JP2017067743A - Non-destructive inspection device and non-destructive inspection method - Google Patents

Non-destructive inspection device and non-destructive inspection method Download PDF

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JP2017067743A
JP2017067743A JP2015197253A JP2015197253A JP2017067743A JP 2017067743 A JP2017067743 A JP 2017067743A JP 2015197253 A JP2015197253 A JP 2015197253A JP 2015197253 A JP2015197253 A JP 2015197253A JP 2017067743 A JP2017067743 A JP 2017067743A
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塚田 啓二
Keiji Tsukada
啓二 塚田
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Abstract

PROBLEM TO BE SOLVED: To provide a non-destructive inspection device capable of performing measurement faster and adaptable to various levels of thickness, and a non-destructive inspection method.SOLUTION: The non-destructive inspection device comprises: an application coil (4-1) for applying a magnetic field to an inspection object; a magnetic sensor (2-1) for detecting a magnetic field induced by the inspection object; detectors (8-1 and 8-2) for detecting a signal in a predetermined frequency from an output signal of the magnetic sensor (2-1); and an analyzer (10-1) for analyzing output signals of the detectors (8-1 and 8-2). The application coil (4-1) is driven by a first AC current in a first frequency and a second AC current in a second frequency lower than the first frequency, and thickness of the inspection object is detected from a phase component of a differential vector obtained as a difference of vectors between a first magnetic field vector based on a signal detected in the first frequency by the detector (8-1) and a second magnetic field vector based on a signal detected in the second frequency by the detector (8-2).SELECTED DRAWING: Figure 1

Description

本発明は、金属構造物の腐食や亀裂を磁気的に検査する非破壊検査装置及び非破壊検査方法に関する。   The present invention relates to a nondestructive inspection apparatus and a nondestructive inspection method for magnetically inspecting corrosion and cracking of a metal structure.

橋梁など鉄鋼材料で作られたインフラ構造物は、作られてから長い年月が経ったものがその安全性確保が現在大きな社会問題となっている。このため、簡単にしかも精度良い検査方法が望まれている。   For infrastructure structures made of steel materials such as bridges, safety has been a major social problem since many years have passed since they were made. For this reason, a simple and accurate inspection method is desired.

検査方法には、超音波検査や、x線検査、打音検査などがあり、そのなかでも簡易に測定でき、検査結果を定量化できるものとして渦電流探傷法がある。これは金属性の対象物に交流磁場を印加して、渦電流を発生させる方法である。対象物に傷などがあると渦電流の分布が変化して、渦電流が作る磁場が変化するので、その変化量を計測している。この方法は表面探傷法とも呼ばれ、表面の傷の検査に多く用いられている。   The inspection method includes an ultrasonic inspection, an x-ray inspection, a hammering inspection, and the like, and among them, an eddy current flaw detection method can be easily measured and the inspection result can be quantified. This is a method of generating an eddy current by applying an alternating magnetic field to a metallic object. If there is a scratch on the object, the distribution of eddy current changes, and the magnetic field created by the eddy current changes, so the amount of change is measured. This method is also called a surface flaw detection method and is often used for inspection of surface flaws.

表面探傷法においては、交流磁場が表皮効果のために深くは浸透しないため、表面の傷の検査に多く用いられることとなっている。表皮効果による磁場の浸透は、周波数が低いほど深くすることができる。さらに、最近では磁場を検出するセンサとして検出コイルの変わりに磁気センサを用いることで、低周波計測による深部の探傷が行われ始めている。   In the surface flaw detection method, an alternating magnetic field does not penetrate deeply due to the skin effect, and is therefore often used for inspection of surface flaws. The penetration of the magnetic field due to the skin effect can be made deeper as the frequency is lower. Furthermore, recently, by using a magnetic sensor instead of a detection coil as a sensor for detecting a magnetic field, deep flaw detection by low frequency measurement has begun.

深部の探傷として、たとえば鋼板で囲まれて、外部からでは見えない内部側の腐食を検査する方法として、印加コイルを取り付けたヨーク材を鋼板に当てて鋼板内部に磁場を生じさせ、表面から漏れてくる表面に平行な磁束成分を磁気センサで計測する磁束漏洩法を報告した。この方法により、厚みのある鋼板の裏面側の腐食を検知できることを報告した(たとえば、特許文献1参照。)。ここでは磁界強度の変化だけでは判別が難しく、位相を含めた磁場強度に変換することにより、厚い鋼板の裏側の信号変化を捉えることが可能となった。   For deep flaw detection, for example, as a method of inspecting internal corrosion that is surrounded by a steel plate and is not visible from the outside, a yoke material with an applied coil is applied to the steel plate to generate a magnetic field inside the steel plate and leak from the surface We reported a magnetic flux leakage method that measures magnetic flux components parallel to the incoming surface with a magnetic sensor. It has been reported that this method can detect corrosion on the back side of a thick steel plate (see, for example, Patent Document 1). Here, it is difficult to discriminate only by changing the magnetic field strength, and it is possible to capture the signal change on the back side of the thick steel plate by converting it to the magnetic field strength including the phase.

一方、ほかの方法として厚い金属板材を計測する方法として、印加コイルと磁気センサからなる渦電流プローブにおいて1Hz前後から数kHzまでの周波数を走査し、その磁気応答における強度と位相による磁気ベクトルを実軸と虚軸のグラフにプロットした応答曲線(以下磁気スペクトルと呼ぶ)によって調べることを報告した(たとえば、非特許文献1参照)。この方法では、厚みによって磁気スペクトルが変化することから、この応答曲線の違いにより判別することができる。この磁気スペクトルを作成することによって、測定対象がアルミニウムや銅などの非磁性体であるか、鉄などの磁性体であるか、また、着磁しているかなどの磁気的特性の違いを判別できた。ここで、厚みの違いを見る方法として、磁気スペクトルにおいて位相情報を抽出し、周波数に対する位相変化のグラフを書くことによって、わかりやすいことを報告した。さらに、磁性体を計測する場合には、位相として印加コイルの参照信号に対する遅れ位相をとることを報告した(たとえば、非特許文献2参照。)。   On the other hand, as another method for measuring a thick metal plate, an eddy current probe consisting of an applied coil and a magnetic sensor is scanned with a frequency from around 1 Hz to several kHz, and the magnetic vector in the magnetic response is measured according to the intensity and phase. It has been reported that investigation is made by a response curve (hereinafter referred to as a magnetic spectrum) plotted on a graph of an axis and an imaginary axis (see, for example, Non-Patent Document 1). In this method, since the magnetic spectrum changes depending on the thickness, it can be determined by the difference in the response curve. By creating this magnetic spectrum, it is possible to determine the difference in magnetic characteristics such as whether the object to be measured is a non-magnetic material such as aluminum or copper, a magnetic material such as iron, or whether it is magnetized. It was. Here, as a method of seeing the difference in thickness, we reported that it is easy to understand by extracting phase information in the magnetic spectrum and writing a graph of phase change against frequency. Furthermore, it has been reported that when measuring a magnetic body, a phase that is delayed with respect to the reference signal of the applied coil is taken as the phase (see, for example, Non-Patent Document 2).

