Method for determining thermal pulse moisture probe calibration formula under any heating power

Abstract

The invention discloses a method for determining a thermal pulse moisture probe calibration formula under any heating power, and aims to solve the problems that a complete test needs to be carried out under each heating power, the workload is large and the time consumption is long in the traditional calibration, three different heating powers Q are randomly selected, a Tt-w calibration test is carried out under the three heating powers, and the thermal pulse moisture probe calibration formula under any heating power is determined. According to the method, a Tt-Q linear relation is established, a corresponding Tt value under the target heating power is calculated in combination with a calibration formula, finally, a Tt-w empirical model is predicted through fitting, calibration formula coefficients A, B and C are obtained, a Tt-w calibration formula under the target power is obtained, and the calibration formula can be rapidly determined without independent calibration for each power. According to the method, the calibration efficiency of the thermal pulse moisture probe can be effectively improved, the test cost is remarkably reduced, the calibration precision is ensured, and the method has the advantages of simplicity, convenience, high efficiency and reliability and has good accuracy and practicability.

Description

Technical Field

[0001] The invention relates to the fields of hydrogeology, engineering geology and environmental science, and in particular to a method for determining a calibration formula of a thermal pulse moisture probe under arbitrary heating power. Background Art

[0002] In fields such as geological engineering, agricultural ecology, and environmental protection, soil moisture is a key parameter affecting its physical and chemical properties and engineering performance. It plays an important role in soil stability, permeability, and ecological regulation. Accurate and efficient soil moisture measurement not only helps prevent geological disasters but also provides scientific guidance for optimizing agricultural irrigation and effectively monitors environmental changes.

[0003] As a non-perturbative, fast-responding and highly adaptable moisture monitoring technology, the thermal pulse moisture probe has been widely used in agriculture, environmental monitoring, hydrogeology and other fields. Its working principle is based on the fact that the heating pulse induces temperature changes in the soil and the soil moisture content (w) is estimated by monitoring the heat diffusion process. However, the response characteristics of the thermal pulse sensor are significantly affected by the heating power. Under different heating power conditions, the output parameter temperature characteristic value (T t ) and soil moisture content (w), which needs to be corrected through calibration tests.

[0004] Currently, most calibration tests are conducted using a fixed heating power. If the heating power changes in actual applications, the system must be recalibrated, which increases labor and time costs, is labor-intensive and inefficient, and makes it difficult to meet the needs of rapid power switching in actual applications. At the same time, the thermal conductivity of soil is also affected by the soil type. Different types of soil have different thermal diffusion capabilities. The existing single calibration formula is prone to introduce large errors when the soil type changes, causing the output results to deviate from reality, limiting the universality of the technology and the effectiveness of engineering applications. Therefore, how to quickly calculate the calibration formula under arbitrary heating power based on limited calibration data to improve the adaptability and monitoring accuracy of the thermal pulse moisture probe has become a key issue that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining the calibration formula of a thermal pulse moisture probe under arbitrary heating power. This method can quickly calculate the calibration formula under different heating powers based on limited calibration data. It aims to reduce the experimental workload, improve monitoring efficiency, and enhance the applicability of the technology under various soil types. It has important engineering application value.

[0006] To achieve the above functions, the present invention designs a method for determining a thermal pulse moisture probe calibration formula under any heating power, comprising the following steps S1 to S4:

[0007] Step S1: bury the thermal pulse moisture probe into soil with different moisture contents, and randomly select at least three different heating powers Q to heat each soil, and measure the temperature characteristic value T t - Calibration test of soil moisture content w to obtain the temperature characteristic value T of each soil under different heating powers t -Fitting curve of soil moisture content w;

[0008] Step S2: Based on the temperature characteristic value T of each soil body under each heating power Q t -Fitting curve of soil moisture content w, establishing temperature characteristic value T for different soil moisture content w t The linear relationship between heating power Q;

[0009] Step S3: Based on the temperature characteristic value T t The linear relationship between the heating power Q and the corresponding temperature characteristic value T under any target heating power is calculated. t , and obtain the temperature characteristic value T under the target heating power t The data points composed of soil moisture w (T t , w);

[0010] Step S4: Based on the multiple data points (T t , w), fitting the temperature characteristic value T under the target heating power t The calibration formula of soil moisture content w, as well as the parameters in the calibration formula.

