Current sensor and measuring device

Abstract

The present application relates to a current sensor and a measuring device. A current sensor (110) for detecting a current flowing through a measurement object comprises: a magnetic core (2) through which the measurement object is inserted; a coil (3) wound around the magnetic core (2); a transmission path (8) for transmitting a current supplied from the coil (3); a terminal resistor (9) for converting a current from a terminal (8b) of the transmission path (8) into a voltage and outputting the voltage; and an impedance matching section (10) for performing impedance matching between the coil (3) and the terminal resistor (9). The impedance matching section (10) increases at least one of an impedance observed when the terminal resistor (9) side is observed from the terminal (8b) of the transmission path (8) and an impedance observed when the coil (3) side is observed from the starting end (8a) of the transmission path (8) to the characteristic impedance of the transmission path (8) in a frequency band of a frequency component in which the amplitude of the voltage output from the terminal resistor (9) is attenuated.

Description

Technical Field

[0001] The present invention relates to a current sensor and a measuring device for detecting a current flowing through a measurement object. Background Art

[0002] JP2016-114585A discloses a current sensor including a coil wound around a magnetic core through which a measurement object is inserted, a start filter for limiting the frequency domain of current input from the coil and outputting the current to a transmission path, and a terminal resistor for converting current from a terminal of the transmission path into a voltage.

[0003] In the current sensor described above, in order to suppress signal waveform distortion caused by reflection due to impedance mismatch in high-frequency transmission, a starting resistor or a terminal resistor having the same resistance value as the characteristic impedance of the transmission path is usually arranged at the starting end or the end end of the transmission path.

[0004] However, there is a problem that when the resistance value of the start-end resistor or the terminal resistor increases because the start-end resistor or the terminal resistor connected to the end of the transmission path is set to the same resistance value as the characteristic impedance of the transmission path, the power consumed by the start-end resistor or the terminal resistor increases. In particular, the larger the current flowing through the measurement object, the more significantly the power consumed in the current sensor increases. Summary of the invention

[0005] The present invention has been made in view of such problems, and an object of the present invention is to suppress an increase in power consumed by a current sensor and to suppress waveform distortion of a signal output from the current sensor.

[0006] According to one embodiment of the present invention, a current sensor for detecting a current flowing through a measurement object comprises: a magnetic core through which the measurement object is inserted; a coil wound around the magnetic core; a transmission path for transmitting the current supplied from the coil; a terminal resistor for converting the current from the terminal of the transmission path into a voltage; and a matching unit for performing impedance matching between the terminal resistor and the coil. The matching unit increases at least one of an impedance observed when the terminal resistor side is viewed from the terminal of the transmission path and an impedance observed when the coil side is viewed from the beginning of the transmission path to the characteristic impedance of the transmission path in a frequency band of a frequency component in which the amplitude of a voltage output from the terminal resistor is attenuated.

[0007] According to this scheme, in the attenuation band which is the frequency band of the frequency component where the amplitude attenuates, at least one of the impedance observed when the terminal resistance side is viewed from the end of the transmission path and the impedance observed when the coil side is viewed from the beginning of the transmission path is increased to the characteristic impedance of the transmission path by the matching unit. As a result, reflection is less likely to occur near the attenuation band where the influence of reflection becomes large, so that waveform distortion of the signal output from the current sensor can be suppressed.

[0008] On the other hand, outside the attenuation band, at least one of the impedance observed when the terminal resistance side is viewed from the end of the transmission path and the impedance observed when the coil side is viewed from the beginning of the transmission path is hardly changed by the matching unit. As a result, the power consumed in the current sensor is hardly increased, thereby suppressing the increase in power consumption of the current sensor.

[0009] Therefore, according to the above-described aspect, it is possible to suppress an increase in the power consumed by the current sensor and suppress a waveform distortion of a signal output from the current sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a diagram showing the configuration of a measuring device including the current sensor according to the first embodiment.

[0011] Figure 2 It is a diagram showing the measurement results of the amplitude characteristics of the current sensor in this embodiment.

[0012] Figure 3 : is a circuit diagram showing an equivalent circuit of the measuring device in this embodiment.

[0013] Figure 4 It means use Figure 3 The figure shown is the result of simulating the frequency characteristics of the impedance on the terminal resistance side using an equivalent circuit.

[0014] Figure 5 It means to make Figure 3 The diagram shows the simulation results of the frequency characteristics of the impedance on the terminal resistance side when the inductance value of the equivalent circuit is changed.

[0015] Figure 6 : is a circuit diagram showing an equivalent circuit of the current sensor in this embodiment.

[0016] Figure 7 It means use Figure 7 The equivalent circuit shown is a diagram of the result of simulating the amplitude characteristics.

[0017] Fig. 8A : is a circuit diagram showing a modification of the matching circuit included in the current sensor.

[0018] Figure 8Bis a circuit diagram showing another modified example of the matching circuit.

[0019] Fig. 9 It is a diagram showing the configuration of a measuring device including a current sensor according to a second embodiment.

[0020] Description of reference numerals:

[0021] 2: Magnetic core;

[0022] 3: Coil;

[0023] 8: Transmission path;

[0024] 9: Terminal resistance;

[0025] 10, 10a: impedance matching part (matching unit);

[0026] 11: Initial resistance;

[0027] 12: Matching circuit;

[0028] 100, 101: measuring device;

[0029] 110, 111: current sensor;

[0030] 120: Measurement unit;

[0031] 121: resistance element;

[0032] 122: Sensing element. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0034] (First Embodiment)

[0035] Figure 1 It is a diagram showing the configuration of the measuring device 100 in the first embodiment.

[0036] The measuring device 100 measures a physical quantity related to a measurement object based on a detection signal that detects a current flowing through the measurement object. The measuring device 100 in this embodiment includes a current sensor 110 and a measuring unit 120 .

[0037] The current sensor 110 detects the current flowing through the measurement circuit 1 as the measurement object. The current sensor 110 in this embodiment is configured as a zero magnetic flux type (magnetic balance type) current sensor, and detects the measurement target current I1 which is the alternating current flowing through the measurement circuit 1 .

[0038] The current sensor 110 includes a magnetic core 2, a coil 3, a transmission path 4, a capacitive load 5, a magnetoelectric conversion output unit 6, a voltage-current conversion unit 7, a transmission circuit 20, and an output terminal 110a. The transmission circuit 20 includes a transmission path 8, a terminal resistor 9, and an impedance matching unit 10.

[0039] The overall shape of the magnetic core 2 is formed into a ring. In the present embodiment, the annular magnetic core 2 is a split type that can be opened and closed, and is configured to be able to insert the measurement circuit 1 in the live wire state, that is, to be able to clamp the measurement circuit 1 in the live wire state. The magnetic core 2 is not limited to the split type, and can also be a through type (non-split type).

