Strain or temperature measurement method, optical fiber sensor, and program

Abstract

To correct inappropriate measurement data generated due to sweep nonlinearity of a light source.SOLUTION: A strain or temperature measurement method includes: a process of, when the average value of Lag values X in a plurality of adjacent division sections including a target division section N is equal to or more than a preset threshold, extracting the division section N as an error section; a process of generating, for the division section N extracted as the error section, M pieces of coupled data obtained by coupling continuous M division sections including the division section N, and performing cross-correlation processing on a reference signal and a measured signal for each of the M pieces of coupled data to calculate the Lag values; a process of calculating the absolute value of the difference between each of the M Lag values and the Lag value X of the division section N; and a process of calculating the average value A of the M Lag values, which is performed when all of the calculated absolute values are equal to or less than the preset threshold, and when the absolute value of the difference between the Lag value X of the division section N and the average value A is equal to or more than a predetermined threshold, substituting the average value A for the Lag value X of the division section N.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a strain or temperature measurement method, an optical fiber sensor, and a program that can correct inappropriate measurement data generated by the sweep nonlinearity of a light source in Optical Frequency Domain Reflectometry (OFDR) used for the maintenance and management of social infrastructure. [Background technology]

[0002] One measurement algorithm for OFDR is disclosed in Non-Patent Document 1. The technology disclosed in Non-Patent Document 1 acquires a reference signal and a measurement signal, performs a fast Fourier transform on each acquired signal, divides the signal into fixed frequency intervals, and then performs an inverse Fourier transform to acquire a cross-correlation function for each divided interval. For each divided interval, the Lag value that maximizes the cross-correlation coefficient is found, and the distortion value is determined according to the Lag value. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] "Cryogenic temperature measurement using Rayleigh backscattering spectra shift by OFDR", IEEE Photon. Technol. Lett., vol. 26, no. 11, pp. 1150-1153, Jun. 2014. Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the strain measurement width is narrowed in the measurement algorithm disclosed in the above-mentioned non-patent document 1, the non-linearity of the frequency swept light source affects the Lag value in the cross-correlation processing, resulting in an inappropriate value.

[0005] This is because the frequency spectrum broadens due to nonlinearity, causing extra frequencies to be superimposed within a certain frequency width ΔX, reducing the similarity between the reference signal and the measurement signal. When the similarity between the reference signal and the measurement signal decreases, the cross-correlation decreases. As the cross-correlation decreases, the cross-correlation peak becomes hidden, and an inappropriate Lag value is detected. This causes a measurement error.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a strain or temperature measurement method, an optical fiber sensor, and a program that can correct inappropriate measurement data generated by the sweep nonlinearity of a light source. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the strain or temperature measurement method of the present invention includes the steps of: dividing a reference signal and a measurement signal obtained by frequency domain optical reflectometry by a frequency width ΔX, and calculating a Lag value X by performing cross-correlation processing of the reference signal and the measurement signal for each divided section; extracting a target divided section N as an error section when the average value of Lag values ​​X in a plurality of adjacent divided sections, including the target divided section N and sections before and after the target divided section N, is equal to or greater than a predetermined threshold; creating M pieces of concatenated data by concatenating M consecutive divided sections including the target divided section N for the divided section N extracted as the error section; and performing cross-correlation processing of the reference signal and the measurement signal for each of the M concatenated data; the step of calculating the absolute value of the difference between each of the M Lag values ​​and the Lag value X of the divided section N; the step of calculating an average value A of the M Lag values, which is performed when all of the calculated absolute values ​​are equal to or less than a predetermined threshold, and substituting the average value A for the Lag value X of the divided section N if the absolute value of the difference between the Lag value X of the divided section N and the average value A is equal to or greater than a predetermined threshold; the step of substituting the Lag value immediately before the absolute value of the difference between the M Lag values ​​and the Lag value X of the divided section N changes significantly for the Lag value X of the divided section N if the absolute value of the difference between the M Lag values ​​and the Lag value X of the divided section N is greater than a predetermined threshold; and the step of converting the Lag value obtained for each divided section into strain or temperature.

