阅读说明：本技术 茎流信号采集节点和利用该节点的基于温补偿的热源自适应茎流测量系统 (Stem flow signal acquisition node and heat source self-adaptive stem flow measuring system based on temperature compensation and using same ) 是由 胡瑾 冯盼 张仲雄 李斌 高攀 汪志胜 于 2019-09-30 设计创作，主要内容包括：一种茎流信号采集节点,包括包裹于植物茎部的环形的加热片,在加热片外表面环绕设置有热电堆,在植物茎部靠近加热片的上端和下端分别设置有上部热电偶组和下部热电偶组,热电堆、上部热电偶组和下部热电偶组的信号输出端连接信号处理模块,信号处理模块的输出端连接单片机的信号输入端,信号处理模块包括依次连接的放大器、滤波器和模数转换器,单片机连接有与数据处理终端双向通信的无线通信模块,本发明还提供了一种利用茎流信号采集节点的基于温补偿的热源自适应茎流测量系统,包括茎流信号采集节点和数据处理终端,茎流信号采集节点采集温度信息和功率信息,数据处理终端向茎流信号采集节点下发功率控制指令,本发明可保证茎流测量精度。(The invention discloses a stem flow signal acquisition node, which comprises an annular heating sheet wrapped on a plant stem, wherein a thermopile is arranged on the outer surface of the heating sheet in a surrounding manner, an upper thermocouple group and a lower thermocouple group are respectively arranged at the upper end and the lower end of the plant stem close to the heating sheet, the signal output ends of the thermopile, the upper thermocouple group and the lower thermocouple group are connected with a signal processing module, the output end of the signal processing module is connected with the signal input end of a single chip microcomputer, the signal processing module comprises an amplifier, a filter and an analog-to-digital converter which are sequentially connected, the single chip microcomputer is connected with a wireless communication module which is in two-way communication with a data processing terminal, the invention also provides a heat source self-adaptive stem flow measurement system based on temperature compensation by utilizing the stem flow signal acquisition node, the system comprises the stem flow signal acquisition node and the data, the data processing terminal issues a power control instruction to the stem flow signal acquisition node, and the method and the system can ensure the measurement precision of the stem flow.)

1. The stem flow signal acquisition node is characterized by comprising an annular heating sheet (3) wrapped on the stem of a plant, wherein a thermopile (4) is arranged on the outer surface of the heating sheet (3) in a surrounding manner, an upper thermocouple group (1) and a lower thermocouple group (5) are respectively arranged at the upper end and the lower end of the plant stem close to the heating sheet (3), the signal output ends of the thermopile (4), the upper thermocouple group (1) and the lower thermocouple group (5) are connected with a signal processing module, the output end of the signal processing module is connected with the signal input end of a single chip microcomputer, the signal processing module comprises an amplifier, a filter and an analog-to-digital converter which are sequentially connected, the heating sheet (3) is connected with a PWM (pulse width modulation) driving module, the PWM driving module uses two field effect tubes to form a common-set amplifying circuit, and the heating power of the heating, the single chip microcomputer is connected with a wireless communication module which is in two-way communication with the data processing terminal.

2. The stem flow signal acquisition node according to claim 1, wherein a foam insulation layer (2) is tightly wrapped outside the heating sheet (3), the thermopile (4) is located between the heating sheet (3) and the foam insulation layer (2), the foam insulation layer (2) is internally provided with a foam insulation material, and the outside is provided with a silvery white flame-retardant waterproof insulation pad.

3. The stem flow signal collection node according to claim 1, wherein the upper thermocouple group (1) and the lower thermocouple group (5) are both composed of two thermocouples which measure the temperature electrical signals of the plant stem at the upper and lower four points of the heating plate (3), respectively, and the thermopile (4) is a thin film type thermopile for measuring the electrical signals of the transverse temperature average difference.