[0011] As a preferred technical solution of the present invention, in step S1, at least three different heating powers Q are arbitrarily selected, and the target soil is continuously heated for a preset time, with the continuous heating time being the same under each heating power; the temperature characteristic value T of the soil during the heating process is recorded; t , and soil moisture w, plot the temperature characteristic value T under different heating power Q t -Fitting curve of soil moisture content w.

[0012] As a preferred technical solution of the present invention: the calibration test heating time in step S1 is consistent with the actual application heating time.

[0013] As a preferred technical solution of the present invention: the temperature characteristic value T established in step S2 t The linear relationship between it and the heating power Q is as follows:

[0014]

[0015] Where, T tis the temperature characteristic value, T(t) is the sensor temperature corresponding to the heating time t, T0 is the initial ambient temperature, Q is the heating power per unit length, λ is the thermal conductivity of the soil, R is the thermal resistance between the sensor and the soil wall per unit length, K is the thermal diffusivity of the soil, a is the outer diameter of the sensor, c = 1.7811 = exp(γ) and γ = 0.5772, and γ is the Euler constant.

[0016] As a preferred technical solution of the present invention: in step S3, based on the temperature characteristic value T t The linear relationship between the heating power Q and the temperature characteristic value T under different soil moisture content w is plotted. t -Fitting curve of heating power Q, find the corresponding temperature characteristic value T under any target heating power under given soil moisture content w on the fitting curve t .

[0017] As a preferred technical solution of the present invention: Step S4 fits the temperature characteristic value T under the target heating power. t The calibration formula of soil moisture content w is as follows:

[0018]

[0019] Where, T t is the temperature characteristic value, w is the soil moisture content, A, B, C are the parameters in the calibration formula, and multiple data points (T t , w) is substituted into the above equation to obtain the fitting result.

[0020] Beneficial effects: Compared with the prior art, the advantages of the present invention include:

[0021] 1. The present invention can greatly reduce the number of calibrations, significantly improve calibration efficiency, reduce test costs, and has good accuracy and applicability;

[0022] 2. The present invention has accuracy and applicability in measuring the moisture content of various soils;

[0023] 3. The present invention requires fewer calibration times, and only three different heating powers need to be arbitrarily selected for calibration, and the process of determining the moisture content is simple;

[0024] 4. The present invention is economical and safe, easy to process, has strong anti-interference ability, and has reliable and effective measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of a method for determining a calibration formula of a thermal pulse moisture probe under arbitrary heating power according to an embodiment of the present invention;

[0026] Figure 2 is the temperature characteristic value T provided according to the embodiment of the present inventiont -Schematic diagram of the calibration test device for soil moisture content w;

[0027] Figure 2 In: 1. Thermal pulse moisture probe; 2. Soil samples with different moisture contents; 3. Plastic film; 4. DC power supply; 5. Computer; 6. Demodulator;

[0028] Figure 3 is the temperature characteristic value T under different heating powers provided by the embodiment of the present invention t - Soil moisture content w calibration test result diagram;

[0029] Figure 4 is the temperature characteristic value T provided according to the embodiment of the present invention t Linear relationship diagram with heating power Q;

[0030] Figure 5 3 is a comparison chart of measured values and estimated values at a target heating power of 25 W / m provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0032] The embodiment of the present invention provides a method for determining the calibration formula of a heat pulse moisture probe under any heating power, referring to Figure 1 , including the following steps S1 to S4:

[0033] Step S1: bury the thermal pulse moisture probe into soil with different moisture contents, and randomly select at least three different heating powers Q to heat each soil, and measure the temperature characteristic value T t - Calibration test of soil moisture content w to obtain the temperature characteristic value T of each soil under different heating powers t -Fitting curve of soil moisture content w;

[0034] Calibration test device schematic diagram Figure 2The test device includes six parts: a heat pulse moisture probe 1, soil samples 2 with different moisture contents, a plastic film 3, a DC power supply 4, a computer 5, and a demodulator 6. The heat pulse moisture probe 1 is inserted into the soil samples 2 with different moisture contents, and the plastic film 3 is covered on the soil samples 2 with different moisture contents to ensure the stability and uniformity of the moisture content of the soil samples. The cable and optical cable of the heat pulse moisture probe are connected to the DC power supply 4 and the demodulator 6 respectively. The DC power supply 4 is used to provide stable heating power. The demodulator 6 is connected to the computer 5 and is controlled and recorded in real time by the computer's demodulation software. In addition, the internal dimensions of the test box are 20cm×15cm×20cm, and a small circular hole with a diameter of 1cm is opened on the side to facilitate the insertion and wiring of the sensor. The internal layout of the test box should ensure that the soil samples are evenly distributed to avoid local density differences.