[0008] The optical fiber sensor of the present invention also includes a processor to which a reference signal and a measurement signal obtained by frequency domain optical reflectometry are input, the processor dividing the frequency range by ΔX and calculating a Lag value X by performing cross-correlation processing of the reference signal and the measurement signal for each divided section, a processor extracting the divided section N as an error section when the average value of Lag values ​​X in a plurality of adjacent divided sections including the target divided section N and sections before and after the target divided section N is equal to or greater than a predetermined threshold, a processor generating M pieces of concatenated data by concatenating M consecutive divided sections including the target divided section N for the divided section N extracted as an error section, and a processor performing cross-correlation processing of the reference signal and the measurement signal for each of the M concatenated data, and a processor extracting M pieces of concatenated data. and the Lag value X of the divided section N; means for calculating an average value A of the M Lag values, which is performed when all of the calculated absolute values ​​are equal to or less than a predetermined threshold, and substituting the average value A for the Lag value X of the divided section N when the absolute value of the difference between the Lag value X of the divided section N and the average value A is equal to or greater than a predetermined threshold; means for substituting the Lag value immediately before the absolute value of the difference between the Lag value X of the divided section N and the Lag value X of the divided section N changes significantly, when the absolute value of the difference between the Lag value X of the M Lag values ​​and the Lag value X of the divided section N among the M Lag values ​​is greater than a predetermined threshold; and means for converting the Lag value obtained for each divided section into strain or temperature.

[0009] The program of the present invention also includes means for dividing a calculation processing device into which a reference signal and a measurement signal obtained by frequency domain optical reflectometry are input, by a frequency width ΔX, and for calculating a Lag value X by performing cross-correlation processing of the reference signal and the measurement signal for each divided section; means for extracting a target divided section N as an error section when an average value of Lag values ​​X in a plurality of adjacent divided sections, including a target divided section N and sections before and after the target divided section N, is equal to or greater than a predetermined threshold; means for creating M pieces of concatenated data by concatenating M consecutive divided sections including the target divided section N for the divided section N extracted as an error section, and for each of the M pieces of concatenated data by performing cross-correlation processing of the reference signal and the measurement signal to calculate a Lag value; The system functions as: means for calculating the absolute value of the difference between each of the g values ​​and the Lag value X of the divided section N; means for calculating an average value A of the M Lag values, which is performed when all of the calculated absolute values ​​are equal to or less than a predetermined threshold, and for substituting the average value A for the Lag value X of the divided section N if the absolute value of the difference between the Lag value X of the divided section N and the average value A is equal to or greater than a predetermined threshold; means for substituting the Lag value immediately before the absolute value of the difference between the M Lag values ​​and the Lag value X of the divided section N fluctuates significantly for the Lag value X of the divided section N if the absolute value of the difference between the M Lag values ​​and the Lag value X of the divided section N is greater than a predetermined threshold; and means for converting the Lag value obtained for each divided section into strain or temperature.

[0010] According to the preferred embodiments of the above-mentioned strain or temperature measurement method, optical fiber sensor, and program, the number M of connected data is equal to or greater than the value obtained by dividing the optical fiber length to be measured by the error occurrence distance in a steady state, and n Meet the following. [Effects of the Invention]

[0011] The strain or temperature measurement method, optical fiber sensor, and program of the present invention have the function of correcting inappropriate measurement data caused by the sweep nonlinearity of the light source, thereby making it possible to avoid measurement errors caused by inappropriate measurement data. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of an optical fiber sensor. [Figure 2] FIG. 1 is a diagram (1) showing the process flow of the strain or temperature measurement method. [Figure 3] FIG. 2 is a diagram (2) showing the process flow of the strain or temperature measurement method. [Figure 4] FIG. 3 is a diagram showing the process flow of the strain or temperature measurement method. [Figure 5] 1A and 1B are schematic diagrams for explaining a strain or temperature measurement method. [Figure 6] FIG. 10 is a diagram showing the measurement results obtained by the optical fiber sensor. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and positional relationship of each component are merely shown in a schematic manner to enable understanding of the present invention. Furthermore, while preferred configuration examples of the present invention will be described below, they are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes and modifications can be made that achieve the effects of the present invention without departing from the scope of the configuration of the present invention.

[0014] An OFDR optical fiber sensor will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of an optical fiber sensor.

[0015] The optical fiber sensor comprises a frequency sweep light source 10, a 1:99 splitter 11, a main interference system 20, an auxiliary interference system 30, a polarizing beam splitter 40, an optical fiber 50 to be measured, and an optical signal acquisition unit 60.

