JP2019128161A - Analysis method, analysis program, and analysis apparatus - Google Patents

Abstract

To provide an analysis method capable of analyzing characteristics of an analysis object simply, at high speed and accurately.SOLUTION: The analysis method of the present invention applies an AC electric signal having a predetermined frequency to a first coil to excite an analysis object, generates an eddy current in the analysis object, obtains using a magnetic field generated by the eddy current, a first electrical state quantity corresponding to an amplitude of voltage generated in the second coil and a second electrical state quantity corresponding to a phase difference between the AC electrical signal and the voltage, and analyzes, based on the first electrical state quantity and the second electrical state quantity, characteristics in a thickness direction of the analysis object.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an analysis method, an analysis program, and an analysis apparatus.

  In recent years, research has been conducted on methods for diagnosing aging of various structures such as bridges, roads, buildings, and industrial facilities. Monitoring aging deterioration is important for grasping safety and durability. For example, as a mode of deterioration that occurs in a bridge, there is physical damage such as a crack or a scratch, local corrosion caused by rainwater stagnation, salt adhesion, or the like, and reduction in plate thickness due to the progress of corrosion. In particular, since deterioration due to corrosion greatly affects the safety and durability of the structure, it is important to detect the corrosion state of the structure.

  As a method for analyzing the corrosion state of the structure, an ultrasonic test method is known. However, in this ultrasonic test method, prior to the test, it is necessary to remove the corrosion products such as the rust layer and the like, to remove the deposit, to apply the penetrating material, and to perform the post-treatment. Moreover, it is necessary to make a test apparatus contact a measuring object and to measure. Furthermore, there is a problem that the measurement can not be performed when a measurement target is present at a location subject to space constraints, for example, a location where workers such as high places and closed places are difficult to approach.

  As another method for analyzing the corrosion state of a structure, the present inventor has disclosed a method using the characteristics of the detection voltage in an eddy current test (see Patent Document 1). In this method, the excitation frequency suitable for the distance between the structure and the test device (lift-off) and the thickness of the healthy part (plate thickness) of the structure is selected, and the current of the excitation frequency is input. In the eddy current test, liftoff and thickness are estimated based on the detected voltage. Since analysis by this method can be performed on a structure without contact, no surface treatment involved in the analysis is necessary, and since it can be performed using a small probe, it is possible to spatially analyze the structure. There are few restrictions.

Japanese Patent Application No. 2016-156441

  In the case of estimation based on the detected voltage, the liftoff near the surface of the structure can be measured by a high frequency current of about 100 Hz, but the high frequency current is hard to be transmitted to the inside of the thick structure. Therefore, it is necessary to measure the thickness of the structure with a low frequency current of about 10 Hz. However, the low-frequency current has a smaller propagation speed than the high-frequency current, and it takes a long time to measure in one thickness direction. Therefore, in the analysis method of Patent Document 1, it is difficult to measure the plate thickness at a plurality of locations of the structure, and it is difficult to improve the measurement accuracy.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an analysis method, an analysis program, and an analysis apparatus capable of analyzing characteristics of an analysis target simply, at high speed, and accurately.

  The present invention provides the following means in order to solve the above problems.

(1) The analysis method according to an aspect of the present invention applies an alternating current electrical signal of a predetermined frequency to the first coil to excite an analysis target, generates an eddy current in the analysis target, and generates the eddy current. The first electric state quantity according to the amplitude of the voltage generated in the second coil and the second electric state quantity according to the phase difference between the AC electric signal and the voltage are determined by the generated magnetic field, Based on the electrical state quantity and the second electrical state quantity, characteristics in the thickness direction of the analysis target are analyzed.

(2) In the analysis method according to (1), the characteristics in the thickness direction of the analysis target are compared by comparing the first electric state quantity and the second electric state quantity with reference data. It may be analyzed.

(3) In the analysis method described in the above (1) or (2), the liftoff of the analysis object is measured based on the first amount of electrical condition, and the liftoff is analyzed based on the second amount of electrical condition. The plate thickness of the analysis target may be measured.

(4) In the analysis method according to the above (1) or (2), the frequency of the alternating current electrical signal applied to the first coil is continuously changed, and the magnetic field generated by the eddy current in the analysis target A time-series electrical state quantity corresponding to the voltage generated in the second coil may be measured.

