Current measuring device and current measuring method

Abstract

This reduces the effects of magnetic saturation in magnetic shielding and allows for accurate measurement of the current flowing through the conductor under test. [Solution] The current measuring device comprises a magnetic shield having a notch for taking in a magnetic field generated by a current flowing through a conductor to be measured into its internal space; a sensor disposed in the internal space of the magnetic shield and outputting a voltage corresponding to the magnetic field at that position; and a circuit unit for detecting the current flowing through the conductor to be measured based on the voltage output from the sensor, wherein the magnetic shield has at least one of a first correction unit that corrects the effect of magnetic flux density saturation of the magnetic shield on the voltage output from the sensor, or a second correction unit that corrects the voltage output from the sensor so as to reduce the effect of magnetic flux density saturation of the magnetic shield.

Description

Technical Field

[0001] The present disclosure relates to a current measuring device and a current measuring method.

Background Art

[0002] There is a current measuring device that measures a magnetic field generated from a current flowing through a conductor to be measured and measures the current flowing through the conductor to be measured from the measured magnetic field.

[0003] Among such current measuring devices, there is a current measuring device having a substantially U-shaped magnetic shield in a sensor head, installing a conductor to be measured in a notch portion of the magnetic shield, and providing a magnetic sensor in an internal space of the magnetic shield.

[0004] In such a current measuring device, the magnetic sensor measures a magnetic field generated by a current flowing through the conductor to be measured, and measures the current flowing through the conductor to be measured based on the measured magnetic field.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the current measuring device described in Patent Document 1, since the magnetic sensor is housed in the internal space of a hollow magnetic shield with a notch, when a large current flows through the conductor under test, the magnetic flux density of the magnetic shield saturates, causing the magnetic flux density that the magnetic sensor is sensitive to to no longer be proportional to the current. This can lead to disturbances in the measurement values, and in some cases, it may not be possible to accurately measure the current flowing through the conductor under test.

[0007] This disclosure has been made in view of the above circumstances and provides a current measuring device that reduces the effect of magnetic flux density saturation of a magnetic shield and accurately measures the current flowing through a conductor under measurement. [Means for solving the problem]

[0008] The current measuring device of the present disclosure comprises: a magnetic shield having a notch for taking in a magnetic field generated by a current flowing through a conductor to be measured into an internal space; a sensor disposed in the internal space of the magnetic shield and outputting a voltage corresponding to the magnetic field at that position; and a circuit unit for detecting a current flowing through the conductor to be measured based on the voltage output from the sensor, wherein the magnetic shield has at least one first correction unit that corrects the effect of magnetic flux density saturation of the magnetic shield on the voltage output from the sensor, or the magnetic shield or the circuit unit corrects the voltage output from the sensor so as to reduce the effect of magnetic flux density saturation of the magnetic shield. [Effects of the Invention]

[0009] One embodiment of the current measuring device reduces the effect of magnetic saturation of the magnetic shield, and by reducing hysteresis and improving linearity, it can accurately measure the current flowing through the conductor under test. [Brief explanation of the drawing]

[0010] [Figure 1] This is a diagram illustrating the overview of a current measuring device according to an embodiment. [Figure 2] This figure shows the external appearance of the current measuring device according to the first embodiment. [Figure 3] This figure illustrates a cross-section of the sensor head in the current measuring device according to the first embodiment, viewed in the front-to-back direction perpendicular to the direction perpendicular to the extension direction of the conductor to be measured. [Figure 4] This figure shows the magnetic shield in the current measuring device according to the first embodiment. [Figure 5] This figure shows a magnetic shield of a first modified example in a current measuring device according to the first embodiment. [Figure 6] This figure shows a short-circuit winding wound around a magnetic shield in a second modified example of the current measuring device according to the first embodiment. [Figure 7] This figure shows the magnetic flux density before and after correction by the short-circuit winding of the current measuring device according to the first embodiment. [Figure 8] This is a diagram illustrating the overview of the current measuring device according to the second embodiment. [Figure 9] This diagram shows the relationship between the voltage detected by a magnetic sensor and the current flowing through the conductor being measured. [Figure 10] This figure shows an example of the pass-through characteristics of a correction circuit. [Figure 11] This figure shows a curve representing the voltage measurement value before correction and a curve representing the voltage measurement value after correction of the current measuring device according to the second embodiment. [Figure 12] This figure shows the circuit configuration of the circuit section of the current measuring device according to the third embodiment. [Figure 13] This is a flowchart illustrating the operation of the current measuring device according to the third embodiment. [Figure 14] This figure shows the configuration of the current measuring device according to the fourth embodiment. [Figure 15] This figure shows a magnetic shield in a first modified example of the current measuring device according to the fourth embodiment. [Figure 16] This is a diagram illustrating the magnetic shield of a current measuring device according to the fifth embodiment. [Figure 17] This figure shows the differences in the cross-sectional area of ​​the lower part of the magnetic shield and the cross-sectional areas of the right side, left side, and upper part in the current measuring device according to the fifth embodiment. [Figure 18] It is a diagram for explaining a first modification example of a magnetic shield in a current measuring device according to the fifth embodiment. [Figure 19] It is a block diagram showing a main configuration of a current measuring device according to the sixth embodiment. [Figure 20] It is a cross-sectional view of a magnetic shield of a sensor head included in a current measuring device according to the seventh embodiment.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0012] <1. Overview of Embodiments> <1.1. Regarding Coreless Current Sensors> In the technical field of vehicles, in order to measure the current flowing through a bus bar, it has been conventionally practiced to provide a magnetic sensor for the bus bar and provide a magnetic shield around this magnetic sensor.

[0013]

[0014] For example, Japanese Patent Application Laid-Open No. 2019-184355 (Patent Document 2) discloses a current measuring device including a magnetic detection element that detects a magnetic field generated from a current path, a shield plate disposed around the magnetic detection element, etc. (Summary of Patent Document 2, FIGS. 2, FIGS. 3, etc.). As magnetic sensors of coreless magnetic detection elements, a Hall element, a magnetoresistive element, and a Hall IC are exemplified (paragraph 0031 of Patent Document 2).

[0015] ​The current measuring devices disclosed in Patent Documents 2 and 3 are intended to be attached to the busbar of a vehicle and used continuously. For example, Patent Document 2 describes an electric vehicle equipped with a coreless current measuring device at the beginning of its embodiment (paragraph 0014, Figure 1, etc., of Patent Document 2). Patent Document 3 describes at the beginning of its embodiment that the current sensor is provided in the internal space of an inverter mounted on an electric vehicle (paragraph 0012, Figure 1, etc., of Patent Document 3). Furthermore, claim 1 of Patent Document 3 specifies the configuration including the busbar as the current sensor.

[0016] The current measuring device of this embodiment is a current sensor that can be attached to and detached from a current cable including a busbar, and examples of such current sensors include those described in Japanese Patent Application Publication No. 2022-29714 (Patent Document 1) and Japanese Patent Application Publication No. 2013-200301 (Patent Document 4).

[0017] Patent documents 1 and 4 disclose a current measuring device in which an electric wire is passed through a notch in a magnetic shield and a magnetic sensor is placed inside the magnetic shield (Figure 3 of Patent Document 1, abstract of Patent Document 4, etc.). However, the current measuring devices disclosed in Patent Documents 1 and 4 do not disclose how to reduce the effect of magnetic flux density saturation of the magnetic shield and how to accurately measure the current flowing through the conductor to be measured.

[0018] <1.2. Overview of Embodiments> Next, an overview of the current measuring device of this embodiment will be described. The current measuring device of this embodiment reduces the effect of magnetic flux density saturation of the magnetic shield, thereby obtaining accurate current measurement values ​​by reducing hysteresis and improving linearity.

[0019] Figure 1 is a diagram illustrating the outline of a current measuring device 1 according to an embodiment. As shown in Figure 1, the current measuring device 1 has a sensor head 11 and a circuit unit 12. Note that the sensor head 11 and the circuit unit 12 do not need to be separate and may be integrated.

[0020] The sensor head 11 has a magnetic shield 13. The magnetic shield 13 has a magnetic sensor 14 and a first correction unit A. The magnetic sensor 14 is located in the internal space of the magnetic shield 13 and outputs a voltage corresponding to the DC magnetic field and low-frequency AC magnetic field generated by the current flowing through the conductor under test. The magnetic sensor 14 may output current instead of voltage. Unless otherwise specified, the current flowing through the conductor under test is assumed to be AC ​​current.

