JP4630401B2 - Current sensor and current detection method - Google Patents

Description

  The present invention relates to a current sensor that is used by scanning the surface of the device or equipment to detect the current flowing on the surface of the device or equipment, and a current detection method using the current sensor.

It is common practice to measure the conductor current by providing a magnetic sensor at a fixed position relative to the conductor.
That is, in (b) of FIG. 11, a is a conductor, s is a magnetic sensor disposed at a distance r from the conductor, a conductor current is I, and a magnetic field measured by the magnetic sensor is H. 2πrH = I is established, and the conductor current can be obtained from the measurement magnetic field H.
Recently, a magneto-impedance effect type magnetic sensor using a magneto-impedance effect element has been developed as a high-sensitivity and high-precision magnetic field sensor, and it has also been proposed to use a magneto-impedance effect type magnetic sensor as a magnetic sensor to measure current. (For example, Patent Documents 1 to 3).
Japanese Patent Laid-Open No. 2002-243766 Japanese Patent Application Laid-Open No. 2002-286664 Japanese Patent Laid-Open No. 2004-132790

The magneto-impedance effect element itself exhibits a magnetosensitive characteristic as shown in FIG. 2 (a) (Hex is an axial magnetic field, Eout is an output), and is non-linear and symmetric. In order to make this characteristic linearly distinguishable and linear as shown in (d) of FIG. 2, it is known to apply a negative magnetic field and a negative feedback, for example. It has also been proposed to measure current using a magnetic sensor (for example, Patent Document 3).
In order to measure the conductor current, it has also been proposed to measure the current using two linearly distinguishable and linear magneto-impedance effect type magnetic sensors (for example, Patent Documents 1 and 2).
In (b) of FIG. 11, a indicates a conductor. S and S ′ are magneto-impedance effect type magnetic sensors capable of discriminating polarities arranged at the same distance r from the conductor a and at an angle of 2θ between them. The orientation is such that the direction is the magnetosensitive direction.
In (b) of FIG. 11, the magnetic field Hy that each magnetoimpedance effect type magnetic sensor senses has the same absolute value and the opposite polarity.
│Hy│ = Isinθ / 2πr
Given in.
Therefore, if the outputs of both magnetic sensors are differentially amplified, a detection output proportional to 2 | Hy | is obtained, and the conductor current I can be measured from this detection value.

When detecting a current flowing on a surface such as a current flowing through a complicated conductor circuit on a printed wiring board or a leakage current flowing through the surface of an insulator, the current flows in any path because the conductor circuit is complex. Often it is uncertain.
The current measurement method described above is based on the premise that the relative positional relationship between the current path and the magneto-impedance effect type magnetic sensor is known, and is not suitable for current detection and measurement in this case.
When applied strongly, since the leakage current is weak, even if the current I is small, in order to sufficiently increase | Hy | = Isinθ / 2πr, that is, in order to guarantee high sensitivity, θ should be increased. Both magneto-impedance effect type magnetic sensors need to be disposed, and the overall size of the sensor cannot be avoided.

  An object of the present invention is to provide a current sensor that can detect a current flowing on a surface with high accuracy using a magneto-impedance effect element.

The current sensor according to claim 1 is a sensor that scans the surface of the equipment or facility in order to detect a current flowing through the surface of the equipment or facility. Each of the demodulating circuits for detecting the outputs of the series connected elements of the magneto-impedance effect element group in one of the magnetic sensing directions and the magneto-impedance effect element group in the other magnetic sensing direction of the plurality of sets and the demodulation thereof A differential amplifier for differentially amplifying the detection output of the circuit, and using the offset of the output of the differential amplifier as an input signal, a compensation signal for canceling the offset is generated, and the compensation signal is supplied to the amplifier A correction circuit that is added as an input for erasing the image is provided.
The current sensor according to claim 2 is characterized in that, in the current sensor according to claim 1 , means for generating a compensation output when the offset of the amplifier or differential amplifier output reaches a predetermined value is added to the correction circuit. And
According to a third aspect of the present invention, there is provided the current sensor according to the second aspect , further comprising means for multiplying the offset of the amplifier or differential amplifier output by n (n> 1) and inputting the result to the correction circuit.
Detection method of a current according to claim 4, claims 1 to 3 What Re of the current sensor is moved across the object to be detected current path, from the left and right symmetry of sandwiching the object to be detected current path of the sensor output It is characterized by detecting current.