(5) In the analysis method according to (4), the relationship between the wavelet coefficient obtained by wavelet transforming the time-series electric state amount and the frequency is determined, and the rate of change of the wavelet coefficient with respect to the frequency The predetermined frequency may be determined based on

(6) In the analysis method described in the above (4) or (5), the structure in the thickness direction of the analysis target may be scanned based on the time-series electric state quantity.

(7) An analysis program according to an aspect of the present invention is an analysis program that causes a computer to analyze characteristics in the thickness direction of the analysis target, and applies an alternating current electrical signal of a predetermined frequency to the first coil An analysis target is excited to generate an eddy current in the analysis target, a voltage is generated in the second coil by a magnetic field generated by the eddy current, and a first electric state quantity measured based on an amplitude of the voltage And a second electrical state quantity measured based on a phase difference between the AC electrical signal and the voltage.

(8) The analysis device according to one aspect of the present invention generates a voltage according to the first coil that generates a magnetic field applied to an analysis target when an alternating current flows, and the eddy current generated in the analysis target. A coil, a power supply unit applying an alternating current electrical signal of a predetermined frequency to the first coil, a control unit controlling a frequency of the alternating current electrical signal generated by the power supply unit, and a second coil detecting Analyzing the characteristics in the thickness direction of the object to be analyzed based on the first electric state quantity based on the amplitude of the voltage, and the second electric state quantity based on the phase difference between the voltage and the AC electric signal And a unit.

  According to one embodiment of the present invention, characteristics of an analysis target can be analyzed simply, at high speed and accurately.

It is a functional block diagram of an analysis device concerning one embodiment of the present invention. It is a flowchart which shows the flow of the process in the analysis method which concerns on one Embodiment of this invention. (A)-(d) It is a graph which shows the relationship between plate | board thickness and phase difference obtained in the analysis method which concerns on one Embodiment of this invention. (A) It is a graph which shows the relationship between the frequency and the lift-off signal intensity | strength obtained in the analysis method which concerns on one Embodiment of this invention. (B) It is a graph which shows the relationship of a frequency, plate | board thickness and a lift-off signal intensity ratio obtained in the analysis method which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the lift-off and detection voltage obtained in the analysis method which concerns on one Embodiment of this invention. It is a graph which shows the relationship between plate | board thickness and phase difference obtained in the analysis method which concerns on one Embodiment of this invention. (A) It is a graph which shows the relationship between the frequency and lift-off signal strength obtained in Example 1 of this invention. (B) It is a graph which shows the relationship between the frequency obtained by Example 1 of this invention, and plate | board thickness and a lift-off signal strength ratio. It is a graph which shows the relationship between lift-off and detection voltage obtained in Example 1 of this invention. It is a graph which shows the relationship between board thickness and phase difference obtained in Example 1 of this invention. (A) It is a graph which shows the position on the structure obtained in Example 1 of this invention, and Comparative Examples 1 and 2, and the relationship of lift-off. (B) It is a graph which shows the relationship between the position on a structure obtained in Example 1 of this invention, and Comparative Examples 1 and 2, and plate | board thickness.

  Hereinafter, the present invention will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show enlarged features for convenience for the purpose of making the features of the present invention easier to understand, and the dimensional ratio of each component may be different from the actual one. is there. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited to these, and can be implemented with appropriate modifications within the scope of the effects of the present invention.

[Analyzer]
FIG. 1 is a functional block diagram of an analysis apparatus 1 according to an embodiment of the present invention. The analysis apparatus 1 is an apparatus for analyzing various characteristics such as plate thickness and lift-off in an analysis target, and is operated by an operator who performs maintenance work of various structures to be analyzed, for example. The analysis device 1 analyzes the eddy current generated in the analysis target by the magnetic field corresponding to the alternating current, using the property that the liftoff of the analysis target and the thickness change. Specifically, the analysis device 1 analyzes the target by using the tendency that the detection voltage accompanying the eddy current decreases as the lift-off increases, and the phase difference between the detection voltage and the input current increases as the plate thickness increases. Check the corrosion status of the

  The analysis apparatus 1 can analyze various conductive materials such as steel materials, non-ferrous metals, and graphite having an arbitrary shape. In addition to being used as an inspection device operated by a worker who performs maintenance work, the analysis device 1 is installed in advance in a structure to be analyzed, and sensing is performed so that the detection result is continuously output to the outside. It may be used as an apparatus.