[0021] The first correction unit A corrects the magnetic field measured by the magnetic sensor 14 to reduce the effect of magnetic flux density saturation of the magnetic shield 13. Specifically, the first correction unit A may generate a magnetic field within the wall of the magnetic shield 13 in the opposite direction to the magnetic field generated by the current flowing through the conductor under test, thereby correcting the effect of magnetic flux density saturation of the magnetic shield 13. The first correction unit A is provided when correction is performed on the magnetic shield 13 side, and may not be provided when correction is not performed on the magnetic shield 13 side.

[0022] When the first correction unit A is provided on the magnetic shield 13, the first correction unit A corrects the voltage corresponding to the magnetic field detected by the magnetic sensor 14 and outputs the corrected voltage to the circuit unit 12.

[0023] The circuit unit 12 measures the current flowing through the conductor under test based on the voltage corresponding to the magnetic field output from the magnetic sensor 14, and outputs or displays the measurement result externally.

[0024] On the other hand, as shown in Figure 8, in this embodiment, the correction of the voltage of the magnetic field detected by the magnetic sensor 14 may be performed by the circuit unit 12. The circuit unit 12 has a second correction unit B that performs calculations on the voltage corresponding to the magnetic field inside the wall of the magnetic shield 13 detected by the magnetic sensor 14. The second correction unit B corrects the voltage corresponding to the magnetic field detected by the magnetic sensor 14 to reduce the effect of magnetic flux density saturation of the magnetic shield 13. The method of this correction on the circuit unit 12 side will be explained in the embodiment described later.

[0025] In the following first to seventh embodiments, the correction performed by the first correction unit A on the magnetic shield 13 side and the correction performed by the second correction unit B on the circuit unit 12 side are performed by either one or the other; however, the correction may be performed on both the magnetic shield 13 side and the circuit unit 12 side. Furthermore, the second correction unit B may be provided on the magnetic shield 13 side and integrated with the first correction unit A. In this case, the second correction unit B may further correct the voltage corrected by the first correction unit A so as to reduce the effect of magnetic flux density saturation of the magnetic shield 13.

[0026] In this way, the current measuring device 1 of the embodiment can accurately detect the value of the current flowing through the conductor to be measured, taking into account the effect of magnetic flux density saturation of the magnetic shield 13.

[0027] Next, the current measuring device 1 of the first embodiment to the current measuring device 1 of the seventh embodiment will be described.

[0028] <2. First Embodiment> The current measuring device 1 of the first embodiment will now be described. The current measuring device 1 of the first embodiment suppresses magnetic flux density saturation on the magnetic shield 13 side and accurately detects the current flowing through the conductor to be measured.

[0029] <2.1. Structure> Figure 2 shows the external appearance of the current measuring device 1 according to the first embodiment. As shown in Figure 2, the current measuring device 1 has a sensor head 11 and a circuit section 12 connected to the sensor head 11 via a cable CB.

[0030] The sensor head 11 is a component for electrically detecting the current I flowing through the conductor MC under test in a non-contact manner. This sensor head 11 is, so to speak, used as a probe for electrically detecting the current I flowing through the conductor MC under test in a non-contact manner. Furthermore, it is desirable that the sensor head 11 be as miniaturized as possible to enable detection of the current I even in situations where the space around the conductor MC under test is limited.

[0031] As shown in Figure 2, the sensor head 11 is fixedly positioned relative to the conductor MC when detecting the current I flowing through the conductor MC. The sensor head 11 has a roughly U-shape with a notch 20 formed at the bottom of its rectangular shape. The conductor MC is inserted through the notch 20, and a fixing mechanism 21 is provided to fix the conductor MC in place. The fixing mechanism 21 has a structure that uniquely determines the positional relationship between the center of the conductor MC and the magnetic sensor 14, regardless of the diameter of the conductor MC. In other words, the sensor head 11 is in physical contact with the conductor MC by the fixing mechanism 21. However, the sensor head 11 is electrically insulated from the conductor MC, and the current I flowing through the conductor MC can be measured non-contact. A cable CB, which connects to the circuit unit 12, is also connected to the sensor head 11.

[0032] The circuit unit 12 measures the current I flowing through the conductor MC to be measured based on the voltage output from the sensor head 11 and displays the measurement result. The circuit unit 12 outputs or displays the measurement result of the current I to the outside. The detection result may be a voltage signal, and the voltage signal may be the voltage from the sensor head 11 itself, or it may be the voltage after processing by the circuit (e.g., amplification). Any cable CB can be used to connect the sensor head 11 and the circuit unit 12. The cable CB is preferably flexible, easy to handle, and resistant to breakage.

[0033] Figure 3 is a diagram illustrating a cross-section of the sensor head 11 in the current measuring device 1 according to the first embodiment, viewed in the front-to-back direction perpendicular to the extension direction of the conductor MC to be measured. In Figure 3, the X-axis direction is the vertical direction of the sensor head 11, the Y-axis direction is the left-to-right direction of the sensor head 11, and the Z-axis direction is the front-to-back direction of the sensor head 11.

[0034] As shown in Figure 3, the sensor head 11 has a substantially rectangular cross-section in the XY direction and a notch 20 at the lower part in the X-axis direction, which is provided so that a portion of the conductor MC to be measured is positioned in the internal space of the magnetic shield 13.

[0035] A fixing mechanism 21 is provided in the notch 20 of the sensor head 11, which is located in the X-axis downward direction of the magnetic shield 13 and fixes a portion of the conductor MC to be measured that extends in the Z-axis direction. The fixing mechanism 21 fixes the sensor head 11 to the conductor MC to be measured so that the distance between the center of the conductor MC inserted into the notch of the magnetic shield 13 and the magnetic sensor 14 becomes a predetermined reference distance (r).

[0036] The magnetic shield 13 is provided on the sensor head 11 so as to cover the fixing mechanism 21 and a portion of the conductor MC to be measured. A magnetic sensor 14 is provided in the internal space of the magnetic shield 13, in close proximity to the conductor MC to be measured.

[0037] The magnetic shield 13, like the sensor head 11, has a notch 20. The conductor to be measured MC is inserted through the notch 20. The conductor to be measured MC is fixed to the magnetic shield 13 by a fixing mechanism 21.

[0038] The magnetic sensor 14 can be used with the best sensitivity when the center of its magnetic sensing surface is positioned on the X-axis passing through the center of the conductor MC to be measured, on the XY plane which includes the center of the thickness of the magnetic shield 13 in the z-axis direction, and the direction of the magnetic sensing surface of the magnetic sensor 14 coincides with the direction tangent to the conductor MC to be measured, i.e., the Y-axis direction. Among these positions, the closer the magnetic sensor 14 is positioned to the notch 20, the stronger the magnetic field generated by the current to be measured becomes, which is advantageous for measurement. In other words, the magnetic shield 13 has a roughly U-shaped cross-section in the XY plane, and the conductor MC to be measured is fixed to the lower center of the magnetic shield 13 (the tip of the roughly U-shape) by the fixing mechanism 21. The magnetic sensor 14 detects the DC magnetic field and low-frequency AC magnetic field at that position in the internal space of the magnetic shield 13.

[0039] The magnetic sensor 14 is positioned close to the conductor MC to be measured so as to be able to detect the magnetic field generated by the current flowing through the conductor MC. The magnetic sensor 14 has, for example, a coil for high-frequency detection and a Hall element for low-frequency detection, but it may be a sensor with other configurations. The voltage corresponding to the magnetic field measured by the magnetic sensor 14 is output to the circuit section 12 through the cable CB.

[0040] Figure 4 shows a magnetic shield 13 in a current measuring device 1 according to the first embodiment. The magnetic shield 13 captures a portion of the magnetic field generated by the current flowing through the conductor MC under measurement into its walls. The magnetic shield 13 is box-shaped, with a cross-section in the XY direction that is approximately U-shaped, and has a right side 13r, a left side 13l, an upper part 13u, and a lower part 13d. In other words, the magnetic shield 13 has walls that define the internal space. The walls of the magnetic shield 13 include side walls that extend along the extending direction of the conductor MC under measurement. In other words, the magnetic shield 13 is a hollow box shape with internal space. The walls extend so that the magnetic shield 13 has an approximately U-shape when viewed from the front.

[0041] As shown in Figure 4, a short-circuit winding 31, wound once, is wound around a portion of the magnetic shield 13. Specifically, as shown in Figure 4, the short-circuit winding 31 is wound around the magnetic shield 13. The short-circuit winding 31 may be wound anywhere on the magnetic shield 13. Specifically, the short-circuit winding 31 is wound once around the wall of the right side 13r of the magnetic shield 13 so as to pass through the internal space. The short-circuit winding 31 is also wound around a portion of the wall so as to extend in a direction intersecting the extending direction of the wall of the magnetic shield 13. The short-circuit winding 31 is wound in a continuous ring shape around the wall of the magnetic shield 13 so as to pass through the internal space and is electrically short-circuited.