The position where the current flows is detected from the left-right symmetry of the magnetic distribution obtained by moving the magneto-impedance effect sensor. Thus, the external noise such as the geomagnetic component passing through the magneto-impedance effect element hardly changes depending on the location, and the left-right symmetry of the magnetic distribution can be maintained even when exposed to the external noise. Also, internal noise generated due to temperature changes of circuit elements such as excitation power supply circuits and diodes of each detection circuit is in phase with the differential amplification and is canceled by using the differential magnetic sensor. Further, even if the output of the differential amplifier is about to be offset, the offset is automatically erased by the adjustment circuit, and even if the temperature or the floating capacitance fluctuates during the movement of the current sensor, it does not appear as a detection output fluctuation.
Therefore, the high detection function of the magnetic sensor using the magneto-impedance effect element can be effectively exerted by eliminating the influence of internal and external noise, and the current flowing can be detected with high accuracy and stability.
Furthermore, with respect to (b) of FIG. 11, both magneto-impedance effect elements are oriented at a right angle to the radial direction centered on the conductor with the mutual angle θ being 0, so that they can be disposed at substantially the same position. Can be miniaturized.

FIG. 1 shows a basic configuration of a magnetic sensor using a magneto-impedance effect element.
In FIG. 1, reference numeral 1 denotes a magneto-impedance effect element, which has a zero magnetostriction or a negative magnetostriction having an outer shell portion in which magnetic domains whose spontaneous magnetization directions are opposite to each other in the circumferential direction of the wire are alternately separated by domain walls. Amorphous alloy wire is used. The inductance voltage component in the output voltage between both ends of the wire generated when a high-frequency excitation current is passed through an amorphous magnetic wire having zero magnetostriction or negative magnetostriction is obtained by the circumferential magnetic flux generated in the cross section of the wire. This occurs due to the magnetization of the easily magnetizable outer shell in the circumferential direction. Therefore, the circumferential magnetic permeability mu _theta depends on the circumferential direction of magnetization of Dosotokara portion. Therefore, when a detected magnetic field is applied in the axial direction of the amorphous wire being energized, the circumferential magnetic flux and the detected magnetic field magnetic flux generated by the energization are combined to generate an externally magnetizable external material. shift direction of the magnetic flux acting on the shell from the circumferential direction, correspondingly hardly occur magnetization in the circumferential direction, the circumferential permeability mu _theta changes, the inductance voltage content will vary. This fluctuation phenomenon is called a magnetic inductance effect, which can be said to be a phenomenon in which the high-frequency excitation current (carrier wave) is modulated by a detected wave (signal wave). Further, when the frequency of the energization current is in the order of MHz, a high-frequency skin effect appears greatly, and the skin depth δ = (2ρ / wμ _θ ) ^1/2 (μ _θ is the circumferential permeability, ρ as described above. electrical resistivity, w is shows the angular frequency, respectively) is changed by mu _theta, as the mu _theta is the so changed by the detected magnetic field, the resistance voltage division also be detected magnetic field in the wire between both ends output voltage It will fluctuate with. This fluctuation phenomenon is called a magneto-impedance effect, which can be said to be a phenomenon in which the high-frequency excitation current (carrier wave) is modulated by a detected wave (signal wave).

  In FIG. 1, 2 is a high-frequency power source for applying a high-frequency excitation current to the magneto-impedance effect element, and 3 is a modulation of the high-frequency excitation current (carrier wave) by a detected magnetic field (signal wave) acting in the axial direction of the magneto-impedance effect element. Demodulator circuit for demodulating the modulated wave thus generated, 4 an amplifier circuit for amplifying the demodulated wave, 5 an output terminal, 6 a negative feedback coil, and 7 a bias magnetic field coil.

