JP2005345267A - Current sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current sensor using a magnetic impedance (MI) element, dispensing with a battery as a power source, or having a reduced current consumption and an elongated battery lifetime. <P>SOLUTION: This current sensor has a type wherein the MI element 11 is arranged on a part formed by notching a part of a ring-shaped magnetic path 141, 142, and an electric wire which is a measuring object is arranged so as to pass the inside of the ring-shaped magnetic path, and a current flowing in the electric wire is detected in a noncontact state. A power source of the sensor is constituted only by providing a simple current transformer 10 on a magnetic shield 19, to thereby become usable as the power source. Hereby, the sensor dispenses with a battery. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention uses a magnetic impedance (MI) effect in which an impedance changes in response to a change in magnetism as a current sensor for detecting a current flowing through a conductor in a non-contact manner, particularly as a current detection element. The present invention relates to a current sensor that can extend the lifetime. The MI element has recently been in the spotlight as it has a higher sensitivity than the Hall element and the magnetoresistive element (if necessary, for example, five members of Higa and others "sputtered thin film micro MI sensor by pulse current excitation") (See Journal of the Japan Society of Applied Magnetics, Vol. 21, No. 4-2, 1997).

FIG. 5 is a schematic diagram showing the current measurement method previously proposed by the applicant (see Japanese Patent Application No. 2004-002822: also called the proposed method).
The current sensor 30 shown in the figure is configured to be openable and closable around a through hole 35 and a movable part 34 as an axis, and has a structure in which an electric wire (current line) 33 can be sandwiched. The upper casing of the current sensor is referred to as the upper body 31, and the lower casing is referred to as the lower body 32. FIG. 5 (a) shows a state where the upper and lower bodies are opened, and FIG. 5 (b) shows a closed state. A current sensor using an MI element is known, for example, as shown in Patent Document 1 below, and a configuration that enables opening and closing of the current sensor is shown in, for example, Patent Document 2 below.

FIG. 6 shows a configuration example of the current sensor.
6A and 6B, the current sensor 30 includes an upper body 31, a lower body 32, an MI element 41, a sensor circuit 43, a battery 44, a magnetic path 45, two magnetic paths 46, a permanent magnet 49, and the like. Consists of The magnetic path includes two magnetic paths 46 disposed in the lower body 32 and a magnetic path 45 disposed in the upper body 31, and is disposed along the through hole 35. That is, the magnetic path 46 has a configuration lacking a part thereof. 6A shows the upper lid portion, and FIG. 6B shows the main body portion.

  The MI element 41 is a current sensor element using a magnetic impedance effect in which the magnetic impedance changes with respect to the change of magnetism. Here, as shown in FIG. 6D, soft (soft) magnetism is formed on the glass 48. It has a simple structure patterned with the film 47. The MI element 41 is disposed at a location where a part of the magnetic path 46 is missing so that the magnetic sensing direction of the MI element 41 and the magnetic path direction are parallel to each other.

The permanent magnet 49 is disposed on the back surface side of the MI element 41 via the sensor circuit 43 (see FIG. 6C), and is approximately 800 to 1600 A in the magnetosensitive direction (parallel to the magnetic path) of the MI element 41. A magnetic field of / m is applied. Since the MI element 41 has a linearity that is not stable with respect to the external magnetic field in the vicinity of the zero magnetic field, and the sensitivity change is large, the permanent magnet 49 is used by shifting to a region where the impedance change of the MI element 41 is stabilized in this way. doing.
The sensor circuit 43 is for processing, as a voltage output signal, a change in impedance of the MI element 41 that changes due to a magnetic field generated by a current flowing through the current line 33 (see FIG. 5). It is for supplying power.

FIG. 7 shows a circuit block of the current sensor.
The current sensor circuit is mainly composed of a power supply circuit 56 and a detection circuit 57. The power circuit 56 includes a battery 44 and a constant voltage circuit 50. The constant voltage circuit 50 is a circuit that can step up or step down to a predetermined voltage even if the battery output fluctuates due to the life of the battery 44, etc. The detection circuit 57 is for outputting the impedance change of the MI element 41 as a voltage signal.

The operation of the detection circuit is as follows.
When a high frequency signal is applied to the MI element 41 from the oscillation circuit 51, the impedance of the MI element 41 changes in proportion to the external magnetic field. That is, the signal at the input of the rectifier circuit 53 is a high-frequency signal having an amplitude proportional to the external magnetic field. This is output as a current sensor output signal S of voltage output via the rectifier circuit 53 and the amplifier circuit 34.

