JP2568302B2 - Metal detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention focuses the magnetic field lines of the primary magnetic field in a required underground space by combining a plurality of coils to increase the detection sensitivity, and at the same time, detects the position of the metal body. The present invention relates to a metal detector with improved measurement accuracy.

[Related Art] Exploration of buried metal bodies (for example, treasures, unexploded ordnance, etc.) underground and under the sea floor, repair work on underground piping and wiring, repair or new construction of roads, new construction of buildings, and even archeology In general surveys, the existence and location of underground buried or buried objects such as underground buried metal bodies, underground pipes, underground wiring, railway structures buried underground, and ancient archeological sites It is important to check. Therefore, various methods using vibration waves, electromagnetic waves, ultrasonic waves, magnetic fields, and the like have been conventionally performed. Among these metal detection methods, the phase difference detection method related to the magnetic field, that is, the difference between the phase of the AC magnetic field given by the primary coil and the phase of the signal given to the secondary coil by the magnetic field induced in the metal body underground by the primary coil. Is widely used because high sensitivity and stable performance can be expected, and a metal detector with a single coil for generating a magnetic field (primary) has been used.

[Problems to be Solved by the Invention] As such a metal detector using a single coil, for example, a metal detector shown in FIG. 6 has conventionally been generally used.

FIGS. 6 (a) and 6 (b) are schematic views of the magnetic field as viewed in plan and vertical sections, respectively, showing the state of the alternating magnetic field at a certain point in time. The magnetic lines of force 10 generated there diverge in four directions as they leave the primary coil 11. For this reason, the magnetic lines of force effective for the exploration are only a small part, and it is difficult to determine the position of a metal body even if it is detected. Further, there is a drawback that if there is another metal body on the surrounding ground, it is susceptible to the influence.

[Means for Solving the Problems] In view of the above problems, the present inventor has conducted various studies. As a result, an electromagnetic induction type metal detector uses one or more primary coils. The present inventors have found that the above-mentioned problem can be solved by doing so, and have reached the present invention.

That is, according to the present invention, in a metal detector of a type in which an induced magnetic field generated by an underground metal body is detected by a secondary coil in response to an AC magnetic field generated from a primary coil, a pair of primary coils is provided with each coil. A metal detector is provided, wherein the direction of the axis is inclined with respect to the ground so that the extension of the axis intersects the ground, and the axis is arranged so as to generate a magnetic field in the opposite direction.

[Function] In the present invention, a pair of primary coils are arranged so that the directions of the respective coil axes are inclined with respect to the ground so that the extensions of the coil axes intersect underground, and generate a magnetic field in the opposite direction. As a result, the magnetic flux density in the middle lower part of each coil is increased, and a relatively strong magnetic field can be applied to a metal body etc. existing in the ground as compared with the case of a single coil, as a result In addition, the detection capability can be improved, and the magnetic field lines of the temporary magnetic field can be focused on the underground space between the two coils, thereby improving the detection capability.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to the illustrated examples, but the present invention is not limited to these illustrated examples.

FIG. 1 is a perspective view for explaining the principle of the metal detector of the present invention.

The primary coil 1a and the primary coil 1b are coils of the same shape, and are arranged on the surface of the earth at an appropriate horizontal interval with the axis being vertical. Here, FIG. 1 shows an example of a series connection, in which a primary coil is connected.
The primary coil 1a and the primary coil 1b are connected with the polarities reversed, and the primary coil 1b is formed to generate an upward magnetic field 4 when the magnetic field 3 of the primary coil 1a is downward. In addition, 5
Is an AC signal source, 6 is a secondary coil for detecting a signal from an underground metal body, and 7 is a secondary signal detection circuit.

Further, the sensitivity of the conventional detector as shown in FIG. 6 is high around the intermediate point between the primary coil 11 and the secondary coil 12, so that under the same excitation conditions, FIG. 1 and FIG. A stronger magnetic field can be expected with the twin coil system shown in FIG. Furthermore, the magnetic flux density in the space between the primary coil 1a and the primary coil 1b is low, and placing the secondary coil 6 there is advantageous in terms of the S / N ratio (direct influence of the primary signal on the secondary signal). I understand that.

