JP6413317B2 - Current sensor - Google Patents

Description

  The present invention relates to a current sensor using a magnetic sensor element. More specifically, the present invention can measure the magnitude of a current flowing through an electric wire in a non-contact manner, and can reduce measurement errors even when the relative position between the current sensor and the electric wire changes. The present invention relates to a sensitive current sensor. In addition, the electric wire in this invention shall include things other than circular in cross-sectional shape, such as a bus bar.

  One type of current sensor uses a magnetic sensor element that converts the magnitude of a magnetic field into an electrical signal such as a change in electrical resistance or an electromotive force and outputs the electrical signal.

  When measuring the magnitude of the current flowing through the electric wire in a non-contact manner, there is a problem in that a measurement error occurs if the relative position between the center of the electric wire and the current sensor is shifted.

  Therefore, it has been proposed to use a magnetic flux collecting core or a plurality of magnetic sensor elements as a method of reducing the misalignment error in the current sensor.

  The positional deviation error is a measurement error that occurs when the relative position between the current sensor and the electric wire through which the current to be measured flows is shifted.

  The magnetic flux collecting core is formed of a soft magnetic metal having a high magnetic permeability and has a high effect of collecting magnetic flux.

  FIG. 11 is a configuration explanatory view showing an example of a conventional current sensor using a magnetic collecting core (Japanese Patent Laid-Open No. 2002-303642). In FIG. 11, when the magnetic flux collecting core 1 is used, since the Hall element 2 measures the magnetic flux along the magnetic flux collecting core 1, even when the position of the electric wire 3 is shifted in the magnetic flux collecting core 1, the amount of magnetic flux to be measured is Almost no change, resulting in little measurement error.

  However, when using a magnetic collecting core, the magnetic collecting core shifts due to vibration, the magnetic collecting core rusts, the characteristics of the magnetic collecting core deteriorates due to temperature changes, and the linearity and hysteresis characteristics of the sensor due to the magnetic collecting core. As a result, the measurement accuracy deteriorates due to deterioration, etc., and the size of the magnetic collecting core needs to be increased in order to use the magnetic collecting core in a magnetically unsaturated state, resulting in an increase in the size of the sensor itself. There are problems such as.

  FIG. 12 is a configuration explanatory view showing an example of a conventional current sensor in which a plurality of Hall elements are arranged so as to surround the periphery of an electric wire (Japanese Patent Laid-Open No. 2007-107972). In FIG. 12, a plurality of hall elements 4 are arranged on the circumference of the substrate 6 with the electric wire 5 as the center, and the hall elements adjacent on the circumference are electrically connected in series.

  As a result, the output of each Hall element 4 changes due to a relative positional shift between the electric wire 5 and the current sensor, but these changes cancel out the change that occurs in the sum of the outputs of the Hall element 4. Even when the positions of are shifted, the sum of the outputs from all the Hall elements 4 hardly changes, and a measurement error hardly occurs.

JP 2002-303642 A JP 2007-107972 A

  However, according to such a conventional configuration, since the plurality of Hall elements 4 are arranged so as to surround the periphery of the electric wire 5, the size of the current sensor increases as the diameter of the electric wire 5 increases. There is a problem that it is difficult to install in a place where electric wires such as terminal blocks are close to each other.

  Moreover, since it is necessary to arrange many magnetic sensors so that the circumference | surroundings of the electric wire 5 may be enclosed, there also existed a problem that the number of sensors increased and cost increased.

  The present invention solves these problems, and its purpose is a shape that can be installed in a place where the wires are close to each other without surrounding the wire, and the number of parts can be reduced. The object is to realize a current sensor capable of measuring current with high accuracy.

In order to solve such a problem, the invention according to claim 1 of the present invention,
In a current sensor configured to measure the current flowing through the wire in a non-contact manner,
Including two magnetic sensor modules that are housed in a frame made of an insulating member and fixed to the electric wire, and are arranged at different distances from the center of the electric wire so that the tangential direction and the magnetic sensitive direction of the magnetic force lines are coincident ,
Each of the magnetic sensor modules includes a magnetoresistive element whose electrical resistance changes with application of a magnetic field, a magnetic impedance element whose electrical impedance changes with application of a magnetic field, and a hole that detects a magnetic field using the Hall effect. Including either elements or fluxgate elements ,
One of the two magnetic sensor modules is mounted on a substrate via a spacer made of a non-magnetic material .