[0042] When the magnetic field generated by the current flowing through the conductor MC under measurement reaches magnetic flux saturation within the magnetic shield 13, no further magnetic flux is input into the magnetic shield 13. Consequently, the magnetic field input to the magnetic sensor 14 increases, affecting the current measurement.

[0043] On the other hand, in the current measuring device 1 according to the first embodiment, as shown in Figure 4, the magnetic flux generated within the wall of the magnetic shield 13 is electromagnetically coupled to the short-circuit winding 31. As the short-circuit winding 31 is short-circuited, a short-circuit current Ic flows according to Lenz's law to cancel out the magnetic flux generated within the magnetic shield 13.

[0044] Therefore, according to the current measuring device 1 of the first embodiment, the short-circuit winding 31 cancels out the magnetic field generated in the magnetic shield 13, which has the effect of making magnetic saturation less likely to occur, and the magnetic sensor 14 can measure with improved performance in terms of the influence of magnetic flux density saturation in the magnetic shield 13.

[0045] <First variation> Next, a first modified example of the current measuring device 1 according to the first embodiment will be described. The short-circuit winding 31 may consist of multiple short-circuit windings. Figure 5 shows a magnetic shield 13 of the first modified example in the current measuring device 1 according to the first embodiment. As shown in Figure 5, a short-circuit winding 31a is wound once on the right side 13r of the magnetic shield 13 of the first modified example in the current measuring device 1 according to the first embodiment, and a short-circuit winding 31b is wound once on the left side 13l. The short-circuit windings 31a and 31b are each wound in a ring shape without breaks so as to pass through the internal space of the wall of the magnetic shield 13 and are electrically short-circuited.

[0046] In this way, by winding the short-circuit windings 31a and 31b around the magnetic shield 13, short-circuit currents flow in the direction that cancels out the magnetic flux, respectively, according to Lenz's law. These short-circuit currents are distributed between the respective short-circuit windings 31a and 31b, and in this case, they are halved.

[0047] Therefore, by using multiple short-circuit windings 31a and 31b, the short-circuit current is halved compared to using a single short-circuit winding, allowing the use of a thinner short-circuit winding. Furthermore, since the multiple short-circuit windings 31a and 31b can be placed in different locations (for example, the upper 13u and lower 13d), the magnetic field generated in the magnetic shield 13 can be precisely controlled.

[0048] <Second variation> Next, a second modified example of the current measuring device 1 according to the first embodiment will be described. The short-circuit winding 31 may be a short-circuit winding wound multiple times around the magnetic shield 13. Figure 6 shows the state of the short-circuit winding 31 wound multiple times around the magnetic shield 13 in the second modified example of the current measuring device 1 according to the first embodiment. As shown in Figure 6, in the second modified example of the current measuring device 1 according to the first embodiment, the short-circuit winding 31 is wound multiple times around the magnetic shield 13, and the beginning and end of the winding are electrically short-circuited. By using a short-circuit winding 31 wound multiple times around the magnetic shield 13 in this way, the short-circuit current is reduced compared to the case where the short-circuit winding 31 is wound once around the magnetic shield 13, and a thinner short-circuit winding can be used for the short-circuit winding 31.

[0049] Figure 6 shows the state in which the signal line / power supply wiring 15 is inserted into the right side of the magnetic shield 13. This signal line / power supply wiring 15 includes a signal line for the voltage measured by the magnetic sensor 14 of the sensor head 11 and a power supply line for the power supplied to the sensor head.

[0050] <2.2. Operation> Next, the operation of the current measuring device 1 according to the first embodiment will be described. When current flows through the conductor MC under measurement and a magnetic field is generated inside the magnetic shield 13, a portion of the magnetic field generates a magnetic field with magnetic flux density Bs inside the wall of the magnetic shield 13. Then, since the short-circuit winding 31 (or short-circuit windings 31a and 31b) is short-circuited, according to Lenz's law, a current Ic flows in a direction that opposes the generation of the magnetic field. As a result, the magnetic flux decreases, and the effect of reducing the saturation of the magnetic flux density inside the wall of the magnetic shield 13 occurs.

[0051] Figure 7 shows the magnetic flux density before and after correction by the short-circuit winding 31 of the current measuring device 1 according to the first embodiment. In Figure 7, the dotted line D shows the uncorrected magnetic flux density Bs of the short-circuit winding 31 of the magnetic shield 13. The solid line E shows the corrected magnetic flux density (Bs + Bc) of the short-circuit winding 31 of the magnetic shield 13. The horizontal axis H is the magnetic field corresponding to the current flowing through the conductor MC under measurement.

[0052] As shown in Figure 7, the solid line E representing the corrected magnetic flux density (Bs + Bc) of the winding 31 of the magnetic shield 13 is more linear than the dotted line D representing the uncorrected magnetic flux density Bs of the winding 31 of the magnetic shield 13. Therefore, by correcting the magnetic flux density within the wall of the magnetic shield 13, the magnetic flux density within the wall of the magnetic shield 13 can be suppressed to below the magnetic flux saturation density, allowing the use of magnetic material in the linear region of the BH curve.

[0053] The voltage of the magnetic field of the current I flowing through the conductor MC under test is detected by the magnetic sensor 14. However, when the magnetic flux within the magnetic shield 13 reaches magnetic flux density saturation, the magnetic flux in the magnetic sensor region begins to increase, and the relationship between the voltage (magnetic field) detected by the magnetic shield magnetic sensor 14 and the current I becomes nonlinear. As a result, the current I cannot be accurately measured by the magnetic sensor 14.

[0054] On the other hand, as in the current measuring device 1 of the first embodiment, when a short-circuit winding 31 is provided on the magnetic shield 13, the short-circuit winding 31 suppresses magnetic saturation within the magnetic shield 13. Therefore, the current measuring device 1 of the first embodiment can make the relationship between the voltage (magnetic field) detected by the magnetic sensor 14 and the current I linear. As a result, the current I can be accurately measured by the magnetic sensor 14.

[0055] <2.3. Effects> Therefore, according to the current measuring device 1 of the first embodiment, the short-circuit winding 31 (or short-circuit windings 31a and 31b) generates a magnetic field in a direction that reduces the magnetic flux density saturation of the magnetic shield 13, so it is less susceptible to the influence of the magnetic flux density saturation of the magnetic shield 13. As a result, the current measuring device 1 of the first embodiment can accurately measure the current flowing through the conductor MC under test.

[0056] Basically, as the volume of a magnetic material increases, it becomes less susceptible to magnetic saturation. Therefore, the thicker the walls of the magnetic shield 13, the higher the magnetic flux saturation density, and the less susceptible the magnetic shield 13 becomes to magnetic saturation. According to the current measuring device 1 of the first embodiment, the effect of magnetic saturation can be reduced, so the wall thickness of the magnetic shield 13 can be made thinner. As a result, the magnetic shield 13 can be made smaller and lighter.

[0057] Furthermore, in the current measuring device 1 of the first embodiment, by using multiple short-circuit windings 31a and 31b or multiple-turn short-circuit windings 31, the magnitude of the current flowing through the short-circuit windings to generate the same magnitude of magnetic field is reduced, so that thinner short-circuit windings (short-circuit windings with low current capacity) can be used.

[0058] <3. Second Embodiment> Next, a current measuring device according to the second embodiment will be described. The current measuring device according to the second embodiment corrects the voltage corresponding to the magnetic field measured by the magnetic sensor 14 in the circuit section 12.

[0059] <3.1. Structure> Figure 8 is a diagram illustrating the overview of the current measuring device 1' according to the second embodiment. As shown in Figure 8, unlike the current measuring device 1 of the first embodiment, the current measuring device 1' according to the second embodiment corrects the analog voltage detected by the magnetic sensor 14 provided on the magnetic shield 13 in the second correction unit B of the circuit unit 12.

[0060] Figure 9 shows the relationship between the voltage Vs detected by the magnetic sensor 14 and the current I flowing through the conductor MC under test. As shown in Figure 9, in the region where the current |I| flowing through the conductor MC under test is small, the voltage |Vs| detected by the magnetic sensor 14 increases proportionally to the current |I|. However, when the current |I| flowing through the conductor MC under test exceeds a certain level, the effect of magnetic saturation of the magnetic shield 13 is detected in the voltage |Vs| by the magnetic sensor 14, and the current |I| flowing through the conductor MC under test and the voltage |Vs| detected by the magnetic sensor 14 are no longer proportional, as shown in the region where the current is large in Figure 9.