FIG. 2 is a schematic view showing an example of a metal detector, wherein FIG. 2 (a) is a plan view and FIG. 2 (b) is a sectional view. In an electromagnetic induction type metal detector, a magnetic field line 8 is focused below the metal detector by using a pair of primary coils of the primary coils 1a and 1b to improve the detection capability of the secondary coil 6. It is.

In this example, a considerable number of lines of magnetic force 8 coming out of the primary coil 1a enter the primary coil 1b while bending under the ground, and the magnetic flux density is low in the central portion between the two coils 1a, 1b, It is convenient for setting up.

FIG. 3 is a schematic diagram showing an example of the metal detector of the present invention, in which both the primary coil 1a and the primary coil 1b are inclined by α ゜ as shown, and their axes intersect underground. It is a schematic diagram of the above, and by changing the angle α between the primary coil 1a and the primary coil 1b and the ground, it is possible to expect more convergence of the lines of magnetic force. The angle α is preferably 5 ° to 10 °.

FIG. 4 is a schematic view showing another example of the metal detector according to the present invention, in which an auxiliary coil 9a and an auxiliary coil 9b are attached to the ends of the primary coil 1a and the primary coil 1b, respectively.
And 9b to achieve the same effect as when the primary coil is tilted.

FIG. 5 is a schematic diagram showing an example of a multiple arrangement method in a metal detector.

In this case, a large number of primary coils 1a, 1b, 1c,... Are arranged linearly so as to generate magnetic fields in opposite directions, and secondary coils 6a, 6b,. By moving the entire coil group formed in this manner in a direction perpendicular to the arrangement line, a wide area can be searched at once. Although three primary coils are arranged in FIG. 5, any number of primary coils can be arranged as needed.

[Effects of the Invention] As described above, according to the metal detector of the present invention,
Since a pair of primary coils are arranged so that the directions of the respective axes are inclined with respect to the ground so that the extension of each coil axis intersects the ground and generate a magnetic field in the opposite direction, the pair of primary coils is The magnetic flux density in the lower middle becomes higher, the magnetic field applied to the metal body becomes relatively stronger than in the case of the conventional single coil, and the detection performance is improved. Also, since the lines of magnetic force dissipated to the surrounding area are reduced, the range in which the reaction of the metal body appears is limited below the detector, so that the accuracy of determining the position of the metal body underground becomes higher, and for the same reason, the metal detector Even if there is another metal body (eg, vehicle) around (side) the area. Furthermore, since the magnetic flux density is low in the space between both coils, the S / N ratio can be increased by placing a secondary coil there. The magnetic field lines can be focused to improve the detection ability. At this time, instead of mechanically inclining the coil axis, an auxiliary coil is inclined and attached to the tip thereof, and the same effect can be obtained by adjusting the current.

The metal detector of the present invention, besides detecting metal objects underground from the ground surface, can also perform metal detection from inside a borehole, and further, for metal detection other than underground such as inside a wall or a container. It is also effective for exploring low electric resistance materials such as groundwater.

[Brief description of the drawings]

FIG. 1 is a perspective view for explaining the principle of the metal detector of the present invention, and FIG. 2 is a schematic view showing an example of the metal detector.
FIG. 2A is a plan view, and FIG. 2B is a sectional view. Third
FIG. 4 to FIG. 4 are schematic diagrams showing an example of the metal detector of the present invention.
FIG. 5 is a schematic diagram showing an example of a multiple arrangement system in a metal detector, and FIG. 6 is a schematic diagram showing an example of a conventional metal detector using a single coil. FIG. 6 (a) is a plan view, FIG. Fig. 6 (b)
Is a sectional view. 1a, 1b, 1c, ... primary coil, 3 ... downward magnetic field, 4 ...
... upward magnetic field, 5 ... AC signal source, 6 ... secondary coil, 7 ... secondary signal detection circuit, 8 ... magnetic field lines, 9a, 9b
…… Auxiliary coil.

Claims (1)

(57) [Claims] In a metal detector of a type in which an induced magnetic field generated by an underground metal body is detected by a secondary coil in response to an alternating magnetic field generated from a primary coil, a pair of primary coils are extended with respective coil axes. A metal detector, wherein the direction of the axis is inclined with respect to the ground so as to intersect underground, and the magnetic detector is arranged to generate a magnetic field in the opposite direction.