JP2004132790A - Current sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current sensor which can measure the current in a wider range, when compared with the conventional. <P>SOLUTION: An MI (magneto-impedance) element 4 is disposed closer to an electrical wire 2 than an MI element 14. The magnetic field from the electrical wire 2 at the MI element 14 is weaker than that at the MI element 4. Even when a large current such that an amplification system connected to the MI element 4 is saturated flows in the electrical wire 2, the amplification system connected to the MI element 14 is not saturated. The detection output is obtained by a detection circuit 17, in which the MI element 4 is used in the current range such that the amplification system of the MI element 4 is not saturated, and in which the MI element 14 is used in the larger current range such that the amplification system of the MI element 4 is saturated. Accordingly, the current in a wider range can be accurately detected, when it is compared with the conventional current sensor consisting of one MI element. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a current sensor, for example, a current sensor for protecting an electric appliance by measuring an overcurrent, a current sensor necessary for electric power measurement such as a watt hour meter, and the like.
[0002]
[Prior art]
Conventionally, a Hall element or a magnetoresistive element has been widely used as a current sensor, but few sensors are satisfactory in terms of detection sensitivity. Thus, as a high-sensitivity magnetic detection element that replaces this magnetoresistance element, for example, a device using a magnetic impedance element (MI element) utilizing the Magneto-Impedance (MI) effect has been reported (see Non-Patent Document 1). . This element exhibits high sensitivity magnetic detection characteristics. The circuit for measuring the magnetic signal, that is, the current signal, is a DC bias coil wound around the MI element, a coil for negative feedback, and an amplifier for amplifying the current detection signal from both ends of the MI element. It is configured to be connected to a negative feedback coil, and the amplifier output is used as a current measurement output (see Patent Documents 1 and 2).
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2001-33533
[Patent Document 2]
JP 2001-264400 A
[Non-patent document 1]
Higa, Uchiyama, Shen, Mori, Unoki, Kikuchi, "Sputtered thin-film micro MI sensor by pulsed current excitation", Journal of the Japan Society of Applied Magnetics, vol. 21, No. 4-2, 1997 [0006]
[Problems to be solved by the invention]
FIG. 5 shows an example of the structure of a conventional current sensor.
[0007]
As shown in FIG. 5, the MI element 4 in the current sensor 1 is installed at a distance Lo from the electric wire 2 through which the measured current flows. The resin mold 3 includes an MI element 4, a bias coil 5 and a negative feedback coil 6 wound around the MI element 4, and a detection circuit 7 including an IC chip for detecting a change in resistance of the MI element 4. Reference numeral 8 denotes a plurality of leads, which are used for supplying necessary power to the detection circuit 7 and for extracting a current measurement signal.
[0008]
However, in the current sensor as shown in FIG. 5, when a large current flows through the electric wire 2, the amplifier system in the detection circuit 7 connected to the MI element 4 is saturated, and accurate current detection cannot be performed. That is, the conventional current sensor has a limited measurement current range, and it has been difficult to widen the measurement current range.
[0009]
Therefore, an object of the present invention is to provide a current sensor that can extend a measurement current range.
[0010]
[Means for Solving the Problems]
In order to solve such a problem, the present invention provides two MI elements arranged at different distances from a current-carrying conductor, and each of the two MI elements is connected to the two MI elements and generated from the conductor. A detection circuit that outputs a detection signal corresponding to a magnetic field applied to the two MI elements; and an output circuit that selects one of the detection outputs of the two detection circuits and outputs the selected signal as a sensor output. I will do it.
[0011]
Further, the present invention is characterized in that, of the two MI elements, an MI element farther from the conductor is shielded.
[0012]
Further, the present invention is characterized in that the two MI elements are shielded.
[0013]
Further, in the present invention, the detection circuit has a bias magnetic field coil for applying a bias magnetic field to the MI element wound around the MI element.
[0014]
Further, according to the present invention, the detection circuit further includes a negative feedback coil for applying a negative feedback magnetic field to the MI element wound around the MI element.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a structural view showing a first embodiment of the present invention. In a current sensor 11 of this embodiment, two MI elements 4 and 14 and a bias coil wound around the MI element 4 are formed in a resin mold 13. 5 and a negative feedback coil 6, a bias coil 15 and a negative feedback coil 16 wound around the MI element 14, and a detection circuit 17 including an IC chip for detecting a current flowing through the MI elements 4 and 14. Reference numeral 18 denotes a plurality of leads, which are used for supplying necessary power to the detection circuit 17 and for extracting a detection output.
[0016]
The two MI elements 4 and 14 are arranged so as to be at different distances from the electric wire 2 through which the detected current flows, that is, the MI element 4 is closer to the electric wire 2 than the MI element 14. Have been. A detection circuit 17 is arranged between the two MI elements 4 and 14.
[0017]
According to such a structure, the magnetic field from the electric wire 2 is weaker for the MI element 14 than for the MI element 4. For this reason, even if the resistance of the MI element 4 greatly changes and a large current flows through the electric wire 2 such that the amplifier system connected thereto is saturated, the amplifier system connected to the MI element 14 is not saturated. Therefore, regarding the current flowing through the electric wire 2, the detection circuit 17 uses the MI element 4 in a current range in which the resistance of the MI element 4 does not greatly change and the amplifier system connected thereto does not saturate. In a larger current range where the resistance greatly changes and the amplifier system connected to it saturates, by using the MI element 14 as a measurement output, compared to a conventional current sensor consisting of one MI element, A wide range of current can be accurately detected.
