Distributed temperature sensor and detection system

Abstract

The invention discloses a distributed temperature sensor and a detection system, and relates to the field of sensing monitoring. The distributed temperature sensor comprises a sensing optical cable and a protection tube, the sensing optical cable is spirally arranged in the protection tube; the sensing optical cable is used for obtaining the temperature of the to-be-measured body so as to determine the temperature change condition of the to-be-measured body. By arranging the distributed temperature sensor which is simple in structure and low in cost, the defect, thickness, heat flux or water content of the to-be-measured body can be accurately detected.

Description

Technical Field

[0001] The present application relates to the field of sensing and monitoring, and in particular to a distributed temperature sensor and detection system. Background Art

[0002] In the field of engineering measurement, different temperature sensors need to be set up for different measurement targets. For example, thermal integrity profiling (TIP) is generally used to detect defects in cast-in-place piles, ground penetrating radar is used to detect the thickness of dry soil layers based on empirical methods, and active heating fiber optic sensors (AHFO) and passive fiber optic sensors are used to detect the moisture content of soil or soil profiles.

[0003] Furthermore, although different temperature sensors can be used to detect different measurement targets, they cannot guarantee accurate temperature measurement due to practical factors. Therefore, providing a universal temperature sensor to improve detection accuracy has become a technical problem that needs to be solved in this field. Summary of the Invention

[0004] In order to solve the above problems existing in the prior art, the present application provides a distributed temperature sensor and detection system.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a distributed temperature sensor comprising: a sensing optical cable and a protective tube;

[0007] The sensing optical cable is spirally arranged in the protective tube;

[0008] The optical sensing cable is used to obtain the temperature of the object to be measured to determine the temperature change of the object to be measured.

[0009] Optionally, the sensing optical cable includes: a sensing optical fiber;

[0010] The sensing optical fiber is used to obtain the temperature of the body to be measured.

[0011] Optionally, the sensing optical cable includes: a heating body;

[0012] The heating body is used to heat the object to be measured; the heating body is sleeved on the sensing optical fiber.

[0013] Optionally, the heating body is a metal wire, a resistance wire or a carbon fiber rod.

[0014] Optionally, the sensing optical fiber is an optical fiber sensor with a Bragg grating.

[0015] Optionally, the protective tube is made of polyvinyl chloride, corundum, SUS301 stainless steel or SUS302 stainless steel.

[0016] In a second aspect, the present application provides a detection system, comprising: a processing device and the distributed temperature sensor provided above;

[0017] The distributed temperature sensor is connected to the processing device;

[0018] The distributed temperature sensor is used to obtain the temperature of the object to be measured; the processing device is used to realize defect detection or thickness, heat flux, and water content detection of the object to be measured based on the temperature.

[0019] Optionally, the processing device includes: a temperature sensing module and a processing module;

[0020] The temperature sensing module is connected to the processing module; the temperature sensing module is used to analyze the temperature of the object to be measured obtained by the distributed temperature sensor to obtain temperature data;

[0021] The processing module is used to realize defect detection or thickness, heat flux, and water content detection of the object to be measured based on the temperature data.

[0022] Optionally, the processing device further includes: a heating module; the heating module is connected to the processing module and the distributed temperature sensor; the heating module is used to provide heating energy for the distributed temperature sensor.

[0023] Optionally, the temperature sensing module is a DTS demodulator, an FBG demodulator or a Bragg grating monitor.

[0024] According to the specific embodiments provided in this application, this application has the following technical effects:

[0025] The present application provides a distributed temperature sensor and detection system. By setting up a distributed temperature sensor with a simple structure and low cost, it can realize accurate detection of defects, thickness, heat flux and water content of the object to be measured during the actual measurement process, and has universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1This is a schematic diagram of the structure of the distributed temperature sensor provided in Example 1 of the present application;

[0028] Figure 2 A schematic diagram of the structure of the detection system provided in Example 1 of the present application;

[0029] Figure 3 A schematic diagram of the structure of a distributed temperature sensor provided in Example 2 of the present application;

[0030] Figure 4 A schematic diagram of the structure of the detection system provided in Example 2 of the present application;

[0031] Figure 5 A flow chart of a method for monitoring the thickness and heat flux of a dry soil layer on a slope provided in Example 2 of the present application;

[0032] Figure 6 This is a schematic diagram of the structure of the distributed temperature sensor provided in Example 3 of the present application;

[0033] Figure 7 This is a schematic diagram of the structure of the detection system provided in Example 3 of the present application;

[0034] Figure 8 This is a schematic diagram of the structure of the distributed temperature sensor provided in Example 4 of the present application;

[0035] Figure 9 This is a schematic diagram of the structure of the detection system provided in Example 4 of the present application.

[0036] Description of reference numerals:

[0037] 1-Distributed temperature sensor, 11-Sensing fiber, 111-Optical fiber, 112-Optical fiber protective coating, 113-Fiber Bragg grating, 114-Epoxy resin, 12-Heating element, 13-Protective cover, 14-Protective tube, 2-Heating module, 3-DTS demodulator, 4-Processing module, 5-Plastic tube, 6-Sandbag, 7-Fiber Bragg grating monitor, 8-Binding post, 9-Cable, 10-FBG demodulator. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0040] In an exemplary embodiment, the present application provides a distributed temperature sensor, including: a sensing optical cable and a protective tube 14 .

