JP2019012002A - Current detecting device and measuring device - Google Patents

Abstract

A zero flux method operation and a CT operation are combined, a decrease in the S / N ratio during the zero flux method operation is avoided, and resonance in a feedback winding during the CT operation is prevented. A magnetic sensor 3 that outputs a detection signal S3 indicating a current value I1 of a current I that is incorporated in a magnetic core 2 and flows through a measurement target electric wire 64; a feedback winding 4 wound around the magnetic core 2; A drive unit 6 that supplies the drive current Id to the feedback winding 4 so as to reduce the amplitude of the detection signal S3, and a drive current Id that is disposed in the current path of the drive current Id is converted into a voltage Vd and output. And a detection resistor 7. The feedback winding 4 is configured by connecting a plurality of windings 4a and 4b arranged in the circumferential direction of the magnetic core 2 in series, and each winding 4a and 4b includes a series circuit of a first resistor and a capacitor. Are connected in parallel. [Selection] Figure 1

Description

  In the present invention, the current flowing through the measurement target wire is detected by the zero flux method when the current is a frequency signal included in the low frequency region, and the feedback winding is detected when the current is a frequency signal included in the high frequency region. The present invention relates to a current detection device that functions as a CT (current transformer) for detection, and a measurement device including the current detection device.

  The present applicant has already proposed the current detection device disclosed in Patent Document 1 below as a current detection device that detects the current flowing through the measurement target wire by the zero flux method. The current detection device includes an annular magnetic core, a fluxgate type magnetic sensor that outputs a detection signal whose amplitude changes in proportion to the current value of the current flowing through the measurement target wire inserted in the magnetic core, and a magnetic A feedback winding formed by winding a conducting wire around the outer surface of the core, a signal generation unit that outputs an excitation signal to the fluxgate sensor element, and a drive current that inputs the detection signal and reduces the amplitude of the detection signal is fed back. As a zero-flux type current detection device using a magnetic sensor, comprising a drive unit to be supplied to the windings, and a detection resistor disposed in the current path of the drive current to convert the drive current into a voltage and output it It is configured. In addition, a drive current from one of the winding start end and the winding end end to the other is supplied to the feedback winding, and the feedback winding includes a first feedback winding on the winding start end side at the intermediate layer portion. It is divided into a line and a second feedback winding on the winding end side. The detection resistor is connected between the first feedback winding and the second feedback winding.

Japanese Patent No. 5710380 (page 5-9, Fig. 1-4)

  By the way, although not disclosed in the above-mentioned Patent Document 1, in the above-described current detection device, the operating frequency band operating in the zero flux system, that is, the drive unit inputs the detection signal from the magnetic sensor and this detection signal. In the high frequency range that exceeds the frequency band that can supply the drive current that reduces the amplitude of the magnetic flux to the feedback winding (that is, the frequency band that can eliminate the magnetic flux generated in the magnetic core), the gain of the magnetic sensor and the drive unit is greatly increased. As a result, the output voltage from the drive unit to the feedback winding becomes approximately zero volts. As a result, both end portions of the feedback winding (the end portion on the winding start end side and the end portion on the winding end end side) are substantially at the same potential and are equivalently connected to each other. The winding functions as a CT (current transformer) in the high frequency region. With this configuration, when the frequency of the current flowing through the measurement target wire is included in the low frequency region, the current detection device operates in the zero flux method to detect this current and the frequency of the current flowing through the measurement target wire. Is included in the high frequency region, the feedback winding operates as CT and detects this current, so that the current flowing through the measurement target wire can be detected over a wide band from the low frequency region to the high frequency region. ing.

  Further, in this current detection device, in the high frequency region where the feedback winding operates as CT, resonance caused by the parasitic capacitance of the feedback winding is prevented and the frequency characteristics are improved (the operating frequency band is further increased). In order to extend it to the region, a configuration in which a resonance preventing resistor is connected in parallel to each of the first feedback winding and the second feedback winding is employed. In this case, if the resistance value of the resonance preventing resistor is too large, the effect of preventing resonance cannot be exerted. Therefore, it is necessary to use a resistor having a somewhat small resistance value as the resonance preventing resistor.