4. The stem flow signal acquisition node according to claim 1, wherein the single chip microcomputer is connected with a power detection module, the power detection module shunts a circuit of the heating plate (3), shunted micro current and voltage are detected by an INA226 chip, detected current and voltage signals are input to the single chip microcomputer in a serial port mode, a real current value is calculated according to a shunting ratio, the wireless communication module is a Lora wireless communication module, a bidirectional transmission mode is adopted, and forward transmission is to acquire temperature information and power information stored in the single chip microcomputer and transmit the temperature information and the power information to a data processing terminal; the reverse transmission is to transmit a power control instruction of the data processing terminal to the heating sheet (3) to the single chip of the signal acquisition node.

5. The stem flow signal acquisition node according to claim 1, wherein the electricity utilization components in the node are all powered by lithium batteries, and the lithium batteries are connected with solar power generation boards capable of charging the lithium batteries.

6. A heat source self-adaptive stem flow measuring system based on temperature compensation and utilizing the stem flow signal acquisition node of claim 1 comprises the stem flow signal acquisition node and a data processing terminal, wherein the stem flow signal acquisition node acquires temperature information and power information, and the data processing terminal issues a power control command to the stem flow signal acquisition node.

7. The heat source self-adaptive stem flow measuring system based on temperature compensation and utilizing the stem flow signal acquisition node as claimed in claim 6, wherein the data processing terminal carries out multi-directional processing through external temperature information, upper and lower temperature differences of the plant stem and diameter information of the plant stem by judging whether the upper and lower temperature differences of the plant stem are within a proper range or not, a stable heating power is calculated through an error reverse transmission neural network model, a control instruction of the heating power is transmitted to the single chip microcomputer, and the single chip microcomputer adjusts the heating power of the heating plate (3) through the PWM driving module according to the control instruction.

8. The system for measuring the stem flow of the heat source self-adaption based on the temperature compensation by utilizing the stem flow signal acquisition node is characterized in that the data processing terminal takes a raspberry pi as a core, the error reverse propagation neural network model adopts a three-layer neural network model structure, the model inputs are the diameter of the stem of a plant, the thermal conductivity of a foam insulation layer (2), the thermal conductivity of water, the distance between the upper part and the lower part of a thermocouple, the plant type, the potential of a thermopile, the power of a heating plate (3) and the temperature of the thermocouple, and the model outputs are the power of the heating plate.

9. The system for measuring the adaptive heat source based on the temperature compensation by utilizing the stem flow signal acquisition node is characterized in that the data processing terminal applies the energy balance processing to the acquired data as follows:

P-(q_u+q_d+q_r+q_f+S)＝0

wherein P is the power of the heating plate (3) and is measured by the power detection module;

q_uand q is_dRespectively, the upper and lower heat diffusion fluxes,K_stthe coefficient of thermal conductivity (W/m. DEG C.) of the plant stem, A is the cross-sectional area (m) of the plant stem²)，The temperature gradient of the upper part and the lower part of the stem of the plant is shown, the unit ℃/m is dT is the temperature difference of the upper point and the lower point measured by a thermocouple, and dx is the distance between the upper point and the lower point of the thermocouple;

q_ris the radial heat conduction rate q outwards through the foam heat-insulating layer (2)_r＝K_shE, E is the voltage measured by the thermopile (4), K_shIs the thermal conductivity constant, in W/deg.C;

q_fis the radial heat transfer rate of liquid stem flow through the stem of the plant, q_f＝C_P·F·(T_u-T_d)，C_PIs the specific heat capacity of water, F is the stem flow, T_uAnd T_dThe temperature of the upper and lower thermocouple groups;

s is the storage and very small part of the heat in the plant stem;

