JPS6331003Y2 - - Google Patents

Description

[Detailed explanation of the idea] The present invention relates to an eddy current flaw detection device.

Eddy current flaw detection uses an excitation coil to generate an alternating magnetic field to generate eddy currents in the inspected object in order to non-destructively detect flaws on the inspected metal object.
Changes in this eddy current due to scratches and the like are detected as changes in the impedance of the detection coil, but in recent years there has been a growing demand for more rigorous flaw detection inspections, even down to the smallest flaws.
However, in order to detect even such minute flaws with high precision, it is important to distinguish them from pseudo flaw signals (noise signals) caused by factors other than the flaws to be inspected.

In other words, there are flaws to be detected on the metal object, i.e.
In addition to harmful flaws (cracks, cracks, local thinning, etc.) that can lead to breakage, destruction, leakage, etc., harmless flaws that do not affect the mechanical strength of the metal object to be inspected (e.g. bruises that occur during handling) etc.) are usually scattered in large numbers. For this reason, as the inspection targets even the smallest flaws, signals generated by electromagnetic non-uniformity detected in these harmless flaws (pseudo flaw signals = noise signals) are detected. The flaws begin to take up a large weight in the flaw signal, making it impossible to achieve the purpose of flaw detection.Furthermore, mechanical vibrations may occur between the flaw detection coil and the object to be inspected during flaw detection, and this vibration Highly accurate flaw detection is also hindered by the resulting pseudo flaw signal.

The present invention has been made to solve these problems. That is, in the present invention, the detection sensitivity of flaws on the object to be inspected is affected by the frequency of the alternating current supplied to the flaw detection coil, and depending on each frequency, it is possible to Focusing on the difference in sensitivity, multiple frequencies are applied to a single flaw detection coil at the same time, and detection signals corresponding to each frequency are output simultaneously, and these multiple detection signals are subjected to addition, subtraction, multiplication, division, etc. Appropriate arithmetic processing is performed to suppress pseudo flaw signals and emphasize harmful flaw signals to improve the signal-to-noise ratio, and the flaw signals are characterized according to the type of flaw through arithmetic processing. It is also possible to identify multiple types of scratches.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing an eddy current flaw detection device according to an embodiment _of the present invention.
₂ ,...B, 1 _o are multiple high frequency oscillators each capable of outputting a sine wave signal of an arbitrary frequency, 11 is n
A mixer 12 mixes the output signals of various high-frequency oscillators 10 ₁ , 10 _{2 ,} . An amplifier 14 for constant current power amplification of the output of the amplifier 12 has n types _of frequencies of the high frequency oscillators 10 ₁ , 10 ₂ , . . . An excitation coil on the primary side of the eddy current flaw detection penetration coil or probe coil to which current is supplied; 15 is a secondary detection coil; 16 ₁ , 16 ₂ ,..., 16 _o
17 ₁ , 17 ₂ , . . . , 17 _o are high-frequency oscillators 10 ₁ , 10 ₂ , respectively. ..., 10 _o so that the outputs of the differential amplifiers 16 ₁ , 16 ₂ , ..., 16 _o in the normal part of the test object A become zero, so that the reference voltage for balance is cancelled. a cancellation voltage generator 18 1 , supplying _a signal to the other input terminal of each differential amplifier 16 ₁ , 16 ₂ , . . . , 16 _o ;
18 ₂ ,..., 18 _o are buffer resistors.

19 ₁ , 19 ₂ , ..., 19 _o are tuned amplifiers, 20
₁ , 20 ₂ , ..., 20 _o are tuned amplifiers 19 ₁ , 19 ₂ ,
..., _19o are respectively phase detectors, 21 ₁ , 21 ₂ , ..., 21 _o are phase detectors, 22 ₁ , 22 ₂ , ..., 22 _o are high-frequency oscillators 10 ₁ , a variable phase shifter that receives a portion of the output signals of 10 ₂ ,..., 10 _o and appropriately adjusts and sets a reference signal for phase detection corresponding to each frequency;
3 ₁ , 23 ₂ ,..., 23 _o are band wave transducers whose cutoff frequencies can be adjusted, and 24 ₁ , 24 ₂ ,..., 24 _o are band wave transducers 23 ₁ , 23 ₂ ,..., 23 _o, respectively. signal output adjuster for adjusting amplitude, 25 ₁ ;
25 ₂ ,..., 25 _o are phase selection switches S ₁ , S ₂ ,
..., the signal output regulator 24 ₁ by switching S _o ,
This is an inverting amplifier that inverts the output signals of 24 ₂ , ..., 24 _o by 180 degrees.

