JPH10185962A - Current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain a current conversion coefficient constant over a wide bandwidth without affecting to lines to be measured in a current detector capable of detecting a high frequency current flowing in the lines without cutting the lines to be measured and prevent the mixing of unnecessary components, disturbance wave, noise, etc., in the current detection output. SOLUTION: A current detector 1 comprises an annular core 2 formed by contacting two core pieces (magnetic pieces) 2a and 2b, a coil 3 for current detection wound around the annular core, a load resistance 4 connected to the two ends of the coil 3 and an output line 5 constituted of a coaxial cable provided with a common mode choke filter 5a. The voltage corresponding to the detection current generated at both ends of the load resistance 4 is taken out through the common mode choke filter 5a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a high-frequency current flowing through a line to be measured without cutting the line.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detection device capable of detecting a wide range from 00 kHz to about 1 GHz with a single detector, and more particularly, to prevent unnecessary components and noise from being mixed into an output related to a detected current. The present invention relates to a current detection device and a current detection device capable of switching between detection of a normal mode current and detection of a common mode current.

[0002]

2. Description of the Related Art A so-called clamp ammeter capable of detecting a current flowing through a line to be measured without cutting the line is disclosed in Japanese Patent Application Laid-Open No. 63-168572.
JP, JP-A-4-220566, JP-B-7-3
No. 8000, Japanese Patent Publication No. 8-3502, and the like.

[0003] A conventional current detecting device has a clamp core (magnetic body) having an annular shape and a part of which is configured to be openable and closable, a detection coil provided on the clamp core (magnetic material), And a display unit for the measurement result.

In Japanese Utility Model Laid-Open Publication No. 2-45467, two current transformers are provided adjacent to each other and include a core formed in a ring shape and divided so as to be clampable, and a coil wound around the core. There is described a minute current detecting device which measures a minute current flowing in a line by using these two current transformers at the same time.

In Japanese Utility Model Laid-Open Publication No. 2-45467,
Various characteristics of two adjacent current transformers are made substantially equal so that the direction of the current induced by the magnetic flux generated in the current transformer core by the current measured in one current transformer becomes positive. And a line for measuring the direction of the current induced by the magnetic flux generated in the current transformer core by the current measured by the other current transformer so as to be negative, and the difference between the outputs of the respective current transformers Is described to measure a current flowing in a line to be measured.

Further, Japanese Utility Model Laid-Open No. 2-45467 discloses that two current transformers provided adjacent to each other have approximately equal characteristics, and a line through which a current to be measured flows into one of the current transformers. The current flowing through the line is measured by clamping, the other current transformer measures the current generated outside by the external magnetic field, and the current value measured by one current transformer and the current value measured by the other current transformer are measured. There is described a minute current measuring device that measures a current flowing in a line to be measured based on a difference from a measured current value.

[0007]

EMI / EMS (El)
electro-Magnetic Interferen
ce / Electro-Magnetic Susce
For example, in the study of pitbilities (for example, a study on preventing an interference wave from being generated from an electronic device and a study on preventing a device from malfunctioning due to a disturbance wave emitted from another device), a so-called clamp ammeter is used. The current of various wirings can be measured without cutting various wirings (wires, harnesses, I / O (input / output) cables, power supply lines, etc.) connected to terminals inside and outside the electronic device and printed circuit boards. It is convenient.

However, in the study of EMI / EMS, not only the current value is simply measured, but also the waveform of the current and the frequency component of the current, especially the digital wave, have a very high frequency range from DC to extremely high GHz.
It contains high frequency components up to the band, and it is often desired to observe this with one detector. In many cases, it is often necessary to check whether these disturbance currents are in a common mode or a normal mode. For this reason, it is desirable to conduct the current detection output of a so-called clamp ammeter to a measuring device such as an oscilloscope or a spectrum analyzer through a measuring cable to perform waveform observation and frequency spectrum analysis. There is no compact and simple current detection device that can measure accurately without a constant current conversion coefficient over a wide band up to the vicinity, without mixing unnecessary components and noise.

In addition, when trying to measure a normal mode current using a clamp ammeter having a single current transformer, the clamp ammeter is attached to only one of the two reciprocating lines. Therefore, the bunras may collapse at high frequencies, and the original current may not be measured. Further, when trying to measure both components of the normal mode current and the common mode current, it takes time to increase the number of measurements and to calculate both components from the measured values.

The present invention has been made to solve such a problem, and has a constant current conversion coefficient over a wide band without significantly affecting the constant of a high-frequency line, and a noise component such as an unnecessary component or an interference wave. A first object is to provide a current detection device capable of extracting a current detection output without being affected.

A second object of the present invention is to provide a current detecting device capable of easily switching between measurement of a normal mode current and measurement of a common mode current.