In the magneto-impedance effect element 1, as described above, the direction of the magnetic flux acting on the outer shell portion that is easily magnetized in the circumferential direction by combining the circumferential magnetic flux based on the excitation current and the axial magnetic flux due to the detected magnetic field. Is shifted from the circumferential direction, the circumferential permeability μ _θ is changed, the inductance is changed, and the impedance is changed by the change of the skin depth of the high frequency skin effect of the circumferential permeability μ _θ . Accordingly, although even the circumferential direction positional shift phi by the synthesized magnetic field by ± of the detected magnetic field becomes ± phi, the circumferential direction of the magnetic field reduction ratio cos (± phi) is unchanged, the degree of reduction in thus mu _theta is of the detected magnetic field It does not change depending on the direction. Accordingly, the detected magnetic field-output characteristics are substantially bilaterally symmetrical with respect to the y axis when the detected magnetic field is taken on the x axis and the output is taken on the y axis as shown in FIG. This detected magnetic field-output characteristic is non-linear. With non-linear characteristics, it is difficult to measure with high sensitivity. Therefore, negative feedback is applied by a negative feedback coil to linearize the output characteristics as shown in FIG. In FIG. 2B, Δw is a linear range in which the gain A without negative feedback is very large and the gain is determined only by the feedback rate β. However, since the polarity of the detected magnetic field cannot be determined with this output characteristic, the bias magnetic field is applied by the bias coil 7 so that the polarity can be determined as shown in FIG. That is, the characteristic of (b) in FIG. 2 is moved in the negative direction of the x-axis by the bias magnetic field, and the maximum range −Hmax to + Hmax of the detected magnetic field is within the range of the single oblique line region. Further, as shown in FIG. 2 (d), a linear characteristic passing through the origin is obtained by adjusting the zero point. Therefore, in FIG. 2D, when the detected magnetic field is + He, the output is + Eo, and when the detected magnetic field is -He, the output is -Eo, and the detected magnetic field can be accurately measured based on polarity discrimination. .
As can be understood from FIG. 2D, when the magnetosensitive effect direction of the magneto-impedance effect element is reversed, the output has a reverse polarity.

As the magneto-impedance effect element, an alloy of transition metal and non-metal having a non-metal composition of 10 to 30 atomic%, particularly an alloy of transition metal and non-metal occupying a non-metal amount of 10 to 30 atomic%, A composition in which the transition metal is Fe and Co and the nonmetal is B and Si or the transition metal is Fe and the nonmetal is B and Si can be used. For example, the composition Co _70.5 B ₁₅ Si ₁₀ Fe _4.5 , length 2000 μm to 6000 μm, outer diameter 30 μm to 50 μmφ can be used. For the magneto-impedance effect element 1, an amorphous ribbon, an amorphous sputtered film, or the like can be used in addition to an amorphous wire having zero magnetostriction or negative magnetostriction.

  In the above, normal high frequency such as continuous sine wave, pulse wave, triangular wave, etc. can be used as the high frequency excitation current, and examples of the high frequency excitation current source include Hartley oscillation circuit, Colpitts oscillation circuit, collector tuned oscillation circuit, base tuning In addition to a normal oscillation circuit such as an oscillation circuit, a square wave generator that integrates the square wave output of a crystal oscillator via a DC component cut-off capacitor with an integration circuit and amplifies the triangular wave of this integration output with an amplification circuit, and oscillates a CMOS-IC The triangular wave generator etc. which were used as a part can be used.

The demodulating circuit includes, for example, a configuration in which a modulated wave is half-wave rectified by an operational amplifier circuit, and this half-wave rectified wave is processed by a parallel RC circuit or an RC low-pass filter to obtain an envelope output of the half-wave rectified wave. A configuration in which the modulated wave is half-wave rectified by a diode and the half-wave rectified wave is processed by a parallel RC circuit or an RC low-pass filter to obtain an envelope output of the half-wave rectified wave can be used. Further, it is possible to use tuning detection in which a signal wave is sampled by multiplying the modulated wave by a square wave having a frequency fs tuned to the modulated wave (frequency fs).
In the above-described embodiment, the detected magnetic field is extracted by demodulating the modulated wave. However, the present invention is not limited to this, and a high-frequency excitation current wave modulated by the detected magnetic field (signal wave) acting on the magneto-impedance effect element ( An appropriate detection means can be used since the detected magnetic field can be detected from a carrier wave.

The negative feedback coil and the bias magnetic field coil can be wound around a magneto-impedance effect element. Further, as shown in FIG. 3, a negative feedback coil and a bias magnetic field coil can be wound around an iron core constituting a magneto-impedance effect element and a loop magnetic circuit. 3A is a side view showing an example of a magnetic impedance effect unit with an iron core, FIG. 3B is a bottom view, and FIG. 3C is a cross-sectional view of FIG. FIG.
In FIG. 3, reference numeral 100 denotes a substrate chip, and for example, a ceramic plate can be used. Reference numeral 101 denotes an electrode provided on one side of the substrate piece, and includes a magneto-impedance effect element connecting projection 102. This electrode can be provided by printing and baking a conductive paste, for example, a silver paste. 1x is a magneto-impedance effect element connected between the protrusions 102 and 102 of the electrodes 101 and 101 by soldering or welding, and an amorphous wire, amorphous ribbon, sputtered film, or the like having zero or negative magnetostriction can be used as described above. 103 is a C-type iron core, 6x is a negative feedback coil wound around the C-type iron core, 7x is also a bias magnetic field coil, and the magneto-impedance effect element 1x and the C-type iron core 103 constitute a loop magnetic circuit. Thus, both ends of the C-shaped iron core 103 are fixed to the other surface of the substrate piece 100 with an adhesive or the like. The iron core material may be a magnetic material having a small residual magnetic flux density. Examples thereof include permalloy, ferrite, iron, amorphous magnetic alloy, magnetic powder mixed plastic, and the like.

