JP6015954B2 - Electromagnetic induction type inspection apparatus and electromagnetic induction type inspection method - Google Patents

Description

  The present invention relates to an electromagnetic induction type inspection apparatus and an electromagnetic induction type inspection method for determining a physical property difference or the like of an inspection object using a harmonic component ratio.

  2. Description of the Related Art Conventionally, eddy current inspection using electromagnetic induction is known as a nondestructive inspection apparatus that performs inspection without destroying an inspection object. In eddy current flaw inspection, an eddy current is induced in a test object having conductivity and a change in the eddy current is detected to detect cracks in the test object and to detect differences in shape, material, dimensions, etc. It performs detection and the like. However, eddy current flaw inspection has the problem that eddy current does not penetrate to the deep part of the inspection object due to the skin effect effect of current and magnetic flux, and it is difficult to obtain information on the deep part. There is also a problem that the surface state of the object and the distance between the inspection object and the inspection sensor (lift-off) greatly affect the detection sensitivity.

  Therefore, as an electromagnetic induction type inspection device using electromagnetic induction, a pair of alternating magnetic fields having the same magnetic field lines are formed by alternating current, and a conductive object to be inspected (inspection object) in one of the pair of alternating magnetic fields. There is one in which inspection is performed by arranging (see Patent Document 1). In the electromagnetic induction type inspection apparatus of Patent Document 1, an electrical signal indicating the amount of change in induced current caused by electromagnetic induction is measured between a pair of alternating magnetic fields, and an electrical signal indicating electrical permeability and electrical resistivity are indicated from the electrical signal. An inspection is performed by obtaining information by detecting an electrical signal and combining these two electrical signals.

The electromagnetic induction type inspection apparatus disclosed in Patent Document 1 detects and synthesizes magnetic permeability and electrical resistivity, so that only the surface is obtained based on signal waveform information including magnetic characteristics and electrical characteristics of the object to be inspected. Not only that, it is said that the inside can be accurately and highly accurately inspected.
Specifically, the technique described in Patent Document 1 uses the phase and amplitude of an electric signal obtained by measurement as an electric signal indicating permeability and electric resistivity, and these electric signals and standard samples (normal samples) Judgment is made by comparing with the inspection result of the inspection object).

JP-A-8-54375

  However, as in Patent Document 1, reproducibility is required in order to accurately perform inspection by comparing the object to be inspected with a standard sample from the phase and amplitude of the electric signal, and particularly in terms of electrically reproducing the signal value. In order to ensure the reproducibility, the stability of the excitation current, that is, the alternating magnetic field is required. Therefore, for example, it is necessary to stabilize the magnetic field by making the excitation current constant or detecting the induced current from an alternating magnetic field and performing feedback control. In addition, since the detection result changes depending on the inspection position and orientation of the inspection object, accuracy and reproducibility are required for the inspection position and arrangement orientation of the inspection object.

  In addition, as defined in Patent Document 1, the phase and amplitude of an electric signal is defined as an electric signal indicating magnetic permeability and electric resistivity, so that an adjustment means adapted to the definition is defined by defining the detected electric signal. It becomes important. Similarly, it is necessary to devise to extract a signal that conforms to the definition of the coil configuration. In addition to the positional relationship, various factors such as the surface condition, physical size, and movement speed of the inspection object are measured and reproduced between the sensor unit that detects the alternating magnetic field and the inspection object. Will affect sex.

  The present invention has been made to solve such a problem, and the object of the present invention is to provide a more accurate inspection object without requiring high magnetic and positional reproducibility as described above. It is an object of the present invention to provide an electromagnetic induction type inspection apparatus and an electromagnetic induction type inspection method capable of performing the above inspection.