  Here, "lift off" refers to the distance between the probe of the analysis device 1 (the first coil 12 and the second coil 13 described later) and the surface of the structure of the conductive material to be analyzed. For example, when the corrosion layer is formed on the surface of the structure of the conductive material to be analyzed, “lift-off” is not the distance between the probe of the analysis device 1 and the surface of the corrosion layer. This is the distance between the probe and the surface of the conductive material structure (not including the corrosion layer). In addition, when the surface of the structure of the conductive material to be analyzed is covered with the coating film, “lift-off” is not the distance between the probe of the analysis device 1 and the coating film, but the probe of the analysis device 1 It refers to the distance between the surface of the conductive material structure.

  The analysis device 1 includes, for example, a control unit 10, a power supply unit 11, a first coil 12, a second coil 13, a detection unit 14, a calculation unit 15 (analysis unit), and a storage unit 16.

  The control unit 10 controls the operation of each unit of the analysis device 1. The control unit 10 is realized by, for example, a central processing unit (CPU).

  The power supply unit 11 applies an AC electrical signal such as an AC current or an AC voltage to the first coil 12 under the control of the control unit 10. The power supply unit 11 can change the frequency of the AC electrical signal applied to the first coil 12. The power supply unit 11 is, for example, an AC power supply.

  The first coil 12 is a driver coil that generates an AC magnetic field in accordance with an AC electrical signal input from the power supply unit 11. The inspection target T is excited by the AC magnetic field, and an eddy induced current (eddy current EC: Eddy Current) is generated in the inspection target T.

  The second coil 13 is a receiver coil that is excited to generate a voltage under the influence of both the alternating magnetic field generated in the first coil 12 and the alternating magnetic field generated due to the eddy current EC.

  The detection unit 14 detects the amount of electrical state based on the voltage generated in the second coil 13. For example, the detection unit 14 is a voltmeter that measures a voltage generated in the second coil 13.

  Arithmetic unit 15 is detected by lift-off reference data indicating the relationship between lift-off and detection voltage stored in storage unit 16 and plate thickness reference data indicating the relationship between plate thickness and detection voltage, and detection unit 14 Based on the detected voltage, the thickness of the inspection object T and the lift-off are calculated.

The storage unit 16 stores a corrosion damage estimated frequency f _c , lift-off reference data, plate thickness reference data, calculation results of the calculation unit 15, detection results of the detection unit 14, and the like. The storage unit 16 is realized by a ROM (Read Only Memory), a RAM (Random Access Memory), a HDD (Hard Disk Drive), a flash memory, or the like.

  Some or all of the functional units of the analysis apparatus 1 may be realized by a processor executing an analysis program (software). In addition, some or all of the functional units of the analysis device 1 may be realized by hardware such as LSI (Large Scale Integration) or ASIC (Application Specific Integrated Circuit), or a combination of software and hardware. It may be realized.

  The analysis program here causes a computer to analyze the characteristics in the thickness direction of the analysis target. For example, an alternating current electrical signal of a predetermined frequency is applied to the first coil 12 to excite the analysis target T to generate the eddy current EC in the analysis target T, and the second coil 13 is generated by the magnetic field generated by the eddy current EC. The first electrical state quantity measured based on the voltage amplitude, and the second electrical state quantity measured based on the phase difference between the AC electrical signal and the voltage. The thing is mentioned.

  The analysis apparatus 1 can also scan (scan) the structure in the depth direction of the analysis target. That is, while a sweep wave is applied to the first coil 12, a voltage is detected as a time-series electric state quantity, and the detection result and a normal (defect-free) test object stored in the storage unit 16 in advance. Compare with reference data. Thereby, it is possible to detect the internal state of the analysis target, for example, the presence or absence of defects such as cavities and cracks.

  FIG. 2 is a flowchart showing the flow of processing executed by the analysis device 1. The flow of processing of the analysis device 1 in the present embodiment will be described based on this flowchart.

