Current Sensors

Abstract

The current sensor (100) of the present invention comprises: a magnetic core (101) that can be configured to surround a conductor (300) through which a current to be measured flows; a magnetic sensor (102) that detects magnetic flux inside the magnetic core (101); an amplifier (103) that amplifies the output of the magnetic sensor (102) and outputs a current corresponding to the output of the magnetic sensor (102); a feedback coil (104) that is wound around the magnetic core (101) and flows the current output by the amplifier (103) in a direction that cancels the magnetic flux; a shunt resistor (105) that is configured between the feedback coil (104) and the ground (33); a differential amplifier (110) that amplifies the voltage across the shunt resistor (105); a negative output terminal (100B) that outputs a reference potential of the differential amplifier (110); and a limiting resistor (116) that is configured between the negative output terminal (100B) and the ground (33).

Description

Technical Field

[0001] The present invention relates to a current sensor. Background Art

[0002] Conventionally, a zero flux type current sensor is known (for example, refer to Patent Document 1).

[0003] In a zero-flux current sensor, a current flows through a feedback coil wound around a magnetic core so as to cancel the magnetic flux generated in the magnetic core arranged around the current to be measured.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2006 / 129389 Summary of the invention

[0007] Problems to be solved by the invention

[0008] It is required to improve the accuracy of current measured by a current sensor in a zero-flux mode.

[0009] Therefore, an object of the present disclosure is to provide a current sensor capable of improving the accuracy of current measured by a zero-flux approach.

[0010] Solutions to Solve Problems

[0011] Several embodiments of the current sensor include: a magnetic core that can be configured to surround a conductor through which a current to be measured flows; a magnetic sensor that detects magnetic flux inside the magnetic core; an amplifier that amplifies the output of the magnetic sensor and outputs a current corresponding to the output of the magnetic sensor; a feedback coil that is wound around the magnetic core and through which the current output by the amplifier flows in a direction that cancels the magnetic flux; a shunt resistor that is configured between the feedback coil and ground; a differential amplifier that amplifies the voltage across the shunt resistor; a negative output terminal that outputs a reference potential of the differential amplifier; and a limiting resistor that is configured between the negative output terminal and the ground. According to such a current sensor, the accuracy of the current measured by the zero flux method can be improved.

[0012] In one embodiment of the current sensor, the current sensor may further include a ground voltage terminal connected to a ground voltage terminal of a measuring device that measures the current detected by the current sensor, thereby connecting the ground of the current sensor and the ground of the measuring device.

[0013] In one embodiment of the current sensor, the measuring device may include a measuring circuit and a power supply circuit, the negative output terminal is connected to a negative input terminal connected to an input on the negative side of the measuring circuit, and the ground voltage terminal of the measuring device is connected to the ground of the power supply circuit.

[0014] In the current sensor of one embodiment, the resistance value of the limiting resistor may be greater than the resistance value of the first wiring resistor, which is the wiring resistance of the wiring connecting the negative output terminal and the negative input terminal, and greater than the resistance value of the second wiring resistor, which is the wiring resistance of the wiring connecting the ground voltage terminal of the current sensor and the ground voltage terminal of the measuring device. In this way, since the resistance value of the limiting resistor is greater than the resistance value of the first wiring resistor and the resistance value of the second wiring resistor, the current flowing from the negative output terminal of the current sensor to the negative input terminal of the measuring device can be reduced, and the potential difference between the negative output terminal and the negative input terminal can be reduced.

[0015] Effects of the Invention

[0016] According to the present disclosure, a current sensor capable of improving the accuracy of current measured by a zero-flux method can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic configuration diagram showing a state where a current sensor according to an embodiment is connected to a measuring device.

[0018] Figure 2 This is a table showing an example of the relationship between limiting resistance and measurement error.

[0019] Figure 3 This is a graph showing an example of the relationship between limiting resistance and measurement error.

[0020] Figure 4 1 is a schematic configuration diagram showing a state where a current sensor according to a comparative example is connected to a measuring device. DETAILED DESCRIPTION

[0021] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0022] Figure 1 1 is a schematic diagram showing a state where a current sensor 100 according to an embodiment is connected to a measuring device 200. Figure 1 , the structure and function of the current sensor 100 are briefly described.

[0023] The current sensor 100 is a zero-flux current sensor and can detect the current to be measured flowing in the conductive wire 300 in a non-contact manner. The current sensor 100 is electrically connected to the measuring device 200 .

