JP2011007596A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable accurate current measurement by reducing noise of a magnetoelectric device caused by the potential of a core by grounding the core at high reliability.SOLUTION: This current sensor includes an annular core having a gap, and a circuit board mounted with the magnetoelectric device to be stored in the gap. In the current sensor, a core grounding member used for grounding of the core is provided. The core grounding member includes a first part connected to a ground line, and a second part that is arranged in the gap and comes into contact with an end surface of the core defining the boundary of the gap. The core grounding member can be formed by die processing of a metal plate.

Description

  The present invention relates to a current sensor using a magnetoelectric conversion element.

  As a current sensor for detecting the magnitude of a current, a sensor using a magnetoelectric conversion element such as a Hall element that converts a magnetic field generated by a current to be measured into an electromotive force is widely used. A general magnetoelectric conversion element type current sensor has a gap (gap) formed by cutting a part of an annular magnetic circuit (core) made of a high permeability magnetic material such as permalloy or silicon steel plate. The magnetoelectric conversion element is arranged on the core, and the current path through which the current to be measured flows passes through the core hole. When a non-measurement current flows through the current path, a magnetic flux focused in the core surrounding the current path is induced. Since the magnetic flux density of this magnetic flux is substantially proportional to the measured current flowing in the current path, the measured current flowing in the current path can be measured by detecting the magnetic flux density in the gap by the magnetoelectric transducer. A Hall element is generally used as the magnetoelectric conversion element. When a constant control current is passed through the hall element, a hall voltage proportional to the magnetic flux density and the control current is generated. Further, since the Hall voltage is weak, an amplified signal is used as a signal. Therefore, many Hall element type current sensors include a circuit board (hereinafter referred to as “sensor”) including a constant current circuit for generating a Hall element control current and an amplifier circuit for amplifying the Hall voltage to obtain a signal voltage. A driving substrate ”).

  In recent years, devices such as general-purpose inverters and UPS (uninterruptible power supply devices) equipped with such current sensors have been reduced in size and frequency. For this reason, current sensors are mounted in a noisy environment, and a decrease in accuracy of the current sensor due to noise has hindered improvement in performance of the apparatus. Examples of main noise sources that cause a decrease in accuracy of the current sensor include a current path to be measured (wire bus bar) and a peripheral switching element.

  In order to reduce the influence of such noise on the current sensor, for example, Patent Document 1 proposes a configuration in which a shield plate is attached to the magnetoelectric conversion element.

JP 2005-024519 A

The following can be considered as measures for reducing the influence of noise on the current sensor.
(A) Grounding the core and giving the core a shielding function (B) Attaching a shield member such as a copper plate to a place vulnerable to noise The configuration proposed in Patent Document 1 is one specific example of the above (B).

As a result of the simulation experiments by the present inventors, it has become clear that (A) is the most effective countermeasure among the above (A) to (C). As the countermeasure (A), that is, a specific method for grounding the core, the following can be considered.
(A1) A wire (covered electric wire, plated wire, etc.) grounded to the ground wire (0 V) of the sensor drive board is directly connected to the core with solder or the like.
(A2) A grounding member made of a metal foil such as copper or a metal plate is attached to the core, and a grounded wire is connected to the grounding wire (0 V) of the sensor driving substrate with solder or the like.

  By the way, a silicon steel plate is widely used as the core material of the current sensor. An insulating oxide film is formed on the surface of the core formed from the silicon steel plate. Therefore, in order to directly ground the core of the silicon steel plate, a process of removing the oxide film by polishing the surface of the core is required. Therefore, the method (a1) has disadvantages in terms of production cost and reliability.

  On the other hand, the method of mounting the grounding member (a2) on the core has a demerit that the number of parts increases and the cost of parts increases. However, if the grounding member can be produced at a low cost, for example, by molding or the like, an increase in the number of parts can be allowed.