The invention according to claim 2 is the current sensor according to claim 1,
Signal processing means for obtaining an effective value of the current from output values at each time of the two magnetic sensor modules is provided.

The invention according to claim 3 is the current sensor according to claim 2 ,
The signal processing means has a function of calculating and storing a distance between the center of the electric wire and the two magnetic sensor modules, and calculates a current value based on the stored distance information .

  Accordingly, it is possible to realize a current sensor that has low power consumption, high sensitivity characteristics, a small and simple structure, can reduce misalignment errors, and is relatively inexpensive.

It is composition explanatory drawing which shows one Example of the current sensor based on this invention. It is a schematic diagram at the time of current measurement based on the present invention. 1 is a circuit diagram of a current sensor using magnetic sensor modules 10 and 12 according to the present invention. FIG. It is a block diagram which shows the structural example of the signal processing circuit 13 based on this invention. 5 is a flowchart for explaining a specific example of a flow of signal processing after AD conversion in the block configuration of FIG. 4. It is a block diagram which shows the other structural example of the signal processing circuit 13 based on this invention. 7 is a flowchart illustrating a specific example of a flow of signal processing after AD conversion in the block configuration of FIG. 6. It is a circuit diagram which shows the other Example of this invention. It is a block diagram which shows the other structural example of the signal processing circuit 13 based on this invention. 10 is a flowchart illustrating a specific example of a flow of signal processing after AD conversion in the block configuration of FIG. 9. It is structure explanatory drawing which shows an example of the conventional current sensor using a magnetic collection core. It is composition explanatory drawing which shows an example of the conventional current sensor with which the several Hall element was arrange | positioned around the electric wire.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of an embodiment of a current sensor according to the present invention, in which (A) is a front view and (B) is a side view.

  In FIG. 1, a current sensor according to the present invention is disposed inside a frame 8 so as to be parallel to the wire 8 and a frame 8 for fixing the current sensor to the wire 7 through which a current to be measured flows. A printed circuit board 9, a first magnetic sensor module 10 mounted on the printed circuit board 9, a second magnetic sensor module 12 disposed on the printed circuit board 9 with a spacer 11 made of a nonmagnetic material, The signal processing circuit 13 is mounted on the printed circuit board 9. Note that the current sensor shown in FIG. 1 can measure the instantaneous value of the current to be measured.

  The frame 8 can be fixed so that when the current sensor is installed on the electric wire 7 having an arbitrary diameter, the magnetic sensing direction of the magnetic sensor module in the current sensor and the direction of the magnetic field generated from the current to be measured are uniquely determined. In the case of the present embodiment, a cutout portion 8a having a cross-sectional shape of "<" is provided on the bottom surface of the wire 7 in a stable manner. The material is preferably a resin having a relatively high insulating property in order to prevent an electric shock accident due to leakage from the current to be measured. In this embodiment, an ABS resin is used. In order to fix the frame 8 to the electric wire 7, a double-sided tape or a binding band can also be used.

  The magnetic sensor module 10 is arranged on a printed circuit board 9 arranged in the frame 8 so as to be parallel to the electric wire 7, passing through the center of the electric wire 7 and on a line perpendicular to the surface of the printed circuit board 9. . In addition, the magnetic sensor module 10 is arranged so that the magnetic sensing direction is in contact with the surface of the printed circuit board 9 and is orthogonal to the longitudinal direction of the electric wires 7.

  The role of the spacer 11 made of a non-magnetic material is to prevent the distance between the center of the electric wire 7 and the magnetic sensor module 10 from being equal to the distance between the center of the electric wire 7 and the magnetic sensor module 12. is there. The shape is not limited as long as the role can be fulfilled.