(Invention of the device)
An electromagnetic induction type inspection apparatus for inspecting an inspection object by arranging a conductive inspection object in an alternating magnetic field and detecting a change in the alternating magnetic field due to electromagnetic induction, and generating the alternating magnetic field A coil, a detection coil for detecting an alternating magnetic field changed by the inspection object, an analysis means for decomposing a waveform of an electric signal detected by the detection coil into a fundamental wave and a plurality of harmonic components, and the analysis means The calculation means for calculating the amplitude ratio between the amplitude of the fundamental wave decomposed by the above and the amplitude of each harmonic component, the amplitude ratio calculated by the calculation means, and the inspection object stored in advance And determining means for determining the inspection object by comparing the amplitude ratio between the amplitude of the fundamental wave of the reference object serving as a reference and each of the harmonic components.

  The calculation means selects the harmonic components up to the nth order necessary for the inspection from the fundamental wave and each harmonic component decomposed by the analysis means, and selects the amplitude of each selected fundamental wave and each harmonic. Each amplitude ratio with each amplitude of the component is calculated, and the determination unit calculates the amplitude ratio calculated by the calculation unit, the amplitude of the fundamental wave of the reference object stored in advance, and each harmonic component. The inspection object is determined by comparing each amplitude ratio with each amplitude.

  The determination means sets a predetermined evaluation range for each amplitude ratio of the reference object, and whether the amplitude ratio calculated by the calculation means is within the evaluation range of the amplitude ratio of the corresponding reference object. The inspection object is determined by comparing whether or not.

(Invention of method)
Moreover, the electromagnetic induction type inspection method according to the present invention is an electromagnetic induction type in which an inspection object is inspected by arranging a conductive inspection object in an alternating magnetic field and detecting a change in the alternating magnetic field due to electromagnetic induction. An inspection method comprising: an alternating magnetic field generating step for generating the alternating magnetic field by an exciting coil; an alternating magnetic field detecting step for detecting an alternating magnetic field changed through the inspection object by a detection coil; and the detection coil detecting the alternating magnetic field. An analysis step for decomposing the waveform of the electrical signal into a fundamental wave and a plurality of harmonic components; a calculation step for calculating an amplitude ratio between the amplitude of the decomposed fundamental wave and each of the harmonic components; The amplitude ratio calculated in the calculation step, and the amplitude ratio between the amplitude of the fundamental wave of the reference object serving as the reference of the inspection object stored in advance and the amplitude of each harmonic component, It is characterized by having, a determining step of determining the inspection object compared.

  In the calculation step, out of the fundamental wave and each harmonic component decomposed in the analysis step, harmonic components up to the nth order necessary for the inspection are selected, and the amplitude and each harmonic of the selected fundamental wave are selected. An amplitude ratio with each amplitude of the wave component is calculated, and in the determination step, each amplitude ratio calculated in the calculation step, the amplitude of the fundamental wave of the reference object stored in advance, and each harmonic component The inspection object is determined by comparing the amplitude ratios with the respective amplitudes.

  The calculation of the amplitude ratio between the amplitude of the fundamental wave and each of the harmonic components is as follows: (amplitude value of the fundamental wave): (amplitude value of the second harmonic wave), (amplitude value of the fundamental wave): (third (Amplitude value of harmonic),... (Amplitude value of fundamental wave): (Amplitude value of nth harmonic), and the method of calculating the amplitude ratio is fundamental wave amplitude value / nth harmonic. Either the amplitude value or the nth harmonic amplitude value ÷ fundamental wave amplitude value is adapted, but it is preferable that the nth harmonic amplitude value ÷ fundamental wave amplitude value be the basis. Further, it is preferable that the maximum value of “n” (n is an integer of 2 or more) of the nth harmonic is adapted to the purpose of the system at that time.

  In the determination step, a predetermined evaluation range is set for each amplitude ratio of the reference object, and each amplitude ratio calculated in the calculation step is within an evaluation range of each amplitude ratio of the corresponding reference object. The inspection object is determined by comparing whether or not it exists.

