An automated high-precision ultra-low temperature control system and method

Abstract

The application belongs to the technical field of intelligent control, and particularly relates to an automatic high-precision ultralow-temperature temperature control system and method, which comprises a liquid nitrogen tank, a gaseous nitrogen tank, a heat exchange pipe and a nitrogen storage tank. The application provides a full-automatic ultralow-temperature temperature control system with one-thousandth precision, so as to solve the problems of low precision and poor reliability in the refrigeration process and quickly provide an ultralow-temperature space. The principle of the temperature control method is to use PLC to realize automatic control of the pressure of the refrigerant in the low-temperature temperature control system, so as to accurately control the boiling point of the refrigerant, and the precision can be controlled to be 0.1%.

Description

Technical Field

[0001] This application belongs to the field of intelligent control technology, specifically relating to an automated high-precision ultra-low temperature control system and method. Background Technology

[0002] In recent years, with the continuous development of science and technology in my country, and because many scientific experiments and production require operation in low-temperature environments, ultra-low temperature testing technology has also made rapid progress. This demand mainly stems from the reliance on extreme low-temperature conditions in cutting-edge fields such as quantum computing, superconducting materials, deep space exploration, and ultra-low temperature preservation of biological samples.

[0003] Conventional cryogenic refrigeration systems use multi-stage compressors to lower the temperature, with PID algorithms for temperature regulation. The accuracy of this method decreases as the temperature drops: below -100℃, the accuracy is 0.1℃; below -150℃, the accuracy is 1℃. Besides multi-stage compressors, there is also cascade compression refrigeration. In this method, the high-temperature and low-temperature stages cycle independently, coupled through a condenser-evaporator. Its temperature range is -80℃ to -150℃. Because R23 (trifluoromethane, the refrigerant) has a low vapor density at -150℃, flow control lags, and accuracy decreases at low temperatures. Therefore, the accuracy also decreases as the temperature decreases: below -85℃, the accuracy is ±1℃; below -120℃, the accuracy is ±2℃; and at -150℃, the accuracy is ±3℃. Summary of the Invention

[0004] This invention provides a fully automatic, 0.1% precision ultra-low temperature control system and method to solve the problems of low precision and poor reliability in the refrigeration process, and can quickly provide an ultra-low temperature space. The principle of its temperature control method is to use a PLC to achieve fully automatic control of the refrigerant pressure in the low-temperature temperature control system, thereby precisely controlling its boiling point with an accuracy of 0.1%. The technical solution is as follows:

[0005] An automated, high-precision ultra-low temperature control system includes a liquid nitrogen tank, a gaseous nitrogen tank, a heat exchange tube, and a nitrogen storage tank. The liquid nitrogen tank is connected to the nitrogen storage tank via a solenoid valve A. The bottom of the liquid nitrogen tank is connected to the heat exchange tube, and the upper port of the liquid nitrogen tank is connected to the gaseous nitrogen tank via a needle valve E. The gaseous nitrogen tank is equipped with a pressure relief valve B, and the liquid nitrogen tank is connected to the pressure relief valve A and to an external nitrogen storage device via the solenoid valve B. The heat exchange tube is connected to an inverted U-shaped pipe, the top of which is at the same height as the liquid nitrogen tank. The inverted U-shaped pipe is connected to the gaseous nitrogen tank via the solenoid valve D, forming a closed-loop refrigeration system. The solenoid valves A, B, and D are respectively connected to a controller.

[0006] Preferably, the nitrogen storage tank is equipped with a pressure gauge J, and a solenoid valve A, a needle valve A, and a filter A are sequentially installed on the pipeline between the nitrogen storage tank and the liquid nitrogen tank; the pressure gauge J and the solenoid valve A are respectively connected to the controller.

[0007] Preferably, the liquid nitrogen tank is equipped with a level gauge and a pressure gauge H, and the pipeline between the liquid nitrogen tank and the external nitrogen storage equipment is sequentially equipped with a filter B, a solenoid valve B and a needle valve B, and the level gauge, pressure gauge H, and solenoid valve B are connected to the controller.

[0008] Preferably, the gaseous nitrogen tank is connected to an external nitrogen storage device via a pressure relief valve B, and a needle valve C is installed between the two. A filter C, a solenoid valve E, and a needle valve D are sequentially installed on the pipeline between the gaseous nitrogen tank and the external nitrogen storage device. The filter C and the solenoid valve E are respectively connected to the controller.

