JP4722717B2 - Current sensor - Google Patents

Description

  The present invention relates to a current sensor and can be used to detect a leakage current or the like of power equipment or equipment. For example, the present invention is useful for measuring the charging current or leakage current of an insulator to determine the degree of deterioration of the insulator.

As a method to detect the insulator deterioration while receiving power, measure the insulator charging current and determine the insulator deterioration from the measured value, or measure the insulator surface potential distribution and determine the insulator deterioration from the measured value. It is known.
When the insulator is healthy, the charging current value and the surface potential distribution are normal. However, when the insulator is deteriorated, the charging current value and the surface potential distribution become abnormal, and the following method is known. (Non-Patent Document 1).
Shingu Shinta, Saeko and Bushing, Ohmsha Showa 32, p252-258

(1) With a pin insulator attached to a wooden pole or brace, the charging current can be measured by grounding one end of the AC ammeter and connecting the other end to the pin of the insulator. Therefore, the deterioration of the pin insulator can be detected from the measurement result.
(2) Connect both electrodes separated by a spark gap to both ends of the insulator via a capacitor, and generate a spark discharge in the gap by adjusting the gap of the spark gap to measure the magnitude of the voltage shared by the insulator. Since the shared voltage becomes abnormally small in the deteriorated insulator, deterioration of the insulator can be detected from the measurement result.
(3) The insulator is regarded as a capacitor, and an oscillation circuit is configured by shunting an appropriate inductance to the insulator, and a vibration wave is generated by contact and separation between one end of the inductance and the insulator, and the vibration wave is measured. This vibration wave has a close relationship with the shared voltage of the insulator, and in the case of a deteriorated insulator, the shared voltage becomes abnormally small, so that deterioration of the insulator can be detected from the measurement result.

However, in any of the above methods, connection between the insulator and the ammeter and the inductance is necessary, and the connection work and the connection / separation of the inductance must be performed at a high place on the steel tower or the utility pole and under the live line. So it is dangerous.
In particular, in the method (1), even if it can be applied to an insulator attached to a wooden pole or arm, there is a problem that it cannot be applied to an insulator attached to a steel tower.

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 FIG. 8A, when a is a conductor, s is a magnetic sensor arranged at a distance r from the conductor, the conductor current is I, and the magnetic field that the magnetic sensor measures magnetically 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. This characteristic is shown in FIG. For example, it is known to apply a bias magnetic field and negative feedback to make the polarity distinguishable and linear as shown in Fig. 1. Measure the current using this magnetic sensor with this polarity distinguishable and linear magnetoimpedance effect type magnetic sensor. It has also been proposed (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 FIG. 8B, a indicates a conductor. Reference numerals s and s ′ denote magneto-impedance effect elements that are equidistant from the conductor r and that are arranged at positions where the angle between them is 2θ. Oriented so as to have a magnetic sensitive direction.
In FIG. 8B, 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 of 2 | Hy | is obtained, and the conductor current I can be measured from this detection value.

The leakage current that flows on the surface of a power receiving insulator or the like is indeterminate in which path the current flows.
The above-described current measurement method is based on the premise that the relative positional relationship between the current path and the magnetoimpedance effect type magnetic sensor is known, and is not suitable for detection and measurement of leakage current flowing on the surface of a power receiving insulator or the like.

  The object of the present invention is to detect a current flowing on a surface such as a leakage current flowing on the surface of an insulator such as an insulator while eliminating the influence of internal and external noises, and easily detecting deterioration of the insulator. It is to provide a sensor.

The current sensor according to claim 1 is a sensor that detects a leakage current flowing on the surface of the device or the equipment by contacting the surface of the device or the equipment, and includes a magneto-impedance effect element in which the magnetosensitive directions are opposite to each other in the parallel arrangement. Multiple sets are arranged on the substrate with the orientation of the elements different for each set with respect to the direction of the same detected linear magnetic field . In a sensor provided with a respective demodulating circuit for detecting the output of each series-connected element of the magneto-impedance effect element group in the magnetic direction and a differential amplifier for differentially amplifying the detected output of these demodulating circuits, the output of the differential amplifier Correction using offset as an input signal to generate a compensation signal for canceling the offset, and applying this compensation signal to the amplifier as an input for erasing the offset Characterized in that a road.
The current sensor according to claim 2 is a sensor that detects a leakage current flowing on the surface of the device or the equipment by contacting the surface of the device or the equipment. A plurality of sets of elements arranged in different directions in the direction of the same linear magnetic field to be detected are arranged on the substrate, and a magneto-impedance effect element having one magnetosensitive direction for each of the plurality of sets. And each of the magneto-impedance effect elements in the other magnetosensitive direction are provided with respective demodulating circuits for detecting the output of the elements and differential amplifiers for differentially amplifying the detected outputs of these demodulating circuits, and the sum of the outputs of these differential amplifiers Is used as a detection output, and an offset of the output of the differential amplifier is used as an input signal to generate a compensation signal for canceling the offset, and this compensation signal is sent to the amplifier. Characterized in that a correction circuit to apply as input for erasing the set.
Current sensor according to claim 3, in claim 1 or 2 something Re of the current sensor, between the two input terminals of the differential amplifier, for compensating for canceling the offset as an input signal the offset of the differential amplifier output A correction circuit for generating a signal and applying the compensation signal as an input for eliminating the offset between both input terminals of the amplifier is provided.
According to a fourth aspect of the present invention, in the current sensor of the third aspect , the correction circuit is provided with means for generating a compensation output when the offset of the amplifier or differential amplifier output reaches a predetermined value. And
According to a fifth aspect of the present invention, there is provided the current sensor according to the fourth aspect , further comprising means for multiplying the offset of the amplifier or differential amplifier output by n (n> 1) and inputting the offset to the correction circuit.
〔The invention's effect〕

