Current detector

Abstract

To provide a current detector for suppressing a decrease in the accuracy of detecting the current to be measured.SOLUTION: Provided is a current detector comprising: a current bar for flowing the current to be measured; a magnetic core provided in the periphery of the current bar and equipped with a gap part; a detection unit provided to the gap part of the magnetic core, mutually connected in series, and equipped with a plurality of coil members; a signal processing circuit for processing a detection signal of the current being measured that is outputted from the detection unit; and a switching circuit for switching the number of the coil members in the detection unit that are connected to the signal processing circuit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a current detection device. [Background technology]

[0002] Conventionally, current detection devices such as current sensors that include a magnetic core surrounding a current bar and detect a current to be measured flowing through the current bar are known. Patent Document 1 discloses a current detection device having a main board and an auxiliary board on which coil members such as a first coil pattern and a second coil pattern are respectively provided in a gap provided in a magnetic core surrounding the current bar. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-48755 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a current to be measured flows through the current bar, an induced voltage proportional to the current value of the current to be measured and the number of turns of the coil member is theoretically generated in the coil member. The induced voltage in the coil member allows the current to be detected. However, when the current to be measured flowing through the current bar is low, the measurement accuracy of the current to be measured may decrease.

[0005] The present disclosure provides a current detection device that suppresses a decrease in the measurement accuracy of a current to be measured. [Means for solving the problem]

[0006] In a first aspect, the device comprises a current bar through which a current to be measured flows, a magnetic core arranged around the current bar and having a gap portion, a detection unit having a plurality of coil members arranged in the gap portion of the magnetic core and connected in series with each other, a signal processing circuit that processes a detection signal of the current to be measured output from the detection unit, and a switching circuit in the detection unit that switches the number of coil members connected to the signal processing circuit. Effect of the Invention

[0007] According to the technique of the present disclosure, it is possible to suppress a decrease in the measurement accuracy of the current to be measured. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an example of an overall configuration of a current detection device according to a first embodiment. [Diagram 2] 1 is a schematic diagram illustrating an example of a circuit configuration of a current detection device according to a first embodiment. [Diagram 3] 4 is a graph showing the relationship between the current value of a current to be measured flowing through a current bar and the voltage value of a voltage signal input to an A / D conversion circuit in the current detection device according to the first embodiment. [Figure 4] 10 is a schematic diagram showing an example of a circuit configuration of a current detection device according to a second embodiment. FIG. [Diagram 5] 13 is a schematic diagram showing an example of the operation of a switching circuit in the current detection device according to the second embodiment. FIG. [Figure 6] 13 is a schematic diagram showing another example of the operation of the switching circuit in the current detection device according to the second embodiment. FIG. [Figure 7] 13 is a schematic diagram showing yet another example of the operation of the switching circuit in the current detection device according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the current detection device 1 according to the embodiment will be described with reference to the drawings. Note that "connection" is not limited to physical connection, and may include electrical connection. For example, connecting an object A to an object B is not limited to the case where the object A is conductively connected to the object B (e.g., at the same potential), but may include the case where the object A is conductively connected to the object B via the object C.

[0010] Here, in each drawing, an X-axis, a Y-axis, and a Z-axis that are perpendicular to each other are shown. The direction parallel to the X-axis is called the X-direction. In this embodiment, the X-direction corresponds to the width direction of the current detection device 1. In the X-direction, the direction in which the arrow points is called the +X-direction, and the opposite direction of the +X-direction is called the -X-direction. The direction parallel to the Y-axis is called the Y-direction. In this embodiment, the Y-direction corresponds to the front-rear direction of the current detection device 1. In the Y-direction, the direction in which the arrow points is called the +Y-direction, and the opposite direction of the +Y-direction is called the -Y-direction. The direction parallel to the Z-axis is called the Z-direction. In this embodiment, the Z-direction corresponds to the height direction of the current detection device 1. In the Z-direction, the direction in which the arrow points is called the +Z-direction, and the opposite direction of the +Z-direction is called the -Z-direction.

[0011] [First embodiment] <Overall composition> An example of the overall configuration of a current detection device 1 according to a first embodiment is shown with reference to Figures 1 and 2. Figure 1 is a schematic diagram showing an example of the overall configuration of the current detection device 1 according to the first embodiment. Figure 2 is a schematic diagram showing an example of the circuit configuration of the current detection device 1 according to the first embodiment.

[0012] The current detection device 1 is placed between an AC power source, such as a commercial power system, and a load, such as a motor. The current detection device 1 detects the AC current flowing from the power source to the load through the current detection device 1. The current detection device 1 also measures a current value, such as the effective value of the AC current, based on a detection signal of the AC current. In the following description, the AC current flowing from the power source to the load through the current detection device 1 is referred to as the "measured current I."

[0013] 1, the current detection device 1 includes a current bar 10, a magnetic core 20, a detection unit 30, a signal processing circuit 60, and a switching circuit 70. The current detection device 1 may include other components as necessary.

[0014] The current bar 10 passes a current I to be measured. The current bar 10 is connected to both a power source and a load. As shown in FIG. 1, the current bar 10 is a long, plate-like conductor extending along the Y direction. An example of the current bar 10 is a bus bar. However, the external shape of the current bar 10 is not limited to that shown in FIG. 1.

[0015] As shown in FIG. 1, the magnetic core 20 is provided around the current bar 10. Specifically, the magnetic core 20 has a substantially annular outer shape surrounding the current bar 10 in a non-contact state with the current bar 10. A hollow region is formed inside the magnetic core 20. The current bar 10 is inserted into the hollow region of the magnetic core 20. The magnetic core 20 of this embodiment has a substantially rectangular annular outer shape. However, the magnetic core 20 may have other outer shapes such as a circular annular shape or an elliptical annular shape.

