JPH07229874A - Eddy current flaw detector - Google Patents

Abstract

(57) [Abstract] [Purpose] To eliminate the imbalance in the characteristics of a pair of sensor coils. [Structure] A pair of sensor coils forming a bridge circuit
In the eddy current flaw detector, which detects the eddy current generated by applying an AC magnetic field to (SC) and applying an AC magnetic field to the object to be inspected, to obtain the flaw detection information signal of the object to be inspected, SC An adjusting means for adjusting the phase of the test signal applied to at least one of the above is provided.

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.

[0002]

2. Description of the Related Art An eddy current flaw detector detects a change in eddy current generated by applying an alternating magnetic field to a metal while moving a sensor coil, and based on this, flaw detection (measurement) such as a structural defect. Is a device that can perform. In this type of eddy current flaw detector, an alternating current (for example, 0.5
The alternating magnetic field generated by the coil in which a current of about 1 kHz is applied causes an eddy current in the inspected object of the conductor, and the magnetic field generated by the eddy current acts on the coil.
It utilizes the fact that a change in electric potential occurs in the coil.

By the way, as shown in FIG. 4, a conventional eddy current flaw detector uses an oscillator 1 which outputs a variable clock signal which changes a pulse number corresponding to a desired frequency at a desired period so as to generate an alternating current of a desired frequency. The variable clock signal is D / A converted by the D / A converter and output amplifier 12 and is amplified to obtain an AC voltage of a desired frequency. Then, this is applied as a test signal to the bridge circuit 4 including the two sensor coils 5. When the surface of the object to be inspected is scanned by the two sensor coils 5 with the alternating voltage applied, an alternating current flows through the two sensor coils 5, so that the inspected object is generated by the alternating magnetic field generated by the alternating current. Eddy currents are induced in the body.

A current is generated in the sensor coil 5 by the alternating magnetic field generated by the eddy current. This current has a phase opposite to that of the test signal. Since the eddy current generated in the object to be inspected changes correspondingly due to the change in thickness or shape of the object to be inspected, the two sensor coils 5 forming the bridge circuit have a change in thickness or shape of the object to be inspected. Therefore, a potential difference that reflects is generated, and the balance of the bridge is lost.

Therefore, the unbalanced voltage of the two sensor coils 5 generated in this way is amplified by the differential amplifier 6, and if the frequency multiplexing method is used, the bandpass filter 12 is passed through to make the frequency and phase of the oscillator 1 equal. Synchronized flaw detection signal,
The AC voltage output from the D / A converter / output amplifier 12 is passed through a phase shifter 18 which shifts the phase by 90 °, and a test signal and a control signal whose phase is different by 90 ° are detected by the phase detector 13. In addition, synchronous detection is performed to remove the test signal component, and the flaw detection information signal that is the measurement information component is obtained.

There is a method using a multiplier, an analog switch, etc. for the synchronous detection, but in either case, since the signal of the oscillation frequency component or the unnecessary signal in the band higher than that is output after the detection, it is sure to pass through the low pass filter 14. . Then, after further amplifying the signal level to a desired level by the gain amplifier 15, the phase of the signal is converted through the phase conversion amplifier 16 and output to the output unit 17 as analog X and Y signals, which are taken out as flaw detection information. . Note that the X signal and the Y signal have a mutual phase of 90 ° by the phase conversion amplifier 16.
It has been staggered.

In the eddy current flaw detector using the digital signal processing method, the signal is digitized and output as X and Y signals by passing through the A / D converter after the low pass filter 14 or the gain amplifier 15 to detect flaw detection information. As a result, it was taken into the processor for signal processing.

[0008]

As described above, in the conventional eddy current flaw detector with a digital signal processing function shown in FIG. 4, the output of the low-pass filter 16 is passed through the DC gain amplifier 17, converted into DC, and then converted into an offset. A digital signal processing method has been adopted in which a bias is applied to bring the level to zero. That is, if there is an unbalanced voltage between the sensor coils 5, a DC component is output to the DC gain amplifier 17, and a voltage that cancels this DC component is negatively fed back for balancing.

