JPH08146064A - Current probe - Google Patents

Abstract

PURPOSE: To easily find a part where current leaks from the inside of an electronic equipment to the surface of a metal enclosure by providing a probe body, a slit, an output terminal, and an insulation member. CONSTITUTION: When a probe body 1 is moved on the surface of an enclosure 100 including an electromagnetic wave occurrence source S inside, an output voltage E increases at the part of a hole Q being present on the surface of the enclosure 100 and reaches 0 at the other parts, thus easily finding a current flow-out port Q. A voltage induced between the slits of the body 1 corresponding to the difference between the magnetic field flowing into the body 1 via the slits 2 from the surface of the enclosure 100 and the magnetic field flowing out of the body 1 via the slits 2. The current flow-out port of the enclosure 100 can be easily found according to the fluctuation of the output voltage. Also, by providing the slits 2 on a bottom plate 11, a measurement error due to the influence of external magnetic field can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current probe,
In particular, the present invention relates to a current probe for detecting a high-frequency current on the surface of a metal housing.

[0002]

2. Description of the Related Art A high-frequency current generated by an electric circuit inside a housing leaks into a metal housing of an electronic device, and this leak current becomes a wave source of electromagnetic waves radiated from the housing. It is desirable to suppress such radiated electromagnetic waves because they cause damage to other devices. Therefore, it is necessary to first identify the outlet of the current to the surface of the housing.

A current density J and a magnetic field H on a metal surface are expressed as follows: H = −n × J (1) Here, J and H are vectors, and n is a unit normal vector directed outward on the metal surface. In addition, x represents an outer product. Generally, the measurement of the current flowing on the metal surface is performed using this equation, and as shown in FIG.
The magnetic field H is measured by the loop sensor 52 at a position very close to 1, the direction of H is determined from the direction of the loop, and the amplitude of H is determined from the output. Then, the current density vector J is obtained by the equation (1). According to this method, for example, a current distribution in a metal housing of an electronic device can be obtained.

[0004]

However, in the above-mentioned conventional example, in order to find the source of the high-frequency current on the housing surface, the current source must be searched from the current distribution measured in a considerably wide range. There are inconveniences
There was a need for a more convenient way to find the current source.

[0005]

An object of the present invention is to provide a current probe which can solve the disadvantages of the prior art and, in particular, can easily find a place where a current leaks from the inside of the metal housing surface of an electronic device. That is its purpose.

[0006]

According to the first aspect of the present invention, the corresponding circumferential portions of the donut-shaped conductive bottom plate and top plate are short-circuited by the conductive inner and outer cylinders. A probe main body, a bottom plate of the probe main body or a slit provided circumferentially in the vicinity of the bottom plate, output terminals connected to both sides of the slit, and an insulating member that covers the entire outer surface of the bottom plate. Is provided.

According to the second aspect of the present invention, a conductive cylindrical member is provided inside the inner cylinder, a space between one end of the cylindrical member and the top plate is sealed with a metal member, and the bottom plate side of the cylindrical member is closed. The configuration is such that it is covered with an insulating member.

The invention according to claim 3 employs a configuration in which the slit is provided in the outer cylinder.

A fourth aspect of the present invention, in the second aspect of the invention, adopts a configuration in which a slit is provided in the inner cylinder.

The invention according to claim 5 employs a configuration in which a magnetic material is partially or entirely filled between the inner cylinder and the outer cylinder.

According to a sixth aspect of the invention, the magnetic material is NiZ.
The sintered body is an n-based ferrite or a MnZn-based ferrite sintered body or a mixed material obtained by mixing these powders.

These are intended to achieve the above-mentioned object.

[0013]

The current probe according to claim 1 or 2 is used with the bottom plate in contact with the surface of the housing to be measured, and a visual recognition device such as a spectrum analyzer is connected to the output terminal. here,
When the probe body is moved on the surface of the case to be measured, the magnetic field (electromagnetic wave) induced by the high-frequency current flowing in the case is introduced into the probe body through the slit.
Then, an output voltage proportional to a circumferential component of a magnetic field generated inside the probe main body (between the inner cylinder and the outer cylinder) is induced at the output terminal.