  However, when such a resistance having a small resistance value is used as a resonance prevention resistor, the signal component of the excitation signal supplied to the magnetic sensor passes through the feedback winding when operated by the zero flux method. It is transmitted to the detection resistor not through the path but through the path through the resonance prevention resistor. For this reason, this current detection device has a problem to be improved that there is a possibility that the S / N ratio (in a low frequency region) is lowered when operated in the zero flux system. In the high frequency region where the feedback winding operates as CT, the gain of the signal generation unit is significantly reduced in the same manner as the magnetic sensor and the drive unit described above, so that the amplitude of the excitation signal becomes almost zero. For this reason, the influence of the signal component of the excitation signal on the detection resistance can be ignored.

  The present invention has been made in order to improve such a problem. The S / N ratio in the operation of the zero flux method is combined with the operation of the zero flux method and the operation of causing the feedback winding to function as CT. A main object of the present invention is to provide a current detection device capable of avoiding a decrease and preventing resonance in the feedback winding in the operation of causing the feedback winding to function as CT, and a measuring device including the current detection device. .

  In order to achieve the above object, the current detection device according to claim 1 is proportional to an annular magnetic core into which a measurement target electric wire is inserted, and a current value of a current that is incorporated in the magnetic core and flows through the measurement target electric wire. A magnetic sensor that outputs a detection signal whose amplitude changes, a feedback winding formed by winding a conductive wire around the outer surface of the magnetic core, and the detection signal is input and the amplitude of the detection signal is reduced. A drive unit that supplies a drive current to the feedback winding; and a pair of resistance connection terminals that are disposed in a current path of the drive current and to which a detection resistor for converting the drive current into a voltage is connected. In the current detection device, the feedback winding is configured by connecting a plurality of windings arranged in a circumferential direction of the magnetic core in series, and each of the plurality of windings includes: First resistor and capacitor directly Resonance preventing circuit is connected in parallel configured to include a circuit.

  The current detection device according to claim 2 is the current detection device according to claim 1, wherein the detection resistor is connected between the pair of resistance connection terminals.

 According to a third aspect of the present invention, there is provided a current detecting device having an annular magnetic core into which the measurement target electric wire is inserted, and an amplitude proportional to a current value of the current that is incorporated in the magnetic core and flows through the measurement target electric wire. A magnetic sensor that outputs a detection signal that changes, a feedback winding formed by winding a conductive wire around the outer surface of the magnetic core, a signal generator that outputs an excitation signal to the magnetic sensor, and the detection signal And a drive unit that supplies a drive current that reduces the amplitude of the detection signal to the feedback winding, and a detection resistor that is disposed in a current path of the drive current and converts the drive current into a voltage and outputs the voltage. A current detection device that detects the voltage converted by the detection resistor as a current value of a current flowing through the measurement target electric wire, wherein the feedback winding is arranged along a circumferential direction of the magnetic core Duplicated Winding which are connected in series, each of said plurality of windings, the resonance preventing circuit configured to include a series circuit of a first resistor and a capacitor are connected in parallel.

  The current detection device according to claim 4 is the current detection device according to any one of claims 1 to 3, wherein the resonance prevention circuit is defined to have a resistance value larger than the first resistance and the series. A second resistor connected in parallel to the circuit is included.

  A measuring device according to claim 5 is the current detecting device according to any one of claims 1 to 4, a processing unit that measures the current value based on the voltage converted by the detection resistor, And an output unit for outputting the measured current value.

  According to the current detection device of claims 1, 2, 3, and 4, and the measurement device of claim 5, each of the plurality of windings constituting the feedback winding includes a series circuit of a first resistor and a capacitor. Because the anti-resonance circuit is connected in parallel, the impedance of the capacitor constituting this series circuit is sufficiently large in the low-frequency region that functions as a zero-flux current detector (that is, the anti-resonance circuit). Therefore, the signal component of the excitation signal is connected between the pair of resistance connection terminals via the resonance prevention circuit (in the current detection device according to claim 1). The occurrence of a situation of flowing into the detection resistor) can be greatly reduced, and a decrease in the S / N ratio can be reliably avoided. Also, in the high frequency region where the feedback winding functions as CT, the impedance of the capacitor constituting this series circuit becomes a sufficiently small value (that is, the impedance of the resonance prevention circuit is the resistance value of the first resistor (sufficiently) Therefore, the occurrence of resonance in the feedback winding (each winding) that may occur due to the parasitic capacitance can be reliably prevented.

