How to calibrate measuring equipment

Abstract

To make it possible to use a measurement value, measured before replacement, as a comparison target even when a measurement device using an optical fiber cable is replaced.SOLUTION: A calibration method for a measurement device includes: a first measurement step of measuring a quantity of state at every predetermined first distance interval d1 over a longitudinal direction of an optic fiber cable 10 by means of a first measurement device 20; a second measurement step of measuring a quantity of state at every predetermined second distance interval d2 in the longitudinal direction of the optical fiber cable 10 by means of a second measurement device 21 different from the first measurement device 20; and a correction step of correcting a second data series so as to increase a degree of correlation between a first data series of the quantity of state measured at every first distance interval d1 in the first measurement step and a second data series of the quantity of state measured at every second distance interval d2 in the second measurement step.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for calibrating a measurement device. [Background technology]

[0002] Patent Document 1 discloses a method for measuring the amount of strain in a concrete structure by using an optical fiber cable buried in the structure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-17656 A Summary of the Invention [Problem to be solved by the invention]

[0004] As in the invention described in Patent Document 1, in order to understand the aging of a structure using an optical fiber cable, it is necessary to continue measurements over a relatively long period of time. Optical fiber cables are not prone to deterioration even with long-term use and do not require replacement, but the measuring device that measures the amount of strain based on the wavelength of scattered light returning from the optical fiber cable is an electronic device and is prone to malfunction after many years of use, so it needs to be replaced periodically.

[0005] However, the distance interval at which a measuring device can measure the amount of strain depends on the clock speed of the CPU (Central Processing Unit) and the clock speed of the data converter installed in the measuring device, as well as constants used in the process of calculating the distance interval, and since there will be some difference in the clock speed even for measuring devices with the same specifications, it is difficult to ensure that the distance interval at which the amount of strain is measured is strictly the same before and after replacing the measuring device.

[0006] In particular, the longer the optical fiber cable used for measurement, the greater the degree of deviation in the position at which the strain amount is measured before and after replacement of the measurement device due to the accumulated deviation in the measurement distance interval. Therefore, if the measurement device is simply replaced, the tendency of the strain amount measured before and after the replacement will change, and past measurement data measured before the replacement cannot be used for comparison, which may result in an inability to accurately grasp the aging of the structure.

[0007] An object of the present invention is to make it possible to use, as a comparison, measurement values ​​measured before replacement of a measuring device using an optical fiber cable, even when the measuring device is replaced. [Means for solving the problem]

[0008] The present invention is a method for calibrating a measuring device that measures state quantities indicating the state of an object to be measured at multiple locations using an optical fiber cable, and includes: a first measurement step of measuring the state quantities at predetermined first distance intervals along the length of the optical fiber cable using a first measuring device; a second measurement step of measuring the state quantities at predetermined second distance intervals along the length of the optical fiber cable using a second measuring device separate from the first measuring device; and a correction step of correcting the second data series so that a degree of correlation between a first data series of the state quantities measured at the first distance intervals in the first measurement step and a second data series of the state quantities measured at the second distance intervals in the second measurement step is increased. Effect of the Invention

[0009] According to the present invention, even when a measuring device using an optical fiber cable is replaced, the measurement value measured before the replacement can be used as a comparison target. [Brief description of the drawings]

[0010] [Figure 1] 1 is a perspective view showing an outline of a concrete structure in which the amount of strain is measured by an optical fiber cable; [Diagram 2]4 is a flowchart showing a procedure for calibrating a measurement device according to a method for calibrating a measurement device according to an embodiment of the present invention. [Diagram 3] 10 is a graph for explaining an estimated second data sequence obtained from the second data sequence in the correction step of the calibration method. [Figure 4] 11 is a graph for explaining a shift amount used in a correction step of the calibration method. [Diagram 5] 11 is a graph for explaining a magnification ratio used in a correction step of the calibration method. [Figure 6] 11 is a graph for explaining an average value ratio used in a correction step of the calibration method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a method for calibrating a measurement device according to an embodiment of the present invention will be described with reference to the drawings.

[0012] The measuring device 20 is a device that uses an optical fiber cable 10 as a sensor section, and measures a state quantity indicating the state of an object to be measured at a plurality of locations using the optical fiber cable 10. Fig. 1 shows an example in which the object to be measured is a concrete structure 1 made of reinforced concrete (RC) or reinforced steel concrete (SRC), and the amount of internal strain is measured as a state quantity using the optical fiber cable 10 buried in the concrete structure 1.

