JPH11271279A - Eddy current flaw detector and adjustment method thereof - Google Patents

Abstract

(57) [Problem] To provide an eddy current flaw detector capable of adjusting a phase and a flaw detection frequency suitable for natural defect detection in a short time, and a method of adjusting the same. SOLUTION: An oscillator for generating a plurality of different frequencies
4-1 to 4-n, mixer for superimposing signals of each frequency of the transmitter
6. An eddy current flaw detection device including a probe 7 for exciting a test material with an alternating current output from the mixer and detecting a flaw detection signal, and a storage device 10 for storing a detection signal of the probe. Inspection of a material to be inspected is performed by superimposing a plurality of different frequencies, and a natural defect detection signal at that time is stored in synchronization with a pulse signal of each frequency, and is repeatedly used as a flaw detection signal. Adjustment of the optimum frequency and the optimum phase corresponding to the detection of.

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 having a parameter adjusting system and a parameter adjusting method thereof.

[0002]

2. Description of the Related Art Eddy current flaw detectors with parameter adjustment are:
For example, it is disclosed in JP-A-52-75488. It is described that the time required for setting the flaw detection sensitivity is remarkably reduced by obtaining a signal corresponding to a standard defect necessary for setting the flaw detection sensitivity by a pure electric method as needed in a simulated manner.

Japanese Patent Application Laid-Open No. 55-46182 discloses a one-input one-output type storage device in which data relating to an artificially formed standard flaw is stored and repeatedly used as necessary for a flaw detection signal. It is described that adjustment and setting work of each part based on a test piece can be performed easily in a short time.

[0004]

In an eddy current flaw detection apparatus capable of selecting a plurality of phases and a plurality of flaw detection frequencies, there are a phase and a flaw detection frequency in addition to the flaw detection sensitivity as parameters largely affecting flaw detection performance. In general, the phase and the flaw detection frequency are determined after online investigation of the phase characteristics and frequency characteristics of the natural defect to be detected. Therefore, it takes a very long time to adjust the optimum phase and the optimum flaw detection frequency. On the other hand, Japanese Unexamined Patent Publication No.
Japanese Patent Publication No. 488 aims at shortening only the work of setting the flaw detection sensitivity based on the simulation signal corresponding to the standard defect, and the work of adjusting the phase and frequency suitable for the natural defect to be detected cannot be shortened. There is a problem.

In Japanese Patent Application Laid-Open No. 55-46182, since the storage device is of the one-input one-output type, a plurality of flaw detection signals cannot be stored in parallel. In the adjustment of the phase and the frequency, first, the data of the standard flaw is stored with the flaw detection frequency fixed, and the phase characteristic at the flaw detection frequency is obtained by repeatedly using the flaw detection signal. next,
The operation of changing the flaw detection frequency, storing the data, and repeatedly using the flaw detection signal to obtain the phase characteristic at the changed flaw detection frequency is repeated a plurality of times. By comparing them, it is necessary to determine the optimum phase and flaw detection frequency. That is, there is a problem that the data of the standard flaw must be stored again every time the flaw detection frequency is changed.

Therefore, the present invention solves the above problems,
It is an object of the present invention to provide an eddy current flaw detector capable of easily adjusting parameters for natural defects and a method for adjusting various parameters of the eddy current flaw detector.

[0007]

(1) In order to achieve the above object, the present invention relates to an eddy current flaw detection device for flaw detection of a test object made of a conductor, a transmitter for generating a plurality of different frequencies, and a transmitter for the transmitter. A mixer for superimposing signals of respective frequencies, a probe which is excited by an alternating current output from the mixer and detects a flaw detection signal, and a storage device for storing a detection signal of the probe are provided.

According to this, instead of performing the flaw detection by changing the flaw detection frequency, it is possible to superimpose a plurality of different frequencies, excite the excitation coil of the probe, and detect a natural defect on the inspection material. . If the flaw detection signal is stored in synchronization with the pulse signal of each frequency, the flaw detection signal is repeatedly used by changing the setting of the filter and the phase shifter, so that different phases and flaw detection are performed for the same natural defect. The flaw can be detected at the frequency, and the phase characteristic and the frequency characteristic with respect to the natural defect can be easily obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (2) In an eddy current flaw detector for eddy current inspection of a material to be inspected online, a probe 7 for detecting a natural defect on the material to be inspected and an equilibrium output of the probe 7 are set to 2 And an A / D for converting one of the outputs of the distributor 8 into a digital signal
A converter 9 and an output of a digital value obtained by conversion by the A / D converter 9 are output to a plurality of control circuits 5-1.
And a multi-input / multi-output storage device 10 that can store data in parallel according to the respective commands from .about.5-n and output the data as needed, and a D / An A converter 11, and switches 12-1 to 12-n for switching between the output of the D / A converter 11 and the other output of the distributor 8,
A plurality of control circuits 5-1 to 5-1 which output a storage start command and an output start command to the storage device 10 in synchronization with a pulse signal.
5-n.