Further, in the conventional eddy current flaw detector, an analog balance function such as variable capacitance is incorporated in the bridge circuit 5 to manually unbalance the sensor coils 6. In the bias method, when the offset voltage in the gain amplifier 15 becomes large, the signal does not fluctuate from the zero level, so that one side is saturated, the gain of the gain amplifier cannot be made large, and the power supply voltage becomes zero. Then, there were times when I couldn't get a signal.

The biggest problem of the prior art is that the characteristics of the sensor coil itself are not balanced, so that an accurate signal, that is, a signal with a good S / N ratio cannot be obtained.

Therefore, the object of the present invention is to
An object of the present invention is to provide an eddy current flaw detector capable of removing an unbalanced portion between sensor coils, obtaining a flaw detection signal with a good S / N, and enabling accurate measurement.

[0012]

In order to achieve the above object, the present invention is configured as follows. That is, an eddy current generated by applying an AC test signal to a pair of sensor coils forming a bridge circuit and applying an AC magnetic field to the object to be inspected is detected by the pair of sensor coils, and the object to be inspected is detected. In the eddy current flaw detector that obtains the differential output generated in this bridge circuit as the detection output according to the state of
It has a phase adjusting function for adjusting the phase of the test signal given to at least one of the pair of sensor coils, and is provided with a test signal generating means for obtaining the test signal given to the pair of sensor coils. To do. Further, it is constituted by providing amplification means with variable amplification factor for adjusting the test signal level applied to the one sensor coil.

[0013]

The present apparatus having the above-described structure is configured so that an eddy current generated by applying an AC test signal generated by the test signal generating means to the pair of sensor coils and applying an AC magnetic field to the object to be inspected. Is detected by the pair of sensor coils, and a differential output generated in the bridge circuit according to the state of the inspection object is obtained as a detection output, which is used as a flaw detection information signal of the inspection object, but a test signal. The generating means can adjust the phase of the test signal applied to at least one of the pair of sensor coils. And
The imbalance of the phase characteristics of the pair of sensor coils is adjusted by the phase adjusting function of the test signal generating means.

Further, when the amplifying means is provided, the test signal level applied to the one sensor coil can be adjusted, and the unbalance of the amplitude characteristics of the pair of sensor coils is corrected. Thus, it is possible to obtain a highly accurate flaw detection information signal that accurately reflects the state of the object to be inspected.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the structure of an eddy current flaw detector as an embodiment of the present invention.
Is a variable phase shifter, 22 is a timing pulse oscillator, 23
Is a variable output amplifier, 24 is a fixed output amplifier, 25 is a bridge circuit, 26a is a variable side sensor coil, 26b is a fixed side sensor coil, 27 is a differential amplifier, 28 is a variable amplifier, 29 is an A / D converter, and 30 is The digital signal processor 31 is a D / A converter.

The variable-type phase shifter 21 is a variable-type phase shifter that also functions as a test frequency oscillator, and is composed of, for example, a 2-channel digital direct synthesizer, and tests a desired frequency according to the setting. The working signal can be generated in the form of a digital signal and the phase of the testing signal can be adjusted.

The variable output amplifier 23 also has the function of a D / A converter, converts the input digital signal into an analog signal, and amplifies the analog signal with a desired amplification factor and outputs it. Is. The variable output amplifier 23 has a configuration in which the control of the amplification factor is controlled by the digital signal processor 30. Further, the fixed output amplifier 24 has a function of a D / A converter, converts an input digital signal into an analog signal, and
This analog signal is amplified and output at a predetermined amplification rate.

Variable type phase shifter 2 which also functions as a test frequency oscillator
The output of No. 1 (test signal) is passed through the variable output amplifier 23 which also functions as a D / A converter to the variable side sensor coil 26a.
And the output of the variable phase shifter 21 is D
Fixed-side sensor coil 2 which is the other sensor coil through the fixed output amplifier 24 also serving as the A / A converter
6b is also supplied.

