Current detection device and measurement device

Abstract

The present invention expands the dynamic range of current measurement.　The present invention comprises: a magnetic sensor 3 for outputting a detection signal S3 having an amplitude that changes in proportion to the magnitude I1 of a current I flowing through an electric wire Wm under measurement; a feedback winding 4 wound around a magnetic core 2; a drive unit 6 for supplying drive currents Id1 to Id4 for reducing the amplitude of the detection signal S3 to the feedback winding 4; and a current-voltage conversion unit 7 for converting the drive currents into drive signals S4a to S4d. The feedback winding 4 has a plurality of winding pairs each including a first feedback winding and a second feedback winding B. The drive unit 6 has a plurality of amplifier circuit pairs corresponding to the respective winding pairs and each including an operational amplifier circuit OPa and an operational amplifier circuit OPb. A calculation unit 8 calculates the difference between a voltage obtained by converting the magnitudes of the drive currents Id1, Id3 flowing through respective opposite ends of the first feedback windings and a voltage obtained by converting the magnitudes of the drive currents Id2, Id4 flowing through respective opposite ends of the second feedback windings, as an amount proportional to the magnitude I1 of the current I flowing through the electric wire Wm under measurement.

Description

Current Detection Device and Measuring Device

[0001] The present invention relates to a current detection device that includes a magnetic sensor configured with a fluxgate element, an s-hole element, or the like and detects a current flowing through a measurement target electric wire, and a measuring device including the current detection device.

[0002] As this type of current detection device, the applicant of the present application has already proposed the current detection device disclosed in Patent Document 1 below. As shown in FIG. 1 of this Patent Document 1, this current detection device has an annular magnetic core and a fluxgate sensor element incorporated in the magnetic core, and outputs a detection signal whose amplitude changes in proportion to the magnitude of the current flowing through the measurement target electric wire inserted through the magnetic core. A fluxgate type magnetic sensor, a feedback winding formed by winding a plurality of layers of conductive wires on the outer surface of the magnetic core, a signal generation unit that outputs an excitation signal to the fluxgate sensor element, and a drive unit that inputs the detection signal and supplies a drive current that reduces (approaches zero) the amplitude of the detection signal to the feedback winding. And a detection resistor disposed in the current path of the drive current that converts the drive current into a voltage and outputs it, and detects (calculates) the voltage converted by the detection resistor as the magnitude of the current flowing through the measurement target electric wire.

[0003] Further, in the feedback winding of this current detection device, for example, a drive current flowing from one of the winding start end and the winding end to the other is supplied. In this case, the feedback winding is divided into a first feedback winding on the winding start end side and a second feedback winding on the winding end side at the intermediate layer part, and the detection resistor is connected between a pair of lead wires drawn from two ends located at the intermediate layer part of the first feedback winding and the second feedback winding.

[0004] Further, as shown in FIG. 4 of this Patent Document 1, the drive unit in this current detection device is composed of a voltage follower circuit that outputs the detection signal non-inverted and an inverting amplifier circuit that outputs the detection signal inverted, and supplies the drive current from the voltage follower circuit to one end of the feedback winding and supplies the drive current from the inverting amplifier circuit to the other end of the feedback winding.

[0005] In this current detection device configuration, the voltage follower circuit of the drive unit supplies the drive current by outputting the amplified detection signal in a non-inverted state to one end of the feedback winding, and the inverting amplifier circuit supplies the drive current by inverting the amplified detection signal and outputting it to the other end of the feedback winding. Therefore, compared to a conventional current detection device in which the detection signal is simply applied to the entire feedback winding, this device makes it possible to increase the amplitude of the drive signal applied to the entire feedback winding (for example, by about twice as much) and increase the drive current (for example, by about twice as much). In other words, it is possible to increase the dynamic range of current measurement in the current detection device (the difference between the maximum and minimum values ​​of the measurable current) by about twice as much.

[0006] Japanese Patent Publication No. 2012-247191 (pages 5-9, Figures 1-4)

[0007] However, the above-mentioned current detection device has the following issues that need improvement. Specifically, when attempting to measure the magnitude of the measurement current flowing through the target wire, the above-mentioned current detection device needs to cancel out the magnetic flux generated in the magnetic core by the measurement current flowing through the target wire and the magnetic flux generated in the magnetic core by the feedback current flowing through the feedback winding. Therefore, it is necessary to flow a drive current of the same magnitude as the measurement current through the feedback winding. Accordingly, when the number of turns in the first feedback winding and the second feedback winding are n, and the magnitude of the drive current is IA, it is necessary to make (n × 2) × IA equal to the magnitude of the measurement current.

[0008] In this case, to increase the dynamic range of current measurement by increasing (n × 2) × IA, it is necessary to increase at least one of the magnitude of the drive current IA and the number of turns n. However, increasing the drive current requires increasing the size of the drive circuits, such as the voltage follower circuit and inverting amplifier circuit, within the drive unit that supplies the drive current, which leads to increased costs and larger circuit configurations, making it impractical. On the other hand, when increasing the number of turns n of the feedback winding, the winding resistance value increases with the increase in the number of turns n. Therefore, when adopting this configuration, the wire diameter of the feedback winding must be increased, which makes it difficult to wind neatly during the winding process, resulting in problems such as reduced winding density and decreased winding work efficiency. For these reasons, there is a current detection device that can increase the dynamic range of current measurement.

[0009] The present invention was made to improve upon these problems, and its main objective is to provide a current detection device and a measuring device that can increase the dynamic range of current measurement with respect to the current flowing through the wire being measured.

[0010] To achieve the above objective, the present invention provides a current detection device and a measuring device equipped with this current detection device, comprising: an annular magnetic core; a magnetic sensor that outputs a detection signal whose amplitude changes in proportion to the magnitude of the current flowing through a wire to be measured, inserted through the magnetic core; a feedback winding configured by winding a conductor around the magnetic core and having a first feedback winding and a second feedback winding; a drive unit configured with a non-inverting amplifier circuit that supplies a first drive current generated based on the detection signal to one end of the first feedback winding, and an inverting amplifier circuit that supplies a second drive current generated based on the detection signal to one end of the second feedback winding; a current-voltage conversion unit connected between the other ends of the first and second feedback windings and converting the first and second drive currents flowing through the other ends into voltages and outputting them; and a calculation unit that calculates an amount proportional to the magnitude of the current flowing through the wire to be measured based on the voltages converted by the current-voltage conversion unit. The device comprises a plurality of winding pairs, each consisting of a first feedback winding and a second feedback winding; the drive unit comprises a plurality of amplifier circuit pairs, each corresponding to one of the winding pairs and consisting of a non-inverting amplifier circuit and an inverting amplifier circuit; each non-inverting amplifier circuit in each amplifier circuit pair supplies the first drive current to one end of the first feedback winding in the corresponding winding pair; each inverting amplifier circuit in each amplifier circuit pair supplies the second drive current to one end of the second feedback winding in the corresponding winding pair; and the calculation unit calculates the difference between the sum of voltages obtained by converting the magnitude of the first drive current flowing through the other end of each first feedback winding in the plurality of winding pairs into voltage magnitudes, and the sum of voltages obtained by converting the magnitude of the second drive current flowing through the other end of each second feedback winding in the plurality of winding pairs into voltage magnitudes, as a quantity proportional to the magnitude of the current flowing through the wire under measurement.

[0011] This current detection and measuring device allows for an increase in the magnitude of the total drive current compared to conventional current detection devices, by a factor of m when the number of winding pairs is m (where m is 2 or more). In other words, when the return winding is wound with a winding of the same wire diameter as the return winding in a conventional current detection device, this current detection and measuring device allows for a larger dynamic range of current measurement relative to the current flowing through the wire being measured compared to a conventional current detection device. Furthermore, when the dynamic range of current measurement is set to the same magnitude as that of a conventional current detection device, the magnitude of the drive current flowing through each winding pair can be reduced. Therefore, this current detection and measuring device allows for winding of the return winding with a winding of a thinner wire diameter than that used in conventional current detection devices. As a result, this current detection and measuring device allows for sufficiently neat winding of the return winding, thereby increasing the winding density of the return winding and significantly improving the efficiency of the winding work. Furthermore, with this current detection and measuring device, when the dynamic range is set to the same size as that of a conventional current detection device, the magnitude of the drive current can be reduced, thus allowing for miniaturization of the operational amplifier circuit used in the drive unit.

[0012] Furthermore, in the current detection device and measuring device according to the present invention, the non-inverting amplifier circuit is composed of a voltage follower circuit, and the inverting amplifier circuit is configured to have a gain equal to or approximately equal to the gain of the voltage follower circuit.

[0013] This current detection and measuring device allows for a reduction in the number of elements constituting the drive unit and simplifies gain adjustment, resulting in a significant reduction in the cost of the current detection device.

[0014] Furthermore, in the current detection device and measuring device according to the present invention, each of the first and second feedback windings is wound with the same number of turns.

[0015] According to this current detection and measuring device, by winding each first and second feedback winding with the same number of turns, it is only necessary to manage so that the number of turns is the same for both, and as a result, the feedback windings can be wound easily.

