JP2012018024A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor capable of suppressing deterioration of measurement accuracy due to noise, even if installed at a location in a severe noise environment.SOLUTION: A current sensor 1 of this invention comprises: a first magnetic sensor 21A and a second magnetic sensor 21B each of which is arranged in periphery of a current line 2 where current to be measured circulates, and outputs an output signal of approximately reverse phase to each other by an induction magnetic field from the current to be measured; a connector 4 connected to an electronic apparatus of an output destination of output signals of the first magnetic sensor 21A and the second magnetic sensor 21B; and a differential unit 23 that is positioned adjacent to the connector 4 of a signal line of each of the first magnetic sensor 21A and the second magnetic sensor 21B and executes differential operation of the output signal of the first magnetic sensor 21A and the output signal of the second magnetic sensor 21B.

Description

  The present invention relates to a current sensor that measures the magnitude of a current, and more particularly, to a current sensor that can reduce electromagnetic noise from disturbance.

  In recent years, in the fields of electric vehicles and solar batteries, the current value handled has increased with the increase in output and performance of electric vehicles and solar battery devices. Sensors are widely used. As such a current sensor, a sensor having a magnetic sensor for detecting a current to be measured flowing through a conductor through a change in a magnetic field around the conductor has been proposed. Also, current sensors that reduce noise from disturbances have been developed.

  As a current sensor for reducing noise from disturbance, for example, a sensor that takes a differential of output signals of two magnetic sensors has been proposed (Patent Document 1). In the current sensor described in Patent Document 1, the current line is the Z axis, the one axis orthogonal to the current line is the X axis, the one axis orthogonal to the Z axis and the X axis is the Y axis, and the X axis is sandwiched in the Y axis direction. A pair of magnetic sensors are arranged adjacent to each other. Further, in the pair of magnetic sensors, the magnetic field detection direction is oriented in the X-axis direction. With this configuration, by causing the pair of magnetic sensors to perform differential operation, the X component of the magnetic field formed by the current to be measured on the signal line is added in the opposite phase, and other disturbances are removed in the same phase.

JP 2002-131342 A

  However, since the current sensor described in Patent Document 1 performs signal processing in the vicinity of a magnetic sensor having a severe noise environment, noise is placed on the signal line when the output signal of the sensor is extracted, and measurement accuracy is reduced. There was a problem.

  The present invention has been made in view of such points, and an object of the present invention is to provide a current sensor that can suppress a decrease in measurement accuracy due to noise even when the noise environment is installed in a severe position.

  The current sensor of the present invention is arranged around a current line through which a current to be measured flows, and outputs a first magnetic sensor and a second magnetic sensor that output output signals having substantially opposite phases by an induced magnetic field from the current to be measured. A sensor, a connection portion connected to an output destination electronic device of the output signals of the first magnetic sensor and the second magnetic sensor, and signals of the first magnetic sensor and the second magnetic sensor, respectively. And a differential section that is connected to the connection section side of the wire and differentially calculates an output signal of the first magnetic sensor and an output signal of the second magnetic sensor.

  According to this configuration, the first and second magnetic sensors output output signals that are substantially opposite to each other, and noise is similarly applied to the signal lines of the first and second magnetic sensors. It is possible to increase the output signal and reduce noise included in the output signal. In addition, since differential calculation is performed on the signal line connection side of the first and second magnetic sensors, the position of the electronic device at the output destination is at a position away from the first and second magnetic sensors where the noise environment is severe. It is possible to output to the electronic device a sensor output in which a noise component is reduced most recently and a decrease in measurement accuracy is suppressed.

  In the current sensor of the present invention, it is preferable that a shield portion provided so as to cover each signal line of the first magnetic sensor and the second magnetic sensor is provided. According to this configuration, it is possible to reduce noise riding on the signal lines of the first and second magnetic sensors, and improve measurement accuracy.

  In the current sensor of the present invention, it is preferable that the first magnetic sensor and the second magnetic sensor are arranged in a point object with the current line as a center, and the sensitivity axis directions are the same. According to this configuration, since the disturbance magnetic field in the sensitivity axis direction can be canceled, the measurement accuracy can be improved.

  In the current sensor of the present invention, the first magnetic sensor and the second magnetic sensor are disposed in the vicinity of the magnetic sensor element and the magnetic sensor element whose characteristics are changed by an induced magnetic field from the current to be measured, It is preferable that the magnetic balance sensor includes a feedback coil that generates a canceling magnetic field that cancels the induction magnetic field. According to this configuration, the measurement accuracy can be further improved by using a magnetic balance sensor as the magnetic sensor.

