Distributed temperature measurement temperature calibration device

Abstract

The utility model relates to the technical field of optical fiber temperature measurement, in particular to a distributed temperature measurement temperature calibration device which comprises a heat preservation shell, a heating cavity is arranged in the heat preservation shell, a cylindrical heating core column is arranged in the heating cavity, a heating piece is arranged at one end of the heating core column, and a first temperature sensor is further fixedly installed on the heating core column. Two sections of calibration optical fibers are wound on the peripheral surface of the heating core column, the two ends of the temperature measuring optical fiber are connected with the two sections of calibration optical fibers respectively, one end, away from the temperature measuring optical fiber, of one section of calibration optical fiber is connected with a reference optical fiber, and a heat preservation layer used for wrapping the heating core column is arranged in the heating cavity; a heating sheet is placed at the top of an aluminum alloy heating core column, a calibration optical fiber is tightly wound on the outer wall of the heating core column, and gaps between the heating core column and the heating sheet and between the heating core column and the calibration optical fiber are filled with heat-conducting silicone grease, so that the calibration optical fiber is uniformly heated.

Description

Technical Field

[0001] The utility model relates to the technical field of optical fiber temperature measurement, in particular to a distributed temperature measurement and temperature calibration device. Background Art

[0002] DTS temperature measurement technology (distributed optical fiber temperature measurement technology) can realize long-distance continuous temperature monitoring and is suitable for a variety of industrial production and safety monitoring scenarios. As costs continue to decrease, the application of DTS temperature measurement technology has become ubiquitous in the industrial field. However, there are still many factors that hinder the field application of this technology. One of the important factors is the lack of an effective calibration method to correct the temperature deviation introduced by Rayleigh scattering in the optical fiber. When light propagates in the optical fiber, Raman scattering is generated by inelastic collisions. The DTS temperature measurement technology uses the temperature-sensitive effect of Raman scattering intensity to detect temperature changes. However, when light propagates in the optical fiber, it not only generates Raman scattering, but also Rayleigh scattering with higher intensity. In the DTS system structure, WDM (wavelength division multiplexer) is used to isolate the two-way Raman scattering and Rayleigh scattering from each other, and the isolation of WDM is usually not high enough to completely remove the influence of Rayleigh scattering, which is several orders of magnitude higher than Raman scattering, in the Raman scattering signal. The intensity of Rayleigh light is independent of temperature, and its own attenuation rate is also different from that of the two-way Raman light. Therefore, the problem of correcting temperature deviation becomes complicated. In addition, the longer the temperature measurement optical cable is, the greater the temperature measurement error caused by this factor at the end of the optical cable.

[0003] At present, during the parameter calibration stage of DTS temperature measurement technology, a water bath is mainly used to perform local constant temperature heating on a part of the optical fiber for temperature calibration. The disadvantage of this traditional method is that it is difficult to operate and not conducive to repeated operation. In addition, there is a certain temperature gradient inside the water bath, and the optical fiber is not heated evenly during the constant temperature heating process, which greatly affects the parameter calibration. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide a distributed temperature measurement and temperature calibration device, which is easy to implement and heats evenly, so as to solve the problems in the prior art.

[0005] In order to solve the above technical problems, the technical solution of the utility model is: a distributed temperature measurement and temperature calibration device, comprising a heat-insulating outer shell, a heating chamber is provided in the heat-insulating outer shell, a cylindrical heating core column is provided in the heating chamber, a heating plate is provided at one end of the heating core column, a first temperature sensor is also fixedly installed on the heating core column, two sections of calibration optical fiber are wrapped on the outer circumference of the heating core column, the two ends of the temperature measuring optical fiber are respectively connected to the two sections of the calibration optical fiber, one end of one section of the calibration optical fiber away from the temperature measuring optical fiber is connected to the reference optical fiber, and an insulation layer for covering the heating core column is provided in the heating chamber.