[0016] Furthermore, in the current detection device and measuring device according to the present invention, the current-voltage conversion unit is composed of a current detection resistor placed between the other end of the first feedback winding and the second feedback winding.

[0017] This current detection and measuring device significantly reduces the manufacturing cost of the current-voltage conversion unit, and consequently the manufacturing cost of the current detection device, compared to configuring the current-voltage conversion unit using an operational amplifier circuit.

[0018] Furthermore, in the current detection device and measuring device according to the present invention, the resistor for current detection is configured by connecting two resistors having the same resistance value in series.

[0019] This current detection and measuring device significantly reduces the manufacturing cost of the current-voltage conversion unit, and consequently, the manufacturing cost of the current detection device.

[0020] Furthermore, in the current detection device and measuring device according to the present invention, the connection point of the two resistors is connected to a reference potential.

[0021] In this current detection and measuring device, even if common-mode noise is superimposed on the wire being measured by the voltage generated in the wire being measured, propagating through coupling capacitance to the feedback winding near the wire being measured, this common-mode noise is superimposed as a potential difference between the ends of two resistors connected in series and a reference potential connected to the connection point of those two resistors. Therefore, with this current detection and measuring device, even if inexpensive elements with a low common-mode rejection ratio are used in the operational amplifier circuit within the calculation unit, common-mode noise can be removed with a sufficiently high common-mode rejection ratio.

[0022] Furthermore, in the current detection device and measuring device according to the present invention, the magnetic sensor is configured to include one of a fluxgate sensor element, a Hall element, or a winding wound around the magnetic core.

[0023] This current detection and measuring device allows for the construction of a magnetic sensor using readily available, inexpensive fluxgate sensor elements and Hall elements, as well as simple and inexpensive windings. This reduces noise and significantly lowers the manufacturing cost of the magnetic sensor, and consequently, the manufacturing cost of the current detection device.

[0024] Furthermore, the measuring device according to the present invention comprises the above-mentioned current detection device, a processing unit that calculates the current value of the current flowing through the target wire based on a quantity proportional to the magnitude of the current detected by the calculation unit, and an output unit that outputs the current value of the current calculated by the processing unit.

[0025] This measuring device can calculate (measure) and output the current value of the current flowing through the target wire.

[0026] The current detection device according to the present invention can significantly increase the dynamic range of current measurement for the current flowing through the wire being measured, and can also sufficiently increase the winding density of the return winding while significantly improving the efficiency of the winding work, compared to conventional current detection devices.

[0027] This is a configuration diagram showing the configuration of the current detection device 1 and the current measuring device 100. This is a cross-sectional view taken along the line W-W in Figure 1. This is a configuration diagram showing the connection relationships of the feedback winding 4, the drive unit 6, and the current-voltage conversion unit 7. This is a circuit diagram of the calculation unit 8. This is a configuration diagram showing the configuration of the current detection device 1A and the current measuring device 100A. This is a configuration diagram showing the connection relationships of the feedback winding 4A, the drive unit 6A, and the current-voltage conversion unit 7A. This is a circuit diagram of the calculation unit 8A. This is a configuration diagram of the current detection device 1B and the current measuring device 100B. This is a configuration diagram of the current detection device 1C and the current measuring device 100C.

[0028] The embodiments of the current detection device and measuring device will be described below with reference to the attached drawings.

[0029] (First Embodiment) The current measuring device 100 shown in Figure 1 corresponds to a measuring device and is configured to include a current detection device 1. In this case, as shown in the figure, the current detection device 1 includes an annular magnetic core 2, a fluxgate type magnetic sensor 3 (hereinafter also referred to as "magnetic sensor 3"), a feedback winding 4, a signal generation unit 5, a drive unit 6, a current-voltage conversion unit 7, and a calculation unit 8, and outputs an output signal So as a quantity proportional to the magnitude I1 of the current I (measured current) flowing through the wire Wm to be measured inserted into the magnetic core 2, the voltage value V1 of which changes in proportion to the magnitude I1 of the current I. The current measuring device 100 is also configured to include a processing unit 9 and an output unit 10. Note that the term "annular" here includes circular, elliptical, rectangular, and polygonal shapes. In this example, the magnetic core 2 is formed in a circular (annular) shape.

[0030] In this case, as an example, as shown in Figures 1 and 2, the magnetic core 2 is constructed by housing two fluxgate sensor elements 31a and 31b (hereinafter also referred to as "sensor element 31" unless otherwise specified) that constitute the magnetic sensor 3 within a gap 21 formed inside the magnetic core 2 along the circumferential direction of the magnetic core 2.

[0031] As shown in Figures 1 and 2, the magnetic sensor 3 is configured, for example, to include a sensor element 31, a differential amplifier 32, and a synchronous detection unit 33, and outputs a detection signal S3 whose amplitude changes in proportion to the magnitude I1 of the current I flowing through the wire Wm to be measured, which is inserted into the magnetic core 2.

[0032] In this case, each sensor element 31, although not shown in the figure, is constructed by winding a detection winding the same number of turns around the surface of an annular insulating substrate formed in the same shape. Furthermore, each sensor element 31 is connected in series such that the winding directions of their detection windings are opposite to each other, and as shown in Figure 2, they are arranged in the gap 21 of the magnetic core 2 in a superimposed state (integrated into the magnetic core 2). Additionally, lead wires 31c and 31d are connected to the non-connected ends (ends that are not connected to each other) of the two series-connected detection windings, respectively, and lead wire 31e is connected to the connected end (end that is connected to each other) of each detection winding, and the two detection windings are connected to the differential amplifier 32 via the lead wires 31c, 31d, and 31e.

[0033] In this configuration, when an excitation current I2 (an alternating current with a constant frequency f) is supplied from the signal generation unit 5, each sensor element 31a and 31b generates detection voltages V11 and V12 between their respective detection windings, with their phases inverted relative to each other, and outputs each detection voltage V11 and V12 to the differential amplifier unit 32 via the respective lead wires 31c, 31d, and 31e.

[0034] As shown in Figure 1, the differential amplifier 32 is connected to each sensor element 31 via its respective lead wires 31c, 31d, and 31e, and receives the detection voltages V11 and V12 output from each sensor element 31 as input, while also detecting the difference voltage (V11 - V12). The differential amplifier 32 also amplifies the detected difference voltage (V11 - V12) and outputs it as a difference signal S1. In this case, when a current I flows through the wire Wm being measured, which is inserted into the magnetic core 2, the magnetic flux inside the magnetic core 2 changes due to the magnetic field generated around the wire Wm being measured, and the amplitude of each detection voltage V11 and V12 changes accordingly. Therefore, the difference voltage (V11 - V12) and the difference signal S1 become amplitude-modulated signals in which a signal component with a frequency (2f) twice that of the excitation current I2 is modulated by the amplitude of the current I.

[0035] The synchronous detection unit 33 synchronously detects the difference signal S1 output from the differential amplifier unit 32 with the synchronization signal S2 (a square wave signal with a frequency (2f) synchronized with the excitation current I2) output from the signal generation unit 5, thereby outputting a detection signal S3 whose amplitude changes in proportion to the magnitude I1 of the current I flowing through the wire Wm to be measured.

[0036] As shown in Figures 1 and 2, the feedback winding 4 is constructed by winding multiple layers of conductors 41 around the outer surface of the magnetic core 2 so as to cover the sensor element 31. Also, as schematically shown in Figure 1, the feedback winding 4 is divided into four A feedback windings 4a, B feedback windings 4b, C feedback windings 4c and D feedback windings 4d, which have the same winding direction and number of turns and maintain an electrically insulated state from one another. In this case, the A feedback windings 4a and C feedback windings 4c constitute the "first feedback winding," and the B feedback windings 4b and D feedback windings 4d constitute the "second feedback winding." Furthermore, the A feedback windings 4a and B feedback windings 4b constitute an example of a "winding pair consisting of a first feedback winding and a second feedback winding" as a single winding pair, and the C feedback windings 4c and D feedback windings 4d constitute an example of a "winding pair consisting of a first feedback winding and a second feedback winding" as a single winding pair. Therefore, in this current detection device 1, two winding pairs are provided as an example of "multiple" winding pairs. However, the configuration is not limited to this one; it is also possible to adopt a configuration in which the number of turns of A feedback winding 4a and B feedback winding 4b are specified to be the same, the number of turns of C feedback winding 4c and D feedback winding 4d are specified to be the same, and the number of turns of A feedback winding 4a and C feedback winding 4c are specified to be different. However, by specifying the same number of turns for all A feedback windings 4a to D feedback windings 4d, it is only necessary to manage them so that the number of turns for each is the same, and as a result, the winding work of the feedback windings 4 can be made easier.

[0037] Furthermore, as shown in Figures 1 and 3, a lead wire is connected to one end a1 of the A feedback winding 4a and is led out to the outside of the feedback winding 4, and connected to the output of the drive unit 6. Similarly, a lead wire is connected to one end b1 of the B feedback winding 4b and is led out to the outside of the feedback winding 4, and connected to the output of the drive unit 6. Similarly, a lead wire is connected to one end c1 of the C feedback winding 4c and is led out to the outside of the feedback winding 4, and connected to the output of the drive unit 6. In addition, a lead wire is connected to one end d1 of the D feedback winding 4d and is led out to the outside of the feedback winding 4, and connected to the output of the drive unit 6.