thus, F ═ P- (K)_st·A·(dT_u+dT_d)/dx)-K_sh·E)/[C_P·(T_u-T_d)]。

10. The adaptive heat source stemflow measurement system based on temperature compensation using stemflow signal acquisition nodes as claimed in claim 9, wherein the error back propagation neural network is a multi-layer feedforward neural network, and the sectional area of the plant, Ksh, Kst, thermopile average temperature, predicted stemflow information, the distance between the thermocouple between the upper and lower points, and the temperature difference between the upper and lower points are used as forward propagation input signals to be transmitted from the input layer, and after layer-by-layer processing by the hidden layer, the forward propagation input signals are transmitted to the output layer, and if the output layer does not meet the desired output (Tu-Td), the backward propagation stage is performed; the error back transmission is to back transmit the output error to the input layer by layer through a hidden layer in a certain form, and distribute the error to all units of each layer, thereby obtaining the error signal of each layer of units, and the error signal is used as the basis for correcting the weight of each unit; after the weight values of all layers are corrected for many times, a model is built.

Technical Field

The invention belongs to the technical field of intelligent agricultural facilities, relates to researches on forestry ecological protection engineering, water resource management, hydrology, crop cultivation, plant moisture relation, plant biomass estimation and the like, and particularly relates to a stem flow signal acquisition node and a heat source self-adaptive stem flow measurement system comprising the same and based on temperature compensation.

Background

The stem flow of plant stems is one of important physiological information of plants, and the acquisition of the stem flow plays an important role in plant physiological research and forest vegetation protection research. The current measurement principles of the stem flow sensor include a thermal pulse method, a thermal equilibrium method and a thermal diffusion method.

The thermal pulse method needs to insert a temperature probe into the stem, and the thermal balance method is used for measuring the stem flow of the plant under the conditions that the transpiration effect is not obvious or the external temperature is low at night, in rainy days and the like, the outward heat conducted transversely is relatively more, and the upward conducted heat along the stem of the plant is relatively low, so that the temperature difference measured by a thermocouple in the radial direction of the stem of the plant is relatively low, and the measurement is inaccurate. Especially in the case of small stem flow, the above methods do not give accurate results.

Meanwhile, most of runoff sensors of the existing thermal balance method directly transmit electric signals of temperature to a data processing terminal through a thermocouple wire, and a wired data transmission mode causes that one data processing terminal can only correspond to a small number of signal acquisition nodes, so that when a large amount of field measurements are carried out, the stem flow acquisition is very inconvenient.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a stem flow signal acquisition node and a heat source self-adaptive stem flow measurement system comprising the same and based on temperature compensation, which are improved on the basis of the existing thermal balance method, can still accurately measure the stem flow under the condition of small stem flow and can intelligently adjust the heating quantity, and on one hand, the invention solves the problem of low precision in stem flow measurement under the conditions of unobvious transpiration effect at night, rainy weather and the like or low external temperature; on the other hand, the problem that a data processing terminal can only correspond to a small number of signal acquisition nodes in a wired data transmission mode is solved.

In order to achieve the purpose, the invention adopts the technical scheme that:

a stem flow signal acquisition node comprises an annular heating sheet 3 wrapped on the stem of a plant, a thermopile 4 is arranged on the outer surface of the heating sheet 3 in a surrounding manner, the upper end and the lower end of the plant stem part close to the heating sheet 3 are respectively provided with an upper thermocouple group 1 and a lower thermocouple group 5, the signal output ends of the thermopile 4, the upper thermocouple group 1 and the lower thermocouple group 5 are connected with a signal processing module, the output end of the signal processing module is connected with the signal input end of the singlechip, the signal processing module comprises an amplifier, a filter and an analog-to-digital converter which are connected in sequence, the heating plate 3 is connected with a PWM (pulse-width modulation) driving module, the PWM driving module uses two field effect tubes to form a co-integrated amplifying circuit, the heating power of the heating plate 3 is adjusted by PWM, and the single chip microcomputer is connected with a wireless communication module which is in two-way communication with the data processing terminal.

The heating plate 3 is externally and closely wrapped with a foam heat-insulating layer 2, the thermopile 4 is positioned between the heating plate 3 and the foam heat-insulating layer 2, the foam heat-insulating layer 2 is internally provided with a foam heat-insulating material, and the outside is a silvery white flame-retardant waterproof heat-insulating pad.

