JP2013156029A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor having a simple structure, capable of performing current measurement with high accuracy.SOLUTION: A coil 35 is wound around the circumference of a magnet 30. In a state that no current flows in a bus bar 50, a microcomputer 40 detects the off-set value of a magnetic resistance element 20 on the basis of the output of the magnetic resistance element 20 in a predetermined first state of magnetic field application at the magnetic resistance element 20 with the coil 35, and detects temperature on the basis of the output of the magnetic resistance element 20 in a second state different from the first state. The microcomputer 40 corrects the output of signals at the magnetic resistance element 20 in response to the current intensity of the measured current flowing in the bus bar 50 in a state that current flows in the bus bar 50 on the basis of the detected off-set value and the detected temperature.

Description

  The present invention relates to a current sensor.

  In addition to measuring physical quantities in the sensor, various auxiliary functions are required. Specifically, in Patent Document 1, temperature correction is performed using a temperature sensor.

JP 11-183273 A

  By the way, it is difficult to measure the current with high accuracy only by sensing the magnetic field (lines of magnetic force) generated by the current flowing in the object to be measured in the current sensor with the magnetoelectric transducer. Specifically, the accuracy is deteriorated due to the offset and temperature characteristics. Therefore, when a correction circuit for the output of the magnetoelectric conversion element is provided, it is necessary to assemble a circuit using a dedicated sensor, which complicates the configuration.

  An object of the present invention is to provide a current sensor capable of measuring current with high accuracy with a simple configuration.

  According to the first aspect of the present invention, a magnetoelectric conversion element, a magnet that generates a magnetic field having a predetermined strength, can apply the generated magnetic field to the magnetoelectric conversion element, and the magnetoelectric conversion element using the magnet are provided. Adjusting means capable of adjusting the strength of the magnetic field, and when the magnetic field application state in the magnetoelectric conversion element is set to a predetermined first state by the adjusting means when no current flows through the object to be measured. The offset value detecting means for detecting the offset value of the magnetoelectric conversion element from the output of the magnetoelectric conversion element, and the magnetic field application state at the magnetoelectric conversion element by the adjusting means when the current does not flow through the measurement object. A temperature detecting means for detecting the temperature from the output of the magnetoelectric conversion element in a second state different from the state of the offset, and an offset detected by the offset value detecting means. The output of a signal corresponding to the magnitude of the current to be measured flowing in the object to be measured in the magnetoelectric transducer when a current flows in the object to be measured based on the value and the temperature detected by the temperature detecting means The gist of the invention is that it comprises a correction means for performing correction.

  According to the first aspect of the present invention, a magnetic field having a predetermined strength is generated in the magnet, and the generated magnetic field can be applied to the magnetoelectric transducer. The adjusting means can adjust the strength of the magnetic field applied to the magnetoelectric transducer by the magnet. When the current is not flowing through the object to be measured by the offset value detection means, the magnetoelectric conversion element is output from the output of the magnetoelectric conversion element when the magnetic field application state in the magnetoelectric conversion element is set to a predetermined first state by the adjustment means. The offset value is detected. When current does not flow through the object to be measured by the temperature detection means, the temperature from the output of the magnetoelectric conversion element when the adjustment means changes the magnetic field application state at the magnetoelectric conversion element to the second state different from the first state. Is detected. The magnitude of the measured current flowing in the measurement object in the magnetoelectric transducer when the current flows through the measurement object based on the offset value detected by the offset value detection means and the temperature detected by the temperature detection means. The signal output is corrected accordingly.

  Thereby, offset correction and temperature correction can be performed using a magnet and an adjustment means. As a result, current measurement can be performed with high accuracy with a simple configuration without using a dedicated sensor.

According to a second aspect of the present invention, in the current sensor according to the first aspect, the adjusting means may be a coil that generates a magnetic field having a strength corresponding to an energization current value.
As described in claim 3, in the current sensor according to claim 2, the magnet may be a permanent magnet, and the coil may be wound around the permanent magnet.