[0040] The coil 3 is formed by winding a wire around the magnetic core 2. In the coil 3, one end 3a is directly or indirectly connected to the grounding device G, and the other end 3b is connected to the starting end 8a of the transmission path 8. The grounding device G is a grounding wire for supplying a reference potential.

[0041] In this embodiment, one end 3a of the coil 3 is connected to the grounding device G via the transmission path 4 and the capacitive load 5. It should be noted that the one end 3a of the coil 3 may be directly connected to the grounding device G. In this case, the current sensor 110 is configured as a current transformer (CT) type current sensor.

[0042] The transmission path 4 is a transmission line whose characteristic impedance is set (defined) to a predetermined value. In the present embodiment, the characteristic impedance of the transmission path 4 is set to 50Ω. The transmission path 4 has one end connected to one end 3a of the coil 3 and the other end connected to the capacitive load 5.

[0043] The transmission path 4 is composed of, for example, a coaxial cable in which a shield (not shown) is connected to a grounding device G. In this case, the characteristic impedance of the transmission path 4 is set to 50Ω or 75Ω. It should be noted that the transmission path 4 is not limited to a coaxial cable, and any transmission path whose characteristic impedance is predetermined to be a constant value may be used, for example, various transmission paths such as a twisted pair cable may be used.

[0044] The capacitive load 5 is composed of a series circuit in which a resistor 5a and a capacitor 5b are connected in series. The resistor 5a has a resistance value of several tens of Ω or less, and the capacitor 5b has a capacitance value such that the impedance is several tens of Ω or less in the frequency band of the measured current I1.

[0045] For example, the resistance value of the resistor 5a is set to 50Ω, and the capacitance of the capacitor 5b is set to 0.1 μF. The capacitive load 5 may be configured such that the resistor 5a is disposed on the grounding device G side instead of the capacitor 5b being disposed on the grounding device G side.

[0046] The magnetoelectric conversion output unit 6 detects the magnetic flux generated inside the magnetic core 2 and outputs an output voltage V1 indicating a voltage value corresponding to the magnetic flux density of the detected magnetic flux. In this embodiment, the magnetoelectric conversion output unit 6 is disposed in a gap formed in the magnetic core 2 and is composed of a Hall element.

[0047] The output voltage V1 of the Hall element represents a voltage value proportional or substantially proportional to the magnitude of the magnetic flux density of the magnetic flux generated inside the magnetic core 2. As the magnetoelectric conversion output unit 6, a fluxgate type magnetic detection element or the like can be used in addition to the Hall element.

[0048] The voltage-current converter 7 generates a negative feedback current I2 as a detection current based on the output voltage V1 of the magnetoelectric conversion output unit 6. The voltage-current converter 7 supplies the generated negative feedback current I2 to one end 3a of the coil 3 via the transmission path 4. For example, the voltage-current converter 7 is composed of an operational amplifier.

[0049] The voltage-current conversion unit 7 controls the current value of the negative feedback current I2 so that the output voltage V1 becomes zero volt (0V), that is, the magnetic flux density of the magnetic flux generated inside the magnetic core 2 becomes zero. The magnetic flux generated inside the magnetic core 2 is the magnetic flux generated by the measured current I1 flowing through the measurement circuit 1 inserted into the magnetic core 2. The magnetic flux generated by the negative feedback current I2 flowing through coil 3 difference Therefore, the voltage-current conversion unit 7 is used to convert the voltage-current into a magnetic flux. To cancel the magnetic flux The current value of the negative feedback current I2 is increased / decreased in this way.

[0050] Thus, the potential of the one end 3a of the coil 3 when the frequency of the negative feedback current I2 supplied to the one end 3a of the coil 3 or the frequency of the current I3 described later is equal to or higher than the crossover frequency is set approximately to the reference potential of the grounding device G. The crossover frequency refers to the frequency at which the frequency characteristics of the negative feedback current I2 and the frequency characteristics of the current I3 cross. The current value of the current I2 or I3 as the detection current supplied from the coil 3 to the transmission path 8 is a value obtained by dividing the current value of the measured current I1 by the number of turns N of the coil 3 (I1 / N).

[0051] The transmission path 8 transmits the detection current supplied from the coil 3. The transmission path 8 is a transmission line whose characteristic impedance is set to a predetermined value, similar to the above-mentioned transmission path 4. The transmission path 8 is composed of various transmission paths such as a coaxial cable whose characteristic impedance is set to 50Ω or 75Ω, or a twisted pair cable whose characteristic impedance is set to a constant value.

[0052] In this embodiment, the length of the transmission path 8 is greater than 1 m, and the characteristic impedance of the transmission path 8 is set to 50Ω. In the transmission path 8, the starting end 8a as one end is connected to the end 3a of the coil 3, and the terminal 8b as the other end is connected to the input terminal 12a of the matching circuit 12.

[0053] The terminal resistor 9 converts the current from the terminal 8b of the transmission path 8 into a voltage, and outputs the converted voltage as the detection voltage V2 to the output terminal 110a. The terminal resistor 9 is composed of, for example, a resistor element connected between the output terminal 110a and the grounding device G or an input resistor of a measuring device such as an oscilloscope. Alternatively, the terminal resistor 9 may also be composed of a plurality of chip resistors.

[0054] The resistance value of the terminal resistor 9 is set to a predetermined value smaller than the characteristic impedance of the transmission path 8. This can reduce the power consumed in the terminal resistor 9, and accordingly, the heat generation of the terminal resistor 9 can be suppressed.

[0055] In the present embodiment, the terminal resistor 9 is formed of a resistor element, one end of the terminal resistor 9 is connected to the output terminal 110 a , and the other end of the terminal resistor 9 is connected to the ground device G. The resistance value of the terminal resistor 9 is set to 5Ω.

[0056] The impedance matching unit 10 is composed of one or more electronic components that perform impedance matching between the coil 3 and the terminal resistor 9. The impedance matching unit 10 matches the impedance on the terminal resistor side with the impedance on the coil side in the frequency band of the frequency component of the amplitude attenuation among the frequency components of the detection voltage V2 output from the terminal resistor 9. Specifically, the impedance matching unit 10 increases at least one of the impedance on the terminal resistor side and the impedance on the coil side to the characteristic impedance of the transmission path 8 in the frequency band of the frequency component of the amplitude attenuation.

[0057] The terminal resistance side impedance is the impedance observed when the terminal resistance 9 side is viewed from the terminal end 8 b of the transmission path 8 , and the coil side impedance is the impedance observed when the coil 3 side is viewed from the starting end 8 a of the transmission path 8 .