[0013] The object to be measured is not limited to an artificial structure, but may be, for example, natural ground or the ground. In this case, the optical fiber cable 10 is buried in a borehole excavated in the natural ground or the ground, and is used to detect the occurrence of a landslide or the like by measuring strain in the ground. Also, the optical fiber cable 10 does not need to be buried, and may be attached to the surface of the concrete structure 1 or the surface of a reinforcing bar. Also, the state quantity measured using the optical fiber cable 10 is not limited to the amount of strain, but may be temperature.

[0014] In the example shown in Fig. 1, an optical fiber cable 10 is buried in a rectangular wave-like meandering manner in a reinforced concrete structure 1 having an L-shaped cross section, and the optical fiber cable 10 is connected to a measuring device 20 via a connector 11 and a patch cable 12. Note that the shape of the concrete structure 1 and the layout of the optical fiber cable 10 shown in Fig. 1 are merely examples and are not limiting. For example, two or more optical fiber cables may be buried, or may be buried linearly.

[0015] Generally, optical fiber cables have a property of slightly scattering incident pulse light backward, and by utilizing this property, it is possible to measure the amount of strain at multiple positions in the optical fiber cable. Specifically, since the frequency of the backward scattered light (Brillouin scattered light) depends on the amount of strain in the optical fiber cable, the amount of strain in the optical fiber cable can be measured by injecting pulse light into the optical fiber cable from one end and measuring the frequency of the scattered light that is reflected and returns to the one end. In addition, by measuring the time from when pulse light is injected into the optical fiber cable from one end to when the scattered light generated in the optical fiber cable returns to the one end, the position where the scattered light occurs, i.e., the position where the strain occurs in the optical fiber cable, can be measured. In addition, similar to the amount of strain, it is also possible to continuously grasp the temperature along the direction in which the optical fiber cable is extended.

[0016] As a method for measuring the amount of strain and its occurrence position using an optical fiber cable, a known method such as a BOTDR (Brillouin Optical Time Domain Reflectometer) can be used. As the optical fiber cable, a fiber Bragg grating (FBG) provided with a plurality of diffraction gratings may be used, but in this case, since the amount of strain is measured only in the portion where the diffraction grating is provided, it is preferable to use a general optical fiber cable in order to continuously grasp the amount of strain along the direction in which the optical fiber cable is extended.

[0017] By utilizing these properties of the optical fiber cable, it is possible to grasp the changes over time of the entire concrete structure 1 by measuring the amount of strain and temperature generated within the concrete structure 1 continuously along the direction in which the optical fiber cable 10 is extended, and in a planar manner along the plane in which the optical fiber cable 10 is arranged.

[0018] Here, in order to understand the changes over time of a structure, etc. using the optical fiber cable 10, it is necessary to perform continuous measurements over a relatively long period of time, such as several years to several decades, and to compare and analyze multiple measurement data measured in the past with the most recently measured measurement data.

[0019] The optical fiber cable 10, which functions as a measurement sensor, is not likely to deteriorate even with long-term use and therefore does not need to be replaced. However, the measuring device 20, which calculates state quantities such as strain and temperature based on the wavelength of the scattered light returning from the optical fiber cable 10, is an electronic device and may break down over many years of use and require replacement.

[0020] Furthermore, when a new measuring device with significantly improved measurement performance is developed, the measuring device 20 may be replaced.

[0021] That is, the fiber optic cable 10 may be in permanent use, while the measurement device 20 may be replaced.

[0022] However, in general, the distance interval at which a measuring device can measure distortion amounts, etc., depends on the clock speed of the CPU (Central Processing Unit) and the clock speed of the data converter (ADC: Analog to Digital Converter, DAC: Digital to Analog Converter) provided in the measuring device. For example, even measuring devices with the same specifications will have slightly different clock speeds, so it is difficult to ensure that the distance interval at which distortion amounts, etc. are measured is strictly the same before and after replacing the measuring device.

[0023] In addition, the distance intervals at which the amount of strain, etc. is measured depend on constants that are preset in the measuring device, such as the speed of light, which are used in the process of calculating the distance intervals. Therefore, for example, if the measuring device is replaced with one from a manufacturer different from the previous one, there is a risk that the distance intervals at which the amount of strain, etc. is measured will be slightly different from that before the replacement.

[0024] Furthermore, the longer the length of the optical fiber cable 10 used for measurement, the more likely it is that the deviation in the measurement distance interval will accumulate, resulting in a greater deviation in the position at which the amount of strain, etc. is measured before and after replacing the measurement device.