  According to the present invention using the above means, an alternating magnetic field is generated by an excitation coil, an alternating magnetic field changed through an inspection object is detected by a detection coil, and an alternating current signal indicating the alternating magnetic field is converted into a fundamental wave and a plurality of harmonics. By breaking down into wave components, the waveform is quantified separately for each fundamental wave component and harmonic component, including distortion of the waveform of the AC signal. Then, necessary harmonic components particularly related to the evaluation / determination of the inspection are selected, the amplitude ratio between the fundamental wave and each selected harmonic component is calculated, and becomes the reference of the inspection object stored in advance. The inspection object is evaluated and judged by comparing the amplitude ratio.

  The AC signal detected by the detection coil is distorted in the waveform by the inspection object. By disassembling the fundamental wave and each harmonic component, including this distortion component, and using the amplitude ratio between the fundamental wave and each harmonic component, magnetic field strength spots, detection sensitivity spots, It is possible to reduce the influence on the reproducibility such as a change in sensitivity due to a change in the amplification degree of the amplifier and a similar analog system over time. Thereby, the accuracy of the inspection can be easily stabilized.

1 is an overall configuration diagram of an electromagnetic induction inspection apparatus according to an embodiment of the present invention. 2A is a front view showing a shape example of a sensor according to an embodiment of the present invention, FIG. 2B is a cross-sectional view taken along line AA in FIG. 2A, and FIG. It is a front view which shows another example of a shape of a sensor. FIG. 3A shows an alternating current waveform fa to the exciting coil, FIG. 3B shows an induced current waveform f in the detection coil, and FIG. 3C shows an induced current waveform as related waveforms according to an embodiment of the present invention. The detection signal waveform f is shown as a waveform decomposed into a fundamental wave f1, a second harmonic f2, and a third harmonic f3 among the frequency components. It is explanatory drawing which shows the amplitude of each harmonic component which has a frequency component of the fundamental wave of the signal wave and the fundamental wave n times (here, the case where n is set to 2 and 3 is illustrated).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the overall configuration of an electromagnetic induction inspection apparatus according to an embodiment of the present invention. As shown in FIG. 1, the electromagnetic induction type inspection apparatus 1 is roughly composed of a detection unit 10, a calculation / analysis unit 20 (calculation unit, analysis unit), and a control unit 30 (determination unit).

The detection unit 10 is a part that electrically detects the electrical and magnetic characteristics of the inspection target T by electromagnetic induction, and specifically includes an oscillator 11, a sensor 12, and an amplifier 13.
The sensor 12 includes an excitation coil 12a and a detection coil 12b. The exciting coil 12a receives an alternating current and is excited to generate an alternating magnetic field, and the detection coil 12b disposed in the alternating magnetic field generates an induced current and an induced electromotive force due to electromagnetic induction accompanying excitation of the exciting coil 12a. Detection is performed with The detection coil 12b detects an alternating magnetic field that changes via the inspection target T when the inspection target T exists in the alternating magnetic field.

The shape of the sensor 12 is set according to the inspection object T. For example, referring to FIG. 2, FIG. 2 (a) is a front view showing an example of a sensor shape, FIG. 2 (b) is a cross-sectional view taken along line AA of FIG. 2 (a), and FIG. The front view which shows another example of a sensor shape is shown, respectively.
When the inspection target T is rod-shaped, it is preferable to use a cylindrical sensor 12 as shown in FIGS. 2 (a) and 2 (b). In the sensor 12 of FIGS. 2A and 2B, an exciting coil 12a is wound along the outer peripheral surface of a cylindrical core (for example, yoke) 12c having a very small magnetic resistance, and the inner periphery of the core 12c. A detection coil 12b is wound along the surface. Thus, the sensor 12 having a cylindrical shape as a whole inserts the inspection object T into the inner hole portion, generates an alternating magnetic field by the excitation coil 12a, and detects an induced current or the like by the detection coil 12b.

