JP2000241517A - Removal system for noise in dc-squid for nondestructive inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a removal system, for a noise in a DC-SQUID for nondestructive inspection, by which a magnetic field, from a magnetic-field application coil, detected by the DC-SQUID is removed in an eddy-current nondestructive inspection using the DC-SQUID. SOLUTION: A DC-SQUID 1, a DC-SQUID drive circuit 2 which is used to drive the DC-SQUID 1, a filter 7, a filter-factor renewal means 6, a magnetic- field application coil 12, a first voltage/current conversion means 10, an oscillator 9, a signal addition means 4 and a lock-in amplifier 20 constitute this removal system for a noise in the DC-SQUID for nondestructive inspection. In this manner, when the filter 7, the filter-factor renewal means 6 and the addition means 4 are used, a signal, from the magnetic-field application coil 12, which is mixed with a desired signal is removed, and only the desired signal from a sample to be measured can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a non-destructive inspection noise elimination system using a DC-SQUID.

[0002]

2. Description of the Related Art A DC-SQUID is a device formed by inserting two Josephson junctions into a superconducting loop. A magnetometer using a DC-SQUID is very sensitive and has a geomagnetic (about 0.5 Gauss)
It is possible to measure a minute magnetism of about one hundred million. Therefore, it is used as a minute magnetic field measuring means in fields such as biomagnetic measurement and industrial measurement. However, due to the high sensitivity, sufficient consideration is required for noise countermeasures.

[0003] One of the applications of DC-SQUID to the field of industrial measurement is non-destructive inspection using eddy current. Hereinafter, the eddy current non-destructive inspection using the DC-SQUID will be described. An alternating current is passed through the magnetic field applying coil to generate a magnetic field. If there is a metal measurement object in this magnetic field,
Due to the electromagnetic induction, a magnetic flux passes and a vertical eddy current flows on the surface of the measurement object. If the measurement object has a flaw such as a crack, the eddy current changes. The change is DC
By observing with SQUID, the state of the scratch on the measurement object can be measured. It is also possible to estimate the depth of the surface flaw.

However, when the magnetic field from the magnetic field applying coil is changed to DC
-SQUID detected, causing noise.

[0005]

In a conventional DC-SQUID eddy current non-destructive inspection device (system), a DC-SQUID directly detects a magnetic field from a magnetic field applying coil.
There has been a problem that the signal from the magnetic field application coil and the desired signal from the measurement sample cannot be distinguished, and a flaw in the measurement sample cannot be detected.

Accordingly, an object of the present invention is to remove a magnetic field from a magnetic field applying coil detected by a DC-SQUID in an eddy current nondestructive inspection using the DC-SQUID.

[0007]

In order to solve the above-mentioned problems, the present invention incorporates a filter and a means for updating the coefficient of the filter into an eddy current flaw detection test using a DC-SQUID. More specifically, DC-SQUID and D
A drive circuit for driving the C-SQUID, a magnetic field applying coil magnetically coupled to the measurement sample, first voltage / current converting means having an output connected to the magnetic field applying coil, and a filter. An oscillator having an output connected to the filter and the first voltage / current conversion means, an addition means having an input connected to the output of the drive circuit and the output of the filter, and an output of the addition means. The apparatus has a filter coefficient updating means for updating the coefficient of the filter.

As described above, by using the filter, the filter coefficient updating means, and the adding means, the signal from the magnetic field application coil mixed into the desired signal is removed, and only the desired signal from the measurement sample can be detected. Also,
A DC-SQUID, a driving circuit for driving the DC-SQUID, a magnetic field applying coil magnetically coupled to the measurement sample, a magnetic coupling to the measurement sample, and connection to the DC-SQUID. A detecting coil, a compensating coil magnetically coupled to the detecting coil, a first voltage / current converting means having an output connected to the magnetic field applying coil, a filter, and an output for the compensation. A second voltage / current conversion means connected to the coil and having an input connected to the output of the filter; and an output connected to the input of the filter and the input of the first voltage / current conversion means. And a filter coefficient updating means for updating the coefficient of the filter by the output of the driving circuit.