[0016] The light generated by the frequency swept light source 10 is sent to a 1:99 splitter 11. The 1:99 splitter 11 splits the light generated by the frequency swept light source 10 into two. One of the two split by the 1:99 splitter 11 is sent to the main interferometer system 20, and the other is sent to the auxiliary interferometer system 30.

[0017] The main interference system 20 is configured to include a 1:99 splitter 21, a circulator 22, and a 50:50 splitter 23. Light sent to the main interference system 20 is split into two by the 1:99 splitter 21. One of the two split by the 1:99 splitter 21 is sent to the circulator 22. The other of the two split by the 1:99 splitter 21 is sent to the 50:50 splitter 23.

[0018] The circulator 22 has first to third ports. Light input to the first port is output from the second port, light input to the second port is output from the third port, and light input to the third port is output from the first port.

[0019] The light sent from the 1:99 splitter 21 is input to a first port of the circulator 22 and output from a second port. The optical fiber 50 to be measured is connected to the second port of the circulator 22. The light output from the second port of the circulator 22 is input to the optical fiber 50, and the Rayleigh scattered light generated in the optical fiber 50 propagates through the optical fiber 50 in the opposite direction to the input direction, and is sent to the main interferometer 20. The Rayleigh scattered light sent to the main interferometer 20 is input to the second port of the circulator 22 and output from a third port. The light output from the third port of the circulator 22 is sent to the 50:50 splitter 23.

[0020] The 50:50 splitter 23 combines the light sent from the 1:99 splitter 21 and the light sent from the circulator 22 .

[0021] The light multiplexed by the 50:50 splitter 23 is sent to the polarizing beam splitter 40. The polarizing beam splitter 40 splits the input light into light with two orthogonal polarization directions and sends each to the optical signal acquirer 60.

[0022] The auxiliary interference system 30 is configured to include a first 50:50 branching unit 31, a delay optical fiber 32, and a second 50:50 branching unit 33. Light sent to the auxiliary interference system 30 is branched into two by the first 50:50 branching unit 31. One of the two branches by the first 50:50 branching unit 31 is sent to the second 50:50 branching unit 33. The other of the two branches by the first 50:50 branching unit 31 is sent to the delay optical fiber 32. The light sent to the delay optical fiber 32 is delayed for a certain time by the delay optical fiber 32 and then sent to the second 50:50 branching unit 33.

[0023] The second 50:50 splitter 33 multiplexes the light sent from the first 50:50 splitter 31 and the light sent from the delay optical fiber 32. The light multiplexed by the second 50:50 splitter 33 is sent to the optical signal acquirer 60.

[0024] The optical signal acquiring unit 60 includes first to third photoelectric converters 61-1 to 61-3, an analog-to-digital converter (ADC) 62, and a processing unit 63.

[0025] The two beams of light split by the polarizing beam splitter 40 are incident on the first and second photoelectric converters 61-1 and 61-2, respectively. The light combined by the second 50:50 splitter 33 of the auxiliary interference system 30 is incident on the third photoelectric converter 61-3. The first to third photoelectric converters 61-1 to 61-3 convert the incident beams into analog electrical signals. The analog electrical signals generated by the first to third photoelectric converters 61-1 to 61-3 are sent to the ADC 62. The ADC 62 converts the analog electrical signals into digital electrical signals and sends them to the arithmetic processing unit 63.

[0026] The arithmetic processing device 63 is a device having the function of processing digital electrical signals, and can have any suitable conventionally known configuration, such as a personal computer (PC), except for the functional means realized by the arithmetic processing device 63. Furthermore, the frequency swept light source 10, 1:99 splitter 11, main interference system 20, auxiliary interference system 30, polarized beam splitter 40, optical fiber 50 to be measured, and optical signal processing device 60 provided in the optical fiber sensor can also have any suitable conventionally known configuration, except for the functional means realized by the arithmetic processing device 63. Therefore, detailed description of these components will be omitted.

[0027] The following processing is performed by the arithmetic processing unit 63 executing a program stored in an arbitrary suitable storage device. That is, the arithmetic processing unit 63 realizes functional means for performing the following processing.

[0028] The processing in the arithmetic processing device 63 will be described with reference to Figures 2 to 5. Figures 2 to 4 are diagrams showing the processing flow of the strain or temperature measurement method. Figure 2(A) is a flow diagram of the detection process, Figure 2(B) is a flow diagram of the Lag value alignment process, Figure 3 is a flow diagram of the error extraction process, and Figure 4 is a flow diagram of the error data correction process. Figure 5 is a schematic diagram for explaining the strain or temperature measurement method.

