JPS58100768A - metal detector - 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 metal detector for detecting metal objects buried underground, for example.

Conventionally, metal detectors that detect metal objects underground have been equipped with an excitation coil that receives a signal from an excitation power source and applies an excitation magnetic field to the metal piece to be detected, and a metal detector that detects metal objects by applying the excitation magnetic field. A receiver that detects a signal magnetic field generated by a magnetic field and converts it into an electric signal is sometimes composed of a coil. When detecting metal objects buried underground using this type of metal detector, it is important to note that some metal objects may be very small in shape, or that the buried point is deep underground. , partly because it is far away from the detection direction.

It is desirable that the metal detector be as sensitive as possible. However, in conventional metal detectors, if the excitation magnetic field is increased in order to improve sensitivity, the excitation magnetic field also affects the receiving coil, so there is a limit to how much sensitivity can be improved.

The object of the present invention is to eliminate the drawbacks of the conventional metal detectors mentioned above, and to provide a metal detector with good sensitivity, that is, good detection performance. The purpose is to provide a metal detector that is more compact than conventional metal detectors with the same sensitivity.

In order to achieve the above object, the metal detector of the present invention is provided with a canceling coil for canceling the influence of the excitation magnetic field on the coil, and the receiving coil is enclosed in the canceling coil. .

The present invention will be described in detail with reference to embodiments shown in the following two drawings.

FIG. 1 is a diagram showing the arrangement of coils of a metal detector showing an embodiment of the present invention, and FIG. 2 is a diagram showing the connections of the metal detector shown in FIG. 1.

As shown in Fig. 1, inside the large-diameter excited carp μm.

A pair of receiving coils/l/2m, 2b are arranged symmetrically with the center Co f of the excitation coil/L/1, and furthermore, this receiving coil lv2m, 2b″f: a pair of canceling coils/
1/3g, 5b are arranged concentrically with receiving coils/I/2a, 2b. The receiving coils /I/2a and 2b are wound around magnetic cores 4a and 4b having high magnetic permeability.

Similarly, a pair of compensation coils/L are included in the excitation coil/v1.
158.5b is also located. Compensation Carp/L15a.

5b passes approximately through the center of the excitation coil 1, and the receiving coil 2a,
It is slidably disposed in a guide hole 6 provided on a line perpendicular to the line connecting 2b.

These coils are connected as shown in FIG.

The excitation coil/l/1 and the canceling coil/l/3a and 3b are connected in series and connected to an oscillator 7 for generating an excitation signal,
The receiving coils/l/2a, 2b and the compensation coils 5a, 5b are connected in series to an amplifier 8.

Now, when current is passed from the second oscillator 7 to the canceling coil tv5a, the excitation coil 1, and the canceling coil 3b, the excitation coil 1 generates an excitation magnetic field H1. If a metal piece 9 to be detected exists in the axial direction of the excitation magnetic field H1, an induced current is generated in the metal piece 9 by the excitation magnetic field H1, and a signal magnetic field H9 weaker than the metal piece 9 is generated. On the other hand, since the current from the oscillator 7 also flows through the canceling coils 3a and 3b, the canceling magnetic fields H3a and H3
However, since the directions of these magnetic fields are configured to be opposite to the excitation magnetic field H1, the excitation magnetic field H1 is canceled by the canceling magnetic fields H3a and Hub. Therefore, the receiver is Koi tv2h, and the receiver 2b detects only the signal magnetic field H9 to generate a detection signal. The receiving coils/I/2a and 2b are differentially connected to an amplifier 8, and the amplifier 8 derives an output of the difference between the detection signal of the receiving coil/1/2a and the detection signal of the receiving coil/1/2b. . Therefore, the metal piece 9 is in its current position in FIG.

If the metal detector moves from the bottom to the top of the drawing for exploration, as the excitation coil 1 approaches the metal piece 9, the detection signal of the receiving coil/1/2m will increase and reach a certain peak value. Decrease after detection. From the time when the center of the excitation coil A/1 passes the metal piece 9, the detection signal of the reception coil I/2b increases, and as the excitation coil 1 moves, it also detects a certain peak value and then decreases. As a result, the amplifier 8 obtains a kind of figure-8 characteristic output, so that the presence of the metal piece 9 can be known. In other words, it can be detected.