  According to a fourth aspect of the present invention, in the current sensor according to the second or third aspect, the offset value detecting means cancels the magnetic field generated by the magnet with the magnetic field generated by the adjusting means. The gist is to detect the offset value of the magnetoelectric conversion element from the output of the conversion element.

  According to the fourth aspect of the invention, the offset value detection means detects the offset value of the magnetoelectric conversion element from the output of the magnetoelectric conversion element in a state where the magnetic field generated by the magnet is canceled by the magnetic field generated by the adjustment means. The Thereby, the offset value of the magnetoelectric transducer can be detected without being affected by the temperature of the magnetic field strength in the magnet.

  As described in claim 5, in the current sensor according to any one of claims 1 to 4, the object to be measured may be a bus bar.

  According to the present invention, current measurement can be performed with high accuracy with a simple configuration.

(A) is a top view of the current sensor in the embodiment, (b) is a right side view of the current sensor, and (c) is a longitudinal sectional view taken along line AA of (a). (A) is a plan view of the current sensor with the case removed, (b) is a right side view of the current sensor with the case removed, and (c) is a front view of the current sensor with the case removed. Figure. The electrical block diagram of a current sensor. The characteristic view which shows the relationship between temperature and the output of a magnetoresistive element. The figure which shows the relationship between temperature and the temperature correction value of a magnetoresistive element. The flowchart for demonstrating an effect | action.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
In the drawings, the horizontal plane is defined by the orthogonal X and Y directions, and the vertical direction is defined by the Z direction.

  As shown in FIG. 1, the current sensor 10 includes a box-shaped case 11, a magnetoresistive element (GMR) 20, a magnet 30, a coil 35, and a microcomputer 40. The bus bar 50 as an object to be measured is a strip-shaped conductive plate having a rectangular cross section, and extends in the Y direction, and the long side of the rectangular cross section is in the X direction.

  The case 11 includes a resin case main body 12 and a resin lid 13. A recess 12a is formed on one surface of the case main body 12, and the opening of the recess 12a of the case main body 12 is closed by the lid 13, so that the case 11 is formed in a box shape.

  A storage chamber R1 is formed inside the recess 12a of the case body 12 in the case 11, and the printed circuit board 14 is stored in the storage chamber R1. Specifically, a recess 15 is formed on the bottom surface of the recess 12a of the case body 12, and the printed board 14 shown in FIG. The printed circuit board 14 is arranged in a standing state.

As shown in FIG. 2, a magnetoresistive element 20 as a magnetoelectric conversion element is mounted on the printed board 14. The magnetoresistive element 20 is packaged.
A microcomputer 40 is mounted on the printed board 14.

  As shown in FIG. 1, a bus bar 50 as an object to be measured is disposed in the case 11 and the printed board 14 so as to penetrate therethrough. A current flows through the bus bar 50. The bus bar 50 is located close to the lower side of the magnetoresistive element 20 as shown in FIG.

  Further, as shown in FIGS. 1 and 2, a magnet 30 is embedded in the case main body 12. As shown in FIG. 1C, the magnet 30 is disposed close to the magnetoresistive element 20. The magnet 30 is a rod-shaped ferrite magnet. That is, the magnet 30 is a permanent magnet.

  The magnet 30 generates a magnetic field B1 having a predetermined strength and can apply the generated magnetic field B1 to the magnetoresistive element 20. Specifically, the magnet 30 can apply to the magnetoresistive element 20 a magnetic field B1 that is opposite to the magnetic field B2 applied to the magnetoresistive element 20 by the current I to be measured.

  Further, a coil 35 as an adjusting means is wound around a rod-shaped magnet (ferrite magnet) 30. The coil 35 generates a magnetic field having a strength corresponding to the energization current value. That is, the intensity of the magnetic field generated by the coil 35 can be adjusted. The coil 35 can adjust the strength of the magnetic field applied to the magnetoresistive element 20 by the magnet 30.