  When using a mold product obtained by molding a metal plate as a grounding member, as a method of mounting the grounding member on the core, for example, using the elastic force of the metal plate as in the shield plate described in Document 1. There is a method of gripping and mounting the outer shape of the core. That is, for example, a method is conceivable in which a grounding member bent in a U-shape is placed on the core, and the core is gripped from the outside by the elastic force of the grounding member. However, the variation in the finished dimensions of the outer shape of the core is large, and is as large as or more than the dimension that the grounding member can be elastically deformed. Therefore, it is difficult to realize a configuration in which the outer shape of the core is elastically gripped by the metal ground member formed by die molding unless the accuracy of the outer shape of the core is significantly increased by additional processing such as cutting. Further, as described above, since an insulating oxide film is formed on the core surface, in order to bring the core and the ground member into electrical contact, the core surface with which the ground member contacts is polished in advance. Therefore, it is necessary to remove the oxide film. Therefore, this configuration is not necessarily a preferable configuration in terms of processing cost and reliability.

  As described above, the above-mentioned (A), which is the most effective measure for reducing the influence of noise on the current sensor, that is, the configuration in which the core is grounded, requires a lot of work and can impair the reliability of the product. There was sex. The present invention has been made in view of the above circumstances. That is, an object of the present invention is to provide a current sensor that achieves high current measurement accuracy by suppressing the entrance of electrostatic noise to the current sensor by grounding the core with low loss and high reliability.

  According to an embodiment of the present invention, a core grounding member used for grounding a core in a current sensor including an annular core having a gap formed therein and a circuit board on which a magnetoelectric conversion element accommodated in the gap is mounted Is provided. The core grounding member has a first part connected to the grounding wire and a second part disposed in the gap and in contact with the end face of the core that defines the gap. The core grounding member can be formed by metal plate mold processing.

  The core grounding member configured as described above enables low-loss grounding by contact with the gap end surface where the insulating layer of the oxide film is not formed. If such a core grounding member is used, the work of removing the insulating layer formed on the outer surface of the core by polishing or the like becomes unnecessary, and the core can be insulated with a small number of man-hours. Further, the core grounding member can be manufactured at a low cost by forming it by metal mold processing.

  The second part preferably has a contact part that contacts the end face of the core, and an elastic deformation part that elastically deforms by being disposed in the gap and pushes the contact part into the end face by an elastic force. By utilizing the elastic deformation of the member, the core grounding member can be attached by a simple mechanism and with an easy operation.

  It is desirable that the second part has at least a first contact part and a second contact part. In this case, the first contact portion and the second contact portion have contact planes that respectively contact the first end surface and the second end surface that are parallel to each other of the core, and the elastic deformation portion is formed between the first contact portion and the second contact portion. It can comprise so that one end may be connected. In this way, by providing a portion in contact with each of the first end surface and the second end surface and connecting them via the elastic deformation portion, even if there is some distortion in the core grounding member, it can be flexibly adapted to each end surface of the core. It becomes possible to ensure good contact between the core and the core grounding member.

  The first portion is preferably formed in a flat plate shape so that one surface is in contact with the outer surface of the core when the second portion is disposed in the gap. With such a configuration, an electrical connection through an outer surface that can ensure a large contact area is additionally obtained, and the connection resistance is reduced and the stability is improved.

  The first part may be formed so as to cover a place where the noise sensitivity of the circuit board is high when the second part is disposed in the gap. By forming the core grounding member in this way, the core grounding member can be used as a shield for the circuit board, and the performance of the current sensor can be further improved.

  The core grounding member preferably further includes a flat plate-like third part formed on the same plane as the first part, and the second part preferably connects the first part and the third part. By providing the third part formed on the same plane as the first part on the side opposite to the first part, positioning when attaching the core grounding member becomes possible. The third part also contributes to the shield of the circuit board and the electrical connection with the outer surface of the core, like the first part.

