Current sensor

1. Field of the Invention

The present application is based on, and claims priority from, JP2020-28577, filed on Feb. 21, 2020, the disclosure of which is hereby incorporated by reference herein in its entirety.

The present invention relates to a current sensor.

2. Description of the Related Art

A current sensor is known that measures electric current that flows in a current line by detecting a magnetic field that is induced by the electric current. JP2013-228315 discloses a current sensor having an open main core that surrounds a busbar (a current line) and a sub-core that is arranged outside of the main core and that is adjacent to the open ends of the main core. A magnetic field detecting element is disposed between the open ends of the main core. The main core is provided to collect magnetic flux. Since the main core is made of a magnetic material, residual magnetization occurs when current does not flow in the current line. The magnetic field detecting element detects a magnetic field that is caused by the residual magnetization when current does not flow. This magnetic field is one of the causes of measurement error because the magnetic field is not generated by electric current that flows in the current line. However, residual magnetization occurs in the sub-core in a direction opposite to the residual magnetization in the main core. Therefore, the magnetic field that is caused by the residual magnetization of the sub-core weakens the magnetic field that is caused by the residual magnetization of the main core, and the influence of the residual magnetization of the main core is reduced.

In the current sensor disclosed in JP2013-228315, the area where the residual magnetization of the sub-core weakens the residual magnetization of the main core is limited. Therefore, the arrangement of the magnetic field detecting element is significantly limited.

The present invention aims at providing a current sensor that is less affected by the residual magnetization.

A current sensor of the present invention comprises a magnetic circuit that is magnetized by electric current; a first magnetic field detecting element that is positioned where a magnetic field, when the electric current is present, is directed in a same direction as a magnetic field that is caused by residual magnetization of the magnetic circuit when the electric current is not present; and a second magnetic field detecting element that is positioned where a magnetic field, when the electric current is present, is directed opposite to a direction of a magnetic field that is caused by residual magnetization of the magnetic circuit when the electric current is not present.

According to the present invention, it is possible to provide a current sensor that is less affected by the residual magnetization.

The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.

FIGS. 1 A to 1 B are schematic views of a current sensor according to a first embodiment;

FIGS. 2 A to 2 D are conceptual views illustrating an external magnetic field that is applied to the current sensor shown in FIGS. 1 A to 1 B ;

FIG. 3 A is a view showing the positions of the first and second magnetic field detecting elements in the first embodiment;

FIG. 3 B is a view showing the position of a magnetic field detecting element in a comparative example;

FIG. 3 C is a graph showing the relationship between the position of the magnetic field detecting element and hysteresis;

FIGS. 4 A to 4 C are schematic views of a current sensor according to a modification of the first embodiment;

FIGS. 5 A to 5 C are schematic views of a current sensor according to a modification of the first embodiment;

FIGS. 6 A to 6 B are schematic views of a current sensor according to a modification of the first embodiment;

FIGS. 7 A to 7 B are schematic views of a current sensor according to a modification of the first embodiment;

FIGS. 8 A to 8 B are schematic views of a current sensor according to a modification of the first embodiment;

FIGS. 9 A to 9 C are schematic views of a current sensor according to a modification of the first embodiment;

FIGS. 10 A to 10 B are schematic views of a current sensor according to a second embodiment;

FIGS. 11 A to 11 B are conceptual views illustrating an external magnetic field that is applied to the current sensor shown in FIGS. 10 A to 10 B ; and

FIGS. 12 A to 12 C are schematic views of a current sensor according to a third embodiment.