The upper thermocouple group 1 and the lower thermocouple group 5 are composed of two thermocouples and are used for measuring temperature electric signals of the plant stem at the upper and lower four points of the heating sheet 3 respectively, and the thermopile 4 is a thin film thermopile and is used for measuring electric signals of transverse temperature average difference.

The single chip microcomputer is connected with a power detection module, the power detection module shunts a circuit of the heating plate 3, shunted micro current and voltage are detected through an INA226 chip, detected current and voltage signals are input to the single chip microcomputer in a serial port mode, a real current value is calculated according to the proportion of shunting, the wireless communication module is a Lora wireless communication module, a bidirectional transmission mode is adopted, forward transmission is to collect temperature information and power information stored in the single chip microcomputer and transmit the temperature information and the power information to a data processing terminal; the reverse transmission is to transmit a power control instruction of the data processing terminal to the heating plate 3 to the single chip of the signal acquisition node.

The power utilization components in the nodes all use lithium batteries as power sources, and the lithium batteries are connected with solar power generation panels capable of charging the lithium batteries.

The invention also provides a heat source self-adaptive stem flow measuring system based on temperature compensation by utilizing the stem flow signal acquisition node, which comprises the stem flow signal acquisition node and a data processing terminal, wherein the stem flow signal acquisition node acquires temperature information and power information, and the data processing terminal issues a power control instruction to the stem flow signal acquisition node.

Data processing terminal is through judging whether temperature difference is in an appropriate within range about the plant stem, if not when this within range, then carries out diversified processing through ambient temperature information, temperature difference and plant stem diameter information about the plant stem, calculates a stable heating power through error reverse pass neural network model to give this heating power's control command the singlechip, the singlechip is adjusted 3 heating power of heating plate through PWM drive module according to this control command.

The data processing terminal takes a raspberry pi as a core, the error reverse-transmission neural network model adopts a three-layer neural network model structure, the input of the model is the diameter of a plant stem, the heat conductivity of the foam heat-insulating layer 2, the heat conductivity of water, the distance between the upper part and the lower part of a thermocouple, the plant type, the potential of a thermopile, the power of the heating plate 3 and the temperature of the thermocouple, and the output of the model is the power of the heating plate.

The data processing terminal applies energy balance processing to the acquired data as follows:

P-(q_u+q_d+q_r+q_f+S)＝0

wherein P is the power of the heating plate 3, and is measured by the power detection module;

q_uand q is_dRespectively, the upper and lower heat diffusion fluxes,K_stthe coefficient of thermal conductivity (W/m. DEG C.) of the plant stem, A is the cross-sectional area (m) of the plant stem²)，The temperature gradient of the upper part and the lower part of the stem of the plant is shown, the unit ℃/m is dT is the temperature difference of the upper point and the lower point measured by a thermocouple, and dx is the distance between the upper point and the lower point of the thermocouple;

q_ris the radial heat conduction rate q outwards through the foam heat insulation layer 2_r＝K_shE, E is the voltage measured by the thermopile 4, K_shIs the thermal conductivity constant, in W/deg.C;

q_fis the radial heat transfer rate of liquid stem flow through the stem of the plant, q_f＝C_P·F·(T_u-T_d)，C_PIs the specific heat capacity of water, F is the stem flow, T_uAnd T_dThe temperature of the upper and lower thermocouple groups;

s is the storage and very small part of the heat in the plant stem;

thus, F ═ P- (K)_st·A·(dT_u+dT_d)/dx)-K_sh·E)/[C_P·(T_u-T_d)]。

The error reverse transmission neural network is a multilayer feedforward neural network, plant sectional area, Ksh, Kst, thermopile average temperature, predicted stem flow information, the distance between a thermocouple of an upper point and a thermocouple of a lower point and the temperature difference of the upper point and the lower point are used as input signals transmitted from an input layer in a forward transmission mode, the input signals are transmitted to an output layer after being processed layer by layer through a hidden layer, and if the output layer does not accord with the expected output Tu-Td, the reverse transmission stage is carried out; the error back transmission is to back transmit the output error to the input layer by layer through a hidden layer in a certain form, and distribute the error to all units of each layer, thereby obtaining the error signal of each layer of units, and the error signal is used as the basis for correcting the weight of each unit; after the weight values of all layers are corrected for many times, a model is established, and Tu-Td can be ensured to be in a proper range through the model, so that the system can perform heat source self-adaptation autonomously.