  According to the current detection device according to claims 1 and 4 and the measurement device according to claim 5, for example, an appropriate resistance value can be obtained according to the current value of the drive current (that is, the current value of the current flowing through the measurement target wire). Since the detection resistor can be appropriately selected and connected to the pair of resistance connection terminals, the measurement range for the current value of the current flowing through the measurement target electric wire can be expanded.

  According to the current detection device according to claim 2, 3 and 4, and the measurement device according to claim 5, a detection resistor for converting the drive current into a voltage is disposed in advance in the current path of the drive current. Therefore, the trouble of separately preparing a detection resistor can be saved.

It is a block diagram of the electric current detection apparatus 61 and the measuring apparatus MS. It is the WW sectional view taken on the line in FIG. 3 is a circuit diagram of a drive unit 6, a feedback winding 4, a detection resistor 7, a differential detection unit 8, and a resonance prevention circuit 9. FIG. 6 is a circuit diagram of a drive unit 6A, a feedback winding 4, a detection resistor 7, a differential detection unit 8, and a resonance prevention circuit 9. FIG. FIG. 6 is a frequency characteristic diagram regarding the impedance of the resonance prevention circuit 9; 6 is a circuit diagram of another example of the resonance prevention circuit 9. FIG.

  Embodiments of a current detection device and a measurement device will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, the measurement device MS includes a current detection device 61 as a current detection device, a processing unit 62, and an output unit 63, and is configured to be able to measure the current value I1 of the current I flowing through the measurement target electric wire 64. ing.

  As shown in FIG. 1, the current detection device 61 includes an annular magnetic core 2 (which is an annular shape as an example in this example, but may be a non-circular annular shape such as an elliptical shape or a rectangular shape), a magnetic sensor, and the like. As a flux gate 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 detection resistor 7, a differential detection unit 8, and a resonance prevention circuit 9. The voltage signal So in which the voltage value V1 changes in proportion to the current value I1 of the current I flowing through the measurement target electric wire 64 inserted through the magnetic core 2 is output.

  As shown in FIGS. 1 and 2 as an example, the magnetic core 2 includes a gap 21 formed inside the magnetic core 2 along the circumferential direction of the magnetic core 2, and the magnetic sensor 3 is configured in the gap 21. A fluxgate sensor element 31 to be described later is housed.

  As shown in FIGS. 1 and 2 as an example, the magnetic sensor 3 includes two fluxgate sensor elements 31a and 31b (hereinafter, also referred to as “sensor element 31” unless otherwise distinguished), a differential amplifier 32, and synchronous detection. A portion 33 is provided. Although not shown, each sensor element 31 is configured by, for example, winding a detection winding on the surface of an annular insulating base formed in the same shape by the same number of turns. In addition, the sensor elements 31 are connected in series so that the winding directions of the detection windings are opposite to each other, and as shown in FIG. 21 (installed in the magnetic core 2). In addition, lead wires 31c and 31d are respectively connected to the non-connected end portions (end portions on the side not connected to each other) of the two detection windings connected in series, and the connection end portions ( The lead wire 31e is connected to the end portion on the side connected to each other, and the two detection windings are connected to the differential amplifying unit 32 through the lead wires 31c, 31d, 31e.

  With this configuration, each of the sensor elements 31a and 31b has a detection voltage whose phase is inverted when a later-described excitation current I2 (an AC current having a constant frequency f) output from the signal generator 5 is supplied. Va and Vb are generated between the respective detection windings, and the detection voltages Va and Vb are output to the differential amplifying unit 32 via the lead lines 31c, 31d, and 31e.