With reference to the drawings, several embodiments of current sensor 1 A to 1 J of the present invention will be described. In the description below, the direction along which current lines 2 A, 2 B extend is referred to as the X direction, the direction along which a normal line, that is drawn from the center axis of current lines 2 A, 2 B to the center of first magnetic field detecting element 5 , extends is referred to as the Z direction, and the direction perpendicular both to the X direction and to the Z direction is referred to as the Y direction. When the current line is a busbar, the Y direction is parallel to the width direction of the busbar. In each drawing, the direction of a magnetic field that is applied to first magnetic field detecting element 5 when current flows in current lines 2 A, 2 B is referred to as the +Y direction, and the opposite direction is the −Y direction. The current sensor of the present invention is configured to measure the electric current that flows in current lines 2 A, 2 B, and current lines 2 A, 2 B themselves are not included in the current sensor. However, it is possible to incorporate the current line near the current sensor as a part of the current sensor. Current lines 2 A, 2 B are examples of a region where electric current flows, and in the following embodiments, a current line is used as an example, but the region where electric current flows is not limited to a current line, and any continuous conductor may be used.

First Embodiment

FIG. 1 A is a perspective view of current sensor 1 A according to the first embodiment, and FIG. 1 B is a section view taken along line A-A in FIG. 1 A . Current sensor 1 A has first magnetic circuit 3 A that surrounds current line 2 A and second magnetic circuit 4 A that is positioned outside of current line 2 A. First magnetic circuit 3 A and second magnetic circuit 4 A are positioned in the same plane (the Y-Z plane) that is perpendicular to the X direction. First magnetic circuit 3 A and second magnetic circuit 4 A are magnetic circuits, each consisting of a core that is made of a soft magnetic material, such as NiFe. Current line 2 A is a plate-like busbar having a rectangular section. Current sensor 1 A is used, for example, to measure electric current that flows in a busbar that is connected to a battery, but the arrangement and type of current line 2 A is not limited.

First magnetic circuit 3 A has a rectangular shape having a pair of long sides 31 A, 31 B that extend in the Y direction and a pair of short sides 32 A, 32 B that extend in the Z direction and that are perpendicular to long sides 31 A, 31 B, as viewed in the X direction. First magnetic circuit 3 A is an open magnetic circuit that surrounds current line 2 A. Void portion 33 is provided at the center of one of the long sides (long side 31 B), and open end 34 A, 34 B of first magnetic circuit 3 A are positioned on both sides of void portion 33 . The remaining part of long side 31 B that has void portion 33 forms both end regions 35 A, 35 B of first magnetic circuit 3 A. Second magnetic circuit 4 A is provided adjacent to first magnetic circuit 3 A in the Z direction. Second magnetic circuit 4 A is positioned outside of current line 2 A and does not surround current line 2 A. Like first magnetic circuit 3 A, second magnetic circuit 4 A has a rectangular shape having a pair of long sides 41 A, 41 B that extend in the Y direction and a pair of short sides 42 A, 42 B that extend in the Z direction. Second magnetic circuit 4 A is also an open magnetic circuit. Void portion 43 is provided at the center of one of the long sides (long sides 41 B), and open ends 44 A, 44 B of second magnetic circuit 4 A are positioned on both sides of void portion 43 . The remaining part of long side 41 B having void portion 43 forms both end regions 45 A, 45 B of second magnetic circuit 4 A. Void portion 43 of second magnetic circuit 4 A faces void portion 33 of first magnetic circuit 3 . Both end regions 45 A, 45 B of second magnetic circuit 4 A extend in the Y direction along both end regions 35 A, 35 B of first magnetic circuit 3 A. Due to this arrangement, second magnetic circuit 4 A is easily magnetized by first magnetic circuit 3 A.

First magnetic field detecting element 5 is disposed in void portion 33 of first magnetic circuit 3 A, i.e., between both open ends 34 A, 34 B. Second magnetic field detecting element 6 is disposed in void portion 43 of second magnetic circuit 4 A, i.e., between both open ends 44 A, 44 B. First and second magnetic field detecting elements 5 , 6 are Hall elements, but may be magneto-resistive elements, such as AMR elements, TMR elements and GMR elements. The direction in which first field detecting element 5 senses a magnetic field and the direction in which second magnetic field detecting element 6 senses a magnetic field are the Y direction, and they are parallel to each other. Specifically, first magnetic field detecting element 5 detects a magnetic field that connects both open ends of 34 A, 34 B of first magnetic circuit 3 A in the Y direction, and second magnetic field detecting element 6 detects a magnetic field that connects both open ends 44 A, 44 B of second magnetic circuit 4 A in the Y direction. The output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 have the same polarity. Specifically, when a magnetic field is applied to first magnetic field detecting element 5 and second magnetic field detecting element 6 in the same direction, the sign of the output of first magnetic field detecting element 5 is the same as the sign of the output of second magnetic field detecting element 6 . First magnetic field detecting element 5 and second magnetic field detecting element 6 are positioned on the same side of current line 2 A and are mounted on common substrate 7 . Therefore, the process of assembling current sensor 1 A is simplified.