[0029] The processing in the calculation processing device 63 includes a detection step (step (hereinafter, step will be abbreviated as S) 100) and a Lag value sorting step (S200).

[0030] A detection process S100 is performed on the signal sent to the arithmetic processing device 63. The detection process S100 includes the following steps S101 to S108.

[0031] In S101, the zero-crossing point is extracted using the signal from the auxiliary interference system 30. In this assumption, the timing at which the signal intensity passes through 0 is extracted for the electrical signal input to the arithmetic processing device 63 via the auxiliary interference system 30.

[0032] In S102, a signal from the main interference system 20 corresponding to the zero-crossing point extracted in S101 is extracted. In this process, a signal having the same timing as the zero-crossing point extracted in S101 is extracted from the two signals split by the polarizing beam splitter 40.

[0033] In S103, for each of the two signals split by the polarizing beam splitter 40, the signal extracted in S102 is subjected to spline interpolation.

[0034] In S104, the spline-interpolated signal is subjected to a fast Fourier transform. When the above steps S101 to S104 are performed on the light generated by the frequency sweep light source 10, the data is aligned on the frequency axis.

[0035] In S105, the frequency spectrum obtained by the fast Fourier transform in S104 is divided into a certain frequency width ΔX from the low frequency side. This frequency width ΔX corresponds to the spatial resolution in OFDR.

[0036] In S106, an inverse fast Fourier transform is performed on each piece of data divided in S105.

[0037] In S107, the inverse fast Fourier transformed signal is subjected to envelope detection to extract amplitude data. Note that S107 may be omitted.

[0038] In S108, the two signals split by the polarized beam splitter 40 are subjected to the processes in S101 to S107, and the two signals obtained are demodulated into one signal that is composite data by polarization diversity processing.

[0039] The above-mentioned detection process S100 (S101 to S108) is performed for each of the reference signal and the measurement signal.

[0040] The reference signal and the measurement signal that have been subjected to the detection process S100 are subjected to the Lag value alignment process S200.

[0041] The Lag value sorting step S200 includes the processes of S201 to S203.

[0042] In S201, a cross-correlation process is performed on the reference signal and the measurement signal for the same division section obtained in the division process in S105 to obtain a Lag value. Here, the Lag value is given by, for example, the difference between the peak positions of the reference signal and the measurement signal.

[0043] In S202, the Lag value at which the cross-correlation is greatest for each divided section is obtained and aligned for each divided section.

[0044] In S203, the Lag value is converted into strain for each divided section. Note that, although an example in which the optical fiber sensor is used as a strain measuring device that converts the Lag value into strain is shown here, it may also be used as a temperature measuring device that converts the Lag value into temperature.

[0045] The detection process S100 (S101 to S108) and the Lag value alignment process S200 (S201 to S203) described above can be configured in any suitable conventional manner.

[0046] However, narrowing the frequency band ΔX poses the problem of not being able to correctly calculate the cross-correlation Lag value. This is because the nonlinearity of the frequency sweep light source 10 broadens the frequency spectrum, causing excess frequencies to be superimposed within a certain frequency band ΔX, reducing the similarity between the reference signal and the measurement signal.

[0047] As the similarity decreases, the cross-correlation decreases. When the cross-correlation decreases, the cross-correlation peak becomes hidden, leading to an inappropriate Lag value being calculated, which causes measurement errors.

[0048] Therefore, in the present invention, an error extraction step S300 and an error data correction step S400 are performed between the processing of S202 and the processing of S203 in the Lag value sorting step S200.

[0049] The error extraction step S300 sequentially determines whether or not the divided section N corresponds to an error section, and extracts the corresponding error section. Specifically, S300 includes, for example, the following steps S301 to S305.

[0050] Here, the divided section N corresponds to the Nth section from the low frequency side when the frequency spectrum is divided by a fixed frequency width ΔX from the low frequency side. END (N END is an integer of 2 or more, N is 1 or more and N END The following integers:

[0051] In S301, the Lag value arranged for each divided section is designated as X, and the average value of the Lag values ​​X for the target divided section N and the sections before and after the divided section N, for example, the divided section N-1 to the divided section N+1, is obtained. The number of divided sections used to obtain the average value of the Lag values ​​X can be set arbitrarily and suitably.