  As shown in FIG. 1, the differential amplifying unit 32 is connected to each sensor element 31 via each lead line 31 c, 31 d, 31 e and inputs detection voltages Va, Vb output from each sensor element 31. At the same time, the differential voltage (Va−Vb) is detected. Further, the differential amplifying unit 32 amplifies the detected differential voltage (Va−Vb) and outputs it as a differential signal S1. When the current I is flowing through the measurement target electric wire 64 inserted through the magnetic core 2, the magnetic flux in the magnetic core 2 is changed by the magnetic field generated around the measurement target electric wire 64, and each detection is performed accordingly. The amplitudes of the voltages Va and Vb change. For this reason, the differential voltage (Va−Vb) and the differential signal S1 are amplitude modulation signals in which a signal component having a frequency (2f) twice the excitation current I2 is modulated by the amplitude of the current I.

  The synchronous detector 33 uses the differential signal S1 output from the differential amplifier 32 as a later-described synchronous signal S2 (rectangular wave signal having a frequency (2f) synchronized with the excitation current I2) output from the signal generator 5. By performing synchronous detection, a detection signal S3 whose amplitude changes in proportion to the current value I1 of the current I flowing through the measurement target electric wire 64 is output.

  As shown in FIG. 1, the feedback winding 4 includes a plurality of windings (one example in this example) disposed on the outer surface of the magnetic core 2 along the circumferential direction of the magnetic core 2 so as to cover the sensor element 31. The two windings 4a and 4b) are connected in series. As shown in FIG. 2, each of the windings 4 a and 4 b is configured by winding a conducting wire 41 around the outer surface of the magnetic core 2 in the same winding direction and the same number of turns. FIG. 2 is a cross-sectional view in a plane orthogonal to the circumferential direction of the portion of the magnetic core 2 in which the winding 4b and the winding 4b in the magnetic core 2 for showing the internal structure of the magnetic core 2 are shown. However, the cross section of the portion of the magnetic core 2 where the winding 4a is disposed is the same cross sectional view.

  As shown in FIG. 1, the winding 4 a has one end 42 connected to the drive unit 6 and the other end 43 connected to one end of the detection resistor 7. One end 44 of the winding 4b is connected to the other end of the detection resistor 7, and the other end 45 is connected to a reference potential (circuit ground G). With this configuration, the windings 4 a and 4 b are connected in series via the detection resistor 7.

  The signal generator 5 generates an excitation current I2 as an excitation signal that is an alternating current having a constant frequency f, and outputs the excitation current I2 to the sensor element 31. The signal generator 5 generates a signal having a frequency (2f) synchronized with the excitation current I2 and outputs the signal to the synchronous detector 33 as the synchronization signal S2.

  The drive unit 6 receives the detection signal S3 output from the synchronous detection unit 33 of the magnetic sensor 3 and amplifies the detection signal S3 to the drive signal S4, and outputs the amplified signal to the one end 42 of the winding 4a constituting the feedback winding 4. In this example, as an example, the drive unit 6 is configured by a voltage follower circuit as illustrated in FIG. 3, and amplifies and outputs the amplified detection signal S3 to the drive signal S4 in a non-inverted state. In this case, the drive current Id flows through the feedback winding 4 and the detection resistor 7 when the drive signal S4 is output (applied) from the drive unit 6. For this reason, a magnetic flux is generated in the magnetic core 2 by the drive current Id flowing through the feedback winding 4. The drive unit 6 cancels out the magnetic flux generated in the magnetic core 2 when the current I flows through the measurement target electric wire 64 by the magnetic flux generated in the magnetic core 2 when the drive current Id flows through the feedback winding 4 ( The amplitude (voltage) of the drive signal S4 is controlled so that the amplitude of the detection signal S3 output from the magnetic sensor 3 is reduced (closed to zero) so that the zero flux state is achieved.

  As shown in FIGS. 1 and 3, the detection resistor 7 is disposed in the current path of the drive current Id including the feedback winding 4, and converts the drive current Id flowing through the feedback winding 4 into a voltage Vd. As described above, as an example in this example, the detection resistor 7 is disposed between the winding 4 a and the winding 4 b that constitute the feedback winding 4. The position where the detection resistor 7 is disposed is not limited to this. For example, although not shown, the other end 43 of the winding 4a and the one end 44 of the winding 4b are directly connected, A configuration in which the detection resistor 7 is disposed between the other end 45 of the winding 4b and the reference potential (circuit ground G) may be employed.