[0038] Furthermore, a lead wire is connected to the other end a2 of the A feedback winding 4a and is led out to the outside of the feedback winding 4, and connected to the input of the current-voltage conversion unit 7. Similarly, a lead wire is connected to the other end b2 of the B feedback winding 4b and is led out to the outside of the feedback winding 4, and connected to the input of the current-voltage conversion unit 7. Similarly, a lead wire is connected to the other end c2 of the C feedback winding 4c and is led out to the outside of the feedback winding 4, and connected to the input of the current-voltage conversion unit 7. In addition, a lead wire is connected to the other end d2 of the D feedback winding 4d and is led out to the outside of the feedback winding 4, and connected to the input of the current-voltage conversion unit 7. In this case, the other ends a2, b2, c2, and d2 constitute the "other end".

[0039] Furthermore, as shown in Figure 3, the A feedback winding 4a and the B feedback winding 4b are connected in series via resistors Rda and Rdb, which will be described later, within the current-voltage conversion unit 7, and the C feedback winding 4c and the D feedback winding 4d are connected in series via resistors Rdc and Rdd, which will be described later, within the current-voltage conversion unit 7. In other words, the feedback winding 4 is configured to include the A feedback winding 4a and the B feedback winding 4b connected in series, and the C feedback winding 4c and the D feedback winding 4d connected in series, in a parallel configuration.

[0040] The signal generation unit 5 generates an excitation current I2, which is an alternating current with a constant frequency f, as an excitation signal, and outputs it to the sensor element 31. The signal generation unit 5 also generates a signal with a frequency (2f) synchronized with the excitation current I2 and outputs it as a synchronization signal S2 to the synchronous detection unit 33.

[0041] As shown in Figure 3, the drive unit 6 is configured with four operational amplifier circuits OPa, OPb, OPc, and OPd. In this case, operational amplifier circuits OPa and OPb correspond to the winding pair composed of the A feedback winding 4a and B feedback winding 4b described above, and constitute one amplifier circuit pair composed of a non-inverting amplifier circuit and an inverting amplifier circuit. Also, operational amplifier circuits OPc and OPd correspond to the winding pair composed of the C feedback winding 4c and D feedback winding 4d described above, and constitute one amplifier circuit pair composed of a non-inverting amplifier circuit and an inverting amplifier circuit. In other words, this current detection device 1 is configured with two amplifier circuit pairs as an example of multiple amplifier circuit pairs.

[0042] In this case, the operational amplifier circuit OPa is composed of a non-inverting voltage follower circuit, and upon receiving the detection signal S3, it generates a drive signal S4a corresponding to the "drive current" by non-inverting amplification with a gain of 1 and outputs (applies) it to one end a1 of the A feedback winding 4a. The operational amplifier circuit OPb is composed of an inverting amplifier circuit, and upon receiving the detection signal S3, it generates a drive signal S4b corresponding to the "drive current" by inverting amplification with a gain equal to or approximately equal to the gain of the operational amplifier circuit OPa and outputs (applies) it to one end b1 of the B feedback winding 4b. The operational amplifier circuit OPc is composed of a non-inverting voltage follower circuit, and upon receiving the detection signal S3, it generates a drive signal S4c corresponding to the "drive current" by non-inverting amplification with a gain of 1 and outputs (applies) it to one end c1 of the C feedback winding 4c. Furthermore, the operational amplifier circuit OPd is composed of an inverting amplifier circuit, and upon receiving the detection signal S3, it inverts and amplifies it with a gain equal to or approximately equal to the gain of the operational amplifier circuit OPc to generate a drive signal S4d corresponding to the "drive current," which is output (applied) to one end d1 of the D feedback winding 4d.

[0043] Note that one end portions a1 and c1 constitute "one end portion of the first feedback winding in the winding pair corresponding to the non-inverting amplifier circuit in the amplifier circuit pair", and one end portions b1 and d1 constitute "one end portion of the second feedback winding in the winding pair corresponding to the inverting amplifier circuit in the amplifier circuit pair". Also, the operational amplifier circuits OPb and OPd can be configured to have not only a gain equal to the gain 1 of the operational amplifier circuits OPa and OPc, but also substantially equal gains (within gain 1 ± 30%, preferably within gain 1 ± 20%, more preferably within gain 1 ± 10%). Hereinafter, as an example, an example in which the gains of the operational amplifier circuits OPb and OPd are defined to be equal to the gain 1 of the operational amplifier circuits OPa and OPc will be described.

[0044] As shown in FIG. 3, when the driving unit 6 outputs a driving signal S4a to one end portion a1 of the A feedback winding 4a, a driving current Id1 flows through the A feedback winding 4a to the reference potential. Also, when the driving unit 6 outputs a driving signal S4b to one end portion b1 of the B feedback winding 4b, a driving current Id2 flows through the B feedback winding 4b to the reference potential. Also, when the driving unit 6 outputs a driving signal S4c to one end portion c1 of the C feedback winding 4c, a driving current Id3 flows through the C feedback winding 4c to the reference potential. Also, when the driving unit 6 outputs a driving signal S4d to one end portion d1 of the D feedback winding 4d, a driving current Id4 flows through the D feedback winding 4d to the reference potential. Therefore, in the magnetic core 2, magnetic fluxes are generated by the driving currents Id1 to Id4 flowing through the feedback windings 4. The driving unit 6 controls the amplitudes (voltages) of the driving signals S4a to S4d so as to cancel out the magnetic flux generated in the magnetic core 2 by the driving currents Id1 to Id4 flowing through the feedback windings 4 with the magnetic flux generated in the magnetic core 2 by the current I flowing through the measurement target wire Wm, that is, to reduce (bring closer to zero) the amplitude of the detection signal S3 output from the magnetic sensor 3.

[0045] In this drive unit 6, the operational amplifier circuit OPa supplies a drive current Id1 by outputting a drive signal S4a, generated by non-inverting amplification of the detection signal S3, to one end a1 of the A feedback winding 4a, and the operational amplifier circuit OPb supplies (attracts) a drive current Id2 by outputting a drive signal S4b, generated by inverting amplification of the detection signal S3, to one end b1 of the B feedback winding 4b. Therefore, in this drive unit 6, compared to a configuration in which the detection signal S3 is simply applied to the entire A feedback winding 4a and B feedback winding 4b, the amplitude of the drive signals S4a and S4b applied to the entire A feedback winding 4a and B feedback winding 4b can be increased (in this example, by about twice as much), thereby increasing the drive currents Id1 and Id2 (in this example, by about twice as much). Furthermore, in this drive unit 6, the operational amplifier circuit OPc supplies a drive current Id3 by outputting a drive signal S4c, generated by non-inverting amplification of the detection signal S3, to one end c1 of the C feedback winding 4c, and the operational amplifier circuit OPd supplies (attracts) a drive current Id4 by outputting a drive signal S4d, generated by inverting amplification of the detection signal S3, to one end d1 of the D feedback winding 4d. For this reason, in this drive unit 6, the amplitude of the drive signals S4c and S4d applied to the entire C feedback winding 4c and D feedback winding 4d can be increased (in this example, increased to about twice the original value) to increase the drive currents Id3 and Id4 (in this example, increased to about twice the original value).

[0046] Furthermore, in this current detection device 1, as described above, the feedback winding 4 is configured to include A feedback winding 4a and B feedback winding 4b connected in series, and C feedback winding 4c and D feedback winding 4d connected in series. Therefore, the drive unit 6 can maintain the amplitude of the drive signals S4a to S4d applied to the entire feedback winding 4 to be as large as that of the conventional current detection device described above, while increasing the overall magnitude of the drive currents Id1 to Id4 by several times (approximately twice in this example) compared to the conventional current detection device. In other words, in this current detection device 1, when the feedback winding 4 is wound with a winding of the same wire diameter as the feedback winding in the conventional current detection device, it is possible to increase the dynamic range of current measurement for the current I flowing through the target wire Wm by approximately twice (approximately twice in this example) compared to the conventional current detection device. Furthermore, in this current detection device 1, when the dynamic range is set to the same size as the dynamic range of current measurement in a conventional current detection device, it becomes possible to wind the feedback winding 4 with a thinner wire diameter than the feedback winding in a conventional current detection device. Also, when the dynamic range is set to the same size as the dynamic range of current measurement in a conventional current detection device, it becomes possible to miniaturize the operational amplifier circuits OPa to OPd used in the drive circuit.