[0025] Therefore, if the measuring device is simply replaced and measurements are continued, the trends in the amount of strain, etc. measured before and after the replacement will change, and past measurement data measured before the replacement will not be able to be used for comparison, which may result in an inability to accurately grasp the changes in the structure over time.

[0026] Therefore, in this embodiment, by calibrating the replaced measuring device 21 using a calibration method described below, it becomes possible to use the past measurement data measured by the measuring device 20 before replacement as a comparison subject.

[0027] A calibration method performed when replacing the measuring device 20 shown in Fig. 1 (hereinafter referred to as "old device 20") with a new measuring device 21 (hereinafter referred to as "new device 21") will be described below with reference to Figs. 2 to 6. Fig. 2 is a flow chart showing the calibration procedure of the new device 21, Fig. 3 is a graph for explaining an estimated second data sequence obtained from the second data sequence measured by the new device 21, Fig. 4 is a graph for explaining a shift amount used in a correction process described later, Fig. 5 is a graph for explaining an enlargement / reduction ratio used in the correction process, and Fig. 6 is a graph for explaining an average value ratio used in the correction process.

[0028] As shown in FIG. 2, in the calibration method according to this embodiment, first, in step S11 (first measurement step), the amount of strain is measured by the old device 20 (first measurement device) using the optical fiber cable 10.

[0029] The distance interval (first distance interval d1) at which the measurement is performed by the old device 20 is calculated by the following formula (1). d1=t1·c1 / n (1)

[0030] In the above formula (1), t1 is the sampling period of the old device 20, and is a time that is set mainly based on the clock frequency of the CPU and data converter provided in the old device 20. Also, c1 is the speed of light in a vacuum (approximately 300,000 km / s), and is a value that is set in advance in the calculation unit of the old device 20. The number of significant digits that is set differs depending on the measurement device and its manufacturer, and is, for example, 2.99×10 8 m / s or 2.99792×10 8 For example, it may be set to m / s.

[0031] Furthermore, n in the above formula (1) is the refractive index of the core of the optical fiber cable 10, and is a value that is specific to the optical fiber cable 10. This value will not change unless the optical fiber cable 10 is replaced.

[0032] Thus, in step S11 (first measurement step), the old device 20 measures the amount of strain at predetermined first distance intervals d1 along the length of the optical fiber cable 10, and obtains a first data series consisting of the distance along the length of the optical fiber cable 10 and the amount of strain at each distance. Note that the first data series is a data series obtained by standardizing the measurement values ​​in order to remove outliers caused by the influence of noise, etc. Normalization may be adopted as a method for processing the measurement values, but it is preferable to adopt standardization when the outliers are relatively large.

[0033] Subsequently, in step S12 (second measurement step), the amount of strain is measured using the optical fiber cable 10 by a new device 21 (second measuring device).

[0034] The distance interval (second distance interval d2) at which the measurement is performed by the new device 21 is calculated by the following formula (2). d2=t2·c2 / n (2)

[0035] In the above formula (2), t2 is the sampling period of the new device 21, and is a time that is set mainly based on the clock rate of the CPU and data converter provided in the new device 21. Also, c2 is the speed of light in a vacuum (approximately 300,000 km / s), and is a value that is set in advance in the calculation unit of the new device 21. Also, n is the refractive index of the core of the optical fiber cable 10, and is a value specific to the optical fiber cable 10.

[0036] Thus, in step S12 (second measurement step), the new device 21 measures the amount of strain at predetermined second distance intervals d2 along the length of the optical fiber cable 10, and obtains a second data series consisting of the distance in the length direction of the optical fiber cable 10 and the amount of strain at each distance. The second data series is a data series obtained by standardizing the measurement values, similar to the first data series.

[0037] Next, in step S13 and after, a correction step is executed to correct the second data series so as to increase the degree of correlation between the first data series of the distortion amount measured at every first distance interval d1 by the old device 20 and the second data series of the distortion amount measured at every second distance interval d2 by the new device 21. Note that the degree of correlation is the degree to which the waveforms (tendencies) of two data series are similar when compared, and whether the degree of correlation is large or not can be determined based on, for example, a correlation coefficient described later.

[0038] As described above, it is difficult to make the first distance interval d1 measured by the old device 20 and the second distance interval d2 measured by the new device 21 exactly the same interval. In addition, it is also difficult to compare data series measured at different intervals and find the degree of correlation therebetween.