  In this embodiment, a rectangular parallelepiped polycarbonate is used as the spacer 11. In addition, a resin that does not contain a nonmagnetic metal or a magnetic substance can be used.

  The magnetic sensor module 12 is disposed on the printed circuit board 9 on a spacer 11 disposed on a line passing through the center of the electric wire 7 and perpendicular to the surface of the printed circuit board 9. Further, the magnetic sensor module 12 is arranged so that the magnetic sensing direction is in contact with the surface of the printed circuit board 9 and is orthogonal to the longitudinal direction of the electric wire 7.

  FIG. 2 is a schematic diagram at the time of current measurement. The positional relationship between the electric wire 7 and the magnetic sensor modules 10 and 12 and the state of the generated magnetic field at the time of current measurement are indicated by magnetic lines of force ML1 and ML2. It is assumed that the current to be measured flows in the line direction of the electric wire 7.

  The two magnetic sensor modules 10 and 12 are installed so that the distance between the center of the electric wire 7 and the magnetic sensor module 10 is L, and the distance between the center of the electric wire 7 and the magnetic sensor module 12 is L + d. In addition, the tangential direction of the magnetic force line in these magnetic sensor modules 10 and 12 and a magnetic sensitive direction correspond.

  The height of the spacer 11 in the direction perpendicular to the substrate surface of the printed circuit board 9 is adjusted so that the distance d in FIG. 2 is one value between 1 mm and 20 mm. When the value of the distance d is small, the difference between the output value V1 and the output value V2 of the two magnetic sensor modules 10 and 12 is small, and an error in the current value I is caused by electrical noise included in the output value V1 and the output value V2. Becomes larger.

  On the other hand, when the value of the distance d is increased, the size of the current sensor is increased in a direction perpendicular to the board surface of the printed board. Therefore, the distance d is adjusted between 1 mm and 20 mm in consideration of the measurement accuracy of the current I and the size of the current sensor.

FIG. 3 is a circuit diagram of a current sensor using the magnetic sensor modules 10 and 12 according to the present invention.
The magnetic sensor module 10 includes a magnetic sensor element 10a and a fixed resistor 10b connected in series. One end of the series circuit is connected to the sensor drive terminal 10c, and the other end is connected to a common potential point and the sensor drive terminal. The connection point 10e between the magnetic sensor element 10a and the fixed resistor 10b is connected to the signal processing circuit 13 as an output terminal.

  The magnetic sensor module 12 includes a magnetic sensor element 12a and a fixed resistor 12b connected in series. One end of the series circuit is connected to the sensor drive terminal 12c, and the other end is connected to a common potential point and the sensor drive terminal. The connection point 12e between the magnetic sensor element 12a and the fixed resistor 12b is connected to the signal processing circuit 13 as an output terminal.

  A voltage for driving the sensor is applied between the sensor drive terminals 10c-10d and 12c-12d of the magnetic sensor modules 10 and 12, respectively. The signal processing circuit 13 is provided with an output terminal 13a for outputting a measured current value to an external device.

  FIG. 4 is a block diagram showing a configuration example of the signal processing circuit 13 according to the present invention. The signal processing circuit 13 includes input terminals IN1 and IN2 to which output signals of the magnetic sensor modules 10 and 12 are input, a multiplexer that switches connection between the input terminals IN1 and IN2, offset correction, signal amplification, low-pass filter processing, and the like. Of the current to be measured from the output values of the AD sensor 13 and 12 and the AD converter 13 c for digitizing the signal output from the analog signal processor 13 b and the AD converted magnetic sensor modules 10 and 12. A current calculation unit 13d that calculates a value and an output terminal 13a that outputs the current value of the current to be measured calculated by the current calculation unit 13d to the outside.

  FIG. 5 is a flowchart illustrating a specific example of the flow of signal processing after AD conversion in the block configuration of FIG. The output values V1 and V2 of the magnetic sensor modules 10 and 12 are input to the AD converter 13c, AD converted, and input to the current calculator 13d (step S1). The current calculation unit 13d calculates a current value I from these output values V1 and V2 (step S2), and outputs the calculation result to the output terminal 13a (step S3).