In order to detect the current by measuring the magnetic field (signal) generated by the current using a magneto-impedance effect sensor, the magneto-impedance effect element is arranged in parallel, the magnetic sensing direction is reversed, and the output of the magneto-impedance effect element is detected. Because the signal obtained by differential amplification is differentially amplified, internal noise that becomes an in-phase input for differential amplification (noise generated due to temperature changes in circuit elements such as the excitation power supply circuit and diodes in each detection circuit) The external noise such as the geomagnetic component hardly changes depending on the location and can be easily eliminated because it does not substantially change even if the position of the current sensor is changed. 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.
Furthermore, the current can be measured without matching the direction of the current sensor with the direction of the current to be detected by changing the axial direction of the magneto-impedance effect element in which the magnetosensitive effect direction is opposite in the parallel arrangement for each arrangement.
Therefore, the charging current and surface current (leakage current) of the insulator can be easily measured with high accuracy by bringing the current sensor according to the present invention into contact with the insulator while receiving power.

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. Thus, when a magnetic field to be detected is applied in the axial direction of the amorphous magnetic wire that is being energized, the circumferential magnetic flux and the magnetic field magnetic flux to be detected are easily magnetized by the synthesis of the magnetic flux to be detected and the magnetic field magnetic flux to be detected. shift direction of the magnetic flux acting on the outer shell portion 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 this μθ is the so changed by the detected magnetic field, the resistance voltage of the in wire ends between the output voltage at the detection field It will fluctuate. 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. For the magneto-impedance effect element 1, an amorphous ribbon, an amorphous sputtered film, or the like can be used in addition to zero magnetostrictive or negative magnetostrictive amorphous wires.

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. There to be offset from the circumferential direction, the circumferential direction permeability μθ changes, be varied inductance, impedance is varied by a change in the skin depth of the radio frequency skin effect of the circumferential permeability mu _theta. 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. 2D, a linear characteristic passing through the origin by zero point adjustment (the gradient coefficient k does not change). 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.

  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. 4-1 shows the arrangement state of the magneto-impedance effect element in one embodiment of the current sensor according to claim 1, and FIG. 4-2 shows a circuit diagram of the embodiment.
4A, 1 ma and 1 mb (m = 1 to n) are sets of magneto-impedance effect elements arranged in parallel to each other, and the magnetosensitive directions are opposite to each other, and the axial direction of the magneto-impedance effect element is set for each arrangement. The direction is different.
In the example illustrated in FIG. 4A, the number of magneto-impedance effect elements is set to 4 (m = 1 to 4), and the direction of other sets of magneto-impedance effect elements is + 45 ° with respect to the set of m = 1. The orientations are 90 ° and 135 °.
In FIG. 4B, Cm (m = 1 to n) represents a sensor unit for a set of magneto-impedance effect elements, and a demodulator circuit 3ma is provided at the output terminal of each of the magneto-impedance effect elements 1ma and 1mb (m = 1 to n). , 3 mb (m = 1 to n) are connected, and the output terminals of these demodulation circuits are connected to the operational differential amplifier circuit 40m, and the output of the amplifier circuit 40m (m = 1 to n) is connected to each magneto-impedance effect element 1ma. , 1 mb (m = 1 to n) through negative feedback coils 6 ma and 6 mb (m = 1 to n) and negative feedback to each magnetoimpedance effect element 1 ma, 1 mb (m = 1 to n). A bias magnetic field is applied via bias magnetic field coils 7ma and 7mb (m = 1 to n) by + Vcc depending on the direction.
In the embodiment shown in FIG. 4B, the output terminals of the differential amplifier circuits 40m (m = 1 to n) of the n sensor units Cm (m = 1 to n) are integrated by the adder 50 or the like to be the detection terminals. A common excitation power supply circuit 2 is connected to all sensor units (m = 1 to n).