The bridge circuit 25 has a bridge circuit configuration including the above-described two sensor coils 26a and 26b. The test signal from the variable output amplifier 23 is supplied to the sensor coil 26b and the fixed output amplifier 24 is supplied. Is supplied to the sensor coil 26a. As a result, an eddy current is generated in the metal inspection object to be inspected by the alternating magnetic field generated by the alternating current generated in the sensor coils 26a and 26b. Then, when a magnetic field corresponding to the eddy current is generated in the object to be inspected, it flows in the sensor coils 26a and 26b to induce a voltage, and the two sensor coils 26a and 2 of the bridge circuit 4 are induced.
When there is a difference in the induced voltage between 6b, a difference voltage is generated in the bridge circuit 25.

The two sensor coils 26a and 26b are
For example, if the winding core directions of the coils cross each other by 90 °, 1
If the arrangement is such that they intersect at points, eddy currents in the X-axis and Y-axis directions can be detected as signals when the metal inspection object is like a pipe. If there is a defect in the pipe-shaped metal inspection object, the generation state of the eddy current changes due to the defect, and the difference in the measuring direction with respect to the defect causes a difference between the two sensor coils 26a and 26b of the bridge circuit 25. Since there is a difference in the induced voltage of, the difference becomes the measurement signal corresponding to the defect.

The two sensor coils 26a and 26a
Various arrangements can be considered for the arrangement relationship of b, and the best arrangement structure is adopted in terms of the shape of the inspection object, the inspection purpose, the inspection efficiency, and the like.

The differential amplifier 27 is a circuit for extracting the difference signal of the bridge circuit 25, and the variable amplifier 28
Is a circuit for amplifying the difference signal extracted by the differential amplifier 27, and the gain can be controlled from the outside. This gain control (amplification factor control) is implemented by the digital signal processor 30.

The A / D converter 29 converts the output of the variable amplifier 28 into digital data, which is sampled by the timing pulse output from the timing pulse oscillator 22 and converted into digital data. Reference numeral 22 is a device that generates a required sampling pulse in synchronization with the phase of the test signal obtained from the variable phase shifter 21.

The D / A converter 31 converts the digital flaw detection signal output from the digital signal processor 30 into an analog signal and outputs the analog signal. The D / A converter 31 passes the signal to an analysis processing system or a display system (not shown). Used for display and analysis. Therefore, if the analysis processing system or the display system is a digital processing system, the data output from the digital signal processor 30 can be directly passed to be processed. In this case, D /
The A converter 31 is unnecessary.

In the measurement mode, the digital signal processor 30 outputs the output digital data of the A / D converter 29 to the X signal and 90 ° with respect to the X signal.
The variable output amplifier 2 has a function of outputting the Y signals whose phases are shifted and controlling the operation of the variable phase shifter 21 and the timing pulse oscillator 22.
4 and the variable amplifier 28 have the function of controlling the amplification factors.

Further, the digital signal processor 30
Is a variable-side sensor coil 2 provided through the differential amplifier 27 and the variable amplifier 28 in the calibration mode.
6a and the fixed side sensor coil 26b, based on the information of the unbalanced component, the variable phase shifter 21 so that the phase of the variable side sensor coil 26a in the bridge circuit 25 is exactly the same as that of the fixed side sensor coil 26b. Has a function of adjusting the phase of the test signal output from the variable phase shifter 21 by oscillating, and when there is an amplitude imbalance, the set gain of the variable output amplifier 23 is changed to change the variable side sensor coil. The operation of aligning the amplitude of 26a with that of the fixed-side sensor coil 26b is performed. Note that all of these control operations are performed by computer software control.

