JP2000019160A - Paint film damaged position detecting method for buried steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of a disturbance noise and grounding resistance between a detection electrode and the ground surface so as to enhance precision, in a paint film damaged position detecting method for a steel pipe using correlation processing relating to voltage impression for pseudo-random signals and detected signals. SOLUTION: A peak value of a correlation result is detected (15) by storing a detected digital data array (11) comprising detected signals converted in order by an AC converter 10 by an amount corresponding to one cycle of pseudo- random signals, and by conducting parallelly with a high speed correlation processings (13, 14) for finding product-sum calculation in all the corresponding positions, while shifting (16) the corresponding of two data array elements between a reference digital data array (12) having a pattern the same at preliminarily prepared pseudo-random signals and the detected digital data array (11) by one cycle of the false random signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a damage position of a coating film of a coated steel pipe buried underground in a non-contact manner from the ground surface.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting paint film damage of a coated steel pipe from the ground surface in a non-contact manner, a voltage is applied between the coated steel pipe and the ground, an electric current flows through the steel pipe, and a coating is applied. There is a method called a potential method for measuring a defect position by measuring a potential distribution generated on the ground surface by a current flowing out of a film damage.

In general, in the potential method, a low frequency sine wave is used as a current flowing through a steel pipe, and a potential difference between two electrodes installed on the ground surface is detected. By moving the position of the electrode on the ground surface along the buried steel pipe, the change in the potential difference is measured, and the damage position is specified. However, in actual measurement, the current flowing out of the damage is very small, and the detected potential difference signal is also weak. Furthermore, signal fluctuations due to fluctuations in the ground resistance between the ground surface and the electrodes, stray currents in the ground, induced currents from a commercial power supply, and the like become noise sources and deteriorate the SN ratio. It has been difficult to accurately and reliably detect damage.

[0004] For this reason, the inventors of the present invention, in the specification of Japanese Patent Application No. 9-57102 filed earlier, used a pseudo-random signal as a signal to be supplied to and applied to a steel pipe in the detection of coating film damage, and used an electrode on the ground surface. The potential difference signal detected in step 2 is subjected to correlation processing between the supplied and applied pseudo-random signal and a reference signal having the same pattern, and the peak value of the result of the correlation processing is used as the detected potential difference signal to improve the SN ratio. is suggesting.

A pseudo random signal is used as a signal to be supplied to and applied to a steel pipe according to the patent application, and a reference signal having the same pattern as the pseudo random signal supplied and applied to a potential difference signal detected by an electrode on the ground surface. In the method in which the peak value of the result of the correlation processing is used as a detected potential difference signal, a signal detected by an electrode installed on the ground surface is subjected to analog-to-digital conversion (AD conversion) by a signal processing device such as a personal computer. And a method of performing correlation processing between detection signal data and reference signal data by a signal processing device.

Here, assuming that the detection signal is f (t) and the reference signal is g (t), the correlation processing result Φ (τ) is
It is expressed by the following equation (1).

[0007]

(Equation 1)

Here, T is the period of the pseudo random signal. In equation (1), when f (t) and g (t) are the same between pseudo-random signals, the correlation processing result becomes an auto-correlation function of the pseudo-random signal, showing a periodic peak, and its period is pseudo. It is equal to the period T of the random signal.

[0009]

The system using the pseudo-random signal according to the above-mentioned patent application and using the correlation processing as the signal processing detects the position of the coating film damage with higher accuracy than the conventional potential difference method. it can. However, in this method, since the peak value of the correlation processing result Φ (τ) is used as the detected potential difference signal, in the correlation processing calculation, g of Expression (1) is used.
Since it is necessary to change τ in (t−τ) over one period of the pseudo-random signal and calculate it, when the detection processing of the detection signal by the signal processing device and the arithmetic processing are sequentially performed, the period is longer than the period of the pseudo-random signal. Is required, and the measurement responsiveness deteriorates. In the above method, the peak value of the correlation processing result Φ (τ) is used as the detected potential difference signal, and its change is plotted. The zero cross point, which is the phase change point of the detected potential difference signal, is used as the coating film damage position. If the shift of the zero-cross point occurs due to a change due to the influence of noise from the outside such as the above, there is a problem that it is difficult to accurately detect a phase change point and an error occurs in a paint film damage detection position.