[0012]

In order to solve the above-mentioned problems, a current detecting device according to the present invention comprises a magnetic path formed in a ring shape and divided into a clampable part, and a current detecting means wound around the magnetic path. Coil, a load resistor connected to both ends of the current detection coil, and a shielded output line for extracting a voltage generated in the load resistor, and a shield conductor of the output line for the current detection. It is characterized in that a part of the coil is formed.

Further, the current detecting device according to the present invention comprises a magnetic path formed in a ring shape and divided so as to be clampable, a current detecting coil wound around the magnetic path, and both ends of the current detecting coil. , And an output line provided with a common mode choke filter, and a voltage generated in the load resistance is taken out via the output line provided with the common mode choke filter.

Further, the current detecting device according to the present invention comprises:
Two sets of current transformers are provided adjacent to each other and formed of a magnetic path formed in a ring shape and divided so as to be clampable and a coil for current detection wound on the magnetic path. One end is connected to the other end of the other current detection coil, and a load resistor is connected between the other end of the one current detection coil and one end of the other current detection coil. The connection state for common mode current measurement, the other end of one current detection coil and the other end of the other current detection coil are connected, and one end of one current detection coil is connected to the other end. In addition to a measurement mode switch for switching between a normal mode current measurement connection state and a load resistance connected to one end of the current detection coil, a voltage generated across the load resistance is connected to the common mode. Chalk fill And wherein the removed via output line having a.

The current detection device according to the present invention reduces the load resistance as long as the detection sensitivity permits, so that the current conversion coefficient is constant over a wide band, and the voltage corresponding to the measured current generated at the load resistance end is detected. It is taken out through the shielded output line, and the shield conductor of the output line was used as a part of the current detection coil, so the current detection output (voltage according to the measured current) can be converted to unnecessary components and interference waves over a wide band. Can be taken out without being affected by noise such as

Further, in the current detection device according to the present invention, the load resistance is reduced as far as the detection sensitivity permits, so that the current conversion coefficient becomes constant over a wide band, and the current conversion device responds to the measured current generated at the load resistance end. Since the voltage is taken out through the common mode choke filter, the current detection output (the voltage corresponding to the measured current) can be taken out over a wide band without being affected by noise such as unnecessary components and interference waves.

Further, the current detecting device according to the present invention is
Since the switch for switching the measurement mode is provided, the connection state for measuring the common mode current and the connection state for measuring the normal mode current can be easily switched.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a basic configuration diagram of a current detection device according to the present invention. The current detection device 1 according to the present invention includes two core pieces (magnetic material pieces) 2a and 2b.
, A current detecting coil 3 wound around the annular core 2, a load resistor 4 connected to both ends A and B of the coil 3, and a common mode And an output line 5 having a choke filter 5a.

The output line 5 is for guiding a voltage corresponding to a measured current generated at both ends of the load resistor 4 to a measuring device (not shown) such as an oscilloscope or a spectrum analyzer. FIG. 1 shows a structure in which a connector (plug) 5b for connecting to a measuring device is provided at the distal end side of the output line 5.

The annular core 2 has a structure that can be opened and closed. The current is measured by penetrating the line to be measured L into the annular core 2 and measuring the voltage generated at the load resistor 4 with a measuring device (not shown).

FIG. 2 shows an example of a graph showing the result of measuring the frequency characteristic of the current conversion coefficient of the current detecting device shown in FIG. 1 with the circuit configuration shown in FIG. In FIG.
The measured line L has one end connected to a frequency sweep signal generator G for measuring characteristics, and the other end side load F portion is terminated with 50Ω. In this current detection device, a coaxial cable is used for the output line 5, and the common mode choke filter 5a is omitted. And
The output line 5 is terminated at 50Ω on the measuring device side.

In the circuit configuration shown in FIG. 3, the ratio between the voltages V ₀ and V ₁ across the two terminating resistors is the same as the ratio between I ₀ and I ₁ , and this ratio is called a current conversion coefficient.

The vertical axis in FIG. 2 shows the current conversion coefficient,
The horizontal axis indicates the frequency on a logarithmic scale.

The parameters of the group of curves shown in FIG. 2 are equivalent load resistances R 'which are connected in parallel with the load resistance R of the current detection device and the resistance as viewed from the measuring device side. Actually, the characteristic impedance of the output line 5 of the current detecting device is 50Ω, and the input impedance of the measuring device is also 50Ω. Here, the load resistance R ′ is R and 50Ω.
It becomes the resistance value of the parallel connection with Ω. In curve a, R is approximately 2.6.
In the case of 3Ω, the curve b is the curve c when R is approximately 12.5Ω.
The curve d corresponds to the case where R is infinite and the impedance on the measuring device side is also infinite when R is infinite.