FIG. 4 shows a circuit diagram of a reference example of the current sensor.
In FIG. 4, reference numerals 1a and 1b denote magneto-impedance effect elements, which are arranged in parallel in close proximity with their magnetic sensing directions being opposite to each other. Reference numeral 2 denotes a high-frequency excitation power source for supplying an excitation current to the magneto-impedance effect element. Reference numerals 3a and 3b denote demodulator circuits connected to the output terminals of the magneto-impedance effect elements 1a and 1b, and reference numeral 40 denotes an operational differential amplifier circuit connected to the output terminals of the demodulator circuits 3a and 3b. Reference numeral 60 denotes a negative feedback circuit for negatively feeding back the amplified output to the magneto-impedance effect elements 1a and 1b to obtain linear output characteristics. Reference numerals 6a and 6b denote negative feedback coils. Reference numerals 7a and 7b denote bias magnetic field coils for applying a bias magnetic field to the magneto-impedance effect elements 1a and 1b so that the polarity of the output characteristics can be discriminated, and a + Vcc power source is used as a magnetomotive force. This + Vcc power source is also used as a power source for the exciting current source circuit 2.

In FIG. 4, if the magnetic field to be detected acting on the magneto-impedance effect elements 1a and 1b in the close array is H, the detection outputs become H and -H because the magnetosensitive directions are opposite to each other, and the differential amplification output E Is k [H − (− H)] (k is an amplification gain), that is, [Equation 1] E = 2 kH
Given in.

Figure 5 (b) is a plan view illustrating a current sensing method according to claim 5, (b) in FIG. 5 B in (b) of FIG. 5 - shows a B cross-sectional view.
As shown in (b) of FIG. 5, there is a conductor c below the surface, and current is flowing through the conductor c. As shown by the arrow lines in (a) and (b) of FIG. The current sensor is moved in the direction of the axis nn of both magneto-impedance effect elements 1a and 1b.
If the angle between the moving direction nn and the conductor c is α, the conductor current is I, the distance from the point p directly above the conductor to the element center position is x, and the distance from the surface to the conductor center is h, the proximity magneto-impedance effect element 1a, the magnetic field component H which acts in the axial direction of 1b is, r = ^[x 2 + ^{h 2] 1/2,} as sinθ = h / r, H = Isinα · sinθ / (2πr) than H = HIsinarufa / {2π [x ² + h ² ]}
Given in.
Therefore, the differential amplification output E = 2 kH of [Equation 1] is
E = (hIksin α / π) · 1 / [x ² + h ² ]
As shown in FIG. 6, the pattern is symmetrical with respect to the conductor c. Therefore, the position immediately above the current conductor can be known by detecting the maximum peak point.
In this case, the common mode noise generated by the characteristic change of the circuit elements of both the demodulating circuits 3a and 3b, for example, the diode temperature or the characteristic change of the excitation power supply circuit is in-phase, and can be canceled by differential amplification. The influence can be eliminated well. Further, since external noise such as geomagnetism is almost constant without changing even if the position is changed, the output shown in FIG. 6 is only shifted in the y-axis direction, and left-right symmetry is maintained. The effect of external noise can be eliminated well. Furthermore, even if the current value I is small or the depth h below the ground surface of the conductor is large, it can be detected with high sensitivity by increasing the detection capability of the magneto-impedance effect element and increasing the amplification gain k. .