The operation of each part of the current sensor according to the present invention will be described in detail.
The magnetic sensor module 10 and the magnetic sensor module 12 have the same configuration. For example, a tunnel magnetoresistive element made of a nanogranular film and a soft magnetic film is used. Besides, magnetoresistive elements such as anisotropic magnetoresistive elements (AMR), giant magnetoresistive elements (GMR), tunnel magnetoresistive elements (TMR), etc., whose electrical resistance changes with application of a magnetic field, A magnetic impedance element composed of an amorphous wire or a thin film made of a soft magnetic material whose electrical impedance changes with application, a Hall element that detects a magnetic field using the Hall effect, and a fluxgate element can be used.

  The positions of the magnetic sensor modules 10 and 12 need only be different from the distance between the center of the electric wire 7 and the magnetic sensor module 10 and the distance between the center of the electric wire 7 and the magnetic sensor module 12. The module 12 may not be on the line connecting the center of the electric wire 7 and the magnetic sensor module 10.

  The output value V1 and the output value V2 of the magnetic sensor modules 10 and 12 are input to the A / D converter 13 and are converted into digital signals at approximately the same time by switching the input signal by a multiplexer (not shown) of the signal processing unit 13, It is output to the current calculation unit 13d.

  The current calculation unit 13d calculates the current value I according to Equation 6 using the output value V1 and the output value V2. Here, the sensitivities α1 and α2 of the magnetic sensor modules 10 and 12 are stored in the current calculation unit 13d. Finally, the calculated current value I is output from the output terminal.

  A method for calculating the current value I from the output values V1 and V2 of the magnetic sensor modules 10 and 12 will be described below. As shown in FIG. 2 described above, when the current I flows through the electric wire 7, the magnetic sensor module 10 and the magnetic sensor module 12 generate circular magnetic fields indicated by the magnetic force lines ML1 and ML2.

Assuming that the magnetic flux densities in the magnetic sensor modules 10 and 12 at this time are B1 and B2, respectively, the magnetic flux densities B1 and B2 are expressed by Equations 1 and 2 according to Bio-Savart's law. Here, μ is the magnetic permeability of the space where the current sensor is installed.
B1 = μI / (2π · L) (1)
B2 = μI / {2π (L + d)} (2)

Here, assuming that the sensitivities of the magnetic sensor modules 10 and 12 are α1 and α2, the output values V1 and V2 of the respective magnetic sensor modules are expressed as Equations 3 and 4.
V1 = α1 · B1 (3)
V2 = α2 · B2 (4)

From these formulas 1 to 4, the distance L is derived as shown in formula 5.
L = α1 · V2 · d / {(α2 · V1) − (α1 · V2)} (5)

Furthermore, the current value I is derived from Equation 1 and Equation 5 as Equation 6.
I = (2π · L · B1) / μ
= {(2π · d · V1 · V2) / μ} / {(α2 · V1) − (α1 · V2)} (6)

  According to such a configuration, the conventional structure surrounding the electric wire is unnecessary, so that the size of the current sensor is small even when the diameter of the electric wire is large compared to the conventional current sensor. There is no need to change.

  And since the structure which surrounds the circumference | surroundings of an electric wire is unnecessary, space saving can be implement | achieved rather than the conventional current sensor, and it can install easily also in the place where electric wires, such as a terminal block, adjoined.

  Furthermore, since the structure surrounding the periphery of the electric wire is unnecessary, the structure can be installed simply by being attached to the surface of the electric wire covering.

As a result,
1) Wire breakage, which was necessary when installing a current sensor with a conventional configuration, is no longer necessary.
2) Since an electric wire fixing mechanism such as a clamp is not required, the installation cost (installation man-hour) can be reduced.

  FIG. 6 is a block diagram showing another embodiment of the signal processing circuit 13 according to the present invention, which is a block diagram showing an example of the configuration of the signal processing circuit of the current sensor for alternating current, in the same part as FIG. Have the same reference numerals.