[0035] Randomly select at least three different heating powers Q, and continuously heat the target soil for a preset time. The continuous heating time is the same under each heating power; record the temperature characteristic value T of the soil during the heating process t , and soil moisture w, plot the temperature characteristic value T under different heating power Q t -Fitting curve of soil moisture content w. The heating time of the calibration test is consistent with the actual application heating time.

[0036] In the embodiment, the calibration test selects soils with moisture contents of 0 g / g, 0.02 g / g, 0.04 g / g, 0.06 g / g, 0.08 g / g, 0.10 g / g, 0.12 g / g, 0.14 g / g, 0.16 g / g, 0.21 g / g, and 0.31 g / g, and configures corresponding soil samples;

[0037] The prepared soil samples were controlled to have a dry density of 1.4 g / cm3 and filled in layers into a 20 cm × 15 cm × 20 cm test box;

[0038] Cover the soil sample with a layer of plastic film to prevent water evaporation and ensure a stable moisture content;

[0039] Slowly insert the 15cm long and 6mm diameter AH-FBG corundum tube sensor into the soil sample prepared in step 1 through the small circular hole on the test box to ensure good contact between the sensor and the soil sample.

[0040] At least three different heating powers are randomly selected for calibration test. The specific heating power range in the test is 10, 20, and 35 W / m. The continuous heating time is the same under each heating power. Figure 3 , T under different heating powers t -w calibration test results show that under different heating power conditions, T tThe -w fitting curve is in good agreement with the calibration test data points. This result shows the significant influence of heating power on the soil moisture measurement results and provides support for the reliability of the model.

[0041] Step S2: Based on the temperature characteristic value T of each soil body under each heating power Q t -Fitting curve of soil moisture content w, establishing temperature characteristic value T for different soil moisture content w t The linear relationship between heating power Q;

[0042] The heat pulse moisture probe buried in the soil is regarded as an infinitely long cylindrical heat source. According to the principle of cylindrical heat source, after it is heated for a certain period of time, the temperature characteristic value T measured by the sensor is established. t The linear relationship between it and the heating power Q is as follows:

[0043]

[0044] Where, T t is the temperature characteristic value (°C), that is, the temperature rise value, T(t) is the sensor temperature corresponding to the heating time t (°C), T0 is the initial ambient temperature (°C), Q is the heating power per unit length (W / m), λ is the thermal conductivity of the soil (W / (m·K)), R is the thermal resistance between the sensor and the soil wall per unit length (m·K / W), and K is the thermal diffusivity of the soil (m 2 / s), a is the outer diameter of the sensor (m), c = 1.7811 = exp(γ) and γ = 0.5772, γ is the Euler constant.

[0045] Temperature characteristic value T t The linear relationship with heating power Q is as follows Figure 4 As shown in the figure, it can be seen that as the heating power increases, T t There is an obvious linear growth, and the degree of fit between each data point and the fitting straight line is high, indicating that there is a good linear correlation between the two.

[0046] Step S3: Based on the temperature characteristic value T t The linear relationship between the heating power Q and the corresponding temperature characteristic value T under any target heating power is calculated. t , and obtain the temperature characteristic value T under the target heating power t The data points composed of soil moisture w (T t , w);

[0047] In step S3, based on the temperature characteristic value T t The linear relationship between the heating power Q and the temperature characteristic value T under different soil moisture content w is plotted. t-Fitting curve of heating power Q, find the corresponding temperature characteristic value T under any target heating power under given soil moisture content w on the fitting curve t .

[0048] In the embodiment, according to the test results at three heating powers of 10W / m, 20W / m and 35W / m, based on its T t -Q linear relationship, T at any power can be calculated t value, and then calculate the target heating power of 25W / m for multiple groups (T t ,w) value.