[0006] As a preferred technical solution, the thermal insulation shell is an EVA thermal insulation shell.

[0007] As a preferred technical solution, the thermal insulation layer is an aerogel thermal insulation layer.

[0008] As a preferred technical solution, the heating core column is an aluminum alloy core column.

[0009] As a further improvement, a constant temperature cavity is further provided in the heat-insulating shell, a wavelength division multiplexer is fixedly installed in the constant temperature cavity, and one end of the reference optical fiber away from the calibration optical fiber is connected to the wavelength division multiplexer.

[0010] As a further improvement, a winding core column is fixedly mounted on the top of the wavelength division multiplexer, a second temperature sensor is fixedly mounted on the winding core column, and the reference optical fiber is wound on the outer circumference of the winding core column.

[0011] After adopting the above technical solution, the beneficial effects of the utility model are:

[0012] (1) The present invention has a compact structure, small size, low power consumption, can be placed inside a standard 3U or 4U instrument, and can be powered by an ordinary switching power supply, which is easy to implement and has strong practicality;

[0013] (2) The present application provides a space for placing the wavelength division multiplexer and the reference optical fiber, which is more convenient to use, and the heat-insulating shell of the EVA material makes the temperature of the reference optical fiber less susceptible to external influences and changes, so the temperature distribution of the reference optical fiber can be more uniform, further reducing the calibration error;

[0014] (3) The present application places a heating plate on the top of the aluminum alloy heating core column, tightly wraps the calibration optical fiber around the outer wall of the heating core column, and fills the gap between the heating core column and the heating plate and between the heating core column and the calibration optical fiber with thermal conductive silicone grease to ensure that the calibration optical fiber is heated evenly;

[0015] (4) The present application provides an aerogel insulation layer so that the temperature of the calibrated optical fiber can be rapidly increased and kept stable for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 It is a schematic diagram of the structure of an embodiment of the utility model;

[0018] Figure 2 is a schematic top view of the bottom shell of an embodiment of the utility model;

[0019] Figure 3 It is a top view schematic diagram of the cover body of an embodiment of the utility model;

[0020] Figure 4 It is a top view schematic diagram of a heating core column of an embodiment of the utility model;

[0021] Figure 5 It is a top view schematic diagram of the annular aerogel felt of an embodiment of the utility model.

[0022] In the figure: 1-insulating shell; 2-bottom shell; 3-cover body; 4-heating chamber; 5-threading hole; 6-heating core column; 7-heating plate; 8-circular groove; 9-first temperature sensor; 10-calibration optical fiber; 11-reference optical fiber; 12-circular aerogel felt; 13-ring-shaped aerogel felt; 14-mounting plate; 15-constant temperature chamber; 16-wavelength division multiplexer; 17-winding core column; 18-second temperature sensor; 19-opening; 20-threading groove. DETAILED DESCRIPTION

[0023] like Figures 1 to 5 As shown, a distributed temperature measurement and temperature calibration device includes a heat-insulating shell 1, which is an EVA heat-insulating shell with good heat-insulating performance. The heat-insulating shell 1 includes a rectangular bottom shell 2, and a cover body 3 is buckled on the top of the bottom shell 2. A circular groove is provided at the left end of the top of the bottom shell 2, and a cylindrical heating chamber 4 is enclosed between the cover body 3 and the circular groove. A threading hole 5 connecting the heating chamber 4 and the left end of the heat-insulating shell 1 is provided between the bottom shell 2 and the cover body 3, which is convenient for the threading of optical fibers and cables.