  The second part preferably further includes an element pressing part for pressing and positioning the element so that the magnetoelectric conversion element is arranged at the center of the gap. By providing such an element pressing portion, the magnetoelectric conversion element can be accurately arranged at the center of the gap, and the measurement accuracy of the current sensor is further improved. This configuration is particularly effective in improving the measurement accuracy of alternating current because it reduces the difference in sensitivity due to the direction of the current.

  It is desirable that the element pressing portion includes first and second element pressing portions. In this case, the first and second element pressing portions can be arranged between the first and second end faces of the core and the magnetoelectric conversion element, respectively, and apply a reverse elastic force to the magnetoelectric conversion element. .

  In addition, according to the embodiment of the present invention, a current sensor including the core grounding member is provided.

  Further, according to the embodiment of the present invention, a current sensor including an annular core having a gap and a circuit board on which a magnetoelectric conversion element accommodated in the gap is mounted is provided. The current sensor further includes a core grounding member for grounding the core. The core grounding member has a first part connected to the grounding wire and a second part arranged in the gap.

  With this configuration, the core can be grounded with less man-hours. The grounding of the core reduces the noise of the magnetoelectric transducer due to the potential of the core and improves the measurement accuracy of the current sensor.

  The ground line may be formed on the circuit board. In this case, it is desirable that a through hole connected to the ground line is formed in the circuit board. Furthermore, it is desirable that a protrusion inserted into the through hole is formed on the first portion of the core grounding member. With such a configuration, the core grounding member can be connected to the grounding wire with a small number of steps by a simple mechanism.

  By using the core grounding member according to the embodiment of the present invention, the core can be grounded with low loss and high reliability without removing the insulating layer formed on the outer surface of the core of the current sensor. Become. As a result, a current sensor excellent in measurement accuracy and reliability can be manufactured at low cost.

It is a disassembled perspective view which shows schematic structure of the principal part of the current sensor which concerns on embodiment of this invention. It is a side view which shows schematic structure of the Hall element vicinity of the current sensor which concerns on embodiment of this invention. It is a schematic perspective view which shows the grounding member which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an exploded perspective view showing a schematic configuration of a main part of a current sensor 1 according to an embodiment of the present invention. FIG. 2 is a side view showing a schematic configuration in the vicinity of the Hall element 210 of the current sensor 1. FIG. 3 is a perspective view showing a schematic configuration of the grounding member 300 according to the embodiment of the present invention. In the following description, the upper direction in FIG. 1 is the Z direction, the lower right direction is the X direction, and the lower left direction is the Y direction. Further, in FIG. 1, the surface viewed in the Y direction reverse direction (surface on the left front side of the paper) is the front surface, the surface viewed in the Z direction reverse direction (the surface on the upper surface of the paper surface) is the top surface, and the surface viewed in the X direction reverse direction ( The surface on the right front side of the paper) is the side surface.

  The current sensor 1 includes a core 100, a circuit board 200, a grounding member 300, and a resin case (not shown) that houses them. The function of the current sensor 1 described later is achieved by the three main members of the core 100, the circuit board 200, and the ground member 300. Since the resin case is a subsidiary member used for holding and protecting each member and fixing the current sensor, detailed description thereof is omitted. The case material may be formed of a metal plate (steel plate, aluminum plate, copper plate, etc.) having an electrostatic shield function in addition to a resin having electrical insulation properties such as polyethylene, polyvinyl chloride, and epoxy resin. Moreover, you may form from the metal plate which has a magnetic shielding function, such as a permalloy and a silicon steel plate.

  The core 100 is an annular member formed from a silicon steel plate and constitutes a magnetic circuit. The core 100 is cut by two adjacent surfaces perpendicular to the magnetic flux lines excited in the core, and a gap 110 sandwiched between two cut surfaces (first end surface 112 and second end surface 114) is formed. ing. The gap is formed by, for example, precise cutting, and the dimensional accuracy (flatness, surface interval, parallelism, etc.) of the first end surface 112 and the second end surface 114 is significantly higher than other dimensional accuracy. The surface interval is processed with an allowable tolerance of 0.2 mm or less.