[0009] An automated, high-precision ultra-low temperature control method includes setting initialization parameters for the controller and entering automatic mode. The pressure relief methods for solenoid valves B and E are as follows:

[0010] When the pressure of the liquid nitrogen tank exceeds 200.0 kPa (the upper limit of the liquid nitrogen tank pressure), the solenoid valve B automatically releases pressure and triggers an alarm.

[0011] When the pressure of the liquid nitrogen tank is greater than 190.0 kPa (the pressure relief value of the liquid nitrogen tank) and less than 200.0 kPa, the solenoid valve B will spray.

[0012] When the pressure of the liquid nitrogen tank is greater than 150.0 kPa (lower limit of liquid nitrogen tank pressure) and less than 190.0 kPa (pressure relief value of liquid nitrogen tank pressure), the solenoid valve B is closed;

[0013] When the pressure of the liquid nitrogen tank is less than 150.0 kPa (the lower limit of liquid nitrogen tank pressure), the solenoid valve B closes and an alarm sounds, indicating a potential risk of leakage.

[0014] When the pressure of the nitrogen tank exceeds 200.0 kPa (the upper limit of the nitrogen tank pressure), the solenoid valve E automatically releases pressure and triggers an alarm; when the pressure of the nitrogen tank exceeds 180 kPa (the nitrogen tank pressure release value) but is less than 200 kPa (the upper limit of the nitrogen tank pressure), the solenoid valve E sprays intermittently.

[0015] When the pressure of the nitrogen cylinder is greater than 150.0 kPa (lower limit of nitrogen cylinder pressure) and less than 180.0 kPa (pressure relief value), the solenoid valve E closes; when the pressure of the nitrogen cylinder is less than 150.0 kPa (lower limit of nitrogen cylinder pressure), the solenoid valve E closes and an alarm is triggered, indicating a potential risk of leakage.

[0016] Preferably, under a certain pressure, the boiling point temperature of liquid nitrogen in the liquid nitrogen tank is fixed. When the pressure is above its boiling point, the liquid nitrogen will vaporize; when the pressure is below its boiling point, the liquid nitrogen will remain in a liquid state. According to the Clausius-Clapeyron equation...

[0017] (1);

[0018] L is the molar latent heat of vaporization, V g V is the molar volume of the gas. l Let V be the molar volume of the liquid, P be the pressure, and T be the temperature. g >>V l V g =RT / P, which can be used to transform equation (1):

[0019] (2);

[0020] According to equation (2), the pressure inside the refrigeration system is set at 280 kPa, and controlled. ,but .

[0021] Preferably, when the liquid nitrogen level in the liquid nitrogen tank is less than 10.0 mm (lower limit), the solenoid valve D first automatically closes to prevent liquid nitrogen from overflowing from the heat exchange tube into the gas nitrogen tank. Then, the solenoid valve A automatically opens, and liquid nitrogen from the storage tank is injected into the liquid nitrogen tank. The liquid nitrogen in the liquid nitrogen tank vaporizes, increasing the pressure. The solenoid valves B and E then automatically depressurize.

[0022] Preferably, as the liquid nitrogen level in the liquid nitrogen tank begins to rise, the pressure in the nitrogen storage tank is slightly higher than that in the liquid nitrogen tank, pushing liquid nitrogen into the liquid nitrogen tank. The liquid nitrogen in the liquid nitrogen tank flows into the heat exchange tube, and the liquid nitrogen levels in the liquid nitrogen tank and the heat exchanger are level. When the liquid level rises to 170.0 mm (liquid level rise value), the solenoid valve A first automatically closes, the nitrogen storage tank stops injecting liquid nitrogen, and after the pressure of the refrigeration system is maintained at 180.0 kPa, the solenoid valve D automatically opens. During the process of the liquid nitrogen level in the liquid nitrogen tank rising from the lower limit to the upper limit, the liquid nitrogen in the liquid nitrogen tank will vaporize, causing the pressure in the liquid nitrogen tank to increase, and the solenoid valves B and E automatically depressurize.