[0058] In addition, the frequency band of the frequency component of the amplitude attenuation mentioned above is referred to as the "attenuation band" below. The attenuation band of the current sensor 110 becomes a frequency range that is roughly the same as the frequency band in which the frequency component of the detection current output from the coil 3 is attenuated due to the number of turns of the coil 3, the parasitic capacitance parasitic on the coil 3, etc.

[0059] The amplitude of the frequency component is attenuated by a predetermined value relative to the amplitude of the frequency component with almost no attenuation, for example, the value of the frequency attenuated by 3dB (decibel) is set as the lower limit frequency, and the above-mentioned attenuation band refers to the frequency band above this lower limit frequency. In this embodiment, the lower limit frequency of the attenuation band is set to 100MHz (megahertz).

[0060] The impedance matching section 10 in the present embodiment includes a start-end resistor 11 and a matching circuit 12 .

[0061] The start-end resistor 11 is a signal source resistor for achieving impedance matching and is provided to adjust the coil side impedance at the start end 8 a of the transmission path 8 to the characteristic impedance of the transmission path 8 .

[0062] The resistance value of the start-end resistor 11 is set so that the coil side impedance becomes the same value or approximately the same value as the characteristic impedance of the transmission path 8. The approximately the same value here means a value that is unlikely to cause reflection at both ends of the transmission path 8. If the characteristic impedance of the transmission path 8 is 50Ω, for example, the resistance value of the start-end resistor 11 can be set to 40Ω. In this way, in the impedance matching of this embodiment, a fluctuation of about 20% from the value of the characteristic impedance of the transmission path 8 is allowed.

[0063] In this embodiment, the starting resistor 11 is connected to the starting end 8a of the transmission path 8 and is connected in parallel with the coil 3. The resistance value of the starting resistor 11 is set to 50Ω. In addition, the starting resistor 11 has a function of shunting a part of the current supplied from the coil 3 to the transmission path 8. Thus, the power consumed by the terminal resistor can be reduced.

[0064] The matching circuit 12 makes the impedance of the terminal resistance side close to the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 110. In the present embodiment, the matching circuit 12 also operates as a low-pass filter circuit (low-band pass filter) to remove high-frequency noise.

[0065] For example, the matching circuit 12 outputs the fundamental frequency component of the frequency component of the detection current supplied from the coil 3 which is lower than the cutoff frequency with almost no attenuation. On the other hand, the matching circuit 12 outputs the frequency component of the detection current which is higher than the cutoff frequency with an amplitude of That is, the matching circuit 12 limits the frequency range of the detection current to a desired frequency band (a frequency band smaller than the cutoff frequency).

[0066] Hereinafter, a frequency band less than the cutoff frequency is referred to as a "passing frequency band". It should be noted that the cutoff frequency is usually set to a frequency slightly higher than the upper limit frequency of the measured current I1 to be detected. For example, the cutoff frequency is set to a frequency slightly higher than the lower limit value of the frequency band composed of the frequency components of the detection current supplied from the coil 3, which attenuate the amplitude.

[0067] The matching circuit 12 is configured using, for example, a plurality of passive elements so that the impedance on the terminal resistance side approaches the characteristic impedance of the transmission path 8 in a high frequency band above the cutoff frequency of the matching circuit 12. Thus, compared with a case where the matching circuit 12 is configured using active elements, noise mixed into the current signal output from the matching circuit 12 can be reduced.

[0068] The matching circuit 12 has at least a resistance component and an inductance component, and the resistance component of the matching circuit 12 is set to a larger value as the resistance value (predetermined value) of the terminal resistor 9 is smaller. In other words, the resistance value of the terminal resistor 9 is set to a predetermined value smaller than the characteristic impedance of the transmission path 8 based on the resistance component of the matching circuit 12.

[0069] In the present embodiment, the matching circuit 12 includes a resistance element 121 as a resistance component and an inductive element (inductive element) 122 as an inductive component. The resistance element 121 and the inductive element 122 are connected in parallel to each other.

[0070] The resistance value of the resistor element 121 is set based on the value obtained by subtracting the resistance value of the terminal resistor 9 from the characteristic impedance of the transmission path 8. In this embodiment, the resistance value of the resistor element 121 is set to 45Ω, which is the value obtained by subtracting the resistance value of the terminal resistor 9 from the characteristic impedance of the transmission path 8, 50Ω.

[0071] On the other hand, the inductance value of the inductive element 122 is set based on the resistance value of the resistive element 121, the characteristic impedance of the transmission path 8, the resistance value of the terminal resistor 9, and the lower limit frequency of the attenuation band of the current sensor 110. The method for setting the inductance value of the inductive element 122 will be described later. Figure 3 Give a narrative.

[0072] It should be noted that, in this embodiment, an example in which the matching circuit 12 is composed of the resistor element 121 and the inductive element 122 is described, but the present invention is not limited to this configuration. For example, the matching circuit 12 may be composed of one or more electronic components. In this case, the constants of each electronic component may be pre-set so that the impedance of the terminal resistance side approaches the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 110.

[0073] In this embodiment, the input terminal 12a of the matching circuit 12 is connected to the terminal 8b of the transmission path 8, and the output terminal 12b is connected to one end of the terminal resistor 9. That is, the matching circuit 12 is connected in series between the terminal 8b of the transmission path 8 and one end of the terminal resistor 9.

[0074] By arranging the matching circuit 12 on the terminal resistor 9 side, the distance between the coil 3 and the matching circuit 12 can be increased compared to the case where the matching circuit 12 is connected to the starting end 8a of the transmission path 8. Therefore, it is possible to suppress the occurrence of an undesirable peak near the cutoff frequency in the frequency characteristics of the matching circuit 12 due to the resonance between the parasitic capacitance of the coil 3 and the inductive element 122 of the matching circuit 12.

[0075] As described above, in the attenuation band of the current sensor 110 , the current sensor 110 includes the matching circuit 12 for impedance matching, and thus it is possible to suppress distortion of the detection signal output from the output terminal 110 a of the current sensor 110 to the measurement unit 120 .

[0076] The measuring unit 120 measures a physical quantity related to the measuring circuit 1 based on the detection signal output from the current sensor 110. Examples of the physical quantity related to the measuring circuit 1 include the value of the alternating current flowing through the measuring circuit 1, the value of the alternating current, or the value of the alternating magnetic field generated around the measuring circuit 1. The measuring unit 120 is composed of, for example, an oscilloscope, a power meter, or an ammeter.

[0077] In the present embodiment, when the measuring unit 120 receives the detection voltage V2 from the output terminal 110a as the detection signal of the current sensor 110, the current I1 to be measured flowing through the measuring circuit 1 inserted into the magnetic core 2 is measured based on the received detection voltage V2. The measuring unit 120 includes, for example, an A / D converter and a CPU (not shown), and the A / D converter converts the detection voltage V2 converted by the current sensor 110 into a digital value, and the CPU measures (calculates) the current value of the current I1 to be measured based on the digital value.

