Low-temperature Dewar liquid nitrogen refrigerant liquid level detection device and measurement method

Abstract

The invention relates to the field of capacitive liquid level meters, in particular to a low-temperature Dewar liquid nitrogen refrigerant liquid level detection device and a measurement method, and solves the problem of low measurement precision in the prior art. The detection device comprises a superconducting polar plate floater arranged on the liquid level of a liquid nitrogen refrigerant in an inner cavity of the low-temperature Dewar; capacitance value information is converted into liquid level information through a microcontroller by means of a hybrid capacitor formed by the superconducting polar plate floater and the low-temperature Dewar. The low-temperature Dewar and the liquid nitrogen refrigerant in the low-temperature Dewar are regarded as a combined capacitor, and the real-time change of the liquid level height of the liquid nitrogen refrigerant in the low-temperature Dewar is deduced through the change of the value of the combined capacitor; the liquid level measuring device can operate in a low-temperature liquid nitrogen refrigerant environment through the superconducting polar plate floater, has the characteristics of low loss, high quality factor and excellent electromagnetic property, and can improve the measurement precision and accuracy of the liquid level height of the liquid nitrogen refrigerant.

Description

Technical Field

[0001] The present invention relates to the field of capacitance type liquid level gauges, in particular to a low-temperature Dewar liquid nitrogen refrigerant liquid level detection device and a measurement method. Background Art

[0002] High-temperature superconducting devices must maintain a superconducting state in an extremely low-temperature environment to provide excellent electromagnetic output. Existing technologies use cryogenic dewars to provide the low-temperature conditions necessary for this superconducting state. A stable low-temperature environment, maintained by sufficient liquid nitrogen refrigerant, is the prerequisite and foundation for the safe and efficient operation of high-temperature superconducting devices. With the emergence of high-temperature superconducting materials, the critical temperature of superconducting materials has surpassed the temperature range of liquid nitrogen refrigerants (77K), significantly reducing the cost and difficulty of cryogenic refrigeration systems.

[0003] However, the cryogenic Dewar is an opaque metal structure with limited internal space, which puts forward new requirements for the reliable and accurate operation of the liquid nitrogen refrigerant level detection device.

[0004] In the existing technology, capacitive liquid level gauges are widely used to detect the liquid nitrogen refrigerant level inside the cryogenic Dewar due to their low cost and good versatility. However, since they need to operate in extremely low temperature areas and low pressure environments for a long time, they are prone to irreversible damage to the functional properties of conventional materials, thereby affecting their real-time capacitance value. The measurement accuracy of the cryogenic liquid nitrogen refrigerant level detection cannot be guaranteed, and the liquid nitrogen refrigerant content inside the cryogenic Dewar cannot be accurately judged, which may affect the safe and stable operation of high-temperature superconducting equipment. Traditional capacitive level gauges work on the principle that changes in the liquid level between two capacitor plates affect the capacitance value. The change in capacitance is used to measure the liquid nitrogen refrigerant level. However, these technical issues exist: (1) The plate capacitor made of conventional materials needs to operate in the liquid nitrogen refrigerant temperature range (77 K), while the external signal capacitance measurement device operates in a room temperature environment (298 K). The two operate in different temperature ranges, and there is a non-negligible temperature difference heat leakage loss, which affects the signal measurement accuracy; (2) Due to the introduction of multiple capacitors and connecting circuits, as well as the influence of liquid nitrogen refrigerant temperature on the performance of conventional plate capacitors, the output of the capacitive level meter has nonlinear characteristics, and parasitic capacitance and distributed capacitance have a greater impact on sensitivity and measurement accuracy; (3) The traditional capacitance level gauge adopts the direct insertion measurement principle, which affects the spatial layout inside the cryogenic dewar.

[0005] There is an urgent need for a new type of liquid level detection device that can solve the above problems. Summary of the Invention

[0006] The present invention proposes a low-temperature dewar liquid nitrogen refrigerant level detection device and measurement method, which solves the problem that conventional capacitor devices affect the internal space of the low-temperature dewar and the resulting low measurement accuracy.

