JPS625652Y2 - - 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 metal object to be inspected, in order to nondestructively detect flaws in the object.
Changes in this eddy current due to scratches, etc. are detected as changes in the impedance of the detection coil, but this detection sensitivity is affected by the frequency of the alternating current applied to the excitation coil, and depends on the nature and size of the scratch on the object to be inspected. It is known that the optimal frequency is determined depending on the size, depth, type, etc.

However, in conventional eddy current flaw detection equipment, the alternating current supplied to the excitation coil is a current with a single frequency. I could not fully achieve my purpose. Therefore, in order to perform flaw detection at multiple frequencies, multiple eddy current flaw detectors each equipped with a flaw detection coil electrically adapted to different frequencies and corresponding to each frequency one-to-one must be placed on the inspection line or at the inspection position. Attempts have been made to do this, but they have had the disadvantage of requiring multiple flaw detection devices, which increases the size of the entire device. In addition, attempts have been made to use a single flaw detection device and replace the flaw detection coil for each frequency with a new flaw detection coil for each flaw detection. There was a drawback that the same gap with the object to be inspected and the same relative velocity were not guaranteed, making it impossible to perform flaw detection with good repeatability and high sensitivity. Furthermore, in both cases, flaw detection at each frequency is not carried out simultaneously, making it inconvenient to mutually compare the flaw detection results at each frequency with temporal consistency. For this reason, flaw detection is carried out using the eddy current flaw detection method using time-division multifrequency shock waves, in which different pulses with damped vibrations are alternately applied to the excitation coil at high speed without overlapping in time, and pulses with short durations are repeatedly generated. Attempts have also been made to extract the flaw signal by applying it to the flaw detection coil and analyzing the response pulse of the detection coil. A transient phenomenon occurs due to differential action, and the change component due to minute scratches is buried in this transient phenomenon wave, so it could not be detected with good sensitivity.

This invention corrects these drawbacks and allows multiple types,
It is an object of the present invention to provide an eddy current flaw detection device that can simultaneously detect physical flaws with high sensitivity.

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 ,...,10 _o are multiple high frequency oscillators each capable of outputting a sine wave signal of an arbitrary frequency, 11 is _o
A mixer 12 mixes the output signals of various high-frequency oscillators 10 ₁ , 10 ₂ , . . . , 10 _o ; 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 , . _. . Excitation coil on the primary side of an eddy current flaw detection penetration coil or probe coil to which current is supplied, 1
5 is a detection coil on the secondary side, 16 ₁ , 16 ₂ ,...,
16 _o is a differential amplifier, 17 ₁ , 17 ₂ , . . . , 17 to which the induced voltage generated by driving the excitation coil 14 is applied to the detection coil 15 at one input terminal of each;
_o are high frequency oscillators 10 ₁ , 10 ₂ , ..., respectively
Each differential amplifier 16 ₁ , 16 ₂ , ..., 16 in the normal part of the test object A receives a part of the output signal of 10 _o .
The balanced reference voltage signal is applied to each differential amplifier 16 ₁ , 16 ₂ , ..., 16 _o so that the output of _o becomes zero.
The canceling voltage generators 18 ₁ , 18 ₂ , . . . , 18 _o that supply one input terminal of each other are buffer resistors.

19 ₁ , 19 ₂ , ..., 19 _o are tuned amplifiers, 2
0 ₁ , 20 ₂ , ..., 20 _o are tuned amplifiers 19 ₁ ,
A flaw detection sensitivity adjuster for appropriately adjusting the amplitude of the outputs of 19 ₂ ,..., 19 _o , 21 ₁ , 21 ₂ ,...,
21 _o is a phase detector, 22 ₁ , 22 ₂ ,..., 22 _o
are the high frequency oscillators 10 ₁ , 10 ₂ , ..., 1, respectively
This is a variable phase shifter that receives the negative part of the output signal of 0 _o and adjusts and sets the phase detection reference signal as appropriate in accordance with each frequency.

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, 23 to 26 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, the high frequency oscillators 10 ₁ , 10
₂ ,..., _10o output 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 signals are output in the amplifier 12. The constant current power 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 types of differential amplifiers 16 ₁ , 16
It is applied to one input terminal of each of ₂ ,..., _16o . The other input terminal is connected to a cancellation voltage generator 17 ₁ , 17 ₂ , which receives a part of the output of each high-frequency oscillator 10 ₁ , 10 ₂ , . . . , 10 _o , respectively.
..., 17 _o A reference voltage for canceling balance is applied. These canceling balance reference voltages are applied to the differential amplifiers 16 ₁ , 16 ₂ , 16 2 , ₁₀ o corresponding to the frequencies of the high frequency oscillators 10 ₁ , 10 2 , . . . , 10 _o , respectively.
..., 16 _o are set to be zero in the normal part of the test object A, so that the phases are reversed and the amplitude levels are made the _same . , 16 ₂ , ..., 16 _o produce unbalanced outputs. Due to the scattering of scratches _etc. on the test object A as the test object A is transported, and depending on the detection sensitivity specific to each _frequency , _the The output signal changes every moment.

The output signal of each differential amplifier 16 ₁ , 16 ₂ , ..., 16 _o is transmitted to a tuned amplifier 19 ₁ , 19 ₂ , ..., 19 _o
After being further amplified by the phase detectors 21 ₁ , 21 ₂ , . . . , 21 _o , the flaw detection signals are demodulated and extracted as flaw signals exhibiting low frequencies. In this phase detection, the variable phase shifters 22 ₁ , 22 ₂ , ..., 22 _o receive a part of the output of each high frequency oscillator 10 ₁ , 10 _{2 , ..., 10 o, and the variable phase shifter 22 1 , 22 2} , ..., 22 _o detects the most emphasized signal corresponding to each frequency. A reference signal for phase detection with a phase difference set appropriately so that extraction can be performed is output.

As explained above, the eddy current flaw detection device of the present invention drives the excitation coil of the eddy current flaw detection coil with a plurality of different frequencies adapted to the types of flaws to be inspected, and generates multiple series of flaw detection signals corresponding to each frequency. Since we tried to obtain various properties, sizes,
It is possible to detect different types of flaws such as depth and flaws. Furthermore, since there is no need to install multiple eddy current flaw detection coils or to replace them every time flaw detection is performed at each frequency, the device does not become bulky and operation becomes simple.

[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.

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. Eddy current flaw detection equipment equipped with multiple phase detectors that output multiple flaw signals corresponding to each frequency.