JPS6355668B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a reflection type electromagnetic ultrasonic flaw detection device,
In particular, the present invention relates to a reflection type electromagnetic ultrasonic flaw detection device that can provide a flaw detection function over a wide area close to the surface of an object.

Regarding conventional reflection type electromagnetic ultrasonic flaw detection equipment,
This will be explained with reference to FIG. A reflection type electromagnetic ultrasonic flaw detection device generally includes a magnetic generator including a magnetic pole 21, an excitation coil 22, and a DC power source 23 for generating a magnetic field facing a metal object 1, and a magnetic pole of the magnetic generator. A transmitting coil 31 and a receiving coil 32 placed near the surface of the subject 1 so as to be orthogonal to the lines of magnetic force generated by the transmitting coil 31, and a pulse generator 4 for applying a pulse current to the transmitting coil 31. , an amplifier 5 for amplifying the output voltage of the receiving coil 32, and a monitor 6 for monitoring the signal output of the amplifier 5.

During operation, an eddy current is generated on the surface of the subject 1 due to the pulse current supplied to the transmitting coil 31 from the pulse generator 4 . Since a magnetic field is applied to this eddy current generating portion, a Lorentz force is generated.

In the reflection type electromagnetic ultrasonic flaw detection device shown in Fig. 1, the magnetic field is applied perpendicularly to the surface of the object to be inspected, that is, the sample 1, so the Lorentz force is applied along the sample surface and in the direction perpendicular to the current vector. Occur. That is, a transverse wave is generated and propagates in the thickness direction of the sample 1.

This transverse wave is reflected by the bottom surface of the sample 1 or by the defect 11 in the sample 1, and returns to the surface as a bottom wave and a defect wave. These bottom waves and defect waves generate eddy currents on the surface of the sample 1 due to interaction with the magnetic field, thereby generating induced electromagnetic power in the receiving coil 32.

The voltage induced in the receiving coil 32 is supplied to the amplifier 5, amplified, and applied to the monitor 6. On the monitor 6, a waveform as shown in FIG. 2, for example, is observed. In FIG. 2, the horizontal axis shows time, and the vertical axis shows the detection output voltage from the receiving coil 32. Moreover, waveform T shows a leakage wave due to induction from the transmitting coil 31, waveform F shows a defective wave, and waveform B shows a bottom wave.

As is clear from FIG. 2, the time tn occupied by the leakage wave T becomes an unmeasurable dead zone when performing defect detection. In other words, the conventional reflection-type electromagnetic ultrasonic flaw detection device has the disadvantage that it cannot perform flaw detection in an area very close to the surface of the object to be inspected (a range up to a depth corresponding to the time tn occupied by the leakage wave T). It was hot.

The present invention is a reflection-type electromagnetic ultraviolet detection method that can expand the flaw detection area to very close to the surface of the object by minimizing the dead zone, which is a drawback of the conventional method as described above. The purpose of this invention is to provide a sonic flaw detection device.

In order to achieve the above object, in the present invention, a compensation coil is provided at a position relatively far from the subject or at a location where the influence of the magnetic field applied to the subject is as small as possible, and the receiving coil The output of the difference obtained by subtracting the output of the compensation coil from the output of There is.

FIG. 3 is a block diagram of one embodiment of the present invention. 33 is a compensation coil, and the same reference numerals as in FIG. 1 represent the same or equivalent parts. As is clear from the comparison between FIG. 2 and FIG. 1, this embodiment has a configuration in which a compensation coil 33 is provided outside the transmitting coil 31, and this and the receiving coil 32 are differentially connected. This is significantly different from the conventional example.

In this case, the compensation coil 33 is connected to the magnetic pole 2
It is preferable that the test object 1 be placed outside the magnetic field of the subject 1, or if it is inside the magnetic field, be set at a position away from the subject 1.

FIG. 4 shows the compensation coil 3 in this embodiment.
3 shows an electrical equivalent circuit of the receiving coil 32, the transmitting coil 31, and the pulse generator 4.
The leakage wave that causes the dead zone generates an induced noise voltage e ₁₂ in the receiving coil 32 due to the mutual inductance M ₁₂ between the transmitting coil 31 and the receiving coil 32.