  The differential detection unit 8 is connected to the detection resistor 7, detects the voltage Vd generated as a voltage across the detection resistor 7, amplifies it, and outputs it as a voltage signal So. As shown in FIGS. 1 and 3, the resonance prevention circuit 9 is connected in parallel to all the windings (in this example, two windings 4 a and 4 b) constituting the feedback winding 4. In this example, as an example, the resonance prevention circuit 9 includes a series circuit of a first resistor 9a (for example, a resistor of about 10 kΩ) and a capacitor 9b (for example, a capacitor of about 500 pF), as shown in FIG. Has been.

  The current detection device 61 configured as described above uses the magnetic sensor 3 when the current I flowing through the measurement target electric wire 64 is a signal having a frequency included in the low frequency region fL (see FIG. 5). When the current I is a signal having a frequency included in the high-frequency region fH (see FIG. 5), the current detection device functions as a zero-flux type current detection device used. Detect by function.

  Further, in this current detection device 61, the frequency characteristic of the impedance of the resonance prevention circuit 9 (in this example, the impedance of the series circuit of the first resistor 9a and the capacitor 9b constituting the resonance prevention circuit 9) is shown by a solid line in FIG. The resistance value R1 of the first resistor 9a and the capacitance value of the capacitor 9b are defined in advance so as to be characteristic. Specifically, in the low frequency region fL where the current detection device 61 functions as a zero flux type current detection device and the frequency region including the frequency f of the excitation current I2, the impedance component of the capacitor 9b has a sufficiently large value (resistance The resistance value R1 and the capacitance value are defined so that the impedance of the series circuit is sufficiently large, that is, a value sufficiently larger than the value R1. Further, in the current detection device 61, the impedance component of the capacitor 9b is sufficiently small in the frequency region where the feedback winding functions as CT, particularly in the frequency region where resonance easily occurs (the frequency region hatched in FIG. 5). The resistance value R1 and the capacitance value are defined such that the impedance of the series circuit becomes the resistance value R1 (value sufficiently smaller than the resistance value R1). The resistance value R1 of the first resistor 9a is defined as a low resistance value that can reliably prevent (avoid) the occurrence of the resonance in the high frequency region fH.

  The processing unit 62 includes, for example, an A / D converter, a memory, and a CPU (all not shown), and measures the voltage value V1 of the voltage signal So output from the current detection device 61. Based on the measured voltage value V1, the current value I1 of the current I flowing through the measurement target electric wire 64 is calculated (measured). Further, the processing unit 62 outputs the measured current value I1 to the output unit 63.

  For example, the output unit 63 includes a display device such as an LCD, and displays the current value I1 output from the processing unit 62 on the screen. The output unit 63 may be configured by various interface circuits instead of the display device. For example, the output unit 63 stores a current value I1 in a removable medium as a media interface circuit, or an external device via a network as a network interface circuit. It is also possible to adopt a configuration in which the current value I1 is transmitted.

  Next, each operation of the current detection device 61 and the measurement device MS will be described with reference to the drawings.

  As described above, in the current detection device 61, in the low frequency region fL, the signal generation unit 5 outputs the excitation current I2 having the frequency f to the feedback winding 4, and the flux gate type magnetic sensor 3 The synchronous signal S2 is output to the synchronous detector 33.

  In this state, in the magnetic sensor 3, the two sensor elements 31 a and 31 b that operate by receiving the supply of the excitation current I 2 have their phases reversed, and the current value I 1 of the current I that flows through the measurement target wire 64. The detection voltages Va and Vb whose amplitude changes accordingly are output. The differential amplifier 32 detects a differential voltage (Va−Vb) between the detection voltages Va and Vb and outputs a differential signal S1. The synchronous detector 33 outputs a detection signal S3 whose amplitude changes in proportion to the current value I1 of the current I flowing through the measurement target wire 64 by synchronously detecting the difference signal S1 with the synchronous signal S2.

