JPH0552962A - Magnetic body detection device - Google Patents

Abstract

PURPOSE:To enable a small amount of a magnetic body to be detected by providing a pair of magnetic field forming coils which are separated by a constant distance and placed in parallel so that a uniform magnetic field is formed around a sensor of a Helmholtz coil which detects a change in the amount of flux and a device which measured the electromotive force which is induced due to change in the amount of flux. CONSTITUTION:Magnetic field forming coils 5 and 6 are wound between side plates 2a and 2b and 4a and 5b, respectively. Sub magnetic field coils 11 and 12 are placed on inner surfaces of frames 2, 3, and 4. The sub magnetic field coils 11 and 12 are placed so that they cross the magnetic field coils 5 and 6. The coils 5 and 6 which form a magnetic field and coils 11 and 12 are operated, thus enabling a combined magnetic field with a uniform strength to be formed within a space 10. Sensor coils 20a, 21a, and 22a and 20b, 21b, and 22b are placed on inner surfaces 7 and 8, respectively. When a magnetic body passes through the space 10, the flux is disturbed, the amount of flux is changed, and an electromotive force is generated at both edges of the coil. A sensor distinguishes the change of the magnetic field from an influence of an external magnetic field clearly even if the magnetic body is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an invention for detecting a magnetic substance, for example, monitoring the entrance and exit of a magnetic medium such as a magnetic tape from a building or a computer room, and finding a foreign substance of the magnetic substance mixed in a product, Alternatively, the present invention relates to an invention for detecting a magnetic substance in order to distinguish and separate a magnetic substance and a non-magnetic substance.

[0002]

2. Description of the Related Art A magnetic sensor is known as a magnetic substance detecting device. This magnetic sensor consists of a search coil for utilizing the electromagnetic induction effect. As a result, when the magnetic body moves near the probe coil, the amount of magnetic flux that crosses the probe coil changes, and a current flows through the coil. As a result, electromotive force is generated at both ends of the coil. Can be detected.

However, the amount of magnetic flux decreases sharply as the distance increases, and since the magnetic sensor is easily affected by the external magnetic field, when a magnetic substance passes away from the magnetic sensor, for example, a person passes through. It was difficult to detect a small amount of magnetic material somewhere in the space where it was possible.

On the other hand, there is an application of a metal detector as a device capable of detecting a magnetic substance in a wide space to some extent. This device is provided with a detection coil, and utilizes the phenomenon that when the non-magnetic material passes near the detection coil, the inductance in the coil decreases and when the magnetic material passes, the inductance increases.

However, according to this device, the magnetic substance and the non-magnetic substance appear as opposite phenomena in which the inductance of the coil increases or decreases, so that the magnetic substance and the non-magnetic substance are simultaneously close to the detection coil. If the non-magnetic material is larger than the non-magnetic material, the phenomenon of only the non-magnetic material changing appears, and the magnetic material cannot be detected.

[0006]

SUMMARY OF THE INVENTION The present invention has a problem that a magnetic sensor cannot detect a small amount of a magnetic substance in a space that a human can pass through, and a metal detector uses only the magnetic substance. It solves the problem that it cannot be detected.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a sensor coil for detecting a change in the amount of magnetic flux, and a pair of magnetic field forming coils arranged in parallel with each other so as to form a uniform magnetic field around the sensor coil. And a measuring device for measuring an electromotive force induced by a change in the amount of magnetic flux that crosses the sensor coil.

[0008]

1 to 5 show a magnetic body detection device 1 according to an embodiment of the present invention. The magnetic substance detection device 1 is provided with square frames 2, 3, and 4 made of aluminum, which are connected to each other.
It stands upright and is fixed. With these frames, the size that humans can pass, for example, the height is 2000
A space 10 having a width of 800 mm and a width of 800 mm is formed. Each frame 2, 3 or 4 is a side plate 2a, 2b, 3a, 3 protruding outward.
It has b, 4a, 4b, which aims to reduce the weight of the device and strengthen the frame itself. Between the side plates 2a and 2b and between the side plates 4a and 4b
Magnetic field forming coils 5 and 6 are respectively wound between and. As the pair of magnetic field forming coils 5 and 6, coils each having the same number of turns, for example, 300 turns are used. However, it is more preferable that the pair of magnetic field forming coils 5 and 6 be configured as Helmholtz coils. These magnetic field forming coils 5 and 6
Is connected to a 100V power supply (not shown), 0.2 to 2
When the current A is applied, a magnetic field of uniform strength is formed in the space 10 as shown in FIG.