(3) Further, the phase characteristic and the frequency characteristic for the same natural defect can be obtained by repeatedly using the on-line natural defect detection signal on the material to be inspected stored in the eddy current flaw detector for the flaw detection signal. The optimal phase,
It is characterized in that the optimum flaw detection frequency is determined.

When an alternating current is applied to an exciting coil placed close to a conductor, a magnetic flux is generated, and an eddy current is generated in the conductor by electromagnetic induction. The magnetic flux generated by the eddy current is generated in a direction to cancel the magnetic flux of the exciting coil. The magnetic flux induces a voltage V in the detection coil placed close to the conductor. The voltage V is expressed by the following equation, where S is the area affected by the magnetic flux density B, and φ is the magnetic flux linked to the detection coil: V = − (dφ / dt) = − (d / dt) ∫ ( SB) ds (1).

The voltage V induced in the detection coil changes due to the magnetic flux due to the eddy current of the conductor. The measurement principle is to analyze the coil impedance based on the voltage V to detect a change in eddy current due to a flaw on the conductor and a change in magnetic flux between the coil and the conductor.

In the eddy current flaw detector, parameters for detecting a coil impedance change due to a flaw with high sensitivity include flaw detection sensitivity, phase, and flaw detection frequency. The flaw detection sensitivity is a parameter for adjusting a flaw signal of a flaw to a specific level. The phase is a parameter determined in consideration of the directivity of the flaw detection signal caused by the flaw shape, and FIG. 2 shows an example of the phase characteristic of a flaw (flaw).

The horizontal axis in FIG. 2 is the phase (degree), the vertical axis is the S / N of the flaw type, and the natural defect A has an optimum phase of 30 degrees.
It can be seen that 60 degrees is the optimal phase for the natural defect B.

The flaw detection frequency is a parameter affecting the penetration depth δ, and is expressed by the following equation: δ = √ (ρ / πfμ) (2) where δ: penetration depth, ρ: Electric resistivity, μ: magnetic permeability, f: frequency.

That is, when the frequency is high, the penetration depth is small, and when the frequency is low, the penetration depth is large. Therefore, it is necessary to select a frequency suitable for the depth of the natural defect to be detected. This is shown in the frequency characteristics of FIG.

FIG. 3 shows the flaw detection frequency on the abscissa and the S / N at the optimum phase of the flaw type on the ordinate, where the natural flaw A is 10 KHz and the natural flaw B is 30 KHz. You can see that there is.

That is, in order to detect the natural defect A,
Phase 30 degrees, flaw detection frequency 10 kHz, natural defect B
60 degrees phase and 30K flaw detection frequency to detect
Hz may be set. As described above, in order to select an optimum phase and frequency for a certain natural defect, it is necessary to perform flaw detection at various phases and flaw detection frequencies and compare them.

According to the present invention, a plurality of different frequencies are superimposed, and the excitation coil of the probe is excited to detect a natural defect on a material to be inspected, instead of performing the inspection by changing the inspection frequency.
If the flaw detection signal is stored in synchronization with the pulse signal of each frequency, the flaw detection signal is repeatedly used by changing the setting of the filter and the phase shifter, so that different phases and flaw detection are performed for the same natural defect. The flaw can be detected at the frequency, and the phase characteristic and the frequency characteristic with respect to the natural defect can be easily obtained.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0021]

FIG. 1 shows an embodiment of the present invention. The eddy current flaw detector of this embodiment detects a natural defect existing on the surface of a wire as a material to be inspected. Oscillation circuit 1
Oscillates a reference pulse, and each dividing circuit 2 having a different dividing ratio.
-1 to 2-n are output. The dividing circuits 2-1 to 2-n are
Pulse signals having different frequencies are generated, and the AC currents are shaped by frequency division shaping circuits 4-1 to 4-n.

Alternating currents of different frequencies are superimposed in the mixer 6 to excite the exciting coil of the probe 7. Further, the probe 7 incorporates an excitation coil and a detection coil, and a single probe 7 can simultaneously obtain flaw detection signals at a plurality of flaw detection frequencies excited by the excitation coil with the detection coil. it can. A flaw detection signal obtained when a material to be inspected (not shown) is passed is branched by a distributor 8, one of which is output to an A / D converter 9 and the other is output to switches 12-1 to 12-n. You.