[0024] The measuring device 200 is a measuring device that measures the current detected by the current sensor 100. The measuring device 200 has a measuring circuit 210 and a power supply circuit 220.

[0025] The measurement circuit 210 is a circuit for measuring the current detected by the current sensor 100. The power supply circuit 220 is a circuit for supplying power to the current sensor 100.

[0026] The current sensor 100 includes a positive output terminal 100A, a negative output terminal 100B, a positive voltage input terminal 100C, a ground voltage terminal 100D, and a negative voltage input terminal 100E as terminals for electrical connection with the measuring device 200 .

[0027] The positive output terminal 100A is a terminal for outputting an output signal of a differential amplifier 110 described later. The negative output terminal 100B is a terminal for outputting a reference potential of the differential amplifier 110 described later. The positive voltage input terminal 100C is a terminal for receiving a supply of a positive voltage from a power supply circuit 220 of the measuring device 200. The ground voltage terminal 100D is a terminal connected to a ground of the power supply circuit 220 of the measuring device 200. The negative voltage input terminal 100E is a terminal for receiving a supply of a negative voltage from the power supply circuit 220 of the measuring device 200.

[0028] The measuring device 200 includes a positive input terminal 200A, a negative input terminal 200B, a positive voltage output terminal 200C, a ground voltage terminal 200D, and a negative voltage output terminal 200E as terminals for electrical connection with the current sensor 100 .

[0029] The positive input terminal 200A is a terminal for receiving an input of an output signal outputted from the differential amplifier 110 of the current sensor 100. The positive input terminal 200A is connected to the positive input of the measurement circuit 210. The negative input terminal 200B is a terminal for receiving an input of a reference potential of the differential amplifier 110 from the differential amplifier 110 of the current sensor 100. The negative input terminal 200B is connected to the negative input of the measurement circuit 210.

[0030] The positive voltage output terminal 200C is a terminal for supplying a positive voltage generated by the power supply circuit 220 to the current sensor 100. The ground voltage terminal 200D is a terminal connected to the ground of the power supply circuit 220. The negative voltage output terminal 200E is a terminal for supplying a negative voltage generated by the power supply circuit 220 to the current sensor 100.

[0031] like Figure 1 As shown, the negative input terminal 200B is short-circuited to the ground voltage terminal 200D within the measuring device 200 .

[0032] The positive output terminal 100A of the current sensor 100 is connected to the positive input terminal 200A of the measuring device 200 via a cable or other wiring. The negative output terminal 100B of the current sensor 100 is connected to the negative input terminal 200B of the measuring device 200 via a cable or other wiring. The positive voltage input terminal 100C of the current sensor 100 is connected to the positive voltage output terminal 200C of the measuring device 200 via a cable or other wiring. The ground voltage terminal 100D of the current sensor 100 is connected to the ground voltage terminal 200D of the measuring device 200 via a cable or other wiring. The negative voltage input terminal 100E of the current sensor 100 is connected to the negative voltage output terminal 200E of the measuring device 200 via a cable or other wiring.

[0033] The current sensor 100 includes a magnetic core 101 , a magnetic sensor 102 , an amplifier 103 , a feedback coil 104 , a shunt resistor 105 , a differential amplifier 110 , and a limiting resistor 116 .

[0034] The magnetic core 101 can be arranged to surround the conductor 300 through which the measured current flows. When the measured current flows through the conductor 300 , a magnetic field is generated around the measured current. When a magnetic field is generated around the measured current, magnetic flux is generated inside the magnetic core 101 .

[0035] The magnetic sensor 102 is arranged at a position where it can be magnetically coupled with the magnetic core 101. The magnetic sensor 102 detects the magnetic flux generated inside the magnetic core 101. The magnetic sensor 102 outputs a signal corresponding to the detected magnetic flux. The magnetic sensor 102 can output the signal corresponding to the detected magnetic flux as a voltage or as a current. The magnetic sensor 102 can also be a magnetic sensor of any type. The magnetic sensor 102 can also be, for example, a fluxgate element, a Hall element, etc.

[0036] The amplifier 103 amplifies the signal output by the magnetic sensor 102 and outputs a current corresponding to the output of the magnetic sensor 102. The current output by the amplifier 103 flows through the feedback coil 104. The amplifier 103 is connected to the positive power supply 31 and the negative power supply 32. The positive power supply 31 is connected to the positive voltage input terminal 100C. The negative power supply 32 is connected to the negative voltage input terminal 100E.