[0041] The optical sensing cable is spirally arranged in the protective tube 14. The optical sensing cable is used to obtain the temperature of the object to be measured to determine the temperature change of the object to be measured.

[0042] As an optional implementation, the optical sensing cable used in the present application includes a sensing optical fiber 11. The sensing optical fiber 11 is used to obtain the temperature of the object to be measured. The sensing optical fiber 11 is an optical fiber sensor with a Bragg grating.

[0043] As an optional implementation, the sensing optical cable may further include a heater 12. The heater 12 is used to heat the object to be measured. The heater 12 is sleeved on the sensing optical fiber 11. The heater 12 is a metal wire, a resistance wire, or a carbon fiber rod.

[0044] As an optional implementation, the protective tube 14 is made of polyvinyl chloride, corundum, SUS301 stainless steel or SUS302 stainless steel.

[0045] In another exemplary embodiment, the present application provides a detection system, which includes: a processing device and the distributed temperature sensor 1 provided above.

[0046] The distributed temperature sensor 1 is connected to the processing device.

[0047] The distributed temperature sensor 1 is used to obtain the temperature of the object to be measured. The processing device is used to detect defects or detect thickness, heat flux, and water content of the object to be measured based on the temperature.

[0048] As an optional implementation, the processing device includes: a temperature sensing module and a processing module 4 .

[0049] The temperature sensing module is connected to the processing module 4. The temperature sensing module is used to analyze the temperature of the object to be measured obtained by the distributed temperature sensor 1 to obtain temperature data. The processing module 4 is used to detect defects or detect thickness, heat flux, and moisture content of the object to be measured based on the temperature data.

[0050] The temperature sensing module is a DTS demodulator 3 , an FBG demodulator 10 or a Bragg grating monitor 7 .

[0051] As another optional implementation, the processing device may further include: a heating module 2. The heating module 2 is connected to the processing module 4 and the distributed temperature sensor 1. The heating module 2 is used to provide heating energy for the distributed temperature sensor 1.

[0052] Based on the specific structure of the distributed temperature sensor 1 and the detection system using the distributed temperature sensor 1 given above, multiple embodiments are provided to illustrate the specific detection process of the distributed temperature sensor 1 and the detection system given above.

[0053] Example 1

[0054] Cast-in-place piles are widely used as deep foundations for superstructures such as high-rise buildings, bridges and offshore wind power stations. If defects occur in the pile body, it may have a negative impact on the bearing capacity of the cast-in-place piles and the load transfer at the pile-soil interface, posing potential risks to the construction and operation of civil infrastructure.

[0055] For a long time, people have conducted in-depth analysis on the integrity testing of cast-in-place piles and proposed many effective testing methods and technologies, such as ultrasonic transmission testing, low-strain reflection wave testing, and borehole coring integrity testing. However, these methods still have some shortcomings. Ultrasonic transmission testing has certain blind spots, and if the sampling shift is not set appropriately, it is easy to miss a judgment. The detection depth of the low-strain reflection wave method is affected by the mechanical properties of the soil (rock) around the pile and the hammer energy. It does not respond significantly to small-sized defects, and its defect resolution and test depth range are inferior to ultrasonic testing. The accuracy of borehole coring testing is affected by the cross-sectional orientation of the coring hole in the pile and the continuity of the coring core sample. These traditional methods are usually implemented one month after pile construction, and it is difficult to fully evaluate pile parameters. In recent years, thermal integrity profiling (TIP) has become a novel and efficient integrity testing method for detecting structural defects of cast-in-place piles based on temperature profiles in the early stages of construction.

[0056] TIP is a nondestructive testing method used to evaluate the integrity and geometric dimensions of bored concrete piles. It utilizes the heat released by hydration during cement setting to measure and record temperature changes along the depth of the pile shaft, thereby evaluating and analyzing the pile's integrity and profile. This method enables full-scale fault detection without blind spots, assessing the structural integrity of cast-in-place piles within a reinforcement cage, and detecting the actual location and size of defects, unaffected by pile length or cross-sectional dimensions. Compared to other methods, TIP can sensitively detect structural defects during pile construction and effectively shorten construction cycles. This fiber-optic technology offers denser measurement points, higher accuracy, easier installation, faster response time, and reduced susceptibility to electromagnetic interference (EMI). Furthermore, the quality of waterproofing measures does not significantly affect sensor durability.

[0057] The temperature of cast-in-place piles, especially the temperature distribution of the pile body during the hydration heat process, is closely related to its integrity. The measurement values ​​recorded by distributed fiber optic sensing can reflect the location of internal defects of abnormal piles, which is of great significance for practical applications.