As described above, by using the filter, the filter coefficient updating means, and the compensation coil, the signal from the magnetic field application coil mixed into the desired signal is removed, and only the desired signal from the measurement sample can be detected. Also,
A driving circuit for driving the DC-SQUID and the DC-SQUID, a magnetic field applying coil magnetically coupled to the measurement sample, a coil magnetically coupled to the DC-SQUID, First voltage / current converting means connected to the magnetic field applying coil, a filter, and second voltage / current converting means having an output connected to the coil and an input connected to the output of the filter. An oscillator having an output connected to the input of the filter and the input of the first voltage / current conversion means, and a filter coefficient updating means for updating the coefficient of the filter by the output of the driving circuit. .

As described above, by using the filter, the filter coefficient updating means, and the coil, the signal from the magnetic field applying coil mixed into the desired signal is removed, and only the desired signal from the measurement sample can be detected. Also, D
A C-SQUID, a drive circuit for driving the DC-SQUID, a magnetic field applying coil magnetically coupled to the measurement sample, and a first voltage / current whose output is connected to the magnetic field applying coil Converting means, a filter having an output connected to the drive circuit, and an oscillator having an output connected to the filter and the first voltage / current converting means;
A configuration is provided that includes a filter coefficient updating unit that updates the coefficient of the filter with the output of the driving circuit.

As described above, by using the filter, the filter coefficient updating means, and the driving circuit, the signal from the magnetic field applying coil mixed into the desired signal is removed, and only the desired signal from the measurement sample can be detected. With the above-described configuration, the DC-SQUID
Can remove the magnetic flux signal from the magnetic field applying coil detected by the magnetic field applying coil.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a block diagram showing a DC-SQUID noise removal system for nondestructive inspection according to Embodiment 1 of the present invention.

The DC-SQUID noise removal system for nondestructive inspection shown in FIG. 1 includes a DC-SQUID1 and a DC-SQUID.
DC-SQUID drive circuit 2 for driving ID1
, Filter 7, filter coefficient updating means 6, magnetic field applying coil 12, first voltage / current converting means 10, oscillator 9, signal adding means 4, and lock-in amplifier 20.

The voltage output from the oscillator 9 is converted into a current by the first voltage / current conversion means 10, and an alternating current flows through the magnetic field applying coil 12. The magnetic field applying coil 12 through which the alternating current flows applies a magnetic field to the measurement target 11. An eddy current flows in a direction perpendicular to the passage of the magnetic flux on the surface of the measurement target 11 to which the magnetic field is applied due to electromagnetic induction. Next, DC-SQ
The UID 1 detects a magnetic flux signal φs + φe which is the sum of the magnetic flux φe from the magnetic field applying coil 12 and the magnetic flux φs from the eddy current.
Subsequently, the DC-SQUID drive circuit 2 outputs a voltage signal Vs + Ve, which is the sum of the voltage signal Vs corresponding to the magnetic flux φs and the voltage signal Ve corresponding to the magnetic flux φe. Next, the voltage output Vs + Ve from the DC-SQUID drive circuit 2 is input to the signal adding means 4.

On the other hand, the voltage output of the oscillator 9 is input to the filter 7. The voltage output Vc of the filter 7 is output by the signal adding means 4 to the voltage output Vs + Ve of the DC-SQUID drive circuit 2.
Is subtracted from Therefore, the output of the signal adding means 4 is Vs + Ve
−Vc. Here, the voltage output from the oscillator 9 is output from the voltage / current converter 10, the magnetic field applying coil 12, the DC-SQUI.
D1, the transfer function transmitted to the signal adding means 4 via the DC-SQUID drive circuit 2 is Wa. Similarly, a transfer function in which the voltage output from the oscillator 9 is transmitted to the signal adding means 4 via the filter 7 is represented by Wb. The filter coefficient updating means 6 optimizes the coefficient of the filter 7 as needed to adjust the transfer function Wb to be equal to Wa. As a result, Wa and Wb become equal.