More specifically, assuming that the magnetic fields are introduced into the probe main body from two locations indicated by positions c and d on the slit in FIG. 1, if the magnetic fields at these two locations have the same direction and the same amplitude, the probe The magnetic fields in the body cancel each other out, resulting in an output voltage of zero. On the other hand, if the two magnetic fields have different directions or different amplitudes, an output voltage proportional to the strength of these magnetic fields is induced. Here, the positions c and d are
The same applies to any position on the slit.

Generally, the voltage induced at the output terminal is
In FIG. 3, a magnetic field H _I flowing into the probe main body from the slit and a magnetic field H _O flowing out of the slit to the outside are shown.
It is determined based on the difference between and. Since the slit is almost in close contact with the surface of the measured housing, there is a relationship between the current density J and the magnetic field H on the surface of the measured housing according to the above formula (1). Therefore, the difference between the current density flowing into the circumferential portion corresponding to the slit on the housing surface and the current density flowing out from the circumferential portion appears as the output voltage of the probe. That is, the output voltage E of the probe is expressed as follows: E = −j2πfμH _sum (2) Here, f is the frequency of the current, μ is the magnetic permeability in the probe main body, and H _sum is the total amount (circumferential component) of the magnetic field existing inside the probe main body. Total amount of magnetic field H _sum
Is the sum of the components H ⁺ and H ⁻ of the magnetic field generated inside the probe main body in mutually opposite directions. For example, the component H ⁺ is the component from the portion A of the cross section shown in FIG. 1 toward the front side of the drawing. , Component H ⁻ is a component extending from the portion of the same reference numeral A toward the back side of the drawing. Therefore, it can be expressed as follows. ^{_{H sum = H + -H - ·····}} (3)

Each of the components H ⁺ and H ^- is guided from the slit into the probe body. Here, H ^- is guided by the magnetic field H _I, H ^- assuming that there is guided by the magnetic field H _O, field H _I, each current density causing a H _O J ^-, as J ^+, the magnetic field H _I , H _O and the current density J ^-, relationship shown in the aforementioned equation (1) between the J ^+.
This means that J ⁻ and J ⁺ are components flowing into the inside of the circle formed by the slit and components flowing out of the circle. Therefore, the output voltage E of the current probe can be expressed as follows ^: E = K (J ⁻⁻ J ⁺ ) (4) Here, K is a proportionality constant. If the radius of the circle created by the slit is infinitely small, it can be expressed as E = K ▽ _t · J (5) Here, ▽ _t · J indicates that the surface divergence of the current density J on the housing surface is taken.

[0017] If smooth surfaces for holes or openings in the housing surface, which minute portion on the surface of the casing take, flows a current equal amount of current flowing into this part, ▽ _t · J = 0
And the output voltage E = 0. That is, if there is no discontinuity in the current density on the surface of the housing, the output voltage E is always 0 no matter how large the amplitude of the current density is. On the other hand, if there is a hole, an opening, or a welded part with incomplete contact on the surface of the housing for some reason, and current flows out from this part, the current density at this part becomes discontinuous and the output The voltage E comes to have a value other than 0.

For this reason, as shown in FIG. 4, for example, when the probe main body is moved on the surface of the housing including the electromagnetic wave source therein, the output voltage E is increased only at the portion of the hole existing on the housing surface. In other parts, E = 0.

According to the third aspect of the present invention, an output signal line is connected to an output terminal provided on the outer cylinder corresponding to the position of the slit.

According to the fourth aspect of the present invention, the entry of an external magnetic field into the slit provided in the inner cylinder is effectively prevented.

According to the fifth aspect of the invention, the output voltage is amplified corresponding to the magnetic permeability of the magnetic material.

In the invention according to claim 6, the output voltage is amplified particularly efficiently by using a material made of NiZn ferrite or MnZn ferrite having magnetic permeability as the magnetic material.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

In FIG. 1, the probe body 1 is formed by connecting (connecting) a donut-shaped conductive bottom plate 11 and top plate 12 with an outer cylinder 13 and an inner cylinder 14. Specifically, the outer cylinder 13 integrally connects the corresponding outer peripheries of the donut formed by the bottom plate 11 and the top plate 12. On the other hand, the inner cylinder 14 integrally connects the corresponding inner circumferences of the donut shape. As a result, a donut-shaped region having a certain volume is formed inside the probe main body.

