JPH03214052A - Heterogeneous layer detector - Google Patents

Abstract

PURPOSE:To make it possible to perform detection even if a heterogeneous layer is orthogonal to a measuring surface by tilting a probe for applying a magnetic field on a material to be measured with respect to the detecting surface of the surface to be measured. CONSTITUTION:In a detecting part 10, a Maxwell bridge is constituted of a detecting coil 14 of a probe 12, a correcting coil 16 and a pair of resistors 18 and 20. A bobbin 22 supports the coil 14 so that the coil 14 is tilted with respect to a detecting surface 26 of a material to be measured 24. The magnetic flux generated in the coil 14 is obliquely inputted into the detecting surface 26. One end of each of the coils 14 and 16 is connected to the output side of an amplifier 32 for amplifying the output of an oscillator 30. The other ends are connected to the resistors 18 and 20 and the input side of an amplifier 36. The amplifier 36 amplifies the output of the Maxwell bridge. The amplified signal is inputted into a phase detector 38 together with the output signal of the oscillator 30. The detector 38 detects the phase of the output signal of the oscillator 30, i.e. the exciting current for the coil 14 and the coil 16, and the phase of the output signal of the Maxwell bridge. The signal corresponding to the difference between both phases is outputted.

Description

[Detailed description of the invention] [Industrial 111 field] The present invention generates an i#l@ flow in an object to be measured such as a metal,
This invention relates to a pulp layer detector that detects changes in the induced electromotive force due to this eddy current (for flaw detection, etc.).

C. Prior Art] A non-destructive inspection device is known that generates an eddy current in a conductive object such as a metal, detects changes in the eddy current, and checks the material for damage or damage to the object. It is being

Such Jl':M fracture inspection equipment places a probe equipped with a coil that generates an alternating magnetic field in contact with or in close proximity to the object to be measured, and applies the alternating magnetic field from the probe to the object to be measured. By generating an eddy current in the probe and detecting changes in the induced electromotive force generated in the detection coil of the probe due to changes in the eddy current, it is now possible to detect foreign layers such as scratches or differences in composition that exist in the object to be measured. There is.

In such conventional inspection equipment, the probe that applies an alternating magnetic field to the object to be measured is placed perpendicular to the measurement surface of the object, so that the tip of the probe is parallel to the measurement surface. . That is, the probe is arranged so as to apply a perpendicular magnetic field to the object to be measured, and scans parallel to the measurement surface to detect abnormalities in the layer. And the penetration depth of eddy current is
The magnitude of the eddy current is adjusted by changing the frequency of the current applied to the coil of the probe, and by changing the value of the current applied to the probe.

(Problems to be Solved by the Invention) When a perpendicular magnetic field is applied to the object to be measured as described above, a magnetic flux is perpendicularly incident on the object to be measured, and a solid concentric eddy current is generated around this magnetic flux. For this reason, in conventional inspection equipment in which the tip surface of the probe is parallel to the measurement surface, when the thickness of the layer such as a defect existing on the object to be measured is small, the influence on the eddy current of the defect is small, and the probe There was no other way to detect the eddy current than by making it smaller than -4.Furthermore, even when the heterogeneous layer is perpendicular to the measurement surface, the magnetic flux passes through the heterogeneous layer in parallel, so the influence of the heterogeneous layer on the eddy current is small. was small, and the changes in the detection signal were minute, making measurement extremely difficult.

The present invention has been made to eliminate the drawbacks of the prior art, and aims to provide a different 1rJi detector that can detect even when the different la layer is perpendicular to the measurement surface.