When the coefficients of the filter 7 are optimized, Wa and Wb
Are equal, the voltage signal Ve corresponding to the magnetic flux φe from the magnetic field applying coil 12 and the voltage output Vc of the filter 7 become equal. Therefore, the voltage output of the signal adding means 4 is Vs + Ve-Vc = Vs. In this manner, noise is removed, and a voltage signal Vs corresponding to the magnetic flux signal φs from the measuring object 11 can be obtained.

Subsequently, the lock-in amplifier 20 takes the output of the oscillator 9 as a reference signal and performs lock-in detection of the voltage signal Vs. The change in the eddy current generated in the measurement target 11, that is, the scratch on the measurement target 11 can be read by the lock-in detected signal. In the present embodiment, LMS (Least Square Mean) or other LSL (Least Square Lattice) can be used as the algorithm of the filter coefficient updating means 6. For example, according to the LMS method, the filter coefficient updating means 6 calculates a root mean square error of the output of the signal adding means 4. This mean square error takes the form of a quadratic function of the filter coefficients. For unknown filter coefficients, the root-mean-square error varies in the shape of a multidimensional parabola with a single base or minimum. The filter coefficient updating means 6 continuously searches for the bottom of the curved surface and updates the filter coefficient as needed. That is, the filter coefficient updating means 6 obtains an optimum filter coefficient and updates it as needed.

The DC-SQUID drive circuit 2 may be a modulation type FLL system or a non-modulation type FLL system (DOIT system). Alternatively, a DC-SQUID to which a detection coil is connected may be used. (Embodiment 2) FIG. 2 is a configuration diagram showing a DC-SQUID noise removal system for nondestructive inspection according to Embodiment 2 of the present invention.

The DC-SQUID noise elimination system for nondestructive inspection shown in FIG. 2 includes a DC-SQUID1 and a DC-SQUID.
DC-SQUID drive circuit 2 for driving ID1
, Filter 7, filter coefficient updating means 6, magnetic field applying coil 12, first voltage / current converting means 10, oscillator 9, signal adding means 4, and lock-in amplifier 20.

The voltage output from the oscillator 9 is converted into a current by the first voltage / current conversion means 10, and an alternating current flows through the magnetic field applying coil 12. The magnetic field applying coil 12 through which the alternating current flows applies a magnetic field to the measurement target 11. An eddy current flows in a direction perpendicular to the passage of the magnetic flux on the surface of the measurement target 11 to which the magnetic field is applied due to electromagnetic induction. Next, DC-SQ
The UID 1 detects a magnetic flux signal φs + φe which is the sum of the magnetic flux φe from the magnetic field applying coil 12 and the magnetic flux φs from the eddy current.
Subsequently, the DC-SQUID drive circuit 2 outputs a voltage signal Vs + Ve, which is the sum of the voltage signal Vs corresponding to the magnetic flux φs and the voltage signal Ve corresponding to the magnetic flux φe. Next, the voltage output Vs + Ve from the DC-SQUID drive circuit 2 is input to the signal adding means 4 and A / D converted and processed.

On the other hand, the voltage output of the oscillator 9 is input to the filter 7. The voltage output Vc of the filter 7 is output by the signal adding means 4 to the voltage output Vs + Ve of the DC-SQUID drive circuit 2.
Is subtracted from Therefore, the output of the signal adding means 4 is Vs + Ve
−Vc. In the first embodiment, the addition process is performed using an analog signal. In the second embodiment, the addition process is performed using a digital signal.

