JPH06313762A - Multiple frequency type eddy current flaw detector - Google Patents

Abstract

PURPOSE:To eliminate noise and unneeded signal efficiently with an operation by accurately extracting an individual signal component for each frequency applied to a test coil. CONSTITUTION:A first switcher 16 for inputting the output signal of transmitters 1 and 2 is provided at the input side of a power amplifier 4. A second switcher 17 is provided at a side for sending signals to synchronous detectors 11 and 12, a timing signal output from a timing signal generator 18 is input to both switchers 16 and 17, and then signals are switched at a determined timing. Further, retention circuits 19 and 20 are provided at the output sides of the synchronous detectors 11 and 12, respectively.

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 for detecting defects on a metal surface and inside, and relates to an improvement of a multi-frequency eddy current flaw detector which uses two or more different flaw detection frequencies as flaw detection frequencies.

[0002]

2. Description of the Related Art Generally, a multi-frequency eddy current flaw detector is
By utilizing the fact that the eddy currents generated inside the metal obtained at each frequency show different skin effects by using multiple flaw detection frequencies, the changes in the eddy currents due to both frequencies are detected at the same time and the correlation between each signal is detected. The flaw detection is performed by performing the arithmetic processing according to the relationship, and is an effective method for suppressing the noise signal and improving the detection accuracy of the flaw signal.

FIG. 3 shows a block diagram of a conventional multi-frequency eddy current flaw detector.

The flaw detection signals of the frequencies f ₁ and f ₂ output from the oscillator 2 and the oscillator 2 are combined by the combiner 3, power-amplified by the amplifier 4, and then output to the bridge circuit 5.

FIG. 4 shows waveforms (a) and (b) before combining and a waveform (c) after combining. The power-amplified waveform changes to a waveform obtained by superimposing the waveforms (a) and (b) like the waveform (c).

Returning to FIG. 3 again, the signal input to the bridge circuit 5 is applied to the test coil 6 to generate an eddy current in the test body at the center thereof. Further, the change in the eddy current is taken out as an unbalanced component of the bridge circuit 5, and the single component of each flaw detection frequency is separated from the combined frequency component of the frequencies f ₁ and f ₂ of the obtained detection signal. ₁
, And f ₂ are separated through filters 7 and 8 having characteristics suitable for extracting frequency components. FIG. 4 shows the waveforms (s) (t) after this separation.

This wave type is an amplifier 9 and an amplifier 1, respectively.
After being amplified by 0, the synchronous detector 11 and the detector 1
2 is synchronously detected and the x-axis (real axis component) and y of the AC signal
After being decomposed into axes (imaginary axis components), they are input to the analyzer 13. The analyzer 13 performs an operation from the obtained x and y axis components of the frequencies f ₁ and f ₂ based on a preset operation condition, removes noise and other unnecessary signals, and then detects a target detection signal component. Output signals Xout and You including
t can be output. In the figure, reference numerals 14 and 15 denote phase shifters.

[0008]

However, such a conventional multi-frequency eddy current flaw detector has the following problems. That is, when the signals of the oscillator 1 and the oscillator 2 are combined and sent to the test coil 6 at the same time, only the applied signal component of each frequency alone is applied to the combined signal of each frequency including the obtained eddy current change information. The time constants of the filters 7 and 8 are selected so that they can be efficiently extracted, but in reality, the waveforms (d) and (e) after passing through the filters 7 and 8 are affected by other frequency signals. , It is difficult to completely separate into two single frequency components. This is the frequency f
_The closer ₁ and f ₂ are to each other, the more difficult it is to separate each frequency component. Further, as the number of frequencies used increases more than two frequencies, it becomes more difficult to separate them into subsequent filters, and the frequency components of each other become more difficult. Will be affected. Thus, if frequency components other than the frequency components of the applied signal remain in the detected waveform, it causes an error when performing synchronous detection, and accurate flaw detection cannot be performed. As a result, noise and unnecessary signals cannot be erased as intended even in the calculation by the analyzer 13.