[0023] Preferably, during the refrigeration process, the liquid nitrogen in the liquid nitrogen tank is continuously consumed, causing the liquid nitrogen to vaporize and the pressure to increase. The solenoid valves B and E automatically release the pressure. After the liquid nitrogen in the liquid nitrogen tank is consumed to less than 10 mm (lower limit of liquid level), the solenoid valve D first automatically closes, and then the solenoid valve A automatically opens to replenish the liquid nitrogen in the liquid nitrogen tank. This process will cause the temperature of the liquid nitrogen tank to drop to -186.0℃.

[0024] Preferably, the control process is divided into automatic mode and manual mode. After setting all parameters, in automatic mode, the refrigeration device can automatically and orderly complete the refrigeration and low temperature maintenance process. In all processes, the pressure set in the liquid nitrogen tank and gas nitrogen tank is maintained by depressurizing through the solenoid valve.

[0025] Compared with the prior art, the beneficial effects of this application are as follows:

[0026] 1. The present invention uses the PLC to control the pressure relief speed of the solenoid valve, releasing the nitrogen gas generated by the vaporization of refrigerant liquid nitrogen, thereby maintaining the pressure of the liquid nitrogen refrigeration system at the set pressure. By adjusting the accuracy of the pressure relief valve and the volume of the gas nitrogen tank, the pressure control accuracy can be better than 0.1%.

[0027] 2. The PLC, acting as the controller of the cryogenic temperature control system, enables full automation. By writing a control program, all the solenoid valves can automatically complete their respective actions under specific conditions. From liquid nitrogen filling to cryogenic maintenance, everything can be performed automatically.

[0028] 3. The automated high-precision low-temperature temperature control system of this invention is simple to manufacture, easy to implement, and low in cost. Its application in scientific research has good benefits. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a refrigeration system;

[0030] Figure 2 This is a flowchart of the refrigeration system.

[0031] 101 Nitrogen storage tank, 102 Solenoid valve A, 103 Needle valve A, 104 Filter A, 106 Level gauge, 107 Pressure gauge H, 108 Pressure relief valve A, 109 Filter B, 110 Solenoid valve B, 111 Needle valve B, 112 Liquid nitrogen tank, 115 Needle valve C, 116 Pressure relief valve B, 117 Pressure gauge G, 118 Filter C, 119 Solenoid valve E, 120 Needle valve D, 121 Gas nitrogen tank, 122 Solenoid valve D, 124 Inverted U-shaped pipe, 125 Pressure gauge J, 126 Heat exchanger tube, 127 Needle valve E. Detailed Implementation

[0032] The technical solution of this application will be described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the embodiments and specific features in the embodiments are detailed descriptions of the technical solution of this application, rather than limitations thereof. Specific technical features can be combined with each other.

[0033] Figure 1As shown, an automated high-precision ultra-low temperature control system includes a liquid nitrogen tank 112, a gaseous nitrogen tank 121, a heat exchange tube 126, and a nitrogen storage tank 101. The liquid nitrogen tank 112 is connected to the nitrogen storage tank 101 via a solenoid valve A. The bottom end of the liquid nitrogen tank 112 is connected to the heat exchange tube 126, and the upper end of the liquid nitrogen tank 112 is connected to the gaseous nitrogen tank 121 via a needle valve E127. The gaseous nitrogen tank 121 is equipped with a pressure relief valve B. The liquid nitrogen tank 112 is connected to the pressure relief valve A and is connected to an external nitrogen storage device via a solenoid valve B110. The heat exchange tube is connected to an inverted U-shaped pipe 124, the top end of which is at the same height as the liquid nitrogen tank 112. The inverted U-shaped pipe 124 is connected to the gaseous nitrogen tank 121 via a solenoid valve D, forming a closed-loop refrigeration system. The solenoid valves A, B, and D are respectively connected to a controller.

[0034] The nitrogen storage tank 101 is equipped with a pressure gauge J. The pipeline between the nitrogen storage tank 101 and the liquid nitrogen tank 112 is equipped with a solenoid valve A102, a needle valve A103 and a filter A104 in sequence. The pressure gauge J125 and the solenoid valve A102 are respectively connected to the controller.

[0035] The liquid nitrogen tank 112 is equipped with a level gauge 106 and a pressure gauge H107. The pipeline between the liquid nitrogen tank 112 and the external nitrogen storage equipment is equipped with a filter B109, a solenoid valve B110 and a needle valve B111 in sequence. The level gauge 106, pressure gauge H107 and solenoid valve B110 are connected to the controller.