Current sensor 1 A has first amplifier 8 that is connected to first magnetic field detecting element 5 , second amplifier 9 that is connected to second magnetic field detecting element 6 and adder 10 that is connected both to first amplifier 8 and to second amplifier 9 . First amplifier 8 , second amplifier 9 and adder 10 are disposed on substrate 7 . First amplifier 8 amplifies the output of first magnetic field detecting element 5 , and second amplifier 9 amplifies the output of second magnetic field detecting element 6 . Adder 10 generates a sum of the output of first amplifier 8 and the output of second amplifier 9 . Current sensor 1 A outputs the output of adder 10 to the outside of current sensor 1 A.

FIG. 2 A and FIG. 2 B conceptually illustrate an external magnetic field that is applied to current sensor 1 A when current flows in current line 2 A and when current does not flow in current line 2 A, respectively. FIG. 2 C and FIG. 2 D show enlarged views of portion A in FIG. 2 A and FIG. 2 B , respectively. FIG. 2 C and FIG. 2 D are based on simulation. As shown by the solid lines in FIG. 2 A , a clockwise magnetic flux is generated around current line 2 A when current flows in current line 2 A. Since first magnetic circuit 3 A has a shape that conforms to magnetic flux that is generated by current line 2 A, first magnetic circuit 3 A is magnetized clockwise, as illustrated, and can collect magnetic flux. As shown in FIG. 2 C , due to the magnetic field that is generated by current line 2 A and the magnetic field that is generated by first magnetic circuit 3 A, a strong magnetic field is generated in the +Y direction between both open ends 34 A, 34 B of first magnetic circuit 3 A. Now assume that the output of first magnetic field detecting element 5 in this state is positive. As shown in FIG. 2 A , a part of the magnetic flux that exits left end region 35 A of first magnetic circuit 3 A is sucked by left end region 45 A of second magnetic circuit 4 A, further progresses clockwise along second magnetic circuit 4 A and is sucked by right end region 35 A of first magnetic circuit 3 A from right end region 45 . As shown in FIG. 2 C , instead of a magnetic field that is directed in the −Y direction from right open end 44 B to left open end 44 A, a magnetic field that is directed in the +Y direction from left open end 44 A to right open end 44 B is generally applied to the area between both open ends 44 A, 44 B of second magnetic circuit 4 A. In other words, second magnetic circuit 4 A is magnetized clockwise, but due to the influence of first magnetic circuit 3 A, a magnetic field that is directed in the same direction as the magnetic field between both open ends 34 A, 34 B is generated between both open ends 44 A, 44 B. As a result, the output of second magnetic field detecting element 6 is also positive.

As shown by the dashed line in FIG. 2 B , when current does not flow in current line 2 A, that is, when the electric current is lost in current line 2 A, residual magnetization is generated in first and second magnetic circuits 3 , 4 . The direction of the residual magnetization of first and second magnetic circuits 3 , 4 coincides with the magnetization direction of first and second magnetic circuits 3 , 4 when current flows. As a result, a magnetic field is generated in the +Y direction between both open ends 34 A, 34 B of first magnetic circuit 3 A, and the output of first magnetic field detecting element 5 is still positive. On the other hand, between both open ends 44 A, 44 B of second magnetic circuit 4 A, a magnetic field is generated in the −Y direction, and the output of second magnetic field detecting element 6 becomes negative. This is because the influence of the magnetic field that is generated by current line 2 A is lost. That is, the output of first magnetic field detecting element 5 between both open ends 34 A, 34 B of first magnetic circuit 3 A that surrounds current line 2 A is positive both when current flows and when current does not flow, while the output of second magnetic field detecting element 6 between both open ends 44 A, 44 B of second magnetic circuit 4 A that is positioned outside of current line 2 A is positive when current flows and is negative when current does not flow. This is because, in essence, first magnetic field detecting element 5 and second magnetic field detecting element 6 are positioned on the same side of current line 2 A.