  The shape of the sensor 12 is not limited to this, and a sensor that matches the shape of the inspection object T or the like is used. For example, if the inspection target T is plate-shaped, it is preferable to use a square cylindrical sensor 12 'as shown in FIG. Also about a core part, it is not restricted to a yoke, For example, a ferrite core, silicon steel, etc. may be sufficient. The shape of the core portion is not limited to the cylindrical shape, and may be a rod-shaped core. In particular, an air core coil without a core portion or a core portion having only a casing function for forming the coil may be provided to form a magnetic air core state. In addition, it is important that the relationship between the excitation coil and the detection coil be matched each time without specifying the inner side and the outer side.

The oscillator 11 connected to the exciting coil 12a supplies an alternating current to the exciting coil 12a. The AC current is, for example, a sine wave current, and the frequency and amplitude of the sine wave current are determined according to the characteristics, shape, and inspection purpose of the inspection target T.
The amplifier 13 connected to the detection coil 12b amplifies a detection signal indicating an induced current generated in the detection coil 12b to a level necessary for processing in the calculation / analysis unit 20 described later. When the detection signal is attenuated, an attenuator may be provided instead of the amplifier 13. It is essential that signal similarity be maintained between the input and output of the amplifier 13.

  The calculation / analysis unit 20 is a part that performs conversion, decomposition processing, and the like of the detection signal detected by the detection unit 10, and includes an A / D (analog / digital) converter 21, a storage unit 22, and a signal processing unit 23. ing. It is one method to use an oscilloscope or the like as a means for determining the detected waveform signal.

The A / D converter 21 connected to the amplifier 13 converts (quantizes) data input as an analog AC signal from the amplifier 13 into digital data. As the A / D converter 21, for example, a successive approximation type high-speed A / D converter is used.
A storage unit 22 connected to the A / D converter 21 temporarily stores the digital data converted by the A / D converter 21. The storage unit 22 is also used as a storage unit of other units (a signal processing unit 23, a determination unit 31, a setting unit 33, and the like described later).

  The signal processing unit 23 connected to the storage unit 22 performs arithmetic processing on the digital data stored in the storage unit 22. Specifically, the signal processing unit 23 performs FFT (Fast Fourier Transform) processing (processing for the purpose of Fourier series expansion) to decompose the input digital data into a fundamental wave and a plurality of harmonic components. The purpose of using FFT processing is to perform high-speed decomposition of harmonic components.

  Subsequently, the control unit 30 determines and evaluates the inspection target T based on the fundamental wave and each harmonic component decomposed in the calculation / analysis unit 20, and the various devices according to the obtained results and setting operations. This is a part for performing setting and the like, and includes a determination unit 31, a display unit 32, a setting unit 33, an operation unit 34, a power supply unit 35, and an input / output unit 36. Specifically, it is more efficient to use a personal computer for the control unit 30 in terms of enhancement of hardware mechanisms and software and cost performance.

  The determination unit 31 connected to the signal processing unit 23 selects a harmonic component necessary for the inspection among the fundamental wave and the plurality of harmonic components decomposed in the signal processing unit 23, and selects each selected harmonic. An amplitude ratio between the amplitude of the wave component and the amplitude of the fundamental wave is calculated. The determination unit 31 performs in advance the same measurement / inspection on a sample body that can be the same type of reference object as the inspection object T, and various data in the reference object are stored as master data. This master data also includes each amplitude ratio between the fundamental wave and each harmonic component in the reference object, and the determination unit 31 determines each amplitude ratio of the master data and each amplitude ratio corresponding to the inspection target T detected this time. And the difference between the reference object and the inspection object T is determined. In this determination, for example, a predetermined evaluation range is set for each amplitude ratio of the reference object, and whether each amplitude ratio of the inspection target T is within the evaluation range of each amplitude ratio of the corresponding reference object is determined. This is done by comparing.