Compared with the prior art, the invention has the beneficial effects that:

1. compared with the heat pulse method, the measuring result can be directly obtained without inserting a temperature probe into the stem.

2. The power of the heating sheet can be changed in real time according to the change of the external environment, so that the radial heat dissipation rate of a stable plant stem is ensured, and the accuracy of stem flow measurement is ensured.

3. The stem flow signal acquisition node is designed in a wrapping mode, the plant cannot be damaged during detection, the energy balance principle is utilized, the influence of unevenness of the xylem of the plant cannot be caused compared with a pin type, and the detection precision is improved to a great extent.

4. The stem flow signal acquisition node uses a lithium battery and a solar power supply device, and the requirements of a large number of field experiments are met.

5. The information collected by the stem flow signal collection node is transmitted to the data processing terminal through the Lora, and data information can be collected and processed in a large batch.

The invention can change the power of the heating sheet in real time according to the change of the external environment, thereby ensuring the radial heat dissipation rate of a stable plant stem, ensuring the precision of stem flow measurement, and solving the problems of larger measurement error caused by small stem flow at night or in rainy days and the problem of field measurement of long-distance plant stem flow.

Drawings

FIG. 1 is a schematic diagram of the overall architecture of the stem flow measurement system of the present invention.

FIG. 2 is a block diagram of the design framework of the stem flow measurement system of the present invention.

Fig. 3 is a hardware platform framework diagram of a stem flow signal acquisition node of the present invention.

FIG. 4 is a flow chart of the training of the temperature control decision model of the present invention.

FIG. 5 is a flow chart of the present invention for prediction using a temperature control decision model.

FIG. 6 is a Raspberry pie operation interface one.

FIG. 7 is a raspberry pi operation interface two.

FIG. 8 is a raspberry pi operation interface three.

Detailed Description

The embodiments of the present invention will be described in detail below with reference to the drawings and examples.

As shown in fig. 1 and fig. 2, the overall architecture of the heat source adaptive stem flow measuring system based on temperature compensation according to the present invention is divided into two modules: the system comprises a stem flow signal acquisition node and a data processing terminal, wherein the stem flow signal acquisition node acquires temperature information and power information, and the data processing terminal issues a power control instruction to the stem flow signal acquisition node.

The stem flow signal acquisition nodes can be designed in a packaging mode, each stem flow signal acquisition node comprises an annular heating sheet 3 wrapped on the stem of a plant, a thermopile 4 is arranged on the outer surface of the heating sheet 3 in a surrounding mode, and an upper thermocouple group 1 and a lower thermocouple group 5 are respectively arranged at the upper end and the lower end, close to the heating sheet 3, of the stem of the plant.

For sealed and adiabatic, can be closely the parcel in the heating plate 3 outside and be provided with foam heat preservation 2, thermopile 4 is located between heating plate 3 and foam heat preservation 2, and foam heat preservation 2 is inside to be foam heat insulating material, and the outside is the fire-retardant waterproof heat preservation pad of silvery white to this guarantees the influence of ambient temperature system.

The upper thermocouple group 1 and the lower thermocouple group 5 can be composed of two thermocouples, the thermocouples can adopt TT-T-30, the distance between the two thermocouples of the upper thermocouple group 1 is fixed and can be positioned at two ends of the diameter, the two thermocouples of the lower thermocouple group 5 are respectively positioned under the two thermocouples of the upper thermocouple group 1 and respectively measure temperature electric signals of plant stems at the upper and lower four points of the heating sheet 3, the thermopile 4 is a thin film type thermopile and is used for measuring electric signals of transverse temperature average difference, and an annular T-shaped thermopile can be specifically adopted.