As is apparent from FIG. 2, if V _{0 is} constant with respect to the frequency, that is, if the current I ₀ flowing through the line L to be measured is constant, V ₁ (or I ₁ ) is lower than the frequency in the low frequency region. It rises in proportion and becomes substantially constant from a certain frequency (cutoff frequency) fc. If a region where the frequency characteristic is substantially constant is used, only one current conversion coefficient V ₁ / V ₀ = I ₁ / without correcting the frequency characteristic each time.
It is very convenient to know I ₀ . Therefore, in the current detection device according to the present invention, the region where the frequency characteristic is substantially constant is set to a wide band, and unnecessary components and noise are prevented from being mixed.

The cutoff frequency fc is fc
= R '/ 2πL' has been experimentally confirmed. L 'is the self-inductance of the measuring device at fc, and R' is the equivalent resistance of the measuring circuit. Therefore, if the load resistance R of the current detection device is sufficiently smaller than 50Ω, fc ≒ R / 2πL ′, and fc shifts to a lower side, and it can be seen from FIG. In addition, the smaller the resistance value is, the less the load on the measured line L is.
For example, if R is 10Ω or less, the loss of the measured line L is 0.5 dB or less, which is advantageous in that the characteristics of the line are not disturbed. L ′ and R that determine this fc are elements that determine the lower limit of use in the low frequency region. In addition, factors that determine the upper limit of the high-frequency region include a self-inductance L ′ of the current detection circuit and a self-resonant frequency due to its distributed capacitance C ′. Therefore, in the current detection device, it is advantageous to make the current detection coil as thick and short as possible so as to increase the resonance frequency, and also to reduce the load resistance in order to suppress the Q.

4 to 6 are views showing a specific structure of the current detecting device according to the present invention. FIG. 4 is a perspective view showing a state where an annular core is opened, and FIG. FIG. 6 is a perspective view showing the state, and FIG. 6 is a cross-sectional view of the measurement state. Each core piece 2a, 2b made of a ferrite core is integrated with a plastic cover 6a, 6b by a movable joint 6c, and both covers 6a, 6b are closed and fixed by a stopper 6d. The core surface is stably contacted to form a closed magnetic path. As shown in FIG. 6, the load resistance 4 has a structure arranged inside the annular core 2.

FIG. 7 is an explanatory view showing a structure of a coil for current detection and a connection structure with a load resistor.

Although the surface of the portion to be the current detection coil actually has an insulating film, it is not shown here because it is for explaining the principle. The first half coil piece 3a of the current detecting coil 3 is shown in a cross-sectional view of the coaxial cable 50 forming the output line 5 in FIG. 7, and is formed using the outer conductor 51. The coil half 3b in the latter half of the coil 3 for current detection is formed using a metal rod or metal pipe 31 having the same outer diameter as the outer diameter of the outer conductor 51. One end of the metal rod or metal pipe 31 is connected to the outer conductor 51 of the coaxial cable 50 at a point P shown in FIG. The other end of the metal rod or metal pipe 31 is connected to the core conductor 52 of the coaxial cable 50.

The outer conductor 51 of the coaxial cable 50
Is connected to one end of a load resistor 4, and the other end of the load resistor 4 is connected to the other end of a metal rod or metal pipe 31. Here, the lengths of the right half and the left half of the current detecting coil 3 and the dimensions and shapes of the outer conductor are the same.
A structure in which the outer conductor 51 of the coaxial cable 50 is used as the current detecting coil 3 will be referred to as a coaxial detection method.

In such a configuration, the induced electromotive force is generated in each of the coil pieces 3 a and 3 b forming the coil 3 for current detection, and the loop current flows through the load resistor 4. The voltage across the load resistor 4 generated by the loop current is led out through the coaxial cable 50.

With such a configuration, it becomes electromagnetically symmetrical left and right, and detection of unnecessary components is much less than in the case of the simple loop coil as shown in FIG. Actually, each coil piece 3a, 3b of the measured line L and the coil 3 for current detection is used.
And the capacitance may be different, and the balance may be lost. Therefore, the current detection device 1 according to the present invention may include a common mode choke filter 5a for preventing the common mode current generated by the imbalance from being supplied to the measurement device side.

By using the coaxial detection method and further including the common mode choke filter 5a, unnecessary electromagnetic field components riding on the current detection coil 3, the output line 5, and the like can be removed, and more stable measurement can be performed.

FIG. 8 is a sectional view showing a specific example of the common mode choke filter. The common mode choke filter 5a is formed by winding the coaxial cable 50 around the ferrite ring core 5c in order to prevent a common mode current from riding on the outer conductor 51 of the coaxial cable 50 constituting the output line 5.