Sub-field coils 11 and 12 are arranged on the inner surfaces 7 and 8 of the frames 2, 3 and 4, respectively. As the pair of sub-magnetic field coils 11 and 12, coils each having the same number of turns, for example, 300 turns are used. This coil is also preferably configured as a Helmholtz coil like the magnetic field forming coils 5 and 6. As shown schematically in FIG.
The pair of auxiliary magnetic field coils 11 and 12 are arranged so as to be orthogonal to the pair of magnetic field forming coils 5 and 6, respectively. Further, the auxiliary magnetic field coils 11 and 12 are connected to a 100V power source (not shown), and when a current of 0.2 to 2 A is applied to the magnetic field forming coils 5 and 6 in the space 10 as shown in FIG. A magnetic field of uniform strength in a direction orthogonal to each other. By operating the magnetic field forming coils 5 and 6 and the sub magnetic field coils 11 and 12, it is possible to form a composite magnetic field having a uniform strength in the space 10. In this case, the direction of the synthetic magnetic field can be freely changed by changing the magnitude of the current flowing through each coil pair. As a result, when a strong magnetic field is present outside, the direction of the composite magnetic field is adjusted so as not to be affected by the magnetic field, and the fluctuation of the magnetic field is effectively captured according to the direction in which the magnetic substance to be detected passes. The orientation of the composite magnetic field can be selected so that

Sensor coils 20a, 21a, 22a are further arranged vertically on the inner surfaces 7 of the frames 2, 3 and 4, and sensor coils 20b, 21b, 22b are arranged on the other inner surface 8 respectively. , 21a, 22a are arranged so as to face each other. All of these sensor coils have the same number of turns and the same shape. In this embodiment, a rectangular coil having a number of turns of 300, a height of 600 mm and a width of 450 mm is used as each sensor coil. Further, these coils are connected to a measuring device (not shown), and the electromotive force is measured for each of them. Mainly, the upper sensor coil 20a,
20b is used to detect the presence of magnetic material above space 10 and intermediate sensor coils 21a, 21b are used to detect the presence of magnetic material in the middle of space 10 and below. The sensor coils 22a, 22b are used to detect the presence of magnetic material below the space 10. An inner shield 13 is provided between the sensor coil and the sub magnetic field coils 11 and 12 and the inner surface 7 of the frames 2, 3 and 4 so that the sensor coil is not easily affected by an external magnetic field. ..

When the sensor coil detects a magnetic substance, a large potential difference is generated at the end of the sensor coil. For example, the voltage of the upper sensor coil 20a is detected as a waveform as shown by signal 1 in FIG. 10, and the voltage of the lower sensor coil 22a is detected as a waveform as shown by signal 2 in FIG. To be done. The voltages of the other sensor coils are similarly detected. The waveforms shown by the signals 1 and 2 in FIG. 10 are voltage waveforms when the magnetic substance to be detected does not exist. In the signals 1 and 2, the waveforms that greatly drop at the positions indicated by D appear. This is because the sensor coil detected a large disturbance of the external magnetic field. Other slight waveform disturbances are also due to the influence of the external magnetic field.

As described above, normally, the influence of the external magnetic field on the sensor coil cannot be completely eliminated. Therefore, when a threshold value is set and a potential difference, that is, a voltage exceeding the threshold value is generated, the magnetic substance exists. Treat it as The threshold value is set in consideration of the influence of the external magnetic field. If there is almost no effect of the external magnetic field, the threshold value can be made small, which makes it possible to detect a small magnetic substance.

However, as indicated by D for signals 1 and 2,
When the influence of the external magnetic field appears significantly, the voltage generated in the sensor coil due to the influence of the external magnetic field exceeds the threshold value. Will be detected.
Therefore, the measuring device is provided with a signal processing circuit to remove the influence of the external magnetic field. The signal processing circuit is connected to the sensor coil so as to take a differential of electromotive force induced between any pair of sensor coils, for example, between the upper sensor coil 20a and the lower sensor coil 22a. Signal processing. The differential signal shown in FIG. 10 is obtained by taking a differential between the signals 1 and 2, and is specifically obtained by inverting the waveform of the signal 2 and superimposing it on the waveform of the signal 1. Is. As can be seen from the waveforms of the differential signals, the waveforms at the positions indicated by D of the signals 1 and 2 are canceled and disappear. This makes it possible to cancel the electromotive force generated by the disturbance of the external magnetic field and prevent the generation of an erroneous signal. The effect of the external magnetic field can be removed by taking the differential because the external magnetic field affects the entire space 10, and therefore, as shown by D of signals 1 and 2, not only one sensor coil but also another sensor This is because the influence of the external magnetic field appears in the coil as well. The way of taking the differential can be changed according to the appearance of the influence of the external magnetic field, and when the influence of the external magnetic field is large in the upper sensor coils 20a, 20b and the intermediate sensor coils 21a, 21b, they can be changed. Between any of the coils between them, and when the influence of the external magnetic field is large in the middle sensor coils 21a, 21b and the lower sensor coils 22a, 22b, any coil between them. Try to take a differential between.