At the center axis position of the inner cylinder 14, each cylinder 1
A conductive columnar member 15 having a length substantially equal to that of 3, 14 is provided. The top plate 12 side of the cylindrical member 15 is short-circuited to the top plate 12 by a metal plate as a metal member. In this embodiment, the opening of the donut-shaped top plate 12 is sealed with a metal plate 16 connected to the columnar member 15 by a short circuit with the columnar member 15 described above. Actually, the entire body including the probe main body 1, the columnar member 15 and the metal plate 16 is composed of one metal member.

The bottom plate 11 is provided with a circumferential slit 2 along the donut shape of the bottom plate 11. In this embodiment, the slit 2 is provided slightly outside the bottom plate 11. Output terminals 3 are provided on both sides of the slit 2. FIG. 1 shows a state in which an output signal line is connected to the output terminal 3. Also, the bottom plate 11
A circular and sheet-like (membrane) insulating member 4 is provided on the outer surface of the cylindrical member 15 and the bottom plate 11 side of the cylindrical member 15.
Fully covered. This is for insulating the case under test 100 and the current probe 10 from each other.

In this embodiment, the width of the slit 2 is 1.
0 mm and the sheet thickness of the insulating member 4 are set to 0.5 mm. These numerical values are determined experimentally, and as a result of the experiment, the slit width is 0.1 mm to 2.0 mm,
It became clear that the sheet thickness is desirably 2 mm or less.
Here, a vinyl sheet is used as the sheet-like insulating member 4, but other materials may be used as long as they are insulators.

Next, the use state and operation of the current probe 10 having the above-described configuration will be described with reference to FIGS.

The current probe 10 of the present embodiment comprises a bottom plate 11
Is used in contact with the surface of the housing 100 to be measured, and a visual recognition device such as a spectrum analyzer is connected to the output terminal 3 (not shown). Here, when the probe main body 1 is moved on the housing surface 100 to be measured, a magnetic field (electromagnetic wave) induced by a high-frequency current flowing in the housing 100 is transmitted to the slit 2.
Through the probe body 1. An output voltage E proportional to the circumferential component of the magnetic field generated inside the probe body 1 (between the inner cylinder 14 and the outer cylinder 13) is induced at the output terminal 3.

More specifically, the slit 2 in FIG.
The magnetic field is generated from the probe main body 1 from the two positions indicated by the positions c and d above.
If they are guided to the inside, if the magnetic fields at these two locations have the same direction and the same amplitude, the magnetic fields in the probe main body 1 cancel each other, and as a result, the output voltage E becomes zero. On the other hand, 2
If the magnetic fields at different locations have different directions or different amplitudes, an output voltage E proportional to the strength of these magnetic fields is induced. Here, the positions c and d are the same even if they are arbitrary positions on the slit.

Generally, the voltage E induced at the output terminal 3
3 is determined based on the difference between the magnetic field H _I flowing into the inside of the probe main body 1 from the slit 2 and the magnetic field H _O flowing out of the slit to the outside. Since the slit 2 is almost in close contact with the surface of the measured housing 100, there is a relationship of the above-described formula (1) between the current density J and the magnetic field H on the surface of the measured housing 100 (conventionally). See example).
Therefore, the difference between the current density flowing into the circumferential portion corresponding to the slit 2 on the surface of the housing 100 and the current density flowing out from the circumferential portion appears as the output voltage E of the probe. That is, the output voltage E of the probe is expressed as follows: E = −j2πfμH _sum (12) Here, f is the frequency of the current, mu is magnetic permeability, H _{su m} of the probe body 1 is the total amount of the magnetic field existing in the probe body 1 (circumferential component). Total amount of magnetic field H
_sum is the _sum of mutually opposite components H ⁺ and H ⁻ of the magnetic field generated inside the probe body 1. For example, the component H ⁺ goes from the reference symbol A portion of the cross section shown in FIG. The component H ⁻ is a component extending from the portion A having the same reference numeral toward the inner side of the drawing. Therefore, it can be expressed as follows. ^{_{H sum = H + -H - ·····}} (13)

