JP2002257865A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current, sensor capable of having a measuring range in a wide band with high precision and corresponding to various wires to be measured from a small diameter to a large diameter. SOLUTION: An insulation resin 12 is coated over the whole periphery of a core 11 and a conductor foil 13 is formed on the circumference. An outside face part 13c of the conductor foil 13 enables a line of slit 13s to go around, and an insulation area is formed by exposing the insulation resin 12. The conductor foil 13 functions as a roll of winding for the core 11, and output accompanying in-core hole penetration current is obtained by connecting lead wires 15, 15 to the arbitrary part of both the ends 13c, 13c respectively. Influence reduction of ideal low inductance and skin effect is achieved, by making the winding the very wide foil and winding it around the core in wide area, the wide band of the measuring range is achieved and the current sensor has the advantage of being hardly depending on the position of the wire to be measured in the core hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor for non-contactly measuring a current flowing through a conductor.

[0002]

2. Description of the Related Art In recent years, information devices such as personal computers which have become widespread due to the development of information technology have realized high-speed operation (operation frequency on the order of GHz) which has not been considered until now according to rapid progress. Such medium wave short wave ~
In a device that handles signals up to GHz, a large amount of electromagnetic waves is emitted from its casing and wiring such as cables, and these components also serve as inductive and receiving antennas, respectively. Has become.

In processing electromagnetic waves, it is necessary to detect what kind of electromagnetic waves are radiated from which parts. For this purpose, a clamp-type current sensor capable of non-contactly measuring a cable or the like is required. It is used.
A typical example is a CT (current transformer) type current sensor, and FIG. 1 shows a basic configuration thereof.

The current sensor 1 is composed of a toroidal coil in which a winding is formed by winding a conductive wire around a ring-shaped core 2, and a measurement is performed through a measured wire through an inner hole of the core 2. An end of the winding 3 drawn out of the coil becomes an output terminal having a terminating resistor 4 provided therebetween, and an amplifier 5 is connected to the output terminal. According to this current sensor 1, the line to be measured passing through the inner hole of the core becomes the primary line, and when a through current flows through the line to be measured, an output appears on the winding 3 which is the secondary line due to the principle of the transformer. , Measurement is performed.

[0005]

SUMMARY OF THE INVENTION As described above, the conventional C
For the purpose of making it possible to measure a high frequency band reaching up to GHz in a T-type current sensor, a method of obtaining high sensitivity over a wide band by increasing the number of turns of a winding around a core is generally adopted. ing. However, if the number of windings is increased, the influence of the coupling capacitance (distributed capacitance) between the windings is correspondingly increased. Therefore, it is practically difficult to extend the characteristic to a target high frequency only by increasing the number of windings.

In order to make the distribution constant, a method of inserting a large number of resistors for the purpose of dumping has been devised. However, there is a limit to this, and unless the core inner diameter is reduced, several hundred MHz are used.
The problem is that it is not possible to cope with high frequencies with a skin effect, such as those up to and including GHz. For example, a current standard commercial product has a core inner diameter of about 3 mm for a 50 MHz compatible sensor and a core inner diameter of about 0.84 mm for a broadband sensor for 1-2 GHz.

That is, it is difficult for the conventional CT type current sensor to have a wide band, and even if it is a product compatible with a wide band, a measurable cable diameter is very small, and a cable of about 10 to 15 φ generally used for an interface cable or the like. Is not suitable for practical use because it cannot be measured. The cables (wirings) used in current information equipment are quite diverse, such as bus cables and interface cables. Even though each of them is a radiation source, there is no current sensor that can measure them all. It is the current situation.

[0008] The present invention is to solve the above problems,
It is an object of the present invention to provide a current sensor having a high-precision and wide-range measurement range and capable of coping with various lines to be measured from a small diameter to a large diameter.

[0009]

SUMMARY OF THE INVENTION The present invention proposes:
The core is covered with a conductive foil and an insulating area of a predetermined width is formed around the outer surface of the conductive foil. This is a current sensor in which generated current is taken out from both ends of a conductor foil facing each other across an insulating region. A structure that covers the periphery of the core with a conductor foil is, for example, to coat the core with an insulating resin with low high-frequency loss, and then wrap the conductor foil on top of it, or wrap a conductor such as an RF conductive metal in a foil shape by plating or sputtering technology. This is possible. The insulating region formed around the outer surface portion of the conductor foil can be formed by cutting one slit in the circumferential direction of the outer surface portion.