When detecting a magnetic substance, the magnetic field forming coils 5 and 6 and the sub magnetic field coils 11 and 12 are operated to form a synthetic magnetic field. In this case, the value of the current flowing through each coil is adjusted in consideration of the characteristics of the magnetic substance to be detected, and the direction of the composite magnetic field is determined in an appropriate direction. For example, although a 1/2 inch cartridge tape is used as the magnetic substance to be detected, it is desirable to determine the direction of the synthetic magnetic field in consideration of the orientation of the tape when passing through the space 10. In addition, the signal processing circuit of the measuring device is connected so as to take a signal differential between any of the coil pairs according to the influence of the external magnetic field on the sensor coil, and the magnitude of the magnetism of the magnetic substance to be detected and Depending on the magnitude of the influence of the external magnetic field, threshold values are set as shown by lines above and below the differential signal in FIG.

When the magnetic material passes through the space 10 formed by the aluminum frames 2, 3 and 4, the magnetism of the magnetic material affects the uniform magnetic field formed in the space 10 and disturbs the magnetic flux.
The turbulence of the magnetic flux changes the amount of magnetic flux that traverses the sensor coil, and as a result, a current flows through each sensor coil and an electromotive force is generated at both ends of each coil. The electromotive force of each coil appears as a waveform as shown by signals 1 and 2 in FIG. For example, the waveform of signal 1 in FIG. 11 shows the output waveform of the upper sensor coil 20a, and the signal 2 of FIG. 11 shows the output waveform of the lower sensor coil 22a. E of each signal waveform
The voltage generated by the magnetic material is shown as the valley of the waveform at the point, and the voltage generated by the influence of the external magnetic field is shown as the valley at the point of D. Since the valley of the signal 1 is deeper than the valley of the signal 2 at the position of E, it can be seen that the magnetic substance has passed near the upper sensor coil 20a, that is, above the space 10. As shown in D of signals 1 and 2 in FIG. 11, when the external magnetic field has a large influence, the signal processing circuit inverts one waveform and superimposes it on the other waveform, Take the differential between the coils. In the differential signal waveform, the waveform of the valley at the point D is canceled out, like the waveform shown as the differential signal in FIG. A waveform remains due to the small influence of the external magnetic field on the differential signal, but this waveform does not exceed the threshold values set above and below the differential signal, and is not erroneously detected as a magnetic signal. .. As a result, when a valley waveform at the portion E shown in the differential signal of FIG. 11 that exceeds the threshold value is generated, it can be determined that the magnetic substance has passed through the space 10. Since a uniform composite magnetic field is formed by the magnetic field forming coils 5 and 6 and the sub magnetic field coils 11 and 12 as described above, even if the magnetic body is a small magnetic body or the magnetic body passes away from the sensor coil, The disturbance of the magnetic field can be clearly detected by the sensor coil from the influence of the external magnetic field, and the existence of such a magnetic substance can be confirmed.

FIG. 8 shows a magnetic substance detecting device 30 according to another embodiment of the present invention. This device 30 is the same as the above-described magnetic substance detection device 1 except for the pair of auxiliary magnetic field coils. As shown in FIG. 6, the sensor coils 20a, 20 are formed by a pair of magnetic field forming coils 5, 6.
A uniform magnetic field can be formed around b, 21a, 21b, 22a 22b.

FIG. 9 shows a magnetic substance detecting device 40 according to a third embodiment of the present invention. This device 40 is the same device except for the pair of magnetic field forming coils from the magnetic substance detection device 1. A pair of auxiliary magnetic field coils 11 and 12
As shown in FIG. 7, the sensor coils 20a, 20b, 21a, 21
A uniform magnetic field can be formed around b, 22a and 22b.

In each of the above-mentioned embodiments, the magnetic field forming coils 5 and 6 and the sub magnetic field coils 11 and 12 are arranged along the vertical plane, but these coils should be arranged along the horizontal plane. However, the present invention is not limited to these, and can be arranged in any direction. The position and the number of the sensor coils are not limited to those in the above embodiment, and for example, only one sensor coil can be used, or the sensor coils can be attached to the upper surfaces or floors of the frames 2, 3, and 4. ..