FIG. 5 shows a measurement state in which a pair of lines to be measured L1 and L2 such as a power supply line are inserted into the annular core 2. In this measurement state, a current component flowing in one direction, that is, a common mode current, can be detected without detecting a reciprocating current flowing through one measured line L1 and the other measured line L2.

FIG. 9 is an explanatory diagram for detecting the current in one of the pair of measured lines. As shown in FIG. 9, by inserting one line L1 of the pair of lines to be measured L1 and L2 into the annular core 2, it is possible to detect a combined current in a part of the normal mode and the common mode.

FIG. 10 is an explanatory view showing a structure in which the current detecting coil has two turns in the coaxial detection method. As shown in FIG. 10, the current detection sensitivity can be increased by setting the number of turns of the current detection coil 3 to two turns. In FIG. 10, the coaxial cable 50 is
A coil for one turn is formed using the outer conductor 51 of the coaxial cable 50 by winding around, and the remaining one turn of the coil is made of a metal rod or a metal pipe having the same outer diameter as the outer diameter of the outer conductor 51. 31. Further, the load resistance 4 is arranged on the outer peripheral side of the annular core 2. The core conductor of the coaxial cable 50 is connected to one end of the load resistor 4,
The outer conductor 51 of the coaxial cable 50 is connected to one end of the metal rod or metal pipe 31. The other end of the metal rod or metal pipe 31 is connected to the outer conductor 51 of the coaxial cable 50 at a point P (a winding start position of a current detection coil using a coaxial cable) shown in FIG. Actually, a coating for insulation is provided so that the outer conductors do not come into electrical contact with each other.

FIG. 11 is an explanatory view showing the structure of a current detecting coil when a load resistor is arranged on a side end face of an annular core. The current detecting device 1 shown in FIG.
A load resistor 4 is disposed on one side of the coil, a coaxial cable 50 is disposed on the outer peripheral side of the annular core 2, and a coil half of the outer half of the current detecting coil 3 using the outer conductor 51 of the coaxial cable 50. In addition to forming the piece 3a, the remaining half coil piece 3b of the coil 3 is formed using a metal rod or a metal pipe 31 having the same outer diameter as the outer diameter of the outer conductor 51.
Then, the core conductor 52 of the coaxial cable 50 is connected to one end of the metal rod or metal pipe 31, one end of the load resistor 4 is connected to this connection point, and the other end of the load resistor 4 is connected to the outer conductor 51 of the coaxial cable 50. Connected to the tip of The other end of the metal rod or metal pipe 31 is connected to the outer conductor 51 of the coaxial cable 50 on the side opposite to the side where the load resistance 4 is arranged.

FIG. 12 is an explanatory view showing the structure of a current detecting coil when a load resistor is arranged on the outer peripheral surface of an annular core. The current detection device 1 shown in FIG. 12 winds the coaxial cable 50 around the annular core 2 and the point P (the winding start position of the current detection coil using the coaxial cable) shown in FIG.
To connect the core conductor 52 on the distal end side of the coaxial cable 50 to the outer conductor 51 at the winding start position of the coaxial cable 50, and connect the connection point P between the core conductor 52 and the outer conductor 51 to the distal end side of the coaxial cable 50 (the coil The load resistance 4 is connected between the outer conductor 51 and the outer conductor 51 on the winding end side.

FIG. 13 is an explanatory view showing the structure of a detection coil formed by using a single-sided flexible substrate, and FIG. 14 is a developed view of a single-sided flexible substrate forming a detection coil.

In FIGS. 13 and 14, the hatched portions are pattern portions corresponding to the copper foil portions of the single-sided substrate. This current detection coil is a type of modification using a coaxial cable, and includes a sheath pattern portion 51 ′ and a core pattern portion 52 ′ corresponding to the sheath conductor 51 and the core wire 52 of the coaxial cable 50.
Is set equal to the characteristic impedance of the coaxial cable 50 to achieve matching, and the core wire pattern 52 ′ is
By sandwiching from both sides with 1 ', the configuration is such that the external space is shielded to some extent. Both ends 51'a, 51'b of the outer skin pattern portion 51 'are electrically connected by metal fittings 51'c. The entire current detection coil is made thin by using a surface mount component as its load resistor 4. Further, the outer skin pattern portion 51 'on the coil piece 3a side has a square-shaped closed loop pattern. The outer skin pattern portion 51 'on the coil piece 3b side is formed in a U-shaped open loop pattern, but is closed when both ends are short-circuited via a jumper wire connected to the hole s. It is also possible to short-circuit the electrodes of the load resistor 4 using surface mount components instead of the jumper wires.