[0016] The magnetic core 20 passes the magnetic flux generated around the current bar 10 in response to the current I to be measured flowing through the current bar 10. An example of a material constituting the magnetic core 20 is an Fe-Ni magnetic alloy, which has a large magnetic collecting effect. However, the material constituting the magnetic core 20 is not limited to this.

[0017] The magnetic core 20 has a spatially discontinuous gap portion 21. As shown in Fig. 1, the gap portion 21 in this embodiment is provided at a position facing the surface of the current bar 10 on the +Z direction side. However, the position of the gap portion 21 is not limited thereto.

[0018] In the magnetic core 20, a spatially continuous region excluding the gap portion 21 is referred to as a "main body portion 22." The main body portion 22 has two end faces 22a and 22b that are boundaries with the gap portion 21. The end faces 22a and 22b face each other at a predetermined distance. The end face 22a corresponds to the end of the gap portion 21 on the -X direction side. The end face 22b corresponds to the end of the gap portion 21 on the X direction side. Each of the end faces 22a and 22b in this embodiment is a plane parallel to the YZ plane. However, each of the end faces 22a and 22b may have other external shapes, such as an inclined surface inclined with respect to the YZ plane or a curved surface.

[0019] The material in the gap 21 is air. Therefore, the magnetic permeability of the gap 21 corresponds to the magnetic permeability of air. The magnetic permeability of air roughly corresponds to the magnetic permeability of a vacuum. In other words, the magnetic permeability of the gap 21 is lower than the magnetic permeability of the magnetic material constituting the main body 22.

[0020] By providing a space (gap portion 21) having a lower magnetic permeability than the main body portion 22 in a part of the magnetic core 20, the magnetic resistance in the magnetic core 20 including the gap portion 21 and the main body portion 22 is increased compared to the magnetic resistance of a completely annular magnetic core. In general, the magnetic flux (magnetic flux density) passing through a magnetic body is inversely proportional to the magnetic resistance in the magnetic body. Therefore, the magnetic flux density passing through the gap portion 21 and the main body portion 22 of the magnetic core 20 is lower than the magnetic flux density passing through a completely annular magnetic core. As a result, even if the current value Iv of the measurement current I flowing through the current bar 10 is large, the magnetic flux density passing through the gap portion 21 and the main body portion 22 is not saturated, so that the situation in which the measurable current value Iv of the measurement current I is limited by the saturation of the magnetic flux density can be suppressed.

[0021] The detection unit 30 is provided in the gap portion 21 of the magnetic core 20. The detection unit 30 detects the current I to be measured from a change in magnetic flux density that occurs in the gap portion 21 in response to the current I to be measured flowing through the current bar 10.

[0022] 1, the detection unit 30 includes a plurality of coil members 31 connected in series with each other. The detection unit 30 of this embodiment includes three coil members 31 (31a, 31b, 31c). However, the number of coil members 31 is not limited to three. The number of coil members 31 may be two, or may be four or more.

[0023] In this embodiment, each of the multiple coil members 31 is an air-core winding coil in which a conductive wire such as an enameled wire is wound multiple times. However, each of the multiple coil members 31 may be, for example, a pattern coil including multiple annular conductor patterns. Also, the multiple coil members 31 may be a combination of a winding coil and a pattern coil.

[0024] It is preferable that each of the multiple coil members 31 physically has multiple turns. In theory, the induced voltage generated in each of the coil members 31 by the current I to be measured flowing through the current bar 10 is proportional to the number of turns of each coil member 31. That is, by making each coil member 31 have multiple turns, the value of the detection signal of the current I to be measured in each coil member 31 can be increased. This can improve the detection accuracy of the current I to be measured. It is preferable that the number of turns of each coil member 31 is the same. Each coil member 31 of this embodiment physically has multiple turns N. However, the number of turns of each coil member 31 may be different from each other.

[0025] The three coil members 31 are arranged in a line along the X direction in a space between the end faces 22a and 22b of the main body 22. As shown in FIG. 1, the first coil member 31a is disposed on one end 30a side (the end on the -X direction side) of the detection unit 30. The second coil member 31b is disposed next to the first coil member 31a. The third coil member 31c is disposed next to the second coil member 31b. In this embodiment, the third coil member 31c is disposed on the other end 30b side (the +X direction side) of the detection unit 30.

[0026] The windings constituting each of the first coil member 31a, the second coil member 31b, and the third coil member 31c are wound around an axis along the X direction. Each of the multiple coil members 31 in this embodiment may be supported by a cylindrical member such as a bobbin that spans from end face 22a to end face 22b of the main body 22. The cylindrical member such as a bobbin is disposed in an air-core region of the multiple coil members 31. Each of the multiple coil members 31 is connected along the X direction with the cylindrical member as the axis.

[0027] When the current I to be measured flows through the current bar 10, a magnetic flux generated around the current bar 10 passes through each of the gap portion 21 and the main body portion 22 of the magnetic core 20. Furthermore, an induced voltage is generated in each of the multiple coil members 31 in response to a change in the magnetic flux that has passed through the gap portion 21. The detection unit 30 detects the current I to be measured that has flowed through the current bar 10 through the induced voltage generated in the coil members 31.

[0028] As will be described separately with reference to FIG. 2, the number of coil members 31 connected to the signal processing circuit 60 is switched by the switching circuit 70. Accordingly, the number of coil members 31 used to detect the current I to be measured is switched. The detection unit 30 outputs a voltage signal S1 corresponding to an induced voltage according to the number of coil members 31 used to detect the current I to be measured. The voltage signal S1 is an example of a "detection signal of the current I to be measured output from the detection unit 30."