The display unit 32 connected to the determination unit 31 displays the waveforms and amplitude ratios of the fundamental wave and the plurality of harmonic components in the inspection target T input to the determination unit 31, master data of the reference object, determination results, and the like. To display.
In addition, the setting unit 33 connected to the determination unit 31 receives the determination result in the determination unit 31 and the like between the oscillator 11, the amplifier 13, the A / D converter 21, the storage unit 22, the signal processing unit 23, and the like. Etc. are controlled. The setting unit 33 adjusts to a more suitable condition when the inspection target T is inspected again, or sets the next inspection condition when performing the stepwise inspection.

The setting unit 33 is also connected to the operation unit 34, and various operation parameters for measurement and control can be set and changed according to the operation of the operation unit 34. And the setting part 33 controls the oscillator 11 and each part according to the set conditions. Furthermore, the power supply unit 35 supplies power to various devices.
The input / output unit 36 connected to the determination unit 31 and the setting unit 33 exchanges signals with external devices. This signal includes a determination result output, an external state signal input, and the like.

Hereinafter, an inspection method using the electromagnetic induction inspection apparatus 1 configured as described above will be described.
The inspection object T is mainly composed of iron or non-ferrous metal having conductivity, and is disposed in the sensor 12. It is preferable to arrange the inspection object T at a position where the value of the induced current (detection signal) detected by the detection coil 12b is most remarkable, for example, as shown in FIGS. 2 (a) and 2 (b). In the case of such a cylindrical sensor 12, it is preferable to arrange the inspection object T at the center position of the inner hole. Alternatively, the inspection target T and the sensor 12 may be continuously inspected while relatively moving the positional relationship between them. In such a case, a technique that uses the data at the maximum amplitude of the detection signal as the inspection value of the inspection object is a good measure.

  After the inspection object T is installed, the oscillator 11 supplies a sinusoidal AC current (AC signal) fa as shown in FIG. 3A to the exciting coil 12a to generate an AC magnetic field (AC magnetic field generation step). . The detection coil 12b in the alternating magnetic field generates an induced current or the like by electromagnetic induction, but is distorted as shown in FIG. 3B due to the influence of the inspection object T in the alternating magnetic field. Is detected (AC magnetic field detection step). Then, the amplifier 13 amplifies the signal waveform detected by the detection coil 12b, the A / D converter 21 converts (quantizes) the analog waveform into digital data, and stores the digital data in the storage unit 22 as the digital data.

  Next, the signal processing unit 23 decomposes the digital data indicating the waveform f stored in the storage unit 22 into a fundamental wave and each harmonic component by FFT processing (analysis step). For example, in this embodiment, the waveform f in FIG. 3B has three fundamental wave components f1, second harmonic component f2, and third harmonic component f3 where f = f1 + f2 + f3 as shown in FIG. 3C. It means that it is the same as the composite wave of the component decomposed. FIG. 4 is a conceptual diagram in which the fundamental wave f1, the second harmonic f2, and the third harmonic f3 with respect to the detection signal wave f are separately described on the frequency axis.

  Subsequently, the determination unit 31 calculates an amplitude ratio between the amplitudes A1 to A3 of f1 to f3 for each frequency component (calculation step). For example, using the amplitude A1 of the fundamental wave component f1 as a reference, the amplitude ratios of the fundamental wave f1, the second harmonic component f2, and the third harmonic component f3 are calculated as A1: A2 and A1: A3, respectively. The determination unit 31 corresponds to the calculated amplitude ratios in advance as ratios (amplitude ratios) Am1: Am2, Am1 of the fundamental wave of the reference object and the amplitudes Am1 to Am3 of the harmonic components fm1 to fm3 as master data. : Am3 is stored, and the amplitude ratios Am1: Am2, Am1: Am3 in the reference object are compared with the amplitude ratios A1: A2, A1: A3 of the inspection object T, respectively, and a determination is made (determination step). . Here, the determination unit 31 sets a predetermined evaluation range for each amplitude ratio in the reference object, and whether each amplitude ratio of the inspection target T is within the evaluation range of each amplitude ratio of the corresponding reference object. Compare whether or not. As a result of the comparison, the determination unit 31 determines whether the amplitude ratio of the two is the same or within a predetermined evaluation range, and outputs the determination result to the display unit 32 and the input / output unit 36.