  According to the current sensor of the present invention, the first magnetic sensor and the second magnetic sensor are arranged around the current line through which the current to be measured flows and output output signals having substantially opposite phases to each other by the induced magnetic field from the current to be measured. Each of the first magnetic sensor and the second magnetic sensor, a connection portion connected to an output destination electronic device of the output signals of the first magnetic sensor and the second magnetic sensor, respectively And a differential unit that performs a differential operation on the output signal of the first magnetic sensor and the output signal of the second magnetic sensor. For this reason, even if it is a case where a current sensor is installed in the position where a noise environment is severe, the fall of the measurement accuracy by noise can be suppressed.

It is a figure which shows the current sensor which concerns on embodiment of this invention. It is a block diagram of the current sensor which concerns on embodiment of this invention. It is explanatory drawing of the noise reduction method by the current sensor which concerns on embodiment of this invention. It is explanatory drawing of the output result using the current sensor which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a current sensor according to an embodiment of the present invention. For convenience of explanation, the attachment housing 3 and the connector side housing 6 are indicated by broken lines. In the present embodiment, the current sensor 1 shown in FIG. 1 outputs an output signal corresponding to the current to be measured flowing through the current line to a device such as an ECU (Electronic Control Unit). The current sensor 1 includes an attachment housing 3 attached to the current line 2 and a connector 4 connected to an output destination device via a shield line 5. The connector 4 is connected to the shielded wire 5 via the connector side housing 6.

  In the mounting housing 3, substrates 11 and 12 are arranged vertically opposite to each other with the current line 2 interposed therebetween. The substrate 11 includes a first magnetic sensor 21 </ b> A, a control unit 22 </ b> A (see FIG. 2), and a substrate. 12, a second magnetic sensor 21B and a control unit 22B (see FIG. 2) are provided. Insulating spacer members 14 and 15 are provided between the substrates 11 and 12 and the current line 2. The substrates 11 and 12 are separated from the current line 2 by the same distance in the vertical direction by the insulating spacer members 14 and 15. Further, the first and second magnetic sensors 21A and 21B have the same sensitivity axis directions of the magnetoresistive elements at the positions that are point targets with respect to the center of the current line 2 on the substrates 11 and 12, respectively. It is arranged to be. The first and second magnetic sensors 21A and 21B are not limited to the arrangement configuration described above, and output substantially opposite phase output signals by the induced magnetic field from the current to be measured flowing through the current line 2. As long as they are arranged, they may be arranged in any way. The term “substantially reversed phase” as used herein includes a range that is shifted in phase so that a sufficient sensor output can be obtained after differential calculation.

  In the connector side housing 6, a differential portion 23 in which a differential circuit is formed on the substrate 17 is accommodated. Signal lines extending from the first and second magnetic sensors 21A and 21B are connected to the differential section 23. The differential unit 23 performs a differential operation on the output signals output from the first and second magnetic sensors 21 </ b> A and 21 </ b> B and outputs the result to the output destination device via the connector 4. As described above, the differential unit 23 is provided on the substrate 17 different from the substrates 11 and 12 on which the first and second magnetic sensors 21A and 21B are provided, and performs differential calculation in the immediate vicinity of the output destination device. It is configured. In addition, the connector side housing | casing 6 may be shielded so that the influence of disturbance noise can be reduced.

  The shield wire 5 accommodates the signal wires of the first and second magnetic sensors 21 </ b> A and 21 </ b> B on the inner side, one end is fixed to the mounting housing 3, and the other end is fixed to the connector-side housing 6. With this configuration, the shield wire 5 prevents noise from being added to the output signals of the first and second magnetic sensors 21A and 21B between the mounting housing 3 and the output destination device. The shield wire 5 may be configured to reduce the influence of disturbance noise on each signal line. For example, the shield wire 5 is configured by grounding a metal film that covers each signal in an insulated state to the ground. .

  FIG. 2 is a block diagram showing a current sensor according to the embodiment of the present invention. The first and second magnetic sensors 21A and 21B are magnetic balance sensors, and are feedback coils 211 arranged so as to be able to generate a magnetic field by a method of canceling the magnetic field generated by the current to be measured, and a magnetic detection element 2 The bridge circuit 212 includes two magnetoresistive elements and two fixed resistance elements. The control unit 22A amplifies the differential output of the bridge circuit 212 of the first magnetic sensor 21A, and controls the feedback current of the feedback coil 211 and the differential / current amplifier 221 and the feedback current of the first magnetic sensor 21A. And an I / V amplifier 222 for converting the voltage. The control unit 22B amplifies the differential output of the bridge circuit 212 of the second magnetic sensor 21B, controls the feedback current of the feedback coil 211, and the feedback current of the second magnetic sensor 21B. And an I / V amplifier 224 for converting the voltage. The differential unit 23 includes a differential amplifier 231 that amplifies the differential output of the I / V amplifiers 222 and 224.