As shown in fig. 3, the signal output ends of the thermopile 4, the upper thermocouple group 1, and the lower thermocouple group 5 are connected to a signal processing module, the output end of the signal processing module is connected to the signal input end of the single chip microcomputer, the signal processing module is used for processing the electric signals collected by the thermocouples, and the signal processing module includes an amplifier, a filter, and an analog-to-digital converter which are connected in sequence, and the electric signals are amplified, filtered, and subjected to digital-to-analog conversion in sequence and then stored in a register; the singlechip is connected with a wireless communication module which is in bidirectional communication with the data processing terminal. The wireless communication module is a Lora wireless communication module and adopts a bidirectional transmission mode, and forward transmission is to collect temperature information and power information stored in the singlechip and transmit the temperature information and the power information to the data processing terminal; the reverse transmission is to transmit a power control instruction of the data processing terminal to the heating plate 3 to the single chip of the signal acquisition node.

The heating plate 3 is connected with a PWM driving module, PWM mainly adjusts the heating plate, and the PWM driving module uses two field effect tubes to form a common-set amplifying circuit, so that the heating power of the heating plate 3 is adjusted by PWM.

Meanwhile, the single chip microcomputer can be further connected with a power detection module, the power detection module shunts a circuit of the heating plate 3, the shunted micro current and voltage are detected through an INA226 chip, signals of the detected current and voltage are input to the single chip microcomputer in a serial port mode, and then the real current value is calculated by means of the single chip microcomputer and stored in a register.

The heating plate 3 of stem flow signal acquisition node, the thermopile 4, upper portion thermocouple group 1 and lower part thermocouple group 5, the singlechip, PWM drive module, power consumption parts such as signal processing module all use the lithium cell as the power, the lithium cell is connected with the solar panel that can charge for it, can supply power to the signal acquisition node by automatic cutout when the lithium cell electric quantity is low excessively, wait for the solar panel to charge for the lithium cell and automatic circular telegram again after sufficient, guarantee signal acquisition node's power supply sufficient.

The heating part of the stem flow signal acquisition node is mainly an execution device which ensures that the radial temperature difference of the plant to be detected in the stem flow is within a reasonable range, has a good physical structure and necessary signal acquisition equipment, and issues a corresponding heating control instruction through a data processing terminal according to the monitored thermoelectric signal.

The data processing terminal is provided with an LCD display screen which can display and set parameters of an upper computer program, and managers can actively issue heating control instructions according to the preset range according to the display. The heat conductivity of the plant stem and the diameter and the serial number of the plant stem can be set in the upper computer, the interval between the upper thermocouple and the lower thermocouple of the plant stem is used for issuing an automatic control instruction by virtue of a program, the heating power is intelligently adjusted, the radial heat conduction quantity is increased, and the measurement precision is improved. The specific scheme is that whether temperature difference is in a proper range or not through judging the upper and lower temperature difference of the plant stem, when the temperature difference is not in the range, the multi-azimuth processing is carried out through external temperature information, the upper and lower temperature difference of the plant stem and the diameter information of the plant stem, a stable heating power is calculated through an established error reverse-propagation neural network model, and a control instruction of the heating power is transmitted to a single chip microcomputer of a system on chip of a signal acquisition node through Lora.

When automatic control is adopted, a raspberry pie is taken as a core, a specific error reverse transmission neural network model adopts a three-layer neural network model structure, wherein four values of the diameter of a plant, the heat conductivity of a heat insulation material, the heat conductivity of water, the distance between the upper part and the lower part of a thermocouple, the type of the plant, the potential of a thermopile, the power of a heating plate and the temperatures of the upper thermocouple and the lower thermocouple are selected for input of the model, and the power of the heating plate is selected for output of the model.