  A magnetoresistive element (GMR) 20 as a magnetoelectric conversion element outputs a signal corresponding to the magnitude of the current to be measured flowing through the bus bar 50. That is, the magnitude of the current to be measured flowing through the bus bar 50 using the magnetoresistive element 20 can be measured as the strength of the magnetic field B2.

  As shown in FIG. 3, the magnetoresistive element 20 is connected to the microcomputer 40, and the microcomputer 40 inputs a signal from the magnetoresistive element 20. A coil current regulator 60 is connected to the coil 35 so that the current flowing through the coil 35 can be adjusted by the coil current regulator 60. The coil current regulator 60 can be controlled by the microcomputer 40. Further, the magnetic field generated by the magnet 30 can be adjusted by adjusting the current flowing through the coil 35.

  The memory 41 of the microcomputer 40 stores temperature characteristics of the magnetoresistive element 20 shown in FIG. 4, that is, data indicating the relationship between the output of the magnetoresistive element 20 and the temperature. Specifically, the magnetoresistive element 20 is negative, that is, has a temperature characteristic in which the output decreases as the temperature increases. Using this data, the microcomputer 40 can detect the temperature from the output of the magnetoresistive element 20.

  The memory 41 stores data indicating the relationship between the temperature shown in FIG. 5 and the temperature correction value of the magnetoresistive element 20. Using this data, the microcomputer 40 can calculate the correction value of the output of the magnetoresistive element 20 from the temperature.

  Further, in FIG. 3, the microcomputer 40 inputs a bus bar state signal, and the microcomputer 40 can detect whether the bus bar 50 is in a live line state (state in which current flows) or in a disconnected state (state in which no current flows). It is like that.

Further, the microcomputer 40 sends out the output (current measurement result) of the magnetoresistive element 20 after correction.
Next, the operation of the current sensor 10 will be described.
The magnet 30 applies to the magnetoresistive element 20 a magnetic field B1 that is opposite to the magnetic field B2 applied to the magnetoresistive element 20 by the current to be measured.

  As shown in FIG. 6, the microcomputer 40 determines in step 100 whether the bus bar 50 is in a live line state (state in which current flows) or is disconnected (state in which no current flows). If the microcomputer 40 is in a disconnected state (a state in which no current flows), the microcomputer 40 proceeds to step 101. In step 101, the microcomputer 40 adjusts the current flowing through the coil 35 so that the magnetic field generated by the magnet 30 is zero, that is, cancels (cancels) the magnetic field generated by the magnet 30. As a result, the magnetic field application state in the magnetoresistive element 20 is set to a state where the magnetic field applied to the magnetoresistive element 20 becomes zero (first state). By doing so, the temperature characteristics of the magnet 30 are not affected.

Further, in step 102, the microcomputer 40 takes in the output V1 of the magnetoresistive element 20 in this state and calculates an offset value α (level of the output V1).
In this way, the processing of steps 100, 101, and 102 is executed. At this time, the microcomputer 40 as the offset value detection means sets the magnetic field application state in the magnetoresistive element 20 to the first state determined in advance by the coil 35 when no current flows through the bus bar 50 as the object to be measured. The offset value of the magnetoresistive element 20 is detected from the output of the magnetoresistive element 20 at that time. Specifically, the microcomputer 40 detects the offset value of the magnetoresistive element 20 from the output of the magnetoresistive element 20 in a state where the magnetic field generated by the magnet 30 is canceled by the magnetic field generated by the coil 35.

  Subsequently, in step 103, the microcomputer 40 reverses the direction of the current flowing through the coil 35 from the direction of the current for calculating the offset value and adjusts the energization current to set a predetermined magnetic field by the magnet 30 and the coil 35. (Constant value). That is, a constant current is passed through the coil 35 to generate a constant magnetic field. Thereby, as a magnetic field application state in the magnetoresistive element 20, a predetermined (constant) magnetic field is applied to the magnetoresistive element 20. This state is a second state different from the first state for detecting the offset value.