  In addition to the Hall element 210, the circuit board 200 generates a voltage signal by amplifying a constant current circuit (not shown) that generates a DC control current supplied to the Hall element 210 and a weak voltage output from the Hall element 210. An amplifier circuit (not shown) is mounted. In addition, the circuit board 200 is formed with a through hole 220 for connecting the ground member 300 to the ground line on the circuit board 200 and fixing the ground member 300 to the circuit board. The circuit board 200 is disposed in close contact with the upper surface of the core 100. The circuit board 200 is formed in a C shape in accordance with the top surface shape of the core 100.

  The ground member 300 is a member for reliably connecting the core 100 to the ground line (0 V) formed on the circuit board 200. The grounding member 300 is formed by die processing from one elongated rectangular copper plate. The grounding member 300 according to the present embodiment includes a rectangular flat plate-shaped first part 310 and a third part 330, and a U-shaped second part 320 that connects the first part 310 and the third part 330. ing. The first part 310 and the third part 330 are formed so as to be arranged on substantially the same plane after assembly. As shown in FIG. 2, the ground member 300 is disposed between the upper surface of the core 100 and the circuit board 200. As shown in FIG. 2, the second part 320 is inserted into the gap 110, and the first part 310 and the third part 330 are disposed in close contact with the upper surface of the core 100. The Hall element 210 is inserted into the U-shaped inner space of the second part 320.

  A detailed configuration of the grounding member 300 will be described with reference to FIG. A part of the first part is formed with a protrusion 312 that is cut out in a U-shape and drawn upward. The protrusion 312 is inserted into the through hole 220 of the circuit board 200 and soldered during assembly. As a result, the ground member 300 is electrically connected to the ground line formed on the circuit board 200. Since the grounding member 300 is made of a copper plate, it can be reliably fixed to the through hole 220 by soldering.

  The second portion 320 includes two pairs of contact portions 322 and 324, a pair of curved portions 326 that connect the contact portions 322 and 324, and a curved element press formed between each pair of the contact portions 322 and 324. It consists of plates 327 and 328. The contact parts 322 and 324 are rectangular flat plate parts bent at right angles at opposite ends of the first part 310 and the third part 330, respectively. When the second part is inserted into the gap 110 of the core 100, the curved part 326 is bent by the contact with the gap end faces 112 and 114, and the outer surfaces of the contact parts 322 and 324 are caused by the elastic repulsive force. The first gap end surface 112 and the second gap end surface 114 are configured to be in surface contact with each other. Specifically, the grounding member 300 is formed such that the space between the outer surfaces of the contact portions 322 and 324 in the natural state is wider than the gap 110 and wider toward the upper side (open end side). Yes. Furthermore, when the contact portions 322 and 324 are pushed in from the outside and deformed so as to be parallel to each other, the grounding member 300 is configured such that the interval between the outer surfaces of the contact portions 322 and 324 is substantially equal to the interval of the gap 110. Is formed.

  With the configuration of the second part 320 as described above, when the second part 320 is inserted into the gap 110 of the core 100, the outer surfaces of the contact parts 322 and 324, the first end surface 112 and the second end surface of the core. 114 and the two come into contact with each other over a wide area. In addition, since the insulating layer is removed from the first end surface 112 and the second end surface 114 by cutting when the gap 110 is formed, the contact resistance with the grounding member 300 is small. Therefore, by inserting the second part 320 into the gap 110, a low-loss and stable electrical connection between the core 100 and the ground member 300 is achieved.