[0018]
FIG. 2 is a circuit diagram of the detection circuit 17. An oscillator 20 generates a high-frequency (for example, 4 to 30 MHz) signal, and supplies a high-frequency current to the two bridge circuits 34 and 35. The two bridge circuits 34 and 35 are composed of two resistors R2 and R4 whose resistance values can be adjusted, two MI elements 4 and 14, and resistors R1, R3, R5 and R6. The output terminals are connected to smoothing circuits 21, 22 and 23, 24 for smoothing the signal output and converting it to a DC output. Outputs of the smoothing circuits 21 and 22 and 23 and 24 are supplied to differential circuits 25 and 26. The outputs of the differential circuits 25 and 26 are amplified and output by the amplifiers 27 and 28.
[0019]
Bias coils 5 and 15 and negative feedback coils 6 and 16 are wound around the MI elements 4 and 14, and constant currents from constant current sources 32 and 33 are supplied to the bias coils 5 and 15. Outputs from the amplifiers 27 and 28 are supplied to 6 and 16, respectively. In such a configuration, by adjusting the resistance values of the resistors R1 and R3 of the two bridge circuits in a state where no current flows through the electric wire 2 and no influence of the magnetic field, it is possible to bring these bridge circuits into a balanced state. it can. Therefore, in this state, when a current flows through the electric wire 2, the MI elements 4 and 14 are placed in a magnetic field proportional to the current, the impedance of the MI elements 4 and 14 changes, and the balance of the bridge circuit is broken. Is output from the output terminal of the bridge circuit, amplified by the amplifiers 27 and 28, and output as a measured current signal.
[0020]
The comparator 29 controls the switch 30 as follows. That is, at the time of actual measurement, one MI element 4 is arranged closer to the electric wire 2 through which the current to be detected flows, and the other MI element 14 is arranged farther than the MI element 4. Here, by adjusting the interval between the two MI elements 4 and 14, or adjusting the size (length) of the MI elements 4 and 14, etc., one of the MI elements 4 and 14 is increased by an increase in the magnetic field from the electric wire. Before the amplifier system leading to the saturation is detected by the other MI element 14, that is, the vicinity of the upper detection limit based on the one MI element 4 and the vicinity of the lower detection limit of the other MI element 14 overlap, In addition, adjustment can be performed so that the output values of the two amplifiers 27 and 28 match at a predetermined magnetic field value. As a result, the comparator 29 compares the detection output values from the two amplifiers 27 and 28, and outputs the detection output from the amplifier 27 to the amplifier 31 via the switch 30 while the current flowing through the electric wire 2 is small. When the current flowing through the electric wire 2 increases and the magnetic field from the electric wire 2 reaches the above-described predetermined value, the detection output from the amplifier 28 is supplied to the amplifier 31 via the switch 30. The switch 30 is controlled as described above. Therefore, according to the present current sensor, it is possible to accurately detect a wider range of current flowing through the electric wire, which is an object to be detected, than in the past.
[0021]
Next, a second embodiment of the present invention will be described with reference to FIG.
[0022]
In this embodiment, a film 40 made of a material having a high magnetic permeability is formed on the resin mold 13 around the MI element 14 on the far side with respect to the electric wire 2 by, for example, vapor deposition. Shield from This can be regarded as equivalent to increasing the distance between the two MI elements 4 and 14 beyond the actual distance. Therefore, it is possible to measure a larger current region.
[0023]
Next, a third embodiment of the present invention will be described with reference to FIG.
[0024]
In this embodiment, a film 50 made of a material having a high magnetic permeability is formed on the entire resin mold 13 by, for example, vapor deposition, and the MI elements 4 and 14 are shielded from a magnetic field. As a result, it is obvious that a larger current can be measured as compared with the case where no shielding is performed. Further, the shield can enhance the electromagnetic noise resistance of the IC chip. Further, by controlling the thickness of the shield, the current measurement range can be changed, and it is possible to cope with various types of current sensors.
[0025]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a current sensor capable of measuring a wide range of current as compared with the related art.
[Brief description of the drawings]
FIG. 1 is a structural diagram showing a first embodiment of the present invention.
FIG. 2 is a circuit diagram of a detection circuit of the embodiment.
FIG. 3 is a structural diagram showing a second embodiment of the present invention.
FIG. 4 is a structural diagram showing a third embodiment of the present invention.
FIG. 5 is a diagram showing an example of the structure of a conventional current sensor.
[Explanation of symbols]
1,11 Current sensor 2 Electric wire 3,13 Resin mold 4,14 MI element 5,15 Bias coil 6,16 Negative feedback coil 7,17 Detection circuit

Claims (5)

Two magneto-impedance elements arranged at different distances from a current-carrying conductor, and magnetic fields respectively connected to the two magneto-impedance elements and generated from the conductor and applied to the two magneto-impedance elements 2. A current sensor comprising: two detection circuits each outputting a detection signal corresponding to the above-mentioned condition; and an output circuit selecting one of the detection outputs of the two detection circuits and outputting the selected signal as a sensor output. 2. The current sensor according to claim 1, wherein a magnetic impedance element farther from the conductor is shielded among the two magnetic impedance elements. 3. The current sensor according to claim 1, wherein the two magnetic impedance elements are shielded. 4. The current sensor according to claim 1, wherein the detection circuit has a bias magnetic field coil for applying a bias magnetic field to the magnetic impedance element wound around the magnetic impedance element. The current sensor according to claim 4, wherein the detection circuit further includes a negative feedback coil for applying a negative feedback magnetic field to the magnetic impedance element.

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