First, the operator places the analysis apparatus 1 close to a structure to be analyzed, and operates a reception unit (not shown) that receives an operation provided in the analysis apparatus 1 to instruct start of measurement. In measurement start analyzing apparatus accepts an instruction 1, the control unit 10, depending on the material to be analyzed, a predetermined frequency for estimating the lift-off and thickness of the (corrosion damage frequency f _c), from the storage unit 16 Read (step S101). In addition, when a measurement target exists in a place subject to spatial restrictions, for example, a place where it is difficult for an operator such as a high place, a closed place, and the sea to approach, the analysis apparatus 1 is mounted on a mobile robot or the like. A person may instruct the start of measurement by remotely operating the mobile robot and the analyzer 1.

Next, under the control of the control unit 10, the power supply unit 11 applies an alternating current electrical signal (AC current) of the corrosion damage frequency f _c to the first coil 12 (step S102). Thereby, an alternating magnetic field (first magnetic field) is induced in the first coil 12, and an alternating eddy current EC (first eddy current) is generated in the analysis target T excited by the alternating magnetic field.

  A voltage is generated in the second coil 13 under the influence of both the alternating magnetic field generated by the eddy current EC and the alternating magnetic field generated by the first coil 12. Here, the detection unit 14 detects (measures) the amplitude of the voltage (first detection voltage) generated in the second coil 13 and the first electric state quantity according to the amplitude (step S103). In addition, the detection unit 14 detects an alternating current electrical signal applied to the first coil 12 and a voltage generated in the second coil 13, and calculates a second electric state quantity according to the phase difference between the two (step S104). The obtained amplitude and phase difference are stored in the storage unit 16.

  Next, the calculation unit 15 analyzes the characteristics in the thickness direction of the analysis target based on the first amount of electric state and the second amount of electric state stored in the storage unit 16.

  Specifically, the liftoff of the analysis target T is estimated by comparing the amplitude stored in the storage unit 16 with the reference data of the liftoff which is the first electric condition quantity (step S105). Further, the plate thickness of the analysis target T is estimated by comparing the phase difference stored in the storage unit 16 with the reference data of the plate thickness which is the second electric state quantity (step S106).

  Here, the estimated lift-off and plate thickness may be displayed on a display unit (not shown) provided in the analysis apparatus 1. Also, the estimated liftoff and thickness may be output to an external management device. Thus, the process of this flowchart is ended.

Subsequently, after described phase basic characteristics to be used for analysis of the present embodiment, as an analysis method of the present embodiment sets the corrosion damage frequency f _c, which describe how to estimate lift-off and thickness.

[Basic phase characteristics in eddy current test]
The inventor generates a sine wave in the power supply unit 11 of the analysis apparatus 1 and performs an eddy current test using the plate thickness, lift-off, and excitation frequency as parameters, and the output voltage with respect to the AC electric signal (input current) is It has been found that the following characteristics can be obtained for the phase difference.

  FIGS. 3A to 3D are graphs showing the relationship between the plate thickness and the phase difference obtained by performing the simulation when the excitation frequency is 1 Hz, 10 Hz, 100 Hz, and 1000 Hz, respectively. The horizontal axis of the graph indicates the plate thickness (mm) of the uncorroded portion (healthy portion). The vertical axis of the graph indicates the amount of change (°) in the phase difference based on the phase difference (90 °) between the current and voltage in the coil. As for the lift-off, it is 0 mm in a healthy state.

  As shown in the graph of FIG. 3, as the thickness is reduced from the initial plate thickness (here, 9 mm), the amount of change in retardation tends to decrease. In addition, regardless of the excitation frequency, the amount of change in the phase difference tends to decrease in proportion to the decrease in the plate thickness in a substantially linear manner. This is because the current density distribution shows the same distribution tendency regardless of the plate thickness, so the amount of generation of the eddy current is reduced by the reduction of the plate thickness, and the amount of phase change is reduced accordingly. It is considered to be.

  In the high frequency band exceeding 100 Hz, the amplitude of the detection voltage becomes extremely small due to the influence of the eddy current loss (a phenomenon in which the power consumption of the eddy current is changed to heat and energy is dissipated), and the above phase characteristics were observed. It is difficult to confirm such a tendency. Therefore, when the amplitude of the detection voltage is used as an index for detecting the plate thickness, it is necessary to set the excitation frequency sufficiently lower than 100 Hz.