[0037] The current output from the amplifier 103 is supplied from the positive power supply 31 or the negative power supply 32. Whether the current output from the amplifier 103 is supplied from the positive power supply 31 or the negative power supply 32 depends on the direction of the current output from the amplifier 103. Figure 1 The current I is supplied from the positive power supply 31 to the amplifier 103.S , the amplifier 103 output current I S situation.

[0038] The feedback coil 104 is wound and arranged on the magnetic core 101. When a current flows through the feedback coil 104, the feedback coil 104 generates a magnetic field inside the feedback coil 104. As a result, the feedback coil 104 generates a magnetic flux inside the magnetic core 101. The feedback coil 104 allows the current output by the amplifier 103 to flow in a direction that cancels the magnetic flux generated by the magnetic core 101 in the magnetic core 101 in response to the current to be measured. That is, the feedback coil 104 is wound in a direction that cancels the magnetic flux generated by the magnetic core 101 in response to the current to be measured.

[0039] The magnetic flux generated by the magnetic core 101 in response to the current to be measured is cancelled out by the magnetic field generated by the feedback coil 104 , so that the magnetic flux inside the magnetic core 101 becomes substantially zero.

[0040] The shunt resistor 105 is disposed between the feedback coil 104 and the ground 33. The ground 33 is the ground of the current sensor 100. One end of the shunt resistor 105 is electrically connected to the feedback coil 104. In addition, the other end of the shunt resistor 105 is electrically connected to the ground 33.

[0041] The current output by the amplifier 103 and flowing through the feedback coil 104 and the shunt resistor 105 flows into the ground 33 .

[0042] The current flowing in the feedback coil 104 is a current for canceling the magnetic flux generated by the magnetic core 101 inside the magnetic core 101 according to the current to be measured, so it is proportional to the current to be measured. Therefore, the current flowing in the shunt resistor 105 is proportional to the current to be measured. The voltage across the shunt resistor 105 is proportional to the current flowing in the shunt resistor 105, so the voltage across the shunt resistor 105 is proportional to the current to be measured.

[0043] Thus, by measuring the voltage across the shunt resistor 105, the value of the current to be measured flowing in the conductor 300 can be measured. Due to such a structure, the current sensor 100 is a zero-flux current sensor. As a zero-flux current sensor 100, regardless of whether the current to be measured is direct current or alternating current, the value of the current to be measured can be measured with high accuracy without contacting the current to be measured.

[0044] The differential amplifier 110 amplifies and outputs a voltage difference between voltages at both ends of the shunt resistor 105. The differential amplifier 110 includes an input terminal 110A, an input terminal 110B, an output terminal 110C, and a reference terminal 110D.

[0045] Input terminal 110A is electrically connected to one end of shunt resistor 105. Input terminal 110B is electrically connected to the other end of shunt resistor 105. Output terminal 110C is electrically connected to positive output terminal 100A. Reference terminal 110D is electrically connected to ground 33 via limiting resistor 116. Limiting resistor 116 is electrically connected to negative output terminal 100B.

[0046] The differential amplifier 110 amplifies the voltage difference between the input terminal 110A and the input terminal 110B, and outputs the amplified signal to the output terminal 110C. The reference terminal 110D outputs the reference potential of the differential amplifier 110. That is, the output signal of the differential amplifier 110 output from the output terminal 110C is a signal based on the reference potential provided by the reference terminal 110D.

[0047] In addition, although the input terminal 110A, the input terminal 110B, the output terminal 110C, and the reference terminal 110D are named “terminals”, they may be simple wirings that do not have a terminal-like structure.

[0048] The differential amplifier 110 includes a first resistor 111 , a second resistor 112 , a third resistor 113 , a fourth resistor 114 , and an operational amplifier 115 .

[0049] One end of the first resistor 111 is electrically connected to the input terminal 110A. The other end of the first resistor 111 is electrically connected to the inverting input terminal of the operational amplifier 115 and the second resistor 112 .

[0050] One end of the second resistor 112 is electrically connected to the inverting input terminal of the operational amplifier 115 and the first resistor 111. The other end of the second resistor 112 is electrically connected to the output terminal 110C.

[0051] One end of the third resistor 113 is electrically connected to the input terminal 110B. The other end of the third resistor 113 is electrically connected to the non-inverting input terminal of the operational amplifier 115 and the fourth resistor 114 .