[0039] For this reason, first, in step S13, an estimated second data sequence is obtained by converting the measurement interval of the second data sequence from the second distance interval d2 to the first distance interval d1.

[0040] Specifically, as shown in Fig. 3, an estimated amount of distortion (estimated state quantity) estimated to be measured when the amount of distortion is measured at every first distance interval d1 by the new device 21 is calculated by linear interpolation using the amount of distortion of the second data series, i.e., the amount of distortion measured at every second distance interval d2 (black circles in Fig. 3). The data series of the estimated amount of distortion at every first distance interval d1 calculated by the interpolation in this way (black triangles in Fig. 3) is regarded as an estimated second data series. Note that the interpolation method is not limited to linear interpolation, and may be a higher-order interpolation such as spline interpolation.

[0041] Then, in step S14, a correlation coefficient indicating the degree of correlation between the first data sequence and the estimated second data sequence is calculated.

[0042] Here, if the optical path length within the old device 20 and the new device 21, i.e., the path length from when the light is guided into the device to when it reaches the photodetector, is different, the origin position, which is the starting point of the measurement, may change. Similarly, if the patch cable 12 is also replaced at the same time when replacing the old device 20 with the new device 21, the difference in the length of the patch cable 12 may cause the origin position, which is the starting point of the measurement, to change.

[0043] Therefore, in order to obtain the degree of correlation between the first data sequence and the estimated second data sequence more accurately, it is necessary to shift the estimated second data sequence by a predetermined shift amount S in the length direction of the optical fiber cable 10, as shown in Fig. 4. The shift amount S is a displacement amount by which the origin position of the data of the estimated second data sequence is moved in the length direction of the optical fiber cable 10 with respect to the first data sequence, and the movement direction of the origin position may be not only the positive direction in the length direction of the optical fiber cable 10 but also the negative direction as shown in Fig. 4.

[0044] 5, the measured total distance L1 of the first data sequence and the measured total distance L2 of the estimated second data sequence may differ depending on the difference between the first distance interval d1 measured by the old device 20 and the second distance interval d2 measured by the new device 21. Furthermore, the total distances L1 and L2 may differ due to differences in the optical path lengths in the devices 20 and 21 and the lengths of the patch cables 12.

[0045] The measured total distance is a measured distance calculated by multiplying the distance interval calculated by the above formula (1) or formula (2) by the total number of data, and although it is approximately equal to the actual length of the optical fiber cable 10, it does not indicate the actual length of the optical fiber cable 10.

[0046] Therefore, in order to obtain the degree of correlation between the first data sequence and the estimated second data sequence more accurately, it is necessary to not only set the above-mentioned shift amount S but also multiply the estimated second data sequence by a scaling factor R that expands or reduces the estimated second data sequence in the length direction of the optical fiber cable 10. The scaling factor R is a ratio that expands or reduces the estimated second data sequence in the length direction of the optical fiber cable relative to the first data sequence, and is a value of about 1, for example, 0.95 to 1.05.

[0047] In this way, the calculation of the correlation coefficient in step S14 is performed while changing the combination of the shift amount S and the enlargement / reduction ratio R. Then, in step S15, the combination of the shift amount S and the enlargement / reduction ratio R that maximizes the correlation coefficient is extracted.

[0048] The correlation coefficient is calculated using a known calculation method in statistics, such as Pearson's product moment correlation coefficient or cosine similarity, which causes the correlation coefficient to approach 1 when the degree of correlation is high. The correlation coefficient may also be calculated using a known calculation method, such as Euclidean distance or Mahalanobis distance, which causes the correlation coefficient to approach 0 when the degree of correlation is high. In this case, in step S15, a combination of the shift amount S and the scaling factor R that causes the correlation coefficient to be closest to 0 is extracted. The method of calculating the correlation coefficient is not limited to the above method, and any method that is used to obtain the degree of correlation in statistics in general may be used.

[0049] In calculating the correlation coefficient, the larger the range of the shift amount S and the range of the enlargement / reduction ratio R are, and the smaller the minimum unit of the shift amount S and the minimum unit of the enlargement / reduction ratio R are, the more accurately the correlation can be obtained, but the longer the time required for the calculation process. Therefore, the ranges and minimum units of the shift amount S and the enlargement / reduction ratio R are appropriately set according to the required accuracy and the allowable calculation process time.

[0050] Next, in step S16, the estimated second data sequence is corrected using the extracted shift amount S and enlargement / reduction ratio R.