  Next, the drive unit 6 inputs the detection signal S3 output from the magnetic sensor 3, amplifies the drive signal S4, and outputs it to the feedback winding 4, thereby supplying the feedback winding 4 with the drive current Id. To do. Further, the drive unit 6 controls the amplitude (voltage) of the drive signal S4 so that the amplitude (voltage) of the detection signal S3 decreases (approaches to zero) (that is, controls the current value of the drive current Id). . 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 current I flows through the measurement target wire 64. Thus, the magnetic flux generated in the magnetic core 2 is in a state where the magnetic flux generated in the magnetic core 2 is canceled by the drive current Id flowing through the feedback winding 4 (zero flux state). That is, the drive unit 6 is in a state of outputting a drive current Id whose current value is proportional to the current value I1 of the current I.

  Subsequently, the detection resistor 7 disposed between the two windings 4a and 4b constituting the feedback winding 4 converts the drive current Id into the voltage Vd, and the differential detection unit 8 converts the voltage Vd into the voltage Vd. Detect and output as voltage signal So. As described above, since the current value of the drive current Id is maintained in a state proportional to the current value I1 of the current I, the voltage signal So output from the current detection device 61 also has its voltage value V1 (amplitude). Is a signal proportional to the current value I1 of the current I.

  Thus, in the low frequency region fL in which the current detection device 61 functions as a zero flux type current detection device, as described above, the impedance of the resonance prevention circuit 9 (mainly the impedance of the capacitor 9b) is a sufficiently large value. Therefore, the occurrence of a situation in which the signal component (frequency f) of the excitation current I2 flows into the detection resistor 7 via the resonance prevention circuit 9 connected in parallel to the windings 4a and 4b is greatly reduced. . Thereby, the current detection device 61 reliably avoids a decrease in the S / N ratio caused by the flow of the signal component (frequency f) of the excitation current I2, which becomes a noise component when the voltage Vd is detected, into the detection resistor 7. Is possible.

  The processing unit 62 measures the voltage value V1 of the voltage signal So output from the current detection device 61, and calculates (measures) the current value I1 of the current I flowing through the measurement target wire 64 based on the measured voltage value V1. And output to the output unit 63. The output unit 63 displays the current value I1 on the screen. Thereby, the measurement of the current value I1 of the current I by the measuring device MS is completed.

  In the current detection device 61, the feedback winding 4 operates as CT in the high frequency region fH. In this state, a voltage proportional to the magnetic flux generated in the magnetic core 2 is induced in the feedback winding 4 due to the current I flowing through the measurement target wire 64, and the feedback winding 4 and the detection resistor 7 have this voltage. A current proportional to the induced voltage flows. The detection resistor 7 converts this current into a voltage Vd, and the differential detection unit 8 detects this voltage Vd and outputs it as a voltage signal So. As described above, since the current value of the current flowing through the detection resistor 7 is proportional to the current value I1 of the current I, the voltage signal So output from the current detection device 61 also has the voltage value V1 (amplitude). The signal is proportional to the current value I1 of the current I.

  The processing unit 62 measures the voltage value V1 of the voltage signal So output from the current detection device 61, and calculates (measures) the current value I1 of the current I flowing through the measurement target wire 64 based on the measured voltage value V1. And output to the output unit 63. The output unit 63 displays the current value I1 on the screen. Thereby, the measurement of the current value I1 of the current I by the measuring device MS is completed.

  On the low frequency side in the high frequency region fH where the feedback winding 4 starts to operate as CT, the gains of the magnetic sensor 3 and the drive unit 6 are greatly reduced, and the gain of the signal generation unit 5 is also greatly reduced. It has become. In this case, the amplitude of the excitation current I2 output from the signal generator 5 may not be sufficiently low, but the impedance of the resonance prevention circuit 9 at this time is as shown in FIG. Since the signal component of the frequency f that leaks into the feedback winding 4 under the influence of the excitation current I2 is maintained at a level that can be sufficiently attenuated, a decrease in the S / N ratio is avoided.