  From the above results, it can be seen that the phase difference can be an index of plate thickness estimation even in a high frequency band exceeding 100 Hz where lift-off estimation with detected voltage is easy. That is, both the lift-off and the plate thickness can be estimated using the detection voltage and the measurement result of the phase difference in the high frequency band. This suggests that the measurement time of the detection voltage and the phase is shortened, and as a result, the analysis of the structure is speeded up.

[Corrosion damage estimated frequency f _c setting]
Corrosion damage estimated frequency f _c, when estimating the lift-off to be analyzed, the frequency of the AC electric signal applied to the first coil 12. Corrosion damage estimated frequency f _L is set in advance for each material to be analyzed. The corrosion damage estimated frequency f _c is set by the following procedure.

First, detection signal data when changing the lift-off L and the plate thickness t as parameters are collected. In order to obtain a necessary plate thickness / lift-off signal strength ratio (TL signal strength ratio) as a database, a plate thickness signal strength ΔWC _t and a lift-off signal strength ΔWC _L represented by the following equations (1) and (2) are obtained.

The WC continuously changes the frequency of the AC electrical signal applied to the first coil 12, and a time-series electrical signal corresponding to the voltage generated in the second coil 13 by the magnetic field generated by the eddy current in the analysis target T. The state quantities are shown by wavelet coefficients obtained by wavelet transform. The plate thickness t ₀ in the initial state is 9 mm, and the lift off L ₀ is ₀ mm.

The resulting obtained relation between wavelet coefficients and frequency, based on the rate of change of the wavelet coefficient for the frequency, to determine the corrosion damage frequency f _c.

4 (a) is a graph showing the lift-off signal intensity .DELTA.WC _L when lift-off increases 0.3 mm, the relationship between the frequency. FIG. 4 (b), and the plate thickness signal strength .DELTA.WC _t relative to the plate thickness 9 mm, TL signal intensity ratio is the ratio between the lift-off signal intensity .DELTA.WC _L relative to the lift-off 0mm and (ΔWC _t / ΔWC _L) , And a graph showing the relationship with frequency.

  From the graph of FIG. 4A, it can be confirmed that the lift-off signal intensity gradually increases from the low frequency side and decreases after exhibiting a peak at around 500 Hz. Also, from the graph in FIG. 4 (b), it can be seen that the TL signal intensity ratio tends to decrease as the frequency rises, and it is confirmed that the signals detected on the high frequency side are mostly signals due to lift off. can do.

[Estimation of lift off and thickness]
A sine wave at the selected estimated corrosion damage frequency is input to the test specimen for calibration as an AC electrical signal, and a lift-off estimation curve using the detected voltage amplitude as an index and a plate thickness estimation curve using the phase difference as an index are calculated. To do.

Figure 5 is obtained when the corrosion damage estimated frequency f _c and a 100 Hz, is a graph showing the detected voltage and lift-off relationship. The horizontal axis of the graph indicates liftoff (mm), and the vertical axis indicates detection voltage (V). Here, although four points are plotted for each of the cases where the plate thickness is 6 mm, 7 mm, 8 mm, and 9 mm, deviation of the plot due to the difference in plate thickness is not seen. Regardless of the thickness of the plate, it is possible to confirm a tendency that the detection voltage monotonously decreases as the lift-off increases.

  Even if the detection voltage is obtained without applying the wavelet transform, as shown in FIG. 5, it is known that the same tendency as in the case of applying the wavelet transform is shown regardless of the plate thickness. , Can be an indicator of liftoff estimation. In the graph of FIG. 5, any curve connecting four points plotted for each plate thickness can be approximated by an exponential function, and this approximate curve is taken as a lift-off estimation curve.

Figure 6 is obtained when the corrosion damage estimated frequency f _c and a 100 Hz, is a graph showing the phase difference and the thickness of the relationship. The horizontal axis of the graph indicates the plate thickness (mm), and the vertical axis indicates the phase difference (°). 6A to 6D correspond to cases where the lift-off is 0 mm, 0.1 mm, 0.2 mm, and 0.3 mm, respectively. Regardless of the size of the lift-off, it can be confirmed that the phase difference monotonously decreases as the plate thickness increases.