Next, the operation of the present apparatus having such a configuration will be described. By applying the clock signal obtained from the variable phase shifter 21 that generates the clock signal whose clock frequency changes corresponding to the AC voltage of the desired frequency to the fixed output amplifier 23 and the fixed output amplifier 24 having the D / A converter function, respectively. The fixed output amplifier 23 and the fixed output amplifier 24 generate a test signal, which is an AC voltage having a desired test frequency, and apply the test signal to the corresponding sensor coils 26 a and 26 b of the bridge circuit 25.

A current signal corresponding to the AC voltage applied to the sensor coils 26a and 26b flows as a test signal into the sensor coils 26a and 26b, respectively. An eddy current is generated, and a magnetic field corresponding to this eddy current is generated in the metal inspection object, which causes the sensor coil 2
6a, 26b to induce a voltage.

As a result, when there is a difference in the induced voltage between the two sensor coils 26a and 26b of the bridge circuit 25, a difference voltage is generated in the bridge circuit 25. Therefore, by applying the output of the bridge circuit 25 to the differential amplifier 27, if there is a voltage difference between the two sensor coils 26a and 26b, the difference voltage is obtained from the differential amplifier 27 as a flaw detection signal.

This flaw detection signal is amplified by the variable amplifier 28, converted by the A / D converter 29 into digital data while being sampled at the sampling timing determined by the timing pulse generated by the timing pulse oscillator 22, and further converted by the digital signal processor 30 into X data. The signal and the Y signal, which is 90 ° out of phase with the X signal, are converted and output. Then, the D / A converter 31 converts each of the X signal and the Y signal into an analog signal to be a final output.

The X and Y signals, that is, the two types of flaw detection information signals having different phases are analyzed by an external analysis processing device (analog signal processing section) or the like to obtain the final measurement result of the object to be inspected. Is obtained.

In this way, the sensor coils 26a, 26
The unbalanced voltage of b is extracted by the differential amplifier 27, further passed through the variable amplifier 28, and then A / D converted at the sampling timing determined by the output of the timing pulse oscillator 22 synchronized with the frequency of the test signal and digitally converted. The signals are taken into the signal processor 30 and the X and Y signals necessary for analysis for flaw detection and the like are obtained.

By the way, in the eddy current flaw detection in which it is important to detect the phase change as the defect judgment information, the sensor coil 2
If the phases of the test signals of 6a and 26b do not match, the obtained X signal and Y signal will include an error from the beginning, and accurate analysis cannot be performed by the analysis processing system. Since a pair of sensor coils is used and it is difficult to prepare coils having exactly the same shape and the same characteristics, variations in characteristics cannot be avoided. Then, the sensor coils 26a and 26b have a phase difference due to the above-mentioned variation.

Therefore, since there is a phase change depending on the variation of the sensor coils 26a and 26b, the change corresponding to the defect of the object to be inspected cannot be read as an accurate phase change. Therefore, the measurement accuracy deteriorates, and accurate flaw detection cannot be performed.

Therefore, in order to eliminate this, the present apparatus is made to be capable of the following automatic calibration control processing. In the device of the present invention, the output (test signal) of the variable phase shifter 21 which also functions as the test frequency oscillation is passed through the variable output amplifier 23 which also functions as the D / A converter to the variable side sensor coil 26.
In addition to being supplied to a, it is also supplied to the fixed side sensor coil 26b which is the other sensor coil via the fixed output amplifier 24 which also serves as a D / A converter.

The unbalance between the variable side sensor coil 26a and the fixed side sensor coil 26b is caused by the differential amplifier 2
7. After passing through the variable amplifier 28, it is digitally converted by the A / D converter 29 and input to the digital signal processor 30.

Here, in the calibration mode, when there is a phase shift of the test signal between the fixed side sensor coil 26b and the variable side sensor coil 26a, it is automatically changed by the computer software control of the digital signal processor 30. The variable phase shifter 21 is controlled so that the phase of the side sensor coil 26a is exactly the same as that of the fixed side sensor coil 26b, and the phase of the test signal output from the variable phase shifter 21 is adjusted.