[0052] One end of the fourth resistor 114 is electrically connected to the non-inverting input terminal of the operational amplifier 115 and the third resistor 113. The other end of the fourth resistor 114 is electrically connected to the reference terminal 110D.

[0053] With such a configuration, the differential amplifier 110 can output to the positive output terminal 100A a voltage corresponding to the current flowing through the shunt resistor 105. At this time, the reference potential of the signal output from the positive output terminal 100A by the differential amplifier 110 is output from the negative output terminal 100B.

[0054] The structure of the differential amplifier 110 is not limited to Figure 1The differential amplifier 110 may also be a differential amplifier with other structures.

[0055] The limiting resistor 116 is disposed between the reference terminal 110D and the ground 33 . One end of the limiting resistor 116 is electrically connected to the reference terminal 110D. One end of the limiting resistor 116 is also electrically connected to the negative output terminal 100B via the reference terminal 110D. The other end of the limiting resistor 116 is electrically connected to the ground 33 .

[0056] Next, refer to Figure 1 The flow of current in the current sensor 100 will be described.

[0057] The current I flowing in the feedback coil 104 of the amplifier 103 S The current is supplied by the power supply circuit 220 of the measuring device 200. The current supplied by the power supply circuit 220 is supplied to the amplifier 103 via the positive voltage output terminal 200C, the positive voltage input terminal 100C, and the positive power supply 31. The amplifier 103 outputs the current supplied by the power supply circuit 220.

[0058] The current I output by the amplifier 103 S The current flows into the ground 33 via the feedback coil 104 and the shunt resistor 105 .

[0059] The current I supplied from the power supply circuit 220 of the measuring device 200 and flowing into the ground 33 of the current sensor 100 S , returns to the ground of the power supply circuit 220 through two paths.

[0060] The first path is a path that returns to the ground of the power supply circuit 220 via the limiting resistor 116, the reference terminal 110D, the negative output terminal 100B, the first wiring resistor 10, and the negative input terminal 200B. Here, the first wiring resistor 10 is the resistance of the wiring connecting the negative output terminal 100B and the negative input terminal 200B. The wiring connecting the negative output terminal 100B and the negative input terminal 200B can be, for example, a cable. Assume that in the first path, the current I P flow.

[0061] The second path is a path that returns to the ground of the power supply circuit 220 via the ground voltage terminal 100D, the second wiring resistor 20, and the ground voltage terminal 200D. Here, the second wiring resistor 20 is the resistance of the wiring connecting the ground voltage terminal 100D and the ground voltage terminal 200D. The wiring connecting the ground voltage terminal 100D and the ground voltage terminal 200D may be, for example, a cable. Assume that in the second path, the current I R flow.

[0062] The current I supplied by the power supply circuit 220 to the amplifier 103 SThe current I supplied by the power supply circuit 220 to the amplifier 103 returns to the ground of the power supply circuit 220 through two paths, the first path and the second path. S , the current I flowing in the first path P , the current I flowing in the second path R The following relationship holds.

[0063] I S =I P +I R

[0064] The resistance value of the first path is the sum of the resistance value of the limiting resistor 116 and the resistance value of the first wiring resistor 10. The resistance value of the second path is the resistance value of the second wiring resistor 20. Here, the resistance value of the limiting resistor 116 is a value sufficiently larger than the resistance value of the first wiring resistor 10 and the resistance value of the second wiring resistor 20.

[0065] Since the first wiring resistor 10 and the second wiring resistor 20 are wiring resistors such as cables, their resistance values ​​are, for example, several tens of mΩ. The limiting resistor 116 is a resistor having a resistance value sufficiently larger than these resistors. The limiting resistor 116 may be, for example, a chip resistor.

[0066] Since the resistance value of the limiting resistor 116 is sufficiently larger than the resistance value of the first wiring resistor 10 and the resistance value of the second wiring resistor 20, the resistance value of the first path is also larger than the resistance value of the second path. As a result, the current I supplied by the power supply circuit 220 is S Basically, the current I flowing in the first path returns to the ground of the power supply circuit 220 through the second path. P becomes a very small current.

[0067] If the current I flowing in the first path P As the voltage decreases, the potential difference between the negative output terminal 100B and the negative input terminal 200B decreases. As a result, the measurement error when the measurement circuit 210 measures the measured current detected by the current sensor 100 is reduced. This is because the output signal output from the positive output terminal 100A by the differential amplifier 110 is a signal based on the potential of the negative output terminal 100B, and the measurement circuit 210 measures the signal input to the positive input terminal 200A based on the potential of the negative input terminal 200B.

