JPH0933489A - Moving exciting coil type eddy current flaw detector employing squid flux meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a moving exciting coil type eddy current flaw meter employing a SQUID(Superconducting Quantum Interference Device) in which eddy current flaw detection can be carried out while fixing an object (specimen). SOLUTION: The inventive eddy current flaw detector comprises an SQUID flux meter including an SQUID 1 and a differentiation type pickup coil 2 for detecting the field, an exciting coil 3 for inducing an eddy current in a specimen 4, and means for moving the exciting coil 3 on a position for equalizing the interlinking flux of coils constituting the pickup coil 2 along the specimen 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detector capable of flaw detection using a SQUID magnetometer while a test body (also referred to as a subject) is fixed. SQ here
What is UID Superconducting Quantum Interference Dev
Ice (superconducting quantum interferometer). SQUID is composed of a combination of superconducting ring and Josephson junction.

[0002]

2. Description of the Related Art In order to improve the sophistication of a device for destructive inspection, a flaw detector using a SQUID magnetometer having high magnetic field sensitivity has been developed. As shown in FIG. 9, a destructive inspection device using a conventional SQUID magnetometer includes an SQUID 1, a pickup coil 2 for detecting a magnetic field, and an XY stage for moving a test body (subject) 4. It is composed of a scanning device, and SQUID 1 and pickup coil 2 are
It was fixed so as not to pick up noise such as changes in the environmental magnetic field due to movement, and when performing flaw detection, the test body (subject) was placed on the scanning device and moved.

[0003]

However, the above-mentioned conventional S
In the flaw detector using the QUID magnetometer, the SQUID magnetometer is fixed, and the specimen was placed on the scanning device and moved on the side of the specimen at the time of flaw detection. Since it lacks in properties, there is a problem that it is not realistic to put it into practical use as a flaw detection device. The present invention aims to provide a device capable of solving these problems.

[0004]

An eddy current flaw detector according to the present invention is (A) an SQUID magnetometer comprising a SQUID and a differential type pickup coil for detecting a magnetic field, and (B).
An exciting coil for generating an eddy current in the subject and (C) means for moving the exciting coil along the subject at a position where the interlinking magnetic flux of the coils forming the pickup coil are equalized. Is characterized by.

That is, in the eddy current flaw detector using the SQUID magnetometer of the present invention, the shape and arrangement of the pickup coil are determined so as to cancel the magnetic field generated by the exciting coil, and the exciting coil receives the exciting signal. The eddy current flaw detector is constructed by moving the pickup coil at a position where it is canceled by the pickup coil. Therefore, eddy current flaw detection can be performed with the SQUID magnetometer while the test body (subject) is fixed.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention is shown in FIGS.
Shown in FIG. 1 is a SQ showing a first embodiment of the present invention.
1 shows an eddy current flaw detector using a UID magnetometer.

In FIG. 1, reference numeral 1 is an SQUID for converting a magnetic field signal into an electric signal. Reference numeral 2 is a pickup coil for detecting a magnetic field, which is an eight-shaped primary differential coil.

Reference numeral 3 denotes an exciting coil, which moves while generating an eddy current in the test body, but the exciting signal is canceled as a signal by the pickup coil due to the positional relationship between the exciting coil and the pickup coil.

In the eddy current flaw detector constructed as described above, when the exciting coil 3 is moved in the direction of the arrow as shown in FIGS. 1B and 1C, the generated magnetic field is picked up by the pickup coil 2. Since it is canceled, it is not detected in SQUID1.

Since the exciting coil 3 moves while generating an eddy current in the test body 4, if there is a flaw at the point where the exciting coil passes, the eddy current is disturbed, and the resulting disturbance of the magnetic field is caused. , SQUID 1 can be detected via the pickup coil 2. Therefore, it becomes possible to detect flaws.

Further, flaw detection can be performed by rotating the excitation coil 3 around the pickup coil 2 as shown in FIG. The reason is that the exciting coil 3
At a position where the generated magnetic field can be canceled by the pickup coil 2, the pickup coil 2 is rotated about the central axis to generate a magnetic field in the cylindrical sample 5,
This is because if there is a flaw in the eddy current, the eddy current is disturbed, the balance of the magnetic field distribution in the pickup coil portion is broken, and a change in the magnetic field is detected. Therefore, the flaw can be detected.