As described above, when current does not flow, the magnetic field that is detected by first magnetic field detecting element 5 and the magnetic field that is detected by second magnetic field detecting element 6 have different directions (signs). Therefore, when current does not flow, by obtaining the sum of the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 , the hysteresis that is caused by the residual magnetization of first and second magnetic circuits 3 , 4 can be cancelled out or reduced. On the other hand, when current flows, the magnetic field that is detected by first magnetic field detecting element 5 and the magnetic field that is detected by second magnetic field detecting element 6 have the same direction (sign). Therefore, by obtaining the sum of the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 , the output can be increased. Accordingly, current sensor 1 A of the present embodiment is less affected by hysteresis while the S/N ratio is improved.

FIGS. 3 A to 3 C Illustrates the influence of the position of the magnetic field detecting elements on hysteresis. As shown in FIG. 3 A , the hysteresis was measured for first and second magnetic field detecting elements 5 , 6 of the present embodiment that are provided at various positions in the Z direction. The gap between first magnetic field detecting element 5 and second magnetic field detecting element 6 in the Z direction is constant. In a comparative example, as shown in FIG. 3 B , the hysteresis was measured for magnetic field detecting element 105 that is provided at various positions in the Z direction. In the comparative example, one magnetic field detecting element 105 is provided between first magnetic field detecting element 5 and second magnetic field detecting element 6 . The hysteresis was calculated as [the density of the residual magnetic flux / the density of the detected magnetic flux]×maximum measured electric current (A). In FIG. 3 C , the horizontal axis is the position of the magnetic field detecting elements in the Z direction, and the vertical axis is the hysteresis (in the present embodiment, the sum of hysteresis of first magnetic field detecting element 5 and hysteresis of second magnetic field detecting element 6 at the positions in the Z direction). In the present embodiment, the sum of the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 when current does not flow is zero at the optimum position. In the comparative example, the output of the magnetic field detecting element when current does not flow is zero at the optimum position. As the distance between the positions of the magnetic field detecting elements and the optimum position increases in the Z direction, the density of the residual magnetic flux increases, and the hysteresis increases.

In the present embodiment, the change of the hysteresis is relatively small, as compared to the change of the positions of first and second magnetic field detecting elements 5 , 6 in the Z direction. On the other hand, in the comparative example, the change of the hysteresis is relatively large, as compared to the change of the position of magnetic field detecting element 105 in the Z direction. This means that the present embodiment allows a wide range for the positions of first and second magnetic field detecting elements 5 , 6 in the Z direction. In the comparative example, the range having small hysteresis is limited. Therefore, the shapes, positional relationship and so on of first and second magnetic circuits 3 , 4 need to be optimized such that the residual magnetic flux becomes as close to zero as possible in the area where magnetic field detecting element 105 is disposed. On the other hand, the need for such optimization is small in the present embodiment. In addition, in the present embodiment, even if the absolute value of the output of first magnetic field detecting element 5 is not the same as the absolute value of the output of second magnetic field detecting element 6 when current does not flow, the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 can be easily cancelled out by adjusting the gains of first amplifier 8 and second amplifier 9 . Specifically, the gains of first amplifier 8 and second amplifier 9 may be set such that the absolute value of the output of first amplifier 8 when current does not flow and the absolute value of the output of second amplifier 9 when current does not flow are about the same level. In the present embodiment, when the shapes, positional relationship and so on of first and second magnetic circuits 3 , 4 are determined, it is not necessary to consider the hysteresis as an important factor. In the comparative example, it is, in principle, impossible to reduce the hysteresis by adjusting the gain of the amplifier.