[0036] The gaseous nitrogen tank 121 is connected to an external nitrogen storage device via a pressure relief valve B, and a needle valve C115 is installed between the two. A filter C118, a solenoid valve E119, and a needle valve D120 are sequentially installed on the pipeline between the gaseous nitrogen tank 121 and the external nitrogen storage device. The filter C118 and the solenoid valve E119 are respectively connected to the controller.

[0037] An automated, high-precision cryogenic temperature control method is provided, wherein the controller is initialized with parameters and enters automatic mode, and the pressure relief methods of solenoid valves B110 and E119 are as follows:

[0038] When the pressure of the liquid nitrogen tank 112 exceeds 200.0 kPa (the upper limit of liquid nitrogen tank pressure), the solenoid valve B110 automatically releases pressure and triggers an alarm;

[0039] When the pressure of the liquid nitrogen tank 112 is greater than 190.0 kPa (the pressure relief value of the liquid nitrogen tank) and less than 200.0 kPa, the solenoid valve B110 sprays at intervals.

[0040] When the pressure of the liquid nitrogen tank 112 is greater than 150.0 kPa (lower limit of liquid nitrogen tank pressure) and less than 190.0 kPa (pressure relief value of liquid nitrogen tank pressure), the solenoid valve B110 is closed;

[0041] The pressure of the liquid nitrogen tank 112 is less than 150.0 kPa (lower limit of liquid nitrogen tank pressure), the solenoid valve B110 is closed and an alarm is triggered, indicating a potential risk of leakage.

[0042] When the pressure of the nitrogen tank 121 is greater than 200.0 kPa (the upper limit of the nitrogen tank pressure), the solenoid valve E119 automatically releases pressure and alarms; when the pressure of the nitrogen tank 121 is greater than 180 kPa (the pressure release value of the nitrogen tank) but less than 200 kPa (the upper limit of the nitrogen tank pressure), the solenoid valve E119 sprays lightly.

[0043] When the pressure of the nitrogen tank 121 is greater than 150.0 kPa (lower limit of nitrogen tank pressure) and less than 180.0 kPa (pressure relief value), the solenoid valve E119 closes; when the pressure of the nitrogen tank 121 is less than 150.0 kPa (lower limit of nitrogen tank pressure), the solenoid valve E119 closes and an alarm is triggered, indicating a potential risk of leakage.

[0044] In liquid nitrogen tank 121, under a certain pressure, the boiling point temperature of liquid nitrogen is fixed. When the pressure is above its boiling point, the liquid nitrogen will vaporize; when the pressure is below its boiling point, the liquid nitrogen will remain in a liquid state. According to the Clausius-Clapeyron equation...

[0045] (1);

[0046] L is the molar latent heat of vaporization, V g V is the molar volume of the gas. l Let V be the molar volume of the liquid, P be the pressure, and T be the temperature. g >>V l V g =RT / P, which can be used to transform equation (1):

[0047] (2);

[0048] According to equation (2), the pressure inside the refrigeration system is set at 280 kPa, and controlled. ,but .

[0049] When the liquid nitrogen level in the liquid nitrogen tank 112 is less than 10.0 mm (lower limit), the solenoid valve D122 automatically closes first to prevent liquid nitrogen from overflowing from the heat exchange tube 126 into the gas nitrogen tank 121. Then, the solenoid valve A102 automatically opens, and liquid nitrogen from the nitrogen storage tank 101 is injected into the liquid nitrogen tank. The liquid nitrogen in the liquid nitrogen tank 112 vaporizes, and the pressure increases. The solenoid valves B110 and E119 automatically depressurize.

[0050] The liquid nitrogen level in the liquid nitrogen tank 112 begins to rise. Since the pressure of the nitrogen storage tank 101 is slightly higher than that of the liquid nitrogen tank 112, liquid nitrogen is pushed into the liquid nitrogen tank 112. The liquid nitrogen in the liquid nitrogen tank 112 flows into the heat exchange tube 126. The liquid nitrogen levels in the liquid nitrogen tank 112 and the heat exchanger 126 are level. When the liquid level rises to 170.0 mm (liquid level rise value), the solenoid valve A102 first automatically closes, the nitrogen storage tank 101 stops injecting liquid nitrogen, and after the pressure of the refrigeration system is maintained at 180.0 kPa, the solenoid valve D122 automatically opens. During the process of the liquid nitrogen level in the liquid nitrogen tank 112 rising from the lower limit to the upper limit, the liquid nitrogen in the liquid nitrogen tank 112 will vaporize, causing the pressure of the liquid nitrogen tank 112 to increase. The solenoid valves B110 and E119 automatically depressurize.