[0078] It should be noted that the measuring unit 120 can send the current value of the measured current I1 to an external device or store it in an external storage device via an external interface circuit not shown. As other physical quantities to be measured, the measuring unit 120 can also measure the strength of the alternating current or magnetic field of the measuring circuit 1 based on the received detection voltage V2.

[0079] The measuring unit 120 has a display screen such as an LCD (Liquid Crystal Display), and displays the waveform of the measured physical quantity on the display screen. For example, the measuring unit 120 displays the time waveform of the measured alternating current on the display screen with the horizontal axis as the time axis. In this case, the detection signal output from the current sensor 110 is used, so the waveform of the alternating current with little distortion caused by the current sensor 110 can be displayed on the display screen as the measured current I1 of the measuring circuit 1.

[0080] Next, the operation of the current sensor 110 will be briefly described.

[0081] First, in the low frequency region where the measured current I1 flowing through the measuring circuit 1 contains direct current, the magnetoelectric conversion output unit 6 and the voltage-current conversion unit 7 mainly operate. In this case, the magnetoelectric conversion output unit 6 detects the magnetic flux generated inside the magnetic core 2. The output voltage V1 corresponding to the density of the detected magnetic flux is supplied to the voltage-current conversion unit 7. The voltage-current conversion unit 7 generates a negative feedback current I2 based on the output voltage V1, and supplies the negative feedback current I2 to one end 3a of the coil 3.

[0082] At this time, the voltage-current conversion unit 7 controls the current value of the negative feedback current I2 so that the output voltage V1 becomes zero volts, that is, the magnetic flux Offsetting magnetic flux Thus, the current value of the negative feedback current I2 is substantially equal to a value obtained by dividing the current value of the measured current I1 by the number of turns N (I1 / N).

[0083] After that, a part of the negative feedback current I2 outputted from the other end 3b of the coil 3 flows to the starting resistor 11, and the remaining current flows as a detection current to the terminal resistor 9 via the coil 3, the transmission path 8, and the matching circuit 12. Then, this detection current is converted into a detection voltage V2 in the terminal resistor 9. In this case, the capacitive load 5 is maintained at a high impedance, thereby preventing the current I3 from leaking to the ground device G via the capacitive load 5.

[0084] At this time, in the matching circuit 12 of the present embodiment, the impedance of the inductive element 122 is extremely low, so the increase of the resistance component is suppressed. As a result, the impedance on the terminal resistance side becomes the combined resistance value of the start-end resistor 11 and the terminal resistor 9 connected in parallel to each other. In the present embodiment, the resistance value of the start-end resistor 11 is 50Ω, and the resistance value of the terminal resistor 9 is 5Ω, so the combined resistance value becomes about 5Ω.

[0085] Thus, in the low frequency region, the resistance component of the matching circuit 12 is smaller than the characteristic impedance of the transmission path 8, so the power consumed in the matching circuit 12 is reduced, and thus the power consumption of the current sensor 110 can be suppressed. In addition, by suppressing the increase in the resistance component of the matching circuit 12, the amount of current flowing through the terminal resistor 9 is suppressed from decreasing, so the level reduction of the detection signal representing the detection voltage V2 can be reduced. Moreover, the resistance value of the terminal resistor 9 is set to a value smaller than the characteristic impedance of the transmission path 8, so the power consumed in the terminal resistor 9 can be reduced.

[0086] On the other hand, when the measured current I1 flowing through the measuring circuit 1 is in the high frequency range from the upper limit frequency of the low frequency range to the cutoff frequency of the matching circuit 12, the coil 3 works as a CT alone instead of the magneto-electric conversion output unit 6 and the voltage-current conversion unit 7.

[0087] In this case, the coil 3 detects the measured current I1 flowing through the measurement circuit 1, and outputs the current I3 whose amplitude (current value) changes according to the amplitude (current value) of the measured current I1 as the detection current. After that, for the current I3 output from the other end 3b of the coil 3, a part flows to the starting resistor 11, and the remaining detection current flows to the terminal resistor 9 via the transmission path 8 and the matching circuit 12. Then, in the terminal resistor 9, the detection current is converted into the detection voltage V2.

[0088] At this time, in the matching circuit 12 of the present embodiment, the impedance of the inductive element 122 is higher than the resistance value of the resistive element 121, which is 45Ω, so the resistance component becomes dominant. Therefore, the impedance on the terminal resistance side becomes a resistance value of about 50Ω obtained by adding the resistance component of the matching circuit 12, which is about 45Ω, and the combined resistance value of the starting resistance 11 and the terminal resistance 9, which is about 5Ω.

[0089] As described above, in the high frequency region, the impedance on the terminal resistance side is close to the characteristic impedance of the transmission path 8, 50Ω, so that impedance matching can be achieved and reflection generated at the terminal of the transmission circuit 20 can be suppressed.

[0090] Next, the frequency characteristics of the current sensor 110 will be described with reference to the drawings.

[0091] Figure 2 1 is a diagram showing an example of the amplitude characteristic (output frequency characteristic) of the current sensor 110 in the present embodiment. In this example, the result of measuring the amplitude characteristic in the frequency domain of the detection signal output from the current sensor 110 is shown, using the current sensor 110 in which the upper limit frequency of the desired frequency band (lower limit frequency of the attenuation band) fe is set to 120 MHz and the output ratio is set to 0.1 (V / A).

[0092] Here, the horizontal axis is the frequency expressed in a logarithmic scale, and the vertical axis is the amplitude ratio relative to 100 kHz expressed in decibels (dB). The amplitude ratio here refers to the ratio of the amplitude of each frequency component to the amplitude of the frequency component of 100 kHz.

[0093] In addition, Figure 2 In FIG. 1 , as a comparative example, the measurement result of the current sensor without the matching circuit 12 of this embodiment is shown by the dotted line. Figure 2 As shown, in the comparative example, impedance matching is not performed in the attenuation band above the lower limit frequency fe of 120 MHz, and therefore the amplitude characteristic is disturbed due to the influence of reflection from the measuring unit 120 .

[0094] In contrast, it can be seen that in the current sensor 110 of the present embodiment, impedance matching is performed in the attenuation band by using the matching circuit 12 , so that disturbance of the amplitude characteristic is suppressed and the amplitude of the frequency component is smoothly attenuated.

[0095] Therefore, even when the measurement device 100 is used to measure the current I1 to be measured with a relatively high frequency and display a response waveform, the influence of reflection is reduced, so that the distortion of the measurement waveform displayed on the screen can be reduced.

[0096] Next, refer to Figure 3 and Figure 4 The frequency characteristics of the impedance on the terminal resistance side in the current sensor 110 will be described.