[0052] In S302, it is determined whether the average value acquired in S301 is equal to or greater than a preset threshold value.

[0053] If the comparison result in S302 indicates that the average value is equal to or greater than the threshold value (Yes), the divided section N is extracted as an error section E in S303.

[0054] In S304, which follows S303, N is incremented by 1, and in S305, the division section N is the last division section (N=N END ) or not.

[0055] If the result of the determination in S302 is that the average value is less than the threshold (No), the divided section N is not extracted as an error section. In this case, S304 and S305 are carried out without carrying out S303.

[0056] As a result of the determination in S305, the division section N is the last division section (N=N END) (Yes), the error extraction step S300 is terminated, and the error data correction step S400 is subsequently performed. On the other hand, if the result of the determination in S305 is that N is not the last divided section (N <N END ) (No), S301 is performed again. The error extraction step S300 is performed when the division section N is the last division section (N=N END ) is repeated until

[0057] The error data correction step S400 corrects errors in the error section E extracted in the error extraction process S300. Specifically, S400 includes, for example, the following steps S404 to S413.

[0058] In S404, the divided interval N extracted as the error interval E is obtained from the extracted interval sequence. Here, the error interval E corresponds to the Eth interval from the low frequency side extracted as the error interval. When the total number of divided intervals extracted as the error interval is E END (E END is an integer of 1 or greater), E is 1 or greater END The following integers:

[0059] In S405, concatenated data is created for the divided section N extracted as the error section E in S404. The concatenated data is a concatenation of M consecutive divided sections (M is an integer equal to or greater than 2) including the divided section N. Here, M is preferably a power of 2. Furthermore, M is preferably equal to or greater than the value of the length [m] of the optical fiber 50 to be measured divided by the distance [m] at which an error occurs in a steady state.

[0060] M pieces of concatenated data are created for each of the reference signal and the measurement signal by shifting the concatenated section, such as N-M+1 to N, N-M+2 to N+1, ..., N to N+M-1. The frequency width of the concatenated data is M × ΔX. For example, if M is 4 (=2 2 ), the width of the concatenated data is 4×ΔX, and there are four pieces of concatenated data: N−3 to N, N−2 to N+1, N−1 to N+2, and N to N+3 (see FIG. 5(A)).

[0061] In S406, cross-correlation processing between the reference signal and the measurement signal is performed for each of the M pieces of connected data created in S405, and a Lag value is calculated.

[0062] In S407, the absolute value of the difference between the Lag value obtained for each of the M pieces of concatenated data and the Lag value X for the divided section N is calculated. Then, it is determined whether the absolute values ​​calculated for each of the M pieces of concatenated data are all equal to or less than a threshold value.

[0063] If the result of the determination in S407 is that all the calculated absolute values ​​are equal to or less than the threshold value (Yes), steps S408 to S410 are carried out. On the other hand, if any of the calculated absolute values ​​is greater than the threshold value (No), step S411 is carried out.

[0064] In S408, an average value A of the M Lag values ​​is calculated.

[0065] In S409, the absolute value of the difference between the average value A of the M Lag values ​​and the Lag value X of the divided section N is compared with a threshold value. If the absolute value of the difference is equal to or greater than the threshold value (Yes), the original data of the Lag value X of the divided section N is determined to be erroneous, and in S410, the Lag value X of the divided section N is corrected by replacing it with the average value A. On the other hand, if the absolute value of the difference is less than the threshold value (No), the original data of the Lag value X of the divided section N is normal, so replacement with the average value A is not performed, and the original data of the Lag value X of the divided section N is used as is.

[0066] For a frequency width ΔX of the divided section N, the frequency width of the concatenated data is M × ΔX. By using such a wide frequency width ΔX, it is possible to prevent a decrease in the similarity between the reference signal and the measurement signal. In addition, using the average value A stabilizes the value.

[0067] In S411, M Lag values ​​are calculated, and the value immediately before a large fluctuation occurs is substituted for Lag value X of divided section N.

[0068] The process of S411 is performed as a countermeasure against data distortion that occurs when concatenated data straddles a distorted section. As an example, we will explain a case where divided section N is an error section and distortion occurs in divided section N+2. Here, M is set to 4.

[0069] For example, as shown in Figure 5(B), the Lag value of the concatenated data for the divided sections N-3 to N and N-2 to N+1, which do not include the divided section N+2 in which distortion occurs (hereinafter referred to as the distorted section), is 0, and the Lag value of the concatenated data for the divided sections N-1 to N+2 and N to N+3, which include the distorted section N+2, is 10,000.