FIG. 15 shows an outer conductor pattern 51 'and a core pattern 52' corresponding to the outer conductor 51 and the core 52 of the coaxial cable 50 using a double-sided flexible board.
It is a development view of a current detection coil that has a strip line configuration and further improves the shielding performance with the external space,
FIG. 15A shows the inner surface pattern of the double-sided flexible substrate, and FIG. 15B shows the outer surface pattern. The end portions 51'b, 51'b 'and the central portions 51'd, 51'd' of the outer skin pattern portion 51 'are connected to each other through through holes so as to have the same potential. The outer conductor at the end of the coaxial cable (not shown) is electrically connected to both ends 51'a 'and 51'b' of the outer pattern portion 51 'by soldering or the like.
2 is electrically connected to the end of the core pattern portion 52 'by soldering or the like, thereby forming a current detection coil.

FIG. 16 is a perspective view showing another structural example of the current detecting device according to the present invention, FIG. 17 is a partial sectional view of the current detecting device shown in FIG. 16, and FIG. 18 is a current detecting device shown in FIG. 3 is an electrical equivalent circuit diagram of FIG. Another current detecting device 11 according to the present invention forms a loop-shaped closed magnetic path 12 by closely attaching a U-shaped core piece 12a in a side view and an I-shaped core piece 12b in a side view. -Shaped core piece 12a
A coil 13 for current detection is formed by winding a conductor such as a copper foil around the coil, a chip resistor is connected as a load resistor 14 to both ends of the coil 13 for current detection, and a voltage generated at both ends of the load resistor 14 is formed. Is output to the output line 15 via a common mode choke coil 15a fixed to the outside of the U-shaped core piece 12a in a side view.

By adopting the structure shown in FIGS. 16 and 17, the current detecting device 11 can be reduced in size and thickness, including the current detecting coil 14, and can have a robust structure. A structure in which the current detection coil 14 is formed using a conductor such as a copper foil is referred to as a simple coil method.

FIG. 19 is a perspective view showing the external appearance of a current detecting device in which a normal mode current and a common mode current of a pair of lines to be measured can be detected by switching with a switch.
20 is an explanatory diagram showing a structure of a current detection coil of the current detection device shown in FIG. Current detection device 2 shown in FIG.
1 forms two sets of closed magnetic paths 22 by closely adhering an I-shaped core piece 22a and an E-shaped core piece 22b, corresponding to each closed magnetic path 22 of the I-shaped core piece 22a. Current detection coils 23A and 23B are provided. Further, a switch 26 for switching a current measurement mode is attached to an I-shaped core piece 22a, and a switch mounting box 27 containing a load resistor 24 is fixed. A voltage output corresponding to a measured current generated at the end of the load resistor 24 (FIG. 23) is taken out from an output line 25 formed by using a coaxial cable via a common mode choke filter 25a attached to a mounting box 27. is there.

The outer peripheral side of the I-shaped core piece 22a is covered with a plastics cover 28a, and the outer peripheral side of the E-shaped core piece 22b is covered with a plastics cover 28b. The covers 28a and 28b are connected to each other so as to be freely opened and closed by a joint 28c. And both covers 28
The core surfaces of the respective core pieces 22a and 22b are stably in contact with each other to form the respective closed magnetic paths in a state in which the a and b are fixed by the closing stoppers 28d.

The coils 23A and 23B for current detection are
As shown in FIG. 20 (explanatory view excluding the switch mounting box and the cover made of plastics), it is provided for each magnetic path. Symbol a is one end of one coil 23A, symbol a 'is the other end of one coil 23A, symbol b is one end of the other coil 23B, and symbol b' is the other end of the other coil 23B.

FIG. 21 is a schematic explanatory view showing a connection state between each coil and a load resistor in each current measurement mode. When measuring the common mode current, the other end a 'of one coil 23A is connected to one end b of the other coil 23B, and one end a of one coil 23A is connected to the other coil 23A.
A load resistor 24 is connected to the other end b ′ of B.

Since the currents reciprocating on the pair of measured lines L1 and L2 have different current directions, one of the measured lines L1 and L2 has a different direction.
The polarity of the voltage induced in one coil 23A by the current flowing in 1 and the polarity of the voltage induced in the other coil 23B by the current flowing in the other measured line L2 are opposite to each other. Therefore, one of the coils 23A
The two coils are connected in series such that the polarity of the voltage induced on the other coil 23B is opposite to that of the voltage induced on the other coil 23B. Canceled. When there is a current component flowing in a pair of the measured lines L1 and L2 in one direction, the voltages induced in the coils 23A and 23B are added in accordance with the current and generated in the load resistor 24. Therefore, a voltage output according to the common mode current can be obtained from both ends of the load resistor 24.