  The feedback coil 211 is disposed in the vicinity of the magnetoresistive effect element of the bridge circuit 212, and generates a cancel magnetic field that cancels the induced magnetic field generated by the current to be measured. Examples of the magnetoresistive effect element of the bridge circuit 212 include a GMR (Giant Magneto Resistance) element and a TMR (Tunnel Magneto Resistance) element. The magnetoresistive element changes its resistance value by applying an induced magnetic field from a current to be measured. By configuring the bridge circuit 212 with two magnetoresistive elements and two fixed resistance elements, a highly sensitive current sensor can be realized. Moreover, by using a magnetoresistive effect element, it is easy to arrange the sensitivity axis in a direction parallel to the substrate surface on which the current sensor is installed, and a planar coil can be used.

  The bridge circuit 212 includes two outputs that generate a voltage difference corresponding to the induced magnetic field generated by the current to be measured. Two outputs of the bridge circuit 212 are amplified by the differential / current amplifiers 221 and 223, and the amplified outputs are given to the feedback coil 211 as current (feedback current). This feedback current corresponds to a voltage difference according to the induced magnetic field. At this time, a cancellation magnetic field that cancels the induction magnetic field is generated in the feedback coil 211. Then, the current flowing through the feedback coil 211 when the induced magnetic field and the canceling magnetic field cancel each other is converted into a voltage by the I / V amplifiers 222 and 224, and this voltage becomes the sensor output.

  In the differential / current amplifier 221, the power supply voltage is set to a value close to the reference voltage for I / V conversion + (maximum value within the rated value of feedback coil resistance × feedback coil current at full scale), thereby providing feedback. The current is automatically limited, and the effect of protecting the magnetoresistive effect element and the feedback coil can be obtained. Here, the differential of the two outputs of the bridge circuit 212 is amplified and used as a feedback current. However, only the midpoint potential is output from the bridge circuit, and the feedback current is based on the potential difference from a predetermined reference potential. It is good.

  The differential amplifier 231 processes the differential value of the output signals of the I / V amplifiers 222 and 224 as a sensor output. By performing such processing, the influence of an external magnetic field such as geomagnetism on the output signals of the first and second magnetic sensors 21A and 21B is canceled, and the current can be measured with higher accuracy. Hereinafter, the noise reduction method will be described with reference to FIG.

  As shown in FIG. 3, the first and second magnetic sensors 21 </ b> A and 21 </ b> B are sensitive to the respective magnetoresistive elements at positions that are point targets with respect to the center of the current line 2 on the substrates 11 and 12. The axial directions are arranged in the same direction. When a current to be measured flows through the current line 2 in this state, a magnetic field as indicated by an arrow Ha is generated around the current line 2. For this reason, the first and second magnetic sensors 21A and 21B can obtain output signals having phases opposite to each other by the induced magnetic field from the current to be measured. Further, the first and second magnetic sensors 21A and 21B are arranged at a severe noise environment, and are affected by a disturbance magnetic field such as geomagnetism as indicated by an arrow Hb. In this case, in-phase noises are superimposed on the output signals of the first and second magnetic sensors 21A and 21B due to the influence of the disturbance magnetic field.

  Output signals from the first and second magnetic sensors 21A and 21B are input to the differential amplifier 231 on the connector 4 side (output destination device side), and are differentially calculated in the differential amplifier 231. In this case, in the output signals of the first and second magnetic sensors 21A and 21B, the output components based on the induced magnetic field of the current to be measured are added to each other because they are in opposite phases. On the other hand, in the output signals of the first and second magnetic sensors 21A and 21B, noise components based on the disturbance magnetic field are removed because they are in phase with each other. In this way, the measurement accuracy of the current sensor 1 is improved. At this time, the differential operation by the differential amplifier 231 is performed on the connector 4 side having a good noise environment that is separated from a severe noise environment position. For this reason, it is possible to reduce noise on the sensor output after the differential calculation, and to suppress a decrease in measurement accuracy.

  In the present embodiment, a magnetic balance type sensor is used as the first and second magnetic sensors. However, the present invention is not limited to this configuration. Any magnetic sensor may be used as long as it outputs output signals having substantially opposite phases by an induced magnetic field from a current to be measured passing through a current line. For example, a magnetic proportional sensor may be used. By using a magnetic proportional sensor, it is possible to reduce power consumption as compared with a configuration using a magnetic balance sensor.