一方、磁気センサを用いないで従来の印加コイルと検出コイルが同じものを使った計測においても、電圧駆動により対象物との相互インダクタンス変化による検出コイル自身のインピーダンスの周波数変化を実軸(抵抗分)と虚軸(リアクタンス分)にプロットしたインピーダンス曲線はよく知られている(たとえば、非特許文献3参照。)。   On the other hand, even in the conventional measurement using the same applied coil and detection coil without using a magnetic sensor, the frequency change of the impedance of the detection coil itself due to the change in mutual inductance with the object due to voltage drive is measured on the real axis (resistance component). ) And the impedance curve plotted on the imaginary axis (reactance) are well known (for example, see Non-Patent Document 3).

また、印加コイルと検出コイルを別に設けたものでの計測された信号の実軸と虚軸の図にプロットして、この軌跡により板厚ではないが、焼結金属の品質判断ができることが報告されている(たとえば、特許文献2参照。)。   In addition, plotting the measured signal with the application coil and the detection coil separately on the real and imaginary axes, it is reported that the quality of the sintered metal can be judged by this trajectory, not the plate thickness (For example, see Patent Document 2).

また、信号強度だけの周波数応答特性を報告しているものもある。ここで、検査のときは時間のかかる周波数応答特性曲線を求めるものでなく、欠陥の深さにより周波数応答曲線が異なるので、任意の2つの周波数での信号強度の差を捕らえることによって欠陥の深さを判定する方法が報告されている(例えば、特許文献3参照。)。   Some report frequency response characteristics of only signal strength. Here, the time-dependent frequency response characteristic curve is not obtained at the time of inspection, and the frequency response curve differs depending on the depth of the defect. Therefore, by detecting the difference in signal intensity at any two frequencies, the depth of the defect can be determined. A method for determining the thickness has been reported (for example, see Patent Document 3).

周波数を広く走査するためには時間がかかるので、時間短縮する方法として、パルス磁場を印加し、得られた信号をフーリエ解析して各周波数における磁場強度と位相の変化を捉える方法が報告されている(例えば、特許文献4参照。)。   Since it takes time to scan a wide range of frequencies, a method of applying a pulsed magnetic field and analyzing the obtained signal by Fourier analysis to capture changes in magnetic field strength and phase at each frequency has been reported as a method of shortening the time. (For example, refer to Patent Document 4).

特許第4487082号公報Japanese Patent No.4487082 特開2011-85502号公報JP 2011-85502 特開2012-68061号公報JP 2012-68061 A 特許第3924626号公報Japanese Patent No. 3924626

Keiji Tsukada, et al., Review of Scientific Instruments 77, pp063703-1-6Keiji Tsukada, et al., Review of Scientific Instruments 77, pp063703-1-6 林孝之 他,日本非破壊検査協会,平成21年度春季大会,公演概要集,pp203-204Takayuki Hayashi et al., Japan Nondestructive Inspection Association, 2009 Spring Meeting, Performance Summary, pp203-204 渦電流探傷試験実技参考書,日本非破壊検査協会pp21-24 (2008)Eddy current flaw detection test reference book, Japan Nondestructive Inspection Association pp21-24 (2008)

コイル用いて電圧駆動して得られるインピーダンス曲線では、非磁性の金属に対しては薄いものならば厚みを検査できるが、高周波を用いるために表皮深さの制限から数cmになる厚いものは計測できなかった。また、対象が鋼板のように磁性体の場合には、同じ板厚でも透磁率の違いや、磁化の状態の違いによって渦電流による磁気信号への影響が大きく、厚み計測が困難であった。   In the impedance curve obtained by voltage driving using a coil, the thickness can be inspected if it is thin for non-magnetic metals, but in order to use high frequency, a thick one that is several centimeters from the skin depth limit is measured. could not. Further, when the object is a magnetic material such as a steel plate, even if the plate thickness is the same, the influence on the magnetic signal due to the eddy current is large due to the difference in magnetic permeability and the difference in the magnetization state, making it difficult to measure the thickness.

非磁性のみならず磁性体の厚み計測を可能とした方法として、電流駆動させた印加コイルにより磁場を印加し、発生した渦電流による磁場を磁気センサを用いて計測する方法によって得られる磁気スペクトルを報告した。しかし、この方法では、周波数を走査する時間がかかる問題があり、また、その得られたスペクトル曲線が厚みによって変化することはわかったが、どのように曲線の違いを扱うのか不明であった。   A magnetic spectrum obtained by applying a magnetic field with a current-driven application coil and measuring the magnetic field due to the generated eddy current using a magnetic sensor as a method that enables thickness measurement of not only non-magnetic materials but also magnetic materials. reported. However, this method has a problem that it takes time to scan the frequency, and it has been found that the obtained spectrum curve changes depending on the thickness, but it is unclear how to deal with the difference between the curves.

また、計測の高速化としてパルス磁場を印加して応答磁場をフーリエ解析する方法も報告したが、この方法では、数Hz以下の低周波を含むと信号のSNが悪く、パルスを何回も加算する必要があり、時間短縮の効果がそれほど大きくなかった。   We also reported a Fourier analysis of the response magnetic field by applying a pulsed magnetic field to speed up the measurement. However, in this method, the signal SN is poor when a low frequency of several Hz or less is included, and the pulse is added many times. The effect of shortening the time was not so great.

さらに、磁気スペクトルにおいて、厚みを見るパラメータとして強度ではなく、得られた信号そのものの位相を見る方法では、特に磁性体の場合において、鋼板の厚みが厚くなるにつれて変化が少なくなり、判別が困難であった。   Furthermore, in the method of viewing the phase of the obtained signal itself, not the intensity as a parameter for viewing the thickness in the magnetic spectrum, especially in the case of a magnetic material, the change decreases as the thickness of the steel plate increases, making discrimination difficult. there were.