Here, the voltage output from the oscillator 9 is supplied to the voltage / current conversion means 10, the magnetic field applying coil 12, the DC-SQUI.
D1, the transfer function transmitted to the signal adding means 4 via the DC-SQUID drive circuit 2 is Wa. Similarly, a transfer function in which the voltage output from the oscillator 9 is transmitted to the signal adding means 4 via the filter 7 is represented by Wb. The filter coefficient updating means 6 optimizes the coefficient of the filter 7 as needed to adjust the transfer function Wb to be equal to Wa. As a result, Wa and Wb become equal.

When the coefficient of the filter 7 is optimized, Wa and Wb
Are equal, the voltage signal Ve corresponding to the magnetic flux φe from the magnetic field applying coil 12 and the voltage output Vc of the filter 7 become equal. Therefore, the voltage output of the signal adding means 4 is Vs + Ve-Vc = Vs. In this manner, noise is removed, and a voltage signal Vs corresponding to the magnetic flux signal φs from the measuring object 11 can be obtained.

Subsequently, the lock-in amplifier 20 takes the output of the oscillator 9 as a reference signal and performs lock-in detection of the voltage signal Vs. The change in the eddy current generated in the measurement target 11, that is, the scratch on the measurement target 11 can be read by the lock-in detected signal. Note that the DC-SQUID drive circuit 2 may be a modulation type FLL system or a non-modulation type FLL system (DOIT system). In addition, DC-
SQUID may be used.

(Embodiment 3) FIG. 3 is a block diagram showing a DC-SQUID noise removal system for nondestructive inspection according to Embodiment 3 of the present invention. DC for non-destructive inspection of FIG.
-SQUID noise removal system is DC-SQUID1
And a DC-SQU for driving the DC-SQUID1
ID drive circuit 2, filter 7, filter coefficient updating means 6, magnetic field applying coil 12, first voltage / current converting means 10, oscillator 9, compensation coil 13, second voltage / current converting means 15, It comprises a detection coil 16 and a lock-in amplifier 20.

The voltage output from the oscillator 9 is converted into a current by the first voltage / current conversion means 10, and an alternating current flows through the magnetic field applying coil 12. The magnetic field applying coil 12 through which the alternating current flows applies a magnetic field to the measurement target 11. An eddy current flows in a direction perpendicular to the passage of the magnetic flux on the surface of the measurement target 11 to which the magnetic field is applied due to electromagnetic induction. Also, the oscillator 9
Is input to the filter 7. Filter 7
Is converted into a current by the second voltage / current conversion means 15 and flows to the compensation coil 13. The current flowing through the compensation coil 13 causes the detection coil 16 to link the magnetic field φc.

Next, the detection coil 16 is the magnetic field application coil 1
2, a magnetic flux signal φs + φe + φc of a magnetic flux φs from the eddy current and a magnetic flux φc from the compensation coil 13. Here, the voltage output from the oscillator 9 is applied to the detection coil 1 via the voltage / current conversion means 10 and the magnetic field application coil 12.
The transfer function transmitted to 6 is Wa. Similarly, the oscillator 9, the filter 7, the second voltage / current converting means 15,
The transfer function transmitted to the detection coil 16 via the compensation coil 13 is Wb. The filter coefficient updating means 6 adjusts the transfer function Wb by optimizing the coefficient of the filter 7 as needed. As a result, the transfer function Wa and the transfer function Wb become equal.

When the coefficient of the filter 7 is optimized and the transfer function Wa and the transfer function Wb become equal, the magnetic flux signal φc from the compensating coil 13 linked to the detection coil 16 and the magnetic flux signal φe from the magnetic field applying coil 12 are obtained. Φc + φ
e becomes 0. Therefore, the total magnetic flux signal linked to the detection coil 16 is φs + φe + φc = φs. In this manner, noise is removed, and the magnetic flux signal φs from the measuring object 11 is removed.
Can be obtained.