[0010] This current sensor is based on the idea that the winding is formed in a very wide foil shape and is wound around a core over a very wide area to form an inductance. As a result, an ideal reduction in inductance and a reduction in the influence of the skin effect are achieved, and the measurement range can be broadened. Also,
Since it is in a state close to an ideal coil in which the inductance is reduced by the foil-shaped winding, there is also an advantage that it is hardly influenced by the position of the line to be measured in the core inner hole. That is,
Since a thin cable can be measured with high sensitivity even with a large-diameter core, clamp measurement can be performed on a wide variety of cables.

In such a current sensor according to the present invention, it is also possible to adopt a configuration in which the influence of an external magnetic field is eliminated by further surrounding the conductor foil with a magnetic shielding foil. The magnetic shielding foil can be provided, for example, by coating an insulating resin on a conductive foil and forming a metal foil thereon by plating or sputtering. In this case, it is more preferable that the outside of the magnetic shielding foil is further covered with an insulating material such as an insulating resin, and the outer coating is applied for electrical insulation, corrosion resistance and impact resistance.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be shown and described with reference to FIG.

The current sensor 10 shown in FIG. 2 is the most basic example. FIG. 2A is a perspective view, and FIG.
It is sectional drawing seen in A '.

The entire area around the ring-shaped core 11 made of ferrite or the like is coated with an insulating resin 12 having a small high-frequency loss.
Are formed. In this embodiment, the conductive foil 13 is a copper foil on which copper is deposited by a sputtering technique.

The conductor foil 13 is formed uniformly over the entire area from the inner side surface portion 13a to the side wall portion 13b, while the outer side surface portion 13c is formed with a single slit 13s formed at the center in the circumferential direction. It is notched, and an insulating region is formed by exposing the lower insulating resin 12. Therefore, the end portions 13c, 13c opposed to each other with the slit 13s interposed therebetween are formed. The conductor foil 13 functions as a single-turn winding for the core 11. By connecting the lead wires 15, 15 to arbitrary portions of both ends 13c, 13c, respectively, the output accompanying the through-hole current in the core can be obtained. can get. Both lead wires 15,1
A terminal resistor 16 and an amplifier 17 can be connected between the terminals 5 as in the prior art.

By using the conductor foil 13 which is a winding having an extremely large area as described above, the inductance is reduced and the effect of the skin effect is reduced. Therefore,
The current sensor 10 of the present example can obtain a stable output impedance over a wide range because of its low inductance. As a result of confirming this by an experiment, 10
Broadband measurement from kHz to 1 GHz (-3 dB down range) was possible. In addition, even when the inner diameter of the coil through which the wire to be measured was passed was increased to about 20 mm, high-precision measurement was possible.

Since the output impedance is stabilized by the low inductance, the terminating resistor 16 of this embodiment can have a very small value. The fact that the output impedance is low (the signal source impedance is low) means that noise is less likely to occur and that a loading error (error) in the amplifier 17 is less likely to occur.
The input to is made pure resistance, and is hardly affected by disturbances such as a change in capacitance. As the amplifier 17, a low-noise broadband amplifier (LN
If A) is used, an excellent sensor having a wide band, high sensitivity and high output can be constructed.

As shown in FIG. 3, the current sensor 10 of this embodiment has both ends 13c, 13c on the outer surface of the conductor foil.
To each other, a signal can be taken out by connecting the ribbon-shaped lead wires 15r, 15r to the respective components. The width of the ribbon-shaped lead 15r can be substantially equal to the width of the end portion 13c of the conductive foil 13, and the wider width is suitable for transmitting signals without loss. Also, using such ribbon-shaped lead wires 15r, 15r,
Is arranged close to the sensor 10, it is possible to obtain a structure capable of eliminating the influence of the external magnetic field as much as possible.

The terminating resistor 16 is provided at both ends 13 of the conductive foil 13.
It is also possible to adopt a structure of connecting between c and 13c. FIG. 4 shows an example in which a large number of resistors 16r, 16r,... Are connected as terminal resistors 16 between both ends 13c, 13c of the conductor foil 13. Each of the resistors 16r may be configured by using a chip resistor or a thin film resistor and having excellent RF characteristics. According to this example, a large number of connected resistors 16r effectively reduce inductance (pure resistance).
Will be achieved. For example, generally, an amplifier 17
Input impedance is often 50Ω,
In this case, if 10 matching resistors 50r of 50Ω are connected between both ends 13c, 13c at equal intervals, the output impedance of the current sensor 10 becomes 5
0Ω / 10 pieces = 5Ω. Therefore, the output voltage of the current sensor 10 can be amplified by the amplifier 17 without loss, and an output signal with a wide band, high sensitivity, and low noise can be generated.