[0007] A technical solution of the present invention is implemented as follows: a low-temperature dewar liquid nitrogen refrigerant level detection device, the low-temperature dewar is used to store liquid nitrogen refrigerant, and includes a metal top cover, a metal wall, and a metal base; the metal wall and the metal base are further provided with an insulation layer near the low-temperature dewar cavity; the detection device includes a superconducting electrode plate float disposed above the liquid nitrogen refrigerant level in the low-temperature dewar cavity; the superconducting electrode plate float includes a low-density dielectric material and upper and lower superconducting electrode plates fixedly disposed above and below the dielectric material, respectively; the superconducting electrode plates are of the same size as the dielectric material; the superconducting electrode plate float is adapted to the size of the low-temperature dewar cavity and is in smooth contact with the insulation layer; the test terminals of the capacitance measuring device are respectively connected to the outer wall of the metal top cover and the outer wall of the metal base; the capacitance measuring device is communicatively connected to a microcontroller; the microcontroller includes: a signal acquisition module for collecting capacitance value information; a signal processing module for collecting capacitance value information and converting the capacitance value information into liquid level information; and a signal transmission module for transmitting the liquid level information; the signal transmission module is communicatively connected to a client or a display device.

[0008] In a further technical solution, the output value of the capacitance measuring device is the series capacitance of three equivalent capacitances C1, C2, and C3; wherein the equivalent capacitances of C1, C2, and C3 are: The series connection of C1, C2, and C3 to the external capacitance, that is, the output value of the capacitance measuring device is: ;in, is the dielectric constant, is the cross-sectional area of the capacitor plates, is the electrostatic force constant, is the distance between the two plates of the capacitor; the series capacitance value and the liquid level are in a one-to-one mapping relationship.

[0009] A further technical solution is that the measurement areas of C1, C2, and C3 are specifically: C1: used to test the hybrid capacitance composed of the outer wall of the metal top cover and the upper superconducting plate, wherein the gas-liquid mixture above the liquid nitrogen refrigerant is the medium between the two; C2 is used to test the hybrid capacitance composed of the lower superconducting plate and the inner wall of the metal wall, wherein the liquid nitrogen refrigerant stored in the low-temperature Dewar is the medium between the two; C3: used to test the hybrid capacitance of the inner wall and the outer wall of the metal base, wherein the low-temperature Dewar insulation layer is the medium between the two.

[0010] In a preferred technical solution, the signal processing module is an intelligent optimization control algorithm, which is used to collect the low-temperature Dewar liquid nitrogen refrigerant level corresponding to the capacitance measuring device at different frequencies as a data set, and further derive the real-time liquid nitrogen refrigerant level inside the low-temperature Dewar.

[0011] The present invention discloses a method for measuring the liquid level of a low-temperature dewar liquid nitrogen refrigerant. The method comprises the following steps: 1. placing a superconducting electrode plate float in the low-temperature dewar, keeping the two adapted to each other, and allowing the superconducting electrode plate float to slide and rise and fall frictionlessly along with the liquid nitrogen refrigerant level; 2. connecting test terminals of a capacitance measuring device to the outer wall of a metal top cover and the outer wall of a metal base, respectively; transmitting the collected capacitance value information of the capacitance measuring device to a microcontroller via a communication device; 3. collecting capacitance value information of the capacitance measuring device by a signal acquisition module of the microcontroller; processing the capacitance value information by a signal processing module and converting the capacitance value information into liquid level information; and transmitting the liquid level information to a client or a display device by a signal transmission module, thereby realizing liquid level detection in the low-temperature dewar.

[0012] A further technical solution is that when the cryogenic Dewar is fully loaded with liquid nitrogen refrigerant, C1 does not contain the gas-liquid mixture above the liquid nitrogen refrigerant, the detection value of C1 is zero, and the series capacitance value of C2 and C3 is output externally.

[0013] A further technical solution is to output the series capacitance value of C1, C2 and C3 to the outside when the liquid nitrogen refrigerant level in the low-temperature Dewar drops.

[0014] A further technical solution is that when the liquid nitrogen refrigerant level inside the cryogenic Dewar drops to zero, that is, the cryogenic Dewar does not contain liquid nitrogen refrigerant and is completely filled with a gas-liquid mixture, the series capacitance value of C1 and C3 is output to the outside.