  Element pressing plates 327 and 328 are formed between the pairs of contact portions 322 and 324, respectively. The element pressing plates 327 and 328 branch from the contact portions 322 and 324 near the base (near the boundary between the first portion 310 and the third portion 330), respectively, and protrude into the inner space of the second portion 320 at a moderate angle. It is a strip-shaped part. The element pressing plates 327 and 328 are configured to be gently curved toward the contact portions 322 and 324 from the middle, and to be in contact with the magnetic sensitive surfaces 212 and 214 of the Hall element 210 at a gentle angle. In the grounding member 300, in the natural state or in the state where the contact portions 322 and 324 are inserted into the gap 110, the inner distance of the portion where the element pressing plates 327 and 328 are closest is the distance between the magnetic sensitive surfaces 212 and 214 of the Hall element 210. It is formed to be narrower than the interval. Therefore, when the Hall element 210 is inserted between the element pressing plates 327 and 328, the element pressing plates 327 and 328 are bent, and the magnetic sensitive surfaces 212 and 214 of the Hall element 210 are pressed from both sides by the repulsive force. At this time, the tip ends of the element pressing plates 327 and 328 come into contact with the gap end surfaces 112 and 114 of the core and cannot move, and a strong reaction force from each end surface is also applied to the magnetosensitive surfaces 212 and 214. As a result, the Hall element 210 is further firmly and elastically held by the element pressing plates 327 and 328. Since the element pressing plates 327 and 328 are formed with high accuracy, the element pressing plates 327 and 328 are uniformly bent, and the distance between the magnetosensitive surface 212 and the first gap end surface 112 is substantially the same as the interval between the magnetosensitive surface 214 and the second gap end surface 114. Will be equal. That is, the main body of the Hall element 210 is accurately positioned in the center in the gap 110 gap direction (X direction). Thereby, the Hall element 210 can measure the magnetic flux focused on the core with high accuracy. In particular, since the sensitivity difference due to the direction of magnetic flux is reduced, the measurement accuracy of alternating current is greatly improved.

  The element pressing plates 327 and 328 are formed so as to cover the magnetic sensing surfaces 212 and 214 of the Hall element, respectively, and are connected to the ground line (0 V) of the circuit board 200, so that the Hall element is shielded. It also has a function to do.

  In addition, since an insulating layer of a thin oxide film is formed on the outer surface of the core 100 (surface other than the gap end surface), the contact resistance with the ground member 300 is relatively high, but the contact area with the ground member 300 If it is taken widely, electrical contact contributing to the grounding characteristics of the core 100 can be obtained. Therefore, the first part in the present embodiment is extended to the tip of the protrusion 312, and the contact area between the core 100 and the ground member 300 is widened to reduce and stabilize the contact resistance.

  Further, the first part 310 and the third part 330 are formed so as to cover a noise-sensitive portion of the circuit board and shield it from a noise source, and are electrically connected to the ground line of the circuit board. Therefore, it also functions as a shield for the circuit board. In the present embodiment, since a circuit with high noise sensitivity such as an amplifier circuit is arranged on the front side of the circuit board 200 (lower left side in FIG. 1), the first part 310 and the third part 330 are formed in a straight line. ing. However, in the case where circuits with high noise sensitivity are distributed over the entire surface of the C-shaped circuit board, for example, a C-shaped circuit that covers the entire surface of the circuit board 200 or a cover that covers the entire upper surface of the core. The first part 310 and the third part 330 formed in a letter shape may be used.

  In the present embodiment, two pairs of grounding portions and curved portions of the grounding member are formed. However, when the width of the grounding member can be widened, three or more pairs of contact portions and curved portions may be formed. As the number of pairs of the contact portion and the curved portion increases, the possibility of contact failure due to adhesion of foreign matter to the contact portion or formation failure can be reduced, and more reliable grounding is realized.

  In this embodiment, a core formed of a silicon steel plate is used, but the material of the core can be appropriately selected depending on the nature of the current to be measured (for example, AC or DC, large current or minute current). . For example, permalloy or ferrite can be used as the core material.