  In each of the graphs of FIGS. 6A to 6D, it is possible to perform multilinear approximation by linear interpolation in any of the curves connecting the four plotted points, and this approximate curve is taken as a plate thickness estimation curve. Since this thickness estimation curve changes not only with frequency but also with lift-off, the coefficient of the approximate straight line is set as a function of lift-off, and the thickness estimation curve is calculated using the value obtained by lift-off estimation.

  For the structure to be measured, a sine wave with the corrosion damage estimation frequency is given, the liftoff value corresponding to the value of the detected voltage obtained is estimated from the liftoff estimation curve, and the obtained phase difference value is used. The corresponding thickness values are estimated from the thickness estimation curve. The database of lift-off estimation curve and plate thickness estimation curve is preferably obtained for each measurement object, but the same database can be used when measuring a structure made of materials of the same steel type.

  As described above, in the analysis method according to the present embodiment, the phase difference between the input current and the output voltage is used as an index for estimating the plate thickness of the structure. As shown in FIG. 3, this phase difference can be sufficiently detected even if the excitation frequency is a signal in a high frequency band of about 100 Hz.

  Therefore, it is possible to measure the plate thickness in the high frequency band in the same way as lift-off, shorten the measurement time compared to the measurement in the low frequency band, and analyze the characteristics of the analysis target at high speed. be able to. By shortening the measurement time at one location, it becomes possible to perform measurement at a number of locations, repeat measurement at the same location, and the like, so that accurate analysis with improved measurement accuracy can be performed. Moreover, since the thickness and the lift-off can be measured in the same frequency band, the analysis can be simplified as compared with the case where they are performed in different frequency bands. The plate thickness can be estimated from both the amplitude of the output voltage and the phase difference between the input current and the output voltage. Therefore, the validity of the measurement result can be confirmed by estimating from both. .

  Hereinafter, the effects of the present invention will be made more apparent by examples. The present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist of the invention.

Example 1
Using the analysis method of the present invention, tests were performed to estimate the lift-off and thickness of the specimen. As a test body, a staircase-like steel plate was used, which was assumed to be thinned by corrosion, and the thickness was intermittently reduced by 1 mm from 9 mm to 6 mm in one direction. As the first coil and the second coil of the measuring means, those having a winding number of 400, a diameter of 16.4 mm, and a height of 3.7 mm were used.

  A lift-off was formed by sandwiching a 0.1 mm thick plastic gap gauge between the specimen and the second coil. The size of the lift-off was adjusted by the thickness of the sandwiching gap gauge.

(Selection of excitation frequency)
A detection signal obtained by changing the lift-off from 0 mm to 0.3 mm for each part of the test specimen having a thickness of 9 mm, 8 mm, 7 mm, and 6 mm was obtained by a sweep wave. By inputting a sweep wave, various frequency bands can be individually viewed, and therefore it is possible to confirm the influence of magnetic permeability, eddy current loss, and the like. In consideration of the analysis result by simulation, a log sweep wave varying from 10 Hz to 500 Hz was generated over 500 seconds in order to obtain a highly accurate database.

7 (a) is the plate thickness and 9 mm, is a graph showing the relationship between the lift-off signal intensity .DELTA.WC _L and frequency in a case where the lift-off and 0 mm. The horizontal axis of the graph represents the frequency (Hz), the vertical axis represents the lift-off signal intensity .DELTA.WC _L. In that the lift-off signal intensity .DELTA.WC _L has a peak at a specific frequency (here about 100 Hz), the same tendency as the analysis result shown in FIG. 4 (a) is observed.

7 (b) is a thickness signal strength .DELTA.WC _t relative to the plate thickness 9 mm, TL signal intensity ratio is the ratio between the lift-off signal intensity .DELTA.WC _L relative to the lift-off 0mm and (ΔWC _t / ΔWC _L) , And a graph showing the relationship with frequency. A tendency similar to the analysis result of FIG. 4B is seen in that the influence of the plate thickness signal intensity is large in the low frequency band, and the influence of the lift-off signal intensity becomes larger toward the high frequency band. The rattling of the signal on the high frequency side is thought to be due to the fact that the plate thickness signal is affected by eddy current loss and is not stable.