[0015] The present invention discloses a low-temperature dewar liquid nitrogen refrigerant level detection device and measurement method. The low-temperature dewar itself, a superconducting electrode float, and the liquid nitrogen refrigerant inside are regarded as a joint capacitor. The real-time change of the internal liquid nitrogen refrigerant level is inferred by the change of the joint capacitance value. The device can greatly save space inside the low-temperature dewar and directly measure the capacitance value externally, without the need for a dedicated measurement channel spanning the low-temperature dewar interior and the normal temperature environment. The device can operate in a low-temperature liquid nitrogen refrigerant environment through the superconducting electrode float. The device has the characteristics of low loss, high quality factor, and excellent electromagnetic properties, and can improve the measurement precision and accuracy of the liquid nitrogen refrigerant level. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0017] Figure 1 : Equivalent schematic diagram of the test device; Figure 2 : Schematic diagram of superconducting plate float; Figure 3 : equivalent capacitance of the test device; Figure 4 : Equivalent capacitance test results of the test device at different liquid nitrogen refrigerant levels; Among them: 1. Metal top cover outer wall 1; 2. Metal top cover 2; 3. Metal base inner wall; 4. Superconducting plate float 4; 5. Liquid nitrogen refrigerant 5; 6. Metal base outer wall 6; 7. Insulation layer 7; 8. Gas-liquid mixture 8; 9. Upper superconducting plate 9; 10. Lower superconducting plate 10. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention. Specific implementation method 1 like Figure 1 The equivalent schematic diagram of the test device is shown, which shows a low-temperature Dewar liquid nitrogen refrigerant level detection device. The low-temperature Dewar is used to store liquid nitrogen refrigerant 5, including a metal top cover 2, a metal wall, and a metal base; the metal wall and the metal base are also provided with an insulation layer 7 near the low-temperature Dewar cavity; the detection device includes a superconducting electrode float 4 provided on the liquid surface of the liquid nitrogen refrigerant 5 in the low-temperature Dewar cavity; Figure 2 As shown in the schematic diagram of the superconducting plate float, the superconducting plate float 4 comprises a low-density dielectric material and an upper superconducting plate 9 and a lower superconducting plate 10 fixedly disposed above and below the dielectric material, respectively. The superconducting plates are the same size as the dielectric material. The superconducting plate float 4 is adapted to the dimensions of the low-temperature Dewar cavity and is in smooth, frictionless contact with the insulation layer 7. The test terminals of the capacitance measuring device are respectively connected to the outer wall 1 of the metal top cover and the outer wall 6 of the metal base. The output value of the capacitance measuring device is the series capacitance of three equivalent capacitances C1, C2, and C3; Figure 3The equivalent capacitance of the test device is shown in Figure 2. The equivalent capacitance of C1, C2, and C3 is: The external capacitance of C1, C2, and C3, i.e. the output value of the capacitance measuring device, is: ;in, is the dielectric constant, is the cross-sectional area of the capacitor plates, is the electrostatic force constant, is the distance between the two plates of the capacitor; Figure 4 The equivalent capacitance test results of the test device at different liquid nitrogen refrigerant levels show a one-to-one mapping relationship between the series capacitance value and the liquid level. The specific measurement areas of C1, C2, and C3 are as follows: C1: used to test the hybrid capacitance composed of the outer wall 1 of the metal top cover and the upper superconducting plate 9, wherein the gas-liquid mixture 8 above the liquid nitrogen refrigerant 5 is the medium between the two; C2 is used to test the hybrid capacitance composed of the lower superconducting plate 10 and the inner wall of the metal wall, wherein the liquid nitrogen refrigerant 5 stored in the low-temperature Dewar is the medium between the two; C3: used to test the hybrid capacitance of the inner wall of the metal base and the outer wall of the metal base, wherein the low-temperature Dewar insulation layer 7 is the medium between the two.

[0020] The capacitance measuring device is communicatively connected to a microcontroller; the microcontroller includes: a signal acquisition module for collecting capacitance value information; a signal processing module for collecting capacitance value information and converting the capacitance value information into liquid level information; a signal transmission module for sending liquid level information; the signal transmission module is communicatively connected to a client or a display device.