[0068] (Calculation example of measurement error)

[0069] exist Figure 2 as well as Figure 3 , an example of calculating the relationship between the resistance value of the limiting resistor 116 and the measurement error is shown. Figure 2 The calculation results are shown in a table. Figure 3 The calculation results are shown as a graph.

[0070] Figure 2 as well as Figure 3 The results shown are calculated based on the following conditions.

[0071] <Conditions>

[0072] Shunt resistance 105 = 2.5Ω

[0073] First resistor 111 = 10 kΩ

[0074] Second resistor 112 = 40 kΩ

[0075] The third resistor 113 = 10 kΩ

[0076] Fourth resistor 114 = 40 kΩ

[0077] Operational amplifier 115 is an ideal operational amplifier

[0078] 1st wiring resistance 10 = 20 mΩ

[0079] Second wiring resistance 20 = 60 mΩ

[0080] I S =400mA

[0081] like Figure 2 as well as Figure 3 As shown, the measurement error is inversely proportional to the resistance value of the limiting resistor 116. Therefore, as the resistance value of the limiting resistor 116 increases, the measurement error decreases. However, as the resistance value of the limiting resistor 116 increases, the reduction of the measurement error becomes slow.

[0082] When there is a target value of the measurement error, the resistance value of the limiting resistor 116 may be set to a resistance value that can achieve the target value of the measurement error.

[0083] If the resistance value of the limiting resistor 116 is excessively increased, the risk of the differential amplifier 110 being affected by the noise increases. Therefore, it is desirable that the resistance value of the limiting resistor 116 is not increased more than necessary. The resistance value of the limiting resistor 116 is preferably about several ohms, for example.

[0084] The limiting resistor 116 does not need to be a high-precision resistor like the first resistor 111, the second resistor 112, the third resistor 113, and the fourth resistor 114. In addition, the limiting resistor 116 only needs to have a small resistance value of about several Ω, and since the current flowing through it is also small, it can be a general-purpose small resistor. In other words, the limiting resistor 116 can be a cheap and small resistor.

[0085] (Comparative Example)

[0086] Figure 4 4 shows a current sensor 400 of a comparative example. The current sensor 400 of the comparative example does not have Figure 1 The current sensor 100 shown in FIG. 1 has a limiting resistor 116. Figure 1 The current sensor 100 shown is different.

[0087] The fourth resistor 114 of the differential amplifier 410 of the current sensor 400 of the comparative example is not connected via Figure 1 The limiting resistor 116 as shown is connected directly to ground 33.

[0088] Therefore, in Figure 4 When the measured current flowing in the conductor 300 is measured in the structure shown, the resistance value of the first path is the resistance value of the first wiring resistor 10. In addition, the resistance value of the second path is the resistance value of the second wiring resistor 20. That is, the resistance value of the first path is substantially the same as the resistance value of the second path.

[0089] Therefore, in the structure of the comparative example, the current I flowing in the first path P The current I flowing in the second path R The current I flowing in the first path is approximately the same as P This is approximately half of the current supplied by the power supply circuit 220 to the current sensor 400 .

[0090] In the comparative example, since such a large current flows in the first path, the potential difference between the negative output terminal 100B and the negative input terminal 200B becomes large. That is, the difference between the potential of the negative output terminal 100B used as a reference for output by the differential amplifier 110 and the potential of the negative input terminal 200B used as a reference for measurement by the measurement circuit 210 becomes large, so the measurement error of the measurement performed by the measurement circuit 210 becomes large.

[0091] The current sensor 100 of the present embodiment includes the limiting resistor 116 , and thus can reduce the measurement error compared to the current sensor 400 of the comparative example.

[0092] According to the current sensor 100 of one embodiment as described above, the accuracy of the current measured by the zero flux method can be improved. More specifically, the current sensor 100 is a zero flux method current sensor, which has: a magnetic core 101 that can be configured to surround the conductor 300 where the measured current flows; a magnetic sensor 102 that detects the magnetic flux inside the magnetic core 101; an amplifier 103 that amplifies the output of the magnetic sensor 102 and outputs a current corresponding to the output of the magnetic sensor 102; a feedback coil 104 that is wound around the magnetic core 101 and flows the current output by the amplifier 103 in a direction that cancels the magnetic flux; a shunt resistor 105 that is configured between the feedback coil 104 and the ground 33; and a differential amplifier 110 that amplifies the voltage across the shunt resistor 105. Since the current sensor 100 has a limiting resistor 116 arranged between the negative output terminal 100B and the ground 33, the current flowing from the negative output terminal 100B to the negative input terminal 200B can be reduced, and the potential difference between the negative output terminal 100B and the negative input terminal 200B can be reduced, so the error when the measuring device 200 measures the current detected by the current sensor 100 can be reduced.