[0051] During the refrigeration process, the liquid nitrogen in the liquid nitrogen tank 112 is continuously consumed, causing the liquid nitrogen to vaporize and the pressure to increase. The solenoid valves B110 and E119 automatically release the pressure. After the liquid nitrogen in the liquid nitrogen tank 112 is consumed to less than 10mm (lower limit of liquid level), the solenoid valve D122 first automatically closes, and then the solenoid valve A102 automatically opens to replenish the liquid nitrogen in the liquid nitrogen tank 112. This process will cause the temperature of the liquid nitrogen tank to drop to -186.0℃.

[0052] The control process is divided into automatic mode and manual mode. After setting all parameters, in automatic mode, the refrigeration device can automatically and orderly complete the refrigeration and low temperature maintenance process. In all processes, the pressure set in liquid nitrogen tank 112 and gas nitrogen tank 121 is maintained by depressurizing through solenoid valves.

[0053] In one embodiment of the present invention, in order to maintain stable pressure, the solenoid valve operates in a point-spray mode (alternating between opening and closing). For example, when the pressure is greater than 2345.0 kPa, the solenoid valve will open for 0.5 s and close for 0.5 s. After testing, the pressure fluctuates between 2344.5 kPa and 2345.2 kPa, with an accuracy ΔP / P = 0.03%. According to formula (2), the temperature accuracy ΔT / T = 0.0053%, which is better than 0.1%. The opening and closing time of the point-spray mode can be adjusted appropriately according to the actual situation.

[0054] In one embodiment of the present invention, the heat exchanger 126 cools the liquid that needs to be cooled. Since the heat exchanger 126 is at a constant temperature, the liquid that needs to be cooled is also cooled to that temperature.

[0055] In one embodiment of the present invention, the liquid nitrogen tank 112 is wrapped with a polyurethane insulation layer to maintain the temperature inside the liquid nitrogen tank 112, thereby achieving the functions of heat preservation and insulation.

[0056] The controller uses a PLC connected to a display screen. The PLC's expansion module connects to pressure gauges H107, G117, and J125, and level gauge 106, to acquire information on the pressure and level of the refrigeration system. Solenoid valves A102, B110, D122, and E119 are connected to intermediate relays, which in turn connect to the PLC's output. By programming the PLC, each solenoid valve automatically performs its corresponding action to maintain the set pressure of the refrigeration system, thereby controlling the boiling point of liquid nitrogen with an accuracy better than 0.1%.

[0057] The PLC is connected to the display screen, such as Figure 2 As shown, the display screen includes: a soft switch for controlling the solenoid valve, and various parameter values ​​for liquid level and pressure.

[0058] In one embodiment of the present invention, the PLC is divided into manual mode and manual mode. When entering the manual mode, the solenoid valve is controlled by the switch button on the display screen. When entering the automatic mode, the solenoid valve can automatically and orderly enter the cooling and low temperature maintenance process, and the solenoid valve can complete the corresponding action according to the conditions in each process.

[0059] In one embodiment of the present invention, when the refrigeration system malfunctions, it can be stopped by using an emergency stop mechanical button or an emergency stop button on the display screen.

[0060] This invention implements an automated, high-precision ultra-low temperature control method. Taking liquid argon refrigerant as an example, the principle of liquid argon refrigerant is that the boiling point of liquid nitrogen at 280.0 kPa (absolute pressure) is the same as that of liquid argon at 100.0 kPa (absolute pressure). By maintaining the pressure of the heat exchanger 126 at 180.0 kPa, the boiling point of liquid nitrogen is controlled, and argon gas in the liquefied liquid argon tank forms a liquid-gas balance at a specified temperature with an accuracy better than 0.1%. Figure 2 As shown, it includes the following steps:

[0061] S1: Power on the PLC and set the initialization parameters. On the display screen, click the "Automatic Mode" button to enter automatic mode. The pressure relief method of solenoid valves B110 and E119 is as follows:

[0062] The solenoid valves B110 and E119 are constantly adjusting the pressure changes of the liquid nitrogen tank 112 and the gas nitrogen tank 121.