In the above method, in addition to disturbance noise, a fluctuation in a detected potential due to a fluctuation in a contact resistance between an electrode and the ground surface at the time of measuring a ground potential causes a fluctuation in a peak value after correlation processing and an increase in noise. There is a problem that the SN ratio is deteriorated, it is difficult to accurately measure a change in the potential difference signal, and the performance of detecting a coating film damage point, particularly a minute damage point, is reduced. The present invention has been made in order to solve the above problems, and provides a method for detecting a coating damage position on a buried steel plate with high responsiveness and stability.

[0011]

According to a first aspect of the present invention, there is provided a method for detecting a paint film damaged position of a buried steel pipe, comprising the steps of: To apply a current through the coated steel pipe, detect a potential difference between two points at a predetermined interval on the ground surface along the pipe axis direction, and detect the detection signal and the pseudo-random signal applied to the steel pipe. Perform correlation processing with the reference signal of the same pattern,
The peak value of this correlation processing result is used as the potential difference signal between the two points, and the position of the two points is continuously moved along the pipe axis direction while the signal is continuously detected and the correlation processing is performed to obtain the potential difference on the ground surface. In the method of measuring the distribution and detecting the coating damage position of the embedded steel pipe from the change of the potential difference distribution, the detection signal between the two points is sequentially converted from analog to digital at a fixed time interval and applied to the steel pipe. A digital data array of a detection signal that is updated to new data with the lapse of time with the number of data for one cycle of the pseudo random signal, and has the same signal pattern as the pseudo random signal previously applied to the steel pipe. A reference digital data array for a cycle is prepared, and the digital data array of the detection signal and the prepared reference digital The sum-of-products calculation process that calculates the sum of the products obtained by multiplying the corresponding array elements of the detected data and the reference data that are updated over time between the data array and the corresponding array elements of the detected data and the reference data Is performed for all correspondences while shifting by one period of the pseudo-random signal, and the correlation between the detected data and the reference data is performed by detecting the peak value of the processing result.

According to a second aspect of the present invention, there is provided a method for detecting a coating film damage position on a buried steel pipe, wherein the correlation processing is performed using the digital data array of the detection signals and the reference digital data array in the method according to the first aspect. In the case where the correlation processing is performed continuously and the peak value of the correlation result is equal to or larger than a predetermined value, the correlation between the detected data and the reference data is shifted in the subsequent correlation processing. The range in which the sum calculation process is performed is limited to a corresponding point within an arbitrary range including a corresponding point of the detection data and the reference data from which the peak value of the correlation result is obtained, and the detection data and the detection data only within this limited corresponding range. The product-sum calculation processing between the reference data is performed, and the correlation processing for detecting the peak of the processing result is repeated for the detected peak value, and the peak value of the correlation processing becomes less than the set constant value. In this case, in the subsequent correlation processing, the correspondence between the detected data and the reference data is made one cycle of the pseudo random signal without limiting the range in which the product-sum calculation processing is performed while shifting the correspondence between the detected data and the reference data. All actions are performed while shifting over minutes.

According to a third aspect of the present invention, there is provided a method of detecting a paint film damage position on a buried steel pipe according to the first or second aspect, wherein the detection signals between the two points are sequentially converted into analog and digital signals at predetermined time intervals. The digital data array of the detection signal which is converted and updated to new data with the lapse of time by the number of data of one cycle of the pseudo random signal applied to the steel pipe is stored, and the digital data array of the stored detection signal is stored. Calculate the moving average data of the arbitrarily set range,
A correlation process is performed between reference data and a data array obtained by subtracting the corresponding moving average data from each of the stored detection signal data as new detection data.