[0021] During use, the superconducting plate float 4 is placed in the cryogenic dewar, and the two are kept compatible. The superconducting plate float 4 slides and rises and falls frictionlessly along with the liquid nitrogen refrigerant 5 liquid level; the test terminals of the capacitance measuring device are respectively connected to the metal top cover outer wall 1 and the metal base outer wall 6; the capacitance measuring device transmits the collected capacitance value information to the microcontroller through the communication device; the signal acquisition module of the microcontroller collects the capacitance value information of the capacitance measuring device; the signal processing module processes the capacitance value information. Since the capacitance value is inversely proportional to the thickness of the "medium" between the two plates and has thickness uniqueness, the real-time change of the capacitance value can indirectly reflect the liquid level of the liquid nitrogen refrigerant 5 inside the cryogenic dewar. Figure 4As shown in the equivalent capacitance test results of the test device at different liquid nitrogen refrigerant level heights, the output capacitance value of the cryogenic Dewar liquid nitrogen refrigerant 5 liquid level detection device of the hybrid capacitor corresponding to different liquid nitrogen refrigerant 5 liquid level heights is different. Therefore, the real-time liquid nitrogen refrigerant 5 liquid level inside the cryogenic Dewar can be obtained by inversely deducing the relationship between the capacitance value and the page height. In addition, the appropriate external capacitance measurement frequency band can be selected according to different measurement accuracy requirements; the capacitance value information is converted into liquid level information; the signal transmission module sends the liquid level information to the client or display device to realize the liquid level detection in the cryogenic Dewar. Specific implementation method 2 like Figure 4 The equivalent capacitance test results of the test device at different liquid nitrogen refrigerant level heights show the working process of the low-temperature Dewar liquid nitrogen refrigerant 5 level detection device based on the hybrid capacitor composed of the superconducting electrode float 4.

[0023] When the cryogenic Dewar is fully loaded with liquid nitrogen refrigerant 5, Figure 1 As shown in the equivalent schematic diagram of the test device, the gas-liquid mixture 8 above the liquid nitrogen refrigerant 5 is not included, so Figure 3 In the equivalent capacitance of the test device, the hybrid capacitance C1 formed by the outer wall 1 of the metal top cover and the upper superconducting plate 9 is zero. At this time, the external output capacitance of the capacitance measurement device is the series capacitance value of the hybrid capacitance C2 formed by the lower superconducting plate 10 and the inner wall of the metal wall, and the hybrid capacitance C3 formed by the inner wall of the metal wall and the outer wall of the metal base 6. When the liquid nitrogen refrigerant 5 level in the low temperature Dewar drops, Figure 1 As shown in the equivalent schematic diagram of the test device, a gas-liquid mixture 8 appears above the liquid nitrogen refrigerant 5. At this time, the mixed capacitance C1 of the mixed capacitance formed by the metal top cover outer wall 1 and the upper superconducting plate 9 is not zero. As the liquid level of the liquid nitrogen refrigerant 5 drops, the mixed capacitance C2 between the lower superconducting plate 10 and the inner wall of the metal wall also changes. At this time, the capacitance measuring device outputs a combined capacitance, which is the series capacitance value of the mixed capacitance C1 formed by the metal top cover outer wall 1 and the upper superconducting plate 9, the mixed capacitance C2 between the lower superconducting plate 10 and the inner wall of the metal wall, and the mixed capacitance C3 formed by the inner wall of the metal wall and the outer wall of the metal base 6. When the liquid level of the liquid nitrogen refrigerant 5 inside the cryogenic dewar drops to zero, that is, the cryogenic dewar is no longer filled with liquid nitrogen refrigerant 5 but is completely filled with the gas-liquid mixture 8, the mixed capacitance C2 between the lower superconducting plate 10 and the inner wall of the metal wall is zero. The capacitance measuring device outputs a combined capacitance, which is the series capacitance value of the mixed capacitance C1 composed of the outer wall of the metal top cover 1 and the upper superconducting plate 9, and the mixed capacitance C3 composed of the inner wall of the metal wall and the outer wall of the metal base 6. Through the influence of the real-time change of the liquid nitrogen refrigerant 5 liquid level height inside the low-temperature Dewar on the capacitance values of C1, C2, and C3, the liquid nitrogen refrigerant 5 liquid level height inside the low-temperature Dewar is accurately calculated and output.

[0024] This study, conducted on the MATLAB platform, sets parameters based on the operating principle and capacitance calculation formula of a hybrid capacitor liquid nitrogen refrigerant level detection device. The equivalent capacitance corresponding to the liquid level is obtained. The correlation between the liquid level and the equivalent capacitance is visualized, verifying the feasibility of the device's ability to detect liquid level through capacitance changes and providing a theoretical basis for practical applications.