(Means for Solving the Problems) ] In order to achieve the above two objects, the tungsten layer detector according to the present invention generates an eddy current in the object to be measured and detects the heterogeneous layer in the object to be measured. In a heterogeneous layer detector for detecting a magnetic field, a probe for applying a magnetic field to the object to be measured is tilted with respect to a detection surface of the object to be measured, and the magnetic field applied to the object to be measured is oriented obliquely to the detection surface. It is characterized by

[Effect]

In the present invention configured as described above, since the probe that applies a magnetic field to the object to be measured is inclined to the detection surface of the object to be measured, the magnetic field applied from the probe to the object to be measured is oblique to the detection surface, and the magnetic field is The magnetic flux that coincides with the tangential direction also intersects obliquely with the detection surface. For this reason, the magnetic flux passing through the object to be measured crosses the heterogeneous layer perpendicular to the detection surface, causing disturbances in the magnetic flux path, and the circular eddy currents generated around the magnetic flux are inclined to the detection surface. This occurs in a state where the foreign layer crosses diagonally with a foreign layer such as a defect perpendicular to the detection surface, making the foreign layer appear larger, the path of the eddy current changes greatly, and the fluctuation of the detection signal also increases. Therefore, foreign layers such as defects perpendicular to the detection surface, which have been difficult to detect in the past, can be easily detected.

In addition, it is possible to easily detect abnormal fl in an object to be measured, such as a welded thin plate, which has no thickness in the depth direction of the detection surface.

(Embodiments) Preferred embodiments of the heterogeneous layer detector according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram of a heterogeneous layer detector according to an embodiment of the present invention.

In FIG. 1, the detection unit 10 constitutes a Maxwell bridge by the detection coil 14 of the probe 12, the correction coil 16, and a pair of resistors 16 and 20.

The detection coil 14 of the probe I2 is wound around a bobbin 22 that supports the coil. This bobbin 22 has its tip facing the object to be measured 24 cut off obliquely, and the detection coil 14
is supported at an angle of about 1 with respect to the detection surface 26 of the object to be measured 24, so that the magnetic flux generated by the detection coil 14 is obliquely incident on the detection surface 26.

The correction coil 16 corrects the output of the detection section IO according to the ambient temperature and the material of the object to be measured 24, and is wound around a bobbin 28 and held perpendicularly to the detection section 2G. ing. These coils 14 and 16 are connected at one end to the output side of an amplifier 32 that amplifies the output of the oscillator 30, and receive excitation current from the oscillator 30.

Then, the detection coil 14, as shown by the arrow 34,
The detection unit 26 moves parallel to the detection surface 26 to scan, and detects the presence or absence of a defect 50, which is a foreign layer, in the object 24.

The other ends of the detection coil 14 and the correction coil 16 are connected to a resistor 16.20 which is grounded and to the input end of the amplifier 36. The amplifier 536 amplifies the output of the Maxwell bridge, and the amplified signal is input to the phase detector 38 together with the output signal of the oscillator 30. The phase detector 38 detects the output signal of the oscillator 30, that is, the phase of the excitation current of the detection coil 14 and the correction coil 16, and the phase of the output signal of the Maxwell bridge, and outputs a signal according to the phase difference between the two. The output signal of the phase detector 38 is then amplified by an amplifier 40.

The operation of the embodiment configured as described above is as follows.

The oscillator 30 detects the excitation current of a predetermined frequency by the coil 1.
4 and the correction coil 1G, and the phase signal of the excitation current is input to the phase detector 38. The detection port 1 I4 and the correction coil 16 are connected to the excitation 6 I1 from the oscillator 30.
When receiving a current, it generates an alternating/A magnetic field in the axial direction of the coil, injects magnetic flux into the object 24 to be measured, and generates an eddy current in the object 24.

When an eddy current is generated in the object to be measured 24, an induced electromotive force due to the eddy current is generated in the detection coil 14 and the auxiliary iE coil I6, and the difference in the induced electromotive force generated in both coils is applied to the amplifier 36.
and sent to the phase detector 38.

Of course, the correction coil 16 adjusts iU'! of the object to be measured 24!
A 4ff flux is directly incident on the part 41 to generate an eddy current lN in that part, and an induced electromotive force corresponding to the magnitude of this eddy current is output as a detection signal. On the other hand, the detection coil 14 of the probe I2 is connected to the bobbin 22 as shown in FIG.
It is supported at an angle θ with respect to the detection surface 26, and in this inclined state, it moves along the detection surface 2G as shown by the arrow 34 in FIG. φ is incident on the object to be measured 24. Therefore, the magnetic flux φ obliquely crossing the detection surface 2G crosses the defect 50 perpendicular to the detection surface 26, causing disturbance in the path of the magnetic flux. Further, an induced electromotive force generated in the object to be measured 24 due to a change in the magnetic flux φ is generated in a plane inclined to the detection surface 26, and an eddy current i due to this induced electromotive force is generated inclined to the detection surface 26. do. Therefore, the eddy current 1 generated in the object to be measured 24 is disturbed, and even if the defect 50 is perpendicular to the detection surface 26, the apparent size increases, causing a large change in the eddy current i.