Note that it is necessary to increase the resolution of the phase change in order to perform the phase balance accurately. For example, about 360 degrees / 2 ³² or more is necessary. Similarly, in the calibration mode, when the amplitude imbalance is input to the digital signal processor 30, the setting gain of the variable output amplifier 23 is changed by computer software control, and the amplitude of the variable side sensor coil 26a is changed to that of the fixed side sensor coil 26b. Align.

The resolution of the amplitude amount is set to about 0.5 V / 2 ¹² or more. In the calibration mode, the digital signal processor 30 is operated in the calibration mode. Then, the test signal is generated by using the standard inspection body for calibration or in the state without the inspection object, and the bridge circuit 2 at this time is generated.
The adjustment can be automatically performed by the digital signal processor 30 performing the above-described control so that the unbalanced output of 5 becomes zero.

As described above, in the automatic analog balance method of the present invention, the unbalance of the characteristics of the sensor-coil is corrected by the correction on the power source side (the side for supplying the test signal). The unbalanced output becomes zero, and a flaw detection signal with a good S / N ratio can be obtained.

In eddy current flaw detection, in which it is important to detect a phase change as defect judgment information, an accurate flaw detection signal cannot be obtained if the phase of the test signal in the sensor coil is different. That is, it is impossible to read the structural change of the inspection object as an accurate phase change due to the variation of the sensor coil. This becomes more remarkable as the test frequency becomes higher.

The fact that the measurement results in a high frequency range, for example, 200 KHz, vary depending on the eddy current flaw detector used is that the characteristics of the sensor coils 26a and 26b used are not uniform, that is, the analog balance is accurately obtained. Not due to not. In the analog balance method of the present invention, as shown in FIG. 2, in the calibration mode, a large phase shift due to the non-uniformity of the characteristics of the sensor coils 26a and 26b can be output, and even a minute phase shift can be output greatly. It is easy to adjust the phase shift to zero, so that a flaw detection signal with a good S / N ratio can be obtained.

When the characteristics of the sensor coils 26a and 26b to be used are the same only in the amplitude of the test signal flowing respectively, that is, both the sensor coils 26a and 26b to be used are balanced in amplitude only. 2A shows the output waveforms (test signals) of the sensor coils 26a and 26b and the flaw detection signal of the sensor coil 26b when the coil has a phase difference. Yes, the output waveform W2 of the sensor coil 26a with respect to the output waveform W20 of the sensor coil 26b
1 is in agreement with the phase adjustment with respect to the sensor coil 26a side, and is shown as the waveform W22 of the flaw detection signal induced in the sensor coil 26a in this case, and FIG. Output waveform of the bridge circuit 25 when a waveform is given (= W21-W2
2; that is, the waveform of the difference signal component of the bridge circuit 25, which is the output waveform of the differential amplifier 27) W23.

Further, FIG. 3A is a diagram showing the output waveforms (test signals) of the sensor coils 26a and 26b and the flaw detection signal of the sensor coil 26b in the case of no adjustment. The sensor coils 26a and 26b to be used are shown in FIG. Of the test signals flowing through the sensor coil 26 are the same, that is, the sensor coil 26 to be used.
In the case where both a and 26b are balanced only in amplitude, but a phase difference is generated, the output waveform (test signal waveform) W20 of the sensor coil 26b and the output waveform (sensor waveform 26a in the sensor coil 26a ( Test signal waveform) W2
4 shows a state in which the phase is not adjusted at all and remains displaced, and the sensor coils 26a, 2 at this time are also shown.
The unbalanced output waveform of 6b is shown as W25 (= W20-W24). 3B is an output waveform of the bridge circuit 25 when the waveform of FIG. 3A is given (that is, the waveform of the difference signal component of the bridge circuit 25, that is, the output of the differential amplifier 27). 3C shows a waveform of a flaw detection signal W28 (= W27−W26 = W24−W2) obtained when the phase shift is removed.
It is a figure which shows 5).