  Further, in step 104, the microcomputer 40 calculates (detects) the temperature T1 from the output V2 of the magnetoresistive element 20 in this state using the temperature characteristic data of FIG. The calculated temperature T1 is stored in the memory 41.

  In this way, the processing of steps 100, 103, and 104 is executed. At this time, the microcomputer 40 serving as the temperature detection means performs the magnetism when the magnetic field application state in the magnetoresistive element 20 is changed to the second state different from the first state by the coil 35 when no current flows through the bus bar 50. The temperature is detected from the output of the resistance element 20.

  Subsequently, in step 105, the microcomputer 40 determines whether the bus bar 50 is in a live line state (a state in which current flows) or a disconnection state (a state in which no current flows). The process proceeds to step 106. In step 106, the microcomputer 40 takes in the output V3 of the magnetoresistive element 20 at the time of actual measurement. During this actual measurement, the microcomputer 40 adjusts the current flowing through the coil 35 to cancel (cancel) the magnetic field generated by the magnet 30 so that no magnetic field is applied to the magnetoresistive element 20 from the magnet 30 and the coil 35.

  In step 106, the microcomputer 40 calculates the correction value β from the temperature T1 calculated in step 104 using the temperature characteristic data of FIG. The microcomputer 40 adds the offset value α calculated in step 102 and the temperature correction value β calculated using FIG. 5 to the acquired output V3 of the magnetoresistive element 20. The microcomputer 40 sends the output (= V3 + α + β) of the magnetoresistive element 20 after correction to the outside.

  In this way, the processing of steps 105 and 106 is executed. At this time, the microcomputer 40 as the correction means outputs a signal corresponding to the magnitude of the current to be measured flowing in the bus bar 50 in the magnetoresistive element 20 when the current flows in the bus bar 50 based on the detected offset value and the detected temperature. Correct the output.

  That is, the magnet 30 and the coil 35 are arranged in the vicinity of the magnetoresistive element 20, the offset value and the temperature are measured before sensing the current flowing through the bus bar 50, and the offset value is measured when sensing the current flowing through the bus bar 50. Compensate and correct temperature. Conventional current sensors require separate sensors to perform offset correction and temperature correction. However, current can be measured by performing offset correction and temperature correction without using a dedicated sensor. Specifically, the offset value is calculated by detecting the output of the magnetoresistive element 20 in a state where a current is passed through the coil 35 so that the magnetic field (magnetic force) at the magnetoresistive element 20 becomes zero and the magnetic field of the magnet 30 is zero. Do it. The temperature is measured by reversing the direction of the current in the coil 35 and using the linear temperature characteristics of the magnetoresistive element 20 to obtain the temperature from the output of the magnetoresistive element 20. Then, offset and temperature are corrected for the measured value when the current flows.

As described above, according to the present embodiment, the following effects can be obtained.
(1) As a configuration of the current sensor, a magnetoresistive element 20 as a magnetoelectric conversion element, a magnet 30, a coil 35 as an adjusting means, and a microcomputer 40 are provided. The microcomputer 40 uses the output of the magnetoresistive element 20 from the output of the magnetoresistive element 20 when the magnetic field application state in the magnetoresistive element 20 is changed to the first predetermined state by the coil 35 when no current flows through the bus bar 50. Detect the offset value. Further, the microcomputer 40 uses the output of the magnetoresistive element 20 when the magnetic field application state in the magnetoresistive element 20 is changed to the second state different from the first state by the coil 35 when no current flows through the bus bar 50. Detect temperature. The microcomputer 40 corrects the output of the signal according to the magnitude of the current to be measured flowing in the bus bar 50 in the magnetoresistive element 20 when the current flows in the bus bar 50 based on the detected offset value and the detected temperature. Do.