According to a fourth aspect of the present invention, there is provided a method for detecting a paint film damage position on a buried steel pipe according to the first, second or third aspect, wherein the correlation processing result between the digital data array of the detection signal and the reference data is obtained. The peak values are sequentially stored, an average value of the stored peak values within a certain period of time is obtained, and this average value is used as the detected potential difference signal between the two points.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing an embodiment of the present invention, the basic operation and effect of the method for detecting a paint film damage position on a buried steel pipe according to the present invention will be described below. Claim 1 of the present invention
In the method for detecting a paint film damage position of a buried steel pipe according to the method, a pseudo-random signal is applied as an AC signal between a painted steel pipe buried underground and a ground electrode, and an electric current is caused to flow through the steel pipe. If the coating on the steel pipe is damaged, current will flow out of the damaged part into the ground. When a potential difference between two points at a predetermined interval on the ground surface is measured by an electrode or the like installed on the ground surface, a potential difference signal due to a potential distribution generated by a current flowing out of the damage is detected near the damage. The detected potential difference signal is a signal having the same pattern as the pseudo-random signal applied to the steel pipe, and the correlation between the detected signal and the reference signal having the same pattern as the pseudo-random signal applied to the steel pipe results in a correlation. As a result of the processing, a pulse-like signal which is an autocorrelation function of the pseudo-random signal used is obtained. The peak value of the pulse signal obtained as a result of the correlation processing corresponds to the potential difference detected by the electrode installed on the ground surface, and the ground surface potential difference can be known from the peak value of the correlation function. Here, when the positions of two points on the ground surface are moved and the signal detection and correlation processing are continuously performed, the peak value of the correlation processing result is used as a potential difference signal. The potential difference distribution on the surface is measured,
On the ground surface above the location of the damage to the buried coated steel pipe, a sharp change in the potential difference signal is measured due to the potential distribution generated by the current flowing out of the damaged part, and the change in the potential difference signal causes damage to the buried coated steel pipe. The position can be specified. In the present invention, one of the pseudo-random signals applied to the steel pipe is converted by sequentially performing analog-to-digital conversion of a detected potential difference signal between two points installed on the ground surface at predetermined time intervals.
The digital data array of the detection signal, which is updated with the passage of time, corresponding to the time range of the cycle, is stored, and the digital data array of the detection signal, which is updated with the passage of time by the analog-digital conversion, is prepared in advance. Between the pseudo random signal applied to the steel pipe and the digital data array of the reference signal having the same signal pattern, the corresponding array elements of the detection data array and the reference data array are all multiplied by the number of array elements, and all By performing the process of multiplying the multiplication result, an operation relating to one point of the correlation function between the detection signal and the reference signal is performed, and the correspondence between the elements of the detection data array and the reference data array is shifted by one period of the pseudo random signal. By doing so, a correlation function expressed as a data array of the operation result is obtained, and the correlation processing between the detection signal and the reference signal is performed. Further, the calculation of the correlation function by the arithmetic processing of the detection data array and the reference data array is repeatedly performed, and the extreme value of the obtained correlation function data is repeatedly output continuously as the potential difference measurement value. As a result, a change in the detected potential difference signal accompanying the update with the passage of time is obtained as an output.

According to a second aspect of the present invention, there is provided a method for detecting a coating film damage position on a buried steel pipe, wherein the correlation function between the detection signal and the reference signal is represented by a digital data array of the detection signal and a corresponding element of the digital data array of the reference signal. In a method of performing multiplication of each other and repetitive calculation of the integration, when the calculation of the detection data array and the reference data array updated with the passage of time is repeatedly performed, and the correlation calculation result is continuously performed, the calculation processing is performed. If the extreme value of the data array of the correlation function obtained as a result, that is, the magnitude (absolute value) of the detected potential difference signal is equal to or greater than a predetermined value, the correlation processing result becomes extremely small in the subsequent arithmetic processing. The correlation processing is a correlation process for a combination of corresponding points in a certain range including a corresponding combination of an array element of a detection data array and an array element of a reference data array having a maximum absolute value. Since the multiplication and the integration of the corresponding elements of the data array and the reference data array are performed for the number of array elements, the calculation is performed for the processing of performing the correspondence between the detection data array and the reference data array for one period of the pseudo random signal. The processing amount is reduced, the data array of the correlation function in the range including the extreme value is obtained at high speed, and the fluctuation of the detected potential difference signal can be measured and output with high responsiveness. In addition, the extreme value (maximum absolute value) of the data array of the correlation function (part of) obtained as a result of repeating the processing by limiting the combination of the array elements of the detection data array and the reference data array to a certain range is obtained. On the other hand, when the detected potential difference signal becomes equal to or less than the predetermined value, the multiplication between the corresponding elements of the detection data array and the reference data array and the integration thereof are performed in the subsequent arithmetic processing. Since all the processing is performed while shifting the corresponding points of the detection data array and the reference data array over one period of the pseudo random signal, the position shift of the extreme value in the data array of the correlation function due to the phase shift of the detection data, An erroneous determination of an extreme value due to a decrease or fluctuation of a signal is suppressed to a minimum.