As a modification of the present embodiment, the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 may have different polarities. Specifically, when a magnetic field is applied to first magnetic field detecting element 5 and second magnetic field detecting element 6 in the same direction, the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 have different signs. In case of a Hall element, electric current that is applied to first magnetic field detecting element 5 and electric current that is applied to second magnetic field detecting element 6 may be directed in opposite directions. As a result, a positively charged surface is changed to a negatively charged surface (and vice versa), and the sign of the output can be reversed. In case of a magneto-resistive element, the magnetization pinned layer of first magnetic field detecting element 5 and the magnetization pinned layer of second magnetic field detecting element 6 may be magnetized in opposite directions. By reversing the polarity of the output of first magnetic field detecting element 5 or the output of second magnetic field detecting element 6 , the sign of the output of first magnetic field detecting element 5 and the sign of the output of second magnetic field detecting element 6 are different from each other when current flows, and coincide with each other when current does not flow. Therefore, in the present modification, by providing means for obtaining a difference between the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 , such as a subtractor, the same effect as the above-described embodiment can be achieved.

FIGS. 4 A to 4 C show another modification of the present embodiment. FIG. 4 A is a perspective view of current sensor 1 B according to the present modification, FIG. 4 B is a section view taken along line A-A in FIG. 4 A , and FIG. 4 C is a section view taken along line B-B in FIG. 4 A . First magnetic circuit 3 A and second magnetic circuit 4 A are aligned in the X direction. Specifically, first magnetic circuit 3 A and second magnetic circuit 4 A are positioned in different Y-Z planes that are perpendicular to the X direction. First magnetic circuit 3 A surrounds current line 2 A, and second magnetic circuit 4 A is positioned outside of current line 2 A. In the present modification, first and second magnetic circuits 3 , 4 are magnetized in the same manner as the embodiment described above. As shown in FIG. 4 A , when current flows, magnetic flux flows in the X direction from end region 35 A of first magnetic circuit 3 A to end region 45 A of second magnetic circuit 4 A, and flows in the X direction from opposite end region 45 B of second magnetic circuit 4 A to end region 35 B of first magnetic circuit 3 . The magnetic flux flows in second magnetic circuit 4 A in the same manner as the embodiment described above. Therefore, the magnetic field between both open ends 44 A, 44 B of second magnetic circuit 4 is directed in opposite directions when current flows and when current does not flow. According to the present modification, the dimension of current sensor 1 B in the Z direction can be limited.

FIGS. 5 A to 5 C show another modification of the present embodiment. FIG. 5 A a perspective view of current sensor 1 C according to the present modification, FIG. 5 B is a section view taken along line A-A in FIG. 5 A , and FIG. 5 C a section view taken along line B-B in FIG. 5 A . First magnetic circuit 3 A is positioned in a Y-Z plane that is perpendicular to the X direction, and second magnetic circuit 4 A is positioned in a X-Y plane that is parallel to the X direction. Since void portion 33 of first magnetic circuit 3 A and void portion 43 of second magnetic circuit 4 A face each other, first magnetic field detecting element 5 and second magnetic field detecting element 6 can be mounted on common substrate 7 . In the present modification, the magnetic flux flows in second magnetic circuit 4 A in the same manner as the embodiments described above, and the same effect as the embodiments described above can be achieved.

FIGS. 6 A to 6 B show another modification of the present embodiment. FIG. 6 A is a perspective view of current sensor 1 D according to the present modification, and FIG. 6 B is a section view taken along line A-A in FIG. 6 A . First magnetic circuit 3 A and second magnetic circuit 4 A are positioned in the same plane that is perpendicular to the direction in which current line 2 A extends. Second magnetic circuit 4 A is positioned inside of first magnetic circuit 3 A. Since void portion 33 of first magnetic circuit 3 A and void portion 43 of second magnetic circuit 4 A face each other, first magnetic field detecting element 5 and second magnetic field detecting element 6 can be mounted on common substrate 7 . In the present modification, magnetic flux flows in second magnetic circuit 4 A in the same manner as the embodiments described above, and the same effect as the embodiments described above can be achieved.