  From the graphs of FIGS. 7A and 7B, it is considered that 100 Hz, in which the TL signal strength ratio is sufficiently small and the lift-off signal strength is the largest, is appropriate as the corrosion damage estimation frequency. This result means that the value of the estimated corrosion damage frequency selected in the above analysis is appropriate. That is, it can be said that the thickness and lift-off of the structure can be estimated by the analysis method of the present invention. However, since the lift-off signal strength and the TL signal strength ratio are considered to differ depending on the material to be measured, and the shape and characteristics of the coil, they need to be acquired in advance as a database.

(Get database)
The detection voltage of the second coil was measured when the excitation frequency was 100 Hz and the plate thickness was an average value of 9 to 6 mm. FIG. 8 is a graph showing the result. The horizontal axis of the graph indicates liftoff (mm), and the vertical axis indicates detection voltage (V). As the lift-off increases, the detected voltage tends to decrease monotonously. The analysis result by the simulation in FIG. 5 is similar to this result, and its validity can be confirmed. That is, it is confirmed that the lift-off of the measurement target can be estimated by the analysis method of the present invention described above.

  The excitation frequency is 100 Hz, the lift-off is 0 (mm), 0.1 (mm), 0.2 (mm), 0.3 (mm), the input current to the first coil and the output voltage from the second coil The phase difference with was measured. FIG. 9 is a graph showing the result. The horizontal axis of the graph indicates the plate thickness (mm), and the vertical axis indicates the phase difference (°). The phase difference tends to monotonously decrease as the thickness decreases. The analysis result by the simulation of FIG. 6 is the same as this result, and its validity can be confirmed. That is, it is confirmed that the plate thickness of the measurement target can be estimated by the analysis method of the present invention described above.

(Estimation of lift-off and plate thickness for measurement)
Prepare a steel plate (corrosion test specimen) having corrosion damage as the structure T to be measured, and set three points P ₁ , P ₂ , P ₃ on the steel plate as measurement points, and directly place a probe at each measurement point. Measurement was performed. The liftoff estimation curve and the plate thickness estimation curve shown in FIGS. 8 and 9 were used as a database, and the liftoff and plate thickness of the structure T were estimated by the procedure of the above-described embodiment. That is, in the analysis apparatus 1, an input current of 1 A, 100 Hz is passed through the first coil 12, the voltage output from the second coil 13 is measured, and the lift-off corresponding to this voltage is estimated as the lift-off in FIG. Estimated from the curve. Further, the phase difference between the input current and the output voltage was measured, and the plate thickness corresponding to this phase difference was estimated from the plate thickness estimation curve of FIG.

(Comparative example 1)
Measurement was performed by directly placing a probe at each measurement point with three points P ₁ , P ₂ and P ₃ on the steel plate as measurement points. Further, the rust layer was not removed, and the shape of the back surface of the steel sheet was measured using a laser displacement meter and evaluated as a thinning due to corrosion. The rust thickness, which is considered as lift-off in the present invention, was measured using a film thickness meter. From the measurement results by the laser displacement gauge and the film thickness gauge, the rust thickness and the remaining thickness of the steel plate were calculated. However, since the measurement with the laser displacement meter includes the rust layer, the thickness of the rust layer was subtracted. For comparison with Example 1, the calculated residual plate thickness is an averaged value in the same area as the overlapping portion of the coil which is the influence range of the eddy current, with the measurement point as the center.

(Comparative example 2)
In the analysis apparatus 1, an input current of 1 A, 100 Hz is supplied to the first coil, a voltage output from the second coil is measured, and a lift-off corresponding to this voltage is estimated from a lift-off estimation curve prepared as a database. did. Furthermore, in the analyzer 1, an input current of 1 A, 10 Hz was supplied to the first coil 12, the voltage output from the second coil 13 was measured, and the plate thickness corresponding to this voltage was prepared as a database. It was estimated from the plate thickness estimation curve.

  FIG. 10A is a graph comparing the lift-off magnitudes obtained in Example 1 and Comparative Examples 1 and 2 described above. The horizontal axis of the graph indicates the position on the steel plate, and the vertical axis indicates the lift-off (mm). The lift-off estimation in the first embodiment uses a raw detection voltage to which the wavelet transform is not applied as an index, and uses the result to perform plate thickness estimation using the phase difference as an index. In the analysis of the first embodiment, evaluation is performed using the obtained raw detection voltage data, and evaluation is performed in the frequency region where the influence of noise is small. Therefore, compared with the analysis of the comparative example 2, the comparative example A reduction in the error relative to the actual measurement of 1 is observed. In addition, since the measured value of Example 1 was calculated using the database, it was set as the value according to the measurement accuracy of the film thickness meter.