[0058] Based on the above description, in order to achieve efficient detection of cast-in-place pile integrity and evaluate pile foundation quality, distributed optical fiber sensing technology can be used to accurately measure the temperature of the cast-in-place pile body, and the defect location can be determined by the temperature distribution of the pile body to achieve pile body integrity detection. Based on this, when performing cast-in-place pile defect detection, the distributed temperature sensor 1 provided in the application is used for detection, such as Figure 1 As shown, this distributed temperature sensor 1 includes a protective tube 14 and a sensing optical fiber 11. In this embodiment, the protective tube 14 can be a stainless steel plastic-coated hose. The stainless steel plastic-coated hose is made of SUS301 or SUS302. The plastic coating layer of the stainless steel plastic-coated hose is made of excellent flame-retardant polyvinyl chloride material. The stainless steel plastic-coated hose has the characteristics of high tensile strength, damage resistance, pressure resistance, impact resistance, and strong corrosion resistance, and has excellent electromagnetic shielding function. The stainless steel plastic-coated hose is waterproof, oil-proof, corrosion-resistant, and has good sealing performance. It is used as an optical fiber protective tube 14 to protect the sensing optical fiber 11 from the influence of the external harsh environment and achieve accurate temperature measurement.

[0059] Fiber optic sensors measure temperature changes in cast-in-place piles, using the different temperature curves between normal and defective areas to determine the distribution of pile defects. A stainless steel plastic-coated hose protects the fiber optic cable from external interference.

[0060] Furthermore, the DTS demodulator 3 is an optical instrument that uses optical fiber as a sensor for temperature sensing. Based on the optical time-domain reflectometry principle and Raman scattering effect of optical fiber, the DTS demodulator 3 utilizes the ratio between anti-Stokes light and Stokes light in the fiber to achieve distributed measurement along the fiber field. A single optical fiber can simultaneously monitor temperature and transmit signals. It can detect minute temperature changes and provide accurate and continuous temperature data in real time, enabling rapid, real-time, and multi-point measurement of spatial temperature distribution over large areas and long distances. Therefore, in this embodiment, the DTS demodulator 3 is used as the temperature sensing module of the detection system to demodulate the signal from the sensing fiber 11.

[0061] The distributed temperature sensor 1 pre-buried in the bored pile is used to measure the temperature distribution along the depth of the pile body at different times during the hydration heat process, and the temperature field of the entire bored pile at different times is obtained. The density at the defective part is very different from that at the normal part, and the heat conductivity is relatively low. Compared with the concrete pile under normal conditions, the heat released during the hydrolysis, coagulation and hardening process is generally less. The structural characteristics of different parts of the bored pile, that is, the integrity of the pile body, can be known through the temperature field.

[0062] In actual application, when pouring concrete piles, the ratio of water-cement-sand is particularly important. In this embodiment, the water-cement-sand ratio (W:C:S) is 0.44:1:1.83, where the cement model is C30, and the sand used is consistent with the soil around the bored piles. This ratio can effectively generate hydration heat (fast heating and high temperature) and has good fluidity.

[0063] For example, Figure 1 As shown, the steel cage used has an outer diameter of 0.9m and a length of 10m. A sensing fiber 11 is laid outside the cage for temperature measurement. To improve accuracy and resist external interference, the sensing fiber 11 is protected with a stainless steel plastic-coated hose. Two sensing fibers 11 are laid symmetrically along the cage, forming two U-shaped loops. During the laying process, the steel bars are kept straight. The sensing fibers 11 are tied every 50cm. An 8m length of sensing fiber 11 is reserved at the top of the cage to facilitate subsequent on-site measurements. To facilitate subsequent temperature distribution comparisons between normal and defective piles, two prefabricated cages are used. One of the cages is equipped with a sandbag 6 for inclusions, located 5m deep within the cage.

[0064] The cast-in-place pile is poured by grouting in a high-strength plastic pipe 5, and a prefabricated steel cage (such as Figure 1 and Figure 2 The plastic pipe (shown) is placed in the center of the pipe. The plastic pipe 5 is placed in the excavated hole. Before injecting cement slurry, the excavated soil is backfilled and compacted in layers. After backfilling, the soil is left to stand for a day to ensure equilibrium, facilitating accurate temperature measurement. Finally, the location of defective piles can be detected based on the measured temperature distribution curve.

[0065] Furthermore, the example of using the distributed temperature sensor 1 provided in this embodiment to monitor the temperature curve of the pile body on site and determine the integrity of the pile foundation is used for explanation:

[0066] The concrete piles were cast by grouting inside a plastic pipe 5, with a steel cage placed at the center. The pipes, 1 meter in diameter and 11 meters in length, were vertically buried on site through excavated holes. Each hole had a diameter of 1.2 meters and a depth of 12 meters. Before the cement grout was injected, the surrounding sand was compacted and filled in layers, each approximately 1 meter long. To prevent the hole from collapsing, the plastic pipe 5 was not immediately removed during the cement pouring. First, the high-strength plastic pipe 5 was vertically lifted 0.2 meters. Then, the remaining cement grout was gradually injected until the liquid level reached the pipe 5. These steps were repeated until the pouring was complete. After the two concrete piles were cast on site, the normal pile was numbered 1 and the defective pile was numbered 2. The two piles were 3 meters apart. After pouring, a sensor fiber 11 cable reserved at the top of the pile was connected to a DTS demodulator 3 to measure the temperature of the fiber in the pile concrete. The DTS data recording period was set to 5 minutes, with each measurement lasting 2 minutes, for a total of 24 hours. Based on the measured temperature curve along the depth of the pile, the temperatures of pile No. 1 and pile No. 2 are compared to determine the location of the defect in the defective pile.