FIGS. 7 A to 7 B show another modification of the present embodiment. FIG. 7 A is a perspective view of current sensor 1 E according to the present modification, and FIG. 7 B is a section view taken along line A-A in FIG. 7 A . In the present modification, long side 31 B of first magnetic circuit 3 A of the embodiments described above that faces second magnetic circuit 4 A is omitted. As viewed in the X direction, first magnetic circuit 3 A consists of one long side 31 A that extends in the Y direction and a pair of short sides 32 A, 32 B that extend in the Z direction and that are connected to both ends of long side 31 A at right angles. Both ends of two short sides 32 A, 32 B opposite to long side 31 A form both open ends 34 A, 34 B of first magnetic circuit 3 A. As viewed in the X direction, in the same manner as the embodiments described above, second magnetic circuit 4 A has a rectangular shape that has a pair of long sides 41 A, 41 B that extend in the Y direction and a pair of short sides 42 A, 42 B that extend in the Z direction. Void portion 43 is provided at the center of one of the long sides (long side 41 B), and open ends 44 A, 44 B are positioned on both sides of void portion 43 . When current flows in current line 2 A, a rightward magnetic field that is induced by current line 2 A dominates where first magnetic field detecting element 5 and second magnetic field detecting element 6 are provided. Therefore, the outputs of first magnetic field detecting element and second magnetic field detecting element 6 are positive. When current does not flow, a rightward magnetic field that is induced by the residual magnetization of first magnetic circuit 3 A dominates where first magnetic field detecting element 5 is provided, and a leftward magnetic field that is induced by the residual magnetization of second magnetic circuit 4 A dominates where second magnetic field detecting element 6 is provided. As a result, the output of first magnetic field detecting element 5 is positive, and the output of second magnetic field detecting element 6 is negative. Therefore, according to the present modification, the same effect as the embodiments described above can be achieved. In the present modification, both open ends 34 A, 34 B of first magnetic circuit 3 A are preferably adjacent to second magnetic circuit 4 A. As a result, when current flows, first magnetic circuit 3 A and second magnetic circuit 4 A are easily magnetically coupled to each other. The magnetic flux that exits open end 34 A of first magnetic circuit 3 A is efficiently sucked by second magnetic circuit 4 A, and the magnetic flux that exits second magnetic circuit 4 A is efficiently sucked by open end 34 B of first magnetic circuit 3 A, and residual magnetization is easily generated in second magnetic circuit 4 A.

FIGS. 8 A to 8 B show another modification of the present embodiment. FIG. 8 A is a perspective view of current sensor 1 F according to the present modification, and FIG. 8 B is a section view taken along line A-A in FIG. 8 A . Current line 2 B of the present modification has a circular section. First magnetic circuit 3 B has a circular shape that conforms to current line 2 B. Second magnetic circuit 4 B has two arch-shaped portions 46 A, 46 B that conforms to first magnetic circuit 3 B and two radial portions 47 A, 47 B that connect respective ends of arch-shaped portions 46 A, 46 B to each other. First magnetic circuit 3 B and two arch-shaped portions 46 A, 46 B are concentric with current line 2 B, with arch-shaped portion 46 A being positioned inside of arch-shaped portion 46 B. Void portion 33 is provided in first magnetic circuit 3 B, and void portion 43 is provided in a portion of arch-shaped portion 46 A that faces void portion 33 . Due to this configuration, second magnetic circuit 4 B is easily magnetized by first magnetic circuit 3 B. Second magnetic circuit 4 B is provided adjacent to first magnetic circuit 3 B in the Z direction in the same manner as the embodiments described above. Current sensor 1 F of the present modification works in the same manner as the embodiments described above.