FIG. 5 shows an example of the current sensor 30 in which the current sensor having the above-described configuration is divided into two pieces so that the current sensor 30 can be easily attached to the line to be measured. The current sensor 30 has the same sectional structure as the current sensor 10 of FIG. 2, but is divided into a piece 31 and a piece 32 in the upper and lower halves in the figure. The pieces 31, 32 are connected at their one end faces by conductor leaf springs 33, 33 so that they can be opened and closed from the other end face side due to their elasticity ... FIG. 5 (b). The leaf spring 33 of the conductor connecting the two pieces 31 and 32 is preferably made of beryllium copper or the like. In addition, both pieces 31,
In order to more reliably maintain the closed state when the 32 is closed, it is also possible to apply an application such as fastening the other end face portion with a conductor clip. Alternatively, application examples such as attaching both parts 31 and 32 to the tip of a clothespin-shaped clip and sandwiching both parts 31 and 32 with dedicated fasteners without providing the leaf spring 33 or the like are possible (for example, special features). 7-198 Kaihei
754, FIG. 12, and JP-A-7-122260, FIGS.
Such). Furthermore, the present invention is not limited to two pieces and may be divided into more pieces such as three pieces and four pieces.

FIG. 6 shows an example of a current sensor in which a magnetic shielding foil is formed. 6A is a cross-sectional view corresponding to FIG. 2B, and FIG. 6B is a cross-sectional view taken along a cross-sectional line BB ′.

In the current sensor 40, a core 41 is covered with an insulating resin 42 and a conductive foil 43 is formed around the core 41. The conductor foil 43 has an inner surface portion 43a, a side wall portion 43b, and an outer surface portion 43c as in the case of the conductor foil 13 described above, but a portion of both end portions 43c, 43c of the outer surface portion insulated by the slit 43s. , Signal extraction terminals 43d, 4
3d is protruded and is exposed to the outside. The terminals 43d can be provided at a plurality of locations.

The periphery of the conductor foil 43 is further covered with an insulating resin 44, and a magnetic shielding foil 45 is formed thereon. It is sufficient that the magnetic shielding foil 45 has an effect in the frequency band to be measured. In this example, the magnetic shielding foil 45 is a copper foil generated by sputtering or the like in the same manner as the conductor foil 43. By forming the magnetic shielding foil 45, the influence of disturbance factors such as an external magnetic field can be eliminated. In this example,
The periphery of the magnetic shielding foil 45 is covered with an insulating resin 46 to improve impact resistance, corrosion resistance, and the like.

FIG. 7 shows an example in which a number of amplifiers 17a to 17d are connected in parallel to the current sensor 10 of FIG. In this example, four ribbon-shaped lead wires 15a to 15d as shown in FIG. 3 are connected at equal intervals to the ends 13c, 13c of the conductor foil outer surface portion of the current sensor 10, and each of the leads 15a to 15d has a low noise amplifier. They are connected to amplifiers 17a-c. Outputs of these amplifiers 17a to 17d are added to an adder SUM.
Is used by being summed up equally. The adder SUM may be one that simply connects the output lines of the amplifiers as long as the outputs of the amplifiers 17a to 17d can be added equally. In this example, the number of amplifiers is four. However, if N amplifiers are connected in parallel, the noise voltage can be reduced to 1 / √N, further lower noise can be achieved, and a stable gain can be obtained over a wide band. This has the effect.

FIGS. 8 and 9 are block diagrams showing four circuit examples using the current sensor as described above.

FIG. 8 shows an example in which one amplifier 17 is provided.
FIG. 8A shows that the amplifier 17 is connected to the current sensor 1 by the lead wire 15 (particularly, a ribbon-like lead wire 15r).
This is a method in which the input impedance Zin is set as a terminating resistor by setting the input impedance close to 0 (or 30 or 40). As described above, when the input impedance Zin of the amplifier 17 is equivalently regarded as a terminating resistor, if the input impedance Zin is low, the signal from the sensor 10 can be accepted without loss and low-noise amplification can be performed. On the other hand, FIG. 8B shows a system in which an amplifier 17 is provided via a terminating resistor 16 as in the related art. In the case of FIG. 8B, a large number of resistors 16r of the type shown in FIG.