In FIGS. 4-1 to 4-2, the magnetosensitive effects of the magnetic impedance effect element 1ma and the magnetic impedance effect element 1mb are opposite to the magnetic field H acting in the axial direction of the magnetoimpedance effect elements 1ma and 1mb. Since the demodulated waves (signal waves) from the tuning circuits 3ma and 3mb of the outputs of the elements 1ma and 1mb are differentially amplified, the output Em of the operational differential amplifier circuit 40m is k [H − (− H)] (k Is the slope coefficient in (c) of FIG.
Em = 2kH
Given in.

In FIGS. 4-1 to 4-2, when the direction of the magnetic field based on the current to be detected is Hm in the same direction as the magnetosensitive direction of the magnetoimpedance effect elements 1ma and 1mb, the magnetoimpedance effect elements 1ma and 1mb are used. The detection output 2kHm based on the magnetic field is maximized, but the other magnetoimpedance effect elements 1xa and 1xb (x ≠ m) also have axial components (sensations) of the magnetoimpedance effect elements 1xa and 1xb (x ≠ m) with respect to the magnetic field Hm. A detection output Ex is generated by the magnetic direction component) Hx (x ≠ m).
That is, if the angle between the magneto-impedance effect elements 1ma and 1mb and the other magneto-impedance effect elements 1xa and 1xb (x ≠ m) is x, the axial components of the magneto-impedance effect elements 1xa and 1xb (x ≠ m) (Magnetic sensing direction component) Hx (x ≠ m) is given by Hx = Hmcosx, and this Hx generates a detection output Ex = 2 kHmcosx.
Therefore, the overall detection output Et is Et = 2 kHz + Σ2 kHz mccosx
And the magneto-impedance effect element in the direction in which cosx becomes negative decreases the overall detection output Et.
However, the overall detection output Et can be made sufficiently large by adjusting the number n of magneto-impedance effect elements in which the magnetic sensing direction is reversed in the parallel arrangement and the direction x for each arrangement of the magneto-impedance effect elements. Even if the direction of is unknown, the current can be detected sufficiently.

In the sensor unit described above, noise generated due to temperature changes of circuit elements such as the diodes of the excitation power supply circuit 2 and the detection circuits 3ma and 3mb can be canceled because they are in-phase input to the differential amplifier circuit 40m. .
Since the external noise such as the geomagnetic component hardly changes depending on the location, the current output is sufficiently separated from the insulator, and the overall output Eout is substantially at a position where the magnetic field Hm based on the insulator current is substantially zero. , The measured value becomes an output due to the external noise substantially, and the influence of the external noise can be eliminated (the zero point adjustment of (D) in FIG. 2 is performed under the output due to the external noise).

  FIG. 5 is a circuit diagram showing an embodiment of a current sensor according to claim 2, and magneto-impedance effect elements 1 ma and 1 mb (m = m = m) having a parallel arrangement as shown in FIG. 1 to n), demodulating circuits 3a and 3b are connected to the respective output terminals of one of the magneto-impedance effect element groups 11a to 1na and the other magneto-impedance effect element groups 11b to 1nb, respectively. The output terminal of 3b is connected to the operational differential amplifier circuit 4, and the amplified output is negatively fed back to each of the magneto-impedance effect element groups 11a to 1na and 11b to 1nb via the negative feedback coils 61a to 6na and 61b to 6nb. Each of the magneto-impedance effect element groups 11a to 1na and 11b to 1nb has a bias magnetic field coil 71a by a + Vcc power supply with a polarity corresponding to the magnetic sensing direction. 7na, it is biased through the 71b~7nb. Reference numeral 2 denotes an excitation power supply circuit.

In the current sensor according to the present invention, the magneto-impedance effect element group, the demodulating circuit, the operational differential amplifier circuit, the exciting current source circuit, the operational differential amplifier circuit, the exciting current, and the like, which are arranged in parallel in a plurality of sets and in opposite directions. The + Vcc power source for the source circuit and the bias magnetic field coil can be mounted on the same substrate.
In addition, a board on which a group of magneto-impedance effect elements having opposite directions of magnetic sensing are mounted in parallel arrangement, a demodulation circuit, an operational differential amplifier circuit, an excitation current source circuit, an arithmetic differential amplifier circuit, and an excitation current source circuit Alternatively, the substrate on which the + Vcc power supply for the bias magnetic field coil is mounted can be separated and the two substrates can be connected by a flexible wire.
In particular, when detecting the current flowing through the insulator during power reception, the latter configuration is used, and a substrate mounted with a plurality of sets of parallel arrangements of magneto-impedance effect element groups in which the magnetosensitive direction is reverse is attached to the tip of the insulating cage, It is safe to perform the insulator surface scanning by the magneto-impedance effect element group using the insulator as a handle.