26 is a signal output regulator 24 ₁ , 24 2 , . . . , 2 by switching the phase selection switches S ₁ , S _{2 ,} . . . , S _o
4 _o output signals or inverting amplifiers 25 ₁ , 25 ₂ ,
..., 25 _o This is an arithmetic unit that performs correlation operations such as addition/subtraction or multiplication/division on signals whose phase has been changed by 180 degrees by o, and outputs a signal with desired characteristics.

27 is a reflexion amplifier that passes only the arithmetic unit output whose level exceeds the threshold value set by the reflexion operation setter 28 and blocks low-level peripheral background noise; 29 is a recording amplifier; 30 is a recorder. It is.

In the above embodiment, a single absolute value measuring coil is used as the detection coil 15, but an adjacent comparison coil may be used as shown in FIG. In FIG. 2, 31 to 34 are buffer resistors.

Next, the operation of the above embodiment will be explained.

The primary excitation coil 14 of the penetration coil for eddy current flaw detection or the probe coil is a high-frequency oscillator 10 of n types.
It is driven by a plurality of sinusoidal currents each having a plurality of frequency components appropriately set at ₁ , 10 ₂ , . . . , 10 _o . That is, high frequency oscillators 10 ₁ , 10 ₂ ,
..., _10o outputs sinusoidal oscillation output signals of a plurality of different frequencies, each of which is optimal for the flaw to be detected on the inspected object A, and after being mixed in the mixer 11, the constant current power is supplied to the amplifier 12. The signal is amplified and drives the excitation coil 14. The object A to be inspected is conveyed, for example, along a line between the excitation coil 14 and the secondary detection coil 15, and each part of the object A to be inspected is sequentially and continuously inspected. An alternating magnetic field is generated by the alternating current flowing through the excitation coil 14, and an induced voltage is generated in the detection coil, but this induced voltage signal is affected by the presence of flaws on the object A placed within the alternating magnetic field. causes minute changes.

This induced voltage is applied to n differential amplifiers 16 ₁ , 16
It is applied to one input terminal of each of ₂ ,..., _16o .
And each high frequency oscillator 1 is connected to the other input terminal.
Cancellation voltage generators 17 ₁ , 17 ₂ , ..., 17 receiving part of the outputs of _{0 1} , 10 ₂ , ..., 10 _o , respectively
A reference voltage for canceling balance from _o is applied. Each of these reference voltages for canceling balance corresponds to the frequency of each high-frequency oscillator 10 ₁ , 10 ₂ , ..., 10 _o , and the output of each differential amplifier 16 ₁ , 16 ₂ , ..., 16 _o Since the phase is set to be reversed and the amplitude level to be the same so that it becomes zero in the normal part of A, each differential amplifier 1 is
Unbalanced outputs are generated from 6 ₁ , 16 ₂ , ..., 16 _o . These differential amplifiers 16 ₁ , 1 may vary depending on the presence of scratches or the like on the test object A as the test object A is being transported, or depending on the detection sensitivity specific to each frequency.
The output signals from 6 ₂ ,..., 16 _o change every moment.

The output signal of each differential amplifier 16 ₁ , 16 ₂ , ..., 16 _o is further amplified by a tuned amplifier 19 ₁ , 19 ₂ , ..., 19 _o , and then a phase detector 21
₁ , 21 ₂ , . . . , 21 _o , the flaw detection signal is demodulated and extracted as a flaw signal exhibiting a low frequency. In this phase detection, each high frequency oscillator 10
₁ , 10 ₂ , ..., 10 _o , the variable phase shifters 22 ₁ , 22 ₂ , ..., 22 _o adjust the phase difference as appropriate so that the most emphasized extraction can be performed corresponding to each frequency. Outputs the reference signal for phase detection that is set.