That is, the waveform shown in FIG. 2 shows an example in which both the amplitude and the phase are in a balanced state, and the waveform shown in FIG. 3 shows an example in which the amplitude is balanced but the phase is in an unbalanced state. Here, since the original phase of the differential amplified output waveform of FIG. 2 is the same as that of the output waveform W21 of the variable side sensor coil 26a, only the amplitude is changed.
Output waveform (test signal waveform) W20 and the same phase.

In this case, the output waveform as the flaw detection signal (the output waveform of the differential amplifier 27) obtained by flaw detection of the inspection object becomes the differential amplification output waveform W23 of FIG. The structure of is faithfully and accurately grasped as the amount of change from the original phase.

That is, it is possible to obtain a flaw detection signal in which the structure of the object to be inspected is reflected as a phase shift only. On the other hand, the differential amplification output waveform W27 of FIG. 3B is also the output waveform of the flaw detection signal obtained by flaw detection of the inspection object, but in this case, the original phase is the sensor coil 6a having a phase shift.
And an unbalanced output waveform W26 of the sensor coil 26b. Then, the output waveform W24 of the variable-side sensor coil 26a having the phase shift is the output of the differential amplifier 28 when the phase shifts to the phase equivalent to the flaw detection signal waveform W25 of the sensor coil 26a having the phase shift. The differential amplification output waveform is shown by W27.

This differential amplified output waveform W27 has a larger amplitude than the original unbalanced output waveform W26. And
Since the phase change point is a point (intersection point) where the subtracted value of the unbalanced output waveform W26 and the differential amplitude output waveform W27 becomes zero, the amount of phase change is as shown in the figure, and an example of phase adjustment is performed. It can be seen that it is significantly smaller than the example in FIG.

As mentioned above, both sensor coils 26
If the phases of the test signals respectively flowing to a and 26b are not matched, even under the condition that the amplitudes of the sensor coils are the same, the flaw detection signal accurately reflecting the state of the object to be inspected cannot be captured. Although not described here, the phase change cannot be accurately detected even when the amplitudes of the test signals flowing through the sensor coils 26a and 26b are not the same. However, in the present apparatus, the variable output amplifier 23 can be used to adjust the amplitude of the test signal applied to the sensor coil 26a, so that this can also be solved.

That is, by adopting the automatic analog balance method as in the present invention, it becomes possible to obtain a flaw detection signal in which the state of the object to be inspected is accurately reflected in the phase for the first time, and highly accurate measurement and flaw detection can be performed. It will be possible. Therefore,
According to the present invention, it is possible to obtain an eddy current flaw detection apparatus capable of highly precise flaw detection.

The present invention is not limited to the above-described embodiments, but may be modified and implemented without departing from the scope of the invention. For example, in the above embodiment, by adopting the variable phase shifter that also serves as the oscillator, the test signals of exactly the same phase are generated and given to the pair of sensor coils. A phase shifter may be provided in the test signal input system for phase shift adjustment.

As described above in detail, in the device according to the present invention, an eddy current is generated by applying an AC test signal to a pair of sensor coils forming a bridge circuit and applying an AC magnetic field to the object to be inspected. Is detected by the pair of sensor coils, and a differential output generated in the bridge circuit according to the state of the inspection object is obtained as a detection output, which is used as a flaw detection information signal of the inspection object to detect the inspection object. In the eddy current flaw detector for measuring, a phase adjusting function is provided for adjusting the phase of the test signal given to at least one of the pair of sensor coils, and for obtaining the test signal given to the pair of sensor coils. The test signal generating means is provided, and further, the amplifying means having a variable amplification factor for adjusting the test signal level applied to the one sensor coil is provided.

In the present apparatus having such a configuration, the alternating test signal generated by the test signal generating means is supplied to the pair of sensor coils to generate an alternating magnetic field on the device under test. The eddy current is detected by the pair of sensor coils, and a differential output generated in the bridge circuit according to the state of the inspection object is obtained as a detection output, which is used as a flaw detection information signal of the inspection object. The test signal generating means can adjust the phase of the test signal given to at least one of the pair of sensor coils. Then, by adjusting the unbalance of the phase characteristics of the pair of sensor coils so as to be balanced by the phase adjusting function of the test signal generating means, accurate flaw detection information that correctly reflects the state of the inspection object. You will be able to get a signal.