[0047] The current-voltage conversion unit 7 is comprised of four resistors Rda, Rdb, Rdc, and Rdd. These four resistors Rda to Rdd function as a current-voltage conversion unit and, as an example, are specified to have the same resistance value. Resistor Rda is disposed in the current path of the drive current Id1, which includes the A feedback winding 4a, and converts the magnitude of the drive current Id1 flowing through the A feedback winding 4a into a detection voltage Va. Resistor Rdb is disposed in the current path of the drive current Id2, which includes the B feedback winding 4b, and converts the magnitude of the drive current Id2 flowing through the B feedback winding 4b into a detection voltage Vb. Furthermore, resistor Rdc is placed in the current path of the drive current Id3, which includes the C feedback winding 4c, and converts the magnitude of the drive current Id3 flowing through the C feedback winding 4c into a detection voltage Vc. Resistor Rdd is placed in the current path of the drive current Id4, which includes the D feedback winding 4d, and converts the magnitude of the drive current Id4 flowing through the D feedback winding 4d into a detection voltage Vd. In this case, resistors Rda and Rdb, and resistors Rdc and Rdd, together constitute a "current-voltage conversion unit that is connected between the other ends of the first feedback winding and the second feedback winding and converts the first drive current and the second drive current flowing through the other ends of each end into voltages and outputs them." Also, the connection point Pc between resistor Rda and resistor Rdb, and the connection point Pc between resistor Rdc and resistor Rdd are connected to a reference potential (circuit ground).

[0048] In this current-voltage conversion unit 7, since the magnitudes of the drive currents Id1 and Id2 flowing through the resistors Rda and Rdb are substantially the same and the resistance values of the resistors Rda and Rdb are the same, the detected voltages Va and Vb converted (detected) by the resistors Rda and Rdb are of substantially the same voltage value. Also, since the magnitudes of the drive currents Id3 and Id4 flowing through the resistors Rdc and Rdd are substantially the same and the resistance values of the resistors Rdc and Rdd are the same, the detected voltages Vc and Vd converted (detected) by the resistors Rdc and Rdd are of substantially the same voltage value. Further, in this current detection device 1, since the gains of the operational amplifier circuits OPa, OPb, OPc, and OPd are each a value of 1, as a result of the magnitudes of the drive currents Id1 to Id4 being substantially equal to each other, the voltage values of the detected voltages Va, Vb, Vc, and Vd are substantially equal to each other. Hereinafter, it will be described on the assumption that the magnitudes of the drive currents Id1 to Id4 are equal to each other and the voltage values of the detected voltages Va, Vb, Vc, and Vd are equal to each other.

[0049] The arithmetic unit 8 is equipped with an operational amplifier circuit that functions as an addition / subtraction circuit internally, and is connected between the A feedback winding 4a and C feedback winding 4c as the first feedback windings and the B feedback winding 4b and D feedback winding 4d as the second feedback windings, and converts the drive currents Id1 to Id4 flowing through the other ends a2 to d2 into voltages and outputs them. As shown in Figure 4, specifically, the arithmetic unit 8 is configured, for example, with an operational amplifier circuit OP1, four input resistors Ria, Rib, Ric, and Rid, and two resistors R1 and R2 for gain setting. In this arithmetic unit 8, as shown in Figures 1 and 4, the operational amplifier circuit OP1 inputs the detected voltage Va to the inverting input terminal via input resistor Ria and inputs the detected voltage Vc to the inverting input terminal via input resistor Ric, and inputs the detected voltage Vb to the non-inverting input terminal via input resistor Rib and inputs the detected voltage Vd to the non-inverting input terminal via input resistor Rid. In this process, the detected voltages Va and Vc are added at the inverting input terminal of the operational amplifier circuit OP1, and the detected voltages Vb and Vd are added at the non-inverting input terminal of the operational amplifier circuit OP1. Furthermore, the operational amplifier circuit OP1 generates an output signal So of voltage value V1 by superimposing a subtracted voltage obtained by subtracting (inverting amplified) the detected voltages Va and Vc and an added voltage obtained by adding (non-inverting amplified) the detected voltages Vb and Vd, and outputs it as a quantity proportional to the magnitude I1 of the current I.

[0050] Specifically, the calculation unit 8 outputs an output signal So as a quantity proportional to the magnitude I1 of the current I flowing through the wire Wm to be measured. This is obtained by superimposing a subtracted voltage, which is the result of subtracting the voltages converted by the current-voltage conversion unit 7 from the drive current Id1 flowing through the other end a2 of the A feedback winding 4a, one of the multiple (two) winding pairs, and the drive current Id3 flowing through the other end a2 of the C feedback winding 4c, the other of the multiple (two) winding pairs, and an added voltage, which is the result of adding the voltages converted by the current-voltage conversion unit 7 from the drive current Id2 flowing through the other end b2 of the B feedback winding 4b, the other of the B feedback winding 4b, and the drive current Id4 flowing through the other end d2 of the D feedback winding 4d, the other of the multiple (two) winding pairs, respectively.

[0051] In other words, the calculation unit 8 outputs the difference between the sum of the voltages obtained by converting the magnitudes of the first drive currents (drive currents Id1, Id3) flowing through the other ends a2, c2 of each first feedback winding (A feedback winding 4a and C feedback winding 4c) in the multiple (two) winding pairs into voltages, and the sum of the voltages obtained by converting the magnitudes of the second drive currents (drive currents Id2, Id4) flowing through the other ends b2, d2 of each second feedback winding (B feedback winding 4b and D feedback winding 4d) in the multiple (two) winding pairs into voltages, as a quantity proportional to the magnitude I1 of the current I flowing through the wire Wm to be measured. The operational amplifier circuit OP1 inverts the voltage input to the negative input terminal and outputs the voltage input to the positive input terminal without inverting it. Furthermore, the arithmetic unit 8 (arithmetic amplifier circuit OP1) can also be configured to amplify the subtracted voltage obtained by subtracting the detected voltages Va and Vc, and the added voltage obtained by adding the detected voltages Vb and Vd, respectively.

[0052] The processing unit 9 calculates the current value (current magnitude I1) of the current I flowing through the target wire Wm based on the output signal So, which indicates the magnitude I1 of the current I flowing through the target wire Wm detected by the calculation unit 8, and generates display data Dd to display the calculated current value, which is output to the output unit 10. The output unit 10 is, for example, composed of a display device such as a liquid crystal panel or an organic EL panel, and takes the display data Dd output from the processing unit 9 as input and outputs the current value of the current I flowing through the target wire Wm on the screen. In other words, the output unit 10 displays the magnitude I1 of the current. Alternatively, instead of a display device, the output unit 10 can be configured with an interface device that communicates data with an external device, and the current value of the current I flowing through the target wire Wm can be output from the output unit 10 to this external device.

[0053] The current detection device 1 configured as described above functions as a zero-flux type current detection device using a magnetic sensor 3.

[0054] Next, the operation of the current detection device 1 will be explained with reference to the drawings.

[0055] As described above, in the current detection device 1, the signal generation unit 5 outputs an excitation current I2 with frequency f to the feedback winding 4, and also outputs a synchronization signal S2 to the synchronous detection unit 33 of the fluxgate type magnetic sensor 3.

[0056] In this state, the magnetic sensor 3 has two sensor elements 31a and 31b that operate in response to the supply of excitation current I2. These two sensor elements invert their phases and output detection voltages V11 and V12, respectively, whose amplitude changes according to the magnitude I1 of the current I flowing through the wire Wm being measured. The differential amplifier 32 detects the difference voltage (V11 - V12) between these detection voltages V11 and V12 and outputs a difference signal S1. The synchronous detection unit 33 then performs synchronous detection of this difference signal S1 with a synchronous signal S2 and outputs a detection signal S3 whose amplitude changes in proportion to the magnitude I1 of the current I flowing through the wire Wm being measured.

[0057] Next, the drive unit 6 receives the detection signal S3 output from the synchronous detection unit 33. At this time, the operational amplifier circuit OPa of the drive unit 6 non-inverts the detection signal S3 and outputs the drive signal S4a to one end a1 of the A feedback winding 4a, the operational amplifier circuit OPb inverts the detection signal S3 and outputs the drive signal S4b to one end b1 of the B feedback winding 4b, the operational amplifier circuit OPc non-inverts the detection signal S3 and outputs the drive signal S4c to one end c1 of the C feedback winding 4c, and the operational amplifier circuit OPd inverts the detection signal S3 and outputs the drive signal S4d to one end d1 of the D feedback winding 4d.

[0058] In this case, the feedback winding 4 is configured to include A feedback winding 4a and B feedback winding 4b connected in series, and C feedback winding 4c and D feedback winding 4d connected in series, in a parallel configuration. Therefore, the drive unit 6 can maintain the amplitude of the drive signals S4a to S4d applied to the entire feedback winding 4 to be as large as that of a conventional current detection device, while increasing the magnitude of the current as a whole (Id1 to Id4) by approximately double. In other words, this current detection device 1 can significantly increase the dynamic range of current measurement for the current I flowing through the target wire Wm compared to a conventional current detection device (in this example, by approximately double).

[0059] Furthermore, the drive unit 6 controls the amplitude (voltage) of the drive signals S4a to S4d so that the amplitude (voltage) of the detection signal S3 decreases (approaches zero). In other words, the drive unit 6 controls the magnitude of the drive currents Id1 to Id4. In this case, when the amplitude (voltage) of the detection signal S3 is zero, the total magnetic flux generated in the magnetic core 2 is zero. That is, the magnetic flux generated in the magnetic core 2 by the current I flowing through the wire Wm to be measured cancels out all or part of the magnetic flux generated in the magnetic core 2 by the drive currents Id1 to Id4 flowing through the feedback winding 4. In other words, the drive unit 6 is outputting drive currents Id1 to Id4 whose magnitude is proportional to the magnitude I1 of the current I.