[0019]

As described above, according to the present invention, since the pair of magnetic field forming coils are arranged in parallel with each other so as to form a uniform magnetic field around the sensor coil, the magnetic field forming coils are spaced apart in parallel.
It becomes possible to detect even a small amount of magnetic material in a space that humans pass through. Further, since the measuring device is provided with a signal processing circuit and the signal processing circuit is connected to the sensor coil to take the differential of the electromotive force induced in any of the coil pairs, the electromotive force generated by the disturbance of the external magnetic field is generated. The erroneous signal can be removed by canceling the electric power, and thus the magnetic substance can be detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a bird's-eye view showing a simplified configuration of a magnetic body detection device according to a first embodiment of the invention.

FIG. 2 is a schematic bird's-eye view showing a partial cross section of the magnetic body detection device.

FIG. 3 is a front sectional view of a magnetic body detection device.

FIG. 4 is a left side sectional view of the magnetic body detection device.

FIG. 5 is a plan sectional view of a magnetic substance detection device.

FIG. 6 is a conceptual diagram viewed from above to show magnetic field formation by a pair of magnetic field forming coils of the magnetic body detection device.

FIG. 7 is a conceptual diagram viewed from above to show magnetic field formation by a pair of auxiliary magnetic field forming coils of the magnetic body detection device.

FIG. 8 is a front sectional view of a magnetic body detection device according to a second embodiment of the invention.

FIG. 9 is a front sectional view of a magnetic body detection device according to a third embodiment of the invention.

FIG. 10 is a waveform diagram of a signal of a sensor coil.

FIG. 11 is a signal waveform diagram of the sensor coil when a magnetic substance is detected.

Claims (12)

[Claims] 1. A sensor coil for detecting a change in the amount of magnetic flux, a pair of magnetic field forming coils spaced apart in parallel by a certain distance so as to form a uniform magnetic field around the sensor coil, and the sensor coil traversing the sensor coil. A magnetic body detection device comprising: a measuring device that measures an electromotive force induced by a change in the amount of magnetic flux. 2. The device of claim 1, wherein the pair of magnetic field forming coils are Helmholtz coils. 3. The device according to claim 1, wherein the sensor coil comprises a pair of sensor coils, the pair of sensor coils are opposed to each other and are spaced apart from each other, and are arranged in a direction orthogonal to the pair of magnetic field forming coils. .. 4. The apparatus according to claim 1, wherein the sensor coil is composed of two or more sensor coil pairs, and the positions of the two or more sensor coil pairs are shifted so that the sensor coils are arranged in a direction orthogonal to the pair of magnetic field forming coils. A device placed facing each other. 5. The apparatus according to claim 1, wherein the measuring apparatus includes a signal processing circuit, the signal processing circuit is connected to the sensor coil, and the electromotive force difference induced in any of the coil pairs is increased. A device that cancels the erroneous signal by canceling the electromotive force generated by the disturbance of the external magnetic field due to the movement. 6. A pair of magnetic field forming coils which are arranged parallel to each other at a fixed distance to form a uniform magnetic field, and a pair of magnetic field forming coils which are arranged orthogonally to the pair of magnetic field forming coils to form a uniform magnetic field. A pair of sub magnetic field forming coils that form a uniform combined magnetic field with the uniform magnetic field generated by the magnetic field forming coil, a sensor coil disposed in the combined magnetic field, and a change in the amount of magnetic flux that crosses the sensor coil. And a measuring device for measuring electromotive force. 7. The apparatus according to claim 6, wherein the pair of magnetic field forming coils are Helmholtz coils. 8. The device according to claim 6, wherein the pair of auxiliary magnetic field forming coils are Helmholtz coils. 9. The apparatus according to claim 6, wherein the directions of the uniform synthetic magnetic field can be changed by adjusting the strengths of the magnetic fields formed by the pair of magnetic field forming coils and the pair of sub magnetic field forming coils, respectively. apparatus. 10. The apparatus according to claim 6, wherein the sensor coil comprises a pair of sensor coils, and the pair of sensor coils are arranged in the same row as the pair of auxiliary magnetic field forming coils. 11. The device according to claim 6, wherein the sensor coil is composed of two or more sensor coil pairs, and the two or more sensor coil pairs are arranged so as to be displaced from each other. 12. The apparatus according to claim 6, wherein the measuring device includes a signal processing circuit, the signal processing circuit being connected to the sensor coil, and a difference in electromotive force induced in any of the coil pairs. A device that cancels the erroneous signal by canceling the electromotive force generated by the disturbance of the external magnetic field due to the movement.