  On the other hand, in the main region (frequency region hatched in FIG. 5) in the high frequency region fH in which the feedback winding 4 operates as CT, the impedance component of the capacitor 9b constituting the resonance prevention circuit 9 has a sufficiently small value (resistance The impedance of the series circuit becomes the resistance value R1. As a result, resonance that may occur in the feedback winding 4 (windings 4a, 4b) due to parasitic capacitance is reliably prevented by the resonance prevention circuit 9.

  Thus, according to the current detection device 61 and the measurement device MS, each of the plurality of windings (in the above example, the two windings 4a and 4b) constituting the feedback winding 4 has the first By connecting the anti-resonance circuit 9 including the series circuit of the resistor 9a and the capacitor 9b in parallel, in the low frequency region fL in which the current detection device 61 functions as a zero-flux type current detection device, the capacitors constituting this series circuit Since the impedance of 9b is a sufficiently large value (a very large value close to infinity when the current I is a signal having a frequency of direct current or near direct current) (that is, the impedance of the resonance prevention circuit 9 is sufficiently large). Therefore, the occurrence of a situation in which the signal component (frequency f) of the excitation current I2 flows into the detection resistor 7 via the resonance prevention circuit 9 can be greatly reduced. A decrease in the S / N ratio can be reliably avoided. Further, in the high frequency region fH in which the feedback winding 4 functions as CT, the impedance of the capacitor 9b constituting this series circuit is sufficiently small (that is, the impedance of the resonance prevention circuit 9 is that of the first resistor 9a). It is possible to reliably prevent the occurrence of resonance in the feedback winding 4 (windings 4a and 4b) that may occur due to the parasitic capacitance because the resistance value R1 (which is a sufficiently small resistance value). .

  Note that the drive unit 6 described above is not limited to the configuration described above. For example, as shown in FIG. 4, a driving unit 6A using a voltage follower circuit and an inverting amplifier circuit may be employed. In the drive unit 6A, the detection signal S3 is input to both the voltage follower circuit and the inverting amplifier circuit, and the output of the voltage follower circuit is connected to one end of the feedback winding 4 (one end 42 of the winding 4a). The output of the inverting amplifier circuit is connected to the other end of the feedback winding 4 (the other end 45 of the winding 4b). Also in the current detection device 61 and the measurement device MS having the drive unit 6A, the same effects as the current detection device 61 and the measurement device MS having the drive unit 6 can be obtained. In addition, the same code | symbol is attached | subjected to the component which has a function equivalent to each component of the above-mentioned current detection apparatus 61, and the overlapping description is abbreviate | omitted.

  In the above example, the resonance prevention circuit 9 is configured only by the series circuit of the first resistor 9a and the capacitor 9b. However, the present invention is not limited to this. For example, the resonance prevention circuit 9 shown in FIG. In addition, another second resistor 9c may be connected in series to this series circuit. In this case, the resistance value R2 of the second resistor 9c is defined to be larger than the resistance value R1 (a sufficiently large value, for example, about 100 kΩ). In the frequency characteristic of the impedance of the resonance prevention circuit 9, the impedance on the low frequency side of the low frequency region fL in which the current detection device 61 functions as a zero flux type current detection device is a resistance value R2 as indicated by a broken line in FIG. However, as described above, by setting the resistance value R2 to a sufficiently large value, the signal component (frequency f) of the excitation current I2 is detected by the detection resistor 7 via the resonance prevention circuit 9. Can be sufficiently reduced, and a decrease in the S / N ratio can be sufficiently avoided.

  Moreover, although the flux gate type magnetic sensor was mentioned and demonstrated as an example of the magnetic sensor 3, it is not limited to a flux gate type magnetic sensor, Other magnetic sensors, such as a Hall element, can also be used. In the Hall element, there is a drive system in which an excitation current as an excitation signal supplied to the Hall element is switched by a switch. In this drive system, it is known that a surge noise is generated when the switch is switched. (For example, refer to Japanese Patent No. 3022995). For this reason, even when using a Hall element as the magnetic sensor of the current detection device 61, the influence of this surge-like noise can be reduced in the same manner as the above configuration using the fluxgate type magnetic sensor. There is an effect.