[0097] Figure 3 1 is a diagram showing an equivalent circuit of a measuring device 100 for simulating the frequency characteristics of the impedance on the terminal resistance side.

[0098] In the equivalent circuit of the current sensor 110, the voltage source 3c as the coil 3 supplies the AC current to the matching circuit 12. The resistance value of the resistor element 121 in the matching circuit 12 is 45Ω, and the inductance value of the inductive element 122 is 100nH (nanohenry). In addition, the resistance value of the terminal resistor 9 is 5Ω, the resistance value of the input resistor 120a in the measuring unit 120 is 1MΩ, and the electrostatic capacitance of the capacitor 120b is 15pF.

[0099] Figure 4 It means use Figure 3 1 is a diagram showing simulation results of the frequency characteristics of the terminal resistance side impedance calculated by using the equivalent circuit of the measuring device 100 shown in FIG. Here, the horizontal axis is the frequency [Hz] expressed in a logarithmic scale, and the vertical axis is the terminal resistance side impedance [Ω].

[0100] exist Figure 4 In FIG. 1 , as a comparative example, the simulation result of the current sensor without the matching circuit 12 of the present embodiment is shown by the dotted line. Figure 4 As shown, in the current sensor without the matching circuit 12, the impedance on the terminal resistance side is a constant resistance value of 5Ω. As a result, reflection occurs at the terminal of the transmission circuit due to the impedance mismatch in the attenuation band.

[0101] It should be noted that if the transmission path 8 is short enough, even if impedance mismatch occurs, there is almost no influence of reflection. Usually, reflection from the lower limit frequency of the attenuation band near 100MHz is generated from about 1m of the transmission path 8. Such reflection influence will appear when observing the waveform response, and it becomes difficult to observe the correct waveform of the measured current I1. Therefore, if the length of the transmission path 8 is more than 1m and the passband is about 100MHz, it is preferable to obtain impedance matching.

[0102] Next, the frequency characteristics of the impedance on the terminal resistance side in the current sensor 110 of the present embodiment will be described.

[0103] like Figure 4 As shown by the solid line, if the frequency of the AC current is less than 1 MHz, the impedance of the inductive element 122 in the matching circuit 12 is sufficiently small compared to the resistance value of the resistor element 121. Therefore, the AC current mainly flows through the inductive element 122, and almost no AC current flows through the resistor element 121, so the impedance on the terminal resistance side becomes a value that is approximately the same as the resistance value of 5Ω of the terminal resistor 9. In addition, the resistance component of the matching circuit 12 is extremely small compared to the characteristic impedance of the transmission path 8, so the power consumed by the matching circuit 12 is also reduced.

[0104] Furthermore, when the frequency of the AC current is higher than 1 MHz, as the frequency increases, the impedance of the inductive element 122 increases, and the AC current easily flows through the resistive element 121. Therefore, the impedance of the terminal resistance side is greater than the resistance value 5Ω of the terminal resistance 9, and the power consumption of the matching circuit 12 also begins to gradually increase.

[0105] When the frequency of the AC current increases to around 100 MHz, the AC current mainly flows through the resistor element 121 of the matching circuit 12. Therefore, the impedance of the terminal resistor side appears to be about 40Ω, which is the result of adding most of the resistance component of the resistor element 121 of 45Ω to the resistance value of the terminal resistor 9 of 5Ω.

[0106] It is also known that when the frequency of the AC current is higher than 120 MHz, the lower limit frequency of the attenuation band of the coil 3 (upper limit frequency of the passband), the impedance on the terminal resistance side approaches 50Ω, which is the same value as the characteristic impedance of the transmission path 8 .

[0107] In this way, in the passband except near the cutoff frequency (lower limit frequency of the attenuation band) of the current sensor 110, the influence of reflection is small, so the matching circuit 12 suppresses the impedance matching in the current sensor 110. As a result, the increase in power consumption of the matching circuit 12 can be suppressed. In addition, in the attenuation band of the current sensor 110, the influence of reflection becomes larger than that in the passband, so the matching circuit 12 makes the impedance on the terminal resistance side close to the characteristic impedance of the transmission path 8. As a result, the reflection generated at the terminal of the current sensor 110 can be suppressed.

[0108] exist Figure 3 and Figure 4 In the example described above, the inductance value of the inductive element 122 constituting the matching circuit 12 is set to 100 nH, but the present invention is not limited to this. Here, a method for setting the inductance value of the inductive element 122 is described.

[0109] Figure 3The impedance Z of the equivalent circuit shown is expressed as in the following equation (1) using the inductance value L of the inductive element 122 , the resistance value R1 of the resistive element 121 , and the resistance value R2 of the terminal resistor 9 .

[0110] [Formula 1]

[0111]

[0112] When the equation (1) is solved for the inductance value L of the inductive element 122 , the inductance value L of the inductive element 122 is expressed as in the following equation (2).

[0113] [Formula 2]

[0114]

[0115] In this embodiment, the impedance Z is set to the same value as the characteristic impedance of the transmission path 8, and the angular frequency ω is set to the value obtained by dividing the lower limit frequency fe of the attenuation band by 2π. By configuring the matching circuit 12 according to the relationship of equation (2), the impedance (Z) on the terminal resistance side can be made close to the same value as the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 110.

[0116] Thus, by changing the inductance value L of the inductive element 122, the frequency characteristic of the impedance on the terminal resistance side changes. Figure 5 The relationship between the inductance value L of the inductive element 122 and the frequency characteristic of the impedance on the terminal resistance side will be described.

[0117] Figure 5 1 is a diagram showing changes in the frequency characteristics of the impedance on the terminal resistance side according to the inductance value L of the inductive element 122 .

[0118] Here, the inductance value L of the inductive element 122 is calculated using the above-mentioned formula (2) so that the frequency f (=ω / 2π) at which the characteristic impedance of the transmission path 8 is reached becomes 100kHz, 1MHz, 10MHz, 100MHz, and 1GHz. In this calculation, although it is preferable to set the impedance Z to 50Ω, which is the same as the characteristic impedance of the transmission path 8, the denominator in the formula (2) becomes zero and diverges, so the impedance Z is set to 49Ω.

[0119] Under the above conditions, the inductance values ​​L of the inductive element 122 are 140 μH, 14 μH, 1.4 μH, 140 nH, and 14 nH. Figure 5 2 shows the frequency characteristics of the terminal resistance side impedance when the inductance value L of the inductive element 122 is set to 140 μH, 14 μH, 1.4 μH, 140 nH, and 14 nH, respectively.

[0120] like Figure 5As shown in the figure, it can be seen that by gradually reducing the inductance value L of the inductive element 122 from 140μH to 14nH, the starting point of the frequency when the impedance on the terminal resistance side starts to change from 5Ω becomes higher. In this way, by changing the inductance value L of the inductive element 122, the starting point of impedance matching can be moved to the low frequency side or the high frequency side in the frequency characteristics of the impedance on the terminal resistance side.