[0029] Here, "the number of coil members 31 connected to the signal processing circuit 60" refers to the number of coil members 31 that constitute a closed circuit together with the signal processing circuit 60 and the switching circuit 70. In the case of this embodiment, the integrating circuit 61 is the circuit in the signal processing circuit 60 that is closest to the detecting unit 30 in terms of the circuit configuration. Therefore, the term "the number of coil members 31 connected to the integrating circuit 61" is synonymous with "the number of coil members 31 connected to the signal processing circuit 60."

[0030] When three coil members 31, namely, a first coil member 31a, a second coil member 31b, and a third coil member 31c, are used to detect a current I to be measured, the detection unit 30 outputs a voltage signal S1 corresponding to the sum of induced voltages generated in each of the three coil members 31. That is, the detection unit 30 outputs a voltage signal S1 corresponding to an induced voltage approximately proportional to the total number of turns "3N" of the three coil members 31.

[0031] When two coil members 31, a first coil member 31a and a second coil member 31b, are used to detect the current I to be measured, the detection unit 30 outputs a voltage signal S1 corresponding to the sum of the induced voltages generated in each of the two coil members 31. In other words, the detection unit 30 outputs a voltage signal S1 corresponding to an induced voltage approximately proportional to the total number of turns of the two coil members 31, "2N."

[0032] When the first coil member 31a (single coil member 31) is used to detect the current I to be measured, the detection unit 30 outputs a voltage signal S1 corresponding to an induced voltage generated in the single coil member 31. That is, the detection unit 30 outputs a voltage signal S1 corresponding to an induced voltage approximately proportional to the number of turns "N" of the single coil member 31.

[0033] In the detection unit 30, the number of turns according to the number of coil members 31 connected to the signal processing circuit 60 (integration circuit 61) is hereinafter referred to as the "effective number of turns." For example, when three coil members 31, the first coil member 31a, the second coil member 31b, and the third coil member 31c, are connected to the integration circuit 61, the effective number of turns of the detection unit 30 is "3N." When two coil members 31, the first coil member 31a and the second coil member 31b, are connected to the integration circuit 61, the effective number of turns of the detection unit 30 is "2N." When the first coil member 31a is connected to the integration circuit 61, the effective number of turns of the detection unit 30 is "N."

[0034] The signal processing circuit 60 is a circuit that processes the voltage signal S1 output from the detection unit 30. As shown in Fig. 2, the signal processing circuit 60 of this embodiment includes an integration circuit 61, an amplifier circuit 62, an A / D conversion circuit 63, and an arithmetic processing circuit 64. The signal processing circuit 60 may include other circuits as necessary.

[0035] The integrating circuit 61 has a first input terminal 61a, a second input terminal 61b, and an output terminal 61c. The first input terminal 61a of the integrating circuit 61 corresponds to the "first input terminal of the signal processing circuit 60." The second input terminal 61b of the integrating circuit 61 corresponds to the "second input terminal of the signal processing circuit 60."

[0036] A first input terminal 61a of the integrating circuit 61 is directly connected to one end 31a1 (the end on the −X direction side) of the first coil member 31a. The one end 31a1 of the first coil member 31a corresponds to one end 30a of the detecting unit 30.

[0037] The second input terminal 61b of the integration circuit 61 is connected to one of the other end 31a2 (end on the +X direction side) of the first coil member 31a, the other end 31b2 (end on the +X direction side) of the second coil member 31b, or the other end 31c2 (end on the +X direction side) of the third coil member 31c. The coil member 31 connected to the second input terminal 61b of the integration circuit 61 is switched by a switching circuit 70.

[0038] When the first input terminal 61a of the integrator circuit 61 is connected to one end 31a1 of the first coil member 31a and the second input terminal 61b of the integrator circuit 61 is connected to the other end 31c2 of the third coil member 31c, the number of coil members 31 that form a closed circuit together with the integrator circuit 61 and the switching circuit 70 is three: the first coil member 31a, the second coil member 31b, and the third coil member 31c.

[0039] When the first input terminal 61a of the integrator circuit 61 is connected to one end 31a1 of the first coil member 31a and the second input terminal 61b of the integrator circuit 61 is connected to the other end 31b2 of the second coil member 31b, the number of coil members 31 that form a closed circuit together with the integrator circuit 61 and the switching circuit 70 is two: the first coil member 31a and the second coil member 31b.

[0040] When the first input terminal 61a of the integrator circuit 61 is connected to one end 31a1 of the first coil member 31a and the second input terminal 61b of the integrator circuit 61 is connected to the other end 31a2 of the first coil member 31a, the number of coil members 31 that form a closed circuit together with the integrator circuit 61 and the switching circuit 70 is one, that is, the first coil member 31a.

[0041] The integrating circuit 61 integrates the voltage signal S1 output from the detecting unit 30. For example, when a first input terminal 61a of the integrating circuit 61 is connected to one end 31a1 of the first coil member 31a and a second input terminal 61b of the integrating circuit 61 is connected to the other end 31c2 of the third coil member 31c, the integrating circuit 61 integrates the voltage signal S1 corresponding to an induced voltage proportional to the effective number of turns of the detecting unit 30, "3N."

[0042] Furthermore, when the first input terminal 61a of the integrator circuit 61 is connected to one end 31a1 of the first coil member 31a and the second input terminal 61b of the integrator circuit 61 is connected to the other end 31b2 of the second coil member 31b, the integrator circuit 61 integrates a voltage signal S1 corresponding to an induced voltage proportional to the effective number of turns "2N" of the detection unit 30.