For the calculation of the final stem flow, on the data processing terminal, for the processing of the acquired data, the energy balance is applied as follows:

P-(q_u+q_d+q_r+q_f+ S) ═ 0 (equation 1)

Where P is the power of the heater, q_uAnd q is_dRespectively, upper and lower heat diffusion fluxes, q_rRate of lateral heat transfer through the foam insulation jacket, q_fRadial rate of heat transfer by liquid stem flow through the plant stem. S is the minimum partial heat in the storage and plant stem, which can be made equal to about 0 for the whole system.

The power P of the heater is measured by a power detection module, and the heat diffusion q above and below the stem of the plant is measured_uAnd q is_dThe calculation of Fourier heat diffusion law of heat conduction shows that:

wherein K_stThe coefficient of thermal conductivity (W/m. DEG C.) of the plant stem, A is the cross-sectional area (m) of the plant stem²) dT/dx is the temperature gradient (DEG C/m) of the upper part and the lower part of the plant stem, dT is the temperature difference of the upper point and the lower point measured by a thermocouple, and dx is the distance between the upper point and the lower point of the thermocouple. Radial thermal radiation power q_rThe voltage E, K is measured by a thin-film thermopile_shAs a heat conduction constant, the unit is (W/DEG C), and the transverse heat dissipation amount can be accurately calculated through a measured thermopile voltage signal. The size is set by the way of setting the zero point, if the plant is in the afternoon with higher temperature, the plant can close the transpiration by itself when the transpiration of the plant reaches the maximum, at the moment, the stem flow is zero, q is_fTo zero, K can be calculated according to equation 5_sh。

q_r＝K_shE (formula 3)

Wherein q is_fI.e. the required amount, is measured. Wherein:

q_f＝C_P·F·(T_u-T_d) (formula 4)

C_pWith respect to the specific heat capacity of water, F is the flow rate, T_uAnd T_dAbove and below, the stem flow rate can be obtained by combining the above formula:

F＝(P-(K_st·A·(dT_u+dT_d)/dx)-K_sh·E)/[C_P·(T_u-T_d)](formula 5)

Temperature control decision model training as shown in fig. 4, a large number of experiments are performed to input known information of stem flow size, plant cross-sectional area, Ksh, Kst and the like into a model for training, wherein Tu-Td is used as a label to train a model. In practical use, as shown in fig. 5, information such as heating plate power, outside temperature, Kst, Ksh, four temperature information, cross-sectional area a, and stem flow size is input into a model prediction Tu-Td, and then compared with the actually measured Tu-Td, the data is used for calculating the actual stem flow when the similarity is high, and zero calibration is performed when the similarity is not high, and finally shutdown is performed.

In summary, the data processing terminal can process the collected temperature information of the four thermocouples and the thermopiles, the heat conductivity of the plant stem, the diameter of the plant stem and other information, measure and calculate the radial heat conduction rate and the transverse heat conduction rate of the liquid flow in the plant stem, finally calculate the size of the stem flow through the radial heat conduction rate and the transverse heat conduction rate of the liquid flow in the plant stem and the power of the heating plate, and display the size on the data processing terminal, wherein the process interfaces are shown in fig. 6, 7 and 8, and simultaneously transmit data to the cloud server, so that the size of the stem flow can be conveniently displayed in real time through the mobile phone app. The lithium battery and the solar power supply device are used on the signal acquisition node, and the requirements of a large number of field experiments are met. The system can accurately measure the stem flow of the plant stems, ensures the convenience and feasibility of field experiments, and plays an important role in plant physiological research and forest vegetation protection research.

The above embodiments are only for illustrating the invention and not for limiting the invention, and those skilled in the relevant art can make various changes and modifications without departing from the spirit and scope of the invention, so that the equivalent technical solution is also equivalent to the scope of the invention, and the scope of the invention is defined by the claims.