[0121] Therefore, when the current sensor 110 is designed so that the impedance of the terminal resistance side reaches 49Ω at a frequency of 100 MHz, the terminal resistor 9, the resistance element 121, and the induction element 122 are set to 5Ω, 45Ω, and 140 nH, respectively. Figure 6 and Figure 7 The amplitude characteristics of the current sensor 110 designed under this condition will be described.

[0122] Figure 6 1 is a diagram showing an equivalent circuit of the transmission circuit 20 constituting the current sensor 110 for simulating the amplitude characteristics of the current sensor 110. Here, the resistance value of the head resistor 11 is 50Ω, the resistance value of the resistor element 121 in the matching circuit 12 is 45Ω, the inductance value of the inductive element 122 is 140nH, and the resistance value of the terminal resistor 9 is 5Ω.

[0123] Figure 7 It means use Figure 6 The equivalent circuit shown is a diagram showing the simulation result of the amplitude characteristic of the transmission circuit 20 in the current sensor 110. Here, the horizontal axis and the vertical axis are Figure 2 The parameters shown are the same.

[0124] like Figure 7 As shown, the amplitude of the frequency component is attenuated by about 4 dB at 100 MHz, and the matching circuit 12 operates as a low-pass filter circuit. The cutoff frequency fc of the matching circuit 12 is lower than the lower limit frequency fe of the attenuation band, so the high-frequency noise included in the detection current from the coil 3 can be reliably removed.

[0125] Furthermore, when the amplitude characteristic of the high-frequency component of the detection current supplied from the coil 3 increases, the output frequency characteristic of the current sensor 110 can be smoothed. On the other hand, when the amplitude characteristic of the high-frequency component does not increase, by reducing the impedance value of the inductive element 122, it is possible to adjust to 3 dB, which is a general attenuation amount, at a frequency of 100 MHz.

[0126] Next, refer to Fig. 8A and 8B Modifications of the current sensor 110 will be described.

[0127] Fig. 8A1 is a diagram showing a modification of the matching circuit 12 in the present embodiment. In this modification, the matching circuit 12 is a first-order impedance filter including an inductive element 201, a resistive element 202, a resistive element 203, and a capacitor 204. The inductive element 201 has its two ends connected to the input terminal 12a and the output terminal 12b of the matching circuit 12, respectively, and is connected in parallel to the resistive element 202 and the resistive element 203 connected in series with each other. The connection point between the resistive element 202 and the resistive element 203 is connected to one end of the capacitor 204, and the other end of the capacitor 204 is connected to the grounding device G.

[0128] Figure 8B 1 is a diagram showing another modified example of the matching circuit 12. In this example, the matching circuit 12 includes an inductive element 211, a resistive element 212, a resistive element 213, and a capacitor 214, and an inductive element 221, a resistive element 222, a resistive element 223, and a capacitor 224. That is, the matching circuit 12 is a series connection of two Fig. 8A A two-stage impedance filter is formed by the first-stage impedance filter shown.

[0129] exist Fig. 8A and Figure 8B In the matching circuit 12 shown, the constants of each passive element are set so that the impedance of the terminal resistance side approaches the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 110. This suppresses reflection in the attenuation band of the current sensor 110, thereby suppressing waveform distortion of the detection signal.

[0130] It should be noted that the matching circuit 12 can also be composed of a multi-stage fixed impedance filter. Fig. 8A The first-order impedance filters shown are connected in series to have a steeper cutoff characteristic.

[0131] Next, the operation and effects of the current sensor 110 according to the first embodiment will be described in detail.

[0132] According to the present embodiment, the current sensor 110 for detecting the current flowing through the measurement circuit 1 as the measurement object comprises: a magnetic core 2, in which the measurement circuit 1 is inserted; a coil 3, which is wound around the magnetic core 2; and a transmission path 8, which transmits the current supplied from the coil 3. It also comprises: a terminal resistor 9, which converts the current from the terminal 8b of the transmission path 8 into a voltage and outputs it; and an impedance matching section 10, which constitutes a matching unit for performing impedance matching between the coil 3 and the terminal resistor 9.

[0133] Furthermore, the impedance matching unit 10 increases at least one of the terminal resistance side impedance observed when observing the terminal resistance 9 side from the terminal end 8b of the transmission path 8 and the coil side impedance observed when observing the coil 3 side from the starting end 8a of the transmission path 8 to the value of the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 110.

[0134] In particular, according to this embodiment, Figure 1 and Figure 4 As shown, the impedance matching unit 10 increases the impedance on the terminal resistor side to the value of the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 110. The attenuation band here refers to the frequency band of the component whose amplitude is attenuated among the frequency components of the voltage output from the terminal resistor 9.

[0135] Thus, by providing the impedance matching unit 10, in the attenuation band where the influence of reflection is large, the impedance on the terminal resistance side increases from the resistance value of the terminal resistor 9 to the value of the characteristic impedance of the transmission path 8. As a result, reflection is less likely to occur near the attenuation band, and thus waveform distortion of the signal output from the current sensor 110 can be suppressed.

[0136] On the other hand, in the passband other than the vicinity of the lower limit frequency of the attenuation band where the influence of reflection is small, the impedance on the terminal resistance side is suppressed from rising toward the characteristic impedance of the transmission path 8 due to the provision of the impedance matching section 10, so that the impedance on the terminal resistance side is almost unchanged. In this way, the power consumed in the impedance matching section 10 is hardly increased, so the increase in power consumption in the impedance matching section 10 can be suppressed.

[0137] Therefore, an increase in power consumed in the current sensor 110 can be suppressed, and waveform distortion of a signal output from the current sensor 110 can be suppressed.

[0138] Furthermore, according to the present embodiment, the impedance matching section 10 includes the matching circuit 12 for bringing the impedance on the terminal resistance side close to the characteristic impedance of the transmission path 8 in the attenuation band.

[0139] In this way, by using the matching circuit 12 to make the impedance of the terminal resistance side close to the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 110, it is possible to suppress reflection in the attenuation band. Figure 2 As shown by the dotted line in , the disturbance of the amplitude characteristic in the attenuation band is suppressed, so the waveform distortion of the detection signal output from the current sensor 110 can be suppressed.

[0140] Furthermore, according to the present embodiment, the resistance value of the terminal resistor 9 is set to a predetermined value smaller than the characteristic impedance of the transmission path 8. This reduces the power consumed in the terminal resistor 9, thereby suppressing heat generation of the terminal resistor 9.