[0025] The capacitance value data measured by the detection device is transmitted to the signal processing module. The signal processing module has a built-in algorithm model based on the mapping relationship, which can quickly and accurately convert the received capacitance value data into the corresponding liquid nitrogen refrigerant 5 liquid level height value. Subsequently, the signal processing module transmits the processed liquid level height data to the display module, which displays the current liquid level height of the liquid nitrogen refrigerant 5 to the user in an intuitive manner such as numbers and graphics through the display module, making it convenient for the user to understand the remaining amount of liquid nitrogen refrigerant 5 in the low-temperature Dewar in real time, so as to replenish it in time or take other related operations. Alternatively, during calibration of the device, the cryogenic dewar can be filled with liquid nitrogen refrigerant 5 at different known liquid levels, and the measured capacitance value of the detection device at the corresponding liquid level can be recorded and compared with the theoretical capacitance value. If there is a deviation, the measurement data is corrected by the signal processing module, and the calibration parameters are updated to ensure the accuracy of subsequent measurements. At the same time, the various components of the device are regularly inspected and maintained to ensure that key components such as the cryogenic metal top cover 2, the inner wall of the cryogenic dewar metal wall, and the superconducting electrode float 4 are free of damage and deformation, and that the connections between the various components are firm and the electrical connections are normal, thereby ensuring that the detection device can operate stably and reliably over a long period of time. Specific implementation method three On the basis of the above specific implementation manner, an intelligent control algorithm is used in the signal processing module to process data information, specifically an artificial neural network model.

[0027] This embodiment utilizes a capacitance measuring device and a signal processing module, and employs an artificial neural network model with a built-in multi-layer feedforward neural network, including an input layer, a hidden layer, and an output layer. The number of nodes in the input layer matches the data dimensions collected by the capacitance measuring device, and is used to receive capacitance data detected by the capacitance measuring device at different frequencies. The hidden layer, with X nodes, performs a nonlinear transformation on the input data using an activation function. The output layer outputs real-time liquid nitrogen refrigerant 5 level data within the cryogenic dewar.

[0028] During the specific operation process, the operating frequency of the capacitance measuring device is varied under different operating conditions. The capacitance values detected by the capacitance measuring device at the corresponding frequencies are collected, and the actual liquid level of the liquid nitrogen refrigerant 5 in the cryogenic dewar at that time is recorded. These data are then mapped to form a data set. During the acquisition process, minimum and maximum frequency values are set, and the frequency is adjusted in intervals of 10 Hz. The collected data serves as a training data set. The collected data set is then input into an artificial neural network model in the signal processing module for training. During the training process, a backpropagation algorithm is used to adjust the model's weights and biases to minimize the error between the model's predicted liquid nitrogen refrigerant 5 level and the actual liquid level. A learning rate is set during the training process. After iterative training, the model's prediction error is reduced to an acceptable range, and the trained model is stored in the signal processing module's memory unit. When the device is in operation, the capacitance measuring device detects the capacitance values at different frequencies in real time and transmits the data to the signal processing module. The signal processing module inputs the received data into the trained artificial neural network model, which, after computational analysis, rapidly outputs real-time data on the liquid nitrogen refrigerant 5 level within the cryogenic dewar. At the same time, the signal processing module can also transmit the detected liquid level data to an external display device or control system through a communication interface, so that operators can monitor and control related equipment in real time.

[0029] This embodiment uses a capacitance measurement device to collect capacitance data at different frequencies as a data set for model training and real-time detection. It can accurately and quickly obtain the real-time liquid level of liquid nitrogen refrigerant 5 inside the cryogenic dewar. Compared with traditional detection methods, the detection accuracy is improved and the real-time performance is significantly enhanced, providing a strong guarantee for the precise control of the liquid level of liquid nitrogen refrigerant 5 in cryogenic experiments and industrial production.

[0030] Of course, without departing from the spirit and essence of the present invention, technicians familiar with the field should be able to make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A low-temperature dewar liquid nitrogen refrigerant level detection device, wherein the low-temperature dewar is used to store liquid nitrogen refrigerant 5, and comprises a metal top cover 2, a metal wall, and a metal base; the metal wall and the metal base are further provided with an insulation layer 7 near the low-temperature dewar cavity; characterized in that: The detection device includes a superconducting plate float 4 disposed on the liquid nitrogen refrigerant 5 in the low-temperature Dewar cavity; the superconducting plate float 4 includes a low-density dielectric material and an upper superconducting plate 9 and a lower superconducting plate 10 fixedly disposed above and below the dielectric material, respectively; the superconducting plate is the same size as the dielectric material; The superconducting plate float 4 is adapted to the size of the low-temperature Dewar cavity and is in smooth contact with the insulation layer 7; The test terminals of the capacitance measuring device are respectively connected to the outer wall 1 of the metal top cover and the outer wall 6 of the metal base; the capacitance measuring device is communicatively connected to a microcontroller; the microcontroller includes: a signal acquisition module for collecting capacitance value information; a signal processing module for collecting capacitance value information and converting the capacitance value information into liquid level information; and a signal transmission module for sending the liquid level information; The signal transmission module is communicatively connected to a client or a display device.

