TWI414788B - Eddy current detector using magnetic gap - Google Patents

Abstract

An eddy current detector uses magnetic gap. Thus, the detector has a small size; and the wire coil number in the detector is reduced. Hence, the detector can move easily inside or outside a tube and detect a target as close as possible.

Description

Magnetic gap eddy current probe

The present invention relates to a magnetic gap type eddy current probe, in particular to a magnetic circuit, in particular to limit the magnetic field range by magnetic gap to make it have higher resolution and smaller structure, and is more favorable for bending. The inside and outside of the tube move to reach a closer to the terminal detector.

According to the general eddy current probe, the eddy current probe is divided into an absolute or differential probe. As shown in Figures 4 and 5, it is a probe with a coil 3 winding as an air core, which can be placed on the outer surface of the object to be tested or On the inner surface, it has the advantage of being simple, inexpensive and sufficient for general applications. However, under certain test conditions, it is also limited by physical properties, such as edge effects, but in the case of broken nuclear fuel rods, many of its defects are also produced at the two ends of the fuel rod.

Furthermore, the coil 3 of the air core is used, and the number of coils is large, so the internal resistance of the coil 3 is high, and the equivalent circuit thereof is as shown in Fig. 6, because the area of the area affected by the eddy current induction is large, and the coil is avoided. The mutual inductance effect between the coil and the coil is bound to increase the distance between the two coils, so the size of the probe is limited. However, the purpose of the test is to determine precisely whether the test item is good or defective, requiring repair, plugging or replacement; and the measuring probe needs to be sufficiently small to extend and move through all of the test object. Part, especially the curved part of the tube. However, in the above-mentioned prior art, due to the limited size reduction of the probe, the detection of all parts of the object to be tested is also limited, and during the period in which the probe moves to the wall of the tube, due to mutual interference between the coils, The measurement or the signal supplied during the movement of the probe during the movement of the tube cannot accurately detect and determine the wall All the defects, so can not effectively improve its discriminating ability. Therefore, the general practitioners cannot meet the needs of the user in actual use.

SUMMARY OF THE INVENTION The primary object of the present invention is to overcome the above-discussed problems encountered in the prior art and to provide a method for improving the discriminating power by approaching the detection of the end of the wall.

A secondary object of the present invention is to provide a magnetic analyzer that can be very narrow and that achieves high resolution as narrow as a few microns (μm).

Another object of the present invention is to provide a terminal having a small influence area so that the generated eddy current induction can be as close as possible to the object to be tested.

Another object of the present invention is to provide a method for effectively reducing the mutual inductance between coils, to provide higher discriminating power, and to reduce the distance between the two coils, thereby reducing the size of the probe to facilitate the bending of the tube. Inside and outside as a mover.

It is still another object of the present invention to provide a high-conducting magnetic core to reduce the number of windings, thereby reducing the internal resistance of the coil and having a high Q value.

For the purpose of the above, the present invention is a magnetic gap type eddy current probe which is applicable to a defect in the tube of the object to be tested and which is close to the terminal to detect the defect, and includes a high-conducting magnetic core and an exciting coil. A support member and a detecting mechanism. The high-conducting magnetic core surrounds the object to be tested, and has an annular magnetic gap on the surface facing the object to be tested; the exciting coil is wound around the high-conducting magnetic core for An eddy current induction is generated in the object to be tested; the support member is provided with an excitation coil disposed around the high-conducting magnetic core; and the detecting mechanism excites the excitation coil to generate a high-frequency magnetic field, and the signal is taken The impedance of the test object is analyzed.

By means of the above components, a specific magnetic circuit is provided, and the annular magnetic gap is The range of the magnetic field makes it more advantageous to move inside and outside the curved rod tube to achieve a detection that can be closer to the end of the tube wall to improve the discriminating power.

Please refer to FIG. 1 to FIG. 3 for a schematic diagram of the outside inspection of the tube of the present invention, a schematic diagram of the inner surface inspection of the tube of the present invention, and an equivalent circuit diagram of the present invention. As shown in the figure, the present invention is a magnetic gap type eddy current probe which can be applied to a tube of the object to be tested 2 and which is close to the terminal to detect defects thereof, and includes a high-conducting magnetic core 11 and an exciting coil. 12. A support member 13 and a detecting mechanism 14.

The high-conducting magnetic core 11 is surrounded by the object to be tested 2 in a horseshoe shape, and has an annular magnetic gap 111 on the surface facing the object to be tested 2 . The high-conducting magnetic core 11 is a soft magnetic metal material or a ferrite magnet.

The excitation coil 12 is wound around the high-conducting magnetic core 11 and the annular magnetic gap 111 faces only one of the exposed objects 2 to generate eddy current induction in the object 2 to be tested.