When measuring the normal mode current, one end a of one coil 23A is connected to one end b of the other coil 23B, and the other end a ′ of one coil 23A is connected.
And the other end b ′ of the other coil 23B.
Connect.

Since the currents reciprocating on the pair of measured lines L1 and L2 have different directions, the current measured on one of the measured lines L1 and L2 is different.
The polarity of the voltage induced in one coil 23A by the current flowing in 1 and the polarity of the voltage induced in the other coil 23B by the current flowing in the other measured line L2 are opposite to each other. Therefore, one of the coils 23A
The two coils are connected in series such that the polarity of the voltage induced on the other coil 23B is the same as the polarity of the voltage induced on the other coil 23B, so that the reciprocating current flowing through the pair of measured lines L1 and L2 (normal mode current ) Can be detected.

When there is a current flowing in one direction through the pair of measured lines L1 and L2, the coils 23A and 23B are connected in series in a direction to cancel the voltage induced in each of the coils 23A and 23B according to the current. Since the connection is made, the current (common mode current) flowing in one direction through the measured lines L1 and L2 is removed. Therefore, the normal mode current can be detected more accurately.

FIG. 22 is a circuit diagram showing a connection state between each coil and a load resistor in each current measurement mode. The switch 26 for switching the current measurement mode has two poles
This is an example in which a slide switch or a snap switch having a contact configuration of (contact) is used.

When the switch 26 for switching the current measurement mode is switched to the common mode current measurement side, one end a of one coil 23A and the load resistance are connected by one contact piece of the switch 26 as shown by a dotted line in FIG. 24, and the other contact piece of the switch 26 connects the other end a 'of one coil 23A and one end b of the other coil 23B. Since the other end b 'of the other coil 23B is connected to the other end of the load resistor 24, a voltage corresponding to the common mode current is generated at both ends of the load resistor 24.

When the switch 26 for switching the current measurement mode is switched to the normal mode current measurement side, as shown by a dotted line in FIG. 22, one contact piece of the switch 26 makes contact with the other end a 'of one coil 23A. A connection is made to one end of the load resistor 24, and one end a of one coil 23A and the other coil 23B are connected by the other contact piece of the switch 26.
Is connected to one end b. Since the other end b 'of the other coil 23B is connected to the other end of the load resistor 24, a voltage corresponding to the normal mode current is generated at both ends of the load resistor 24.

FIG. 23 is an overall circuit diagram of the current detecting device shown in FIG. The induced voltage generated in each of the coils 23A and 23B is supplied to a load resistor 24 via a switch 26 whose circuit configuration is shown in FIG. 22, and a voltage corresponding to a measured current generated across the load resistor 24 is a common mode choke. It is extracted through an output line 25 that is formed of a coaxial cable or the like through a filter 25a.

FIG. 24 is an external perspective view of a current detecting device for detecting a common mode current. The current detecting device 31 for detecting the common mode current shown in FIG.
The common mode current detecting coil 32 and the load resistor 24
I-shaped core assembly for common mode current detection having
3 and an E-shaped core piece 22b. The common mode current detecting coil 32 is configured using a coaxial cable. The connection state of the coil and the connection state between the coil and the load resistor 24 are the same as the connection state of the common mode in FIG.

FIG. 25 is an external perspective view of a current detecting device for detecting a normal mode current. The current detection device 41 for normal mode current detection shown in FIG.
A normal mode current detecting I-shaped core assembly 43 having a normal mode current detecting coil 42 and a load resistor 24 in 2a, and an E-shaped core piece 22b. The coil 42 for normal mode current detection is configured using a coaxial cable. The connection state of the coil and the connection state between the coil and the load resistor 24 are the same as the connection state in the normal mode in FIG.

As shown in FIGS. 24 and 25, by preparing I-shaped core assemblies 33 and 43 in accordance with the current measurement mode, the E-shaped core piece 22b is made common, and the E-shaped core piece 22b is formed. By selecting the type of the I-shaped core assemblies 33 and 43 to be in close contact with the core piece 22b, it is possible to switch between the measurement of the common mode current and the measurement of the normal mode current.

FIG. 26 is an explanatory view showing a structure for regulating the winding position of the current detecting coil and the arrangement position of the line to be measured. When the winding position of the coil 3 for current detection moves, there is a possibility that the measurement result may fluctuate. Therefore, FIG.
As shown in (1), a groove 61 for winding the coil 3 for current detection may be formed on the outer peripheral side of the one core piece 2b to regulate the winding position of the coil 3. Also, FIG.
As shown in (b), a groove 62 for winding the coil 3 for current detection is formed on the inner peripheral side of the I-shaped core piece 12b.
The winding position of the coil 3 may be regulated. Furthermore, a groove is formed on both the outer peripheral side and the inner peripheral side of the core piece,
The winding position of the coil 3 may be regulated.