以上のことから、より高速に計測可能であって、さらに様々な厚みに対応できる計測方法が望まれていた。   From the above, there has been a demand for a measurement method that can measure at higher speed and can cope with various thicknesses.

本発明の非破壊検査装置では、検査対象物に磁場を印加する印加コイルと、この印加コイルに所定の周波数の交流電流を通電させる交流定電流源と、印可コイルで印加した磁場により検査対象物に誘引された磁場を検出する磁気センサと、この磁気センサの出力信号のうち所定周波数の信号を検波する検波器と、この検波器の出力信号を解析する解析器とを有する非破壊検査装置である。   In the nondestructive inspection apparatus of the present invention, an inspection object is applied by an application coil for applying a magnetic field to the inspection object, an AC constant current source for supplying an alternating current of a predetermined frequency to the application coil, and a magnetic field applied by the application coil. A non-destructive inspection apparatus having a magnetic sensor for detecting a magnetic field attracted by a magnetic sensor, a detector for detecting a signal having a predetermined frequency among output signals of the magnetic sensor, and an analyzer for analyzing the output signal of the detector. is there.

特に、本発明の非破壊検査装置では、交流定電流源において、第1の周波数とした第1の交流電流と、第1の周波数よりも周波数の小さい第2の周波数とした第2の交流電流で印加コイルを駆動させ、解析器では、検波器で第1の周波数で検波して得られた信号の強度と位相とを成分とする第1の磁場ベクトルと、検波器で第2の周波数で検波して得られた信号の強度と位相とを成分とする第2の磁場ベクトルとのベクトルの差として得られる差ベクトルの位相成分を検出して、この位相成分から前記検査対象物の厚みを検出することとしている。   In particular, in the nondestructive inspection apparatus of the present invention, in an AC constant current source, a first AC current having a first frequency and a second AC current having a second frequency smaller than the first frequency. In the analyzer, the application coil is driven, and the analyzer uses a first magnetic field vector having components of the intensity and phase of the signal obtained by detection at the first frequency by the detector, and a second frequency by the detector. The phase component of the difference vector obtained as a vector difference between the second magnetic field vector having the intensity and phase of the signal obtained by the detection as components is detected, and the thickness of the inspection object is determined from this phase component. Trying to detect.

さらに、本発明の非破壊検査装置では、第1と第2の磁場ベクトルの位相を、第2の周波数より小さい1Hz以下の周波数として得られた磁場ベクトルの位相を基準としていることにも特徴を有し、さらには、第1と第2の周波数は可変として、予め設定されている検査対象物の厚みに対応させた周波数の組み合わせとすることにも特徴を有するものである。   Furthermore, the nondestructive inspection apparatus of the present invention is characterized in that the phase of the first and second magnetic field vectors is based on the phase of the magnetic field vector obtained as a frequency of 1 Hz or less, which is smaller than the second frequency. Furthermore, the first and second frequencies are variable, and a combination of frequencies corresponding to a preset thickness of the inspection object is also characteristic.

また、本発明の非破壊検査方法では、印加コイルで検査対象物に所定の周波数の交流磁場を印加して、検査対象物に誘引した磁場を磁気センサで検出し、この磁気センサの出力信号の所定周波数成分を検波器で検波し、この検波器の出力信号を解析器で解析することで検査対象物の厚みを検出する非破壊検査方法において、印加コイルには、第1の周波数とした第1の交流電流と、第1の周波数よりも周波数の小さい第2の周波数とした第2の交流電流とを通電し、解析器では、検波器で第1の周波数で検波して得られた信号の強度と位相とを成分とする第1の磁場ベクトルと、検波器で第2の周波数で検波して得られた信号の強度と位相とを成分とする第2の磁場ベクトルとのベクトルの差として得られる差ベクトルの位相成分を検出して、この位相成分から検査対象物の厚みを検出するものである。   Further, in the nondestructive inspection method of the present invention, an alternating current magnetic field having a predetermined frequency is applied to the inspection object by the application coil, the magnetic field attracted to the inspection object is detected by the magnetic sensor, and the output signal of the magnetic sensor is detected. In a nondestructive inspection method for detecting a thickness of an inspection object by detecting a predetermined frequency component with a detector and analyzing an output signal of the detector with an analyzer, the applied coil has a first frequency set as the first frequency. A signal obtained by applying a first alternating current and a second alternating current having a second frequency lower than the first frequency and detecting the first frequency with the detector in the analyzer. Difference between the first magnetic field vector having the intensity and phase as components and the second magnetic field vector having the intensity and phase of the signal obtained by detection at the second frequency by the detector as components. Detect the phase component of the difference vector obtained as And it detects the thickness of the test object from the phase component.

本発明によれば、差ベクトルの位相成分から検査対象物の厚みを検出することで、短時間で精度の高い検査対象物の厚み検査を可能とすることができる。検査対象物の厚み検査が可能となったことにより、例えば検査対象物が鋼板等である場合には、腐食などでの鋼板の表面ならず裏面に生じた減肉や亀裂を検知することもできるようになる。   According to the present invention, by detecting the thickness of the inspection object from the phase component of the difference vector, it is possible to perform a highly accurate inspection of the inspection object in a short time. By enabling inspection of the thickness of the inspection object, for example, when the inspection object is a steel plate, it is possible to detect thinning and cracks occurring on the back surface as well as the surface of the steel plate due to corrosion or the like. It becomes like this.