The support member 13 is provided with a set of the excitation coil 12 around which the high-conducting magnetic core 11 is wound.

The detecting mechanism 14 excites the exciting coil 12 to generate a high frequency magnetic field, extracts its signal and analyzes the impedance of the object 2 to be tested. As described above, a new type of magnetic gap eddy current probe is constructed.

When the present invention is applied, the nuclear fuel rod tube is used as the object 2 to be tested, and can be applied to the outside of the rod tube (as shown in FIG. 1) and the inner surface (as shown in FIG. 2) for detection. The annular magnetic gap 111 of the high-conducting magnetic core 11 can be in the form of a very narrow number of micrometers (μm) as desired by the user. Yu Yi In a preferred embodiment, when the excitation coil 12 is excited by the high-frequency current outputted by the detecting mechanism 14, each coil system senses the object to be tested to generate a corresponding impedance, and detects the excitation by processing the sampled signal. The impedance of the coil 12 changes, and it is further determined whether the fuel rod tube 2 has defects such as perforations and cracks, changes in texture, materials, and the like.

It can be seen from the above that the present invention is composed of the above-mentioned components, and the excitation coil is wound on the high-conducting magnetic core having the annular magnetic gap to provide a specific magnetic circuit, and the annular magnetic gap limits the magnetic field range, which is related to the prior art. In comparison, the present invention has the following several advantages, including: (1) high resolution, the magnetic gap can be very narrow, and narrow to several μm (ie, less than a few thousandths of a millimeter) depending on the demand; (2) small influence area The generated eddy current induction can be as close as possible to the terminal of the object to be tested; (3) effectively reduce the mutual inductance between the coils, can provide higher discriminating power, and can reduce the distance between the two coils, thereby achieving the reduction of the probe The appearance size is more favorable for moving inside and outside the curved tube; and (4) high Q value, the invention uses a high-conducting magnetic core to reduce the number of windings, thereby reducing the internal resistance of the coil.

In summary, the present invention is a magnetic gap type eddy current probe, which can effectively improve various shortcomings of the conventional use, and provides a specific magnetic circuit, and the magnetic gap limits the magnetic field range to reduce the area and reduce the mutual inductance between the coils and The internal resistance, when reducing the distance between the two coils and further reducing the size of the probe, can be more beneficial to move inside and outside the curved rod tube, so as to achieve closer to the detection of the end of the tube wall and improve the discriminating power, thereby enabling The invention can be made more progressive, more practical, and more in line with the needs of the user. It has indeed met the requirements for the creation of a patent application, and has filed a patent application according to law.

However, the above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto; therefore, the simple equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the invention are modified. All should remain within the scope of the invention patent.

(part of the invention)

11‧‧‧High-conducting magnetic core

111‧‧‧Circular magnetic gap

12‧‧‧Exciting coil

13‧‧‧Support members

14‧‧‧Detection agencies

2‧‧‧Test object

(customized part)

3‧‧‧ coil

4‧‧‧Test object

Fig. 1 is a schematic view showing a first embodiment of the present invention.

Fig. 2 is a schematic view showing a second embodiment of the present invention.

Figure 3 is a schematic diagram of an equivalent circuit of the present invention.

Figure 4 is a schematic diagram of the outside inspection of the tube.

Figure 5 is a schematic diagram of the inner surface inspection of the tube.

Figure 6 is a schematic diagram of an equivalent circuit that is conventional.

11‧‧‧High-conducting magnetic core

111‧‧‧Circular magnetic gap

12‧‧‧Exciting coil

13‧‧‧Support members

2‧‧‧Test object

Claims (4)

A magnetic gap type eddy current probe is applicable to the inside and outside of a tube to be tested, and the defect is detected near the terminal, and includes: a high-conducting magnetic core surrounding the object to be tested, and the surface The surface of the object to be tested has an annular magnetic gap; an exciting coil is wound around the core of the high-conducting magnetic core, and the annular magnetic gap is exposed to the object to be tested, and only one part is used. An eddy current induction is generated in the object to be tested; a support member is provided to fix the excitation coil around the high-conducting magnetic core; and a detecting mechanism is configured to excite the excitation coil to generate a high-frequency magnetic field, and capture The signal is analyzed and the impedance change of the coil is analyzed; and by the components of the above components, a specific magnetic circuit is provided, and the annular magnetic gap limits the magnetic field range to make it more favorable to move inside and outside the curved object tube. More close to the terminal detector. The magnetic gap type eddy current probe according to claim 1, wherein the high-conducting magnetic core is a soft magnetic metal material or a ferrite magnet. The magnetic gap eddy current probe according to claim 1, wherein the annular magnetic gap can be narrowed to less than a few thousandths of a millimeter. The magnetic gap type eddy current probe according to claim 1, wherein the object to be tested is a nuclear fuel rod tube.