Also, when the positions of the lines to be measured L1 and L2 are moved, there is a possibility that the measurement results may fluctuate. Therefore,
As shown in FIG. 26 (a), a line-to-be-measured L1 and L2 penetrating through a closed magnetic circuit is provided on the inner peripheral side of one of the core pieces 2b with a position-regulating member P made of a sponge or the like to be measured.
May be restricted from approaching the current detecting coil 3 side. Further, as shown in FIG. 26B, a rail-shaped measured line arrangement position regulating member P for regulating the arrangement position of the pair of measured lines L1 and L2 on the inner peripheral side of the U-shaped core piece 12a. May be provided to regulate the arrangement position of the pair of measured lines L1 and L2.

FIG. 27 is a perspective view showing a specific example of an openable / closable clamp structure. As shown in FIG. 27A, a pair of core pieces 2a and 2b constituting a closed magnetic circuit may be opened and closed at a substantially central portion of the closed magnetic circuit, or as shown in FIG. 27B. One end may be opened and closed.

FIG. 28 is a perspective view showing a specific example of a slide type clamp structure, FIG. 29 is a side view showing a clamp state of the slide type clamp structure, and FIG. 30 is a non-clamp state of the slide type clamp structure. It is a side view. FIG.
As shown in FIGS. 8 to 30, by operating the slide knob K, the I-shaped core piece 12b may be slid into the holder M attached to the side surface of the U-shaped core piece 12a.

FIG. 31 shows an example of a configuration in which the outer periphery of the current detecting device shown in FIG. 4 is covered with a metal conductor to shield an external high-frequency electromagnetic field.

In FIG. 31, metal conductors 70-a,
70-b is electrically connected via the movable part 70-c. Further, the stopper 6d 'is connected to the metal conductor 70-a,
It has a contact portion for electrically connecting 70-b, and as a whole, constitutes a short ring of one circumference, thereby enhancing the shielding effect. By doing so, the leakage of the internal magnetic field can be prevented at the same time as the shielding of the high-frequency electromagnetic field from the outside, and the coupling between the current detection coil and the measured line can be strengthened. Furthermore, the metal conductor 70-a and the coaxial cable 50
And the outer conductor 51 are integrally connected by soldering or the like, thereby reducing the self-inductance of the current detection coil and improving the high-frequency characteristics.

In FIG. 31, the metal conductors 70-a and 70-a
-B, the metal conductor 70
The above effect can be obtained only with -a.

[0067]

As described above, in the current detection device according to the present invention, the load resistance is reduced as far as the detection sensitivity permits, the current conversion coefficient is made constant over a wide band, and the current generated at the load resistance end. A voltage corresponding to the measured current is taken out via a shielded output line, and the shield conductor of the output line is used as a part of the current detection coil. As a result, a current detection output (a voltage corresponding to the measured current) can be taken out without maintaining a constant current conversion coefficient and without being affected by noise such as unnecessary components and interference waves.

Further, in the current detecting device according to the present invention,
Because the load resistance is reduced as much as the detection sensitivity allows, the current conversion coefficient is kept constant over a wide band, and a voltage corresponding to the measured current generated at the load resistance end is taken out through a common mode choke filter. In addition, a constant current conversion coefficient can be maintained over a wide band with almost no influence on the line to be measured, and a current detection output can be taken out without being affected by noise such as unnecessary components and interference waves.

Further, the current detecting device according to the present invention
Since the switch for switching the measurement mode is provided, the connection state for measuring the common mode current and the connection state for measuring the normal mode current can be easily switched.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a current detection device according to the present invention.

FIG. 2 is a graph showing a frequency characteristic of a current conversion coefficient of the current detection device according to the present invention.

FIG. 3 is a principle configuration diagram of a device for evaluating a frequency characteristic of a current conversion coefficient of the current detection device according to the present invention.

FIG. 4 is a perspective view (with an annular core opened) showing a specific structural example of the current detection device according to the present invention.

FIG. 5 is a perspective view showing a current measurement state of a line to be measured by the current detection device shown in FIG.

6 is a cross-sectional view of the current measurement state shown in FIG.

FIG. 7 is an explanatory diagram showing a connection structure between a coil structure for current detection and a load resistor.

FIG. 8 is a sectional view showing a specific example of a common mode choke filter.

FIG. 9 is an explanatory diagram when detecting a current in one of a pair of lines to be measured.

FIG. 10 is an explanatory diagram showing a structure when a current detection coil has two turns in a coaxial detection method.

FIG. 11 is an explanatory diagram showing a structure of a current detecting coil when a load resistor is arranged on a side end surface of an annular core.