[0141] Furthermore, when a large current flows through the measuring circuit 1 by making the resistance value of the terminal resistor 9 smaller than the characteristic impedance value of the transmission path 8, even if the detection current supplied from the coil 3 to the terminal resistor 9 along with the large current increases, the heating of the terminal resistor 9 is suppressed due to the small resistance value of the terminal resistor 9. Therefore, even for the measuring circuit 1 in which the measured current I1 with a large current value flows, the use of the current sensor 110 can eliminate the need for measures to prevent the heating of the terminal resistor 9.

[0142] Furthermore, according to the present embodiment, the smaller the resistance value (predetermined value) of the terminal resistor 9 is, the larger the resistance value of the resistor element 121 as the resistance component of the matching circuit 12 is set to. In this way, by relatively increasing the resistance value of the resistor element 121 of the matching circuit 12, the resistance value of the terminal resistor 9 can be reduced, and thus the heat generated by the terminal resistor 9 can be further reduced.

[0143] In addition, according to this embodiment, if Figure 7 As shown, the cutoff frequency fc of the matching circuit 12 may be set to a value lower than the lower limit frequency fe of the attenuation band of the current sensor 110. Thus, in the case where the amplitude characteristic of the high-frequency component of the detection current supplied from the coil 3 is higher than the amplitude characteristic of the low-frequency component, the amplitude characteristic of the current sensor 110 can be smoothed.

[0144] According to the present embodiment, the matching circuit 12 is configured using a plurality of passive elements so that the impedance on the terminal resistance side approaches the characteristic impedance of the transmission path 8 in a high frequency band above the cutoff frequency fc.

[0145] In this way, since the matching circuit 12 is composed of a plurality of passive elements, impedance matching can be achieved in a frequency band above the cutoff frequency, and noise generated from the matching circuit 12 itself can be reduced compared to a case where the matching circuit 12 is composed of active elements. Therefore, noise mixed into the detection current supplied from the coil 3 can be reduced, and waveform distortion of the detection signal output from the current sensor 110 can be suppressed.

[0146] In addition, according to this embodiment, if Figure 1 As shown, the matching circuit 12 includes a resistance element 121 and an induction element 122 connected in parallel to each other. As a result, the number of components of the matching circuit 12 can be reduced, and thus the configuration of the matching circuit 12 can be simplified.

[0147] According to the present embodiment, as shown in the above equation (2), the inductance value L of the inductive element 122 is set based on the lower limit frequency fe of the attenuation band, the characteristic impedance Z of the transmission path 8, the resistance value R1 of the resistor element 121, and the resistance value R2 of the terminal resistor.

[0148] Thus, the matching circuit 12 can be configured such that the impedance on the terminal resistance side approaches the value of the characteristic impedance of the transmission path 8 as the frequency component of the detection current supplied from the coil 3 approaches the lower limit frequency fe of the attenuation band of the current sensor 110 .

[0149] Furthermore, according to the present embodiment, the impedance matching unit 10 includes a starting resistor 11 connected to the starting end 8a of the transmission path 8 and connected in parallel with the coil 3. The matching circuit 12 is connected in series to the terminal 8b of the transmission path 8, and the resistance value of the starting resistor 11 is set to a value greater than the resistance value of the terminal resistor 9.

[0150] In this way, by arranging the matching circuit 12 on the terminal end 8b side of the transmission path 8, the distance between the coil 3 and the matching circuit 12 can be increased compared to the case where the matching circuit 12 is arranged on the starting end 8a side of the transmission path 8. Therefore, in the frequency characteristics of the matching circuit 12, an undesirable peak caused by the resonance between the parasitic capacitance of the coil 3 and the inductive element 122 of the matching circuit 12 can be made less likely to occur near the cutoff frequency.

[0151] In addition, by providing the starting resistor 11 at the starting end 8a of the transmission path 8, the detection current flowing through the terminal resistor 9 is reduced, so that the power consumed by the terminal resistor 9 can be reduced. Therefore, the heat generation of the terminal resistor 9 can be suppressed. Therefore, the necessity of implementing measures for the heat generation of the terminal resistor 9 is reduced, so the manufacturing cost of the current sensor 110 can be reduced.

[0152] Furthermore, by making the resistance value of the start-end resistor 11 larger than the resistance value of the terminal resistor 9, in the passband, the detection current flows more easily through the terminal resistor 9 than through the start-end resistor 11, thereby increasing the signal level of the detection voltage V2. Therefore, the S / N (signal / noise) ratio of the detection signal can be increased.

[0153] According to the present embodiment, the length of the transmission path 8 is set longer than a predetermined length at which reflection occurs based on the lower limit frequency of the attenuation band of the current sensor 110. Therefore, by using the matching circuit 12, reflection of the current sensor 110 in the attenuation band can be reliably suppressed.

[0154] According to the present embodiment, the matching circuit 12 is configured as a low-pass filter circuit. This can suppress waveform distortion of the detection signal and remove noise components in the attenuation band of the current sensor 110 as described above.

[0155] Furthermore, according to the present embodiment, the measuring device 100 includes the above-mentioned current sensor 110 and the measuring unit 120 for measuring the physical quantity related to the measuring circuit 1 based on the detection signal output from the current sensor 110. Thus, the waveform response of the measured current I1 flowing through the measuring circuit 1 can be measured with high accuracy, and the power consumption of the current sensor 110 can be suppressed.

[0156] (Second Embodiment)

[0157] It should be noted that, in the first embodiment, an example in which the matching circuit 12 is connected in series to the terminal 8b of the transmission path 8 is described, but the matching circuit 12 may be connected to the starting end 8a of the transmission path 8 in addition to or instead of this configuration. Fig. 9 A configuration in which the matching circuit 12 is connected to the start end 8 a side of the transmission path 8 will be briefly described.

[0158] Fig. 9 1 is a diagram showing a configuration of a measuring device 101 including a current sensor 111 according to the second embodiment. Here, for convenience of explanation, the transmission path 4, the capacitive load 5, the magneto-electric conversion output unit 6, and the voltage-current conversion unit 7 are omitted.

[0159] The matching circuit 12 of this embodiment is similar to Figure 1 Same as shown, but with Figure 1 The connection position is different from that shown in FIG. 1 , and it is connected to the starting end 8a of the transmission path 8. In addition, in the transmission circuit 21 constituting the current sensor 111 of this embodiment, instead of Figure 1 The start-end resistor 11 shown in the figure includes a start-end resistor 11a.

[0160] In the transmission circuit 21, the start resistor 11a is connected in series to the matching circuit 12 and connected in parallel with the coil 3 to the start end 8a of the transmission path 8. Specifically, one end of the start resistor 11a is connected to the output terminal 12b of the matching circuit 12 and the other end is connected to the grounding device G.

[0161] In this embodiment, the resistance value of the start resistor 11 a is set to 5Ω, and the resistance value of the terminal resistor 9 is set to 50Ω. That is, the resistance value of the start resistor 11 a is set to a value larger than the resistance value of the terminal resistor 9.