Further, by providing the amplifying means so that the test signal level given to the one sensor coil can be adjusted, the unbalance of the amplitude characteristics of the pair of sensor coils can be corrected. As a result, it is possible to obtain a highly accurate flaw detection information signal that accurately reflects the state of the object to be inspected, and thus it is possible to perform accurate eddy current flaw detection.

In the present invention, for example, by adopting a variable type phase shifter which also functions as an oscillator and is constituted by a two-channel digital direct synthesizer, it is possible to generate and give waveforms of exactly the same phase to a pair of sensor coils. In addition, the variable amplifier can give the same amplitude. That is, it is possible to easily change the phase and amplitude applied to the sensor coil to zero the imbalance of the bridge circuit in the bridge circuit.

[0056]

As described above in detail, according to the present invention,
By making it possible to adjust the imbalance of the characteristics of the sensor coil, it becomes possible to provide an eddy current flaw detection device capable of highly precise flaw detection.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention and is a circuit configuration diagram according to the embodiment of the present invention.

FIG. 2 is a diagram for explaining an embodiment of the present invention,
The figure for demonstrating the effect | action of this invention at the time of performing unbalance adjustment.

FIG. 3 is a diagram as a comparative example for explaining the effect of the embodiment of the present invention, and is a diagram for explaining the action when the unbalance adjustment is not performed.

FIG. 4 is a diagram for explaining a conventional example and is a diagram showing a circuit configuration of a conventional device.

[Explanation of symbols]

21 ... Variable phaser 22 ... Timing pulse oscillator 23 ... Variable output amplifier 24 ... Fixed output amplifier 25 ... Bridge circuit 26a ... Variable side sensor coil 26b ... Fixed side sensor coil 30 ... Digital signal processor W20 ... Output waveform of sensor coil 26b W21 ... Output waveform of sensor coil 26a W22 ... Waveform of flaw detection signal (defect signal) by sensor coil 26a, W23 ... Differential amplification output waveform (= W21-W22) W24 ... Output waveform of sensor coil 26a with phase shift, W25 ... Waveform of flaw detection signal (defect signal) of sensor coil 26a having phase shift W26 ... Unbalanced output waveform of sensor coil 26a having phase shift and sensor coil 26b (= W20-W24) W27 ... Sensor coil 6a having phase shift and sensor Of coil 6b Dynamic amplified output waveform (= W20-W25) W28 ... if flaw detection signal by removing the phase shift (defect signal) waveform

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Naoji Nakaya 1-11-13 Higashi-Tenma Kita-ku, Osaka City, Osaka Prefecture Aswan Electronics Co., Ltd. Nikko Inspection Service Co., Ltd.

Claims (2)

[Claims] 1. An eddy current generated by applying an AC test signal to a pair of sensor coils forming a bridge circuit and applying an AC magnetic field to an object to be inspected is detected by the pair of sensor coils. In the eddy current flaw detection apparatus for obtaining the detection output of the differential output generated in the bridge circuit according to the state of the inspection object and utilizing this as a flaw detection information signal of the inspection object, An eddy current flaw detection device comprising an adjusting means for adjusting the phase of the test signal applied to at least one of the sensor coils. 2. An eddy current generated by applying an AC test signal to a pair of sensor coils forming a bridge circuit and applying an AC magnetic field to an object to be inspected is detected by the pair of sensor coils. In the eddy current flaw detection apparatus for obtaining the detection output of the differential output generated in the bridge circuit according to the state of the inspection object and utilizing this as a flaw detection information signal of the inspection object, Adjusting means for adjusting the phase of the test signal given to at least one of the sensor coils, and amplification means with variable amplification factor for amplifying the test signal given to the one sensor coil. Eddy current flaw detector.