Next, the magnetic flux signal φs is transmitted to the DC-SQUID drive circuit 2 via the DC-SQUID1,
The SQUID drive circuit 2 generates a voltage signal Vs corresponding to the magnetic flux φs.
Is output. Subsequently, the lock-in amplifier 20 takes the output of the oscillator 9 as a reference signal and performs lock-in detection of the voltage signal Vs. The change in the eddy current generated in the measurement target 11, that is, the scratch on the measurement target 11 can be read by the lock-in detected signal.

In this embodiment, LMS (Least Square Mean) or other LSL (Least Square Lattice) can be used as the algorithm of the filter coefficient updating means 6. Note that the DC-SQUID drive circuit 2 may be a modulation type FLL system or a non-modulation type FLL system (DOIT system). Further, the detection coil may be of any type. (Embodiment 4) FIG. 4 is a configuration diagram showing a DC-SQUID noise removal system for nondestructive inspection according to Embodiment 4 of the present invention.

The DC-SQUID noise removal system for nondestructive inspection shown in FIG. 4 includes a DC-SQUID1 and a DC-SQUID.
DC-SQUID drive circuit 2 for driving ID1
A filter 7, a filter coefficient updating unit 6, a magnetic field applying coil 12, a first voltage / current converting unit 10, an oscillator 9, a coil 14 magnetically coupled to the DC-SQUID1, and a third voltage / current converting unit. It comprises a current conversion means 17 and a lock-in amplifier 20.

The voltage output from the oscillator 9 is converted into a current by the first voltage / current converting means 10, and an alternating current flows through the magnetic field applying coil 12. The magnetic field applying coil 12 through which the alternating current flows applies a magnetic field to the measurement target 11. An eddy current flows in a direction perpendicular to the passage of the magnetic flux on the surface of the measurement target 11 to which the magnetic field is applied due to electromagnetic induction. Also, the oscillator 9
Is input to the filter 7. Filter 7
Is converted by the third voltage / current conversion means 17 into a current and flows through the coil 14. Current flowing coil 1
4 links the magnetic flux φd to the DC-SQUID1.

Next, the DC-SQUID 1 receives the magnetic flux φe from the magnetic field applying coil 12, the magnetic flux φs from the eddy current and the coil 1.
The magnetic flux signal φs + φe + φd of the magnetic flux φd from 1 is detected. Here, the voltage output from the oscillator 9 is applied to the DC-SQUI via the voltage / current converting means 10 and the magnetic field applying coil 12.
The transfer function transmitted to D1 is Wa. Similarly, the voltage output from the oscillator 9 is applied to the DC-SQUID 1 through the filter 7, the third voltage / current conversion unit 17, and the coil 14.
Wb the transfer function transmitted to. The filter coefficient updating means 6 optimizes the coefficient of the filter 7 as needed to transfer the transfer function Wb.
To adjust.

As a result, the transfer function Wa and the transfer function Wb become equal. The coefficient of the filter 7 is optimized and the transfer function Wa
And the transfer function Wb become equal, the sum of the magnetic flux φe from the magnetic field applying coil 12 and the magnetic flux φd from the coil 14 becomes φe + φd = 0. Therefore, the magnetic flux signal φs + φe + φd = φs detected by the DC-SQUID 1 is obtained, and the magnetic flux signal φs from the measurement target 11 from which noise has been removed can be obtained. The magnetic flux signal φs is transmitted to the DC-SQUID drive circuit 2, and the DC-SQUID drive circuit 2
Is output as a voltage signal Vs.

Subsequently, the lock-in amplifier 20 takes the output of the oscillator 9 as a reference signal and performs lock-in detection of the voltage signal Vs. The change in the eddy current generated in the measurement target 11, that is, the scratch on the measurement target 11 can be read by the lock-in detected signal. In the present embodiment, LMS (Least Square Mean) or other LSL (Least Square Lattice) can be used as the algorithm of the filter coefficient updating means 6. The DC-SQUID drive circuit 2 is a modulation type FL
The L method and the non-modulation FLL method (DOIT method) may be used. Alternatively, a DC-SQUID to which a detection coil is connected may be used. (Embodiment 5) FIG. 5 is a block diagram showing a DC-SQUID noise removal system for nondestructive inspection according to Embodiment 5 of the present invention.