[0070] In this case, if the processes of S408 to S410 are performed, 5000 (= (0 + 0 + 10000 + 10000) / 4) is calculated as the average value A of the M Lag values ​​in S408. Then, in S409, the absolute value of the difference between the average value A of the M Lag values ​​and the Lag value X of the divided section N is |5000 - 0| = 5000, so the original data for the Lag value X of the divided section N is determined to be erroneous. Therefore, in S410, the Lag value X of the divided section N is replaced with the average value A, 5000.

[0071] Similarly, the original data of 0 for Lag value X in division section N+1 is determined to be an error and is replaced with average value A of 7500. In this way, when concatenated data straddles a distorted section, the processed data (shown by the dotted circle in Figure 5(C)) will be distorted compared to the normal data (shown by the solid circle in Figure 5(C)).

[0072] Therefore, to prevent this, the process of S411 is performed.

[0073] In this example, for the target divided interval N, the Lag value of the concatenated data for divided intervals N-3 to N and N-2 to N+1 is 0, and the Lag value of the concatenated data for divided intervals N-1 to N+2 and N to N+3, which include the distortion interval N+2, is 10000, so the value fluctuates greatly between divided intervals N-2 to N+1 and N-1 to N+2. Therefore, the Lag value X for divided interval N is substituted with the Lag value of 0 for divided interval N-2 to N+1, which is the value immediately before the large fluctuation in value.

[0074] Similarly, for the target divided section N+1, the Lag value of the concatenated data for divided sections N-2 to N+1 is 0, and the Lag value of the concatenated data for divided sections N-1 to N+2, N to N+3, and N to N+4 is 10000, so there is a large fluctuation in value between divided sections N-2 to N+1 and N-1 to N+2. Therefore, the Lag value X for divided section N+1 is substituted with the Lag value of 0 for divided sections N-2 to N+1, which is the value immediately before the large fluctuation.

[0075] After S410 or S411, S412 is performed.

[0076] In S412, 1 is added to E in the error section E, and the process proceeds to the next error section.

[0077] Then, in S413, the error section E reaches the last error section (E=E END If the last error section has been reached (Yes), the process ends. If the end of the divided section has not been reached, the process of S404 is performed.

[0078] After the process of S400 is completed, S203 is performed.

[0079] As described above, according to the present invention, even if a cross-correlation error occurs due to narrowing of the frequency width ΔX of the divided sections and false distortion is detected, correct measurement data can be estimated by replacing the false distortion with correction data, thereby reducing the possibility of erroneous measurements.

[0080] Measurement results when S300 and S400 of the present invention are applied and when they are not applied will be described with reference to Fig. 6. Fig. 6 is a diagram showing the measurement results. In Fig. 6, the horizontal axis represents the position [m] in the optical fiber, and the vertical axis represents the strain [ε / m]. Curve I shows the case when S300 and S400 are not applied (original data), and curve II shows the case when S300 and S400 are applied (corrected data).

[0081] Shown here are the measurement results when a strain of 170 με was applied to the 12-14.35 m section. In the original data, a waveform can be observed from around 12 m, but a response is seen in the entire section up to the 30 m point, making it difficult to identify the strain. In contrast, in the corrected data, it can be seen that a strain equivalent to that applied to the section where strain was applied is observed. In this way, measurement errors can be avoided by applying this algorithm. [Explanation of symbols]

[0082] 10 Frequency Swept Light Source 11, 21 1:99 Junction 20 Main interference system 22 Circulator 23, 31, 33 50:50 branch 30 Auxiliary interference system 32 Delay optical fiber 40 Polarizing Beam Splitter 50 Optical Fiber 60 Optical signal acquisition unit 61 Photoelectric converter 62 ADC 63 Processing Unit