[0067] Example 2

[0068] Extreme droughts cause soil moisture and groundwater levels to drop, leading to ground subsidence and soil cracking, causing widespread damage to infrastructure on the Earth's surface. The essence of drought-induced disasters lies in changes in temperature and moisture distribution during soil-atmosphere interactions. Water evaporation is the primary process for the exchange of water and energy between the soil and the atmosphere. The soil evaporation process is generally divided into a constant-rate phase, a decreasing-rate phase, and a residual phase. While the processes and mechanisms of soil evaporation during the constant-rate phase are relatively well understood, the processes and mechanisms of soil evaporation during the decreasing-rate and residual phases require further investigation. A key reason for this is the formation of a dry soil layer (DSL) as pore water in the surface soil depletes. Soil evaporation is an energy-consuming process. When a dry soil layer appears, the energy directly contributing to water evaporation shifts from net radiation to soil heat flux (G). At this point, the evaporation surface is located at the bottom of the dry soil layer. As evaporation proceeds, the evaporation surface deepens, further reducing the evaporation rate. Therefore, when studying water evaporation during the decreasing-rate and residual phases, it is crucial to consider the thickness of the dry soil layer and the heat flux distribution within it.

[0069] Currently, visual inspection is the most commonly used method for determining DSL thickness. However, this method is time-consuming and labor-intensive, and often leads to errors in visually determining DSL thickness. Using the depth corresponding to the residual moisture content as the DSL thickness has achieved good results, but this method only works in the absence of precipitation. Ground-penetrating radar (GPR) can empirically estimate an electromagnetic wave velocity based on the medium type, inputting this velocity into the GPR host and interpreting the soil thickness represented by the GPR image as the actual soil thickness. However, due to the complex nature of the subsurface medium and the variable soil moisture content, empirically determined soil thickness often results in errors. In-situ methods for measuring G primarily utilize heat flux plates. However, this method is often limited by measurement errors caused by the difference between the plate and the soil. Heat flux plates are only suitable for measuring heat flux at a specific depth, significantly limiting their application to measuring the entire dry soil layer.

[0070] Based on the above description, in order to solve the above problems, in this embodiment, the distributed temperature sensor and detection system provided by the present application are used to detect the thickness and heat flux of the dry soil layer on the slope.

[0071] The structure of the distributed temperature sensor provided in this embodiment is obtained by adding a heating body to the structure provided in embodiment 1. Figure 3 As shown, it includes: a sensing optical cable and a protective tube 14.

[0072] The optical sensing cable is spirally arranged in the protective tube 14. The optical sensing cable comprises, from the inside out, an optical sensing fiber 11, a heating element and a protective cover 13. The outer diameter of the optical sensing cable is at least 5 mm, but is not limited thereto.

[0073] The sensing optical fiber 11 and the heating element are both disposed in a protective cover 13. The heating element is used to heat the object to be measured. The sensing optical fiber 11 is used to deform based on the temperature of the object to be measured.

[0074] The optical sensing cable used in this embodiment is a distributed temperature sensor (DTS). DTS is a device that measures temperature based on the Raman scattering effect. It uses optical time-domain reflectometry to locate the temperature sensor, utilizing the temperature effect of backscattered Raman scattering from the sensing fiber. The intensities of the two light signals from Raman scattering are related to temperature, and the temperature can be calculated from the ratio of the two intensities.

[0075] When measuring soil temperature, the distributed temperature sensor provided in this embodiment is based on the active heating sensing fiber method of high-precision sensing fiber Bragg grating temperature measurement. When power is applied to the protective sheath 13 protecting the sensing fiber, the heating body acts as a heat source to generate heat pulses. The soil temperature increases over time, and the sensing fiber 11 acts as a heat source sensing device to monitor the thermal response generated in the soil to characterize the soil temperature.

[0076] In order to simplify the structure of the sensor and reduce costs, the heating element used in this embodiment can be a metal wire (such as a steel wire) with a resistance of 0.02Ω / m. The specific resistance value can be determined according to actual needs and is not limited to 0.02Ω / m.

[0077] To extend the service life of the distributed temperature sensor, in this embodiment, polyvinylidene fluoride (PVDF) is used as the material for the protective cover 13. PVDF is a highly non-reactive thermoplastic fluoropolymer with multiple excellent properties, including elasticity, low weight, and high chemical corrosion resistance. PVDF has a thermal decomposition temperature exceeding 300°C and can withstand high temperatures without performance degradation in most cases.

[0078] To enhance the robustness of the distributed temperature sensor and facilitate its deployment and measurement, in this embodiment, polyvinyl chloride (PVC) is used as the material for the protective tube 14. In this case, the protective tube 14 is a PVC tube. For example, the diameter of the PVC tube is 30 mm, but this is not limited to this. The PVC tube is a specially made polyolefin heat-shrinkable tubing, with an outer layer made of high-quality, soft, cross-linked polyolefin material and an inner layer made of hot-melt adhesive. The outer layer material is insulating, corrosion-resistant, and wear-resistant, while the inner layer material has the advantages of a low melting point, waterproof sealing, and high adhesion.

[0079] In order to improve spatial resolution, the length of the protection tube 14 is not less than 36 meters, and the spiral pitch of the sensor optical cable spirally arranged in the protection tube 14 can be 30 cm, but is not limited thereto.