The display unit 32 displays the signal from the determination unit 31 while including other information in a necessary and clear expression method.
The input / output unit 36 mainly outputs the quality of the determination result to the external device based on the signal from the determination unit 31. In the present embodiment, the decomposed fundamental wave and the harmonic components f1 to f3 are selected, but it is preferable to select the fundamental wave and the harmonic components necessary for the inspection.

  The evaluation based on the amplitude ratio is different from the absolute evaluation of the voltage value of the electric signal, and the ratio between the fundamental wave and each harmonic is the same regardless of the magnitude of the voltage value if the waveform is similar. This is the waveform evaluation method. This reduces the necessity of depending on the magnitude of the voltage value, that is, the reproducibility at the time of measurement.

  The setting unit 33 receives the determination result information from the determination unit 31 or the operation information from the operation unit 34, and adjusts each component unit or the like to a more suitable condition in order to perform an inspection suitable for the inspection target T again. In the case of performing stepwise inspection, the following inspection conditions are set. For example, since the permeability of the magnetic flux with respect to the induced current of the inspection target T is determined by the skin effect depending on the frequency, when the penetration is changed and the inspection corresponding to the depth is intended, Set the frequency and amplitude values as needed, or set the necessary values even when changing the frequency step by step, perform control corresponding to them, and the signals under that control The amplitude ratio of the fundamental wave and each harmonic can be obtained, and the necessary oscillator control is performed. In addition to this, the setting unit 33 includes the amplification degree of the signal in the amplifier 13, the accuracy and timing of the conversion by the A / D converter 21, the timing of the waveform analysis processing in the signal processing unit 23, and the determination information to the determination unit 31. Control transmission and judgment timing.

  Specifically, the electromagnetic induction type inspection apparatus 1 according to the present embodiment as described above is used for identification of the material of the inspection object T, identification of quenching and determination of damage, surface and internal flaw detection, and other quality control. It is possible to adapt. That is, it is preferable that the inspection target T is one in which iron loss (for example, hysteresis loss, eddy current loss) clearly occurs, or one that can magnetically measure the magnetic permeability. For example, it is applicable to the determination of the depth of quenching layer in induction hardening of industrial products, the presence or absence of quenching, and the amount of powder in compression sintered products, powder sintered alloys, etc. of powder like philite It can also be applied to quality control during the process, such as chipping after compression, quenching after sintering, and chipping. Furthermore, the present invention can be applied to a processed surface, internal flaw detection, and the like.

  Thus, in the electromagnetic induction type inspection apparatus 1 according to the present embodiment, an alternating magnetic field is generated by the excitation coil 12a, an alternating magnetic field that is changed via the inspection target T is detected by the detection coil 12b, and the alternating magnetic field is shown. By breaking the AC signal waveform f into a fundamental wave and a plurality of harmonic components f1 to f3, the distortion of the waveform of the AC signal is separately quantified for each fundamental wave and harmonic component. Then, ratios A1: A2 and A1: A3 between the amplitudes A1 to A3 of the fundamental wave and the harmonic components f1 to f3 are calculated, and the fundamental wave of the signal wave serving as a reference for the inspection object stored in advance. And the ratios Am1: Am2 and Am1: Am3 between the respective amplitudes Am1 to Am3 of the respective harmonic components are respectively compared to determine the inspection target T. It should be noted that it is only necessary to determine how many of the n-order components of the harmonics (third-order components in the present embodiment) are handled according to the purpose of the system.