  Thereby, offset correction and temperature correction can be performed using the magnet 30 and the coil 35. As a result, current measurement can be performed with high accuracy with a simple configuration without using a dedicated sensor.

  (2) The adjustment means is a coil 35 that generates a magnetic field having a strength corresponding to the energization current value. As a result, a magnetic field is generated, and the strength of the magnetic field applied to the magnetoresistive element 20 by the magnet 30 can be easily adjusted.

  (3) The magnet 30 is a permanent magnet, and a coil 35 is wound around the permanent magnet 30. Thereby, the magnetic field generated by the magnet 30 can be easily canceled by the magnetic field generated by the coil 35 (adjusting means).

  That is, the microcomputer 40 as the offset value detection means detects the offset value of the magnetoresistive element 20 from the output of the magnetoresistive element 20 in a state where the magnetic field generated by the magnet 30 is canceled by the magnetic field generated by the coil 35. Thereby, the offset value of the magnetoresistive element 20 can be detected without being influenced by the temperature of the magnetic field in the magnet 30.

The embodiment is not limited to the above, and may be embodied as follows, for example.
When calculating the offset value, the magnetic field is “0”, that is, the magnetic field generated by the magnet 30 is canceled (cancelled). In this case, when the current flowing through the bus bar 50 is measured by the magnetoresistive element 20, when the magnetic field component by the magnet 30 is included, the final current measurement result is obtained by removing the magnetic field component by the magnet 30.

  In FIG. 1, the magnet 30 applies a magnetic field B 1 opposite to the magnetic field B 2 applied to the magnetoresistive element 20 by the current I to be measured to the magnetoresistive element 20. Instead of this, the magnet 30 may apply a magnetic field in the same direction as the magnetic field B <b> 2 applied to the magnetoresistive element 20 by the measured current I to the magnetoresistive element 20.

Although a magnetoresistive element is used as the magnetoelectric conversion element, other magnetoelectric conversion elements such as a Hall IC (Hall element) may be used instead.
-Although the bus-bar 50 was used as a to-be-measured object, it is not limited to this. For example, a round bar may be used.

  -An electromagnet may be used as a magnet, and what is necessary is just to generate a magnetic field having a predetermined strength.

  DESCRIPTION OF SYMBOLS 10 ... Current sensor, 20 ... Magnetoresistive element, 30 ... Magnet, 35 ... Coil, 40 ... Microcomputer, 50 ... Busbar.

Claims (5)

A magnetoelectric conversion element;
A magnet capable of generating a magnetic field having a predetermined strength and applying the generated magnetic field to the magnetoelectric transducer;
Adjusting means capable of adjusting the strength of the magnetic field applied to the magnetoelectric transducer by the magnet;
The offset value of the magnetoelectric conversion element from the output of the magnetoelectric conversion element when the magnetic field application state in the magnetoelectric conversion element is set to a predetermined first state by the adjusting means when no current flows through the object to be measured. Offset value detecting means for detecting
When no current flows through the object to be measured, the temperature is determined from the output of the magnetoelectric conversion element when the magnetic field application state in the magnetoelectric conversion element is changed to the second state different from the first state by the adjusting means. Temperature detecting means for detecting;
Based on the offset value detected by the offset value detecting means and the temperature detected by the temperature detecting means, the current to be measured flowing in the object to be measured in the magnetoelectric transducer when the current flows in the object to be measured Correction means for correcting the output of the signal according to the magnitude;
A current sensor comprising:   The current sensor according to claim 1, wherein the adjustment unit is a coil that generates a magnetic field having a strength corresponding to an energization current value.   The current sensor according to claim 2, wherein the magnet is a permanent magnet, and the coil is wound around the permanent magnet.   The offset value detection means detects the offset value of the magnetoelectric conversion element from the output of the magnetoelectric conversion element in a state where the magnetic field generated by the magnet is canceled by the magnetic field generated by the adjustment means. 2. The current sensor according to 2 or 3.   The current sensor according to claim 1, wherein the object to be measured is a bus bar.