The induced noise voltage _e12 is expressed as follows, where Ip is the pulse current value from the pulse generator 4, and ω is its frequency.
It is expressed by equation (1).

e ₁₂ = jωM ₁₂ Ip −(1) On the other hand, if the mutual inductance generated between the transmitting coil 31 and the compensation coil 33 by providing the compensation coil 33 is M ₁₃ , then the compensation Induced noise voltage in coil 33
e ₁₃ becomes as shown in equation (2).

e ₁₃ =jωM ₁₃ Ip −(2) Therefore, both induced noise voltages e ₁₂ and e ₁₃
Each mutual inductance M ₁₂ is equal to
In addition to making M ₁₃ and M 13 equal, if the receiving coil 32 and the compensation coil 33 are connected differentially as shown in FIG. 4, the induced noise voltage can be canceled out and removed.

In reality, it is extremely difficult to completely cancel out or eliminate the induced noise voltage due to the unbalanced components, but the dead band can be reduced to a fraction of what it is, so in practice the effect is significantly larger.

Incidentally, at this time, it is necessary that no ultrasonic signal is induced in the compensation coil 33. To do this, as described above, the compensation coil 33 must be connected to the magnetic pole 2.
1, or in the case of a magnetic field, place it away from the specimen 1, or change the angle of the coil surface with respect to the sample surface (No. 5).
(See figure).

In the above, an example has been described in which the compensating coil 33 is directly differentially connected to the receiving coil 32 so that the outputs of both coils cancel each other out, but this is not necessarily necessary.

For example, the output signals of the compensation coil 33 and the reception coil 32 may be input to a differential amplifier and canceled, or after being amplified by separate amplifiers, both signals may be differentially added and canceled. It is also possible to do so.

FIG. 5 is a sectional view of a main part of another embodiment of the present invention, and the same reference numerals as in FIG. 1 represent the same or equivalent parts.

In this embodiment, a transmitting coil 31 and a receiving coil 32 are provided on the tip surface of the magnetic pole 21 in the same way as in the case of FIG. 33 is provided. Moreover, 36 is a connector for connecting the lead wire of each coil to the outside.

With this configuration, the compensation coil 33 can be easily placed away from the subject 1 and outside the magnetic field of the magnetic pole 21, without damaging signal components such as bottom waves and defect waves. , there is an advantage that it becomes easy to cancel the leakage wave component and reduce the dead zone.

FIG. 6 shows the present invention applied to a reflection type electromagnetic ultrasonic flaw detection device for longitudinal waves. It is a sectional view of a main part of still another embodiment, and the same reference numerals as in FIGS. 1 and 5 represent the same or equivalent parts. In the figure, 3
4 is a conductive case, and 35 is an insulating plate.

In this case, all the coils are connected to magnetic poles 21 and 2.
The device can be configured compactly by arranging it in a space between 1 and 2. Also, as in the case of Figure 5,
Since the compensation coil 33 can be easily placed away from the subject 1 and outside the magnetic field of the magnetic poles 21, 21, leakage wave components can be removed without damaging signal components such as bottom waves and defective waves. This has the advantage of making it easier to offset the dead zone and reduce the dead zone.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a conventional reflection type electromagnetic ultrasonic flaw detection device, Fig. 2 is a diagram showing an example of the waveform displayed on the monitor at that time, and Fig. 3 is a block diagram of an embodiment according to the present invention. 4 are electrical equivalent circuit diagrams for explaining the operation of the present invention, and FIGS. 5 and 6 are sectional views showing essential parts of other embodiments of the present invention, respectively. DESCRIPTION OF SYMBOLS 1...Metal object, 4...Pulse generator, 5...Amplifier, 6...Monitor, 21...Magnetic pole, 31...Transmission coil, 32...Reception coil, 33...Compensation coil.

Claims (1)

[Claims] 1. A magnetic pole that faces one surface of a metal object and generates a magnetic field, a transmitting coil and a receiving coil placed near the surface of the object, and a pulse current applied to the transmitting coil. a pulse generator for generating an eddy current on the surface of the object under test; an amplifier for amplifying the voltage induced in the receiving coil; and a monitor for monitoring the signal output of the amplifier. In a reflection-type electromagnetic ultrasonic flaw detection device, the compensation coil is provided in the vicinity of the transmitting coil at a position where the influence of the magnetic field due to the magnetic pole is as small as possible, or at a position away from the test object. A reflection type electromagnetic ultrasonic flaw detection device comprising: a means for canceling the voltage induced in the receiving coil by the voltage induced in the compensation coil. 2. The reflection type electromagnetic ultrasonic flaw detection device according to claim 1, wherein the magnetic field from the magnetic pole is applied substantially perpendicularly to the surface of the object to be inspected. 3. The reflection type electromagnetic ultrasonic flaw detection device according to claim 1, wherein the magnetic field from the magnetic pole is applied substantially parallel to the surface of the object to be inspected.