  Further, in the present embodiment, the differential unit 23 is provided adjacent to the connector 4, but the differential unit 23 is the connector 4 of each signal line of the first and second magnetic sensors 21A and 21B. What is necessary is just to be provided in the side. That is, the differential unit 23 may be provided apart from the connector 4 as long as the differential part 23 is located sufficiently away from the first and second magnetic sensors 21A and 21B having a severe noise environment.

  Here, an output result using the current sensor of the present invention will be described. Here, the output result using the current sensor of the present invention will be described while comparing the output result using the current sensor of the comparative example. FIG. 4 is a diagram showing the output result of the current sensor. The solid line shows the output result of the current sensor of the present invention, and the broken line shows the output result of the current sensor of the comparative example. The current sensor according to the comparative example is different from the current sensor of the present invention in that differential calculation processing is performed in the immediate vicinity of the first and second magnetic sensors 21A and 21B.

  As shown by the broken line in FIG. 4, the sensor output of the current sensor according to the comparative example includes a large noise component for each predetermined period. This noise oscillates between about -5V and about + 15V, which significantly reduces the measurement accuracy. Therefore, in the current sensor according to the comparative example, it is necessary to provide a filter circuit that removes a noise component from the output signal, and much time is spent on designing the filter circuit. On the other hand, as shown by the solid line in FIG. 4, a large noise component is removed from the sensor output of the current sensor 1 according to the present invention by the differential operation of the differential amplifier 231, and a constant output is obtained at about + 6V. Yes. Thus, according to the current sensor 1 of the present invention, the noise component included in the sensor output can be significantly reduced with a simple configuration as compared with the current sensor according to the comparative example.

  As described above, in the present embodiment, the differential amplifier 231 is separated from the first and second magnetic sensors 21A and 21B having a severe noise environment and is provided adjacent to the connector 4 closest to the output destination device. ing. Therefore, the output signals of the first and second magnetic sensors 21A and 21B are subjected to differential calculation immediately in the vicinity of the output destination device to remove noise, so that a highly accurate sensor output is output to the output destination device. be able to. In addition, since the differential amplifier 231 is provided away from a severe noise environment position, it is possible to suppress noise from entering the sensor output after the differential calculation and improve the measurement accuracy.

  The present invention is not limited to the above embodiment, and can be implemented with various modifications. For example, the connection relationship, size, and the like of each element in the above embodiment can be changed as appropriate. Further, in the above embodiment, a case where a magnetoresistive effect element is used for the magnetic balance type current sensor has been described. However, a Hall element or other magnetic detection element is used for the magnetic balance type current sensor. Also good. Further, in the above embodiment, the signal line extending from the first and second magnetic sensors is shielded by the shield line, but the shield line may not be provided. Even with such a configuration, it is possible to output a sensor output with a reduced noise component to an output destination device. In addition, the present invention can be implemented with appropriate modifications without departing from the scope of the present invention.

  The present invention can be applied to a current sensor that detects the magnitude of a current for driving a motor of an electric vehicle or a hybrid car.

DESCRIPTION OF SYMBOLS 1 Current sensor 2 Current line 3 Mounting housing 4 Connector (connection part)
5 Shielded wire (shield part)
6 Connector side housing 21A First magnetic sensor 21B Second magnetic sensor 22A, 22B Control unit 23 Differential unit 211 Feedback coil 212 Bridge circuit 221, 223 Differential / current amplifier 222, 224 I / V amplifier 231 Differential Amplifier

Claims (4)

A first magnetic sensor and a second magnetic sensor, which are arranged around a current line through which a current to be measured flows, and which output output signals having substantially opposite phases by an induced magnetic field from the current to be measured;
A connection unit connected to an electronic device to which an output signal of the first magnetic sensor and the second magnetic sensor is output;
The first magnetic sensor and the second magnetic sensor are connected to the connection portion side of the respective signal lines, and the output signal of the first magnetic sensor and the output signal of the second magnetic sensor are differentially calculated. A current sensor.   The current sensor according to claim 1, further comprising a shield portion provided so as to cover each signal line of the first magnetic sensor and the second magnetic sensor.   The said 1st magnetic sensor and said 2nd magnetic sensor are arrange | positioned by the point object centering | focusing on the said current line, The sensitivity axis direction is mutually the same, The Claim 1 or Claim 2 characterized by the above-mentioned. Current sensor.   The first magnetic sensor and the second magnetic sensor are arranged in the vicinity of a magnetic sensor element whose characteristics are changed by an induced magnetic field from the current to be measured and the magnetic sensor element, and cancels the induced magnetic field. The current sensor according to any one of claims 1 to 3, wherein the current sensor is a magnetic balance type sensor including a feedback coil for generating a current.

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