The output signals of the phase detectors 21 ₁ , 21 ₂ , ..., 21 _o are transmitted to the bandpass detector 23 whose cutoff frequency is set appropriately.
₁ , 23 ₂ , . . . , 23 _o , unnecessary noise is reduced, and the phase of the flaw signal after phase detection is appropriately advanced or delayed according to the set cutoff frequency. Bandwidth wave generators 23 ₁ , 23 ₂ ,..., 23 _o
The outputs of the signal output regulators 24 ₁ , 24 ₂ , ..., 24
After setting the input ratio to the calculator 26 by _o ,
A certain signal is passed through the inverting amplifiers 25 ₁ , 25 ₂ ,..., 25 _o
The phase is inverted by 180° at
5 ₁ , 25 ₂ , . . . , 25 _o are inputted to the arithmetic unit 26 without going through them. This operation is performed using switches S ₁ , S ₂ , and
..., carried out by S _o . The arithmetic unit 26 performs correlation calculation processing by adding, subtracting, multiplying, and dividing the plurality of series of flaw signals corresponding to each of these frequencies. That is,
Adjustments in the variable phase shifters 22 ₁ , 22 ₂ , ..., 22 _o , bandpass filters 23 ₁ , 23 ₂ , ..., 23 _o and signal output adjusters 24 ₁ , 24 ₂ , ..., 24 _o , and the like; For example, by switching the phase selection switches S ₁ , S ₂ , ..., S _o , unnecessary noise signals (for example, pseudo flaw signals due to harmless flaws, or vibrations of the object A to be inspected, etc.) are detected among multiple series of flaw signals. Distinguish between harmful flaw signals and unnecessary noise signals by inputting the harmful flaw signal to be detected by inputting it in phase or close to the same phase and adding it to the input signal (noise generated by Or, by using the flaw signal specific to each frequency series and adding/subtracting or multiplying/dividing the phase, amplitude, etc. as input, it is possible to distinguish the type of flaw, for example. You can get the output.

The output of the arithmetic unit obtained by correlating multiple series of flaw signals has background noise suppressed by the repositioning amplifier 27, and is sent to the recorder 3 via the recording amplifier 29.
Recorded as 0.

As explained above, the eddy current flaw detection device according to the present invention drives the excitation coil of the eddy current flaw detection coil using a plurality of different frequencies, simultaneously obtains multiple series of flaw detection signals corresponding to each frequency, and Since the correlation calculation is performed based on multiple series of flaw detection signals, it is possible to improve the discrimination between harmful flaw signals and unnecessary noise, and it is possible to easily identify multiple types of flaws.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a block diagram showing another embodiment of the present invention. 10... High frequency oscillator, 11... Mixer, 14
... Excitation coil, A ... Test object, 15 ... Detection coil, 16 ... Differential amplifier, 17 ... Cancellation voltage generator, 18 ... Buffer resistor, 19 ... Tuning amplifier, 20 ... ...Flaw detection sensitivity adjuster, 21...Phase detector, 22...Variable phase shifter, 23...Bandwidth wave generator, 24...Signal output adjuster, 25...Inverting amplifier, 26...Arithmetic unit, 27... ... Resiexion amplifier, 28 ... Resiexion operation setting device, 29
...recording amplifier, 30...recorder.

Claims (1)

[Claims for Utility Model Registration] A plurality of high-frequency oscillators that output sine wave signals of different frequencies; a mixer that mixes the respective sine wave signals from the plurality of high-frequency oscillators; and a feedback loop that controls output current. a constant current power amplifier that includes a current-voltage conversion resistor for constant current amplification of the output of the mixer; a primary excitation coil that is excited in response to the output of the constant current power amplifier; a secondary detection coil that is provided opposite to the primary excitation coil at a distance that allows the object to be inspected to be placed between the excitation coil and generates an induced voltage signal by an alternating magnetic field from the primary excitation coil; Cancellation corresponding to each high-frequency oscillator is provided to cancel the induced voltage corresponding to the frequency of each high-frequency oscillator from the secondary side detection coil in the normal part of the object to be inspected. a plurality of canceling voltage generators that output balancing reference voltage signals; and a plurality of canceling voltage generators that are provided corresponding to the canceling voltage generators, and each input terminal of which receives an induced voltage signal from the secondary detection coil. a plurality of differential amplifiers that receive at their other input terminals a reference voltage signal for cancellation balance from each of the corresponding cancellation voltage generators, and generate an unbalanced output signal of both input signals; a plurality of tuned amplifiers, each of which is provided corresponding to the differential amplifier, and amplifies the unbalanced output signal from each differential amplifier; a plurality of flaw detection sensitivity adjusters that respectively adjust; a plurality of variable phase shifters that are provided corresponding to each of the high-frequency oscillators and that each receive an output signal of each of the high-frequency oscillators and output a reference signal for phase detection; is provided corresponding to each of the flaw detection sensitivity adjusters, and performs phase detection on the output signal of each of the flaw detection sensitivity adjusters based on a phase detection reference signal from each of the corresponding variable phase shifters. An eddy current flaw detection device comprising: a plurality of phase detectors that respectively output a plurality of flaw signals corresponding to each frequency; and a computing unit that adjusts the flaw signal output from each of the phase detectors and performs correlation calculation processing.