Each of the components H ⁺ and H ⁻ is guided from the slit 2 into the probe body 1. Where H
Assuming that ⁺ is guided by the magnetic field H _I and H ⁻ is guided by the magnetic field H _O , the current densities that generate the magnetic fields H _I and H _O are J ⁻ and J ⁺ , respectively, and the magnetic fields H _I and H _O. Current density J
^-, relationship shown in the aforementioned equation (1) between the J ^+. This means that J ⁻ and J ⁺ are also components flowing into the circle formed by the slit 2 and components flowing out of the circle. Therefore, the output voltage E of the current probe 10
Can be expressed as E = K (J ⁻⁻ J ⁺ ) (14) Here, K is a proportionality constant. If the radius of the circle created by the slit 2 is infinitely small, it can be expressed as E = K ▽ _t · J (15) Here, ▽ _t · J represents taking the surface divergence of the current density J on the housing 100 surfaces.

If the surface of the housing 100 is a smooth surface having no holes or openings (symbol Q in FIG. 4), any minute portion on the surface 100 of the housing can take an amount equal to the current flowing into this portion. The current flows, _Δt · J = 0, and the output voltage E = 0
Becomes That is, if there is no discontinuous portion of the current density J on the surface of the housing 100, the output voltage E is always 0, no matter how large the amplitude of the current density J is. On the other hand, if there is a hole, an opening, or a welded portion (reference numeral Q in FIG. 4) where contact is incomplete on the surface of the housing 100 for some reason, and current is flowing out from such a portion, this portion The current density J becomes discontinuous, and the output voltage E has a value other than 0.

Therefore, as shown in FIG. 4, for example, when the probe main body 1 is moved on the surface of the housing 100 including the electromagnetic wave generation source S therein, the output voltage E is a hole Q on the surface of the housing 100. Since it becomes large only in the portion and the output voltage E = 0 in the other portions, the current outlet Q can be found very easily.

As described above, according to the present embodiment, the probe main body 1 is separated from the surface of the measured housing 100 through the slit 2.
The voltage induced between the slits of the probe body corresponding to the difference between the magnetic field flowing into the probe body and the magnetic field flowing out of the probe body through the slit 2 is taken out from the output terminal. , The current outlet of the case to be measured can be found very easily. Also,
Since the slit is provided on the bottom plate, measurement errors due to the influence of the external magnetic field can be prevented.

Next, another embodiment of the present invention will be described with reference to FIGS.
It will be described based on.

In the embodiment shown in FIG. 5, the whole inside of the probe main body 1 is filled with the magnetic material 5, and the other structure is the same as that of the first embodiment. In this embodiment,
A doughnut-shaped NiZn-based ferrite sintered body was used as the magnetic body 5. Since the output voltage E is proportional to the magnetic flux density μH in the probe main body 1, by filling the probe main body 1 with a magnetic substance, the output voltage E amplified to the magnetic permeability μ times can be obtained. In addition to the effects of the first embodiment,
The sensitivity of the current probe can be improved. here,
When the current probe of this embodiment is used in a relatively low frequency band having a frequency of about 1 MHz or less, MnZn-based ferrite having a low frequency and a high magnetic permeability may be used as the magnetic body 5. In addition, when using only in the high frequency band of about 100 MHz or more, the loss at the high frequency is high in the sintered body. Therefore, the mixed material of the ferrite powder and the resin, whose magnetic permeability is reduced and the loss at the high frequency is suppressed, is made magnetic. It may be used as the body 4.

In the embodiment shown in FIG. 6, a slit 22 is provided in the vicinity of the bottom plate 11 of the outer cylinder 13, and the other structure is the same as the embodiment shown in FIG. As a result of performing a test using the configuration of this example, an output equivalent to that of the example shown in FIG. 5 could be obtained. Even in this case, the same effect as the embodiment shown in FIG. 1 or 5 can be obtained, and the connection of the output signal line to the output terminal 3 can be facilitated.
There is an advantage.