Japanese Patent Laid-Open No. 10-232259 (page 2-3, FIGS. 1-2) Japanese Patent Laid-Open No. 10-185962 (page 4, FIG. 4)

However, a current sensor composed of the above-described MI element requires a high-frequency oscillation circuit of several MHz to several hundred MHz compared to a current sensor such as a CT (current transformer), so that a CMOS (complementary metal) There is a problem that power consumption of an electronic circuit including an oxide semiconductor circuit increases.
Therefore, an object of the present invention is to reduce the power consumption of the sensor circuit using the MI element so that it is not necessary to use a battery as a power source, or to extend the life when a battery is required. It is in.

  In order to solve such a problem, in the invention of claim 1, a housing in which a through-hole for passing an electric wire to be measured is formed, and a ring-shaped magnet arranged along the through-hole of the housing. A current detection element disposed in a notch formed in the magnetic path, a detection circuit for converting a signal from the current detection element into a voltage signal proportional to an external magnetic field, and the detection circuit A power supply circuit for supplying power to the power supply, and the power supply circuit includes a power supply current transformer formed by winding a coil around a disturbance countermeasure shield made of a magnetic material disposed around the casing, and a constant voltage circuit. It is characterized by that.

  In the invention of claim 2, a housing in which a through-hole for passing an electric wire to be measured is formed, a ring-shaped magnetic path disposed along the through-hole of the housing, and formed in the magnetic path A current detection element disposed in the cut-out portion, a detection circuit that converts a signal from the current detection element into a voltage signal proportional to an external magnetic field, and a power supply circuit that supplies power to the detection circuit And the power supply circuit comprises a current transformer for power supply formed by winding a coil around a disturbance countermeasure shield made of a magnetic material arranged around the casing, a battery, a power supply switching circuit, and a constant voltage circuit. It is characterized by.

  In the invention of claim 2, the power supply switching circuit can be switched to either a battery or a current transformer for power supply according to a detected current value (invention of claim 3). In the third aspect of the invention, the power supply switching circuit can select the battery when the detected current value is a predetermined value or less, and can select the current transformer for the power supply when the detected current value exceeds the predetermined value. (Invention of Claim 4). Moreover, in any invention of Claims 1-4, the said housing can be comprised so that opening and closing or isolation | separation is possible in the part containing the said through-hole (Invention of Claim 5). Furthermore, in the invention according to any one of claims 1 to 5, the current detecting element is a magnetic impedance element, and bias magnetic field applying means for applying a bias magnetic field to the magnetic impedance element can be provided. Item 6).

  In the invention of claim 6, the bias magnetic field applying means can be a permanent magnet (invention of claim 7). In the invention of claim 7, the magneto-impedance element and the detection circuit are combined into one. It is possible to mount on one substrate and arrange the permanent magnet on the back surface thereof (Invention of Claim 8). Furthermore, in the invention of any one of claims 1 to 8, communication means capable of transmitting a sensor output signal to the outside can be provided in the detection circuit (invention of claim 9).

According to the present invention, since a current transformer having a simple configuration in which a coil is wound around a magnetic shield for disturbance countermeasures is used, a battery as a power source becomes unnecessary, and it is freed from battery maintenance and the like.
Further, if the current transformer and the battery are used in combination, the battery life can be greatly extended.

FIG. 1 shows the configuration of a current sensor according to the present invention. Since the basic configuration is the same as that of the proposed method shown in FIGS. 5 to 7, different points will be mainly described below.
That is, the current sensor according to the present invention includes a magnetic path 13 including the magnetic path 13 disposed in the upper body 17 and the two magnetic paths 141 and 142 disposed in the lower body 7, the sensor circuit 5, and the magnetic paths 141 and 142. In addition to the MI element 11 and the permanent magnet 12 disposed therebetween, a disturbance countermeasure shield 19 is provided around the housing 18.

  The disturbance countermeasure shield 19 is made of, for example, a magnetic material, and is disposed so as to cover the outer peripheries of the upper body 17 and the lower body 7 in order to remove the influence from the electric wires disposed in the vicinity of the current sensor. The disturbance countermeasure shield 19 is wound with a coil constituting the current transformer 10 for power supply. However, it is significantly simplified (number of windings, winding density, etc.) as compared with a normal transformer, and is as low in cost as possible. The power supply current transformer 10 and the constant voltage circuit 21 constitute a power supply circuit 28.