[0043] Furthermore, when the first input terminal 61a of the integrator circuit 61 is connected to one end 31a1 of the first coil member 31a and the second input terminal 61b of the integrator circuit 61 is connected to the other end 31a2 of the first coil member 31a, the integrator circuit 61 integrates a voltage signal S1 corresponding to an induced voltage proportional to the effective number of turns “N” of the detection unit 30.

[0044] The integrating circuit 61 integrates various voltage signals S1 output from the detecting unit 30 to generate a voltage signal S2 having a waveform corresponding to the measured current I flowing through the current bar 10. The integrating circuit 61 is connected to the amplifying circuit 62 via an output terminal 61c. The integrating circuit 61 outputs the voltage signal S2 to the amplifying circuit 62.

[0045] The amplifier circuit 62 amplifies the voltage signal S2 output from the integrating circuit 61. The amplifier circuit 62 of this embodiment amplifies the voltage signal S2 output from the integrating circuit 61 using a constant amplification factor G. As a result, the amplifier circuit 62 generates a voltage signal S3. The amplifier circuit 62 outputs the voltage signal S3 to the A / D conversion circuit 63.

[0046] Incidentally, the current detection device 1 may be set with a measurement allowable range Ra of the measurement target current I to ensure the reliability of the measurement result. When the current value Iv of the measurement target current I is the upper limit value Imax of the measurement allowable range Ra, the integration circuit 61 outputs a voltage signal S2 corresponding to the voltage value Vmax to the amplifier circuit 62. The amplifier circuit 62 amplifies the voltage signal S2 based on the amplification factor G. That is, the amplifier circuit 62 generates a voltage signal S3 of "Vmax×G" and outputs it to the A / D conversion circuit 63. Here, a maximum voltage related to the input voltage is set in the A / D conversion circuit 63. Therefore, the amplification factor G of the amplifier circuit 62 is adjusted so that the voltage value "Vmax×G" of the voltage signal S3 output to the A / D conversion circuit 63 does not exceed the maximum voltage allowed for input to the A / D conversion circuit 63.

[0047] The A / D conversion circuit 63 executes the processes of sampling, quantization, and encoding of the voltage signal S3 output from the amplifier circuit 62. As a result, the A / D conversion circuit 63 converts the voltage signal output from the amplifier circuit 62 into a digital signal S4. The A / D conversion circuit 63 outputs the digital signal S4 to the arithmetic processing circuit 64.

[0048] The arithmetic processing circuit 64 executes various arithmetic processing. The arithmetic processing circuit 64 of this embodiment includes a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores programs executed by the CPU, and the like. The arithmetic processing circuit 64 may be another electronic circuit having the same function as the CPU.

[0049] The arithmetic processing circuit 64 calculates the effective current value of the measurement target current I flowing through the current bar 10 based on the digital signal S4 output from the A / D conversion circuit 63. In this way, the arithmetic processing circuit 64 measures the current value Iv of the measurement target current I. However, the arithmetic processing circuit 64 may also calculate the maximum value or average value of the measurement target current I flowing through the current bar 10 based on the digital signal S4 output from the A / D conversion circuit 63.

[0050] The arithmetic processing circuit 64 outputs a control signal CK to the switching circuit 70 to switch the coil member 31 connected to the second input terminal 61b of the integrating circuit 61 among the multiple coil members 31 according to the current value Iv of the current I to be measured.

[0051] For example, when the measured current I is a relatively small current at or near the lower limit Imin of the measurement allowable range Ra, the arithmetic processing circuit 64 outputs a control signal CK to the switching circuit 70 to connect the other end 31c2 of the third coil member 31c to the second input terminal 61b of the integrating circuit 61. The switching circuit 70 connects the other end 31c2 of the third coil member 31c to the second input terminal 61b of the integrating circuit 61. As a result, the number of coil members 31 connected to the integrating circuit 61 becomes three, and the number of effective turns of the detecting unit 30 becomes "3N". As a result, the detecting unit 30 can output a voltage signal S1 reflecting a high induced voltage according to the effective number of turns 3N (the largest number of effective turns). That is, the integrating circuit 61, the amplifying circuit 62, the A / D conversion circuit 63, and the arithmetic processing circuit 64 can process various voltage signals S2, S3, and S4 derived from the voltage signal S1 reflecting the high induced voltage. Therefore, the measurement accuracy of the current I to be measured in the signal processing circuit 60 (arithmetic processing circuit 64) can be improved.

[0052] On the other hand, for example, when the measured current I is a relatively large current at or near the upper limit Imax of the measurement allowable range Ra, the arithmetic processing circuit 64 outputs a control signal CK to the switching circuit 70 to connect the other end 31a2 of the first coil member 31a to the second input terminal 61b of the integrating circuit 61. The switching circuit 70 connects the other end 31a2 of the first coil member 31a to the second input terminal 61b of the integrating circuit 61. As a result, the number of coil members 31 connected to the integrating circuit 61 becomes one, and the number of effective turns of the detecting unit 30 becomes "N". As a result, the detecting unit 30 can output a voltage signal S1 reflecting an induced voltage according to the effective number of turns "N" (the smallest number of effective turns). That is, the voltage signal S1 output from the detecting unit 30 is prevented from increasing excessively. As a result, even if a limit on the input voltage, etc. is set in at least one of the circuits, for example, the integration circuit 61, the amplification circuit 62, the A / D conversion circuit 63, and the arithmetic processing circuit 64, the various voltage signals S2, S3, and S4 derived from the voltage signal S1 are appropriately processed without exceeding the limit on the input voltage, etc.