FIG. 12 is an explanatory diagram showing the structure of a current detecting coil when a load resistor is arranged on the outer peripheral surface of an annular core.

FIG. 13 is an explanatory view showing the structure of a detection coil formed using a single-sided flexible substrate.

FIG. 14 is a development view of a single-sided flexible substrate forming the detection coil shown in FIG.

FIG. 15 is a developed view of a detection coil configured using a double-sided flexible substrate.

FIG. 16 is a perspective view showing another example of the structure of the current detection device according to the present invention.

FIG. 17 is a partial cross-sectional view of the current detection device shown in FIG.

18 is an electrical equivalent circuit diagram of the current detection device shown in FIG.

FIG. 19 is an external perspective view of a current detection device that can detect a normal mode current and a common mode current of a pair of measured lines by switching with a switch.

20 is an explanatory diagram showing a structure of a current detecting coil of the current detecting device shown in FIG.

FIG. 21 is a schematic explanatory view showing a connection state between each coil and a load resistor in each current measurement mode.

FIG. 22 is a circuit diagram showing a connection state between each coil and a load resistor in each current measurement mode.

FIG. 23 is an overall circuit diagram of the current detection device shown in FIG.

FIG. 24 is an external perspective view of a current detection device for detecting a common mode current.

FIG. 25 is an external perspective view of a current detection device for normal mode current detection.

FIG. 26 is an explanatory view showing a structure for restricting a winding position of a current detection coil and an arrangement position of a line to be measured.

FIG. 27 is a perspective view showing a specific example of an openable / closable clamp structure.

FIG. 28 is a perspective view showing a specific example of a slide-type clamp structure.

FIG. 29 is a side view showing a clamped state of the slide type clamp structure.

FIG. 30 is a side view showing a non-clamp state of the slide-type clamp structure.

FIG. 31 is a perspective view showing a specific example of a current detection device having a structure in which the outer periphery is shielded by a metal conductor.

[Explanation of symbols]

1, 11, 31, 41 Current detecting device, 2a, 2b, 1
2a, 12b, 22a, 22b Core pieces, 3, 13, 2
3A, 23B, 32, 42 Current detection coil, 4,
14, 24 load resistance, 5, 15, 25 output line, 5
a, 15a, 25a common mode choke filter,
26 Current measurement mode switching switch, 50 coaxial cable, 51 coaxial cable outer conductor, 52 coaxial cable core

Claims (12)

[Claims] A magnetic path formed in a ring shape and divided so as to be clampable; a current detection coil wound around the magnetic path; a load resistance connected to both ends of the current detection coil; And a shielded output line for extracting a voltage generated in the load resistance, wherein a part of the current detection coil is formed by a shield conductor of the output line. 2. The current detection device according to claim 1, wherein said output line is constituted by a coaxial cable. 3. The current detecting device according to claim 1, wherein an outer periphery of said magnetic path is shielded by a conductive metal. 4. The current detection device according to claim 2, wherein an outer periphery of said magnetic path is shielded by a conductive metal. 5. A magnetic path formed in a ring shape and divided so as to be clampable, a current detecting coil wound around the magnetic path, a load resistance connected to both ends of the current detecting coil, and a common. An output line having a mode choke filter, wherein a voltage generated in the load resistance is taken out through the output line. 6. The current detection device according to claim 5, wherein the output line is formed of a coaxial cable, and a part of the current detection coil is formed using an outer conductor of the coaxial cable. . 7. The current detecting device according to claim 5, wherein said output line is formed of a coaxial cable, and said common mode choke filter is formed by penetrating or winding a coaxial cable around a ferrite ring core. 8. The current detecting device according to claim 5, wherein an outer periphery of said magnetic path is shielded by a conductive metal. 9. The current detecting device according to claim 6, wherein an outer periphery of said magnetic path is shielded by a conductive metal. 10. The current detecting device according to claim 7, wherein an outer periphery of said magnetic path is shielded by a conductive metal. 11. A current transformer comprising a magnetic path formed in a ring shape and divided into a clampable part and a current detection coil wound on the magnetic path is provided adjacent to each other, and two sets of current transformers are provided adjacent to each other. One end of the current detection coil and the other end of the other current detection coil are connected, and a load resistor is connected between the other end of one current detection coil and one end of the other current detection coil. The connection state for common mode current measurement, the other end of one current detection coil and the other end of the other current detection coil are connected, and one end of one current detection coil and the other current detection A switch for measuring mode switching to switch between a normal mode current measurement connection state and a load resistance connected to one end of the load coil, and a common mode choke filter for the voltage generated at both ends of the load resistance A current detecting device for extracting the electric current through the output line. 12. The current detecting device according to claim 11, wherein an outer periphery of said magnetic path is shielded by a conductive metal.