[0080] like Figure 4 As shown, the detection system used in this embodiment includes: a heating module 2, a DTS demodulator 3, a processing module 4, and the distributed temperature sensor 1 provided above. The heating module 2 can be an adjustable transformer. The processing module 4 can be a host computer or an intelligent terminal.

[0081] The distributed temperature sensor 1 is connected to the heating module 2 and the DTS demodulator 3 respectively. The DTS demodulator 3 is connected to the processing module 4.

[0082] Heating module 2 provides heating energy to distributed temperature sensor 1. Distributed temperature sensor 1 heats the dry soil layer of the slope and deforms based on the temperature of the dry soil layer. DTS demodulator 3 converts the resulting deformation into temperature data. Processing module 4 determines the thickness of the dry soil layer and the soil heat flux distribution based on the temperature data.

[0083] Based on the above description, the process of using the detection system provided in this embodiment to monitor the thickness, thermal conductivity, heat flux distribution and other data of the dry soil layer of the slope in situ includes:

[0084] A distributed temperature sensor was vertically lowered into the test pit, located at the center of the pit. Epoxy resin was used to seal the ends of the PVC pipe to prevent water infiltration and affect measurement accuracy. The pit was then backfilled with undisturbed soil and compacted layer by layer, with each layer approximately 2 m thick (not limited to this) to ensure uniform soil distribution and good contact between the distributed temperature sensor and the soil. Finally, the backfilled pit was left to stand for one month. During this period, the deformation of the backfill soil gradually stabilized and gradually reached hydrothermal equilibrium with the undisturbed soil, maintaining the same properties as closely as possible. The sampling interval was set to 5 seconds. During the test, the initial temperature was recorded under unheated conditions, followed by a heating test. The minimum initial temperature was used to determine the thickness of the dry soil layer on the slope. The temperature characteristic values ​​obtained during the heating process were then used to calculate the soil thermal conductivity. As the heating time changes, the energy distribution of the surrounding soil changes, which allows the soil temperature distribution to be determined. The soil heat flux is then determined from the temperature and thermal conductivity, demonstrating the feasibility of using distributed temperature sensors to monitor the dry soil layer.

[0085] For example, the heating power and heating time are 10 W and 30 min respectively. The thermal conductivity can be determined based on the temperature-time curve measured by the distributed temperature sensor during the heating process. Finally, the initial soil temperature and thermal conductivity are converted into heat flux to obtain the heat flux distribution along the depth of the dry soil layer.

[0086] Further, based on the above description, in this embodiment, the monitoring method of the thickness and heat flux of the slope dry soil layer is as follows: Figure 5 Shown, including:

[0087] Step 100: Obtain the initial temperature distribution of the soil area to be detected, and use the depth of the soil area to be detected corresponding to the minimum temperature value in the initial temperature distribution as the thickness of the dry soil layer of the slope in the soil area to be detected.

[0088] Step 101: heating the dry soil layer of the slope according to a set power and a set time, and obtaining the heating temperature according to a set sampling time to generate a temperature-time curve.

[0089] Step 102: Obtain the thermal conductivity of the dry soil layer of the slope based on the temperature-time curve.

[0090] Step 103: Based on the initial temperature distribution and thermal conductivity, the heat flux distribution of the slope dry soil layer along the depth is obtained.

[0091] Example 3

[0092] Soil moisture content significantly influences soil properties such as strength, specific heat capacity, and thermal conductivity, and is a key indicator in soil property research. Currently, widely used methods for measuring soil moisture include oven-drying gravimetric methods, neutron methods, soil moisture sensors, dielectric properties methods, nuclear magnetic resonance (NMR), separation tracer methods, and remote sensing. While oven-drying gravimetric methods are the simplest and most accurate, they require stratified sampling, are complex, soil-damaging, and time-consuming, and cannot measure soil moisture over large areas. Sensors offer rapid, inexpensive, and long-term soil moisture measurement, but the sensor itself significantly affects the measurement results. Neutron methods can meet the need for continuous soil moisture measurement over a specific area and depth, but they pose a radiation hazard. Time-domain reflectometry (TDRS), a dielectric properties method, is convenient, rapid, and offers significantly higher accuracy than neutron instruments, but the equipment is expensive and complex to operate. Radar detection allows for large-scale measurements but is not suitable for all soil types. NMR methods are susceptible to electromagnetic noise interference. The isolated tracer method can measure the horizontal and vertical distribution of soil moisture over a large area, but the cost increases with the measured area. Remote sensing methods are more affected by soil factors, and reducing errors requires increasing costs.

[0093] Fiber optic sensing technology has developed rapidly in recent years, achieving significant success in both field monitoring systems and laboratory model testing. Compared to other sensing technologies, fiber optic technology enables distributed, long-distance measurements and is corrosion-resistant and resistant to interference. Fiber Bragg grating sensors are a rapidly developing method for measuring temperature and humidity. Actively heated fiber optic sensors (AHFO) and passive fiber optic sensors have been used to measure soil moisture based on thermal effects. As a new multi-point measurement technology with significant economic advantages, AHFO sensors hold great potential for soil moisture measurement and are continuously being refined.