In the current sensor according to the present invention, normally, as shown in FIG. 7, the magneto-impedance effect elements 1a and 1b, the demodulating circuits 3a and 3b, the differential amplifier circuit 4, the high frequency excitation power supply circuit 2, the bias magnetic field arranged in close proximity and parallel arrangement. And a + Vcc power source of exciting current is mounted on a common substrate 8. In this case, the magneto-impedance effect elements 1a and 1b arranged in close proximity and parallel on one side of the substrate 8, the demodulation circuits 3a and 3b, the differential amplifier circuit 4, the high frequency excitation power supply circuit 2, the bias magnetic field and the excitation current on the other side. A + Vcc power source is mounted, and the magneto-impedance effect element can be moved close to the current detection surface.
When the detection signal is displayed on the display, the display is connected to the signal detection end of the substrate via a flexible lead wire so that the substrate can be moved relative to the fixed display.
In the present invention, in order to widen the current detection range, a pair of magneto-impedance effect elements 1ma and 1mb having a parallel arrangement close to each other as shown in FIG. As shown in (b) of FIG. 8A, magnetoimpedance effect elements 11 a to 1 na and 11 b to 1 nb in the same magnetosensitive direction are connected in series as shown in FIG. Demodulator circuits 3a and 3b are connected to the output terminals, the output terminals of both demodulator circuits 3a and 3b are connected to the operational differential amplifier circuit 4, and the amplified outputs are connected to the magneto-impedance effect elements 1ma and 1mb (m = 1 to 1). n) is negatively fed back through the negative feedback coils 6ma and 6mb (m = 1 to n), and each magneto-impedance effect element 1ma and 1mb (m = 1 to n) is + Vcc with a polarity corresponding to the magnetic sensing direction. For bias magnetic field at power supply Yl 7 mA, can be biased through the 7mb (m = 1~n). Reference numeral 2 denotes an excitation power supply circuit.

Further, as shown in FIG. 8B, for the pair (1 ma, 1 mb) of the magneto-impedance effect elements, the demodulating circuits 3 ma, 3 mb (at the output terminals of the magneto-impedance effect elements 1 ma, 1 mb (m = 1 to n)). m = 1 to n), the output terminals of these demodulation circuits are connected to the operational differential amplifier circuit 40m (m = 1 to n), and the output of this amplifier circuit 40m (m = 1 to n) is connected to each magnetic field. The impedance effect elements 1ma and 1mb (m = 1 to n) are negatively fed back via the negative feedback coils 6ma and 6mb (m = 1 to n), and the magneto-impedance effect elements 1ma and 1mb (m = 1 to n) are returned. The output of the differential amplifier circuit 40m (m = 1 to n) of n unit circuits for applying a bias magnetic field via the bias magnetic field coils 7ma and 7mb (m = 1 to n) by + Vcc according to the magnetic sensing direction. End to adder 50 Continued to the detection end and the adder output, it can be connected in common to the excitation power supply circuit 2.
In the current sensor according to the present invention, the substrate on which the magneto-impedance effect element is mounted and the substrate on which the detection amplification circuit, the excitation power supply circuit, the + Vcc power supply, and the like are separated and are connected by a flexible wire. You can also.

If the ambient temperature fluctuates significantly or the stray capacitance fluctuates significantly while the current sensor is running, offset fluctuation occurs in the output of the differential amplifier and the detection output becomes unstable.
FIG. 9-1a shows a reference example different from the above, and FIG. 9-1b shows an embodiment of the current sensor according to the present invention . In contrast to the current sensor shown in FIGS. The output offset fluctuation is suppressed and the detection output is stabilized.
In FIGS. 9-1a and 9-1b, reference numeral 400 denotes an output correction circuit, and other configurations are the same as those of the current sensor shown in FIGS. The output correction circuit 400 uses the offset of the output of the operational operational amplifier 4 as an input signal, generates a compensation signal for canceling the offset, and uses the compensation signal as an input for erasing the offset in the operational amplifier. In addition to the offset adjustment terminal 4, the offset is erased.

FIG. 9-2 shows an example of an output correction circuit. The difference output and input of the operational differential amplifier are compared to detect an offset. If the offset is positive (negative), the electronic volume switch SW ₋₁ , SW ₋₂ ,... (SW ₊₁ , SW ₊₂ ,...) _Are sequentially turned on / off by the control IC, and a negative (positive) output voltage is sent to the offset adjustment terminal of the operational differential amplifier to output the amplifier. When the offset of the amplifier is reduced and the offset of the amplifier output becomes zero, the current switch state is maintained.
The offset of the output of the operational differential amplifier may be set within a predetermined range, for example, a range of -1v to + 1v. In this case, when the offset of the amplifier output exceeds -1v or + 1v, the electronic volume is manipulated. .
Furthermore, when a buffer having a gain of 1 or more, for example, 2 times, is incorporated in the control IC and exceeds ± 0.5 V, the electronic volume is operated so that the offset of the output of the operational differential amplifier is −0.5 V to +0. It can also be set within the range of 5v.