[0061] The second correction unit B according to the second embodiment includes a correction circuit B-1 that outputs a corrected voltage when a voltage from the magnetic sensor 14 is input. The correction circuit B-1 has a pass-through characteristic in which the gain when the input voltage is high is smaller than the gain when the input voltage is low. It is desirable that the second correction unit B has characteristics that can correct the characteristics in Figure 9 so that they increase linearly.

[0062] Figure 10 shows an example of the pass-through characteristics of the correction circuit B-1. As shown in Figure 10, when the magnitude of the input voltage |Vin| is small, that is, when it is not affected by the saturation of the magnetic flux density of the magnetic shield 13, the output voltage |Vo| of the correction circuit B-1 has a linear characteristic with respect to the voltage |Vi|. On the other hand, as the voltage |Vin| increases, the gain of the output voltage |Vout| is reduced so that the characteristics in Figure 9 become closer to linear. In other words, the correction circuit B-1 of the second correction unit B according to the second embodiment performs a correction to reduce the gain of the input voltage with respect to the voltage of the magnetic field inside the wall of the magnetic shield 13 measured by the magnetic sensor 14, by utilizing the pass-through characteristics of the circuit unit 12. The correction by the correction circuit B-1 of the second correction unit B is performed so that the voltage measured by the magnetic sensor 14 is not affected by the saturation of the magnetic flux density inside the magnetic shield 13. For example, the correction circuit B-1 of the second correction unit B may output a voltage corresponding to the input voltage output from the magnetic sensor 14. Furthermore, the correction circuit B-1 of the second correction unit B may output a voltage by multiplying the input voltage output from the magnetic sensor 14 by a predetermined gain.

[0063] Figure 11 shows a curve 45 representing the voltage measurement value before correction and a curve 46 representing the voltage measurement value after correction, according to the current measuring device 1' of the second embodiment. As shown in Figure 11, the corrected curve 46 shows a more stable waveform of the measured value compared to the uncorrected curve 45, and the effect of magnetic flux density saturation of the magnetic shield 13 is reduced. In other words, the corrected curve 46 is free from distortion compared to the uncorrected curve 45.

[0064] Furthermore, the correction circuit B-1 of the second correction unit B may output a voltage that has been corrected according to the magnitude of the input voltage output from the magnetic sensor 14. This correction is necessary because the larger the input voltage detected by the magnetic sensor 14, the closer the magnetic shield 13 approaches magnetic flux density saturation. As a result, the difference between the voltage output from the magnetic sensor 14 and the voltage of the current flowing through the conductor MC under test becomes larger, necessitating a correction to increase the gain.

[0065] In the current measuring device 1' of the second embodiment, the case in which the analog voltage measured by the magnetic sensor 14 is corrected was described, but the second correction unit B may also perform correction on the digital voltage converted from the analog voltage measured by the magnetic sensor 14.

[0066] <3.2. Operation> Next, the operation of the current measuring device 1' according to the second embodiment will be described. The magnetic sensor 14 generates a magnetic field due to the current flowing through the conductor MC under measurement. A portion of the generated magnetic field enters the wall of the magnetic shield 13, and a magnetic field with magnetic flux density Bs is generated within the wall of the magnetic shield 13.

[0067] The magnetic sensor 14 measures the voltage corresponding to the magnetic field generated within the magnetic shield 13 and outputs the measured voltage to the circuit unit 12.

[0068] The correction circuit B-1 of the second correction unit B of the circuit unit 12 receives the voltage output from the magnetic sensor 14 and performs correction using the pass-through characteristics of the circuit unit 12.

[0069] <3.3. Effects> Therefore, according to the current measuring device 1' of the second embodiment, the effect of magnetic flux density saturation of the magnetic shield 13 can be reduced without modifying the magnetic shield 13 by correcting the voltage corresponding to the magnetic field measured by the magnetic sensor 14 in the circuit section 12.

[0070] <4. Third Embodiment> Next, a current measuring device according to the third embodiment will be described. Similar to the second embodiment, the current measuring device according to the third embodiment corrects the digital voltage corresponding to the magnetic field measured by the magnetic sensor 14 in the circuit unit 12. Similar to the current measuring device 1' according to the second embodiment, the current measuring device according to the third embodiment corrects the voltage corresponding to the magnetic field measured by the magnetic sensor 14 on the circuit unit 12 side.

[0071] <4.1. Structure> Figure 12 is a diagram showing the circuit configuration of the circuit section 12 of the current measuring device 1'' according to the third embodiment. As shown in Figure 12, the circuit section 12 has a control circuit section 40 and a storage section 41. The control circuit section 40 has an acquisition circuit 42 and a magnetic flux density correction circuit 43. The storage section 41 has a correction value storage section 44.

[0072] The acquisition circuit 42 receives the analog voltage output from the magnetic sensor 14, converts it to a digital voltage, and outputs the converted digital voltage to the magnetic flux density correction circuit 43.

[0073] The magnetic flux density correction circuit 43 corrects the first voltage, which is above the sensor threshold among the acquired voltages, when the voltage acquired by the acquisition circuit 42 exceeds the sensor threshold corresponding to the magnetic flux density saturation value of the magnetic shield 13, by using a correction value corresponding to the first voltage to reduce the gain of the first voltage.

[0074] The correction value storage unit 44 stores a second voltage that is equal to or greater than the sensor threshold, and a correction value corresponding to the second voltage. The magnetic flux density correction circuit 43 corrects the acquired first voltage using the correction value of the second voltage corresponding to the first voltage stored in the correction value storage unit 44, if the voltage acquired by the acquisition circuit 42 is equal to or greater than the first voltage.

[0075] <4.2. Operation> Next, the operation of the current measuring device 1'' according to the third embodiment will be described. Figure 13 is a flowchart illustrating the operation of the current measuring device 1'' according to the third embodiment.

[0076] As shown in Figure 13, first, the acquisition circuit 42 acquires the voltage output from the magnetic sensor 14 (step S1).

[0077] Next, the magnetic flux density correction circuit 43 determines whether the acquired voltage is equal to or greater than the first voltage corresponding to the magnetic flux density saturation value of the magnetic shield 13 (step S2).

[0078] In step S2, if the voltage is not equal to or greater than the first voltage (No. in step S2), the magnetic flux density correction circuit 43 continues the decision-making process in step S2.

[0079] On the other hand, if the sensor value in step S2 is greater than or equal to the first voltage (Yes in step S2), the magnetic flux density correction circuit 43 proceeds to the processing in step S3.

[0080] In step S3, the magnetic flux density correction circuit 43 corrects the first voltage, which was obtained in step S1, using the correction value of the second voltage corresponding to the obtained first voltage, to reduce the gain of the obtained first voltage, and then terminates the process.

[0081] <4.3. Effects> Therefore, according to the current measuring device 1'' of the third embodiment, the effect of magnetic flux density saturation of the magnetic shield 13 can be reduced without modifying the magnetic shield 13 by correcting the voltage corresponding to the magnetic field measured by the magnetic sensor 14 in the circuit section 12.

[0082] <5. Fourth Embodiment> <5.1. Structure> Figure 14 shows the configuration of the current measuring device 1'' according to the fourth embodiment. As shown in Figure 14, a canceling magnetic field generating coil 51 is wound around the upper part 13u of the magnetic shield 13, passing through the internal space of the magnetic shield 13.

[0083] A power supply circuit 52 is connected to the canceling magnetic field generating coil 51. The power supply circuit 52 supplies power to the canceling magnetic field generating coil 51. The canceling magnetic field generating coil 51 generates a magnetic field that reduces the magnetic field generated by the current flowing through the conductor MC under test within the magnetic shield 13. That is, the canceling magnetic field generating coil 51 generates a magnetic field with magnetic flux density Bc in a direction that reduces the magnetic flux density Bs of the magnetic field within the magnetic shield 13.

[0084] Furthermore, a measuring coil 53 is wound around the right side portion 13r of the magnetic shield 13, passing through the internal space of the magnetic shield 13. A detection circuit 54 is connected to the measuring coil 53.

[0085] The detection circuit 54 controls the current source of the power supply circuit 52 when the voltage corresponding to the change in magnetic flux measured by the measuring coil 53 is higher than the voltage corresponding to the magnetic saturation density of the magnetic shield 13. The detection circuit 54 controls the current source of the power supply circuit 52 when a change in magnetic flux is detected by the measuring coil 53. In this case, the power supply circuit 52 does not always need to supply current to the short-circuit winding 31, resulting in energy savings. The detection circuit 54 is connected to the measuring coil 53 and controls the current source of the power supply circuit 52 that supplies current to the canceling magnetic field generating coil 51 based on the voltage corresponding to the change in magnetic flux measured by the measuring coil 53.