In addition, the receiving coil /I/2m, 2b incorporates magnetic cores 4a, 4b with high magnetic permeability in order to increase the detection sensitivity of the signal magnetic field H9, but in this case, if there is no canceling coil) tz3a+3b, the receiving coil 7L /2a and 2b will be exposed to the strong excitation magnetic field H1, and the magnetic core 4a @ 4b provided to improve detection sensitivity will be magnetically saturated and will no longer perform its function. Further, if the same sensitivity is obtained by incorporating the magnetic cores 4a and 4b into the receiving coils 2a and 2b, the receiving coil/v2a.

Since the cross-sectional area of 2b and the number of turns can be reduced, the entire metal detector can be made smaller.

Next, the action of the compensation coils /L15a and '5b will be explained.

In the above embodiment, if the characteristics of the receiving carp/v2a, 2b are ideal and balanced.

When the metal piece 9 is not present or when a metal piece is present, when the center of the excitation coil /l/1 of the metal detector reaches the metal piece 9, the output of the amplifier 8 should be 0. The output of the amplifier 8 may not become 0 due to distortion of the receiving coil/L/2a, 2b, etc., and an error amount may be output. A compensation coil 5a is provided to compensate for this error.

5bf is provided. The compensation coil 5a + 5b is slidable along the guide hole 6, and its position is changed from the center CO of the excitation coil/L/1 to the winding surface C of the excitation coil/I/1.
You can move up to 1. Also, at that time, a compensation magnetic field H5a is generated in the compensation coils 5a and 5b.

As shown in Fig. 6, the magnetic field strength H5 of H5b increases from the center CD of the excitation coil/L/1 toward the winding surface C1 of the excitation coil 1, so the compensation magnetic fields H5a and H5b can be freely selected. , it is possible to perform highly accurate compensation. In addition, instead of making the guide hole 6 slidable, the compensation coils 5a, 5b are provided with a plurality of appropriate holes on the same line as the guide hole 6, and the compensation coils 5a, 5b can be freely inserted into and removed from the holes. The position may also be adjusted.

Further, in the above embodiment, the canceling coils 1L/3a, 3b are connected in series with the excitation coil/1/1, and the compensation coils 1L15a, 5b
shows the case where the receiving coils Az2a and 2b are connected in series, but the invention is not limited to this, and other connection methods may be used as long as the canceling coil cancels the excitation magnetic field and the compensation coil μ compensates for the receiving coil. It may be.

According to the metal detector of the present invention as described above.

A canceling coil is arranged to enclose the receiving coil, and the canceling magnetic field generated by this canceling coil cancels the excitation magnetic field to the receiving coil, so that the receiving coil receives the signal magnetic field from the metal object to be detected. A metal detector with high detection performance can be obtained by detecting only the metal.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the coil arrangement of a metal detector showing an embodiment of the present invention, FIG. 2 is an electrical connection diagram of the metal detector shown in FIG. 1, and FIG. FIG. 2 is a diagram showing the magnetic field distribution of the compensation coil used in the embodiment shown in FIG. 2; 1: Excitation coil, 2a/2b: Receiving coil. 3g-3b: Cancellation coil l 4a-4b: Magnetic core. 5B/5b: Compensation coil, 6: Guide hole. 7: Oscillator, 8: Amplifier, 9: Metal piece. Hl: excitation magnetic field, H2a-H2b: signal magnetic field. H3a-H3b: Cancellation magnetic field, H5a-H5b: Compensation magnetic field, H9: Signal magnetic field 1 H5: Strength of magnetic field, CO: Center of excitation coil. C1: Winding surface of excitation coil μ. Patent applicant Yukie Omori, director of the Technology Research Headquarters, Defense Agency (and one other person) Agent: Shigeru Nakamura, patent attorney Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) An oscillator that generates an excitation signal, an excitation coil that receives the signal from this oscillator and applies an excitation magnetic field to the metal piece to be detected, and a signal magnetic field that is generated from the metal piece by applying the excitation magnetic field. A metal detector comprising a receiving coil that detects and converts into an electric signal, a canceling coil that is arranged to enclose the receiving coil and generates a magnetic field that cancels the influence of the excitation magnetic field on the receiving coil. A metal detector characterized by the following: (2) What is the receiving coil included in the canceling coil μ? The metal detector according to claim 1, wherein the metal detector is wound around a high magnetic permeability magnetic core. (3) What is the receiving coil included in the cancellation coil? Claim 1: A pair of coils that operate differentially, and a compensation coil Vf that compensates for errors caused by coil distortion, noise, etc. is attached to the pair of coils. The metal detector described in paragraph 2 or paragraph 2.