With such a configuration, the magnetic field from the electric wire or current line to be measured can be collected not only in the magnetic paths 13, 141, and 142 but also in the disturbance countermeasure shield 19. Therefore, if the current transformer 10 is formed by winding a coil around the shield 19 as shown in FIG. 1B, electric power can be obtained and used as a power source. As a result, the battery as shown in FIG. 7 can be omitted from the power supply circuit 28 of the sensor circuit 5 of FIG.
Therefore, when a magnetic field proportional to the current flowing through the electric wire is applied to the MI element 11 via the magnetic paths 13, 141, 142 by the magnetic field generated by the electric wire passing through the through hole 1, the detection circuit shown in FIG. From 29, an output signal S proportional to the current flowing through the electric wire can be obtained in exactly the same manner as in the proposed method.

FIG. 3 shows another configuration of the current sensor according to the present invention.
This is characterized in that a battery 3 is provided with respect to that shown in FIG. That is, in FIG. 1, since power is supplied only from the current transformer 10, when a very small current is measured, power is insufficient, and the detection circuit may not be driven. Therefore, by installing the battery 3 as shown in FIG. 3, power is supplied using the battery 3 when measuring a small current, and power is supplied from the current transformer 10 when measuring a large current.

FIG. 4 shows a sensor circuit.
As is clear from the figure, a current transformer 10 and a battery 3 are provided, and a power supply switching circuit 281 for switching the power supply system is added so that stable measurement can be performed even at a small current.
The sensor output S can also be transmitted to the outside by adding a communication circuit to the sensor circuit of FIG. 2 or FIG.

Configuration diagram showing a sensor according to the present invention Block diagram showing the sensor circuit of FIG. The block diagram which shows another example of the sensor by this invention Block diagram showing a sensor circuit corresponding to FIG. Outline diagram showing the proposed sensor The block diagram which shows the internal structure of the current sensor used in FIG. Block diagram of the current sensor of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Through-hole, 3 ... Battery, 5 ... Current sensor circuit, 7 ... Lower body, 10 ... Current transformer for power supplies, 11 ... Magnetic impedance (MI) element, 12 ... Permanent magnet, 13, 141, 142 ... Magnetic path, DESCRIPTION OF SYMBOLS 16 ... Movable part, 17 ... Upper body, 18 ... Housing, 19 ... Magnetic shield for disturbance countermeasures), 21 ... Constant voltage circuit, 22 ... Oscillator circuit, 23 ... Fixed resistor, 25 ... Rectifier circuit, 26 ... Amplifier circuit, S ... Current sensor output.

Claims (9)

A housing in which a through hole for passing an electric wire to be measured is formed, a ring-shaped magnetic path disposed along the through hole of the housing, and a notch formed in the magnetic path A current detection element, a detection circuit that converts a signal from the current detection element into a voltage signal proportional to an external magnetic field, and a power supply circuit that supplies power to the detection circuit,
The current sensor comprises a power source current transformer formed by winding a coil around a disturbance countermeasure shield made of a magnetic material disposed around the casing, and a constant voltage circuit. Arranged in a housing in which a through hole for passing an electric wire to be measured is formed, a ring-shaped magnetic path disposed along the through hole of the housing, and a notch formed in the magnetic path A current detection element, a detection circuit that converts a signal from the current detection element into a voltage signal proportional to an external magnetic field, and a power supply circuit that supplies power to the detection circuit,
The power supply circuit includes a current transformer for power supply formed by winding a coil around a disturbance shield made of a magnetic material disposed around the casing, a battery, a power supply switching circuit, and a constant voltage circuit. And current sensor.   The current sensor according to claim 2, wherein the power supply switching circuit switches to one of a battery and a current transformer for power supply according to a detected current value.   The power supply switching circuit selects the battery when a detected current value is a predetermined value or less, and selects the power supply current transformer when the detected current value exceeds a predetermined value. The current sensor described in 1.   The current sensor according to claim 1, wherein the casing is configured to be openable / closable or separable at a portion including the through hole.   6. The current sensor according to claim 1, wherein the current detecting element is a magnetic impedance element, and bias magnetic field applying means for applying a bias magnetic field to the magnetic impedance element is provided.   The current sensor according to claim 6, wherein the bias magnetic field applying unit is a permanent magnet.   The current sensor according to claim 7, wherein the magneto-impedance element and the detection circuit are mounted on a single substrate, and the permanent magnet is disposed on the back surface thereof. The current sensor according to claim 1, wherein communication means capable of transmitting a sensor output signal to the outside is provided in the detection circuit.

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