[0086] When the power supply circuit 52 receives control of the current source from the detection circuit 54, it supplies a current to the magnetic field generating coil 51 that corresponds to a voltage lower than the voltage corresponding to the magnetic saturation density of the magnetic shield 13. The current supplied from the power supply circuit 52 to the magnetic field generating coil 51 may be a current corresponding to a predetermined voltage, or a current corresponding to the magnitude of the voltage corresponding to the change in magnetic flux measured by the measuring coil 53, as long as it is a current lower than the voltage corresponding to the magnetic saturation density. When the power supply circuit 52 does not receive control from the detection circuit 54, it does not need to supply current to the magnetic field generating coil 51.

[0087] Furthermore, the mounting position of the canceling magnetic field generating coil 51 to the magnetic shield 13 may be the right side 13r, left side 13l, or lower part 13d of the magnetic shield 13, as long as it is a position that generates a magnetic field that reduces the effect of magnetic flux density saturation of the magnetic shield 13.

[0088] <First variation> Furthermore, there may be multiple cancellation magnetic field generating coils 51. Figure 15 shows a magnetic shield 13 in a first modified example of the current measuring device 1'' according to the fourth embodiment. As shown in Figure 15, the magnetic shield 13 of the first modified example of the current measuring device 1'' according to the third embodiment has a cancellation magnetic field generating coil 51a and a cancellation magnetic field generating coil 51b wound around it.

[0089] Specifically, a canceling magnetic field generating coil 51a is wound around the upper part of the magnetic shield 13, and a canceling magnetic field generating coil 51b is wound around the left side part 13l. The positions in which the canceling magnetic field generating coils 51a and 51b are wound are not limited to these.

[0090] The power supply circuit 52a is connected to the canceling magnetic field generating coil 51a, and the power supply circuit 52b is connected to the canceling magnetic field generating coil 51b. Power supply circuit 52a supplies power to the canceling magnetic field generating coil 51a. Power supply circuit 52b supplies power to the canceling magnetic field generating coil 51b.

[0091] <5.2. Operation> Next, the operation of the current measuring device 1'''' according to the fourth embodiment will be described.

[0092] The detection circuit 54 controls the current supply from the power supply circuit 52 to the cancellation magnetic field generating coil 51 based on the voltage corresponding to the change in magnetic flux measured by the measuring coil 53. Specifically, the detection circuit 54 controls the current supply from the power supply circuit 52 to the cancellation magnetic field generating coil 51 when the voltage corresponding to the change in magnetic flux measured by the measuring coil 53 is higher than the voltage corresponding to the magnetic saturation density of the magnetic shield 13. The detection circuit 54 controls the current supply from the power supply circuit 52 when a change in magnetic flux measured by the measuring coil 53 occurs.

[0093] When the power supply circuit 52 receives control from the detection circuit 54, it supplies a current to the magnetic field generating coil 51 that corresponds to a voltage lower than the voltage corresponding to the magnetic saturation density of the magnetic shield 13. Specifically, when the power supply circuit 52 receives control from the detection circuit 54, it supplies a current to the magnetic field generating coil 51 that corresponds to a voltage lower than the voltage corresponding to the magnetic saturation density of the magnetic shield 13.

[0094] When current flows through the conductor MC under test, a magnetic field is generated within the magnetic shield 13, resulting in a magnetic field with magnetic flux density Bs within the magnetic shield 13. This magnetic field is positive within the magnetic shield 13. In other words, the magnetic field generated by the current flowing through the conductor MC under test is a magnetic field that extends from the lower to the upper part of the right side 13r of the magnetic shield 13.

[0095] The canceling magnetic field generating coil 51 generates a magnetic field with magnetic flux density Bc in a direction that reduces the magnetic field with magnetic flux density Bs generated in the magnetic shield 13. That is, current flows through the canceling magnetic field generating coil 51 in a direction that generates a magnetic field with magnetic flux density Bc in the opposite direction to the magnetic field with magnetic flux density Bs. The direction of the magnetic field generated by the canceling magnetic field generating coil 51 is opposite to the direction of the magnetic field generated by the current flowing through the conductor MC under test. In other words, the magnetic field generated by the current flowing through the conductor MC under test is a positive magnetic field in the direction from the bottom to the top of the right side 13r of the magnetic shield 13, while the magnetic field generated by the canceling magnetic field generating coil 51 is a negative magnetic field in the direction from the top to the bottom of the right side 13r of the magnetic shield 13.

[0096] As shown in Figure 15, even when the canceling magnetic field generating coils 51a and 51b are wound around the magnetic shield 13, the canceling magnetic field generating coils 51a and 51b generate a magnetic field in a direction that reduces the magnetic flux density Bs of the magnetic field generated in the magnetic shield 13, similar to the canceling magnetic field generating coil 51. That is, current flows through the canceling magnetic field generating coils 51a and 51b in such a way that they generate a magnetic field in the opposite direction to the direction of the magnetic field of the magnetic flux density Bs. The direction of the magnetic field generated by the canceling magnetic field generating coils 51a and 51b is opposite to the direction of the magnetic field generated by the current flowing through the conductor MC under test. In other words, the magnetic field generated by the current flowing through the conductor MC under test is a positive magnetic field in the direction from the bottom to the top of the right side portion 13r of the magnetic shield 13, while the magnetic fields generated by the canceling magnetic field generating coils 51a and 51b are negative magnetic fields in the direction from the top to the bottom of the right side portion 13r of the magnetic shield 13.

[0097] <5.3. Effects> Therefore, according to the current measuring device 1'' of the fourth embodiment, the canceling magnetic field generating coil 51 (or canceling magnetic field generating coil 51a and canceling magnetic field generating coil 51b) generates a magnetic field in a direction that reduces the saturation density of the magnetic shield 13, so it is less susceptible to the influence of the magnetic flux density saturation of the magnetic shield 13. As a result, the current measuring device 1'' of the fourth embodiment can accurately measure the current flowing through the conductor MC under test.

[0098] Furthermore, the current measuring device 1'' of the fourth embodiment can use thinner coils compared to a single winding magnetic field generating coil 51 by using multiple canceling magnetic field generating coils 51a and 51b.

[0099] <6. Fifth Embodiment> Next, a current measuring device according to the fifth embodiment will be described. The current measuring device according to the fifth embodiment prevents disturbances in the detected value of the current flowing through the conductor MC under test from occurring in relation to the magnetic flux density saturation of the magnetic shield 13 by changing the thickness and material of a part of the magnetic shield 13, and accurately measures the current flowing through the conductor under test.

[0100] <6.1. Structure> Figure 16 is a diagram illustrating the magnetic shield 13 of the current measuring device 1'''' according to the fifth embodiment. The lower part 13d (first part) of the magnetic shield 13 has a first cross-sectional area of ​​the wall facing the notch of the magnetic shield 13. The right side 13r, left side 13l, and upper part 13u (second part) of the magnetic shield 13, other than the lower part 13d, have a second cross-sectional area with a length b (a > b) that is smaller than the first cross-sectional area with a length a of the wall facing the notch of the magnetic shield 13.

[0101] The positions of the right side 13r, left side 13l, and upper part 13u of the magnetic shield 13 are further away from the lower part 13d of the notch of the magnetic shield 13. In other words, the thickness of the tip portion of the roughly U-shaped magnetic shield 13 is increased.

[0102] Figure 17 shows the difference in cross-sectional area between the lower part 13d and the right side 13r, left side 13l, and upper part 13u of the magnetic shield 13 in the current measuring device 1'''' according to the fifth embodiment. As shown in Figure 17, the cross-sectional area of ​​the lower part 13d is larger than the cross-sectional areas of the right side 13r, left side 13l, and upper part 13u. Note that the shape of the cross-sectional area is not limited to a rectangular shape, but may be other shapes.

[0103] In other words, the shape of the magnetic shield 13 is modified so that the magnetic flux density saturation at the tip of the U-shaped part of the magnetic shield 13, which is prone to saturation, is increased compared to other parts of the magnetic shield 13.

[0104] For example, when changing the shape, the area of ​​the magnetic shield 13 through which the magnetic field passes in areas prone to saturation is increased. As one example, the thickness of the tip portion of a U-shaped magnetic shield 13 is increased.

[0105] <First variation> Next, a first modified example of the current measuring device 1'''' according to the fifth embodiment will be described. In Figure 16, the case in which the thickness of the lower part 13d of the magnetic shield 13 is increased was described, but in the first modified example of the fifth embodiment, the material of the lower part 13d of the magnetic shield 13 is different.