The flaw detection signals converted into digital signals by the A / D converter 9 are stored in the storage device 10 in parallel in accordance with storage start commands from the plurality of control circuits 5-1 to 5-n. At this time, it is assumed that each storage start command from each of the control circuits 5-1 to 5-n is synchronized with a pulse signal having a different frequency. The other flaw detection signal branched by the distributor 8 is transmitted to the switch 1
The signals are amplified by amplifiers 13-1 to 13-n through 2-1 to 12-n, and output to phase detectors 15-1 to 15-n through filters 14-1 to 14-n.

At the time of normal flaw detection, a flaw detection signal passes through this route. However, if an important natural defect occurs during the inspection material inspection, the data stored in the storage device 10 at this time is repeatedly used to determine the phase characteristics and frequency characteristics of the natural defect. This is performed as follows. First, the switches 12-1 to 12-n are connected to the D / A converter 11
And outputs the data stored in the storage device 10. The output at this time follows an output start command from the control circuits 5-1 to 5-n synchronized with the pulse signal. The filters 14-1 to 14-n are set in a band having one of a plurality of flaw detection frequencies excited in the excitation coil as a center frequency. In this state, the phase setting of the transfer units 3-1 to 3-n is changed by 10 degrees for each signal output, and the S / N is measured by the recorder output after the signal processing at that time, and the phase characteristics are measured. investigate.

These operations are performed by changing the settings of the filters 14-1 to 14-n for all excitation frequencies.
The phase and the flaw detection frequency when the S / N is the largest are defined as the optimum phase and the optimum flaw detection frequency. As described above, the optimum phase and the optimum frequency corresponding to each natural defect during the inspection material inspection are determined. The type of natural defect varies depending on operating conditions and the like, and it usually takes several months for a series of important natural defects to occur in the inspection of a material to be inspected. The optimum phase and the optimum frequency for the natural defect are determined for the natural defect generated during this time by the above-described method, and the adjustment of the eddy current flaw detection is completed.

In this embodiment, the case of a multi-frequency eddy current flaw detector in which a plurality of different frequencies are superimposed on one probe 7 has been described, but different frequencies are excited in a plurality of probes. The present invention can be similarly implemented in the case of the multi-probe multi-frequency eddy current flaw detector described above. In this case, the probe 7 becomes a plurality of probe groups, and each probe i in the probe group is connected to the frequency dividing / shaping circuit 4-i and the switch 12-i. A signal obtained by mixing the outputs of the n / m frequency dividing and shaping circuits with each probe using a plurality of m probes (7), a mixer and an amplifier (6), and a switch (8). May be given.

[0027]

According to the eddy current flaw detector, a plurality of different frequencies are superimposed to detect a natural defect, and the flaw detection signal is stored in synchronization with the pulse signal of each frequency, whereby any natural defect can be detected. It has become possible to adjust the frequency and phase suitable for detection in a short time and easily.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of one embodiment of the present invention.

FIG. 2 is a graph showing a change in S / N with respect to a phase shift when a flaw detection frequency is fixed.

FIG. 3 shows S of two types of natural defects at each flaw detection frequency.
4 is a graph showing / N.

Claims (3)

[Claims] An eddy current flaw detector for flaw-insulating a test object made of a conductor, a transmitter for generating a plurality of different frequencies, a mixer for superimposing signals of the respective frequencies of the transmitter, and an output AC from the mixer. An eddy current flaw detection device comprising: a probe that is excited by a current to detect a flaw detection signal; and a storage device that stores a detection signal of the probe. 2. An eddy current flaw detector for eddy current inspection of a material to be inspected online, a probe 7 for detecting a natural defect on the material to be inspected, and a distributor for branching the balanced output of the probe 7 into two. And an A / D converter 9 for converting one of the outputs of the distributor 8 into a digital signal.
And the digital value output obtained by the conversion by the A / D converter 9 can be stored in parallel according to each command from the plurality of control circuits 5-1 to 5-n, and simultaneously output as needed. A possible multi-input multi-output storage device 10;
A D / A converter 11 for converting the data output from the storage device 10 into an analog signal, and switches 12-1 to 12-n for switching between the output of the D / A converter 11 and the other output of the distributor 8; A plurality of control circuits 5-1 to 5-n for outputting a storage start command and an output start command to the storage device 10 in synchronization with a pulse signal, and converting the conversion output of the D / A converter 11 into eddy current flaw detection. Eddy current flaw detector that has a system that can be used repeatedly as an instrument adjustment signal and that can select multiple phases and multiple flaw detection frequencies. 3. The phase characteristic and frequency characteristic for the same natural defect are determined by repeatedly using the on-line natural defect detection signal on the material to be inspected stored in the eddy current flaw detection apparatus as the flaw detection signal, thereby obtaining an optimum. 3. The method for adjusting an eddy current flaw detection device according to claim 1, wherein the phase and the optimum flaw detection frequency are determined.