The DC-SQUID noise elimination system for nondestructive inspection shown in FIG. 5 includes a DC-SQUID1 and a DC-SQUID.
DC-SQUID drive circuit 2 for driving ID1
, Filter 7, filter coefficient updating means 6, magnetic field applying coil 12, first voltage / current converting means 10, oscillator 9, and lock-in amplifier 20.

The voltage output from the oscillator 9 is converted into a current by the first voltage / current converting means 10, and an alternating current flows through the magnetic field applying coil 12. The magnetic field applying coil 12 through which the alternating current flows applies a magnetic field to the measurement target 11. An eddy current flows in a direction perpendicular to the passage of the magnetic flux on the surface of the measurement target 11 to which the magnetic field is applied due to electromagnetic induction. Also, the oscillator 9
Is input to the filter 7. Subsequently, the voltage output Vc of the filter 7 is input to the DC-SQUID drive circuit 2.

Next, the DC-SQUID 1 detects the magnetic flux φe from the magnetic field applying coil 12 and the magnetic flux signal φs + φe of the magnetic flux φs from the eddy current. At the same time, the voltage output Vc of the filter 7 input to the DC-SQUID drive circuit 2 is converted into a magnetic flux signal φc and applied to the DC-SQUID1. Therefore, the total magnetic flux signal detected by DC-SQUID1 is φs +
φe + φc.

Here, the voltage output from the oscillator 9 is supplied to the DC-S
The transfer function transmitted to QUID1 is Wa. Similarly, the voltage output from the oscillator 9 is applied to the filter 7, the DC-SQ
The transfer function transmitted to DC-SQUID1 via the UID drive circuit 2 is Wb. The filter coefficient updating means 6 adjusts the transfer function Wb by optimizing the coefficient of the filter 7 as needed. As a result, the transfer function Wa and the transfer function Wb become equal.

When the coefficient of the filter 7 is optimized and the transfer function Wa and the transfer function Wb become equal, the sum of the magnetic flux signal φc corresponding to the voltage output Vc of the filter and the magnetic flux signal φe from the magnetic field applying coil becomes 0. become. Therefore DC-
The magnetic flux signal detected by SQUID1 is φs + φe + φc =
φs. In this manner, the noise is removed, and the magnetic flux signal φs from the measuring object 11 can be obtained.

Subsequently, the DC-SQUID drive circuit 2 outputs a voltage signal Vs corresponding to the magnetic flux φs. Lock-in
The amplifier 20 takes the output of the oscillator 9 as a reference signal and performs lock-in detection of the voltage signal Vs. The change in the eddy current generated in the measurement target 11, that is, the scratch on the measurement target 11 can be read by the lock-in detected signal. In the present embodiment, LMS (Least Square Mean) or other LSL (Least Square Lattice) can be used as the algorithm of the filter coefficient updating means 6. Note that the DC-SQUID drive circuit 2 uses a modulation type FLL method and a non-modulation type FLL method (DOIT method).
But it doesn't matter. In addition, DC-SQ with connecting detection coil
UID may be used.

[0042]

The present invention is embodied in the form as described above. In the eddy current non-destructive inspection, a DC-SQUID is obtained by using a filter and a filter coefficient updating means.
This has the effect that the magnetic flux signal from the magnetic field application coil detected by the magnetic field can be removed. More specifically, D
Since the signal from the magnetic field applying coil 12 detected by the C-SQUID 1 can be removed and a desired signal from the measurement target 11 can be detected, a flaw on the measurement target 11 can be detected.