According to a third aspect of the present invention, in the method for detecting a coating film damage position on a buried steel pipe, the correlation function between the detection signal and the reference signal is determined by using a digital data array of the detection signal and a corresponding element of the digital data array of the reference signal. In a method of performing a multiplication of two and a repetitive calculation of the integration, a digital data array of the detection signal corresponding to one cycle updated with the passage of time is set in advance from the digital data array of the detection signal. By calculating moving average data in the range of the number of array elements by the number of detected data arrays, a data array of a moving average processing result corresponding to a low-frequency fluctuation component in the detection signal is obtained, and the corresponding moving data is calculated from the detected data array elements. The data array obtained by subtracting the data of the average processing result is used as the data array of the detection signal, and the correlation calculation process is performed with the reference data array. Since, the fluctuation component of the low frequency in the detection signal is removed, remove the variation of the correlation function caused by the signal variation of the low frequency, the data sequence of the correlation function suppresses is obtained,
A stable detection potential difference signal is obtained.

According to a fourth aspect of the present invention, in the method for detecting a coating film damage position on a buried steel sheet, the correlation function between the detection signal and the reference signal is determined by using a digital data array of the detection signal and a corresponding element of the digital data array of the reference signal. In a method of performing a multiplication operation and a multiplication operation of each other, the data of the extreme value in each correlation data array, that is, the magnitude of the detection potential signal is calculated from the data array of the correlation function between the detection signal and the reference signal obtained as a result of the repeated operation. Are sequentially stored, and the average value of the stored extreme values (potential difference intensity) during a predetermined period of time (the number of elements) is calculated and output as a detected potential difference signal. The effect of the variation in the function data array is suppressed, and a stable potential difference signal is output.

Hereinafter, a correlation processing method according to each embodiment of the present invention will be described. Embodiment 1 FIG. 2 is a diagram showing a configuration of a test apparatus for detecting a paint film damage position of a buried steel pipe according to each embodiment of the present invention, where 1 is a pseudo-random signal generator, 2 is a coated steel pipe, 3 Is the terminal,
4 indicates a ground electrode, 5 indicates an electrode, 6 indicates a correlation operation processing device, and 7 indicates damage. FIG. 1 is an explanatory diagram showing a correlation processing method according to the first embodiment of the present invention, and shows a configuration of the correlation operation processing device 6 in FIG. In FIG. 1, reference numeral 10 denotes an AD converter, 11 and 12 shift registers, 13 a multiplier, 14 an integrator, 15 a signal discriminating device, and 16 a shift control device. FIG. 3 is a waveform diagram for explaining each signal of FIGS. 1 and 2. The operation of FIGS. 1 and 2 will be described with reference to FIG.

In the test apparatus shown in FIG. 2, a pseudo-random signal generated by a pseudo-random signal generator 1 is applied between a terminal 3 from a buried coated steel pipe 2 and a ground electrode 4, and the buried coated steel pipe is applied. Electric current flows into the steel pipe. In this embodiment, an M-sequence signal generator composed of a shift register having a feedback loop is used as a pseudo-random signal generator, and a shift clock frequency of 440 Hz,
An M-sequence signal having a code length of 127 was generated and applied to a steel pipe.
At this time, the cycle of the M-sequence signal is 1/440 × 127 (seconds)
Becomes The frequency of one code and the code length of one cycle of the M-sequence signal used here can be set to arbitrary values. By changing the frequency and the code length, the SN improvement effect by the pseudo-random signal processing can be improved. It is also possible to use a high power amplifier for adjusting the inflow current into the steel pipe when applying the actual signal to the steel pipe. The two electrodes 5 installed at regular intervals on the ground surface detect a potential difference on the ground surface due to a potential distribution generated by a current flowing into the ground from damage 7 on the coated steel pipe. In this embodiment, two electrodes are arranged in the tube axis direction of the buried coated steel pipe, and the interval between the electrodes is 1 m. The detected ground surface potential difference signal is input to the correlation operation processing device 6.