Therefore, an object of the present invention is to provide a multi-frequency eddy current flaw detector capable of accurately extracting a single signal component for each frequency applied to a test coil and efficiently eliminating noise and unnecessary signals by calculation. To do.

[0010]

In order to achieve the above object, the present invention provides a first switching device for time-divisionally inputting output signals of a plurality of oscillators to a bridge circuit, and an output signal of the bridge circuit. A second switching device that separates into flaw detection waveforms for each frequency and inputs to a plurality of synchronous detectors, and a holding circuit that temporarily holds the signals output by synchronous detection by the synchronous detectors are provided. It is characterized by.

[0011]

In the above-mentioned eddy current flaw detector, signals of different flaw detection frequencies are not combined and applied to the test coil at the same time, but the respective frequency signals are applied to the test coil in a time division manner by the first switch. Therefore, the second switching device, which switches the output signal from the test coil with the same timing as when applying, obtains the flaw detection result at each frequency in time series, and the flaw detection for each frequency is influenced by the signals of the other frequencies. It is possible to perform flaw detection with a single frequency in the same way without receiving it, and since no signal separation means such as a filter is used, even if a frequency close to the frequency or many frequencies are selected, the flaw detection accuracy is completely Stable flaw detection with high accuracy can be performed without affecting.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the first switch 1 for inputting the output signals of the oscillators 1 and 2 to the input side of the power amplifier 4.
6 is provided. Further, a second switching device 17 is provided on the side that sends signals to the synchronous detectors 11 and 12, and both switching devices 1
The timing signal output from the timing signal generator 18 is input to 6 and 17, and switching can be performed at a predetermined timing.

Further, holding circuits 19 and 20 are provided on the output sides of the synchronous detectors 11 and 12, respectively. The timing signal of the timing signal generator 18 is also input to the synchronous detectors 11 and 12 and the holding circuits 19 and 20, respectively.

The respective outputs of oscillator 1 and oscillator ₂ which generate different frequencies f ₁ and f ₂ are the timing signal generator 18
The first switching device 16 switches and combines the signals according to the timing signal generated from the. By this synthesizing, a waveform of different frequency continuous in time (waveform (d) in FIG. 2) is input to the power amplifier 4. Here, the switching times T ₁ and T ₂ of the timing signal generator 18 may be set in advance or may be changed depending on the frequency of the oscillator 1 or the oscillator 2. It is necessary to set the cycle of the timing signal so that it lasts for one wavelength or more.

The combined signal amplified by the power amplifier 4 is input to the bridge circuit 5. In the bridge circuit 5, the composite signal is applied to the balanced bridge including the test coil 6. When an abnormality occurs in the test body and an impedance change occurs in the test coil 6, the bridge is out of balance and an output is produced. The waveform after the output is amplified by the amplifier 9 is basically the same as the waveform (d) shown in FIG. 2 except for changes in the signal amplitude, phase, inclusion of an abnormal signal, etc. Waveforms (a) and (b) of frequencies f ₁ and f ₂ such as
A continuous waveform is generated.

Therefore, the second switch 17 is switched by switching the second switch 17 at the same timing as the first switch 16.
2 is time-divided and separated into a flaw detection waveform for the frequency f _{1 and} a flaw detection waveform for the frequency f ₂ like the waveforms (u) and (v) in FIG.

These flaw detection waveforms are synchronously detected by a synchronizing signal obtained by shifting the outputs of the oscillator 1 and the oscillator 2 which generate respective frequencies by 0 ° and 90 ° by the phase shifter 14 and the phase shifter 15, respectively. The flaw detection waveform is separated into an x component (real number component) and ay component (imaginary number component).