Further, since the signal from the magnetic field applying coil 12 detected by the detection coil 16 can be removed by the compensation coil 13, a desired signal from the measurement object 11 can be detected.
A scratch on the measurement target 11 can be detected. Further, the magnetic field applying coil 1 detected by the DC-SQUID 1 by the coil 14
2 can be removed and a desired signal from the measurement target 11 can be detected, so that a scratch on the measurement target 11 can be detected.

Then, the DC-SQUID driving circuit 2 can remove the magnetic field signal from the magnetic field applying coil 12 detected by the DC-SQUID 1 and detect the desired signal from the measurement target 11, so that the measurement target 11 can be prevented from being damaged. Can be detected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a DC-SQUID noise removal system for nondestructive inspection according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a DC-SQUID noise removal system for nondestructive inspection according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a DC-SQUID noise removal system for nondestructive inspection according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram showing a DC-SQUID noise removal system for nondestructive inspection according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram showing a DC-SQUID noise removal system for nondestructive inspection according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC-SQUID 2 DC-SQUID drive circuit 3 First A / D converter 4 Signal adding means 5 D / A converter 6 Filter coefficient updating means 7 Filter 8 Second A / D converter 9 Oscillator 10 First voltage / Current conversion means 11 Measurement object 12 Magnetic field application coil 13 Compensation coil 14 Coil 15 Second voltage / current conversion means 16 Detection coil 17 Third voltage / current conversion means 18 Digital filter 19 Digital filter coefficient updating means 20 Lock In-amplifier 21 Analog signal adding means 22 Digital signal adding means

Claims (4)

[Claims] 1. A DC-SQUID, a driving circuit for driving the DC-SQUID, a magnetic field applying coil magnetically coupled to a measurement sample, and a second output having an output connected to the magnetic field applying coil. One voltage /
Current converting means, a filter, an oscillator having an output connected to the filter and the first voltage / current converting means, and an adding means having inputs connected to the output of the driving circuit and the output of the filter. A DC-SQUID noise removal system for non-destructive inspection, comprising a filter coefficient updating unit for updating a coefficient of the filter by an output of the adding unit. 2. A DC-SQUID, a drive circuit for driving the DC-SQUID, a magnetic field application coil magnetically coupled to a measurement sample, and a magnetic field coupling coil with the measurement sample, and -SQUID
A compensating coil magnetically coupled to the detecting coil; and a first voltage / output connected to the magnetic field applying coil.
Current conversion means, a filter, second voltage / current conversion means having an output connected to the compensation coil and an input connected to the output of the filter, and an output connected to the input of the filter and the second DC-SQUID noise removal for non-destructive inspection, comprising: an oscillator connected to an input of one voltage / current conversion means; and a filter coefficient updating means for updating a coefficient of the filter by an output of the driving circuit. system. 3. The DC-SQUID and the DC-SQUI
A drive circuit for driving D; a magnetic field applying coil magnetically coupled to the measurement sample; a coil magnetically coupled to the DC-SQUID; and an output connected to the magnetic field applying coil. First voltage /
Current conversion means, a filter, second voltage / current conversion means having an output connected to the coil and an input connected to the output of the filter, and an output connected to the input of the filter and the first A DC-SQUID noise removal system for non-destructive inspection, comprising: an oscillator connected to an input of a voltage / current converter; and a filter coefficient updating unit for updating a coefficient of the filter by an output of the driving circuit. 4. A DC-SQUID, a driving circuit for driving the DC-SQUID, a magnetic field applying coil magnetically coupled to a measurement sample, and a second output having an output connected to the magnetic field applying coil. One voltage /
A current conversion means, a filter having an output connected to the drive circuit, an oscillator having an output connected to the filter and the first voltage / current conversion means, and a coefficient of the filter based on an output of the drive circuit. DC-SQUID noise removal system for non-destructive inspection, comprising: a filter coefficient updating unit for updating the noise reduction coefficient.