In the correlation operation processing device 6 shown in FIG. 1, the potential difference signal (see FIG. 3A) detected by the AD conversion device 10 is converted from analog to digital at a constant cycle (see FIG. b)), the digital data is input to the shift register 11. The shift register 11 operates in synchronization with the conversion cycle of the A / D converter 10, inputs the latest digital data obtained by the A / D conversion, sequentially shifts each component, and discards the oldest data. In step 11, data equal in number to one period of the pseudo-random signal is always stored. In the present embodiment, the conversion clock frequency of the AD conversion is set to 4400 Hz for an M-sequence signal having a frequency of 440 Hz for one code, and AD conversion of 10 points is performed for one pulse constituting the M-sequence signal to output digital data. . The shift register is 1270
The data is driven in synchronization with the AD conversion frequency, and data for one cycle of the pseudo-random signal is stored and accumulated. The shift register 12 has the same number of stages as the shift register 11, and the shift register is formed in a loop. Digitized data for one cycle of the pseudo-random signal applied to the steel pipe (see (c) of FIG. 3) is input to the shift register in advance. The contents of each configuration of the shift register 11 and the shift register 12 are individually multiplied by the multiplier group 13 to obtain multiplication results for the number of components of the shift register. Each multiplication result is input to the integrator 14, where all the multiplication results are integrated, and the integration result is input to the signal discriminating device 15.

When the multiplication by the multiplier group 13 and the first integration processing by the integrator 14 are completed, the contents of the shift register 12 are shifted by one data by the shift control device 16, and The correspondence of the shift register 12 is shifted by one. When the first shift of the shift register 12 is completed, the second multiplication and integration processing is performed, and the result of the arithmetic processing is input to the signal determination device 15. In this way, the reference digital data in the shift register 12 is shifted by one data at a time, and the correlation between the detected digital data and the reference digital data is shifted by one period of the pseudo random signal, and the product sum for all the correspondences is shifted. A calculation process is performed (see (e) and (f) of FIG. 3). The signal discriminating device 15 discriminates the maximum value of the absolute value of the integration result while the input of the integration result from the integrator is performed by the number of components of the shift register, and outputs the corresponding integration result as a detection signal.

Here, the operating frequency of the shift register 12 can be set arbitrarily, and high-speed signal processing can be performed at the operation limit of each component (shift register, multiplier, integrator, etc.). . Further, in the present embodiment, the method in which the correlation operation is performed by the correlation operation processing device 6 has been described.
It is also possible to realize the same operation by computer signal capture and software processing, in which case the frequency of the pseudo-random signal used,
Correlation processing capable of flexibly coping with a change in code length can be realized.

Embodiment 2 FIG. 4 is an explanatory diagram showing a correlation processing method according to Embodiment 2 of the present invention, and FIG. 5 is a flowchart showing the correlation processing order of FIG. Numerical values following S in FIG. 5 indicate step numbers.
In FIG. 4, a signal level discrimination device 17 is added to the configuration of FIG. 1, but the basic configuration and operation of the second embodiment are the same as those of the first embodiment shown in FIGS. Electrode 5 of FIG.
(See S1 in FIG. 5) to obtain a digital data array of the correlation processing result and determine the maximum absolute value in the correlation data array (see FIG. 5). 5, S2), and is output from the signal determination device 15 as a potential difference detection signal.