FIGS. 9 A to 9 C show another modification of the present embodiment. FIG. 9 A is a perspective view of current sensor 1 G according to the present modification, FIG. 9 B is a section view taken along line A-A in FIG. 9 A , and FIG. 9 C is a section view taken along line B-B in FIG. 9 A . According to the present modification, current line 2 B has a circular section. First magnetic circuit 3 B has the same shape as the modification shown in FIGS. 8 A to 8 B , but second magnetic circuit 4 B is different from the modification shown in FIGS. 8 A to 8 B , and void portion 43 is provided in arch-shaped portion 46 B. Furthermore, first magnetic circuit 3 B and second magnetic circuit 4 B are positioned in different Y-Z planes. The positional relationship between first magnetic circuit 3 B and second magnetic circuit 4 B is the same as the modification shown in FIGS. 4 A to 4 C . Current sensor 1 G of the present modification works in the same manner as the modification shown in FIGS. 4 A to 4 C .

Second Embodiment

FIG. 10 A is a perspective view of current sensor 1 H according to the second embodiment, and FIG. 10 B is a section view taken along line A-A in FIG. 10 A . FIGS. 11 A and 11 B conceptually illustrate the external magnetic field that is applied to current sensor 1 when current flows in current line 2 A and when current does not flow in current line 2 A, respectively. First magnetic circuit 3 A and second magnetic circuit 4 A have the same shapes as the first embodiment. Second magnetic circuit 4 A is positioned outside of first magnetic circuit 3 A, and long side 41 A of second magnetic circuit 4 A faces long side 31 A of first magnetic circuit 3 A. Therefore, in the present embodiment, first magnetic field detecting element 5 and second magnetic field detecting element 6 are positioned on opposite sides with regard to current line 2 A. The output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 have the same polarity.

As shown in FIG. 11 A , when current flows in current line 2 A, a clockwise magnetic flux is formed around current line 2 A. First magnetic circuit 3 A is magnetized in the same manner as the first embodiment. The output of first magnetic field detecting element 5 is positive. Long side 41 A of second magnetic circuit 4 A that faces first magnetic circuit 3 A is magnetized in the −Y direction by the magnetic field that is induced by current line 2 A and by the leakage magnetic flux from first magnetic circuit 3 A, but long side 41 B is hardly magnetized. Second magnetic field detecting element 6 A mainly receives a magnetic field that is induced by current line 2 A. Therefore, the output of second magnetic field detecting element 6 is negative.

As shown by the dashed lines in FIG. 11 B , when current does not flow in current line 2 A, that is, when the electric current that flows in current line 2 A is lost, residual magnetization is generated in the first and second magnetic circuits 3 A, 4 A. A magnetic field is generated in the +Y direction between both open ends 34 A, 34 B of first magnetic circuit 3 A, and the output of first magnetic field detecting element 5 is still positive. On the other hand, second magnetic circuit 4 A is magnetized counterclockwise by the residual magnetization of long side 41 A, and a magnetic field is generated in the +Y direction between both open ends 44 A, 44 B. Therefore, the output of second magnetic field detecting element 6 is positive. In other words, regardless of whether or not current flows, a magnetic field is applied in the +Y direction to first magnetic field detecting element 5 that is positioned between both open ends 34 A, 34 B of first magnetic circuit 3 A that surrounds current line 2 A. On the other hand, at second magnetic field detecting element 6 between both open ends 44 A, 44 B of second magnetic circuit 4 A that is positioned outside of current line 2 A, the magnetic field when current flows and the magnetic field when current does not flow are directed in opposite directions.

However, unlike the first embodiment, when current does not flow, the magnetic field that is detected by first magnetic field detecting element 5 and the magnetic field that is detected by second magnetic field detecting element 6 have the same sign. On the other hand, when current flows, the magnetic field that is detected by first magnetic field detecting element 5 and the magnetic field that is detected by second magnetic field detecting element 6 are directed in opposite directions. Therefore, in the present embodiment, when current does not flow, by calculating a difference between the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 by means of subtractor 11 , the hysteresis of first magnetic circuit 3 A that is caused by the residual magnetization and the hysteresis of second magnetic circuit 4 A that is caused by the residual magnetization can be cancelled out or reduced. Since a difference between the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 is obtained, the output of current sensor 1 H can also be increased. As a result, it is possible to reduce the hysteresis while the S/N ratio is improved. In the present embodiment, the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 may have different polarities in the same manner as the modification of the first embodiment. In this case, current sensor 1 H has means for calculating the sum of the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 (adder 10 ).