[0094] In order to solve the above problems, the distributed temperature sensor and detection system provided in this application can be used to realize the slope moisture content measurement. Based on this, in this embodiment, the temperature is mainly measured based on the active heating optical fiber sensor, and the fitting relationship between temperature and moisture content is established to realize the soil moisture content measurement.

[0095] Among them, Figure 6 As shown, the structure of the distributed temperature sensor provided in this embodiment is similar to that of the distributed temperature sensor provided in the above-mentioned embodiment 2, with the main difference being that in this embodiment, a corundum shell is used as the protective tube 14, and a resistance wire is used as the heating element 12. The corundum shell is mainly composed of aluminum oxide, has an operating temperature of 1200-1800°C, high density, good thermal shock resistance, acid and alkali resistance, erosion resistance, and long service life. Used as the protective tube 14, it can protect the distributed temperature sensor from external environmental influences, and provide more accurate measurement results.

[0096] For example, the diameter of the corundum shell can be 50 mm, and the internal heating resistor wire has a resistance of 30 Ω / m, which is coated on the sensing optical fiber 11. The length of the distributed temperature sensor is 1000 mm. Hot melt adhesive is used to seal the ends of the corundum shell to prevent soil water from penetrating and affecting the internal sensing optical fiber 11 and the resistor wire.

[0097] In this embodiment, if Figure 7 As shown, the structure of the detection system using distributed temperature sensors is similar to that of the above-mentioned embodiment 2, with the main difference being that in this detection system, an FBG demodulator 10 is used as the temperature sensing module, and a DC power supply is used as the heating module 2. Based on this, the implementation process of on-site determination of slope moisture content can be described as follows:

[0098] A distributed temperature sensor was placed in the soil. A test pit was excavated on the slope, with the distributed temperature sensor positioned in the center of the pit. The original soil was then backfilled into the pit and compacted layer by layer, with each layer approximately 200 mm thick. Finally, the backfilled pit was left to stand for 30 days to allow the backfill and original soil to reach hydrothermal equilibrium and stabilize soil properties. A DC power supply powered the resistance wire within the distributed temperature sensor, and the sampling interval for the FBG demodulator 10 and the computer was set to 10 seconds. During the measurement process, the heating power was 3 W / m² and the heating time was set to 25 minutes. The computer established a fitting relationship between the collected temperature data and the soil moisture content, thus converting the temperature into moisture content.

[0099] In practical applications, distributed temperature sensors are embedded in the soil to measure soil temperature distribution. The relationship between temperature and moisture content is then fitted to determine slope moisture content. By energizing the resistance wire within the distributed temperature sensor to generate a heat pulse, which applies a certain amount of heat to the surrounding soil, the sensing fiber 11 acts as a temperature sensor to measure the soil's thermal response. This thermal parameter allows for soil temperature measurement, and can be expanded from point-based measurement to quasi-distributed measurement, enabling large-area, high-precision monitoring.

[0100] Example 4

[0101] Soil moisture is a measure of the water content in the soil. Monitoring soil moisture content is of great significance to agricultural production, environmental protection, and water resources management.

[0102] Soil moisture content is a crucial factor affecting plant growth and yield, and is a crucial parameter in agricultural production. Monitoring soil moisture allows for timely understanding of soil moisture conditions, enabling rational adjustments to irrigation and fertilization plans to ensure crops receive the appropriate amount of water, thereby improving crop yield and quality. This helps prevent over-irrigation and water waste, conserving water resources while also improving irrigation efficiency.

[0103] Excessively high or low soil moisture can lead to soil erosion, affecting soil quality and the ecological environment. Soil salt content is also closely related to soil moisture; excessively high or low soil moisture can lead to soil salinization. By monitoring soil moisture, timely measures can be taken to prevent soil erosion and effectively prevent soil salinization.

[0104] Monitoring soil moisture content is of great significance for improving agricultural production efficiency, saving water resources, protecting the environment and maintaining ecological balance. It is an important link in achieving sustainable development and building ecological civilization.

[0105] Common soil moisture monitoring methods can be categorized into two main types: point measurement and distributed measurement. Point measurement includes thermogravimetry, time-domain reflectometry, frequency-domain reflectometry, as well as capacitance and frequency-domain techniques. Distributed techniques include ground-penetrating radar (GPR), remote sensing, infrared detectors, and actively heated fiber optic cables. Thermogravimetry requires disruption of the soil structure. Technologies such as time-domain reflectometry and frequency-domain reflectometry are expensive, highly susceptible to environmental influences, and require regular calibration. The spatial resolution of actively heated fiber optic cables is insufficient for small-scale model testing. Ground-penetrating radar, infrared, and remote sensing measurements have low accuracy, making it difficult to reliably detect soil moisture.

[0106] In order to solve the above problems, in this embodiment, the distributed temperature sensor and detection system provided by this application can be used to realize in-situ monitoring of soil moisture.

