JPH0441300B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an eddy current flaw detection device having a plurality of detection coils and a plurality of excitation frequencies.

When identifying flaws using conventional eddy current flaw detection equipment (ECT), we focus on the phase angle of the flaw signal if the same coil is used, and when using various coils, we use a coil with high detection sensitivity for the flaw to be detected. We are working on ways to improve this. In addition, it has recently become clear that changing the excitation frequency is another effective method for identifying flaws, and this has been applied to through-coil type ECT to determine flaws on the inner and outer surfaces of pipes.

In the steel industry, probe coil type ECT has been introduced to detect surface flaws on wide machines such as thick plates and slabs, and flaw type identification has become an important consideration. In particular, regarding economic efficiency, if the current ECT device is introduced to wide materials, it would require an extremely large increase in the number of channels in the coil and signal processing section (up to 1000 channels) in order to accurately detect defects, making it expensive. This has become the biggest hurdle in the introduction. The present invention provides an effective means for accurately and conveniently detecting surface flaws on such wide specimen materials, and its features include a plurality of probe-type detection coils and a plurality of An excitation unit that sequentially excites the detection coils in a time-sharing manner, a frequency control unit that controls a plurality of excitation frequencies of the excitation unit, a switching control unit that controls switching timing of the detection coils and the device, and a plurality of detection coils This is because the signal processing circuit is provided with a program section for classifying the frequencies.

The present invention will be described in detail below based on drawings showing embodiments. FIG. 1 is an electrical block diagram of the signal processing circuit of the ECT device of the present invention. B, C and E in the diagram
Each column corresponds to three different excitation frequencies. Although three cases are shown in the embodiment, the present invention is not limited thereto. The case where the excitation frequency is selected as frequency B will be described below. The excitation section 1 generates burst oscillation of coil excitation power using a burst gate (not shown) of the switching control section 2. The intermittent oscillating sine wave which is the output of the excitation section is applied to the coil section 4 of, for example, 15 channels via the switch section 3. The impedance change information of the test material obtained by the coil section 4 is inputted to the balance section 6 via a set of switch sections 5. Since the switch unit 5 for switching the 15 channel coils performs the switching operation at the breaks in the intermittent oscillation sine wave, almost no switching noise is generated.

The output of the balance section 6 is input via a switch section 7 to a filter section 8, which is a cascade connection of two low-pass filters with the cut-off frequency selected as the excitation frequency. Filter unit outputs, which are the outputs of each low-pass filter, are input to each input terminal of a waveform correction unit 9 consisting of a differential amplifier. The output of the waveform correction section is input to the phase detection section 10, and the phase is detected by two sets of gates having a detection angle of 180 degrees and having a phase relationship different from each other by 90 degrees.

The output of the phase detection section 10 is input to an integration processing section 11 consisting of a complete integration circuit, and is converted into an integral value for each excitation period. A part of the output of the integral processing section 11 is passed through a switch section 12, converted into an appropriate voltage by an amplification section 13 and an attenuator section 14, and inputted into a memory section via a switch section 15. The memory section is composed of a digital memory section 16 and an analog memory section 17. The output of the memory section is input to the balance control section 19 via the switch section 18. The balance control section 19 outputs a control signal to the balance section 6 in order to return the input signal change to a balanced state. Integral processing section 11
The other part of the output signal is input to the polar coordinate rotation unit 20. The output signal of the polar coordinate rotation unit 20 is sampled and held (SH) via the switch unit 21.
The final integrated value is input to the circuit 22 and held.
The output signal of the SH section circuit 22 is input to the zero point convergence section 23, and variations in the outputs of the 15 channel coils in a balanced state are corrected. Zero point convergence section 23
The waveform of a part of the output is directly monitored by the monitor section 24.
The other part is displayed in XY via the squaring circuit section 25. A portion of the input signal of the monitor section 24 is input to a 5-channel parallel output section 26, and signals from the first to fifth channels (ch) are output in parallel. This is for recording the signals of channels 1 to 5 on chart paper.
When recording all 15 channels on chart paper, select 1~
It is necessary to output 15 channels in parallel. The above are B and C
The multi-frequency operation will be described next when the circuit of the section E and the section E are selected.

First, the output signal of the switching control section 2 is input to the program section 27, and each of the 15 channels of coils is classified into, for example, 1 block and 5 channels, and 3 blocks are classified into one of the 3 frequencies by pin connection.
The output signal of the program section 27 is transmitted to the frequency control section 28.
is input. The frequency control unit 28 outputs three types of VCO voltages in time series according to the output signal of the program unit 27. VCO which is the frequency control section output
The voltage is input to the excitation section 1. Frequency control section 28
Another output signal is input to each switch section 7, 12, and 21 of B, C, and E (those of C and E are shown with the same symbols followed by ``,''), and the programmed frequency of each coil is Depending on the frequency, one of the switches B, C, or E is turned on, and the filter sections 8, 8', and 8'' are adjusted for each of the three frequencies.
Phase detection units 10, 10', and 10'' are selected. Three sets of polar coordinate rotation units 20, 20', and 20'' are also provided so that polar rotation of the monitor display signal can be performed independently for each frequency.