本発明に係わる非破壊検査装置の構成図である。It is a block diagram of the nondestructive inspection apparatus concerning this invention. 各周波数における磁場ベクトルをプロットした磁気スペクトルである。It is the magnetic spectrum which plotted the magnetic field vector in each frequency. 0.5Hzの磁気ベクトルを基準ベクトルとしてその差ベクトルをプロットした磁気スペクトルの板厚依存性を示した図である。(a)周波数0.5Hzから1kHzまでの周波数帯域、(b)原点付近の拡大図It is the figure which showed the plate | board thickness dependence of the magnetic spectrum which plotted the difference vector by making a 0.5Hz magnetic vector into a reference | standard vector. (A) Frequency band from 0.5Hz to 1kHz, (b) Enlarged view near the origin 本発明に係わる0.5Hz磁場ベクトルと各周波数における磁場ベクトルとの差ベクトルの位相の板厚依存性を示した図である。It is the figure which showed the plate | board thickness dependence of the phase of the difference vector of the 0.5Hz magnetic field vector concerning this invention, and the magnetic field vector in each frequency. 本発明に係わる任意の周波数の組み合わせによる差ベクトルの位相の板厚依存性。The thickness dependence of the phase of the difference vector by the combination of the arbitrary frequencies concerning this invention. 磁場ベクトルにおけるリフトオフ変化を示した図である。(a)磁場ベクトルの強度,(b)磁場ベクトルの位相It is the figure which showed the lift-off change in a magnetic field vector. (a) Magnetic field vector strength, (b) Magnetic field vector phase 本発明に係わる漏洩磁束法を用いた非破壊検査装置の構成図を示す。The block diagram of the nondestructive inspection apparatus using the leakage magnetic flux method concerning this invention is shown. 本発明に係わる10Hzと5Hzの周波数における磁場ベクトルの差ベクトルの位相の板厚変化を示した図である。It is the figure which showed the plate | board thickness change of the phase of the difference vector of the magnetic field vector in the frequency of 10Hz and 5Hz concerning this invention.

本発明の非破壊検査装置及び非破壊検査方法は、金属構造物の腐食や亀裂を磁気的に検査可能とした非破壊検査装置及び非破壊検査方法である。   The nondestructive inspection apparatus and the nondestructive inspection method of the present invention are a nondestructive inspection apparatus and a nondestructive inspection method that can magnetically inspect corrosion and cracks of metal structures.

すなわち、本発明の非破壊検査装置では、検査対象物に磁場を印加する印加コイルと、この印加コイルに所定の周波数の交流電流を通電させる交流定電流源と、印可コイルで印加した磁場により検査対象物に誘引された磁場を検出する磁気センサと、この磁気センサの出力信号のうち所定周波数の信号を検波する検波器と、この検波器の出力信号を解析する解析器とを設けている。   That is, in the nondestructive inspection apparatus of the present invention, an inspection is performed by an application coil that applies a magnetic field to an inspection object, an AC constant current source that supplies an AC current of a predetermined frequency to the application coil, and a magnetic field applied by an application coil. A magnetic sensor for detecting a magnetic field attracted by an object, a detector for detecting a signal having a predetermined frequency among output signals of the magnetic sensor, and an analyzer for analyzing the output signal of the detector are provided.

そして、交流定電流源では、第1の周波数とした第1の交流電流と、第1の周波数よりも周波数の大きい第2の周波数とした第2の交流電流で印加コイルを駆動させ、検波器では、検波器で第1の周波数で検波して得られた信号の強度と位相とを成分とする第1の磁場ベクトルと、検波器で第2の周波数で検波して得られた信号の強度と位相とを成分とする第2の磁場ベクトルとのベクトルの差として得られる差ベクトルの位相成分を検出して、この位相成分から検査対象物の厚みを検出することとしている。   In the AC constant current source, the application coil is driven by the first AC current having the first frequency and the second AC current having the second frequency higher than the first frequency, and the detector Then, the first magnetic field vector whose components are the intensity and phase of the signal obtained by detection at the first frequency by the detector, and the intensity of the signal obtained by detection at the second frequency by the detector. The phase component of the difference vector obtained as a vector difference between the first magnetic field vector and the second magnetic field vector having the phase component is detected, and the thickness of the inspection object is detected from the phase component.

なお、第1と第2の磁場ベクトルの位相の基準は、第2の周波数より小さい1Hz以下の周波数として得られた磁場ベクトルの位相を基準とすることが望ましい。また、第1と第2の周波数は可変として、予め設定されている検査対象物の厚みに対応させた周波数の組み合わせとすることで、たとえば検査対象物に減肉が生じている場合の評価精度を高めることができる。   Note that the phase reference of the first and second magnetic field vectors is preferably based on the phase of the magnetic field vector obtained as a frequency of 1 Hz or less which is smaller than the second frequency. In addition, the first and second frequencies are variable, and a combination of frequencies corresponding to a preset thickness of the inspection object is used, for example, evaluation accuracy when the inspection object is thinned Can be increased.

以下において、具体的な実施例を示しながら説明する。   In the following, a specific example will be described.

図1は、第1の実施例の非破壊検査装置の概略模式図を示している。この非破壊検査装置では、検査対象物である金属性の試験体1−1に印加コイル4−1で磁場を印加して、試験体1−1に渦電流を誘引させている。この渦電流が作る磁場を磁気センサ2−1で計測している。本実施例では、磁気センサ2−1は磁気抵抗素子(MR)であるが、トンネル型抵抗素子(TMR)や、磁気インピーダンス素子(MI)、超伝導量子干渉素子(SQUID)など、低周波から感度があるものであれば、なんでも使うことができる。   FIG. 1 shows a schematic diagram of the nondestructive inspection apparatus of the first embodiment. In this nondestructive inspection apparatus, a magnetic field is applied to the metallic test body 1-1, which is an inspection object, by the application coil 4-1, and an eddy current is induced in the test body 1-1. The magnetic field generated by this eddy current is measured by the magnetic sensor 2-1. In this embodiment, the magnetic sensor 2-1 is a magnetoresistive element (MR), but from a low frequency such as a tunneling resistive element (TMR), a magnetic impedance element (MI), a superconducting quantum interference element (SQUID), or the like. Anything that has sensitivity can be used.

印加コイル4−1は、交流の定電流源3−1で駆動して、試験体1−1に一定の交流磁場を印加している。ここで周波数の異なる複数種類の磁場を印加できるように、複数の周波数を含む信号を周波数発振器5−1等で合成して定電流源3−1に入力することで、印加コイル4−1に所定の周波数の交流電流を通電している。なお、各周波数における印加電流値は、試験体1−1に同じ磁場を印加させるために同一の交流電流値としている。   The application coil 4-1 is driven by an AC constant current source 3-1, and applies a constant AC magnetic field to the test body 1-1. Here, a plurality of types of magnetic fields having different frequencies can be applied, and a signal including a plurality of frequencies is synthesized by the frequency oscillator 5-1 or the like and input to the constant current source 3-1, thereby applying to the application coil 4-1. An alternating current having a predetermined frequency is applied. The applied current value at each frequency is the same alternating current value in order to apply the same magnetic field to the specimen 1-1.