[0060] Next, resistors Rda and Rdb in the current-voltage conversion unit 7, connected between the two A feedback windings 4a and B feedback windings 4b that constitute the feedback winding 4, convert the drive currents Id1 and Id2 into voltages Va and Vb, respectively. Resistors Rdc and Rdd in the current-voltage conversion unit 7, connected between the two C feedback windings 4c and D feedback windings 4d that constitute the feedback winding 4, convert the drive currents Id3 and Id4 into voltages Vc and Vd, respectively. In this case, the connection point Pc between resistor Rda and resistor Rdb, and the connection point Pc between resistor Rdc and resistor Rdd, are connected to a reference potential (circuit ground) in this current-voltage conversion unit 7. Therefore, even if common-mode noise is superimposed on the feedback winding 4 near the target wire Wm by propagation via coupling capacitance due to the voltage generated in the target wire Wm, this common-mode noise is superimposed as a potential difference between the ends of the two resistors Rda and Rdb connected in series, and the ends of the two resistors Rdc and Rdd, and the reference potential connected to the connection point Pc of the two resistors Rda and Rdb and the two resistors Rdc and Rdd. For this reason, even if an inexpensive element with a low common-mode rejection ratio is used in the operational amplifier circuit OP1 in the calculation unit 8, common-mode noise can be removed with a sufficiently high common-mode rejection ratio.

[0061] Next, the calculation unit 8 receives the detected voltages Va to Vd, subtracts the detected voltages Va and Vc, and adds the detected voltages Vb and Vd. The calculation unit 8 also superimposes the subtracted voltage (obtained by subtracting the detected voltages Va and Vc) and the added voltage (obtained by adding the detected voltages Vb and Vd) to generate an output signal So with a voltage value V1, which is then output to the processing unit 9. In this case, as described above, the magnitude of the drive currents Id1 to Id4 is maintained in proportion to the magnitude I1 of the current I flowing through the wire Wm to be measured, so the voltage value V1 (amplitude) of the output signal So output from the calculation unit 8 (current detection device 1) is proportional to the magnitude I1 of the current I.

[0062] Next, the processing unit 9 calculates (measures) the current value of the current I flowing through the target wire Wm based on the output signal So output from the calculation unit 8, that is, based on a quantity proportional to the magnitude I1 of the current I detected by the calculation unit 8, and generates display data Dd to display the calculated current value and outputs it to the output unit 10. The output unit 10 then displays the current value of the current I flowing through the target wire Wm based on the input display data Dd.

[0063] Thus, in this current detection device 1 and current measuring device 100, the feedback winding 4 is configured to have multiple winding pairs (two in this example) consisting of a first feedback winding (A feedback winding 4a and C feedback winding 4c) and a second feedback winding (B feedback winding 4b and D feedback winding 4d), and the drive unit 6 corresponds to each of the two winding pairs and has multiple amplifier circuit pairs (two in this example) consisting of a non-inverting amplifier circuit (operational amplifier circuit OPa and operational amplifier circuit OPc) and an inverting amplifier circuit (operational amplifier circuit OPb and operational amplifier circuit OPd). The circuit is configured such that the non-inverting amplifier circuit in each amplifier pair supplies drive currents Id1 and Id3 to one end (end a1 and end c1) of the first feedback winding (A feedback winding 4a and C feedback winding 4c) in the corresponding winding pair, and the inverting amplifier circuit (operational amplifier circuit OPb and operational amplifier circuit OPd) in each amplifier pair supplies drive currents Id2 and Id4 to one end (end b1 and end d1) of the second feedback winding (B feedback winding 4b and D feedback winding 4d) in the corresponding winding pair.

[0064] Therefore, with this current detection device 1 and current measuring device 100, compared to a conventional current detection device, the amplitude of the drive signals S4a to S4d applied to the entire feedback winding 4 can be kept as large as that of a conventional current detection device, while the magnitude of the total current ((|Id1| + |Id2| + |Id3| + |Id4|) of the drive currents Id1 to Id4 can be increased by m times (in this example, about twice) when the number of winding pairs is m (where m is 2 or more). In other words, with this current detection device 1 and current measuring device 100, compared to a conventional current detection device When the return winding 4 is wound with a winding of the same wire diameter as the return winding in the conventional current detection device, the dynamic range of current measurement for the current I flowing through the target wire Wm can be increased compared to a conventional current detection device. For example, if the number of turns of the A return winding 4a, B return winding 4b, C return winding 4c, and D return winding 4d are the same, the dynamic range can be doubled. Furthermore, with this current detection device 1 and current measuring device 100, the dynamic range of current measurement can be the same as that of a conventional current detection device. When the mixed range is specified, the magnitude of the drive currents Id1 to Id4 flowing through each winding pair can be reduced. For example, if the number of turns of the A feedback winding 4a, B feedback winding 4b, C feedback winding 4c, and D feedback winding 4d are the same, the magnitude of the drive currents Id1 to Id4 flowing through each winding pair can be halved. Therefore, in this current detection device 1 and current measuring device 100, the feedback winding 4 can be wound with a thinner wire diameter than the feedback winding in conventional current detection devices. For this reason, in this current detection device 1 and current measuring device 100 The constant device 100 allows the return winding 4 to be wound neatly, thereby increasing the winding density of the return winding 4 and significantly improving the efficiency of the winding work. Furthermore, with this current detection device 1 and current measuring device 100, when the dynamic range is set to the same size as the dynamic range of current measurement in a conventional current detection device, the magnitude of the drive currents Id1 to Id4 can be reduced, thus allowing the operational amplifier circuits OPa to OPd used in the drive unit 6 to be miniaturized.

[0065] Furthermore, with this current detection device 1 and current measuring device 100, by configuring the non-inverting amplifier circuit (operational amplifier circuits OPa, OPc) as a voltage follower circuit and configuring the inverting amplifier circuit (operational amplifier circuits OPb, OPd) to have a gain equal to or approximately equal to the gain of the voltage follower circuit, the number of elements constituting the drive unit 6 can be reduced and the gain adjustment work can be made easier. As a result, the cost of the current detection device 1 and, consequently, the cost of the current measuring device 100 can be significantly reduced.

[0066] Furthermore, with this current detection device 1 and current measuring device 100, by winding each first feedback winding (A feedback winding 4a and C feedback winding 4c) and each second feedback winding (B feedback winding 4b and D feedback winding 4d) with the same number of turns, it is only necessary to manage so that the number of turns for each is the same, and as a result, the feedback winding 4 can be wound easily.

[0067] Furthermore, with this current detection device 1 and current measuring device 100, by configuring the current-voltage conversion unit 7 with current detection resistors Rda to Rdd, the manufacturing cost of the current-voltage conversion unit 7, and consequently the manufacturing cost of the current detection device 1 and current measuring device 100, can be significantly reduced compared to configuring the current-voltage conversion unit using an operational amplifier circuit.

[0068] Furthermore, with this current detection device 1 and current measuring device 100, by connecting two resistors with the same resistance value (two resistors, Rda and Rdb, and two resistors, Rdc and Rdd) in series to form a resistor for current detection, the manufacturing cost of the current-voltage conversion unit 7, and consequently the manufacturing cost of the current detection device 1 and current measuring device 100, can be significantly reduced.

[0069] Furthermore, in this current detection device 1 and current measuring device 100, the connection point Pc of two resistors (two resistors, Rda and Rdb, and two resistors, Rdc and Rdd) is connected to a reference potential. Therefore, in this current detection device 1 and current measuring device 100, even if common-mode noise is superimposed by the voltage generated in the wire Wm being measured, propagating through coupling capacitance to the feedback winding 4 close to the wire Wm being measured, this common-mode noise is superimposed as a potential difference between the ends of the two series-connected resistors Rda and Rdb and the two resistors Rdc and Rdd, and the reference potential connected to the connection point Pc of the two resistors Rda and Rdb and the two resistors Rdc and Rdd. For this reason, with this current detection device 1 and current measuring device 100, even if inexpensive elements with a low common-mode rejection ratio are used in the operational amplifier circuit OP1 in the calculation unit 8, common-mode noise can be removed with a sufficiently high common-mode rejection ratio.

[0070] Furthermore, with this current detection device 1 and current measuring device 100, by configuring the magnetic sensor 3 with a generally available and inexpensive fluxgate sensor element 31, the manufacturing cost of the magnetic sensor 3, and consequently the manufacturing cost of the current detection device 1 and current measuring device 100, can be significantly reduced.

[0071] (Second Embodiment) In the first embodiment described above, two examples were given for the number of winding pairs and amplifier circuit pairs, but the invention is not limited to these. The winding pairs and amplifier circuit pairs can be configured with any number of three or more.

[0072] As an example, the following will describe an example in which the winding pair and the amplification circuit pair are each configured with three units. Note that components identical to those in the current detection device 1 and current measuring device 100 described above are denoted by the same reference numerals, and redundant explanations are omitted.