[0049] Step S4: Based on the multiple data points (T t , w), fitting the temperature characteristic value T under the target heating power t The calibration formula of soil moisture content w, as well as the parameters in the calibration formula.

[0050] Fitting the temperature characteristic value T under the target heating power t The calibration formula of soil moisture content w is as follows:

[0051]

[0052] Where, T t is the temperature characteristic value (℃), w is the soil moisture content (g / g), A, B, C are the parameters in the calibration formula, and multiple data points under the target heating power (T t , w) is substituted into the above equation to obtain the fitting result.

[0053] The T calculated under the target heating power t -w Temperature characteristic value T calculated by calibration formula t Compared with the experimentally measured temperature characteristic value T t For comparison, such as Figure 5 As shown in the figure, good consistency is shown, verifying the reliability and accuracy of the model. This shows that the formula derived based on this method can well reflect the actual calibration results, providing reliable support for further measurement and analysis.

[0054] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in this field without departing from the spirit of the present invention.

Claims

1. A method for determining a thermal pulse moisture probe calibration formula under arbitrary heating power, characterized in that: The method includes the following steps S1 to S4: Step S1: bury the thermal pulse moisture probe into soil with different moisture contents, and randomly select at least three different heating powers Q to heat each soil, and measure the temperature characteristic value T t - Calibration test of soil moisture content w to obtain the temperature characteristic value T of each soil under different heating powers t -Fitting curve of soil moisture content w; Step S2: Based on the temperature characteristic value T of each soil body under each heating power Q t -Fitting curve of soil moisture content w, establishing temperature characteristic value T for different soil moisture content w t The linear relationship between heating power Q; Step S3: Based on the temperature characteristic value T t The linear relationship between the heating power Q and the corresponding temperature characteristic value T under any target heating power is calculated. t , and obtain the temperature characteristic value T under the target heating power t The data points composed of soil moisture w (T t , w); Step S4: Based on the multiple data points (T t , w), fitting the temperature characteristic value T under the target heating power t The calibration formula of soil moisture content w, as well as the parameters in the calibration formula.

2. The method for determining a thermal pulse moisture probe calibration formula under arbitrary heating power according to claim 1, characterized in that: In step S1, at least three different heating powers Q are randomly selected, and the target soil is continuously heated for a preset time. The continuous heating time is the same under each heating power; the temperature characteristic value T of the soil during the heating process is recorded. t , and soil moisture w, plot the temperature characteristic value T under different heating power Q t -Fitting curve of soil moisture content w.

3. The method for determining a thermal pulse moisture probe calibration formula under arbitrary heating power according to claim 1, characterized in that: The calibrated test heating time in step S1 is consistent with the actual application heating time.

4. The method for determining a thermal pulse moisture probe calibration formula under arbitrary heating power according to claim 1, characterized in that: The temperature characteristic value T established in step S2 t The linear relationship between it and the heating power Q is as follows: Where, T t is the temperature characteristic value, T(t) is the sensor temperature corresponding to the heating time t, T0 is the initial ambient temperature, Q is the heating power per unit length, λ is the thermal conductivity of the soil, R is the thermal resistance between the sensor and the soil wall per unit length, K is the thermal diffusivity of the soil, a is the outer diameter of the sensor, c = 1.7811 = exp(γ) and γ = 0.5772, and γ is the Euler constant.

5. The method for determining a thermal pulse moisture probe calibration formula under arbitrary heating power according to claim 1, characterized in that: In step S3, based on the temperature characteristic value T t The linear relationship between the heating power Q and the temperature characteristic value T under different soil moisture content w is plotted. t -Fitting curve of heating power Q, find the corresponding temperature characteristic value T under any target heating power under given soil moisture content w on the fitting curve t .

6. The method for determining a thermal pulse moisture probe calibration formula under arbitrary heating power according to claim 1, characterized in that: Step S4: Fitting the temperature characteristic value T under the target heating power t The calibration formula of soil moisture content w is as follows: Where, T t is the temperature characteristic value, w is the soil moisture content, A, B, C are the parameters in the calibration formula, and multiple data points (T t , w) is substituted into the above equation to obtain the fitting result.

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