Third Embodiment

FIG. 12 A is a perspective view of current sensor 1 J according to the third embodiment, FIG. 12 B is a section view taken along line A-A in FIG. 12 A , and FIG. 12 C is a section view taken along line B-B in FIG. 12 A . First magnetic circuit 3 A is the same as the modification shown in FIGS. 4 A to 4 C . On the other hand, second magnetic circuit 4 A is rotated 90 degrees about current line 2 A relative to second magnetic circuit 4 A of the modification shown in FIGS. 4 A to 4 C . Accordingly, second magnetic field detecting element 6 is rotated about 90 degrees about current line 2 A relative to second magnetic field detecting element 6 of the modification shown in FIGS. 4 A to 4 C . In other words, first magnetic field detecting element 5 and second magnetic field detecting element 6 are positioned such that they are rotated 90 degrees from each other about current line 2 A. Therefore, first magnetic field detecting element 5 senses a magnetic field in the Y direction, and second magnetic field detecting element 6 senses a magnetic field in the Z direction. Furthermore, when defining the +Z direction and the −Z direction, as shown in FIGS. 12 B, 12 C , the polarity of the direction in which first magnetic field detecting element 5 senses a magnetic field is positive in the +Y direction, and the polarity of the direction in which second magnetic field detecting element 6 senses a magnetic field is positive in the −Z direction. That is, when a magnetic field is applied to magnetic field detecting element 5 and to second magnetic field detecting element 6 in the same rotational direction (clockwise in FIG. 12 A ), i.e., in the +Y direction an in the −Z direction, respectively, the output of first magnetic field detecting element and the output of second magnetic field detecting element 6 are positive. In other words, the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 have the same polarity with regard to the rotational direction of a magnetic field about current line 2 A.

In the present embodiment, when current flows in current line 2 A, a clockwise magnetic field that is induced by current line 2 A dominates where first magnetic field detecting element 5 and second magnetic field detecting element 6 are provided. Therefore, the output of first magnetic field detecting element and the output of second magnetic field detecting element 6 are both positive. When current does not flow, a right ward (clockwise) magnetic field that is induced by the residual magnetization of first magnetic circuit 3 A dominates where first magnetic field detecting element 5 is provided, and an upward (counterclockwise) magnetic field that is induced by the residual magnetization of second magnetic circuit 4 A dominates where second magnetic field detecting element 6 is provided. As a result, the output of first magnetic field detecting element 5 is positive, but the output of second magnetic field detecting element 6 is negative. Therefore, according to the present embodiment, by providing means for calculating the sum of the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 , the same effect as the embodiments described above can be achieved.

Conversely, in case that the polarity of the direction in which second magnetic field detecting element 6 senses a magnetic field is positive in the +Z direction, the output of second magnetic field detecting element 6 is negative when current flows in current line 2 A, and the output of second magnetic field detecting element 6 is positive when current does not flow. The output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 have different polarities with regard to the direction of a magnetic field about current line 2 A. Therefore, by providing means for calculating a difference between the output of first magnetic field detecting element 5 and the output of second magnetic field detecting element 6 , the same effect as the embodiments described above can be achieved.

As described above, each embodiment and each modification of the present invention comprises magnetic circuits 3 A, 4 A ( 3 B, 4 B) that are magnetized by electric current that flows in current line 2 A ( 2 B), first magnetic field detecting element 5 and second magnetic field detecting element 6 . First magnetic field detecting element 5 is positioned where a magnetic field, when there is electric current that flows in current line 2 A ( 2 B), is directed in the same direction as a magnetic field that is caused by the residual magnetization of the magnetic circuit when there is no electric current that flows in current line 2 A ( 2 B). Second magnetic field detecting element 6 is positioned where a magnetic field, when there is electric current that flows in current line 2 A ( 2 B), is directed opposite to the direction of a magnetic field that is caused by the residual magnetization of the magnetic circuit when there is no electric current that flows in current line 2 A ( 2 B).

Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made without departing from the spirit or scope of the appended claims.