FIG. 9 shows an example in which the number of amplifiers 17 is N. FIG. 9A shows that a plurality of terminating resistors 16 are connected to the end 13c of the current sensor 10 (30, 40). , 1
3c, and amplifiers 17-1 to 17c respectively.
To 17-N as shown in FIG. The terminating resistor 16 can be a number of resistors 16r as shown in FIG.
A configuration in which −N is connected is possible. On the other hand, FIG. 9B shows that the amplifiers 17-1 to 17-N are provided closer to the lead wire 15 (particularly, the ribbon-like lead wire 15r), and the input impedance Zin is used as a terminating resistor. It is a method. For example, a commonly used 50Ω input → 5
Assuming that 10 RF-LNAs with 0Ω output are connected in parallel as amplifiers 17-1 to 17-N, equivalently, 50Ω /
It can be regarded as 10 = 5Ω termination resistance (Total-Zin), and low-noise amplification can be performed without losing the signal from the sensor 10. In addition, as shown in the figure,
Input line (lead wire 15) of each amplifier 17-1 to 17-N
The output line and the output line may be configured such that the signals are evenly distributed and uniformly combined by simple connection, but a circuit (e.g., an adder) for the uniform distribution and the uniform combination may also be configured.

[0028]

According to the current sensor of the present invention, it is possible to measure all wirings currently used in information equipment without using a large-scale device. Its broadband and high sensitivity characteristics are based on EMC (Electro Magnetic Compat
This is particularly effective when applied to evaluation. That is, since the desktop measurement can be performed by using the sensor of the present invention, first, an apparatus to be measured such as a personal computer is placed in an actual use environment, and the sensor of the present invention is clamped on its wiring to perform electromagnetic measurement. As a result, the noise generation position and its intensity can be grasped, so that it is possible to use an EMC countermeasure against the noise generation position. Therefore, it is not necessary to perform a large-scale EMC evaluation using a site as in the related art.
The advantage of evaluation is obtained.

[Brief description of the drawings]

FIG. 1 is a side view showing a conventional current sensor.

FIG. 2 is a perspective view (a) and a cross-sectional view (b) showing an example of a current sensor according to the present invention.

FIG. 3 is a side view of an example in which ribbon lead wires are connected.

FIG. 4 is a side view of an example in which many resistors are connected.

FIG. 5 is a perspective view of an example divided into two pieces.

FIG. 6 is a sectional view of an example in which a magnetic shielding foil is formed.

FIG. 7 is a side view of an example in which many amplifiers are connected in parallel.

FIG. 8 is a block diagram showing an example of a circuit using the current sensor of the present invention.

FIG. 9 is a block diagram showing another example of a circuit using the current sensor of the present invention.

[Explanation of symbols]

 10, 30, 40 Current sensor 11, 41 Core 13, 43 Conductor foil 45 Magnetic shielding foil

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinya Sasaki 4-11, Shinamachi, Akita-shi, Akita Prefecture Inside the Industrial Technology Center, Akita Prefecture (72) Inventor Yasuo Kondo, Yatsuo Kondo, Akita-shi, Akita 4-11 Inside the Akita Prefectural Industrial Technology Center (72) Inventor Takeshi Kumagai 4-11 Sanda-Yoro, Aiyamachi, Akita City, Akita Prefecture F-term in the Akita Prefectural Industrial Technology Center 2G025 AA03 AA07 AA11 AA17 AB14

Claims (7)

[The claims] An insulating region having a predetermined width is formed around an outer surface of the conductor foil so as to extend around an inner surface of the core, and a measurement line is passed through an inner hole of the core. A current generated in the conductor foil in accordance with the current of (a), is taken out from both ends of the conductor foil facing each other across the insulating region. 2. The current sensor according to claim 1, wherein the core and the conductive foil are divided into a plurality of pieces. 3. The current sensor according to claim 1, wherein a periphery of the conductive foil is covered with a magnetic shielding foil. 4. The current sensor according to claim 3, wherein the periphery of the magnetic shielding foil is covered with an insulating material. 5. The current sensor according to claim 1, wherein one or more resistors are connected between both ends of the conductive foil. 6. The current sensor according to claim 1, wherein ribbon-shaped lead wires are connected to both ends of the conductive foil. 7. The current sensor according to claim 1, wherein a number of amplifiers are connected in parallel at both ends of the conductive foil.