  The signal processing circuit of FIG. 6 includes a storage unit 13e that stores output values of the magnetic sensor modules 10 and 12 between the AD conversion unit 13c and the current calculation unit 13d of the signal processing circuit 13 of FIG. An effective value calculation unit 13f for calculating effective values of outputs 10 and 12 is inserted.

  FIG. 7 is a flowchart illustrating a specific example of the flow of signal processing after AD conversion in the block configuration of FIG. The output values V1 and V2 (step S1) measured by the magnetic sensor modules 10 and 12 are input to the AD conversion unit 13c, converted into digital signals and stored (step S2), and these converted values are stored. The operation is repeated a predetermined N times (step S3). The number and period of these repetitions are set in advance according to the frequency of the current to be measured and the required measurement accuracy.

  After repeating N times, the effective value calculation unit 13f performs a fitting process by, for example, the least square method based on the output values V1 and V2 of the magnetic sensor modules 10 and 12 at each measurement time stored in the storage unit 13e. The effective values V1rms and V2rms of the output value V1 and the output value V2 are calculated, and the calculation results are output to the current calculation unit 13d (step S4).

  The current calculator 13f calculates the effective value Irms of the current (step S5), and outputs the calculation result to the output terminal 13a (step S6).

  Accordingly, the distance L can be expressed by Expression 7, and the effective value Irms of the current can be expressed by Expression 8.

L = α1 · V2rms · d / {(α2 · V1rms) − (α1 · V2rms)} (7)
Irms = {(2π · d · V1rms · V2rms) / μ} / {(α2 · V1rms) − (α1 · V2rms)} (8)

  With the configuration as shown in FIG. 6, the effective value of the current to be measured can be output as a measured value, and the alternating current can be quantitatively evaluated. In particular, since AC is generally used as a commercial power source, it is suitable for monitoring the current consumption of the commercial power source.

  FIG. 8 is a circuit diagram showing another embodiment of the present invention, in which sensitivity and temperature characteristics are improved, and parts common to FIG. 3 are given the same reference numerals.

  In FIG. 8, a magnetic sensor module 10 includes magnetic sensor elements 10a and 10f connected in series. One end of the series circuit is connected to a sensor drive terminal 10c, and the other end is connected to a common potential point and the sensor. Connected to the drive terminal 10d, a connection point 10e between the magnetic sensor element 10a and the fixed resistor 10b is connected to the signal processing circuit 13 as an output terminal.

  The magnetic sensor module 12 has magnetic sensor elements 12a and 12f connected in series. One end of the series circuit is connected to the sensor drive terminal 12c, and the other end is connected to a common potential point and to the sensor drive terminal 12d. A connection point 12e between the magnetic sensor element 12a and the fixed resistor 12b is connected to the signal processing circuit 13 as an output terminal.

In the configuration of FIG. 8, the following two points are taken into consideration.
1) For the magnetic sensor elements 10a and 10f constituting the magnetic sensor module 10 and the magnetic sensor elements 12a and 12f constituting the magnetic sensor module 12, responses that are electrically opposite to each other with respect to the magnetic field generated from the current to be measured. As shown, a bias magnetic field is applied. As a method for applying the bias magnetic field, a magnet or a coil can be used.

  2) The sensitivity of the magnetic sensor element 10f and the magnetic sensor element 12f is adjusted so that the sensitivity is negligibly small compared to the sensitivity of the magnetic sensor element 10a and the magnetic sensor element 12a. In this case, it is not necessary to change the bias magnetic field direction between the magnetic sensor elements 10a and 10f and the magnetic sensor elements 12a and 12f.

  In such a configuration, the electrical resistances of the magnetic sensor elements 10a and 10f and the magnetic sensor elements 12a and 12f change according to the sensitivity of these magnetic sensor elements due to the magnetic field generated by the current flowing through the electric wire 7.

  By configuring as in 1) above, the magnetic sensor elements 10a and 10f of the magnetic sensor module 10 have their electrical resistance values changing in opposite directions, so that the voltage change caused by the magnetic sensor element 10a at the connection point 10e and the magnetism are changed. The voltage changes due to the sensor element 10f are in the same direction. Similarly, the sensitivity at the connection point 12e of the magnetic sensor module 12 is improved. As a result, the sensitivity as a current sensor is improved.