[0051] Here, as shown by the solid line in the lower part of Fig. 6, the estimated second data series corrected by the extracted shift amount S and expansion / contraction ratio R has a higher correlation in the distance direction (the length direction of the optical fiber cable 10) with respect to the first data series shown by the solid line in the upper part of Fig. 6, but the correlation of the strain amount, which is a measured value, remains small. In other words, the difference occurring between the calculation process for calculating the strain amount in the old device 20 and the calculation process for calculating the strain amount in the new device 21 has not yet been corrected.

[0052] Therefore, in the next step S17, the estimated distortion amount (estimated state amount) of the estimated second data sequence is corrected (state amount correction) to increase or decrease according to the distortion amount of the first data sequence.

[0053] Specifically, first, in a section where the data of the corrected estimated second data series and the first data series overlap in the distance direction (the length direction of the optical fiber cable 10), a first average value A1 (dashed line in Figure 6), which is the average value of the measurement values ​​of the first data series, and a second average value A2 (dashed line in Figure 6), which is the average value of the measurement values ​​of the corrected estimated second data series, are calculated.

[0054] Then, an average value ratio (A1 / A2) which is the ratio between the first average value A1 and the second average value A2 is obtained as a correction coefficient for adjusting the estimated amount of distortion of the estimated second data sequence to the amount of distortion of the first data sequence.

[0055] Then, by multiplying the estimated second data sequence by the average value ratio (A1 / A2) thus calculated, the estimated distortion amount of the estimated second data sequence is made to match the distortion amount of the first data sequence. As a result, the degree of correlation between the distortion amount of the first data sequence and the estimated distortion amount of the estimated second data sequence becomes large.

[0056] As a correction coefficient for adjusting the estimated distortion amount of the estimated second data sequence to the distortion amount of the first data sequence, an integral value ratio (I1 / I2) may be used instead of the average value ratio (A1 / A2) as described above. The integral value ratio (I1 / I2) is found by calculating a first integral value (I1) which is the integral value of the first data sequence and a second integral value (I2) which is the integral value of the estimated second data sequence after correction, respectively, in a section where the data of the estimated second data sequence after correction and the first data sequence overlap in the distance direction, as shown in Fig. 6.

[0057] The shift amount S, the enlargement / reduction ratio R, and the average value ratio (A1 / A2) obtained in the correction process (steps S13 to S17) as described above are stored as correction coefficients in step S18.

[0058] Then, by correcting the data series measured by the new device 21 using the stored shift amount S, enlargement / reduction ratio R, and average value ratio (A1 / A2), it is possible to obtain a data series that can be compared with the past data series measured by the old device 20.

[0059] According to the above embodiment, the following effects are achieved.

[0060] According to the calibration method for the measuring device of this embodiment, a second data series of distortion amounts (state quantities) measured at every first distance interval d1 by the old device 20, which is the measuring device before replacement, is corrected so as to increase the correlation between the first data series of distortion amounts (state quantities) measured at every second distance interval d2 by the new device 21, which is the measuring device after replacement.

[0061] In this way, by correcting the second data series measured by the new device 21 so that the trend (waveform) of the distortion amount measured by the new device 21 approaches the trend of the distortion amount measured by the old device 20, it is possible to connect the data series measured by the old device 20 and the data series measured by the new device 21, that is, to smoothly link data from the old device 20 to the new device 21. As a result, the past data series measured by the old device 20 can be used as a comparison target for the data series measured by the new device 21.

[0062] As a result, when the optical fiber cable 10 is buried in, for example, a concrete structure 1, even if the measuring device is replaced from the old device 20 to a new device 21, the changes in the concrete structure 1 over time can be accurately grasped over a long period of time.

[0063] Next, modified examples of the above embodiment will be described. The following modified examples are also within the scope of the present invention, and it is possible to combine the configurations shown in the modified examples with the configurations described in the above embodiment, or to combine the configurations described in the following different modified examples.

[0064] In the above embodiment, in step S17, a state quantity correction is performed to increase or decrease the estimated distortion amount of the estimated second data sequence in accordance with the distortion amount of the first data sequence. When the time elapsed between the measurement of the distortion amount by the old device 20 and the measurement of the distortion amount by the new device 21 is relatively short and it is estimated that there will be almost no change in the state quantity such as the distortion amount, it is preferable to perform the state quantity correction performed in the above step S17. On the other hand, when the time elapsed after the old device 20 breaks down is relatively long due to a delay in obtaining the new device 21, etc., and there is a possibility that a change has occurred in the state quantity such as the distortion amount, it is preferable not to perform the state quantity correction performed in the above step S17, since there is a possibility that the magnitude of the state quantity has actually changed.