The potential difference detection signal output from the signal discriminating device 15 is input to a signal level discriminating device 17. The signal level determination device 17 determines whether or not the input potential difference signal level is equal to or higher than a predetermined fixed value (see S3 in FIG. 5). If the input potential difference signal level is not equal to or greater than the fixed value (threshold), the process returns to S1 in FIG. 5 and performs the same correlation processing as in the first embodiment. When the input potential difference signal level is equal to or higher than the predetermined value (threshold), the operation of the shift control device 16 and the signal discrimination device 15 is controlled as described below (see S4 in FIG. 5).
That is, in the case of the first embodiment, the product-sum calculation processing is performed for each shift while sequentially shifting the contents of the shift register 12 at a fixed period. In the second embodiment, when the potential difference signal level is equal to or more than a certain value, In the arithmetic processing that has obtained the correlation processing result, first, the shift register 12 is shifted to a shift amount obtained by subtracting a certain number from the shift amount of the shift register 12 from which the extreme value of the potential difference signal was obtained, and then the multiplication and integration processes are performed. Start. Then, the extreme value of the potential difference signal is sequentially shifted to a shift amount obtained by adding a fixed number to the obtained shift amount.

At this time, the signal discriminating device 15 sets the shift register 1 within the range of (the shift amount at which the extreme value is obtained ± a fixed number).
2 is sequentially shifted, and an integration result indicating an extreme value (maximum absolute value) in the result of the obtained multiplication and integration processing is output;
The signal level determination device 17 controls the shift control device 16 and the signal determination device 15 according to the output result. Further, the shift control device 16 sets (the shift amount for one data cycle−
(The shift amount at which the extremum was obtained + a fixed number)) and the data array in the shift register 12 is returned to the initial state. Now the number of shift register stages is 1270
In the case of (1), the extreme value of the data of 1270 (one cycle) correlation processing results obtained by shifting the shift register 12 1270 times is obtained by shifting the shift register 12 by 25.
Assuming that the point is shifted by 0, the next multiplication and integration operation starts from the point where the shift register 12 is shifted by 200, and 3
The shift is performed until the shift is 00, and when the operation with the shift amount 300 is completed, the shift register 12 is shifted 970 to return the data array to the state at the start of the operation. The above multiplication,
Shift register 1 while repeating the integration
If the content of No. 1 is updated (shifted) in accordance with the clock frequency of the AD conversion, an extreme value of the correlation result is obtained, but if processing within a certain range is performed as described above, the extreme value within the range is obtained. Value can be obtained. Further, the present embodiment can also be realized by signal capture by a computer, calculation by software, and signal processing.

Third Embodiment FIG. 6 is an explanatory diagram showing a correlation processing method according to a third embodiment of the present invention. FIG. 6 shows a configuration in which a data storage register 18 and a computing unit 19 are added to the configuration of FIG. I have. In the third embodiment, the potential difference signal detected by the electrodes by the AD converter 10 is subjected to analog-digital conversion at a constant cycle, and a predetermined number (four in this example) of data input from the data input to the shift register 11 is obtained. Is input to the computing unit 19. The arithmetic unit 19 averages the input data, outputs data obtained by subtracting the average value from predetermined data in the input data, and inputs the data to the corresponding register of the data storage register 18. In the example of FIG. 6, the arithmetic unit 19 shown at the top of the figure is the shift register 11
, F (0) to f (3) are input, the average value fm0 is obtained, and data f '(0) obtained by subtracting fm0 from data f (0) is stored in the first stage of the data storage register 18. To enter. The arithmetic unit 19 shown in the next stage inputs four data f (1) to f (4) from the shift register 11, finds an average value fm1, and subtracts fm1 from the data f (1). The data f '(1) thus obtained is input to the second stage (next to f' (0)) of the data storage register 18.

The processing by the arithmetic unit group 19 is performed for the number of registers of the shift register 11. As a result, the data storage register 18 has a signal obtained by subtracting the moving average of the potential difference signal from the potential difference signal in the shift register 11, that is, Data obtained by subtracting the low frequency fluctuation of the potential difference signal is recorded. The contents of the data storage register 18 are updated as the contents of the shift register 11 are updated with AD conversion. In the present embodiment, a correlation operation is performed using the contents of the data storage register 18 as a potential difference signal.
Also, the present embodiment can be realized by computer signal capture, software calculation, and signal processing.