This large change in the eddy current i causes the detection coil 14
This increases the variation in the induced electromotive force induced by the sensor, thereby causing the detection signal of the detection coil 14 to vary. As a result, the defect 50 was minute, and even though it was perpendicular to the detection surface 2G,
The fluctuation of the detection signal becomes large and can be easily detected. Moreover, even if the object to be measured 24 is extremely thin, about 0.1 mm, it is possible to detect welds and the like.

Changes in the output signal of the detection coil 14 are amplified by an amplifier 36 and sent to a phase detector 38.

The phase detector 3B determines the phase difference between the signal based on the difference in the induced electromotive force of both coils and the output signal of the oscillator 30, and detects the defect 5.
A signal corresponding to the magnitude of 0 is output.

The penetration depth δ of the eddy current is determined by the frequency f of the magnetic field and the pyrotechnic (
The relationship is as follows, and it changes depending on the frequency of the excitation current that flows through the detection coil 14 and the correction coil 16.

δ-l/f1] - "a, where σ is the electrical conductivity of the object to be measured 24, and μ is the magnetic permeability of the object to be measured 24.

Therefore, by changing the frequency at which the detection coil 14 is excited, the immersion depth i8 of the eddy current generated in the object to be measured 24 can be changed, and the depth of penetration i8 of the eddy current generated in the object to be measured 24 can be changed. presence can be detected. The position of the defect 50 can be determined by determining the position of the probe 12 scanning the object to be measured 24.

Further, the magnitude of the eddy current can be adjusted by changing the magnitude of the excitation MW flow applied to the coil as described above.

In the above embodiments, the case of metal has been described, but the present invention can also be applied to conductive plastic or the like. Furthermore, in the embodiment described above, a case has been described in which a magnetic field is applied to the object to be measured 24 by the detection coil 14 and the correction coil I6, and an eddy current generated in the object to be measured 24 is detected. A coil for detecting eddy current may be provided separately.Although in the above embodiment, the size of a foreign layer is detected using a phase detector, changes in impedance due to the coil and capacitor may be used. The size of the heterogeneous layer may be determined by a method such as reading .

Furthermore, the core may be provided in the bobbin 22.28 of each coil 14.16, or the coil may be wound directly around the core. In this case, the core is tilted and supported at the tip of the core of the detection coil 14. Attach the support member.

(Effects of the Invention) As explained above, according to the present invention, since the probe that applies a magnetic field to the object to be measured is inclined to the detection surface of the object to be measured, the magnetic field applied from the probe to the object to be measured is The magnetic flux obliquely intersecting the detection surface and flowing through the object to be measured crosses the heterogeneous layer perpendicular to the detection surface, causing disturbance in the path of the magnetic flux, and
Concentric eddy currents generated around the magnetic flux are generated at an angle to the detection surface, and intersect diagonally with foreign layers such as defects perpendicular to the detection surface, making the material layer appear larger and causing eddy currents. By greatly changing the path of the sensor, it is possible to easily detect foreign layers such as defects perpendicular to the detection surface, which were previously difficult to detect.

[Brief explanation of drawings]

':j Figure 41 is an explanatory diagram of a heterogeneous layer detector according to an embodiment of the present invention, and Fig. 2 is an explanatory diagram of the operation of the embodiment. 1O detection section, 12 probes, 14 detection coils, 1G correction coil.

Claims (1)

[Claims] (1) In a heterogeneous layer detector that detects a heterogeneous layer within an object to be measured by generating an eddy current in the object, a probe that applies a magnetic field to the object is directed toward the detection surface of the object. A heterogeneous layer detector characterized in that the magnetic field applied to the object to be measured is obliquely crossed to the detection surface.