[0024] A cylindrical heating core column 6 is provided in the heating chamber 4. The heating core column 6 is specifically an aluminum alloy core column with high thermal conductivity. A heating plate 7 is fixedly installed at one end of the heating core column 6. A circular groove 8 for placing the heating plate 7 is provided at the upper end of the heating core column 6. A first temperature sensor 9 is also fixedly installed on the heating core column 6. The first temperature sensor 9 is a thermocouple temperature sensor. A mounting hole is provided on the side wall of the heating core column 6. The first temperature sensor 9 is bonded in the mounting hole or the first temperature sensor 9 is threaded in the mounting hole. Two sections of calibration optical fiber 10 are wound around the outer circumference of the heating core column 6. The two ends of the temperature measuring optical fiber are respectively connected to the two sections of calibration optical fiber 10. One end of one section of the calibration optical fiber 10 away from the temperature measuring optical fiber is connected to the reference optical fiber 11. A thermal insulation layer for covering the heating core column 6 is provided in the heating chamber 4 to keep the temperature of the calibration optical fiber 10 stable.

[0025] The thermal insulation layer is specifically an aerogel thermal insulation layer. Aerogel has an ultra-low thermal conductivity and better thermal insulation. Specifically, the thermal insulation layer includes two circular aerogel felts 12 and one annular aerogel felt 13. The outer diameter of the circular aerogel felt 12 matches the inner diameter of the heating chamber 4. The outer diameter of the annular aerogel felt 13 matches the inner diameter of the heating chamber 4, and the inner diameter matches the outer diameter of the heating core column 6.

[0026] During assembly, a circular mounting plate 14 is fixedly installed at the lower end of the heating core column 6 by screws, and the outer diameter of the mounting plate 14 matches the inner diameter of the heating chamber 4; first, a circular aerogel felt 12 is placed at the bottom of the heating chamber 4; the first temperature sensor 9 is installed on the heating core column 6, and two sections of calibration optical fiber 10 are respectively wound around the side walls of the heating core column 6, and the gap between the heating core column 6 and the calibration optical fiber 10 is filled with thermal conductive silicone grease; the heating core column 6 and the mounting plate 14 are placed in the heating chamber 4, and a nylon with low thermal conductivity is used. The circular aerogel felt 12 and the mounting plate 14 at the bottom of the heating chamber 4 are fixed to the bottom shell 2 by screws at the same time, and then the annular aerogel felt 13 is placed between the inner wall of the heating chamber 4 and the heating core column 6; the heating plate 7 is placed in the circular groove 8 at the top of the heating core column 6, and the gap between the heating core column 6 and the heating plate 7 is also filled with thermal conductive silicone grease; a circular aerogel felt 12 is placed on the top of the heating core column 6, and the cover body 3 is buckled, so that the surrounding of the heating core column 6 is sealed by the aerogel insulation layer to prevent heat loss and uneven temperature distribution. In addition, a reserved groove for the passage of optical fibers and cables is provided between the circular aerogel felt 12 and the annular aerogel felt 13 at the top, and one end of the calibration optical fiber 10, the first temperature sensor 9 and the heating plate 7 are led out through the reserved groove and the threading hole 5, and the first temperature sensor 9 and the heating plate 7 are connected to the PID temperature control module.

[0027] In addition, a rectangular groove is provided at the right end of the top of the bottom shell 2, and a rectangular constant temperature chamber 15 is enclosed between the cover body 3 and the rectangular groove. A wavelength division multiplexer 16 is provided in the constant temperature chamber 15, and the four corners of the wavelength division multiplexer 16 are fixedly installed in the constant temperature chamber 15 by bolts. A cylindrical winding core column 17 is provided at the top of the wavelength division multiplexer 16, and a bottom plate is provided at the lower end of the winding core column 17. The bottom plate is fixedly installed on the top of the wavelength division multiplexer 16 by screws. A second temperature sensor 18 is fixedly installed on the winding core column 17, and the reference optical fiber 11 is wound on the outer peripheral surface of the winding core column 17. Two openings 19 connecting the heating chamber 4 and the constant temperature chamber 15 are provided between the bottom shell 2 and the cover body 3, which are used to place the connection line between the reference optical fiber 11 and the calibration optical fiber 10. The end of the reference optical fiber 11 away from the calibration optical fiber 10 is connected to the wavelength division multiplexer 16. The wavelength division multiplexer 16 is also connected to the photoelectric avalanche diode APD and the pulse laser. The right end of the heat-insulating housing 1 is provided with a threading groove 20 connected to the constant temperature cavity 15, and the pigtails of the photoelectric avalanche diode APD and the pulse laser pass through the threading groove 20. The reference optical fiber 11 is arranged in the heat-insulating housing 1, so that the temperature of the reference optical fiber 11 is not easily affected by external influences and changes. The setting of the heat-insulating layer makes it impossible for the temperature of the heating plate 7 to affect the reference optical fiber 11, so that the temperature distribution of the reference optical fiber 11 can be more uniform, further reducing the calibration error.