[0162] Thus, in the attenuation band of the current sensor 111, the resistance value of 5Ω of the head resistor 11a and the resistance value of 45Ω of the resistor element 121 constituting the matching circuit 12 are combined, so that the coil side impedance becomes 50Ω. That is, due to the matching circuit 12, the coil side inductance increases to the value of the characteristic impedance of the transmission path 8.

[0163] Therefore, the impedance of the terminal resistor and the inductance of the coil can be matched in the attenuation band of the current sensor 111. As a result, reflection is less likely to occur at the start end 8a of the transmission path 8, and waveform distortion of the detection signal caused by the current sensor 111 can be suppressed.

[0164] According to the second embodiment, the impedance matching unit 10a increases the coil side impedance to the value of the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 111. Thus, as in the first embodiment, an increase in the power consumed by the current sensor 111 in the passband of the current sensor 111 can be suppressed, and waveform distortion of the signal output from the current sensor 111 can be suppressed.

[0165] It should be noted that the measuring device 101 of the second embodiment may include the terminal resistor 9 with a resistance value of 5Ω and the matching circuit 12 in the first embodiment in addition to the impedance matching unit 10a. As a result, the impedance on the coil side and the impedance on the terminal resistor side can be increased to the value of the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 111.

[0166] Therefore, according to the above-described embodiments, the impedance matching units 10 and 10 a can increase at least one of the terminal resistance side impedance and the coil side impedance to the value of the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor 110 .

[0167] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate a part of application examples of the present invention and do not limit the technical scope of the present invention to the specific configurations of the above embodiments.

[0168] For example, in the present embodiment, the zero-flux type (magnetic balance type) current sensor 110 includes the transmission path 4 , the capacitive load 5 , the magneto-electric conversion output unit 6 , and the voltage-current conversion unit 7 , but the transmission path 4 may be omitted.

[0169] In addition, in the present embodiment, the matching circuit 12 performs impedance matching and operates as a low-pass filter, but the impedance matching function and the low-pass filter function may be realized by different circuits.

[0170] In addition, in this embodiment, the lower limit frequency fe of the attenuation band is set to the value of the frequency at which the amplitude of the passband is attenuated by 3 dB, but it is not limited to this. The lower limit frequency fe can also be the value of the frequency at which the amplitude of the passband starts to attenuate, or the value of the frequency attenuated by 1 dB.

[0171] In addition, in the present embodiment, the resistance value of the terminal resistor 9 is set to a value smaller than the characteristic impedance of the transmission path 8, but the resistance value of the terminal resistor 9 may be set to a value larger than the characteristic impedance of the transmission path 8. In this case, the inductive element (coil) or the series circuit formed by connecting the inductive element and the resistive element in series is connected in parallel with the terminal resistor 9, and the constant of the inductive element or the series circuit is set in such a way that the impedance of the resistive element side is close to the characteristic impedance of the transmission path 8 in the attenuation band. Alternatively, a resistive element having the same value as the characteristic impedance of the transmission path 8 is arranged in parallel with the terminal resistor 9, and when the frequency of the detection current is close to the vicinity of the attenuation band, a switch that switches the current path from the terminal resistor 9 to the resistive element is arranged at the connection portion between the terminal resistor 9 and the resistive element.

[0172] This makes it possible to reduce the impedance on the terminal resistance side to the characteristic impedance of the transmission path 8 in the attenuation band of the current sensor, and reduce the power consumption of the current sensor.

Claims

1. A current sensor for detecting a current flowing through a measurement object, the current sensor comprising: a magnetic core through which the object to be measured is inserted; A coil, wound around the magnetic core; a transmission path for transmitting the current supplied from the coil; a terminal resistor, one end of which is connected to the terminal of the transmission path and the other end of which is connected to a reference potential, the terminal resistor converting a current from the terminal of the transmission path into a voltage and outputting the voltage; as well as A matching unit, wherein the input end is connected to the starting end of the transmission path and the output end is connected to the reference potential via the starting end resistor, and / or the input end is connected to the terminal end of the transmission path and the output end is connected to one end of the terminal resistor, and the matching unit performs impedance matching. The matching unit has at least a resistance component and an inductance component connected in parallel to each other, and in a frequency band of a frequency component in which the amplitude of a frequency component of a voltage output from the terminal resistor is attenuated, the impedance observed when the terminal resistor side is observed from the terminal end of the transmission path and / or the impedance observed when the coil side is observed from the starting end of the transmission path is increased to the characteristic impedance of the transmission path.

2. The current sensor according to claim 1, wherein: The matching unit includes a matching circuit that makes an impedance observed when the terminal resistance side is viewed from the terminal end of the transmission path close to a characteristic impedance of the transmission path in a frequency band of the frequency component attenuated by the amplitude.

3. The current sensor according to claim 2, wherein: The resistance value of the terminal resistor is set to a predetermined value that is smaller than the characteristic impedance of the transmission path.

4. The current sensor according to claim 3, wherein: The resistance component of the matching circuit is set to a larger value as the predetermined value is smaller.

5. The current sensor according to any one of claims 2 to 4, wherein: The cutoff frequency of the matching circuit is set to a value lower than the lower limit frequency of the frequency band of the frequency component whose amplitude is attenuated.

6. The current sensor according to any one of claims 2 to 5, wherein: The matching circuit is formed using a plurality of passive elements so that in a frequency band above a cutoff frequency, an impedance observed when the terminal resistor side is viewed from the terminal end of the transmission path is close to a characteristic impedance of the transmission path. The plurality of passive elements are connected in such a manner that at least the resistance component and the inductance component are connected in parallel.

7. The current sensor according to any one of claims 2 to 6, wherein: The matching circuit includes a resistance element and an induction element connected in parallel with each other, The resistance element has the resistance component, The inductive element has the inductive component.

8. The current sensor according to claim 7, wherein: The inductance value of the inductive element is set based on the lower limit frequency of the frequency band of the frequency component of the amplitude attenuation, the characteristic impedance of the transmission path, the resistance value of the resistive element, and the resistance value of the terminal resistor.

9. The current sensor according to any one of claims 2 to 8, wherein: The matching unit includes a starting resistor connected in parallel with the coil at the starting end of the transmission path. In the matching unit, the input end is connected to the terminal of the transmission path and the output end is connected to one end of the terminal resistor. The matching circuit is connected in series to a terminal of the transmission path. The resistance value of the start-end resistor is set to be greater than the resistance value of the end resistor.

10. The current sensor according to any one of claims 2 to 9, wherein: The matching circuit includes a low-pass filter circuit.

11. A measuring device comprising: The current sensor according to any one of claims 1 to 10; and The measuring unit measures a physical quantity related to the measurement object based on the detection signal output from the current sensor.

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