  Unlike the one that evaluates the absolute value of the voltage value of an electric signal, the ratio of each amplitude is always the same if the waveform is similar, so in this embodiment, the distortion of the waveform is the fundamental and harmonic components. The waveform distortion is evaluated by comparing the amplitude ratio between the fundamental wave and each harmonic component and making a determination. This greatly contributes to uniformity in coil manufacturing and reproducibility of inspection, that is, it is possible to reduce magnetic flux spots and detection sensitivity spots due to coil winding spots.

  In addition, physical roughness occurs in the winding process of the coil, which is one factor that hinders the strength and uniformity of the generated magnetic field. Furthermore, the magnetic flux in the coil is dense at the center, diffused and rough at the end, and is greatly different between the center and the end face, so the magnetic flux density in the coil is not uniform and uniform, Depending on the arrangement position of the inspection object, the detection sensitivity changes, that is, the absolute value of the voltage varies. On the other hand, by evaluating the waveform distortion as in the present embodiment, the importance of the reproducibility of the detection sensitivity is reduced as compared with the evaluation of the voltage value. For example, it is not necessary to make the AC magnetic field extremely uniform. This eliminates the need for a constant excitation current for generating an alternating magnetic field or a feedback control method for quantifying the magnetic field by detecting the induced current from the alternating magnetic field, thus reducing the burden on the electric control circuit side. It becomes.

  Further, the waveform of the AC signal detected by the detection coil 12b usually has some distortion regardless of the presence or absence of the inspection object. Therefore, the waveform distortion when the inspection object is not arranged is the distortion inherent to the system of the electromagnetic induction inspection apparatus 1, and the inherent distortion value of the system is determined by measuring the component in advance. And, when the inspection object is placed, it is possible to improve the inspection accuracy by selecting only the signal component necessary for inspection by removing the inherent distortion value from the signal decomposed into the fundamental wave and the harmonic component It becomes. From the above, by comparing the amplitude ratio between the fundamental wave and the harmonic component and the amplitude ratio between the fundamental wave and the harmonic component of the reference object, it becomes possible to perform a more accurate inspection with higher accuracy.

  Although the description about the electromagnetic induction type inspection apparatus and the electromagnetic induction type inspection method according to the present invention has been completed above, the embodiment is not limited to the above configuration. The configuration of the electromagnetic induction type inspection apparatus 1 shown in FIG. 1 is merely an example, and the positional relationship between the parts may be changed or the functions may be combined. For example, the storage unit 22 and the signal processing unit 23 of the calculation / analysis unit 20 may be interchanged, or the storage unit 22 may be incorporated in the setting unit 33.

  Furthermore, in the above-described embodiment, the input AC signal is decomposed into a fundamental wave and a harmonic component by FFT processing in the signal processing unit. However, the Fourier series expansion method is not limited to FFT processing, and the fundamental wave. As long as an equivalent or more efficient technique that can be quantified into the harmonic components based thereon is applicable, they may be used.

  In the above embodiment, the signal processing unit 23 decomposes the second harmonic component f2 and the third harmonic component f3 as the harmonic components of the waveform f of the induced current and selects them. The number of harmonic components to be decomposed and selected is not limited to this. The signal processing unit may select harmonic components up to the nth order necessary for the inspection from the decomposed fundamental wave and each harmonic component.

  In the above embodiment, the amplitude ratios A1: A2 and A1: A3 with the other harmonic components f2, f3 are calculated based on the amplitude A1 of the fundamental wave component f1. That is, the amplitude ratio between the fundamental wave and each harmonic component is adopted, but the amplitude ratio between each frequency component (fundamental wave, second harmonic, third harmonic,... Nth harmonic) is used. If this is the case, it can be regarded as isomorphic or homogeneous.