本実施例では、磁気センサ2−1の近傍に、印加コイル4−1で生起した磁場が直接入ってこないようにキャンセルコイル6を設けている。なお、キャンセルコイル6は用いなくてもよいが、キャンセルコイル6を用いない場合は、磁気センサ2−1で得られた信号に、印加コイル4−1による印加磁場の信号も直接はいるので、ダイナミックレンジが狭くなる問題がある。このため、キャンセルコイル6を用いたほうが、微弱な磁場を計測することができる。   In the present embodiment, the cancel coil 6 is provided in the vicinity of the magnetic sensor 2-1 so that the magnetic field generated by the application coil 4-1 does not enter directly. The cancel coil 6 may not be used. However, when the cancel coil 6 is not used, the signal obtained by the magnetic sensor 2-1 also includes the signal of the magnetic field applied by the application coil 4-1. There is a problem that the dynamic range becomes narrow. For this reason, a weak magnetic field can be measured by using the cancel coil 6.

本実施例では、磁気センサ2−1は計測回路7−1に接続しており、計測回路7−1を介して磁気センサ2−1の出力信号を取り出している。   In this embodiment, the magnetic sensor 2-1 is connected to the measurement circuit 7-1, and the output signal of the magnetic sensor 2-1 is taken out via the measurement circuit 7-1.

磁気センサ2−1の出力信号は、検波器に入力して、印加コイル4−1による印加磁場の周波数での検波を行っている。特に、印加コイル4−1による印加磁場は、周波数の異なる複数種類の交流磁場の合成磁場であり、周波数ごとに検波するために合成した周波数の数だけ検波器を設けて、それぞれの周波数での検波を行うこととしている。説明の便宜上、本実施例では2種類の異なる周波数を用いていることとし、2台のロックイン検波器8−1,8−2によって、第1の周波数と第2の周波数での検波を行っている。3種類の異なる周波数を用いた場合には、3台のロックイン検波器を用いることとなる。   The output signal of the magnetic sensor 2-1 is input to the detector, and is detected at the frequency of the applied magnetic field by the application coil 4-1. In particular, the magnetic field applied by the application coil 4-1 is a combined magnetic field of a plurality of types of alternating magnetic fields having different frequencies, and detectors are provided as many as the combined frequencies for detection at each frequency. Detection is to be performed. For convenience of explanation, it is assumed that two different frequencies are used in this embodiment, and detection at the first frequency and the second frequency is performed by the two lock-in detectors 8-1 and 8-2. ing. When three different frequencies are used, three lock-in detectors are used.

ロックイン検波器8−1,8−2による検波では、参照信号と同位相である実数成分の信号と、90°位相がずれた虚数成分の信号を検波している。印加磁場の周波数と同じ周波数でロックイン検波した信号は、実数成分が強度、虚数成分が位相である2成分ベクトルとして見なすことができ、これを磁場ベクトルと呼ぶこととする。   In detection by the lock-in detectors 8-1 and 8-2, a real component signal that is in phase with the reference signal and an imaginary component signal that is 90 ° out of phase are detected. A signal lock-in detected at the same frequency as the frequency of the applied magnetic field can be regarded as a two-component vector in which the real component is intensity and the imaginary component is phase, and this is referred to as a magnetic field vector.

ロックイン検波器8−1,8−2の各出力信号は、マルチプレクサ9−1を介して切り替えながら解析器10−1に取り込み、データ収録するとともに解析することとしている。本実施例では、解析器10−1はパーソナルコンピュータで構成している。   The output signals of the lock-in detectors 8-1 and 8-2 are taken into the analyzer 10-1 while being switched via the multiplexer 9-1, recorded and analyzed. In this embodiment, the analyzer 10-1 is composed of a personal computer.

本実施形態ではロックイン検波器8−1,8−2を用いているが、ロックイン検波器8−1,8−2を使わなくても、磁気センサ2−1の出力信号の時間波形をAD変換してデータ収録し、解析器10−1でデジタル的に同相成分と、90°位相成分を解析することもできる。この場合にはロックイン検波器8−1,8−2が必要ないので、装置の小型化ができる。あるいは、本実施例では、印加コイル4−1による印加磁場を周波数の異なる複数種類の交流磁場の合成磁場としているが、所定の時間で印加磁場の周波数を切り替えながら測定するようにすることで、1台のロックイン検波器で対応可能としてもよい。   In this embodiment, the lock-in detectors 8-1 and 8-2 are used, but the time waveform of the output signal of the magnetic sensor 2-1 can be obtained without using the lock-in detectors 8-1 and 8-2. Data can be recorded after AD conversion, and the in-phase component and 90 ° phase component can be analyzed digitally by the analyzer 10-1. In this case, since the lock-in detectors 8-1 and 8-2 are not necessary, the apparatus can be reduced in size. Alternatively, in this embodiment, the magnetic field applied by the application coil 4-1 is a combined magnetic field of a plurality of types of alternating magnetic fields having different frequencies, but by measuring while switching the frequency of the applied magnetic field in a predetermined time, One lock-in detector may be applicable.

本実施例の非破壊検査装置はこのように構成しており、以下において本発明の非破壊検査装置の原理を説明する。   The nondestructive inspection apparatus of the present embodiment is configured as described above, and the principle of the nondestructive inspection apparatus of the present invention will be described below.

まず、試験体1−1は鋼板として、板厚の異なる鋼板を用いて印加コイル4−1による印加磁場の周波数を0.5Hzから1kHzの間で走査した際における磁気センサ2−1の出力信号の解析結果を図2に示す。   First, the specimen 1-1 is a steel plate having a different thickness, and the output signal of the magnetic sensor 2-1 is scanned when the frequency of the magnetic field applied by the application coil 4-1 is scanned between 0.5 Hz and 1 kHz. The analysis results are shown in FIG.

磁気センサ2−1の出力信号は、上述したように参照信号と同位相である実数成分と、90°位相がずれた虚数成分の信号として表され、実数成分は信号の強度、虚数成分は信号の位相であり、図2は横軸を実軸、縦軸を虚軸とした2次元平面として、それぞれの板厚で各周波数における磁場ベクトルを計測して描いた磁気スペクトルとなっている。ここで、磁気スペクトルは周波数を上げていくにつれ時計回りする曲線となっている。しかし、これらの曲線には特に板厚の依存性は見られず強度がばらばらである。   As described above, the output signal of the magnetic sensor 2-1 is expressed as a signal of a real component that is in phase with the reference signal and an imaginary component that is 90 ° out of phase, where the real component is the signal strength and the imaginary component is the signal. FIG. 2 shows a magnetic spectrum drawn by measuring magnetic field vectors at respective frequencies with respective plate thicknesses as a two-dimensional plane with the horizontal axis as the real axis and the vertical axis as the imaginary axis. Here, the magnetic spectrum is a curve that rotates clockwise as the frequency is increased. However, these curves are not particularly dependent on the plate thickness, and the strength is uneven.