In the embodiment shown in FIG. 7, a slit 32 is provided in the vicinity of the bottom plate 11 of the inner cylinder 14, and the other configuration is the same as the embodiment shown in FIG. As a result of performing a test using the configuration of this example, an output equivalent to that of the example shown in FIG. 5 could be obtained. Even in this case, the same operation and effect as those of FIG. 1 or FIG. 5 can be obtained, and there is an advantage that an external magnetic field which causes a measurement error can be prevented from entering through the slit 32.

Here, in each of the above embodiments, the cylindrical member 15
Although the configuration including the metal plate 16 and the metal plate 16 has been described, the configuration may not include these components.

[0041]

Since the present invention is constructed and functions as described above, according to the present invention, the magnetic field flowing into the probe main body through the slit from the surface of the measured housing and the outside of the probe main body through the slit are formed. By taking out the voltage induced between the slits of the probe body from the output terminal corresponding to the difference with the magnetic field flowing out from the output terminal, from the fluctuation of this output voltage,
The current source of the measured housing can be found very easily. Also, because the slit is provided on the bottom plate,
It is possible to prevent the measurement error due to the influence of the external magnetic field.

According to the third aspect of the present invention, since the slit is provided in the outer cylinder, it is possible to easily connect the output signal line to the output terminal, and there is an advantage in use or manufacturing.

According to the fourth aspect of the present invention, since the slit is provided on the side of the inner cylinder sealed by the metal member, an external magnetic field hardly enters the probe main body from the slit, and the external magnetic field is used for measurement. It is possible to effectively prevent a situation in which an error is caused, and thereby a stable output can be obtained.

According to the fifth aspect of the present invention, since the entire body of the probe is filled with the magnetic material, the output voltage is amplified to μ times the magnetic permeability of the magnetic material, so that the sensitivity of the probe can be improved. Thus, the source of the current can be reliably identified.

According to the sixth aspect of the present invention, the magnetic material is NiZ
Since the material is made of an n-based ferrite or a MnZn-based ferrite sintered body, particularly the output voltage can be efficiently amplified, and the sensitivity of the probe can be dramatically improved.

Thus, it is possible to provide an unprecedented excellent current probe that can easily find a location where current leaks from the inside of the metal housing surface of an electronic device.

[Brief description of drawings]

FIG. 1 is a partially cut-away configuration view showing an embodiment of the present invention.

FIG. 2 is a perspective view showing a bottom plate portion of the embodiment shown in FIG.

FIG. 3 is an explanatory diagram for explaining a current measurement principle of the embodiment shown in FIG. 1;

FIG. 4 is an explanatory diagram showing a use state of the embodiment shown in FIG. 1 and an output voltage obtained as a result.

FIG. 5 is a configuration diagram showing a second embodiment of the present invention.

FIG. 6 is a configuration diagram showing a third embodiment of the present invention.

FIG. 7 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram showing a conventional example.

[Explanation of symbols]

 1, 21, 31 Probe body 2, 22, 32 Slit 3 Output terminal 4 Insulating member 5 Magnetic body 10 Current probe 11 Bottom plate 12 Top plate 13 Outer cylinder 14 Inner cylinder 15 Column member 16 Metal member (metal plate) 51 Metal surface 52 Loop sensor 100 Measured housing (housing) Q Current source (hole) S Electromagnetic wave source

Claims (6)

[Claims] 1. A probe main body comprising a donut-shaped conductive bottom plate and a top plate, each of which has a corresponding circumferential portion short-circuited by a conductive inner cylinder and an outer cylinder. A slit provided circumferentially in the vicinity of the bottom plate, and output terminals connected to both sides of the slit,
A current probe, comprising: an insulating member that entirely covers the outer surface of the bottom plate. 2. A conductive column member is provided inside the inner cylinder, a space between one end of the column member and the top plate is sealed with a metal member, and the bottom plate side of the column member is insulated by an insulating member. The current probe according to claim 1, wherein the current probe is coated. 3. The current probe according to claim 1, wherein the slit is provided in the outer cylinder. 4. The current probe according to claim 2, wherein said slit is provided in said inner cylinder. 5. A magnetic material is partially or entirely filled between the inner cylinder and the outer cylinder.
The current probe as described. 6. The current probe according to claim 5, wherein the magnetic body is a NiZn-based ferrite or a MnZn-based ferrite sintered body or a mixed material obtained by mixing powders thereof.