[0053] Also, for example, when the measured current I is an intermediate current in the measurement allowable range Ra, the arithmetic processing circuit 64 outputs a control signal CK to the switching circuit 70 to connect the other end 31b2 of the second coil member 31b to the second input terminal 61b of the integrating circuit 61. The switching circuit 70 connects the other end 31b2 of the second coil member 31b to the second input terminal 61b of the integrating circuit 61. As a result, the number of coil members 31 connected to the integrating circuit 61 becomes two, and the number of effective turns of the detecting unit 30 becomes "2N". As a result, the detecting unit 30 can output a voltage signal S1 reflecting a relatively high induced voltage corresponding to the effective number of turns 2N (intermediate effective number of turns). As a result, the detecting unit 30 can output a voltage signal S1 reflecting a relatively high induced voltage corresponding to the effective number of turns 2N. In addition, it is possible to suppress the voltage signal S1 output from the detecting unit 30 from increasing excessively.

[0054] The switching circuit 70 switches the number of coil members 31 connected to the signal processing circuit 60. The switching circuit 70 of the present embodiment switches the number of coil members 31 connected to the integration circuit 61 by switching the coil members 31 connected to the second input terminal 61b of the integration circuit 61 among the multiple coil members 31.

[0055] The switching circuit 70 of the present embodiment is a selector circuit such as a multiplexer. However, the switching circuit 70 is not limited to a multiplexer as long as it is a circuit capable of switching the connection point of the detection unit 30 that is connected to the second input terminal 61b of the integration circuit 61.

[0056] 2, the switching circuit 70 of this embodiment includes a plurality of input terminals 71 (71a, 71b, 71c) respectively connected to the other end 31a2 of the first coil member 31a, the other end 31b2 of the second coil member 31b, and the other end 31c2 of the third coil member 31c, and an output terminal 72 connected to the second input terminal 61b of the integrating circuit 61. The input terminal 71a is connected to the other end 31c2 of the third coil member 31c. The input terminal 71b is connected to the other end 31b2 of the second coil member 31b. The input terminal 71c is connected to the other end 31a2 of the first coil member 31a. The number of input terminals 71 increases or decreases depending on the number of coil members 31.

[0057] The switching circuit 70 further includes a selector 73 (control terminal) that selects the input terminal 71 to be connected to the output terminal 72. The selector 73 of this embodiment selects the input terminal 71 that transmits the voltage signal S1 to the output terminal 72 in response to a control signal CK output from the arithmetic processing circuit 64 of the signal processing circuit 60. In other words, the selector 73 switches the connection point of the detection unit 30 that is connected to the second input terminal 61b of the integration circuit 61 among the other end 31a2 of the first coil member 31a, the other end 31b2 of the second coil member 31b, and the other end 31c2 of the third coil member 31c. However, the component that controls the selector 73 is not limited to the arithmetic processing circuit 64.

[0058] <Operation> Next, the operation of the current detection device 1 according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a graph showing the relationship between the current value Iv of the measurement target current I flowing through the current bar 10 and the voltage value of the voltage signal S3 input to the A / D conversion circuit 63. The voltage value of the voltage signal S3 input to the A / D conversion circuit 63 may be rephrased as the voltage signal S3 output from the amplifier circuit 62 to the A / D conversion circuit 63.

[0059] The solid line in FIG. 3 indicates the relationship between the current value Iv of the current to be measured I and the voltage value of the voltage signal S3 input to the A / D conversion circuit 63 in this embodiment. For ease of explanation, in the example shown in FIG. 3, the physical number of turns N of each coil member 31 is set to "1". In other words, the physical number of turns of the detection unit 30 is set to "3". In contrast, the dashed line in FIG. 3 indicates the relationship between the current value Iv of the current to be measured I and the voltage value of the voltage signal input to the A / D conversion circuit 63 for a comparative example in which the detection unit has a single coil member 31. The physical number of turns of the detection unit in the comparative example is set to "1".

[0060] The horizontal axis of FIG. 3 indicates the current value Iv of the measurement current I flowing through the current bar 10. Hereinafter, the "current value Iv of the measurement current I flowing through the current bar 10" will be referred to as the "measurement current I." Also, "Imin" shown on the horizontal axis of FIG. 3 is the lower limit of the current in the measurement allowable range Ra of the measurement current I set in the current detection device 1. Hereinafter, the lower limit of the current in the measurement allowable range Ra of the measurement current I will be referred to as the "lower limit Imin" or "Imin." "Imax" shown on the horizontal axis of FIG. 3 is the upper limit of the current in the measurement allowable range Ra of the measurement current I. Hereinafter, the upper limit of the current in the measurement allowable range Ra of the measurement current I will be referred to as the "upper limit Imax" or "Imax."

[0061] 3 is the maximum voltage value of the voltage signal S3 that is permitted to be input to the A / D conversion circuit 63. Here, "Vmax" indicates the maximum voltage value of the voltage signal S2 output from the integration circuit 61 to the amplifier circuit 62. "G" indicates the amplification factor of the amplifier circuit 62.

[0062] When the measured current I is in a first range Ra1 including the lower limit Imin of the measurement allowable range Ra, the arithmetic processing circuit 64 outputs a control signal CK to the switching circuit 70 to connect the other end 31c2 of the third coil member 31c to the second input terminal 61b of the integrating circuit 61. The switching circuit 70 connects the other end 31c2 of the third coil member 31c to the second input terminal 61b of the integrating circuit 61 in response to the control signal CK output from the arithmetic processing circuit 64. As a result, the number of coil members 31 connected to the integrating circuit 61 becomes three, and the number of effective turns of the detecting unit 30 becomes "3". The integrating circuit 61 processes a voltage signal S1 output from the detecting unit 30 with the effective number of turns "3". An example of the first range Ra1 is a current range of the measured current I from "I=0" to "I=(Imax / 3)".