ここで、もっとも低い周波数の0.5Hzでの磁場ベクトルを基準磁場ベクトルとして、各周波数の磁場ベクトルから0.5Hzの基準磁場ベクトルを引いた差ベクトルを求めてプロットを描くと、図3左図となる。そうすると一見,すべてが重なっているようにみえるが、低周波領域を拡大してみると、図3右図に示すように基準磁場ベクトルとの差ベクトルを用いた磁気スペクトルには、板厚依存性がはっきりとしてきて、板厚が厚くなるにつれ内側の曲線となっていることがわかる。   Here, if the magnetic field vector at the lowest frequency of 0.5 Hz is used as a reference magnetic field vector, a difference vector obtained by subtracting the 0.5 Hz reference magnetic field vector from the magnetic field vector of each frequency is obtained, and a plot is drawn as shown in the left figure of FIG. . At first glance, all seem to overlap, but when the low frequency region is expanded, the magnetic spectrum using the difference vector from the reference magnetic field vector as shown in the right figure of FIG. It becomes clear that the curve becomes the inner curve as the plate thickness increases.

すなわち、差ベクトルを用いることで、板厚の判別ができることがわかった。ただし、0.5Hzから1kHzの間で多くの周波数を走査することは、検査時間が長くなってしまうことが考えられた。   That is, it was found that the thickness can be determined by using the difference vector. However, scanning many frequencies between 0.5 Hz and 1 kHz may have a longer inspection time.

そこで、差ベクトルを用いた磁場スペクトルをさらに解析してみたところ、図4に示すように同じ周波数での各板厚において位相の相関を調べると、位相と板厚に依存性があることがわかった。   Therefore, when the magnetic field spectrum using the difference vector was further analyzed, as shown in FIG. 4, it was found that there was a dependency on the phase and the plate thickness when the correlation between the phases at each plate thickness at the same frequency was examined. It was.

このことから、少なくとも2種類の任意の周波数の交流信号でそれぞれ得られた磁気ベクトルの差である差ベクトルを用いることで、板厚を判別できることがわかった。この差ベクトルは上述した基準磁場ベクトルを使わなくても求めることができ、最低でも2種類の周波数の交流信号による計測で、試験体1−1の板厚の検査ができ、検査時間の大幅な短縮が可能となることを示している。   From this, it was found that the plate thickness can be discriminated by using a difference vector which is a difference between magnetic vectors respectively obtained by AC signals of at least two kinds of arbitrary frequencies. This difference vector can be obtained without using the above-mentioned reference magnetic field vector, and the thickness of the specimen 1-1 can be inspected by measuring with an AC signal of at least two kinds of frequencies, which greatly increases the inspection time. This shows that shortening is possible.

特に、図4から、10mm以上の厚い鋼板の場合では高い周波数の方では10Hz以下の極低周波が必要であるが、10mm以下の薄い鋼板では周波数を上げて20Hzから50Hzの周波数での差ベクトルの方が板厚変化に対して大きな位相変化が得られることが分かった。   In particular, from Fig. 4, in the case of a thick steel plate of 10 mm or more, an extremely low frequency of 10 Hz or less is necessary for a high frequency, but for a thin steel plate of 10 mm or less, the frequency is increased and the difference vector at a frequency of 20 Hz to 50 Hz. It was found that a larger phase change was obtained with respect to the plate thickness change.

このことから、差ベクトルを生成するための2つの磁場ベクトルの選び方も、計測対象において予め設定されている板厚に応じて適宜選択することで、腐食などにより予め設定されている板厚からどのくらい減肉したかを最も感度良く検出することができる。   Therefore, how to select the two magnetic field vectors for generating the difference vector is also appropriately selected according to the thickness set in advance in the measurement object, so that how much from the thickness set in advance due to corrosion or the like. It is possible to detect the thinning with the highest sensitivity.

一方、差ベクトルを生成する際における一方の磁場ベクトルとして周波数が20Hzの磁場ベクトルを用いた場合の位相の板厚依存性を調べたところ、図5に示すように板厚が10mm以上の厚い方では、他方の磁場ベクトルとして周波数が0.5Hzや1Hzの磁場ベクトルが必要であるが、板厚が10mm以下であれば他方の磁場ベクトルとして周波数が5Hzや10Hzの磁場ベクトルの方が変化量である感度が高いことが分かった。したがって、試験体1−1の板厚に応じて、周波数の組み合わせを最適化することにより、最適な感度を得ることが分かった。特に、できるかぎり大きい周波数を利用することで、計測に要する時間を短縮させることもできる。   On the other hand, when the thickness dependence of the phase when a magnetic field vector having a frequency of 20 Hz is used as one magnetic field vector when generating the difference vector, the thicker one having a thickness of 10 mm or more as shown in FIG. However, a magnetic field vector with a frequency of 0.5 Hz or 1 Hz is required as the other magnetic field vector, but if the plate thickness is 10 mm or less, a magnetic field vector with a frequency of 5 Hz or 10 Hz is the amount of change as the other magnetic field vector. It was found that the sensitivity was high. Therefore, it was found that the optimum sensitivity was obtained by optimizing the combination of frequencies according to the plate thickness of the specimen 1-1. In particular, the time required for measurement can be shortened by using as large a frequency as possible.

実際の検査においては、試験体1−1等の対象物にはごみの付着や塗装はがれなどのように、表面に凸凹が生じていて平らでない場合が多い。このため試験体1−1等の対象物と、磁気センサ2−1との間のギャップ(リフトオフ)が変動することが多い。   In actual inspection, the object such as the specimen 1-1 is often uneven due to irregularities on the surface, such as dust adhering or paint peeling. For this reason, the gap (lift-off) between the object such as the specimen 1-1 and the magnetic sensor 2-1 often varies.