[0063] S2: When the liquid nitrogen level in the liquid nitrogen tank 112 is less than 10.0 mm (lower limit), the solenoid valve D122 automatically closes first to prevent liquid nitrogen from overflowing from the heat exchange tube 126 into the gas nitrogen tank 121. Then, the solenoid valve A102 automatically opens, and the liquid nitrogen in the nitrogen storage tank 101 is injected into the liquid nitrogen tank. The liquid nitrogen in the liquid nitrogen tank 112 vaporizes, the pressure increases, and the solenoid valves B110 and E119 automatically depressurize.

[0064] S3: The liquid nitrogen level in the liquid nitrogen tank 112 begins to rise. Since the pressure in the nitrogen storage tank 101 is slightly higher than that in the liquid nitrogen tank 112, liquid nitrogen flows into the liquid nitrogen tank 112, and then into the heat exchange tube 126. The liquid nitrogen levels in the liquid nitrogen tank 112 and the heat exchanger 126 are maintained. When the liquid level rises to 170.0 mm (upper limit), the solenoid valve A102 automatically closes, the nitrogen storage tank 101 stops injecting liquid nitrogen, and the pressure of the refrigeration system is maintained at 180.0 kPa before the solenoid valve D122 automatically opens. During the process of the liquid nitrogen level in the liquid nitrogen tank 112 rising from the lower limit to the upper limit, the liquid nitrogen in the liquid nitrogen tank 112 vaporizes, causing the pressure in the liquid nitrogen tank 112 to increase. The solenoid valves B110 and E119 then automatically depressurize.

[0065] S4: During the refrigeration process, the liquid nitrogen in the liquid nitrogen tank 112 is continuously consumed, causing the liquid nitrogen to vaporize and the pressure to increase. Solenoid valves B110 and E119 automatically release pressure. After the liquid nitrogen in the liquid nitrogen tank 112 is consumed to less than 10mm (lower liquid level limit), solenoid valve D122 first automatically closes, and then solenoid valve A102 automatically opens to replenish the liquid nitrogen in the liquid nitrogen tank 112. This process lowers the temperature of the liquid argon tank to -186.0℃, with an accuracy better than 0.1%. Once the liquid argon tank temperature drops to -186.0℃, it enters a process of maintaining the low temperature, and the pressure release method during this process is the same as that during the refrigeration process.

[0066] S5: The heat exchanger 126 cools the liquid argon. Because the heat exchanger is at a constant temperature, the liquid argon is also cooled to that temperature. By repeating S2, S3, and S4, the liquid argon tank is kept at a low temperature of -186.0℃ with an accuracy better than 0.1%.

[0067] Unless otherwise specified, all pressure parameters in the above steps are relative pressures. In addition, for safety reasons, an emergency stop button is provided. Pressing the emergency stop button resets all solenoid valves and stops the refrigeration system. This case study uses the formation of liquid-gas equilibrium at a specified temperature in a liquefied argon tank as an application example to describe the refrigeration principle.

[0068] This invention presents an automated, high-precision cryogenic temperature control device that utilizes liquid nitrogen refrigeration. The PLC acts as the controller, enabling automated cryogenic temperature control with an accuracy better than 0.1%. The PLC control process includes automatic and manual modes. After setting the parameters, in automatic mode, the refrigeration device automatically and systematically completes the refrigeration and cryogenic maintenance process. Throughout the process, the pressure in the liquid nitrogen tank 112 and the gaseous nitrogen tank 121 is maintained by depressurization via solenoid valves, thereby controlling the boiling point of liquid nitrogen with an accuracy better than 0.1%. The entire device features high precision, automation, temperature uniformity, and high temperature stability. The device can be designed to meet specific needs and is primarily intended for cryogenic experimental research.

[0069] The above provides a detailed description of an automated high-precision ultra-low temperature temperature control device and method provided by the embodiments of the present invention. Specific embodiments have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. The content of the above embodiments should not be construed as a limitation of the present invention.