Next, the shape of the pickup coil 2 will be described. The detection of the magnetic signal in the SQUID magnetometer is
A pickup coil is used to pick up only a necessary signal instead of picking it up directly by the SQUID ring in consideration of flexibility and noise countermeasures. Although various shapes of the pickup coil have been considered depending on the purpose, they are generally the primary differential type coil shown in FIG. 3 or the secondary differential type coil shown in FIG.

The first-order differential coil can eliminate a spatially uniform magnetic field by differentially connecting the two coils. That is, the first-order type differential coil can reduce environmental noise and detect only a necessary magnetic signal in the vicinity of the pickup coil.

Next, the position of the exciting coil 3 that can cancel the magnetic field with respect to the pickup coil 2 will be described. Two coils are differentially connected to the pickup coil 2.

Therefore, if the interlinkage magnetic fluxes of the two coils are equal, the output of the pickup coil 2 becomes zero. More specifically, referring to FIG. 5, when the two coils forming the pickup coil 2 have the same area and the same number of windings, the distances of the straight lines connecting the centers of the two coils and the exciting coil are equal. When the exciting coil is moved at the position, the difference between the interlinking magnetic fluxes of the two coils becomes 0, and the magnetic field from the exciting coil is canceled.

This is the same as in FIG. 6, and if the exciting coil is moved vertically on a plane that is at the same distance from the two coils constituting the pickup coil 2 and is perpendicular to the axis of the pickup coil 2, The difference between the interlinkage magnetic fluxes of the two coils constituting the above becomes 0, and the magnetic field is canceled.

Next, the means for moving or rotating the exciting coil 3 will be described. The moving device of the exciting coil 3 first determines a position where the magnetic field from the exciting coil 3 is canceled by the pickup coil, and sets the device so as to move the position.

FIG. 7 shows a moving device by rotating a screw as an example of moving the exciting coil. This is X-
This is a mechanism used for the Y stage and the like. However, since the motor that rotates the screw generates magnetism, SQUI
It is necessary to separate the SQUID so as not to affect D or shield the motor itself.

Basically, the exciter coil moving device must be a non-magnetic material. Further, as a method that does not use a motor, there is a method that uses hydraulic pressure or air. In FIG. 8, the exciting coil 3 is mounted on a rotating body such as a cylinder, and the rotating body is driven by a motor to rotate the exciting coil 3 around the fixed pickup coil 2. However, also in this case, the motor needs to be charged and separated from the SQUID or covered with a shield.

[0020]

【The invention's effect】

(1) According to the present invention, eddy current flaw detection can be performed by the SQUID magnetometer without moving the test body (subject). (2) Therefore, it is possible to detect a test object (inspection object) that cannot be moved and a test object (including an actual device) that is too large to be placed on the scanning device because it has more flexibility than the conventional device. become.

[Brief description of the drawings]

FIG. 1 is an eddy current flaw detector using a SQUID magnetometer showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a flaw detection device using the present invention for a cylindrical conductor.

FIG. 3 is a diagram showing a primary differential coil.

FIG. 4 is a diagram showing a secondary differential coil.

FIG. 5 is an explanatory view (1) of the interlinkage magnetic flux of the pickup coil.

FIG. 6 is an explanatory diagram of a magnetic flux linkage of the pickup coil (No. 2).

FIG. 7 shows a moving device of an exciting coil (No. 1).

FIG. 8 shows a moving device of an exciting coil (No. 2).

FIG. 9 is a view showing an eddy current flaw detector using a conventional SQUID magnetometer.

[Explanation of symbols]

 1 ... SQUID, 2 ... Pickup coil, 3 ... Excitation coil, 4 ... Test object (subject), 5 ... Cylindrical sample, 10 ... Screw, 11 ... Motor, 12 ... Magnetic shield.

Claims (1)

[Claims] 1. A SQUID comprising (A) an SQUID (1) and a differential type pickup coil (2) for detecting a magnetic field.
The magnetic flux meter, (B) the exciting coil (3) for generating an eddy current in the subject (4), and (C) the exciting coil (3), the interlinkage magnetic flux of the coils forming the pickup coil (2). And a means for moving the object along the subject (4) at a position where they are equal to each other.