図6はリフトオフの変化による信号変化を調べたもので、リフトオフを1mm、2mm、3mm、4mmとして複数の周波数で出力信号を計測した結果である。図6(a)は出力信号の強度の変化を示したグラフであり、周波数が大きくなるにつれ、同じ対象物を計測しても信号強度が大きく変化することが分かる。特に、リフトオフが大きくなると信号強度が小さくなっている。図6(b)は出力信号の位相の変化を示したグラフであり、各周波数においてリフトオフ変化に対して位相は変化しなかった。このことから、差ベクトルの位相を用いることによりリフトオフに影響を受けにくい検査を実現することができる。   FIG. 6 shows the change in signal due to the change in lift-off, and shows the result of measuring output signals at a plurality of frequencies with lift-off being 1 mm, 2 mm, 3 mm, and 4 mm. FIG. 6A is a graph showing the change in the intensity of the output signal, and it can be seen that the signal intensity greatly changes as the frequency increases even if the same object is measured. In particular, the signal strength decreases as the lift-off increases. FIG. 6B is a graph showing a change in the phase of the output signal, and the phase did not change with respect to the lift-off change at each frequency. From this, it is possible to realize an inspection that is hardly affected by lift-off by using the phase of the difference vector.

このように、2つの磁場ベクトルの差である差ベクトルの位相から板厚がわかることを示したが、他の方法として、例えば、1Hz以下で計測した磁場ベクトルを基準磁場ベクトルとして、任意の2つの磁場ベクトルそれぞれに対して基準磁場ベクトルからの位相差を算出し、さらにそれぞれの位相の差を求めても、板厚依存性を得ることができる。しかし、この場合には任意の2つの周波数の磁場ベクトルのほか、1Hz以下の基準磁場ベクトルが必要であるため、3つの周波数測定が最低でも必要となる。   As described above, it has been shown that the plate thickness can be found from the phase of the difference vector, which is the difference between the two magnetic field vectors. However, as another method, for example, a magnetic field vector measured at 1 Hz or less is used as a reference magnetic field vector, and an arbitrary 2 The plate thickness dependency can be obtained by calculating the phase difference from the reference magnetic field vector for each of the two magnetic field vectors, and further obtaining the phase difference. However, in this case, since a reference magnetic field vector of 1 Hz or less is required in addition to magnetic field vectors of arbitrary two frequencies, three frequency measurements are required at a minimum.

上述した実施例では、試験体として特に難しい強磁性体である鋼板の測定例を示したが、アルミニウムや銅など非磁性の金属でも同様に適用ができる。ここで非磁性体では磁気スペクトルは0.5Hzなどの極低周波では信号が非常に弱く、原点からの曲線となるので、1Hz以下の基準磁場ベクトルは必要としない。   In the embodiment described above, an example of measurement of a steel plate which is a particularly difficult ferromagnetic material as a test body has been shown, but nonmagnetic metals such as aluminum and copper can be similarly applied. Here, in the non-magnetic material, the magnetic spectrum has a very weak signal at an extremely low frequency such as 0.5 Hz and becomes a curve from the origin, so a reference magnetic field vector of 1 Hz or less is not required.

他の実施例として、印可コイルで検査対象物に磁場を印可するのではなく、例えば図7に示すように、両端に励磁コイル4−2を設けたヨーク材11で検査対象物に磁場を印可し、検査対象物の表面から漏洩した磁場を検査対象物の表面に設けた磁気センサ2−2で検出する漏洩磁束法の非破壊検査装置とすることもできる。   As another embodiment, the magnetic field is not applied to the inspection object with the application coil, but the magnetic field is applied to the inspection object with the yoke material 11 provided with the exciting coil 4-2 at both ends as shown in FIG. And it can also be set as the nondestructive inspection apparatus of the leakage magnetic flux method which detects the magnetic field leaked from the surface of the test object with the magnetic sensor 2-2 provided in the surface of the test object.

なお、漏洩磁束法では、ヨーク材11と測定対象物1−2の間で磁気回路を形成する必要があるので、測定対象は磁性体に限定される。   In the leakage magnetic flux method, since it is necessary to form a magnetic circuit between the yoke material 11 and the measurement object 1-2, the measurement object is limited to a magnetic material.

励磁コイル4−2は、印加コイル4−1と同様に、複数の周波数を含む信号を周波数発振器5−2等で合成して定電流源3−2に入力することで、励磁コイル4−2に所定の周波数の交流電流を通電している。   Similar to the application coil 4-1, the excitation coil 4-2 synthesizes a signal including a plurality of frequencies by the frequency oscillator 5-2 or the like and inputs the synthesized signal to the constant current source 3-2. Is supplied with an alternating current of a predetermined frequency.

磁気センサ2−2は計測回路7−2に接続しており、計測回路7−2を介して磁気センサ2−2の出力信号を取り出し、2台のロックイン検波器8−3,8−4によって、第1の周波数と第2の周波数での検波を行い、ロックイン検波器8−3,8−4の各出力信号をマルチプレクサ9−2を介して切り替えながら解析器10−2に取り込み、データ収録するとともに解析することとしている。   The magnetic sensor 2-2 is connected to the measuring circuit 7-2, and the output signal of the magnetic sensor 2-2 is taken out via the measuring circuit 7-2, and two lock-in detectors 8-3 and 8-4. To detect at the first frequency and the second frequency, and take the output signals of the lock-in detectors 8-3 and 8-4 to the analyzer 10-2 while switching them through the multiplexer 9-2, The data is recorded and analyzed.

図8は、第1の周波数を5Hzとし、第2の周波数を10Hzとして数発振器5−2で合成して定電流源3−2に入力することで励磁コイル4−2に交流電流を通電した場合の差ベクトルの位相をとって板厚による変化を調べた結果である。図8から明らかなように、位相は板厚依存性を示しており、この曲線から板厚を検査できることが分かる。   In FIG. 8, the first frequency is set to 5 Hz, the second frequency is set to 10 Hz, synthesized by the number oscillator 5-2, and input to the constant current source 3-2, thereby supplying an alternating current to the exciting coil 4-2. This is the result of examining the change due to the plate thickness by taking the phase of the difference vector. As is clear from FIG. 8, the phase shows a plate thickness dependency, and it can be seen from this curve that the plate thickness can be inspected.

このように本発明では、磁場を印加することで誘引される渦電流が作る磁場を磁気センサで検出する非破壊検査装置全般に適用することができる。   As described above, the present invention can be applied to all non-destructive inspection apparatuses that detect a magnetic field generated by an eddy current induced by applying a magnetic field with a magnetic sensor.