[0107] Bragg gratings have the advantages of small size, resistance to electromagnetic interference, corrosion resistance and high sensitivity. Bragg gratings are a grating structure formed in an optical fiber by periodically changing the refractive index. When light passes through the Bragg grating, light of a specific wavelength will be reflected, while other wavelengths pass through the optical fiber. This reflected wavelength is called the Bragg wavelength. The core characteristic of the Bragg grating is its sensitivity to temperature changes. Temperature changes will cause the refractive index of the optical fiber to change, resulting in changes in the Bragg wavelength. By manufacturing periodic micro-nanoscale gratings in the optical fiber, the optical signal can be subjected to slight changes in the external environment and produce frequency shifts. By measuring the wavelength change of the reflected light, the temperature change can be accurately inferred. Based on this, in this embodiment, the structure of the distributed temperature sensor is similar to the structure provided in the above-mentioned embodiment 2, except that the sensing optical fiber 11 provided in this embodiment uses an optical fiber sensor with a Bragg grating. As shown in FIG. Figure 8 As shown, the optical fiber sensor with Bragg grating includes: optical fiber 111 and optical fiber protective coating 112. According to measurement requirements, Bragg grating 113 is manufactured on the optical fiber 111 at a certain distance D and connected to the Bragg grating monitor 7 through cable 9.

[0108] The thermal conductivity of soil is closely related to its humidity. Higher humidity increases the soil's thermal conductivity. Therefore, when heated, soil with higher humidity conducts heat more quickly, causing the temperature around the sensor to change more rapidly. The temperature change of the sensor after heating is related to the soil's thermal conductivity. By monitoring the rate of temperature change over time, the soil's humidity can be indirectly inferred, thereby indirectly reflecting soil moisture.

[0109] Carbon fiber is a material with good electrical conductivity. It is driven by an external power source and uses the electrical conductivity of carbon fiber to make carbon fiber rods. By applying current to the carbon fiber rods, the current heating can generate a thermal effect to heat the carbon fiber rods, thereby achieving local heating of the soil. Carbon fiber rods have the characteristics of high efficiency, energy saving, precise temperature control, high temperature resistance, and wear resistance. Based on this, in this embodiment, the heating body adopts carbon fiber rods. Figure 9 As shown, during the actual monitoring process, binding posts 8 are installed at both ends of the carbon fiber rod and connected to a heating module 2 (e.g., a DC power supply) via a cable 9. The carbon fiber rod is used as a heating element, and a fiber optic sensor with a Bragg grating is very sensitive to temperature and is used to accurately measure the temperature change of the carbon fiber rod. When the measurement begins, the carbon fiber rod is heated under a constant current from the power supply. The temperature change of the carbon fiber rod is recorded by the Bragg grating monitor and converted into a Bragg wavelength drift. Through the calibration relationship, the actual moisture content of the current soil can be calculated, thereby realizing in-situ monitoring of the moisture content of the soil profile.

[0110] Based on the above description, in this embodiment, the principle of the detection system for realizing in-situ monitoring of soil profile moisture is:

[0111] This technique is based on the observed correlation between the thermal response of a carbon fiber rod and the moisture content of the surrounding soil. When the measurement begins, the carbon fiber rod is heated under a constant current, and the temperature changes during heating are recorded by a Fiber Bragg Grating (FBG) monitor. Based on a series of calibration tests, the temperature characteristic can then be used to calculate soil moisture. The FBG monitor quantifies temperature by measuring the thermal sensitivity of the backscattered Bragg wavelength shift.

[0112] Based on the above description, for example, a carbon fiber rod with a diameter of 5 mm is used for heating monitoring. The length of the carbon fiber rod can be adjusted according to actual needs. Cables 9 connect the ends of the carbon fiber rod to the electrodes of the power supply. One cable is used for the positive electrode, and the other for the negative electrode. Direct current is used because it is more stable and more adjustable than alternating current, especially when the carbon fiber rod length is less than 1 meter.

[0113] The carbon fiber rod not only serves as a framework for in-situ soil profile moisture monitoring but also conducts electrical current. The carbon fiber rod has a resistance of 26.2 Ω / m, and the heating power per unit length is constant. Optical fiber 111 is bonded to the inner surface of the carbon fiber rod using epoxy resin 114.

[0114] For monitoring scenarios of different soils, indoor calibration tests can be conducted to obtain the parameters of distributed temperature sensors in different soils, thus realizing in-situ monitoring of soil profile moisture.

[0115] Distributed temperature sensors have the advantages of fast response, high precision, and good stability in soil profile moisture monitoring. They can provide accurate soil moisture information for agricultural production, help achieve precise irrigation, and improve crop yield and quality. They also help save water resources and protect the ecological environment.

[0116] The detection system for in-situ monitoring of soil profile moisture combines fiber Bragg grating sensing technology and carbon fiber heating technology. It monitors soil moisture in real time through a Bragg grating monitor and uses carbon fiber rods to regulate soil temperature, thereby achieving in-situ monitoring of soil profile moisture.

[0117] By implementing a detection system for in-situ soil profile moisture monitoring, real-time monitoring and regulation of soil moisture conditions can be achieved, providing reliable technical support for precision irrigation and water resource management. This technology has the advantages of fast response, high accuracy, and good stability, and has broad application prospects.

[0118] Furthermore, by selecting appropriate fiber Bragg grating (FBG) parameters, a periodically varying refractive index Bragg grating (FBG) 113 is created in optical fiber 111. Since temperature changes cause the Bragg wavelength to vary, the wavelength of the reflected wave changes with temperature and strain. By monitoring the changes in the reflected wavelength from the distributed temperature sensor and measuring these wavelength variations, environmental conditions such as temperature and strain can be inferred. The period and length of FBG 113 determine its sensitivity to temperature changes. This allows for accurate temperature measurement in soil monitoring.