[0028] Calibration process:

[0029] Two sections of calibration optical fiber 10 are about 20 meters long each and are wound around the heating core column 6. One end of the first section of calibration optical fiber 10 is connected to the reference optical fiber 11 or the optical switch, and the other end is connected to the head of the temperature measurement optical fiber. One end of the second section of calibration optical fiber 10 is connected to the tail of the temperature measurement optical fiber, and the other end is not connected to any device.

[0030] The temperature T0 of the first temperature sensor 9 installed on the heating core column 6 is read out, and the reading of the first temperature sensor 9 and the reading of the two parts of the calibration optical fiber 10 at the current temperature and the offset behind the optical fiber tail end are recorded.

[0031] At this time, both the Stokes and anti-Stokes lights are mixed with Rayleigh light of a certain intensity. At the same time, the intensity of the two scattered lights and Rayleigh scattering will decay with the propagation distance when propagating in the optical fiber. It can usually be considered that the attenuation coefficients of the three lights are fixed, and they all decay exponentially with the distance from the scattering point. For ease of calculation, the optical fiber in the first section of the calibration optical fiber 10 can be set to the initial light intensity. At the same time, because the length of the calibration optical fiber 10 is very short, only 20m, the attenuation of the optical fiber inside the calibration optical fiber 10 and the difference in attenuation coefficients between the calibration optical fiber 10 and the temperature measurement optical fiber can be ignored. Based on the above conditions, the light intensity composition in the calibration optical fiber 10 at this time can be obtained.

[0032] In the first section of the calibration optical fiber 10

[0033] Is +I RS =I S1_l (1)

[0034] I A +I RA =I A1_l (2)

[0035] In the second section of the calibration optical fiber 10

[0036] C*(P S *I S +P R *I RS )=I S2_l (3)

[0037] C*(P A *I A +P R *I RA )=I A2_l (4)

[0038] Among them, I s is the intensity of the Stokes light in the first section of the calibration optical fiber 10, I RS is the intensity of the Rayleigh light in the first calibration optical fiber 10 in the Stokes path, I S1_l is the total light intensity of the Stokes path in the first section of the calibration optical fiber 10 collected by the system; A is the intensity of the anti-Stokes light in the first section of the calibration optical fiber 10, I RA is the intensity of the Rayleigh light in the first calibration optical fiber 10 in the anti-Stokes path, I A1_l is the total light intensity of the anti-Stokes path in the first section of calibration optical fiber 10 collected by the system; C is the ratio of the light intensity remaining after the fusion loss in the second section of calibration optical fiber 10 after the optical switch to the light intensity of the first section of calibration optical fiber 10, where the loss of the optical switch can be measured by an optical power meter, and the fusion loss can be approximated by 0.15dB per joint, because the joint loss is usually between 0.1-0.2dB, and the error caused by the approximation will not be very large, P S is the ratio of the remaining light intensity in the second calibration optical fiber 10 after the Stokes light is attenuated in the optical fiber to the Stokes light intensity in the first calibration optical fiber 10, P R is the ratio of the remaining light intensity in the second section of the calibration optical fiber 10 after the Rayleigh light is attenuated in the optical fiber to the Rayleigh light intensity in the first section of the calibration optical fiber 10, I S2_l is the total light intensity of the Stokes path in the second section of the calibration optical fiber 10 collected by the system; P A is the ratio of the remaining light intensity in the second section of the calibration optical fiber 10 after the anti-Stokes light is attenuated in the optical fiber to the anti-Stokes light intensity in the first section of the calibration optical fiber 10, I A2_lIt is the total light intensity of the anti-Stokes path in the first section of calibration optical fiber 10 collected by the system.