  FIG. 10B is a graph comparing the thicknesses obtained in Example 1 and Comparative Examples 1 and 2 described above. The horizontal axis of the graph indicates the position on the steel plate, and the vertical axis indicates the plate thickness (mm). Also in the plate thickness estimation of Example 1, it can be confirmed that each measurement point error with respect to the actual measurement result of Comparative Example 2 can be calculated with an accuracy of 5% or less. The plate thickness estimation curve of Example 1 is calculated from the obtained lift-off value, and the fact that the lift-off error is reduced by using the detected voltage as it is also has a positive effect on the improvement of the plate thickness estimation accuracy. Conceivable.

  From the above, it was shown that the rust thickness (lift-off) and the remaining thickness of the corroded steel member can be evaluated experimentally by the analysis method of Example 1 utilizing the phase characteristics. In the analysis method of Comparative Example 2, it was necessary to use two different frequencies, but according to the analysis method of Example 1, two corrosion damage information of rust thickness and residual plate thickness can be obtained with only one frequency. That was confirmed. In fact, the maximum error was about 5%, and the measurement time per point was about 10 seconds, and it was possible to realize labor savings in measurement by improving the accuracy and shortening the measurement time.

DESCRIPTION OF SYMBOLS 1 ... Analysis apparatus 10 ... Control part 11 ... Power supply part 12 ... 1st coil 13 ... 2nd coil 14 ... Detection part 15 ... Calculation part 16 ... Memory | storage part

Claims (8)

Applying an alternating electrical signal of a predetermined frequency to the first coil to excite the analysis object, generating an eddy current in the analysis object;
The first electric state quantity according to the amplitude of the voltage generated in the second coil by the magnetic field generated by the eddy current, and the second electric state quantity according to the phase difference between the AC electric signal and the voltage Seeking
An analysis method for analyzing characteristics in the thickness direction of the analysis object based on the first electrical state quantity and the second electrical state quantity.   The analysis method according to claim 1, wherein the characteristics in the thickness direction of the analysis target are analyzed by comparing the first electric state quantity and the second electric state quantity with reference data.   The analysis according to claim 1 or 2, wherein the liftoff of the analysis target is measured based on the first electric state quantity, and the plate thickness of the analysis target is measured based on the second electric state quantity. Method.   The frequency of an alternating current electrical signal applied to the first coil is continuously changed, and a time-series amount of electric state quantity according to a voltage generated in the second coil is generated by a magnetic field generated by an eddy current in the analysis object. The analysis method of Claim 1 or 2 which measures.   The relationship between the frequency and the wavelet coefficient obtained by wavelet transformation of the time-series electric state quantities is determined, and the predetermined frequency is determined based on the rate of change of the wavelet coefficient with respect to the frequency. The analysis method described in 4.   The analysis method according to claim 4, wherein a structure in the thickness direction of the analysis target is scanned based on the time-series electrical state quantity. An analysis program that causes a computer to analyze the characteristics in the thickness direction of the analysis target,
Applying an alternating electrical signal of a predetermined frequency to the first coil to excite the analysis target, generating an eddy current in the analysis target, generating a voltage in the second coil by a magnetic field generated by the eddy current,
An analysis program performed based on a first amount of electric state measured based on the amplitude of the voltage and a second amount of electric state measured based on a phase difference between the AC electric signal and the voltage . A first coil that generates a magnetic field to be applied to an analysis object by flowing an alternating current;
A second coil that generates a voltage according to the eddy current generated in the analysis target;
A power supply unit for applying an alternating current electrical signal of a predetermined frequency to the first coil;
A control unit that controls the frequency of the alternating current electrical signal generated by the power supply unit;
A thickness of the analysis target based on a first amount of electric state based on the amplitude of the voltage detected in the second coil, and a second amount of electric state based on a phase difference between the voltage and the AC electric signal An analysis device comprising: an analysis unit that analyzes characteristics of directions.

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