[0119] Drill a hole in the soil profile with a diameter slightly larger than the diameter of the optical fiber 111 and its protective tube 14. Insert the Bragg grating 113 and the carbon fiber rod into the hole, ensuring their accurate and stable positioning. Use soil to fill the hole in situ or inject an appropriate encapsulating material (such as epoxy resin or cement) to secure the Bragg grating 113 and the carbon fiber rod in place, ensuring they do not move in the soil.

[0120] The distributed temperature sensor is buried in the monitored soil, and the spacing D between adjacent Bragg gratings 113 on the optical fiber 111 can be set according to specific monitoring requirements. After the optical fiber 111 is installed, it is necessary to apply a fiber protective coating 112 to protect the optical fiber 111 from damage and power leakage. Finally, the terminal 8 is installed at both ends of the carbon fiber rod and connected to the power supply via the cable 9. The optical fiber 111 is connected to the spectrum monitor 7, and the data is transmitted to the processing device on the surface via the optical fiber 111. By controlling the heating mode of the carbon fiber rod and the monitoring parameters of the Bragg grating monitor 7, the soil moisture distribution can be obtained, and precise regulation and management of the soil can be achieved.

[0121] Based on the above description, this embodiment achieves high-precision in-situ monitoring of soil profile moisture by combining fiber optic sensing technology and active heating mechanism, and is suitable for various application scenarios that require accurate soil moisture data.

[0122] In summary, the distributed temperature sensor and detection system provided by this embodiment also has the following advantages:

[0123] 1. High-precision and high-reliability measurement: Fiber Bragg grating (FBG) technology offers high resolution and sensitivity, enabling precise monitoring of soil profile moisture. Fiber sensing fibers are also resistant to interference and electromagnetic interference, improving the stability and reliability of the monitoring system.

[0124] 2. Real-time monitoring: Distributed measurement can comprehensively monitor the distribution of target parameters along the entire length of the optical fiber, enabling real-time monitoring and data collection. This eliminates the need for destructive soil sampling, minimizing impact on soil structure.

[0125] 3. Wide coverage: Distributed temperature sensors can cover a wider monitoring area and are suitable for monitoring the distribution of target parameters over a wide range. Sensing fibers of different lengths and sensitivities can be selected based on monitoring needs to meet different depth and accuracy requirements.

[0126] 4. Reduce the number of sensors: Compared with point measurement, distributed measurement can achieve multi-point monitoring through one optical fiber, reducing the number of sensors and system complexity.

[0127] Based on the above description, Examples 1 to 4 provided in this application are based on different distributed temperature sensors and detection systems that can realize accurate detection of defects, thickness, heat flux and water content of different objects to be measured. The components used in the distributed temperature sensors and detection systems in each embodiment and the settings between the components can be referred to each other.

[0128] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0129] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A distributed temperature sensor, characterized in that: The distributed temperature sensor includes: a sensing optical cable and a protective tube; The sensing optical cable is spirally arranged in the protective tube; The optical sensing cable is used to obtain the temperature of the object to be measured to determine the temperature change of the object to be measured.

2. The distributed temperature sensor according to claim 1, characterized in that The sensing optical cable comprises: a sensing optical fiber; The sensing optical fiber is used to obtain the temperature of the body to be measured.

3. The distributed temperature sensor according to claim 2, characterized in that: The sensing optical cable includes: a heating body; The heating body is used to heat the object to be measured; the heating body is sleeved on the sensing optical fiber.

4. The distributed temperature sensor according to claim 3, characterized in that The heating body is a metal wire, a resistance wire or a carbon fiber rod.

5. The distributed temperature sensor according to claim 2, characterized in that: The sensing optical fiber is an optical fiber sensor with a Bragg grating.

6. The distributed temperature sensor according to claim 1, characterized in that The protective tube is made of polyvinyl chloride, corundum, SUS301 stainless steel or SUS302 stainless steel.

7. A detection system, characterized in that: The detection system comprises: a processing device and a distributed temperature sensor according to any one of claims 1 to 6; The distributed temperature sensor is connected to the processing device; The distributed temperature sensor is used to obtain the temperature of the object to be measured; the processing device is used to realize defect detection or thickness, heat flux, and water content detection of the object to be measured based on the temperature.

8. The detection system according to claim 7, characterized in that: The processing device includes: a temperature sensing module and a processing module; The temperature sensing module is connected to the processing module; the temperature sensing module is used to analyze the temperature of the object to be measured obtained by the distributed temperature sensor to obtain temperature data; The processing module is used to realize defect detection or thickness, heat flux, and water content detection of the object to be measured based on the temperature data.

9. The detection system according to claim 8, characterized in that: The processing device further includes: a heating module; the heating module is connected to the processing module and the distributed temperature sensor; the heating module is used to provide heating energy for the distributed temperature sensor.

10. The detection system according to claim 8, characterized in that: The temperature sensing module is a DTS demodulator, an FBG demodulator or a Bragg grating monitor.

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