Fourth Embodiment FIG. 7 is an explanatory diagram showing a correlation processing method according to a fourth embodiment of the present invention. In FIG. 7, an average calculator 20 is added to the configuration of FIG. The operation of each component in this embodiment is the same as that of the embodiment shown in FIGS. 1, 4, and 6. The signal discriminator 15 outputs the extreme value of the correlation processing waveform (data) between the detected potential difference signal and the reference signal. Becomes (the absolute value becomes maximum)
Point data, that is, a potential difference detection signal is output. The average calculator 20 receives the output data from the signal discriminating device,
An average value (number) of input signals (data) within a predetermined time interval is calculated and output. Further, the present embodiment can also be realized by signal capture by a computer, calculation by software, and signal processing.

[0030]

As described above, according to the present invention, a pseudo-random signal is applied as an AC voltage between a coated steel pipe buried underground and the ground to generate a current in the coated steel pipe. Flow, and detects a potential difference between two points at a predetermined interval on the ground surface along the pipe axis direction, sequentially stores a detection digital data array obtained by A / D conversion of this detection signal, and in parallel with this, A correlation process for calculating the product sum between both data at all corresponding positions while shifting the correspondence of array elements between the detected digital data array and the reference digital array prepared in advance by one period of the pseudo random signal. High-speed scanning is performed at the two points installed on the ground surface in the axial direction of the buried steel pipe, and the responsiveness of signal detection and signal processing for measuring the change in potential difference between the two points is improved. Scan and measure faster than Theft is possible.

According to the present invention, in the method for performing the correlation processing using the digital data array of the detection signals and the digital data array for reference in the method of detecting the coating film damage position of the buried steel pipe, the correlation processing is performed continuously. If the peak value of the correlation result is equal to or larger than a predetermined value, the range in which the product-sum calculation process is performed while shifting the correspondence between the detected data and the reference data in the subsequent correlation process is defined as the correlation result. The peak value is limited to the corresponding point within an arbitrary range including the corresponding point between the detected data and the reference data, and the product-sum calculation process between the detected data and the reference data is performed only within the limited corresponding range. As a result, the correlation processing time is shortened, and a measurement result with better responsiveness is obtained as compared with the case where the corresponding range is shifted by one period of the pseudo random signal without limiting the range. That.

According to the present invention, in the method for detecting a paint film damage position on a buried steel pipe, a moving average in a range arbitrarily set for each data from a digital data array of detection signals sequentially stored after A / D conversion. Data is calculated, and the data array obtained by subtracting the corresponding moving average data from each data of the stored detection signal is subjected to correlation processing with reference data as a new detection signal. Therefore, the low-frequency fluctuation component in the detection signal is removed, the fluctuation of the correlation function caused by the low-frequency signal fluctuation is removed, and a data array of the correlation function is obtained, in which a stable detected potential difference signal is obtained.

According to the present invention, in the method for detecting a paint film damage position of a buried steel pipe, peak values of a correlation process result between a digital data array of detection signals and reference data are sequentially stored, and the stored peak values are compared with each other. Since the average value of the data within a certain time is obtained and the average value is used as the detected potential difference signal between the two points, the influence of the fluctuation of the correlation function data array due to the fluctuation of the offset of the detection signal and the like is suppressed and stabilized. A potential difference signal is output.

According to the present invention, the potential difference between the two-point electrodes installed on the ground surface is obtained by employing a combination of the moving average processing of the detected digital data and the averaging processing of the peak detection value within a predetermined time. Eliminates the effects of detection noise due to disturbance noise in signal detection and fluctuations in contact resistance between the electrode and the ground surface, and obtains stable correlation processing results, and realizes stable coating film damage detection and measurement. It becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a correlation processing method according to a first embodiment.

FIG. 2 is a diagram showing a configuration of a coating film damage position detection test device for a buried steel pipe according to each embodiment of the present invention.

FIG. 3 is a waveform chart for explaining each signal of FIGS. 1 and 2;

FIG. 4 is an explanatory diagram illustrating a correlation processing method according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing the correlation processing order of FIG. 4;

FIG. 6 is an explanatory diagram illustrating a correlation processing method according to a third embodiment of the present invention.