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.
FIGS. 6-1a and 6-1b show current sensors according to claim 6. In contrast to the current sensors shown in FIGS. 4-2 and 5, the offset fluctuation of the output of the differential amplifier is suppressed, and the detection output is reduced. Stabilization is planned.
In FIGS. 6-1a and 6-1b, 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. 6B shows an example of the output correction circuit. The difference output and the input of the operational differential amplifier are compared to detect the 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.

    FIGS. 7-1a and 7-1b show a current sensor according to claim 7. The output correction circuit 400 is connected between both input terminals of the operational differential amplifier 4 with respect to the current sensor shown in FIGS. , And a compensation signal for canceling the offset is generated using the offset of the output of the operational differential amplifier 4 as an input signal, and this compensation signal is input to cancel the offset between the input terminals of the amplifier. Add as.

FIG. 7-2 (a) shows an example of the output correction circuit. The offset 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.

With the current sensor according to the present invention, when the current flowing through the insulator is measured and the measurement result is abnormal, it is determined that the insulator has deteriorated, and the insulator deterioration can be detected.
It can also be used to measure stray currents in electric railways that cause electrical corrosion of underground metal.
In addition, the density distribution of the current flowing through the metal pipe changes due to cracks and thinning on the inner surface of the metal pipe, and changes in the magnetic field distribution based on the current. It can also be used to determine the degree of cracking and thinning of the inner surface of a metal pipe.

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 example of arrangement | positioning of the magneto-impedance effect element of the current sensor which concerns on this invention . It is drawing which shows the circuit structure of the current sensor which concerns on this invention. It is drawing which shows the circuit structure of the sensor of the electric current different from the above which concerns on this invention . It is drawing which shows one Example of another current sensor which concerns on this invention . It is drawing which shows the Example of another current sensor different from the above based on this invention . 6 is a diagram illustrating an example of an output correction circuit 400 in the current sensor illustrated in FIGS. 6-1a and 6-1b. It is drawing which shows the Example of another current sensor different from the above based on this invention . It is drawing which shows the Example of another current sensor different from the above based on this invention . 7 is a diagram illustrating an example of an output correction circuit 400 in the current sensor illustrated in FIGS. 7-1a and 7-1b. It is drawing used for description of the conventional current sensor.

1 ma (m = 1 to n) magneto-impedance effect element 1 mb (m = 1 to n) magneto-impedance effect element 2 high frequency excitation current source 3 ma (m = 1 to n) demodulation circuit 3 mb (m = 1 to n) demodulation circuit 4 Operational differential amplifier circuit 4m (m = 1 to n) Operational differential amplifier circuit 400 Output correction circuit Cm (m = 1 to n) Sensor unit

Claims (5)

The leakage current flowing through the equipment and facilities of the surface, equipment and the equipment surface a sensor for detecting contact, magneto-sensitive direction a plurality of sets of opposite magnetic impedance effect element together in a parallel arrangement, the same to be detected linear magnetic field The elements are arranged on the substrate with the orientations of the elements being different for each set, and the plurality of sets of magneto-impedance effect element groups in one magnetic sensing direction and the magneto-impedance effect element group in the other magnetic sensing direction are arranged. In a sensor provided with each demodulating circuit for detecting the output of each series connection element and a differential amplifier for differentially amplifying the detected output of these demodulating circuits, the offset of the output of the differential amplifier is canceled as an input signal. And a compensation circuit for providing the compensation signal as an input for erasing the offset to the amplifier. Flow sensor. . The leakage current flowing through the equipment and facilities of the surface, equipment and the equipment surface a sensor for detecting contact, magneto-sensitive direction a plurality of sets of opposite magnetic impedance effect element together in a parallel arrangement, the same to be detected linear magnetic field The element is arranged on the substrate with the direction of the element being different for each set, and the magneto-impedance effect element in one magnetic sensitive direction and the magnetic impedance in the other magnetic sensitive direction for each of the plurality of sets. Each of the effect elements is provided with a demodulating circuit for detecting the output of the element and a differential amplifier for differentially amplifying the detected output of the demodulating circuit. An input for canceling the offset is generated in the amplifier using the offset of the output of the dynamic amplifier as an input signal to generate a compensation signal for canceling the offset. Current sensors, characterized in that a correction circuit is added to. A compensation signal for canceling the offset is generated between the input terminals of the differential amplifier using the offset of the differential amplifier output as an input signal, and the offset is erased between the input terminals of the amplifier. 3. A current sensor according to claim 1, further comprising a correction circuit to be added as an input for the input. 4. The current sensor according to claim 3, 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. 5. The current sensor according to claim 4, further comprising means for multiplying the offset of the amplifier or differential amplifier output by n (n> 1) and inputting the offset to the correction circuit.

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