[0073] As shown in Figure 5, the current detection device 1A and the current measuring device 100A are equipped with a return winding 4A, a drive unit 6A, and a current-voltage conversion unit 7A, instead of the return winding 4, drive unit 6, and current-voltage conversion unit 7 of the current detection device 1. In this case, the current measuring device 100A corresponds to the measuring device.

[0074] The feedback winding 4A is constructed by winding multiple layers of conductors 41 around the outer surface of the magnetic core 2 so as to cover the sensor element 31. As schematically shown in Figure 5, the feedback winding 4A is divided, for example, into six A feedback windings 4a, B feedback windings 4b, C feedback windings 4c, D feedback windings 4d, E feedback windings 4e, and F feedback windings 4f, each having the same winding direction and number of turns, and maintaining an electrically insulated state from one another. In this case, the A feedback windings 4a, C feedback windings 4c, and E feedback windings 4e constitute the "first feedback winding," and the B feedback windings 4b, D feedback windings 4d, and F feedback windings 4f constitute the "second feedback winding." Furthermore, the A feedback winding 4a and the B feedback winding 4b constitute an example of a "winding pair consisting of a first feedback winding and a second feedback winding" as a single winding pair, the C feedback winding 4c and the D feedback winding 4d constitute an example of a "winding pair consisting of a first feedback winding and a second feedback winding" as a single winding pair, and the E feedback winding 4e and the F feedback winding 4f constitute an example of a "winding pair consisting of a first feedback winding and a second feedback winding" as a single winding pair. Therefore, in this current detection device 1, three winding pairs are provided as an example of "multiple" winding pairs. It should be noted that this configuration is not limited to this one. It is also possible to adopt a configuration in which the number of turns of the A feedback winding 4a and the B feedback winding 4b are specified to be the same, the number of turns of the C feedback winding 4c and the D feedback winding 4d are specified to be the same, and the number of turns of the E feedback winding 4e and the F feedback winding 4f are specified to be the same, while the number of turns of the A feedback winding 4a, the C feedback winding 4c and the E feedback winding 4e are specified to be different from each other. However, by specifying the same number of turns for all of the A feedback windings 4a to the F feedback windings 4f, it is only necessary to manage them so that the number of turns for each is the same, and as a result, the winding work of the feedback winding 4A can be made easier.

[0075] In this case, the A feedback winding 4a and the B feedback winding 4b constitute one winding pair, forming an example of a "winding pair consisting of a first feedback winding and a second feedback winding," the C feedback winding 4c and the D feedback winding 4d constitute one winding pair, forming an example of a "winding pair consisting of a first feedback winding and a second feedback winding," and the E feedback winding 4e and the F feedback winding 4f constitute one winding pair, forming an example of a "winding pair consisting of a first feedback winding and a second feedback winding." Therefore, in this current detection device 1A, three winding pairs are provided as an example of "multiple" winding pairs.

[0076] Furthermore, similar to the feedback winding 4 of the current detection device 1, as shown in Figure 5, lead wires are connected to one end a1 to f1 of each of the A feedback winding 4a to F feedback winding 4f, and these wires are led out to the outside of the feedback winding 4A and connected to the output section of the drive unit 6A. Additionally, lead wires are connected to the other ends a2 to f2 of each of the A feedback winding 4a to F feedback winding 4f, and these wires are led out to the outside of the feedback winding 4A and connected to the input section of the current-voltage conversion unit 7A.

[0077] Furthermore, as shown in Figure 6, the E feedback winding 4e and the F feedback winding 4f are connected in series via resistors Rde and Rdf, which will be described later, within the current-voltage conversion unit 7A. The feedback winding 4A is configured with the A feedback winding 4a and B feedback winding 4b connected in series, the C feedback winding 4c and D feedback winding 4d connected in series, and the E feedback winding 4e and F feedback winding 4f connected in series, all in parallel.

[0078] Furthermore, the drive unit 6A is configured with six operational amplifier circuits OPa, OPb, OPc, OPd, OPe, and OPf. In this case, the operational amplifier circuits OPe and OPf correspond to the winding pair composed of the E feedback winding 4e and F feedback winding 4f described above, and also constitute one amplifier circuit pair composed of a non-inverting amplifier circuit and an inverting amplifier circuit. In other words, this current detection device 1 is configured with three amplifier circuit pairs as an example of multiple amplifier circuit pairs.

[0079] In this case, the operational amplifier circuit OPe is configured similarly to the operational amplifier circuit OPa, and is composed of a non-inverting voltage follower circuit. It receives the detection signal S3 and amplifies it non-inverting with a gain of 1 to generate a drive signal S4e corresponding to the "drive current," which is output (applied) to one end e1 of the E feedback winding 4e. Furthermore, the operational amplifier circuit OPef is configured similarly to the operational amplifier circuit OPb, and is composed of an inverting amplifier circuit. It receives the detection signal S3 and amplifies it inverting with a gain equal to or approximately equal to the gain of the operational amplifier circuit OPe to generate a drive signal S4f corresponding to the "drive current," which is output (applied) to one end f1 of the F feedback winding 4f.

[0080] Furthermore, one end e1 constitutes "one end of the first feedback winding in the winding pair corresponding to the non-inverting amplifier circuit in the amplifier circuit pair," and one end f1 constitutes "one end of the second feedback winding in the winding pair corresponding to the inverting amplifier circuit in the amplifier circuit pair." In addition, the operational amplifier circuit OPe is defined to have a gain equal to the gain of 1 of the operational amplifier circuit OPa, and the operational amplifier circuit OPef is defined to have a gain equal to the gain of 1 of the operational amplifier circuit OPb. However, the configuration is not limited to this, and the gains can be set to be approximately equal (gain within 1 ± 30%, preferably within 1 ± 20%, more preferably within 1 ± 10%), but below, as an example, an example in which the gains of operational amplifier circuits OPb, OPd, and OPf are defined to be equal to the gain of 1 of operational amplifier circuits OPa, OPc, and OPe will be described.

[0081] In this case, as shown in Figure 6, the drive unit 6A outputs a drive signal S4a to one end a1 of the A feedback winding 4a, causing a drive current Id1 to flow to the reference potential via the A feedback winding 4a. The drive unit 6A also outputs a drive signal S4b to one end b1 of the B feedback winding 4b, causing a drive current Id2 to flow to the reference potential via the B feedback winding 4b. Furthermore, the drive unit 6A outputs a drive signal S4c to one end c1 of the C feedback winding 4c, causing a drive current Id3 to flow to the reference potential via the C feedback winding 4c. Additionally, the drive unit 6A outputs a drive signal S4d to one end d1 of the D feedback winding 4d, causing a drive current Id4 to flow to the reference potential via the D feedback winding 4d. Finally, the drive unit 6A outputs a drive signal S4e to one end e1 of the E feedback winding 4e, causing a drive current Id5 to flow to the reference potential via the E feedback winding 4e. Furthermore, the drive unit 6A outputs a drive signal S4f to one end f1 of the F feedback winding 4f, causing the drive current Id6 to flow to the reference potential via the F feedback winding 4f. As a result, magnetic flux is generated in the magnetic core 2 as the drive currents Id1 to Id6 flow through the feedback winding 4A. The drive unit 6A controls the amplitude (voltage) of the drive signals S4a to S4f so as to cancel out the magnetic flux generated in the magnetic core 2 by the current I flowing through the target wire Wm, that is, to reduce the amplitude of the detection signal S3 output from the magnetic sensor 3 (bring it closer to zero).

[0082] In this drive unit 6A, the operational amplifier circuits OPe and OPf operate in the same manner as the operational amplifier circuits OPa and OPb of the drive unit 6, supplying a drive current Id5 by outputting a drive signal S4e generated by non-inverting amplification of the detection signal S3 to one end e1 of the E feedback winding 4e, and supplying (attracting) a drive current Id6 by outputting a drive signal S4f generated by inverting amplification of the detection signal S3 to one end f1 of the F feedback winding 4f.

[0083] Therefore, as described above, the current detection device 1A is configured such that the feedback winding 4A comprises A feedback winding 4a and B feedback winding 4b connected in series, C feedback winding 4c and D feedback winding 4d connected in series, and E feedback winding 4e and F feedback winding 4f connected in series, all in parallel. Consequently, the drive unit 6A is able to maintain the amplitude of the drive signals S4a to S4f applied to the entire feedback winding 4A to be as large as that of a conventional current detection device, while increasing the magnitude of the total current (|Id1| + |Id2| + |Id3| + |Id4| + |Id5| + |Id6|) of the drive currents Id1 to Id6 to approximately three times that of a conventional current detection device. In other words, in this current detection device 1A, when the feedback winding 4A is wound with a winding of the same wire diameter as the feedback winding in a conventional current detection device, it is possible to increase the dynamic range of current measurement for the current I flowing through the target wire Wm compared to a conventional current detection device. For example, if the number of turns of the A feedback winding 4a, B feedback winding 4b, C feedback winding 4c, D feedback winding 4d, E feedback winding 4e, and F feedback winding 4f are the same, the dynamic range can be increased by approximately three times. Furthermore, in this current detection device 1A, when the dynamic range is set to the same size as the dynamic range of current measurement in a conventional current detection device, it is possible to wind the feedback winding 4A with a winding of a thinner wire diameter than the feedback winding in a conventional current detection device. Also, when the dynamic range is set to the same size as the dynamic range of current measurement in a conventional current detection device, it is possible to miniaturize the operational amplifier circuits OPa to OPf used in the drive circuit.