Claims

1. a step of dividing the reference signal and the measurement signal obtained by the frequency domain optical reflectometry by a frequency width ΔX and performing cross-correlation processing of the reference signal and the measurement signal for each divided section to calculate the Lag value X; extracting the target divided section N as an error section when the average value of the Lag values ​​X in a plurality of adjacent divided sections, including the target divided section N and sections before and after the target divided section N, is equal to or greater than a preset threshold value; a step of generating M pieces of concatenated data by concatenating M consecutive divided sections including the divided section N extracted as an error section, and performing cross-correlation processing between the reference signal and the measurement signal for each of the M pieces of concatenated data to calculate a Lag value; calculating the absolute value of the difference between each of the M Lag values ​​and the Lag value X of the corresponding divided section N; a step of calculating an average value A of the M Lag values ​​when all the calculated absolute values ​​are equal to or less than a predetermined threshold, and substituting the average value A for the Lag value X of the divided section N when the absolute value of the difference between the Lag value X of the divided section N and the average value A is equal to or greater than a predetermined threshold; a step of substituting the Lag value immediately before the absolute value of the difference between the M Lag values ​​and the Lag value X of the divided section N changes significantly, when the absolute value of the difference between any of the M Lag values ​​and the Lag value X of the divided section N is greater than a preset threshold value; and A process of converting the Lag value obtained for each divided section into strain or temperature. A strain or temperature measurement method comprising:

2. The number M of connected data is equal to or greater than the value obtained by dividing the length of the optical fiber to be measured by the distance at which an error occurs in a steady state, and ｎ fulfill The strain or temperature measuring method according to claim 1 .

3. a processing unit to which a reference signal and a measurement signal obtained by frequency domain optical reflectometry are input, a means for dividing the frequency range by ΔX and performing cross-correlation processing of the reference signal and the measurement signal for each divided section to calculate a Lag value X; means for extracting a target divided section N as an error section when an average value of Lag values ​​X in a plurality of adjacent divided sections, including the target divided section N and sections before and after the target divided section N, is equal to or greater than a preset threshold value; a means for generating M pieces of concatenated data by concatenating M consecutive divided sections including a divided section N extracted as an error section, and for each of the M pieces of concatenated data, performing cross-correlation processing between a reference signal and a measurement signal to calculate a Lag value; means for calculating the absolute value of the difference between each of the M Lag values ​​and the Lag value X of the corresponding divided section N; a means for calculating an average value A of the M Lag values, which is executed when all the calculated absolute values ​​are equal to or less than a predetermined threshold, and substituting the average value A for the Lag value X of the divided section N when the absolute value of the difference between the Lag value X of the divided section N and the average value A is equal to or greater than a predetermined threshold; means for substituting the Lag value immediately before the absolute value of the difference between the M Lag values ​​and the Lag value X of the division section N changes significantly when the absolute value of the difference between any of the M Lag values ​​and the Lag value X of the division section N is greater than a preset threshold value; and Means for converting the Lag value obtained for each divided section into strain or temperature An optical fiber sensor comprising:

4. The number M of connected data is equal to or greater than the value obtained by dividing the length of the optical fiber to be measured by the distance at which an error occurs in a steady state, and ｎ fulfill 4. The optical fiber sensor according to claim 3.

5. a processing unit to which a reference signal and a measurement signal obtained by frequency domain optical reflectometry are input, a means for dividing the frequency range by ΔX and performing cross-correlation processing of the reference signal and the measurement signal for each divided section to calculate a Lag value X; means for extracting a target divided section N as an error section when an average value of Lag values ​​X in a plurality of adjacent divided sections, including the target divided section N and sections before and after the target divided section N, is equal to or greater than a preset threshold value; a means for generating M pieces of concatenated data by concatenating M consecutive divided sections including a divided section N extracted as an error section, and for each of the M pieces of concatenated data, performing cross-correlation processing between a reference signal and a measurement signal to calculate a Lag value; means for calculating the absolute value of the difference between each of the M Lag values ​​and the Lag value X of the corresponding divided section N; a means for calculating an average value A of the M Lag values, which is executed when all the calculated absolute values ​​are equal to or less than a predetermined threshold, and substituting the average value A for the Lag value X of the divided section N when the absolute value of the difference between the Lag value X of the divided section N and the average value A is equal to or greater than a predetermined threshold; means for substituting the Lag value immediately before the absolute value of the difference between the M Lag values ​​and the Lag value X of the division section N changes significantly when the absolute value of the difference between any of the M Lag values ​​and the Lag value X of the division section N is greater than a preset threshold value; and Means for converting the Lag value obtained for each divided section into strain or temperature A program to function as a

6. The number M of connected data is equal to or greater than the value obtained by dividing the length of the optical fiber to be measured by the distance at which an error occurs in a steady state, and ｎ fulfill The program according to claim 5.

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