FIG. 7 is an explanatory diagram illustrating a correlation processing method according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pseudo-random signal generator 2 Painted steel pipe 3 Terminal 4 Grounding electrode 5 Electrode 6 Correlation processor 7 Damage 10 A / D converter 11, 12 Shift register 13 Multiplier 14 Integrator 15 Signal discriminator 16 Shift controller 17 Signal Level discriminator 18 Data storage register 19 Computing unit 20 Average computing unit

Continued on the front page F term (reference) 2F063 AA02 BA30 BB02 BC02 BC09 BD07 CA08 DA01 DB04 EB25 FA09 KA10 LA18 LA19 LA22 LA24 LA30 2G053 AA11 AB21 BA12 BA19 BA26 BC02 BC14 CA02 CA18 CB14 CB17 CB22 CB23 CB24 DB20 DB25

Claims (4)

[Claims] 1. A pseudo-random signal is applied as an AC voltage between a coated steel pipe buried in the ground and the ground to cause a current to flow in the coated steel pipe, and a ground along the pipe axis direction is provided. A potential difference between two points at a constant interval on the surface is detected, and a correlation process is performed between the detection signal and a reference signal having the same pattern as the pseudo random signal applied to the steel pipe. A potential difference signal between points is measured, and a potential difference distribution on the ground surface is measured by continuously detecting a signal and performing a correlation process while moving the positions of the two points along the pipe axis direction. In the method for detecting a coating film damaged position of a buried steel pipe from a situation, the detection signal between the two points is sequentially converted from analog to digital at a fixed time interval, and data for one cycle of a pseudo-random signal applied to the steel pipe. Number of hours A digital data array of a detection signal that is updated to new data with time is stored, and a reference digital data array for one cycle having the same signal pattern as a pseudo-random signal applied to the steel pipe is prepared in advance. In parallel with the analog-to-digital conversion, between the digital data array of the detection signal and the prepared reference digital data array, the corresponding array elements of the detection data and the reference data updated with the passage of time are multiplied by the corresponding array elements. The sum-of-products calculation processing for calculating the sum of the products obtained is performed for all the correspondences while shifting the correspondence between the detection data and the array element of the reference data by one period of the pseudo random signal, and the peak value of the processing result is detected. A method for detecting a coating film damage position on a buried steel pipe, which performs a correlation process between data and reference data. 2. A method of performing a correlation process using a digital data array of detection signals and a digital data array for reference in the method for detecting a coating film damage position of a buried steel pipe according to claim 1, wherein the correlation process is performed continuously. If the peak value of the correlation result is equal to or greater than a predetermined value, the range in which the product-sum calculation process is performed while shifting the correspondence between the detection data and the reference data in the subsequent correlation process is defined as the correlation result. The peak value is limited to the corresponding point within an arbitrary range including the corresponding point between the detected data and the reference data, and the product sum calculation process between the detected data and the reference data is performed only within the limited corresponding range. The correlation processing for detecting the peak of the processing result is repeated for the detected peak value, and when the peak value of the correlation processing becomes smaller than the set value, the subsequent correlation processing is performed. Without limiting the range in which the product-sum calculation process is performed while shifting the correspondence between the detection data and the reference data, all the correspondences are shifted while the correspondence between the detection data and the reference data is shifted by one period of the pseudo random signal. A method for detecting a damaged position of a coating film on a buried steel pipe. 3. The method according to claim 1, wherein the detection signal between the two points is sequentially converted from analog to digital at a fixed time interval and applied to the steel pipe. A digital data array of detection signals that is updated to new data with the passage of time with the number of data for one cycle of the signal, and a range arbitrarily set for each data from the stored digital data array of the detection signals. The moving average data is calculated, and the data array obtained by subtracting the corresponding moving average data from each of the stored detection signal data is used as new detection data to perform correlation processing with reference data. A method for detecting a paint film damage position on a buried steel pipe. 4. The method according to claim 1, wherein the peak value of the correlation processing result between the digital data array of the detection signal and the reference data is sequentially stored. A method of detecting a coating film damage position on a buried steel pipe, wherein an average value of data within a predetermined time of a peak value is obtained, and the average value is used as a detected potential difference signal between the two points.