[0106] Figure 18 is a diagram illustrating a first modified example of the magnetic shield 13 in the current measuring device 1'''' according to the fifth embodiment. As shown in Figure 18, the magnetic shield 13 includes a lower part 13d containing a first material and a second material different from the first material. The lower part 13d is closer to the notch of the magnetic shield 13 than the right part 13r, the left part 13l, and the upper part 13u. In other words, the tip portion of the roughly U-shaped magnetic shield 13 contains the first material different from the second material.

[0107] The first material in the lower part 13d has a higher magnetic flux density saturation value than the second material in the right side 13r, left side 13l, and upper part 13u.

[0108] For example, when changing materials, use a material with a high magnetic flux density saturation in areas prone to saturation. As an example, the material at the tip of the U-shaped magnetic shield 13 can be switched to one with a high magnetic flux density saturation.

[0109] <6.2. Operation> Next, the operation of the current measuring device 1'''' according to the fifth embodiment will be described. When a current flows through the conductor MC under measurement and a magnetic field is generated inside the magnetic shield 13, a magnetic field with magnetic flux density Bs is generated inside the magnetic shield 13.

[0110] Since the cross-sectional area of ​​the lower part 13d of the magnetic shield 13 is larger than the cross-sectional areas of the right side 13r, left side 13l, and upper part 13u, the magnetic flux density saturation value is larger and it is less susceptible to the effects of magnetic flux density saturation. Furthermore, since the material of the lower part 13d of the magnetic shield 13 is a material with a higher magnetic flux density saturation value than the materials of the right side 13r, left side 13l, and upper part 13u, the magnetic flux density is larger and it is less susceptible to the effects of magnetic flux density saturation.

[0111] <6.3. Effects> Therefore, the current measuring device 1'''' according to the fifth embodiment can reduce the effect of magnetic flux density saturation by changing the shape and material of the magnetic shield 13. As a result, the detected value of the magnetic sensor 14 becomes less prone to disturbance, and the current flowing through the conductor MC to be measured can be accurately detected.

[0112] <Sixth Embodiment> Next, a current measuring device according to the sixth embodiment will be described. The current measuring device according to the sixth embodiment measures the current flowing through the conductor MC by adding a Rogowski sensor in addition to the magnetic sensor 14.

[0113] Figure 19 is a block diagram showing the main components of the current measuring device 1'''''' according to the sixth embodiment. In Figure 19, the same reference numerals are used for the blocks corresponding to the configuration shown in Figure 1. The details of the internal configuration of the circuit section 12 will be described below, mainly with reference to Figure 19. As shown in Figure 19, the sensor head 11 has a Logonski sensor 61 in addition to the magnetic sensor 14.

[0114] The current measuring devices 1 in the first to fifth embodiments described above measured the DC and low-frequency components of the current I flowing through the conductor MC under test. In contrast, the current measuring device 1 of this embodiment is capable of measuring not only the DC and low-frequency components of the current I flowing through the conductor MC under test, but also components from low to high frequencies.

[0115] The Rogowski sensor 61 detects AC magnetic fields ranging from low frequencies (e.g., a few kHz) to high frequencies (e.g., tens of MHz) generated by the current I flowing through the conductor MC under test. The Rogowski sensor 61 is a sensor using a Rogowski coil (air-core coil) and is positioned to surround the conductor MC under test. In order to facilitate its placement around the conductor MC under test, one end of the Rogowski sensor 61 is configured to be detachably attached to the sensor head 11.

[0116] The circuit unit 12 measures the current I flowing through the conductor MC based on the detection results output from the sensor head 11 (detection results from the magnetic sensor 14 and the Rogowski sensor 61). The circuit unit 12 outputs or displays the measurement result of the current I to the outside. The cable CB is preferably flexible, easy to handle, and resistant to breakage, similar to the first embodiment.

[0117] The circuit unit 12 includes a calculation unit 71, a calculation unit 72, a synthesis unit 81, and an output unit 90.

[0118] The calculation unit 71 determines the current I flowing through the conductor MC under test from the detection result of the Rogowski sensor 61. Here, as mentioned above, the Rogowski sensor 61 detects AC magnetic fields from low to high frequencies, so the current I determined by the calculation unit 71 is the low to high frequency component. The detection result of the Rogowski sensor 61 indicates the voltage induced in the Rogowski coil by the AC magnetic field generated around the current I (AC current) flowing through the conductor MC under test. The calculation unit 71 determines the current I flowing through the conductor MC under test by performing a calculation to convert the detection result (voltage) of the Rogowski sensor 61 into a current value.

[0119] The calculation unit 72 determines the current I flowing through the conductor MC under test from the detection result of the magnetic sensor 14. Here, as mentioned above, the magnetic sensor 14 detects DC magnetic fields and low-frequency AC magnetic fields, so the current I obtained by the calculation unit 21 is the DC and low-frequency components. Distance information indicating the reference distance r mentioned above is pre-stored in the calculation unit 72. The calculation unit 71 determines the current I flowing through the conductor MC under test by calculating the product of the detection result (magnetic field H) of the magnetic sensor 14 and a constant uniquely determined from the reference distance r.

[0120] Specifically, the calculation unit 72 has the second correction unit B described above. The second correction unit B performs a correction on the voltage corresponding to the magnetic field detected by the magnetic field sensor 14 to reduce the effect of magnetic flux saturation of the magnetic shield 13. Then, the calculation unit 72 performs calculations on the voltage corrected by the second correction unit B to determine the current I flowing through the conductor MC under test.

[0121] The second correction unit B may also be provided on the sensor head 11 side, as described above. In this case, the calculation unit 72 receives the corrected voltage corresponding to the magnetic field detected from the sensor head 11, performs calculations on the received voltage, and determines the current I flowing through the conductor MC under test. The second correction unit B may also be provided on the calculation unit 71. In this case, the calculation unit 71 performs a correction on the voltage corresponding to the magnetic field detected by the Rogowski sensor 61 to reduce the effect of magnetic flux saturation of the magnetic shield 13. The calculation unit 71 then performs calculations on the voltage corrected by the second correction unit B to determine the current I flowing through the conductor MC under test.

[0122] The combining unit 81 combines the calculation results of the calculation unit 71 and the calculation results of the calculation unit 72. Specifically, the combining unit 81 includes a high-pass filter 82, a low-pass filter 83, a signal level adjustment unit 84, and an adder 85. The low-pass filter 83 removes high-frequency components from the calculation results of the calculation unit 72 and allows low-frequency components to pass through, resulting in a signal with a desired frequency characteristic suitable for the combining process described later. The high-pass filter 82 removes low-frequency components from the calculation results of the calculation unit 71 and allows high-frequency components to pass through, resulting in a signal with a desired frequency characteristic suitable for the combining process described later.

[0123] The signal level adjustment unit 84 adjusts the level of the signal output from the low-pass filter 83. For example, when DC current and AC current with the same effective value are flowing through the conductor MC under test, the signal level adjustment unit 84 adjusts the signal level of the signal output from the low-pass filter 83 to be the same as the signal level of the signal output from the high-pass filter 82. A variable resistor can be used as this signal level adjustment unit 84.

[0124] In this embodiment, a signal level adjustment unit 84 is provided to adjust only the level of the signal output from the low-pass filter 83, but this embodiment is not limited to this. For example, a signal level adjustment unit for adjusting the level of the signal output from the high-pass filter 82 may be provided instead of the signal level adjustment unit 84, or it may be provided in addition to the signal level adjustment unit 84. Alternatively, a signal level adjustment unit capable of adjusting the levels of the first signal and the second signal may be provided separately.

[0125] The summing unit 85 adds the signal whose signal level has been adjusted by the signal level adjustment unit 84 and the signal output from the high-pass filter 82. The signal whose signal level has been adjusted by the signal level adjustment unit 84 is a signal that represents the DC and low-frequency components of the current I. The signal output from the high-pass filter 82 is a signal that represents the high-frequency component of the current I. Therefore, by adding these together, a signal representing the DC and AC components up to high frequencies can be obtained.

[0126] The output unit 90 outputs the signal (measurement result of current I) synthesized by the combining unit 81 to the outside. The output unit 90 may also be equipped with an output terminal for outputting a signal indicating the measurement result of current I to the outside, or it may be equipped with a display device (for example, a liquid crystal display device) for displaying the measurement result of current I to the outside.