2. A low-temperature Dewar liquid nitrogen refrigerant level detection device according to claim 1, characterized in that: The output value of the capacitance measuring device is the series capacitance of three equivalent capacitances C1, C2, and C3; Among them, the equivalent capacitance of C1, C2, and C3 is: ； The series connection of C1, C2, and C3 corresponds to an external capacitance, that is, the output value of the capacitance measuring device is: ； in, is the dielectric constant, is the cross-sectional area of the capacitor plates, is the electrostatic force constant, is the distance between the two plates of the capacitor; The series capacitance value and the liquid level are in a one-to-one mapping relationship.

3. The low-temperature Dewar liquid nitrogen refrigerant level detection device according to claim 2, characterized in that: The measurement areas of C1, C2, and C3 are specifically: C1: used to test the hybrid capacitor composed of the metal top cover outer wall 1 and the upper superconducting plate 9, in which the gas-liquid mixture 8 above the liquid nitrogen refrigerant 5 is the medium between the two; C2 is used to test the hybrid capacitor composed of the lower superconducting plate 10 and the inner wall of the metal wall, wherein the liquid nitrogen refrigerant 5 stored in the low-temperature Dewar is the medium between the two; C3: used to test the mixed capacitance of the inner wall of the metal base and the outer wall 6 of the metal base, wherein the low-temperature Dewar insulation layer 7 is the medium between the two.

4. The low-temperature Dewar liquid nitrogen refrigerant level detection device according to claim 3, characterized in that: The signal processing module is an intelligent optimization control algorithm, which is used to collect the low-temperature Dewar liquid nitrogen refrigerant 5 liquid level corresponding to the capacitance measurement device at different frequencies as a data set, and further obtain the real-time liquid nitrogen refrigerant 5 liquid level inside the low-temperature Dewar.

5. A method for measuring the liquid level of a low-temperature Dewar liquid nitrogen refrigerant, characterized in that: Step 1: Place the superconducting plate float 4 in the low-temperature Dewar, keep the two adapted to each other, and the superconducting plate float 4 slides and rises and falls frictionlessly along with the liquid nitrogen refrigerant 5; Step 2: The terminals of the capacitance measuring device are respectively connected to the outer wall 1 of the metal top cover and the outer wall 6 of the metal base, and the collected capacitance value information is transmitted to the microcontroller through the communication device; Step 3: The signal acquisition module of the microcontroller collects the capacitance value information of the capacitance measuring device; the signal processing module processes the capacitance value information and converts the capacitance value information into liquid level information; the signal transmission module sends the liquid level information to the client or display device to realize the liquid level detection in the low-temperature Dewar.

6. A method for measuring the liquid level of a low-temperature Dewar liquid nitrogen refrigerant according to claim 5, characterized in that: When the cryogenic Dewar is fully loaded with liquid nitrogen refrigerant 5, C1 does not contain the gas-liquid mixture 8 above the liquid nitrogen refrigerant 5, the detection value of C1 is zero, and the capacitance measuring device outputs the series capacitance value of C2 and C3.

7. The method for measuring the liquid level of a cryogenic Dewar liquid nitrogen refrigerant according to claim 5, wherein: When the liquid level of the liquid nitrogen refrigerant 5 in the low-temperature Dewar drops, the capacitance measuring device outputs the series capacitance value of C1, C2 and C3.

8. The method for measuring the liquid level of a low-temperature Dewar liquid nitrogen refrigerant according to claim 5, wherein: When the liquid level of the liquid nitrogen refrigerant 5 inside the cryogenic Dewar drops to zero, that is, the cryogenic Dewar does not contain the liquid nitrogen refrigerant 5 but is completely filled with the gas-liquid mixture 8, the capacitance measuring device outputs the series capacitance value of C1 and C3.

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