FIG. 10-1a shows a reference example different from the above, FIG. 10-1b shows an embodiment different from the above of the current sensor according to the present invention, and the current sensor shown in FIG. 4 and FIG. The output correction circuit 400 is connected between both input terminals of the operational differential amplifier, and the compensation signal for canceling the offset is generated using the offset of the output of the operational differential amplifier 4 as an input signal. The offset is added as an input for canceling the offset between both input terminals of the amplifier.

FIG. 10B shows an example of the output correction circuit. The output of the differential amplifier is compared with the difference input of the differential amplifier to detect the offset, and the offset is shown in FIG. ) Is set to 0 by the volume operation shown in FIG. 4B, and the offset value is used as an input signal to control the electronic volume switches SW- ₀ , SW- ₁ , SW- ₂ ,..., SW- ₀ , SW _{+ 1} , SW _{+ 2} This is done by operating.
Similarly to the above, the offset of the output of the operational differential amplifier may be set within a predetermined range, for example, the range of -1v to + 1v. In this case, if the offset of the amplifier output exceeds -1v or + 1v, Volume is manipulated. In this case, the offset of the output of the operational differential amplifier is set to −0.5v to +0 so that the electronic volume is manipulated when a gain of 1 or more, for example, a double buffer is incorporated in the control IC and exceeds ± 0.5v. It is also possible to fit within the range of .5v.

  The current sensor according to the present invention detects a minute current flowing through a conductor of a printed circuit board incorporated in an electronic device, or measures an insulator current (charging current or surface current) during transmission of an insulator of a transmission line. Can be used to detect the deterioration of the insulator.

It is drawing which shows the circuit structure of the magnetic sensor using a magneto-impedance effect element. It is drawing which shows the output characteristic of the magnetic sensor which uses a magneto-impedance effect element. It is drawing which shows the element unit of the magnetic sensor using a magneto-impedance effect element. It is a circuit diagram which shows the reference example of a current sensor. The present invention is a drawing showing the engagement Ru current detection method. It is drawing which shows the detection characteristic in the said current detection method. It is a plane surface which shows the reference example different from the above of an electric current sensor. It is drawing which shows the reference example with respect to the current sensor which concerns on this invention . It is a plane surface which shows the reference example different from the above of an electric current sensor. It is drawing which shows the reference example different from the above with respect to the current sensor which concerns on this invention . It is drawing which shows another Example of the current sensor which concerns on this invention . It is drawing which shows an example of the output correction circuit 400 in the current sensor shown to FIGS. 9-1a and 9-1b. It is drawing which shows the reference example different from the above with respect to the current sensor which concerns on this invention . It is drawing which shows the Example different from the above of the current sensor which concerns on this invention. It is drawing which shows an example of the output correction circuit 400 in the current sensor shown to FIGS. 10-1a and 10-1b. It is drawing used for description of the conventional current sensor.

DESCRIPTION OF SYMBOLS 1a Magneto-impedance effect element 1b Magneto-impedance effect element 21 Coil 22 Permeable core 2 High frequency excitation power supply 3a Demodulation circuit 3b Demodulation circuit 4 Operational differential amplification circuit 40 Output correction circuit 8 Insulating substrate

Claims (4)

A sensor that scans the surface of the equipment or facility to detect the current flowing on the surface of the equipment or facility, and has a plurality of sets of magneto-impedance effect elements that are arranged in parallel and opposite to each other in the magnetosensitive direction. Each demodulating circuit for detecting the output of each serially connected element of the magneto-impedance effect element group in one magnetic sensing direction and the magneto-impedance effect element group in the other magnetic sensing direction, and differential detection of the detection output of these demodulation circuits A correction having a differential amplifier, generating a compensation signal for canceling the offset by using the offset of the output of the differential amplifier as an input signal, and applying the compensation signal to the amplifier as an input for erasing the offset A current sensor comprising a circuit. 2. The current sensor according to claim 1, wherein means for generating a compensation output when the offset of the amplifier or differential amplifier output reaches a predetermined value is added to the correction circuit. 3. A current sensor according to claim 2, further comprising means for multiplying an offset of an amplifier or differential amplifier output by n (n> 1) and inputting the result to a correction circuit. The current sensor of claim 1 what Re claimed or moving across the object to be detected current path, the current and detecting a current from the left-right symmetry of sandwiching the object to be detected current path of the sensor output Detection method.

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