  Further, the resistance value of the magnetic sensor element changes according to the temperature change, but the change of the resistance value is in the same direction in the magnetic sensor elements 10a and 10f and the magnetic sensor elements 12a and 12f. As a result, the voltage change at the connection point 10e of the magnetic sensor module 10 and the connection point 12e of the magnetic sensor module 12 due to the temperature change is greatly reduced.

  In addition, although the sensitivity is hardly changed by the configuration as in 2) above, the connection point 10e of the magnetic sensor module 10 and the connection point of the magnetic sensor module 12 due to temperature change are the same as in the case of 1). The change in voltage at 12e is greatly reduced.

  The configurations of 1) and 2) may be applied alone or in combination.

  FIG. 9 is also a block diagram showing another configuration example of the signal processing circuit 13 according to the present invention, in which the power consumption of the arithmetic unit is reduced, and the same reference numerals are given to the parts common to FIG. ing.

  The signal processing circuit of FIG. 9 is obtained by adding a storage unit 13e and a distance calculation unit 13g to the signal processing circuit 13 of FIG. That is, the output signal of the AD conversion unit 13c is input to the current calculation unit 13d and the distance calculation unit 13g, and the output signal of the distance calculation unit 13g is input to the current calculation unit 13d via the storage unit 13e. Yes.

  Here, the distance calculation unit 13g has a function of calculating the distance between the center of the electric wire 7 and the magnetic sensor modules 10 and 12.

  FIG. 10 is a flowchart illustrating a specific example of the flow of signal processing after AD conversion in the block configuration of FIG. The AD conversion unit 13c converts the output values V1 and V2 of the magnetic sensor modules 10 and 12 into digital signals and outputs them to the current calculation unit 13d and the distance calculation unit 13g (step S1). The distance calculation unit 13g determines whether the calculation result of the distance has been stored in the storage unit 13e (step S2).

  If the distance calculation result is not yet stored, the distance calculation is executed according to the above-described equation 5, and the value of the distance L is stored in the storage unit 13e (step S3). If the distance calculation result has already been stored, the process proceeds to the calculation of the current value I by the current calculation unit 13d without executing the distance calculation (step S4), and the calculation result is output to the output terminal 13a (step S4). S5).

  That is, the current calculation unit 13d calculates the current value I according to Equation 6 based on the output value V1 and the output value V2 output from the AD conversion unit 13c and the value of the distance L stored in the storage unit 13e.

  With the configuration shown in FIG. 10, when the current value I is calculated by the current calculation unit 13 d, the calculation amount is reduced by using Equation 5 rather than Equation 6, and as a result, the power consumption in the signal processing circuit 13 is reduced. Can be reduced.

  As described above, according to the present invention, there is provided a current sensor using a magnetic sensor element that has low power consumption, high sensitivity characteristics, a small and simple structure, can reduce misalignment errors, and is relatively inexpensive. realizable.

7 Electric wire 8 Frame 9 Printed circuit board 10, 12 Magnetic sensor module 11 Spacer

Claims (3)

In a current sensor configured to measure the current flowing through the wire in a non-contact manner,
Including two magnetic sensor modules that are housed in a frame made of an insulating member and fixed to the electric wire, and are arranged at different distances from the center of the electric wire so that the tangential direction and the magnetic sensitive direction of the magnetic force lines are coincident ,
Each of the magnetic sensor modules includes a magnetoresistive element whose electrical resistance changes with application of a magnetic field, a magnetic impedance element whose electrical impedance changes with application of a magnetic field, and a hole that detects a magnetic field using the Hall effect. Including either elements or fluxgate elements ,
One of the two magnetic sensor modules is mounted on a substrate via a spacer made of a non-magnetic material .   The current sensor according to claim 1, further comprising a signal processing unit that obtains an effective value of the current from output values at each time of the two magnetic sensor modules. It said signal processing means, the claims have the function of storing and calculating the distance between the center of the wire and the two magnetic sensor module, and calculates the current value based on the distance information stored 2. The current sensor according to 2 .