DESCRIPTION OF SYMBOLS 1 Electromagnetic induction type inspection apparatus 10 Detection part 20 Calculation / analysis part (calculation means, analysis means)
30 Control unit (determination means)
DESCRIPTION OF SYMBOLS 11 Oscillator 12 Sensor 12a Excitation coil 12b Detection coil 13 Amplifier 21 A / D converter 22 Memory | storage part 23 Signal processing part 31 Determination part 32 Display part 33 Setting part 34 Operation part 35 Power supply part 36 Input / output part

Claims (6)

An electromagnetic induction inspection apparatus that inspects the inspection object by arranging a conductive inspection object in an alternating magnetic field and detecting a change in the alternating magnetic field due to electromagnetic induction,
An exciting coil for generating the alternating magnetic field;
A detection coil for detecting an alternating magnetic field changed by the inspection object;
Analyzing means for decomposing the waveform of the electrical signal detected by the detection coil into a fundamental wave and a plurality of harmonic components;
Calculating means for calculating an amplitude ratio between the amplitude of the fundamental wave decomposed by the analyzing means and the amplitude of each harmonic component;
The plurality of amplitude ratios calculated by the calculation means, the amplitude of the fundamental wave of the reference object serving as the reference of the inspection object stored in advance, and the amplitude of each harmonic component corresponding to each harmonic component A determination means for determining the inspection object by evaluating a waveform distortion by comparing each of the plurality of amplitude ratios with each other . The calculation means selects the harmonic components up to the nth order necessary for the inspection from the fundamental wave and each harmonic component decomposed by the analysis means, and selects the amplitude of each selected fundamental wave and each harmonic. Calculate each amplitude ratio with each component amplitude,
The determination means compares each amplitude ratio calculated by the calculation means with each amplitude ratio between the amplitude of the fundamental wave of the reference object and the amplitude of each harmonic component stored in advance. The electromagnetic induction inspection apparatus according to claim 1 , wherein an inspection object is determined. The determination means sets a predetermined evaluation range for each amplitude ratio of the reference object, and whether the amplitude ratio calculated by the calculation means is within the evaluation range of the amplitude ratio of the corresponding reference object. by comparing whether the electromagnetic induction type inspection device as claimed in claim 1 or 2, characterized in that a determination of the inspection object. An electromagnetic induction inspection method for inspecting an inspection object by arranging a conductive inspection object in an alternating magnetic field and detecting a change in the alternating magnetic field due to electromagnetic induction,
An alternating magnetic field generating step for generating the alternating magnetic field by an exciting coil;
An alternating magnetic field detection step of detecting an alternating magnetic field changed through the inspection object by a detection coil;
An analysis step of decomposing the waveform of the electrical signal detected by the detection coil into a fundamental wave and a plurality of harmonic components;
A calculation step of calculating an amplitude ratio between the amplitude of the decomposed fundamental wave and the amplitude of each harmonic component;
The plurality of amplitude ratios calculated in the calculation step, the amplitude of the fundamental wave of the reference object serving as the reference of the inspection object stored in advance, and each harmonic component corresponding to each harmonic component A determination step of determining the inspection object by evaluating distortion of the waveform by comparing each of a plurality of amplitude ratios with amplitude;
An electromagnetic induction inspection method characterized by comprising: In the calculation step, out of the fundamental wave and each harmonic component decomposed in the analysis step, harmonic components up to the nth order necessary for the inspection are selected, and the amplitude and each harmonic of the selected fundamental wave are selected. Calculate the amplitude ratio of each wave component to the amplitude,
In the determination step, the amplitude ratio calculated in the calculation step is compared with the amplitude ratio between the amplitude of the fundamental wave of the reference object stored in advance and the amplitude of each harmonic component. The electromagnetic induction inspection method according to claim 4 , wherein the inspection object is determined. In the determination step, a predetermined evaluation range is set for each amplitude ratio of the reference object, and each amplitude ratio calculated in the calculation step is within an evaluation range of each amplitude ratio of the corresponding reference object. by comparing whether the electromagnetic induction type inspection method according to claim 4 or 5, characterized in that the determination of the test object.

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