[0127] Accordingly, the current measuring device 1''''' according to the sixth embodiment includes a magnetic sensor 14 housed in a magnetic shield 13 that detects a DC magnetic field and a low-frequency AC magnetic field generated by the current flowing through the conductor MC under test, and a Rogowski sensor 61 that detects a low-frequency to high-frequency AC magnetic field generated by the current flowing through the conductor MC under test. The current flowing through the conductor MC under test (DC current and low-frequency AC current) is determined from the detection result of the magnetic sensor 14, and the current flowing through the conductor MC under test (low-frequency to high-frequency) is determined from the detection result of the Rogowski sensor 61, and the respective calculation results are combined. Therefore, in this embodiment, the current I (DC and low-frequency components and low-frequency to high-frequency components) flowing through the conductor MC under test (DC and low-frequency components) can be measured non-contact and with high accuracy in a compact size.

[0128] <Seventh Embodiment> Next, a current measuring device according to the seventh embodiment will be described. The current measuring device according to the seventh embodiment measures the current flowing through the conductor MC to be measured by adding a coil 91 in addition to the magnetic sensor 14.

[0129] Figure 20 is a cross-sectional view of the magnetic shield 13 of the sensor head of the current measuring device according to the seventh embodiment. Note that Figure 20 corresponds to Figure 4. In the seventh embodiment, the sensor head is configured to have a coil 91 instead of the Rogowski sensor 61 of the sensor head of the sixth embodiment.

[0130] The coil 91, like the Rogowski sensor 61, detects AC magnetic fields ranging from low frequencies (e.g., a few kHz) to high frequencies (e.g., tens of MHz) generated by the current I flowing through the conductor MC under test. The coil 91 is designed according to the maximum current (upper limit current) and the maximum frequency measurable by the current measuring device, and is housed inside the magnetic shield 12.

[0131] Specifically, the coil 91 is positioned within the magnetic shield 13 such that, when the sensor head is fixed to the conductor MC under test by the fixing mechanism, its detection axis (magnetic sensing direction) is in the direction of the magnetic field generated by the current I (tangential direction of the conductor MC under test). By positioning the coil 91 in this way, the influence of the external magnetic field flowing into the magnetic shield 12 from the notch 20 on the coil 91 can be reduced. In the example shown in Figure 20, the coil 91 is positioned inside the magnetic shield 13 such that its distance from the center of the conductor MC under test is greater than the distance between the magnetic sensor 14 and the center of the conductor MC under test. Note that the position of the coil 91 inside the sensor head is not limited to the position exemplified in Figure 20, and may be located in a different position than the one exemplified in Figure 20.

[0132] The circuit section 12 has the same configuration as the circuit section 12 provided in the current measuring device 1'''''' according to the sixth embodiment. The circuit configuration of the current measuring device in this embodiment can be understood by replacing the Rogowski sensor 61 shown in Figure 19 with the coil 91.

[0133] In the seventh embodiment, a magnetic sensor 14 that detects the DC magnetic field and low-frequency AC magnetic field generated by the current flowing through the conductor MC under test, and a coil 91 that detects the AC magnetic field from low to high frequency generated by the current flowing through the conductor MC under test are housed inside the magnetic shield 13. The current flowing through the conductor MC under test (DC current and low-frequency AC current) is determined from the detection result of the magnetic sensor 14, and the current flowing through the conductor MC under test (from low to high frequency) is determined from the detection result of the coil 91, and the results of each calculation are combined. Therefore, in this embodiment, the current I (DC and low-frequency components and low-to-high frequency components) flowing through the conductor MC under test can be measured non-contact and with high accuracy in a compact size.

[0134] Furthermore, in this embodiment, instead of the Rogowski sensor 61 provided in the current measuring device 2 of the sixth embodiment, a coil 91 housed inside the magnetic shield 13 is provided. As a result, the work of arranging the Rogowski sensor 61 (the work of arranging the Rogowski sensor 61 so as to surround the conductor MC to be measured), which was necessary in the sixth embodiment, can be omitted, and the sensor head can be made smaller.

[0135] Some examples of the combinations of technical features that will be disclosed are listed below.

[0136] (1) A magnetic shield having a notch for taking in the magnetic field generated by the current flowing through the conductor under test into its internal space, A sensor is placed in the internal space of the magnetic shield and outputs a voltage corresponding to the magnetic field at that location. A circuit unit that detects the current flowing through the conductor to be measured based on the voltage output from the sensor, A current measuring device comprising, The magnetic shield has at least one of the following: a first correction unit that corrects the effect of magnetic flux density saturation of the magnetic shield on the voltage output from the sensor, or the magnetic shield or the circuit unit has at least one second correction unit that corrects the voltage output from the sensor so as to reduce the effect of magnetic flux density saturation of the magnetic shield. Current measuring device.

[0137] (2) The magnetic shield has walls that define the internal space, The first correction unit has a winding that is wound around a portion of the wall of the magnetic shield so as to pass through the internal space. (1) The current measuring device described above.

[0138] (3) The magnetic shield has a hollow box shape with the internal space inside, (1) or (2) the current measuring device described above.

[0139] (4) The sensor detects the DC magnetic field and the low-frequency AC magnetic field generated by the current flowing through the conductor under measurement, The conductor to be measured is inserted through the notch. The circuit unit includes a calculation unit that determines the current flowing through the conductor to be measured based on the output voltage of the sensor. A fixing mechanism for fixing the conductor to be measured so that the distance between the center of the conductor to be measured, which is inserted into the notch of the magnetic shield, and the sensor is a predetermined reference distance. A current measuring device as described in (1), having the following:

[0140] (5) When viewed in the direction of extension of the conductor to be measured, the wall of the magnetic shield extends in a substantially U-shape, and the winding is wound around a part of the wall in a direction intersecting the direction of extension of the wall of the magnetic shield. (2) The current measuring device described above.

[0141] (6) The winding is a winding that is wound once around a part of the wall of the magnetic shield. (2) The current measuring device described above.

[0142] (7) The winding is A first winding that is wound once around the first wall of the wall of the magnetic shield, The second winding of the magnetic shield is wound once around the second wall of the wall and The current measuring device described in (2), having the following:

[0143] (8) The winding is a winding that has been wound multiple times. (2) The current measuring device described above.

[0144] (9) A fixing mechanism is provided for fixing the conductor to be measured to the magnetic shield such that the conductor to be measured is located in the notch of the magnetic shield. (1) The current measuring device described above.

[0145] (10) The voltage from the first sensor increases by adding the voltage that detects the magnetic flux overflowing from the magnetic shield when the magnetic shield is saturated to the voltage that detects the magnetic flux proportional to the magnitude of the current generated by the current flowing through the conductor under measurement. The second correction unit corrects the voltage from the first sensor in such a way as to suppress the voltage rise from the first sensor. (1) The current measuring device described above.

[0146] (11) The second correction unit includes a correction circuit to which the voltage from the first sensor is input, The correction circuit has a pass-through characteristic in which the gain when the input voltage is high is smaller than the gain when the input voltage is low. (10) The current measuring device described above.

[0147] (12) When the voltage exceeds a first sensor threshold corresponding to the magnetic flux density saturation value of the magnetic shield, the second correction unit corrects the first voltage that is equal to or greater than the first sensor threshold using a correction value corresponding to the first voltage. (10) The current measuring device described above.

[0148] (13) A correction value storage unit is provided which stores a second voltage that is equal to or greater than the first sensor threshold and a correction value corresponding to the second voltage, The second correction unit corrects the first voltage using the correction value of the second voltage corresponding to the first voltage stored in the correction value storage unit. (12) The current measuring device described above.

[0149] (14) The first correction unit, A power supply circuit that supplies magnetic field generation current to the winding, A measuring coil wound around a portion of the wall of the magnetic shield so as to pass through the internal space, A detection circuit for detecting the voltage generated in the measuring coil, Equipped with, The power supply circuit supplies the magnetic field generating current to the winding so as to generate a magnetic field that cancels out the magnetic flux passing through the wall of the magnetic shield, in accordance with the detection result of the detection circuit. (2) The current measuring device described above.

[0150] (15) The power supply circuit supplies the magnetic field generating current to the winding when the voltage detected by the detection circuit is higher than the voltage corresponding to the magnetic saturation density of the magnetic shield. (14) The current measuring device described above.

[0151] (16) The magnetic shield has walls that define the internal space, The first correction portion of the magnetic shield has a first wall having a cross-section facing the notch of the magnetic shield, and a second wall connected to the first wall on the opposite side of the notch, with the first wall in between. The cross-sectional area of ​​the first wall is larger than the cross-sectional area of ​​the second wall. (1) The current measuring device described above.