In the above embodiment, three sets of filter section 8, waveform correction section 9, phase detection section 10, integral processing section 11, polar coordinate rotation 20, etc. were provided for three different excitation frequencies to correspond to each frequency. By making full use of digital technology, the filter section 8, waveform correction section 9, phase detection section 10, static processing section 11, polar coordinate rotation 20, etc. can correspond to each weekly wave number instantly by digitally programming. Therefore, there is no need to have three sets (multiple sets) of essentially the same items, and only one set is sufficient.

Next, specific coil arrangement, excitation method, etc. in the embodiment will be described. FIG. 2 is an example of a coil arrangement when inspecting five channels of coil width at different frequencies f ₁ , f ₂ and f ₃ . Although the 5-channel coils are arranged in a direction perpendicular to the traveling direction of the specimen 30, a constant inspection width is secured by keeping the detection coil stationary. In the example, if the flaw detection width of one coil is 20 mm, 20 mm x 5 = 100
For example, if a slab is 1 m wide, 10 slabs with 5 channels are lined up in the width direction and measured. Also, the frequencies f ₁ , f ₂ ,
_f3 quantifies the flaw depth, and obtaining a sensitive flaw signal with a detection coil with a lower frequency means that the flaw is deep. It is possible to accurately identify bald spots 31, cracked spots 32, and the like. Next is the excitation order of the detection coil, which is f ₁ 1ch → 5ch, then
One possible method is f ₂ 1ch → 5ch, then f ₃ 1ch → 5ch. Also, 1ch f ₁ → f ₃ , 2ch f ₁ → f ₃ , 3ch
f ₁ → f ₃ , 4ch f ₁ →f ₃ , and 5ch f ₁ →f ₃ are also considered.
Furthermore, it is conceivable to randomly select the 15 channels of coils and their excitation frequencies, but this can all be handled by the switching control section 2 and the program 27.

As described above, according to the present invention, it is possible to provide an economical ECT device that can operate in combination with a plurality of detection coils and a plurality of excitation frequencies, making it possible to accurately identify surface flaws on wide materials. ,
This invention is extremely useful in improving the quality and reliability of products.

[Brief explanation of drawings]

FIG. 1 is an electrical block diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing an example of arrangement of coils. 1...excitation section, 2...switching control section,
3, 5, 7, 12, 21, 15, 18...Switch section, 4...Coil section, 6...Balance section, 8...
... Filter section, 9 ... Waveform correction section, 10 ... Phase detection section, 11 ... Integral processing section, 13 ... Amplification section, 14 ... Attenuator section, 16 ... Digital memory section, 17 ... Analog memory section ,
19...Balance control section, 20...Polar coordinate rotation section, 22...Sample and hold section, 23...
...Zero point convergence section, 24...Monitor section, 25...2
Multiplication processing section, 26...5ch parallel output section, 27...
...Program section, 28...Frequency control section.

Claims (1)

[Claims] 1. A plurality of detection coils, an excitation section that sequentially excites the plurality of detection coils in a time-sharing manner and oscillates coil excitation power in bursts, and a plurality of excitation frequencies of the excitation section. a frequency control section that controls the output signal using the VCO voltage, a switch section that switches the signal during the stop period of the burst oscillation, a balance section that returns the impedance change of each detection coil to a balanced state, and an output signal of the balance section. a filter section in which two low-pass filters with cut-off frequencies selected as excitation frequencies are connected in cascade; a waveform correction section consisting of a differential amplifier that receives the outputs of the two filter sections; and the waveform correction section. A phase detection unit that detects the phase of the output signal of the output signal with two sets of gates having a detection angle of 180° and a phase relationship that is 90° different from each other with respect to the excitation frequency, and a phase detection unit that completely integrates the output signal of the phase detection unit. an output voltage adjustment section comprising an integral processing section, an amplification section and an attenuator section that adjust the output voltage of the integral processing section; and an output signal of the voltage adjustment section is made to correspond one-to-one with the plurality of detection coils. a balance control section that controls the balance section using the output signal of the memory section; a switching control section that controls the switching timing of the detection coils and the device; A multi-probe coil multi-frequency eddy current flaw detection device comprising a classification program section. 2. The multi-probe coil multi-frequency eddy current flaw detection device according to claim 1, characterized in that the device has a filter section, a waveform correction section, a phase detection section, and an integral processing section as many as the number of different excitation frequencies. . 3 The above device has only one set of filter section, waveform correction section, phase detection section, and integral processing section,
The multi-probe coil multi-frequency eddy current flaw detection device according to claim 1, characterized in that it has an electronic setting function for each component in order to correspond to different frequencies.