[0039] The core column 6 is heated by the heating plate 7, and the heating temperature is controlled to a certain specified value T1 higher than the T0 value. After the reading of the first temperature sensor 9 is stable, it can be considered that the temperature of the core column in the cylindrical direction is uniform at this time. The reading of the first temperature sensor 9 and the readings of the front and rear two parts of the calibration optical fiber 10 and the offset after the optical fiber tail end are recorded. At this time, the light intensity in the calibration optical fiber 10 is composed as follows:

[0040] In the first section of the calibration optical fiber 10:

[0041] n S *I S +I RS =I S1_h (5)

[0042] n A *I A +I RA =I A1_h (6)

[0043] In the second section of the calibration optical fiber 10

[0044] C*(P S *n S *I S +P R *I RS )=I S2_h (7)

[0045] C*(P A *n A *I A +P R *I RA )=I A2_h (8)

[0046] Among them, n S is the ratio of the Stokes intensity before and after heating, n A is the ratio of the anti-Stokes intensity before and after heating, and its value is as follows

[0047]

[0048]

[0049] Where a is a constant, T h is the temperature after heating, T l Temperature before heating

[0050] In formulas (5) to (8), I S1_his the total light intensity in the Stokes path of the first section of the calibration optical fiber 10 after heating, I A1_h is the total light intensity in the anti-Stokes path of the first section of the calibration optical fiber 10 after heating, I S2_h is the total light intensity in the Stokes path of the second section of the calibration optical fiber 10 after heating, I A2_h The total light intensity in the anti-Stokes path of the optical fiber 10 is calibrated for the second section after heating.

[0051] In formulas (1)-(8), I s , I RS , I A , I RA , P S , P A , P R Seven variables. By solving the values ​​of these seven variables, the influence of Rayleigh scattering in the two paths of light can be corrected. To ensure the accuracy of the seven variables, the heating core column 6 can be heated to a higher temperature to obtain four equations again. By repeatedly calculating the values ​​of the seven variables and averaging them, more accurate and stable results can be obtained.

[0052] At the same time, the dispersion of the two paths of light can also be corrected by heating the heating stem 6 .

[0053] The wavelengths of Stokes light and anti-Stokes light generated by Raman scattering are different, so the refractive index in the light is different, and the propagation speed is also different. The DTS system locates the temperature measurement point through the OTDR principle, that is, Where c is the speed of light propagation in the medium. It can be seen that at the same time, due to the different light speeds, the positions of the collected temperature measurement points L are also different, that is, the two beams of light gradually diverge as the propagation distance increases. Usually, when the length of the temperature measurement optical fiber is short, the influence of dispersion is not easy to detect, but when the optical fiber length is 1km, it may appear. When the length is greater than 3km, the phenomenon is very obvious. When it is greater than 10km, it will cause serious measurement errors. This is also one of the main reasons why the temperature measurement distance of various DTS systems usually does not exceed 10km. For multimode optical fibers, this problem is particularly difficult because there are many propagation modes and there is uncertainty in the difference in propagation speed in theory. Therefore, the patented method uses a heated core column 6 to cause a sudden change in local temperature (i.e., the amplitude of Stokes and anti-Stokes light), and calibrates the difference in propagation speed through experiments to correct the dispersion. The specific method is:

[0054] 1. After the temperature of the heating core column 6 reaches the set temperature and stabilizes, record the intensity curves of Stokes light and anti-Stokes light several times and average them respectively.

