showing an 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 Figure 5 is,
Fig. 7 shows a coil device according to another embodiment of the invention. 1... Excitation power supply, 2... Amplification circuit, 3... Cancellation power supply,
W1a, W1b...excitation coil, W2a, W2b...
Detection coil, W3a, W3b...cancellation coil, 4,
7... Core, 5, 8, 10... Bobbin, 6, 9, 11
…coil.

Claims (1)

[Claims] 1. An excitation coil, a cancellation coil for canceling the earth's magnetic field, and a signal detection coil are wound around the core via a bobbin, and an excitation power source is connected to the excitation coil,
In a flux gate type magnetic detection element in which a canceling power source is connected to a geomagnetism canceling coil and a magnetic detection signal is derived from the signal detecting coil, the winding width of the coil of the bobbin is 1.2 times or more larger than the length of the core. A magnetic sensing element characterized in that the bobbin is made of a material having a small coefficient of thermal expansion. 2. The magnetic sensing element according to claim 1, wherein the coil is a conductor deposited directly on the bobbin in a spiral shape.