  Further, the current detection device 61 employs a configuration in which the detection resistor 7 is connected to the feedback winding 4 in advance and the trouble of separately preparing the detection resistor 7 can be saved, but the configuration is limited to this configuration. is not. For example, when the current value I1 of the current I flowing through the measurement target electric wire 64 can be roughly predicted and the current value I1 is in a wide range, the voltage value of the voltage Vd generated in the detection resistor 7 is It is desirable that the detection resistor 7 having a resistance value matching the input rating of the differential detection unit 8 can be appropriately selected. Therefore, as shown in FIG. 1, in the current detection device 61, a pair of resistance connection terminals 46, 46 are provided in the current path of the drive current Id, and the detection resistor 7 having a desired resistance value is connected to the pair of resistance connection terminals 46, 46. It can also be set as the structure which can be connected between the resistance connection terminals 46 and 46. FIG.

  In addition, although an example in which the feedback winding 4 is configured by connecting two windings 4a and 4b in series has been described, although not illustrated, three or more windings are connected in series to provide a feedback winding. Also in the structure to comprise, the effect equivalent to an above-described effect can be show | played by connecting said resonance prevention circuit 9 in parallel with each of each winding. Further, the current measuring device 61 is described as an example of the measuring device MS provided with the current detecting device 61. However, as the measuring device MS provided with the current detecting device 61, there are various power measuring devices such as a power measuring device. It can be a measuring device.

DESCRIPTION OF SYMBOLS 2 Magnetic core 3 Magnetic sensor 4 Feedback winding 4a, 4b Winding 5 Signal generation part 6, 6A Drive part 7 Detection resistance 9 Resonance prevention circuit 11 Measuring object wire 31 Sensor element 61 Current detection apparatus I Current I1 Current value I2 Excitation current Id drive current S3 detection signal MS measuring device Vd voltage

Claims (5)

An annular magnetic core into which the measurement target electric wire is inserted; a magnetic sensor that outputs a detection signal that is incorporated in the magnetic core and that changes in amplitude in proportion to the current value of the current that flows through the measurement target electric wire; A feedback winding configured by winding a conducting wire around the outer surface of the magnetic core; a drive unit that inputs the detection signal and supplies a drive current to the feedback winding that reduces the amplitude of the detection signal; and the drive A current detection device comprising a pair of resistance connection terminals disposed in a current path of a current and connected to a detection resistance for converting the drive current into a voltage;
The feedback winding is configured by connecting a plurality of windings arranged in the circumferential direction of the magnetic core in series,
A current detection device in which a resonance prevention circuit including a series circuit of a first resistor and a capacitor is connected in parallel to each of the plurality of windings.   The current detection device according to claim 1, wherein the detection resistor is connected between the pair of resistance connection terminals. An annular magnetic core into which the measurement target electric wire is inserted; a magnetic sensor that outputs a detection signal that is incorporated in the magnetic core and that changes in amplitude in proportion to the current value of the current that flows through the measurement target electric wire; A feedback winding formed by winding a conducting wire on the outer surface of the magnetic core, a signal generator for outputting an excitation signal to the magnetic sensor, and a drive current for inputting the detection signal and reducing the amplitude of the detection signal And a detection resistor that is disposed in the current path of the drive current and converts the drive current into a voltage and outputs the voltage, and converted by the detection resistor. A current detection device for detecting a voltage as a current value of a current flowing through the measurement target wire,
The feedback winding is configured by connecting a plurality of windings arranged in the circumferential direction of the magnetic core in series,
A current detection device in which a resonance prevention circuit including a series circuit of a first resistor and a capacitor is connected in parallel to each of the plurality of windings.   The said resonance prevention circuit is prescribed | regulated by the larger resistance value than the said 1st resistance, and is comprised including the 2nd resistance connected in parallel with the said series circuit. Current detection device. The current detection device according to any one of claims 1 to 4,
A processing unit for measuring the current value based on the voltage converted by the detection resistor;
A measuring device comprising: an output unit that outputs the measured current value.

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