[0065] In the above embodiment, the step of converting the measurement interval of the second data series from the second distance interval d2 to the first distance interval d1 by interpolation is performed before changing the shift amount S and the expansion / reduction rate R. Alternatively, the conversion of the measurement interval of the second data series may be performed every time either one or both of the shift amount S and the expansion / reduction rate R are changed. In this case, when calculating the correlation coefficient in step S14, it is possible to match not only the measurement interval but also the position where the strain amount is measured in the distance direction (the length direction of the optical fiber cable 10) between the first data series and the estimated second data series. Therefore, the degree of correlation between the first data series and the estimated second data series can be obtained with higher accuracy.

[0066] In the above embodiment, in step S12 (second measurement step), the measurement values ​​are standardized to obtain the second data series. The timing of standardization is not limited to this, and standardization may be performed after the measurement interval of the measurement values ​​measured by the new device 21 is converted from the second distance interval d2 to the first distance interval d1 by interpolation. In this case, in step S12, non-standardized measurement data is obtained as the second data series.

[0067] In the above embodiment, the second distance interval d2 at which the new device 21 performs the measurement is set to an interval substantially equal to the first distance interval d1 at which the old device 20 performs the measurement. Alternatively, the second distance interval d2 at which the new device 21 performs the measurement may be set to a larger interval, for example, two or more times larger than the first distance interval d1 at which the old device 20 performs the measurement, in order to reduce the data volume. Even when the second distance interval d2 is set to a relatively large value in this way, it is possible to calculate data for each first distance interval d1 by interpolation. Therefore, as in the above embodiment, if correction coefficients such as the shift amount S, the enlargement / reduction ratio R, and the average value ratio (A1 / A2) are obtained when replacing the device, the past data series measured by the old device 20 can be used as a comparison target for the data series measured by the new device 21.

[0068] In the above embodiment, the object to be measured of the optical fiber cable 10 is the concrete structure 1. The object to be measured is not limited to a solid such as the concrete structure 1, and may be something that has fluidity such as gas or liquid.

[0069] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments.

[0070] In the above embodiment, the optical fiber cable 10 is used to grasp the aging of a concrete structure, but the optical fiber cable may be laid over a relatively wide area, such as within the grounds of a facility, to detect the occurrence of an abnormality such as a fire from a change in temperature. In this case, the object to be measured is air. [Explanation of symbols]

[0071] 1. Concrete structure (measurement object) 10...Fiber optic cable 20. Old equipment (measuring equipment, first measuring equipment) 21 New equipment (measuring equipment, second measuring equipment)

Claims

1. A calibration method for a measuring device that measures a state quantity indicating the state of an object to be measured at a plurality of locations by an optical fiber cable, comprising: a first measurement step of measuring the state quantity at predetermined first distance intervals over the length direction of the optical fiber cable by a first measuring device; a second measurement step of measuring the state quantity at predetermined second distance intervals over the length direction of the optical fiber cable by a second measuring device different from the first measuring device; a correction step of correcting the second data series so that the correlation degree between a first data series of the state quantity measured at each of the first distance intervals in the first measurement step and a second data series of the state quantity measured at each of the second distance intervals in the second measurement step becomes large. A calibration method for a measuring device.

2. In the correction step, an estimated state quantity estimated to be measured when the second measuring device measures the state quantity at each of the first distance intervals is obtained by interpolation using the state quantity of the second data series, and a data series of the estimated state quantity obtained by the interpolation is used as an estimated second data series; a correction coefficient for correcting the estimated second data series is obtained so that the correlation degree between the first data series and the estimated second data series becomes large. The calibration method for a measuring device according to Claim 1.

3. The correction coefficient is a shift amount for shifting the second data series or the estimated second data series with respect to the first data series in the length direction of the optical fiber cable. The calibration method for a measuring device according to Claim 2.

4. The correction coefficient is a magnification or reduction ratio for magnifying or reducing the second data series or the estimated second data series with respect to the first data series in the length direction of the optical fiber cable. The calibration method for a measuring device according to Claim 2 or 3.

5. In the correction step, a state quantity correction for increasing or decreasing the estimated state quantity of the estimated second data series in accordance with the state quantity of the first data series is further performed. The calibration method for a measuring device according to any one of Claims 2 to 4.

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