[0055] 2. The curves of the two scattered lights may be slightly misaligned at the first calibration optical fiber 10. This is caused by the different optical paths of the two lights inside the instrument. At the second calibration optical fiber 10, the signals of the two lights may produce a different misalignment from that in the first calibration optical fiber 10, that is, compared with the first calibration optical fiber 10, in the Stokes light path, the amplitude bulge corresponding to the high temperature is located further forward than the corresponding bulge in the anti-Stokes light path. Usually, this situation is not easy to detect when the length of the temperature measuring optical fiber is short, but it may occur when the optical fiber length is 1 km, and it is very obvious when the length is greater than 3 km.

[0056] 3. The Stokes and anti-Stokes curves in the first section of the calibration optical fiber 10 and the second section of the calibration optical fiber 10 are respectively calculated using a cross-correlation function to calculate the translation amounts S1 and S2 so that the two high-temperature zones can be aligned after the translation.

[0057] 4. After calculating the translation amounts S1 and S2, the period N = L / (S2-S1) is obtained according to the total length L of the temperature measuring optical fiber, and then the new Stokes intensity is calculated by interpolation. The calculation method is as follows:

[0058]

[0059] It should be noted that, in theory, this method is also only applicable to temperature measuring optical fibers with longer lengths, because the temperature measuring optical fiber and the calibration optical fiber 10 use different optical fibers. When the optical fiber is shorter, it will cause a larger error; however, when the optical fiber is shorter (within a few hundred meters), there is actually no need to correct the dispersion, so the defects of this method in short-distance optical fiber applications do not have a big impact.

[0060] The above shows and describes the basic principle, main features and advantages of the utility model. Those skilled in the art should understand that the utility model is not limited by the above embodiments. The above embodiments and descriptions are only for explaining the principle of the utility model. Without departing from the spirit and scope of the utility model, the utility model may have various changes and improvements, which fall within the scope of the utility model to be protected. The scope of protection claimed by the utility model is defined by the attached claims and their equivalents.

Claims

1. A distributed temperature measurement and temperature calibration device, characterized in that: It comprises a heat-insulating outer shell, a heating cavity is arranged in the heat-insulating outer shell, a cylindrical heating core column is arranged in the heating cavity, a heating plate is arranged at one end of the heating core column, a first temperature sensor is also fixedly mounted on the heating core column, two sections of calibration optical fiber are wound on the outer circumference of the heating core column, two ends of the temperature measuring optical fiber are respectively connected to the two sections of the calibration optical fiber, one end of one section of the calibration optical fiber away from the temperature measuring optical fiber is connected to the reference optical fiber, and a heat-insulating layer for covering the heating core column is arranged in the heating cavity.

2. A distributed temperature measurement and temperature calibration device as claimed in claim 1, characterized in that: The heat-insulating shell is an EVA heat-insulating shell.

3. A distributed temperature measurement and temperature calibration device as claimed in claim 1, characterized in that: The thermal insulation layer is an aerogel thermal insulation layer.

4. A distributed temperature measurement and temperature calibration device as claimed in claim 1, characterized in that: The heating core column is an aluminum alloy core column.

5. A distributed temperature measurement and temperature calibration device as claimed in claim 1, characterized in that: A constant temperature cavity is also provided in the heat-insulating shell, a wavelength division multiplexer is fixedly installed in the constant temperature cavity, and one end of the reference optical fiber away from the calibration optical fiber is connected to the wavelength division multiplexer.

6. A distributed temperature measurement and temperature calibration device as claimed in claim 5, characterized in that: A winding core column is fixedly mounted on the top of the wavelength division multiplexer, a second temperature sensor is fixedly mounted on the winding core column, and the reference optical fiber is wound around the outer peripheral surface of the winding core column.

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