[0152] (17) The magnetic shield has walls that define the internal space, The first correction section of the magnetic shield has a first wall facing the notch and a second wall connected to the first wall on the opposite side of the notch, with the first wall in between. The magnetic flux density saturation value of the material of the first wall is higher than the magnetic flux density saturation value of the second wall. (1) The current measuring device described above.

[0153] (18) The sensor outputs voltages corresponding to the DC magnetic field and low-frequency AC magnetic field generated by the current flowing through the conductor under measurement, The magnetic shield includes a second sensor disposed in the internal space of the magnetic shield, which outputs a voltage corresponding to a low-frequency to high-frequency alternating magnetic field generated by the current flowing through the conductor under measurement, The aforementioned circuit section is A first calculation unit performs a correction on the voltage output from the sensor to reduce the effect of magnetic flux density saturation of the magnetic shield, and calculates the current flowing through the conductor under measurement from the corrected voltage. A second calculation unit that determines the current flowing through the conductor under measurement based on the voltage output from the second sensor, A combining unit that combines the calculation result of the first calculation unit and the calculation result of the second calculation unit. A current measuring device as described in (1), having the following:

[0154] (19) A magnetic shield having a notch for taking in the magnetic field generated by the current flowing through the conductor under test into the internal space, A sensor is placed in the internal space of the magnetic shield and outputs a voltage corresponding to the magnetic field at that location. A circuit unit that detects the current flowing through the conductor to be measured based on the voltage output from the sensor, In a current measuring device equipped with a current measuring device, The magnetic shield performs a correction to reduce the effect of magnetic flux density saturation of the magnetic shield on the voltage output from the sensor, or the magnetic shield or the circuit unit performs at least one of the following: Current measurement method. [Explanation of Symbols]

[0155] 1, 1', 1'', 1''', 1'''', 1''''' Current measuring device 11 Sensor head 12 Circuit section 13 Magnetic Shielding 13u top 13d Lower part 13r Right side 13l left side 14 Magnetic Sensors 15 Signal line and power supply wiring 20 Notches 21 Fixing mechanism 22 Power line connection section 31 Short-circuit winding 40 Control circuit section 41 Storage section 42 Acquisition circuit 43 Magnetic flux density correction circuit 44 Correction value storage unit 45. Curve before correction 46 Corrected curve 51. Cancellation magnetic field generating coil 52 Power supply circuit 53 Measuring coil 54 Detection circuit 61 Rogowski sensor 91 coil MC Conductor under test CB cable A. First Correction Unit B. Second Correction Unit B-1 Correction circuit

Claims

1. A magnetic shield having a notch for capturing the magnetic field generated by the current flowing through the conductor under test into its internal space, A sensor is placed in the internal space of the magnetic shield and outputs a voltage corresponding to the magnetic field at that location. A circuit unit that detects the current flowing through the conductor to be measured based on the voltage output from the sensor, A current measuring device comprising, The magnetic shield has at least one of the following: a first correction unit that corrects the voltage output from the sensor to reduce the effect of magnetic flux density saturation of the magnetic shield, or the magnetic shield or the circuit unit has at least one second correction unit that corrects the voltage output from the sensor to reduce the effect of magnetic flux density saturation of the magnetic shield. Current measuring device.

2. The magnetic shield has walls that define the internal space, The first correction unit has a winding that is wound around a part of the wall of the magnetic shield so as to pass through the internal space. The current measuring device according to claim 1.

3. The magnetic shield has a hollow box shape with the internal space on the inside. The current measuring device according to claim 1 or 2.

4. The sensor detects the DC magnetic field and low-frequency AC magnetic field generated by the current flowing through the conductor under measurement. The conductor to be measured is inserted through the notch. The circuit unit includes a calculation unit that determines the current flowing through the conductor to be measured based on the output voltage of the sensor. A fixing mechanism for fixing the conductor to be measured so that the distance between the center of the conductor to be measured, which is inserted into the notch of the magnetic shield, and the sensor is a predetermined reference distance. The current measuring device according to claim 1, having the following features.

5. When the magnetic shield is viewed from the front, the wall of the magnetic shield extends in a substantially U-shape, and the winding is wound around a portion of the wall in a direction intersecting the extending direction of the wall of the magnetic shield. The current measuring device according to claim 2.

6. The winding is a winding that is wound once around a part of the wall of the magnetic shield. The current measuring device according to claim 2.

7. The aforementioned winding is, A first winding that is wound once around the first wall of the wall of the magnetic shield, The second winding of the magnetic shield, which is wound once around the second wall of the wall, The current measuring device according to claim 2, having the following features.

8. The aforementioned winding is a winding that has been wound multiple times. The current measuring device according to claim 2.

9. The device includes a fixing mechanism for fixing the conductor to be measured to the magnetic shield so that the conductor to be measured is positioned in the notch of the magnetic shield. The current measuring device according to claim 1.

10. The voltage from the sensor increases as the voltage detecting the magnetic flux, which is proportional to the magnitude of the current generated by the current flowing through the conductor under measurement, is added to the voltage detecting the magnetic flux that has overflowed from the magnetic shield when the magnetic shield is saturated. The second correction unit corrects the voltage from the sensor in such a way as to suppress the rise in the voltage from the sensor. The current measuring device according to claim 1.

11. The second correction unit includes a correction circuit to which the voltage from the sensor is input. The correction circuit has a pass-through characteristic in which the gain when the input voltage is high is smaller than the gain when the input voltage is low. The current measuring device according to claim 10.

12. The second correction unit corrects the first voltage, which is equal to or greater than the sensor threshold, using a correction value corresponding to the first voltage, when the voltage exceeds the sensor threshold, when the voltage exceeds the sensor threshold. The current measuring device according to claim 10.

13. The system includes a correction value storage unit that stores a second voltage equal to or greater than the sensor threshold and a correction value corresponding to the second voltage. The second correction unit corrects the first voltage using the correction value of the second voltage corresponding to the first voltage stored in the correction value storage unit. The current measuring device according to claim 12.

14. The first correction unit is, A power supply circuit that supplies magnetic field generation current to the winding, A measuring coil wound around a portion of the wall of the magnetic shield so as to pass through the internal space, A detection circuit for detecting the voltage generated in the measuring coil, Equipped with, The power supply circuit supplies the magnetic field generating current to the winding so as to generate a magnetic field that cancels out the magnetic flux passing through the wall of the magnetic shield, in accordance with the detection result of the detection circuit. The current measuring device according to claim 2.

15. The power supply circuit supplies the magnetic field generating current to the winding when the voltage detected by the detection circuit is higher than the voltage corresponding to the magnetic saturation density of the magnetic shield. The current measuring device according to claim 14.

16. The magnetic shield has walls that define the internal space, The first correction portion of the magnetic shield has a first wall having a cross-section facing the notch of the magnetic shield, and a second wall connected to the first wall on the opposite side of the notch, with the first wall in between. The cross-sectional area of ​​the first wall is larger than the cross-sectional area of ​​the second wall. The current measuring device according to claim 1.

17. The magnetic shield has walls that define the internal space, The first correction portion of the magnetic shield has a first wall facing the notch and a second wall connected to the first wall on the opposite side of the notch, with the first wall in between. The magnetic flux density saturation value of the material of the first wall is higher than the magnetic flux density saturation value of the second wall. The current measuring device according to claim 1.

18. The sensor outputs voltages corresponding to the DC magnetic field and low-frequency AC magnetic field generated by the current flowing through the conductor under measurement. The magnetic shield includes a second sensor disposed in the internal space of the magnetic shield, which outputs a voltage corresponding to a low-frequency to high-frequency alternating magnetic field generated by the current flowing through the conductor under measurement, The aforementioned circuit section is A first calculation unit performs a correction on the voltage output from the sensor to reduce the effect of magnetic flux density saturation of the magnetic shield, and calculates the current flowing through the conductor under measurement from the corrected voltage. A second calculation unit that determines the current flowing through the conductor to be measured based on the voltage output from the second sensor, A combining unit that combines the calculation result of the first calculation unit and the calculation result of the second calculation unit. The current measuring device according to claim 1, having the following features.

19. A magnetic shield having a notch for capturing the magnetic field generated by the current flowing through the conductor under test into its internal space, A sensor is placed in the internal space of the magnetic shield and outputs a voltage corresponding to the magnetic field at that location. A circuit unit that detects the current flowing through the conductor to be measured based on the voltage output from the sensor, In a current measuring device equipped with a current measuring device, The magnetic shield performs a correction to reduce the effect of magnetic flux density saturation of the magnetic shield on the voltage output from the sensor, or the magnetic shield or the circuit unit performs at least one of the following: Current measurement method.

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