The result of the synchronous detection is calculated by the analyzer 13 according to a predetermined arithmetic expression. At this time, the output of the synchronous detection is switched at the timing (T ₁ and T ₂ ) of the timing signal generator 18, Since they are not output at the same time, the frequency f _{1 is set} by using the holding circuit 19 and the holding circuit 20.
The output of the synchronous detection is temporarily held so that the flaw detection results for the frequencies f and f ₂ appear at the same time.

As a result, the analyzer 13 can simultaneously perform arithmetic processing using the latch output and can output the analysis result. In reality, the analysis result cannot be calculated in real time and cannot be calculated until the cycle of T ₁ + T ₂ ends, but in normal use, the scanning speed of the test body relative to the test body is lower than that of the test body. _Since the cycle of ₁ + T ₂ can be set extremely fast, there is no problem in practical use, and the processing of the result can be performed in almost real time.

Needless to say, the present invention is not limited to the above-mentioned embodiments, and can be carried out by appropriately modifying it without departing from the scope of the invention.

That is, the embodiment shown in FIG. 1 is an example of a multi-frequency eddy current flaw detector using two frequencies.
The frequency is not limited to this, and even if three or more frequencies are used, it is only necessary to change the period setting of the timing signal and the number of switching of the switching device according to the number of frequencies, and the oscillator, the phase shifter, the synchronous detector, the holding It suffices to prepare as many circuits as the frequencies to be used. Further, there is no decrease in analysis accuracy due to the increase in frequency, and the greater the number of frequencies, the more remarkable the improvement in accuracy compared to the conventional method.

Further, the holding circuits 19 and 20 shown in FIG.
Also, the analyzer 13 can be replaced by a computer or the like.

Further, since the synchronous detection can detect a signal of each frequency with a wave of several cycles, in the case of a high frequency signal,
It is possible to shorten the detection time. Therefore, the timing of the timing signal generator 18 changes with respect to the frequency setting of the oscillators 1 and 2, and a function for automatically setting the timing signal for several cycles can be provided to shorten the time for synchronous detection, and in more real time. A near flaw detection method can be realized.

[0025]

As described above, according to the present invention, the output signals of a plurality of oscillators that generate flaw detection signals of different frequencies are time-divisionally input to the bridge circuit, and the output signals of the bridge circuit are input to the respective frequencies. Since the first and second switching devices are provided so as to separate into flaw detection waveforms for the flaw detection, flaw detection inside the metal can be performed with high accuracy equivalent to flaw detection with a single frequency.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an eddy current flaw detector according to the present invention.

FIG. 2 is a waveform diagram showing a flaw detection waveform before and after synthesis and a flaw detection waveform after frequency separation according to the present invention.

FIG. 3 is a block diagram showing a conventional eddy current flaw detector.

FIG. 4 is a waveform diagram showing a conventional flaw detection waveform before and after synthesis and a flaw detection waveform after frequency separation.

[Explanation of Codes] 1, 2 ... Oscillator 5 ......... Bridge circuit 11, 12 ... Synchronous detector 13 ......... Analyzer 16 ......... First switch 17 ......... Second switch 18 ... Timing signal generator 19, 20 ... Holding circuit

Claims (1)

[Claims] 1. A plurality of oscillators that generate flaw detection signals of different frequencies, and a bridge circuit that amplifies output signals from these oscillators and applies the amplified signals to a test coil to generate an eddy current in a test body. The change of the eddy current is taken out as an unbalanced component through the bridge circuit, the detected waveform is synchronously detected by a plurality of synchronous detectors, and the obtained frequency components are calculated according to a predetermined arithmetic expression to calculate the metal. In a multi-frequency eddy current flaw detector configured to detect an internal flaw, a first switching device that time-divisionally outputs the output signals of a plurality of the oscillators and inputs them to the bridge circuit, and the output signals of the bridge circuit, respectively. A second switching device which separates into a flaw detection wave type for the frequency of and inputs to a plurality of the frequency detectors;
A multi-frequency type eddy current flaw detector, comprising: a holding circuit for temporarily holding a signal output by synchronous detection by the synchronous detector.