[0063] In the first range Ra1, the number of effective turns of the detection unit 30 is "3", and therefore the induced voltage generated in the detection unit 30 is about three times higher than the induced voltage generated in the detection unit of the comparative example, which has an effective number of turns of "1". In other words, the voltage value of the voltage signal S1 output from the detection unit 30 is about three times higher than the voltage value of the voltage signal generated by the detection unit of the comparative example.

[0064] The voltage signal output from the detection unit 30 of this embodiment and the voltage signal output from the detection unit of the comparative example are input to an A / D conversion circuit 63 via an integration circuit 61 and an amplification circuit 62, respectively. That is, in this embodiment, in the first range Ra1, the voltage value of the voltage signal S3 input to the A / D conversion circuit 63 is increased by about three times compared to the comparative example. As a result, a voltage signal reflecting a high voltage value can be input to the A / D conversion circuit 63 and the arithmetic processing circuit 64. This increases the resolution and S / N ratio in the A / D conversion circuit 63, and improves the measurement accuracy of the measured current I in the arithmetic processing circuit 64.

[0065] On the other hand, when the measured current I exceeds, for example, "I=(Imax / 3)", the voltage value of the voltage signal S3 input to the A / D conversion circuit 63 exceeds "Vmax×G". That is, if the effective number of turns of the detection unit 30 is "3", the voltage signal S3 based on the measured current I exceeding "I=(Imax / 3)" cannot be input to the A / D conversion circuit 63. At this time, the arithmetic processing circuit 64 determines that the measured value of the measured current I exceeds the first switching value SV1 (for example, I=(Imax / 3)), and outputs a control signal CK to the switching circuit 70 to switch the effective number of turns of the detection unit 30 from "3" to "2". That is, the arithmetic processing circuit 64 outputs a control signal CK to the switching circuit 70 to connect the other end 31b2 of the second coil member 31b and the second input terminal 61b of the integration circuit 61. The number of effective turns of the detection unit 30 is switched to "2", and the range of the measured current I is set as a second range Ra2. An example of the second range Ra2 is a current range of the measured current I from "I=(Imax / 3)" to "I=(Imax / 2)". The "second range Ra2" is an example of "a current range of the measured current I between a current range including the lower limit Imin and a current range including the upper limit Imax within the measurement allowable range Ra".

[0066] The switching circuit 70 connects the other end 31b2 of the second coil member 31b to the second input terminal 61b of the integrating circuit 61 in response to the control signal CK output from the arithmetic processing circuit 64. As a result, the number of coil members 31 connected to the integrating circuit 61 is reduced from three to two. Accordingly, the number of effective turns of the detecting section 30 is reduced from "3" to "2". As a result, the voltage value of the voltage signal S3 input to the A / D conversion circuit 63 becomes lower than "Vmax×G". Therefore, the A / D conversion circuit 63 can process the voltage signal S3. Furthermore, the arithmetic processing circuit 64 can measure the measured current I based on the voltage signal S4 output from the A / D conversion circuit 63.

[0067] In the second range Ra2, since the effective number of turns of the detection unit 30 is "2", the induced voltage generated in the detection unit 30 is about twice as high as the induced voltage generated in the detection unit of the comparative example having the effective number of turns of "1". That is, in the second range Ra2, the voltage value of the voltage signal S1 output from the detection unit 30 is about twice as high as the voltage value of the voltage signal generated from the detection unit of the comparative example. That is, in the second range Ra2, the voltage value of the voltage signal S3 input to the A / D conversion circuit 63 is about twice as high as the comparative example. As a result, even in the second range Ra2, a voltage signal reflecting a high voltage value can be input to the A / D conversion circuit 63 and the arithmetic processing circuit 64. This improves the resolution and S / N ratio in the A / D conversion circuit 63, and improves the measurement accuracy of the measured current I in the arithmetic processing circuit 64.

[0068] On the other hand, when the measured current I exceeds, for example, "I=(Imax / 2)", the voltage value of the voltage signal S3 input to the A / D conversion circuit 63 exceeds "Vmax×G". That is, if the effective number of turns of the detection unit 30 is "2", the voltage signal S3 based on the measured current I exceeding "I=(Imax / 2)" cannot be input to the A / D conversion circuit 63. At this time, the arithmetic processing circuit 64 determines that the measured value of the measured current I exceeds the second switching value SV2 (for example, I=(Imax / 2)), and outputs a control signal CK to the switching circuit 70 to switch the effective number of turns of the detection unit 30 from "2" to "1". That is, the arithmetic processing circuit 64 outputs a control signal CK to the switching circuit 70 to connect the other end 31a2 of the first coil member 31a and the second input terminal 61b of the integration circuit 61. The range of the measurement current I measured when the effective number of turns of the detection unit 30 is switched to "1" is set as a third range Ra3. The third range Ra3 includes the upper limit value Imax of the measurement allowable range Ra. One example of the third range Ra3 is a current range in which the measurement current I is from "I=(Imax / 2)" to "I=Imax". The "third range Ra3" is an example of "a current range in which the measurement current I includes the upper limit value Imax of the measurement allowable range Ra".