[0084] The current-voltage conversion unit 7A is composed of six resistors Rda, Rdb, Rdc, Rdd, Rde, and Rdf. These six resistors Rda to Rdf function as a current-voltage conversion unit and, as an example, are specified to have the same resistance value. Resistor Rde is disposed in the current path of the drive current Id3 including the E feedback winding 4e and converts the magnitude of the drive current Id3 flowing through the E feedback winding 4e into a detection voltage Ve, and resistor Rdf is disposed in the current path of the drive current Id3 including the F feedback winding 4f and converts the magnitude of the drive current Id3 flowing through the F feedback winding 4f into a detection voltage Vf. In this case, resistors Rde and Rdf constitute a "current-voltage conversion unit that is connected between the other ends of the first feedback winding and the second feedback winding and converts the drive current flowing between the other ends into a voltage and outputs it." Furthermore, the connection points Pc between resistors Rda and Rdb, Rdc and Rdd, and Rde and Rdf are connected to a reference potential (circuit ground). Also, in this current-voltage conversion unit 7A, similar to the current-voltage conversion unit 7, the voltage values ​​of the detected voltages Va, Vb, Vc, Vd, Ve, and Vf are equal to each other.

[0085] The arithmetic unit 8A includes an operational amplifier circuit that functions as an addition / subtraction circuit internally, and is connected between the first feedback windings A feedback winding 4a, C feedback winding 4c and E feedback winding 4e, and the second feedback windings B feedback winding 4b, D feedback winding 4d and F feedback winding 4f, and converts the drive currents Id1 to Id6 flowing to the other ends a2 to f2 into voltages and outputs them. As shown in Figure 7, specifically, the arithmetic unit 8A is configured, for example, with an operational amplifier circuit OP1, six input resistors Ria, Rib, Ric, Rid, Rie, and Rif, and two resistors R1 and R2 for gain setting. In this calculation unit 8A, similar to the calculation unit 8, the operational amplifier circuit OP1 generates an output signal So of voltage value V1 by superimposing a subtracted voltage obtained by subtracting (inverting amplification) the detected voltages Va, Vc, and Ve, and an added voltage obtained by adding (non-inverting amplification) the detected voltages Vb, Vd, and Vf, and outputs it as a quantity proportional to the magnitude I1 of the current I.

[0086] Specifically, the calculation unit 8A subtracts the voltage converted by the current-voltage conversion unit 7A from the drive current Id1 flowing through the other end a2 of the A feedback winding 4a in the first of the multiple (three) winding pairs, the drive current Id3 flowing through the other end c2 of the C feedback winding 4b in the second of the multiple (three) winding pairs, and the drive current Id5 flowing through the other end e2 of the E feedback winding 4e in the third of the multiple (three) winding pairs to obtain a subtracted voltage. The drive current Id2 flowing through the other end b2 of the B feedback winding 4b in the first one, the drive current Id4 flowing through the other end d2 of the D feedback winding 4d in the second one, and the drive current Id6 flowing through the other end f2 of the F feedback winding 4f in the third one are superimposed on an added voltage obtained by adding the voltages converted by the current-to-voltage conversion unit 7A, and output a signal So as a quantity proportional to the magnitude I1 of the current I flowing through the target wire Wm.

[0087] In other words, the calculation unit 8A outputs the difference between the sum of the voltages obtained by converting the magnitudes of the first drive currents (drive currents Id1, Id3, Id5) flowing through the other ends a2, c2, e2 of each first feedback winding (A feedback winding 4a, C feedback winding 4c, and E feedback winding 4e) in the multiple (three) winding pairs into voltages, and the sum of the voltages obtained by converting the magnitudes of the second drive currents (drive currents Id2, Id4, Id6) flowing through the other ends b2, d2, f2 of each second feedback winding (B feedback winding 4b, D feedback winding 4d, and F feedback winding 4f) in the multiple (three) winding pairs into voltages, as a quantity proportional to the magnitude I1 of the current I flowing through the wire Wm to be measured. The calculation amplifier circuit OP1 inverts the voltage input to the negative input terminal and outputs the voltage input to the positive input terminal without inverting it. Furthermore, the arithmetic unit 8A (arithmetic amplifier circuit OP1) can also be configured to amplify the subtracted voltage obtained by subtracting the detected voltages Va, Vc, and Ve, and the added voltage obtained by adding the detected voltages Vb, Vd, and Vf, respectively.

[0088] Next, the operation of the current detection device 1A will be explained with reference to the drawings. Note that redundant explanations will be omitted for operations similar to those of the current detection device 1.

[0089] When the synchronous detection unit 33 outputs a detection signal S3, the drive unit 6A receives the detection signal S3 output from the synchronous detection unit 33. At this time, the operational amplifier circuit OPa of the drive unit 6A amplified the detection signal S3 in a non-inverting manner and output the drive signal S4a to one end a1 of the A feedback winding 4a, the operational amplifier circuit OPb amplified the detection signal S3 in an inverting manner and output the drive signal S4b to one end b1 of the B feedback winding 4b, the operational amplifier circuit OPc amplified the detection signal S3 in a non-inverting manner and output the drive signal S4c to one end c1 of the C feedback winding 4c, the operational amplifier circuit OPd amplified the detection signal S3 in an inverting manner and output the drive signal S4d to one end d1 of the D feedback winding 4d, the operational amplifier circuit OPe amplified the detection signal S3 in a non-inverting manner and output the drive signal S4e to one end e1 of the E feedback winding 4e, and the operational amplifier circuit OPf amplified the detection signal S3 in an inverting manner and output the drive signal S4f to one end f1 of the F feedback winding 4f.

[0090] In this case, the feedback winding 4 is configured to include, in parallel, A feedback winding 4a and B feedback winding 4b connected in series, C feedback winding 4c and D feedback winding 4d connected in series, and E feedback winding 4e and F feedback winding 4f connected in series. Therefore, the drive unit 6A is able to increase the magnitude of the total current Id1 to Id6 by approximately three times while maintaining the amplitude of the drive signals S4a to S4f applied to the entire feedback winding 4 to be as large as that of a conventional current detection device. In other words, this current detection device 1A is able to increase the dynamic range of current measurement for the current I flowing through the target wire Wm by approximately three times compared to a conventional current detection device.

[0091] Furthermore, the drive unit 6A controls the amplitude (voltage) of the drive signals S4a to S4f in the same manner as the drive unit 6, so that the amplitude (voltage) of the detection signal S3 decreases (approaches zero). In other words, the drive unit 6A controls the magnitude of the drive currents Id1 to Id6. In this case, when the amplitude (voltage) of the detection signal S3 is zero, the total magnetic flux generated in the magnetic core 2 is zero. That is, the magnetic flux generated in the magnetic core 2 by the current I flowing through the wire Wm to be measured cancels out all or part of the magnetic flux generated in the magnetic core 2 by the drive currents Id1 to Id6 flowing through the feedback winding 4. In other words, the drive unit 6A is outputting drive currents Id1 to Id6 whose magnitude is proportional to the magnitude I1 of the current I.

[0092] Next, resistors Rda and Rdb in the current-voltage conversion unit 7A convert the drive currents Id1 and Id2 into voltages Va and Vb, respectively; resistors Rdc and Rdd convert the drive currents Id3 and Id4 into voltages Vc and Vd, respectively; and resistors Rde and Rdf convert the drive currents Id5 and Id6 into voltages Ve and Vf, respectively. At this time, in this current detection device 1A, since the connection point Pc is connected to the reference potential (circuit ground), it is possible to remove common-mode noise propagated via coupling capacitance to the feedback winding 4 near the target wire Wm by the voltage generated in the target wire Wm from the detected voltages Va to Vf with a sufficiently high common-mode rejection ratio, similar to the current detection device 1.

[0093] Next, the calculation unit 8A receives the detected voltages Va to Vf as input, and superimposes the subtracted voltage obtained by subtracting the detected voltages Va, Vc, and Ve with the added voltage obtained by adding the detected voltages Vb, Vd, and Vf to generate an output signal So of voltage value V1, which is then output to the processing unit 9. After this, the processing unit 9, through the above operation, causes the output unit 10 to display the current value I of the current flowing through the measured wire Wm.

[0094] Thus, with this current detection device 1A and current measuring device 100, it is possible to increase the magnitude of the total current Id1 to Id6 while maintaining the amplitude of the drive signals S4a to S4f applied to the entire feedback winding 4A to be as large as that of a conventional current detection device, similar to the current detection device 1 and current measuring device 100, and to achieve the same effects as the current detection device 1 and current measuring device 100. For example, if the number of turns of the six windings 4a to 4f is the same, the current detection device 1A and current measuring device 100 can triple the dynamic range of current measurement. Furthermore, with this current detection device 1A and current measuring device 100, when the dynamic range is set to be the same as that of a conventional current detection device, the magnitude of the drive current flowing through each winding pair can be reduced. For example, if the number of turns of the six windings 4a to 4f is the same, the current detection device 1A and current measuring device 100 can reduce the magnitude of the drive current flowing through each winding pair to one-third.