本発明は上記の実施形態に限定されるものではなく、本発明の技術的思想を逸脱しない範囲における種々の変形例・設計変更などをその技術的範囲内に包含することは云うまでもない。   The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications, design changes, and the like are included within the technical scope without departing from the technical idea of the present invention.

本発明は、金属性の構造物の腐食などの欠陥検出に広く用いることができ、特に従来困難であった鉄鋼製の構造物、たとえば橋梁やビル、工場プラント、発電設備など幅広い分野での応用ができる。   INDUSTRIAL APPLICABILITY The present invention can be widely used for detecting defects such as corrosion of metallic structures, and is particularly applicable to a wide range of fields such as steel structures, such as bridges, buildings, factory plants, and power generation facilities, which have been difficult in the past. Can do.

1−1 試験体
1−2 試験体
2−1 磁気センサ
2−2 磁気センサ
3 定電流源
4−1 印加コイル
4−2 励磁コイル
5−1 周波数発信器
5−2 周波数発信器
6 キャンセルコイル
7−1 計測回路
7−2 計測回路
8−1 ロックイン検波器
8−2 ロックイン検波器
8−3 ロックイン検波器
8−4 ロックイン検波器
9−1 マルチプレクサ
9−2 マルチプレクサ
10−1 解析器
10−2 解析器
11−1 ヨーク材
1-1 Test body 1-2 Test body 2-1 Magnetic sensor 2-2 Magnetic sensor 3 Constant current source 4-1 Applied coil 4-2 Excitation coil 5-1 Frequency transmitter 5-2 Frequency transmitter 6 Cancel coil 7 -1 Measurement circuit 7-2 Measurement circuit 8-1 Lock-in detector 8-2 Lock-in detector 8-3 Lock-in detector 8-4 Lock-in detector 9-1 Multiplexer 9-2 Multiplexer 10-1 Analyzer 10-2 Analyzer 11-1 Yoke material

Claims (4)

検査対象物に磁場を印加する印加コイルと、
この印加コイルに所定の周波数の交流電流を通電させる交流定電流源と、
前記印可コイルで印加した磁場により前記検査対象物に誘引された磁場を検出する磁気センサと、
この磁気センサの出力信号のうち所定周波数の信号を検波する検波器と、
この検波器の出力信号を解析する解析器と
を有する非破壊検査装置において、
前記交流定電流源は、第1の周波数とした第1の交流電流と、第1の周波数よりも周波数の小さい第2の周波数とした第2の交流電流で前記印加コイルを駆動させ、
前記解析器は、前記検波器で前記第1の周波数で検波して得られた信号の強度と位相とを成分とする第1の磁場ベクトルと、前記検波器で前記第2の周波数で検波して得られた信号の強度と位相とを成分とする第2の磁場ベクトルとのベクトルの差として得られる差ベクトルの位相成分を検出して、この位相成分から前記検査対象物の厚みを検出する非破壊検査装置。
An application coil for applying a magnetic field to the inspection object;
An alternating current source for supplying an alternating current of a predetermined frequency to the application coil;
A magnetic sensor for detecting a magnetic field attracted to the inspection object by a magnetic field applied by the application coil;
A detector for detecting a signal having a predetermined frequency among the output signals of the magnetic sensor;
In a nondestructive inspection apparatus having an analyzer for analyzing the output signal of this detector,
The AC constant current source drives the application coil with a first AC current having a first frequency and a second AC current having a second frequency lower than the first frequency,
The analyzer detects a first magnetic field vector whose components are the intensity and phase of a signal obtained by detection at the first frequency by the detector, and detects at the second frequency by the detector. The phase component of the difference vector obtained as a vector difference between the second magnetic field vector having the signal strength and phase as components is detected, and the thickness of the inspection object is detected from the phase component. Nondestructive inspection equipment.
前記第1の磁場ベクトルと前記第2の磁場ベクトルの位相は、前記第2の周波数より小さい1Hz以下の周波数として得られた磁場ベクトルの位相を基準としている請求項1に記載の非破壊検査装置。   2. The nondestructive inspection apparatus according to claim 1, wherein the phase of the first magnetic field vector and the second magnetic field vector is based on the phase of the magnetic field vector obtained as a frequency of 1 Hz or less smaller than the second frequency. . 前記第1と第2の周波数は可変として、予め設定されている前記検査対象物の厚みに対応させた周波数の組み合わせとする請求項1または請求項2に記載の非破壊検査装置。   The nondestructive inspection apparatus according to claim 1, wherein the first and second frequencies are variable, and a combination of frequencies corresponding to a preset thickness of the inspection object is used. 印加コイルで検査対象物に所定の周波数の交流磁場を印加して、前記検査対象物に誘引した磁場を磁気センサで検出し、この磁気センサの出力信号の所定周波数成分を検波器で検波し、この検波器の出力信号を解析器で解析することで前記検査対象物の厚みを検出する非破壊検査方法において、
前記印加コイルには、第1の周波数とした第1の交流電流と、第1の周波数よりも周波数の小さい第2の周波数とした第2の交流電流とを通電し、
前記解析器では、前記検波器で前記第1の周波数で検波して得られた信号の強度と位相とを成分とする第1の磁場ベクトルと、前記検波器で前記第2の周波数で検波して得られた信号の強度と位相とを成分とする第2の磁場ベクトルとのベクトルの差として得られる差ベクトルの位相成分を検出して、この位相成分から前記検査対象物の厚みを検出する非破壊検査方法。
Applying an alternating magnetic field of a predetermined frequency to the inspection object with the application coil, detecting the magnetic field attracted to the inspection object with a magnetic sensor, detecting a predetermined frequency component of the output signal of this magnetic sensor with a detector, In the nondestructive inspection method for detecting the thickness of the inspection object by analyzing the output signal of this detector with an analyzer,
The application coil is energized with a first alternating current having a first frequency and a second alternating current having a second frequency smaller than the first frequency,
In the analyzer, a first magnetic field vector whose components are the intensity and phase of the signal obtained by the detection at the first frequency by the detector and the second frequency by the detector are detected. The phase component of the difference vector obtained as a vector difference between the second magnetic field vector having the signal strength and phase as components is detected, and the thickness of the inspection object is detected from the phase component. Non-destructive inspection method.
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