[0069] The switching circuit 70 connects the other end 31a2 of the first coil member 31a to the second input terminal 61b of the integrating circuit 61 in response to the control signal CK output from the arithmetic processing circuit 64. As a result, the number of coil members 31 connected to the integrating circuit 61 is reduced from three to two. Accordingly, the number of effective turns of the detecting section 30 is reduced from "2" to "1". As a result, the voltage value of the voltage signal S3 input to the A / D conversion circuit 63 becomes lower than "Vmax×G". Therefore, the A / D conversion circuit 63 can process the voltage signal S3, and the arithmetic processing circuit 64 can continue to measure the measured current I even if the measured current I exceeds "I=(Imax / 2)".

[0070] In the third range Ra3, the effective number of turns of the detection unit 30 and the effective number of turns of the detection unit in the comparative example are both "1". Therefore, the voltage signal S3 input to the A / D conversion circuit 63 of this embodiment is almost the same as the voltage signal input to the A / D conversion circuit 63 in the comparative example. The measured current I in the third range Ra3 is the highest in the measurement allowable range Ra. That is, even in the third range Ra3, a voltage signal reflecting a high voltage value can be input to the A / D conversion circuit 63 and the arithmetic processing circuit 64. This improves the resolution and S / N ratio in the A / D conversion circuit 63, and improves the measurement accuracy of the measured current I in the arithmetic processing circuit 64. The first switching value SV1 is not limited to "Imax / 3". The second switching value SV2 is not limited to "Imax / 2".

[0071] The same explanation is also valid when the number of coil members 31 in the detection unit 30 is four or more. In this case as well, the switching circuit 70 gradually reduces the number of coil members 31 connected to the integrating circuit 61 as the measured current I increases. These switching operations in the switching circuit 70 may be based on a control signal CK output from the arithmetic processing circuit 64.

[0072] <Action and effect> According to this embodiment, the switching circuit 70 switches the number of coil members connected to the signal processing circuit 60. For example, when the current value Iv of the current I to be measured is relatively small, the switching circuit 70 increases the number of coil members 31 connected to the signal processing circuit 60. This allows the detection unit 30 to detect the current I to be measured with a large number of effective turns. As a result, even if the current value Iv of the current I to be measured is relatively small, a voltage signal reflecting a high voltage value can be input to the A / D conversion circuit 63 and the arithmetic processing circuit 64 of the signal processing circuit 60. This improves the measurement accuracy of the current I to be measured in the signal processing circuit 60.

[0073] On the other hand, when the current value Iv of the current to be measured I is relatively large, a relatively high induced voltage is generated in the detection unit 30 regardless of the number of effective turns. That is, even if the number of coil members 31 connected to the signal processing circuit 60 is small, a voltage signal reflecting a high voltage value can be input to the A / D conversion circuit 63 and the arithmetic processing circuit 64 of the signal processing circuit 60. This improves the measurement accuracy of the current to be measured I in the signal processing circuit 60. The same applies to the case where the current value Iv of the current to be measured I is intermediate. For these reasons, according to this embodiment, the measurement accuracy of the current to be measured I can be improved regardless of the current value of the current to be measured I.

[0074] [Second embodiment] Next, an example of a circuit configuration of a current detection device 1A according to a second embodiment will be shown with reference to Fig. 4. Fig. 4 is a schematic diagram showing an example of a circuit configuration of a current detection device 1A according to a second embodiment. However, in the second embodiment, explanations of components similar to those in the first embodiment will be omitted as appropriate.

[0075] The current detection device 1A according to the second embodiment includes a current bar 10, a magnetic core 20, a detection unit 30, a signal processing circuit 60, and a switching circuit 80. In this embodiment, the configuration of the switching circuit 80 is different from the configuration of the switching circuit 70 in the first embodiment.

[0076] The switching circuit 80 of the present embodiment includes a plurality of analog switches 81. In response to the switching operation of each of the plurality of analog switches 81, the number of coil members 31 connected to the signal processing circuit 60 is switched.

[0077] 4, when the number of coil members 31 is "m" (where "m" is a positive integer equal to or greater than 2), the switching circuit 80 includes (2m-1) analog switches 81. The switching circuit 80 further includes (2m-1) input terminals 82, (2m-1) output terminals 83, and a control unit (control terminal) 89 that controls the operation of the multiple analog switches 81. The control unit 89 may control the multiple analog switches 81 through a control signal CK output from the arithmetic processing circuit 64.

[0078] Since the number of coil members 31 in this embodiment is "3", the switching circuit 80 includes five analog switches 81a, 81b, 81c, 81d, and 81e, five input terminals 82a, 82b, 82c, 82d, and 82e, and five output terminals 83a, 83b, 83c, 83d, and 83e.

[0079] The input terminal 82a is connected to the other end 31a2 of the first coil member 31a through a wiring 85a. The input terminal 82b is connected to the other end 31a2 of the first coil member 31a through a wiring 85b. The input terminal 82c is connected to the other end 31b2 of the second coil member 31b through a wiring 85c. The input terminal 82d is connected to the other end 31b2 of the second coil member 31b through a wiring 85d. The input terminal 82e is connected to the other end 31c2 of the third coil member 31c through a wiring 85e.

[0080] The output terminal 83a is connected to one end 31b1 of the second coil member 31b through a wiring 86a. The output terminal 83b is connected to the second input terminal 61b of the integrating circuit 61 through a wiring 86b. The output terminal 83c is connected to one end 31c1 of the third coil member 31c through a wiring 86c. The output terminal 83d is connected to the second input terminal 61b of the integrating circuit 61 through a wiring 86d. The output terminal 83e is connected to the second input terminal 61b of the integrating circuit 61 through a wiring 86e. The one end 31a1 of the first coil member 31a is connected to the first input terminal 61a of the integrating circuit 61.