1 Current sensor 100 Core 110 Gap 112 Gap end face (first end face)
114 Gap end face (second end face)
200 Circuit board 210 Hall element 220 Through hole (grounding member mounting hole)
300 Grounding member 310 First part 312 Protrusion (board fixing part)
320 Second part 322 Contact part (first contact part)
324 contact part (second contact part)
326 Bending part 328 Element pressing plate 330 Third part

Claims (20)

In a current sensor including an annular core having a gap formed therein and a circuit board on which a magnetoelectric conversion element accommodated in the gap is mounted, a core grounding member used for grounding the core,
A first part connected to the ground wire;
A second portion disposed within the gap and in contact with an end face of the core that delimits the gap;
A core grounding member characterized by comprising: The second part is:
A contact portion in contact with the end face of the core;
The core grounding member according to claim 1, further comprising: an elastic deformation portion that is elastically deformed by being disposed in the gap and that pushes the contact portion into the end face by an elastic force. The second part has a first contact part and a second contact part,
The first contact portion and the second contact portion have contact planes that respectively contact the first end surface and the second end surface parallel to each other of the core,
The core grounding member according to claim 2, wherein the elastic deformation portion connects one end of the first contact portion and the second contact portion. The first part is formed in a flat plate shape, and when the second part is disposed in the gap, the first part is formed so as to come into contact with the outer surface of the core. 4. The core grounding member according to any one of 3 above. 5. The device according to claim 1, wherein the first part is formed so as to cover a portion of the circuit board where the noise sensitivity is high when the second part is disposed in the gap. 6. The core grounding member as described. A flat plate-like third part formed on the same plane as the first part;
The core grounding member according to any one of claims 1 to 5, wherein the second part connects the first part and the third part. The second part further includes an element pressing part that presses and positions the magnetoelectric conversion element so that the magnetoelectric conversion element is arranged in the center of the gap. Core grounding member. The element pressing part includes first and second element pressing parts,
The first and second element pressing portions are respectively disposed between the first and second end faces of the core and the magnetoelectric conversion element, and apply elastic forces in opposite directions to the magnetoelectric conversion element, respectively. The core grounding member as described in. The core grounding member according to any one of claims 1 to 8, wherein a protrusion for inserting into a grounding through hole formed in the circuit board is formed in the first part.   The core grounding member according to claim 1, wherein the core grounding member is formed by metal mold processing of a metal plate. An annular core with a gap formed;
A current sensor including a circuit board on which a magnetoelectric conversion element housed in a gap is mounted,
A core grounding member for grounding the core;
The core grounding member has a first part connected to the grounding wire and a second part disposed in the gap. Part 2
A contact portion in contact with the end face of the core;
The current sensor according to claim 11, further comprising: an elastically deforming portion that is elastically deformed by being disposed in the gap and that pushes the contact portion into the end face by an elastic force. The core has a first end face and a second end face parallel to each other,
The second part has a first contact part and a second contact part,
The first contact portion and the second contact portion have contact planes that contact the first end surface and the second end surface of the core, respectively.
The current sensor according to claim 12, wherein the elastic deformation portion connects one end of the first contact portion and the second contact portion. The first part is formed in a flat plate shape, and when the second part is disposed in the gap, the first part is formed so as to contact the outer surface of the core. 14. The current sensor according to any one of items 13. 15. The first part according to claim 11, wherein the first part is formed so as to cover a portion where the noise sensitivity of the circuit board is high when the second part is disposed in the gap. The current sensor described. The core grounding member further has a flat plate-like third part formed on the same plane as the first part,
The current sensor according to any one of claims 11 to 15, wherein the second part connects the first part and the third part. The second part further includes an element pressing part that presses and positions the magnetoelectric conversion element so that the magnetoelectric conversion element is arranged at the center of the gap. Current sensor. The element pressing part includes first and second element pressing parts,
The first and second element pressing portions are respectively disposed between the first and second end faces of the core and the magnetoelectric conversion element, and apply elastic forces in opposite directions to the magnetoelectric conversion element, respectively. The current sensor described in 1. The ground wire is formed on a circuit board;
The circuit board has the through hole connected to the ground line,
The current sensor according to claim 10, wherein a protrusion is formed on the first portion, and the protrusion is inserted into a through hole.   The current sensor according to claim 11, wherein the core grounding member is formed by metal mold processing.

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