[0095] (Third Embodiment) As shown in Figure 8, the current detection device 1B and the current measuring device 100B are equipped with a magnetic sensor 3B instead of the magnetic sensor 3 in the current detection device 1. In this case, the current measuring device 100B corresponds to a measuring device. Furthermore, this magnetic sensor 3B is configured to include a Hall element Eh and an amplification circuit 11 instead of the two fluxgate sensor elements 31a and 31b, differential amplifier 32 and synchronous detection unit 33 in the magnetic sensor 3. Note that in this current detection device 1B, since the sensor element 31 is not provided, a configuration without an air gap 21 in the magnetic core 2 can also be adopted.

[0096] In this current detection device 1B, the Hall element Eh outputs a detection signal S11 whose amplitude changes in proportion to the magnitude I1 of the current I flowing through the wire Wm to be measured. The amplification circuit 11 amplifies this detection signal S11 with a predetermined gain, thereby outputting a detection signal S3 to the drive unit 6 that is the same as the detection signal S3 of the magnetic sensor 3. Furthermore, this current detection device 1B operates in the same manner as the current detection device 1 and can achieve the same effect.

[0097] According to this current detection device 1B and current measuring device 100B, by configuring the magnetic sensor 3B with a Hall element Eh instead of a fluxgate sensor element, noise in the current detection device 1B and current measuring device 100B can be reduced.

[0098] (Fourth Embodiment) As shown in Figure 9, the current detection device 1C and the current measuring device 100C are equipped with a magnetic sensor 3C instead of the magnetic sensor 3 in the current detection device 1. In this case, the current measuring device 100C corresponds to a measuring device. Furthermore, this magnetic sensor 3C is configured to be equipped with a detection winding Wd, which is an example of a winding wound around a magnetic core 2, instead of the Hall element Eh in the current detection device 1B. Note that in this current detection device 1B, a configuration in which no air gap 21 is provided in the magnetic core 2 can also be adopted.

[0099] In this current detection device 1C, the detection winding Wd outputs a detection signal S12 whose amplitude changes in proportion to the magnitude I1 of the current I flowing through the wire Wm to be measured. The amplification circuit 11 amplifies this detection signal S12 with a predetermined gain, thereby outputting a detection signal S3 to the drive unit 6 that is the same as the detection signal S3 of the magnetic sensor 3. Furthermore, this current detection device 1C can operate in the same manner as the current detection device 1 and achieve the same effect.

[0100] With this current detection device 1C and current measuring device 100C, by configuring the magnetic sensor 3C with a detection winding Wd that can be easily manufactured and is inexpensive, the manufacturing cost of the magnetic sensor 3C, and consequently the manufacturing cost of the current detection device 1C and current measuring device 100C, can be significantly reduced.

[0101] It should be noted that the present invention is not limited to the above embodiments and can be modified as appropriate. For example, by specifying the number m of winding pairs and amplifier circuit pairs to be 2 or more, the amplitude of the drive signal applied to the entire feedback winding can be kept the same as that of a conventional current detection device, while increasing the magnitude of the total drive current. For example, when the number of turns of all windings is the same, the dynamic range of current measurement can be increased by m. Also, when the dynamic range is set to the same magnitude as the dynamic range of the measured current in a conventional current detection device, the magnitude of the drive current flowing through each winding pair can be reduced. For example, when the number of turns of all windings is the same, the magnitude of the drive current flowing through each winding pair can be reduced to 1 / m.

[0102] Furthermore, while we have described an example in which the non-inverting amplifier circuit is constructed using a voltage follower circuit and the inverting amplifier circuit is configured to have a gain equal to or approximately equal to that of the voltage follower circuit, it is also possible to construct the non-inverting amplifier circuit using an amplifier circuit with an arbitrary gain of 1 or more or less than 1, and then construct the inverting amplifier circuit to have a gain equal to or approximately equal to that of the non-inverting amplifier circuit.

[0103] Furthermore, although an example in which the arithmetic unit is configured using an operational amplifier circuit has been described, the system is not limited to this. For example, it is also possible to omit the arrangement of the arithmetic unit 8 and directly input the detected voltages Va to Vd (or detected voltages Va to Vf) to the processing unit 9, thereby having the processing unit 9 perform the same processing as the arithmetic unit 8 (or arithmetic unit 8A). In other words, it is also possible to adopt a configuration in which the processing unit 9 functions as the arithmetic unit.

[0104] Furthermore, in a configuration where the number of turns and winding resistance values ​​of the A feedback winding 4a, B feedback winding 4b, C feedback winding 4c, and D feedback winding 4d are equal, in Figure 3, the other end a2 of the A feedback winding 4a and the other end c2 of the C feedback winding 4c can be connected to one end of resistor Rda (the end on which the detected voltage Va is output), and the other end b2 of the B feedback winding 4b and the other end d2 of the D feedback winding 4d can be connected to one end of resistor Rdb (the end on which the detected voltage Vb is output). With this configuration, it is possible to omit the arrangement of resistors Rdc, Rdd and input resistors Ric, Rid in Figure 4. Note that even in current detection devices where three or more winding pairs are specified, the number of detection resistors can be maintained at two, and the number of input resistors can be maintained at two by configuring them in the same way.

[0105] According to the present invention, compared to conventional current detection devices, the dynamic range of current measurement for the current flowing through the wire being measured can be increased, and the winding density of the return winding can be sufficiently increased, while the efficiency of winding work can be significantly improved. As a result, the present invention can be widely applied to such current detection devices.

[0106] 100, 100A to 100C Current measuring device 1A to 1C Current detection device 2 Magnetic core 3 Magnetic sensor 4, 4A Feedback winding 4a A feedback winding 4b B feedback winding 4c C feedback winding 4d D feedback winding 4e E feedback winding 4f F feedback winding 5 Signal generation unit 6, 6A Drive unit 7, 7A Current-voltage conversion unit 8, 8A Calculation unit I Current I1 Current magnitude Id1 to Id6 Drive current Va to Vf Detected voltage Wm Wire to be measured

Claims

1. A current detection device comprising: an annular magnetic core; a magnetic sensor that outputs a detection signal whose amplitude changes in proportion to the magnitude of the current flowing through a wire to be measured inserted through the magnetic core; a feedback winding configured by winding a conductor around the magnetic core and having a first feedback winding and a second feedback winding; a drive unit configured by including a non-inverting amplifier circuit that supplies a first drive current generated based on the detection signal to one end of the first feedback winding and an inverting amplifier circuit that supplies a second drive current generated based on the detection signal to one end of the second feedback winding; a current-voltage conversion unit connected between the other ends of the first feedback winding and the second feedback winding and outputting the first drive current and the second drive current flowing through the other ends, respectively, as voltages; and a calculation unit that calculates an amount proportional to the magnitude of the current flowing through the wire to be measured based on the voltages converted by the current-voltage conversion unit, wherein the feedback winding is configured by having a plurality of winding pairs composed of the first feedback winding and the second feedback winding. The drive unit is configured to have a plurality of amplifier circuit pairs, each corresponding to one of the winding pairs and each consisting of a non-inverting amplifier circuit and an inverting amplifier circuit, wherein the non-inverting amplifier circuit in each amplifier circuit pair supplies the first drive current to one end of the first feedback winding in the corresponding winding pair, and the inverting amplifier circuit in each amplifier circuit pair supplies the second drive current to one end of the second feedback winding in the corresponding winding pair, and the calculation unit calculates the difference between the sum of voltages obtained by converting the magnitude of the first drive current flowing at the other end of each of the plurality of winding pairs into voltage magnitudes, and the sum of voltages obtained by converting the magnitude of the second drive current flowing at the other end of each of the plurality of winding pairs into voltage magnitudes, as a quantity proportional to the magnitude of the current flowing through the wire to be measured.

2. The current detection device according to claim 1, wherein the non-inverting amplifier circuit is composed of a voltage follower circuit, and the inverting amplifier circuit is configured to have a gain equal to or approximately equal to the gain of the voltage follower circuit.

3. The current detection device according to claim 1 or 2, wherein each of the first and second feedback windings is wound with the same number of turns.

4. The current detection device according to any one of claims 1 to 3, wherein the current-voltage conversion unit is configured with a current detection resistor connected between the other end of the first and second feedback windings.

5. The current detection device according to claim 4, wherein the resistor for detecting the current is configured by connecting two resistors having the same resistance value in series.

6. The current detection device according to claim 5, wherein the connection point of the two resistors is connected to a reference potential.

7. The current detection device according to any one of claims 1 to 6, wherein the magnetic sensor comprises a fluxgate sensor element, a Hall element, and a winding wound around the magnetic core.

8. A measuring device comprising: the current detection device according to any one of claims 1 to 7; a processing unit that calculates the current value of the current flowing through the wire to be measured based on a quantity proportional to the magnitude of the current detected by the calculation unit; and an output unit that outputs the current value of the current calculated by the processing unit.

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