[0081] The connection / disconnection between the input terminal 82a and the output terminal 83a is switched depending on whether the analog switch 81a is opened or closed. The connection / disconnection between the input terminal 82b and the output terminal 83b is switched depending on whether the analog switch 81b is opened or closed. The connection / disconnection between the input terminal 82c and the output terminal 83c is switched depending on whether the analog switch 81c is opened or closed. The connection / disconnection between the input terminal 82d and the output terminal 83d is switched depending on whether the analog switch 81d is opened or closed. The connection / disconnection between the input terminal 82e and the output terminal 83e is switched depending on whether the analog switch 81e is opened or closed.

[0082] <Operation> Next, the operation of the switching circuit 80 in the current detection device 1A according to the present embodiment will be described with reference to FIGS.

[0083] 5, an operation of the switching circuit 80 connecting the other end 31c2 of the third coil member 31c to the second input terminal 61b of the integrating circuit 61 and connecting the three coil members 31 to the integrating circuit 61 will be described. Here, the two-dot chain line shown in FIG. 5 indicates the signal path of the voltage signal S1 output from the detection unit 30 to the integrating circuit 61.

[0084] As shown in FIG. 5, the switching circuit 80 closes each of the analog switches 81a, 81c, and 81e based on the control signal CK output from the arithmetic processing circuit 64. The analog switch 81a connects the input terminal 82a to the output terminal 83a. The analog switch 81c connects the input terminal 82c to the output terminal 83c. The analog switch 81e connects the input terminal 82e to the output terminal 83e. This forms a closed circuit including the first coil member 31a, the second coil member 31b, the third coil member 31c, the switching circuit 80, and the integrating circuit 61. As a result, the number of coil members 31 connected to the integrating circuit 61 becomes three.

[0085] 6, an operation of the switching circuit 80 connecting the other end 31b2 of the second coil member 31b to the second input terminal 61b of the integrating circuit 61 and connecting the two coil members 31 to the integrating circuit 61 will be described. Here, the two-dot chain line shown in FIG. 6 indicates the signal path of the voltage signal S1 output from the detecting unit 30 to the integrating circuit 61.

[0086] 6, the switching circuit 80 closes the analog switches 81a and 81d based on the control signal CK output from the arithmetic processing circuit 64. The analog switch 81a connects the input terminal 82a to the output terminal 83a. The analog switch 81d connects the input terminal 82d to the output terminal 83d. This forms a closed circuit including the first coil member 31a, the second coil member 31b, the switching circuit 80, and the integrating circuit 61. As a result, the number of coil members 31 connected to the integrating circuit 61 becomes two.

[0087] 7, an operation of the switching circuit 80 connecting the other end 31a2 of the first coil member 31a to the second input terminal 61b of the integrating circuit 61 and connecting the single coil member 31 to the integrating circuit 61 will be described. Here, the two-dot chain line shown in FIG. 7 indicates the signal path of the voltage signal S1 output from the detection unit 30 to the integrating circuit 61.

[0088] 7, the switching circuit 80 closes the analog switch 81b based on the control signal CK output from the arithmetic processing circuit 64. The analog switch 81b connects the input terminal 82b and the output terminal 83b. This forms a closed circuit including the first coil member 31a, the switching circuit 80, and the integrating circuit 61. As a result, the number of coil members 31 connected to the integrating circuit 61 becomes one.

[0089] <Action and effect> According to the switching circuit 80 of this embodiment, the input signals input to each of the multiple input terminals 82 are output from different output terminals 83 through different analog switches 81. This makes it possible to suppress defects such as crosstalk in which the voltage signal S1 input to an arbitrary input terminal 82 is mixed with a path different from the original path. As a result, noise in the voltage signal S1 can be suppressed. In addition, the second coil member 31b is cut off from the signal processing circuit 60 by the multiple analog switches 81 in the open state. Similarly, the third coil member 31c is cut off from the signal processing circuit 60 by the multiple analog switches 81 in the open state. This makes it possible to further improve off-isolation for the second coil member 31b and the third coil member 31c. Other effects of this embodiment are the same as those of the first embodiment.

[0090] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited by the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made within the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. For example, the switching circuit that switches the number of coil members connected to the signal processing circuit may be a circuit having a configuration different from that of a multiplexer or an analog switch. [Explanation of symbols]

[0091] 1 Current detection device 10 Current Bar 20 Magnetic Core 21 Gap section 22 Main body 30 Detection unit 31 Coil parts 31a First coil member 31b Second coil member 31c Third coil member 60 Signal Processing Circuit 61 Integral circuit 62 Amplification circuit 63 A / D conversion circuit 64 Arithmetic processing circuit 70,80 switching circuit

Claims

1. A current bar for passing a current to be measured; a magnetic core provided around the current bar and having a gap; a detection unit including a plurality of coil members provided in the gap portion of the magnetic core and connected in series with each other; a signal processing circuit for processing a detection signal of the current to be measured outputted from the detection unit; a switching circuit for switching the number of the coil members connected to the signal processing circuit in the detection unit; A current detection device comprising:

2. The current detection device according to claim 1 , wherein the switching circuit switches the number of the coil members to switch the effective number of turns of the detection section.

3. 3. The current detection device according to claim 1, wherein the switching circuit gradually reduces the number of the coil members connected to the signal processing circuit as the measured current increases.

4. The switching circuit includes a plurality of analog switches, 3. The current detection device according to claim 1, wherein the number of the coil members connected to the signal processing circuit is changed in response to switching operations of the respective analog switches.

Images