[0093] In the current sensor 100, since the limiting resistor 116 can be a general-purpose resistor element, the error in measuring current can be reduced at low cost. In addition, since the limiting resistor 116 can be a chip resistor, for example, the limiting resistor 116 can be introduced into a small packaging space.

[0094] As those skilled in the art will appreciate, the present disclosure may be implemented in other prescribed ways other than the above-described embodiments without departing from its spirit or its essential features. Therefore, the previous description is illustrative and not limited thereto. The scope of the disclosure is defined not by the previous description but by the appended claims. Several changes within the scope of their equivalence are included in all changes.

[0095] For example, the arrangement and number of the above-mentioned components are not limited to the contents of the above-mentioned description and the drawings, and the arrangement and number of the above-mentioned components can be arbitrarily configured as long as the functions can be achieved.

[0096] In the above-mentioned embodiment, the case where the power supply circuit 220 supplies current to the positive power supply 31 of the current sensor 100 via the positive voltage output terminal 200C and the positive voltage input terminal 100C is cited as an example for explanation, but there is also a case where the power supply circuit 220 supplies current to the negative power supply 32 of the current sensor 100 via the negative voltage output terminal 200E and the negative voltage input terminal 100E.

[0097] Description of symbols

[0098] 101st wiring resistance

[0099] 20 2nd wiring resistance

[0100] 31 Positive power supply

[0101] 32 Negative power supply

[0102] 33 land

[0103] 100 Current Sensor

[0104] 100A positive output terminal

[0105] 100B negative output terminal

[0106] 100C positive voltage input terminal

[0107] 100D ground voltage terminal

[0108] 100E negative voltage input terminal

[0109] 101 core

[0110] 102 Magnetic Sensor

[0111] 103 Amplifier

[0112] 104 Feedback coil

[0113] 105 Shunt Resistor

[0114] 110 Differential Amplifier

[0115] 110A input terminal

[0116] 110B input terminal

[0117] 110C output terminal

[0118] 110D reference terminal

[0119] 111 No.1 resistor

[0120] 112 2nd resistor

[0121] 113 3rd resistor

[0122] 114 4th resistor

[0123] 115 Operational Amplifier

[0124] 116 limiting resistor

[0125] 200 measuring devices

[0126] 200A positive input terminal

[0127] 200B negative input terminal

[0128] 200C positive voltage output terminal

[0129] 200D ground voltage terminal

[0130] 200E negative voltage output terminal

[0131] 210 Measurement circuit

[0132] 220 power supply circuit

[0133] 300 wire

[0134] 400 Current Sensor

[0135] 410 Differential Amplifier

Claims

1. A current sensor, comprising: A magnetic core that can be configured to surround a conductor through which a current to be measured flows; A magnetic sensor for detecting the magnetic flux inside the magnetic core; an amplifier, amplifying the output of the magnetic sensor and outputting a current corresponding to the output of the magnetic sensor; A feedback coil, wound around the magnetic core, for flowing the current output by the amplifier in a direction to cancel the magnetic flux; A shunt resistor is arranged between the feedback coil and ground; A differential amplifier amplifies the voltage across the shunt resistor; A negative output terminal, outputting a reference potential of the differential amplifier; a limiting resistor, arranged between the negative output terminal and the ground; as well as Ground voltage terminal, The measuring device for measuring the current detected by the current sensor comprises a measuring circuit and a power supply circuit. The negative output terminal is connected to a negative input terminal connected to an input on a negative side of the measurement circuit through wiring, The ground voltage terminal is connected to a ground voltage terminal of the measuring device connected to the ground of the power supply circuit through wiring, The negative input terminal is short-circuited to the ground voltage terminal of the measuring device inside the measuring device.

2. The current sensor according to claim 1, wherein: The resistance value of the limiting resistor is greater than the resistance value of the first wiring resistor, which is the wiring resistance of the wiring connecting the negative output terminal and the negative input terminal, and is greater than the resistance value of the second wiring resistor, wherein the first wiring resistor is the wiring resistance of the wiring connecting the ground voltage terminal of the current sensor and the ground voltage terminal of the measuring device.

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