Claims

1. An automated, high-precision, ultra-low temperature control system, characterized in that, The system includes a liquid nitrogen tank, a gaseous nitrogen tank, heat exchange tubes, and a nitrogen storage tank. The liquid nitrogen tank is connected to the nitrogen storage tank via a solenoid valve A. The bottom of the liquid nitrogen tank is connected to the heat exchange tubes, and the top of the liquid nitrogen tank is connected to the gaseous nitrogen tank via a needle valve E. The gaseous nitrogen tank is equipped with a pressure relief valve B, and the liquid nitrogen tank is connected to the pressure relief valve A and to an external nitrogen storage device via the solenoid valve B. The heat exchange tubes are connected to an inverted U-shaped pipe, the top of which is at the same height as the liquid nitrogen tank. The inverted U-shaped pipe is connected to the gaseous nitrogen tank via a solenoid valve D, forming a closed-loop refrigeration system. A solenoid valve B and a needle valve B are sequentially installed on the pipeline between the liquid nitrogen tank and the external nitrogen storage equipment, and a solenoid valve E and a needle valve D are sequentially installed on the pipeline between the gaseous nitrogen tank and the external nitrogen storage equipment. Solenoid valves A, B, D, and E are respectively connected to the controller.

2. The automated high-precision ultra-low temperature control system according to claim 1, characterized in that, The nitrogen storage tank is equipped with a pressure gauge J, and a solenoid valve A, a needle valve A, and a filter A are sequentially installed on the pipeline between the nitrogen storage tank and the liquid nitrogen tank; the pressure gauge J and the solenoid valve A are respectively connected to the controller.

3. The automated high-precision ultra-low temperature temperature control system according to claim 2, characterized in that, The liquid nitrogen tank is equipped with a level gauge and a pressure gauge H. A filter B, a solenoid valve B, and a needle valve B are sequentially installed on the pipeline between the liquid nitrogen tank and the external nitrogen storage equipment. The level gauge and pressure gauge H are connected to the controller.

4. The automated high-precision ultra-low temperature control system according to claim 3, characterized in that, The gaseous nitrogen tank is connected to an external nitrogen storage device via a pressure relief valve B, and a needle valve C is installed between the two. A filter C, a solenoid valve E, and a needle valve D are sequentially installed on the pipeline between the gaseous nitrogen tank and the external nitrogen storage device. The filter C is connected to a controller.

5. An automated high-precision ultra-low temperature control method, employing the automated high-precision ultra-low temperature control system as described in any one of claims 3-4, characterized in that, The controller sets initialization parameters and enters automatic mode. The pressure relief methods for solenoid valves B and E are as follows: When the pressure of the liquid nitrogen tank exceeds the upper limit of the liquid nitrogen tank pressure, the solenoid valve B automatically releases pressure and triggers an alarm; When the pressure of the liquid nitrogen tank is greater than the pressure relief value of the liquid nitrogen tank but less than the upper limit value of the liquid nitrogen tank pressure, the solenoid valve B will spray. When the pressure of the liquid nitrogen tank is greater than the lower limit of the liquid nitrogen tank pressure but less than the pressure relief value of the liquid nitrogen tank, the solenoid valve B is closed; When the pressure in the liquid nitrogen tank is less than the lower limit of the liquid nitrogen tank pressure, the solenoid valve B closes and an alarm sounds, indicating a potential risk of leakage. When the pressure of the nitrogen cylinder exceeds the upper limit of the nitrogen cylinder pressure, the solenoid valve E automatically releases pressure and triggers an alarm; when the pressure of the nitrogen cylinder exceeds the pressure release value but is less than the upper limit of the nitrogen cylinder pressure, the solenoid valve E sprays intermittently. When the pressure of the nitrogen cylinder is greater than the lower limit of the nitrogen cylinder pressure but less than the pressure relief value, the solenoid valve E closes; when the pressure of the nitrogen cylinder is less than the lower limit of the nitrogen cylinder pressure, the solenoid valve E closes and an alarm sounds, indicating a possible risk of leakage.

6. The automated high-precision ultra-low temperature control method according to claim 5, characterized in that, Under a certain pressure, the boiling point of liquid nitrogen in a liquid nitrogen tank is fixed. When the pressure is above its boiling point, the liquid nitrogen will vaporize; when the pressure is below its boiling point, the liquid nitrogen will remain in a liquid state, according to the Clausius-Clapeyron equation: （1）； L is the molar latent heat of vaporization, V g V is the molar volume of the gas. l Let V be the molar volume of the liquid, P be the pressure, and T be the temperature. g >>V l V g =RT / P, which can be used to transform equation (1): （2）； According to equation (2), the pressure inside the refrigeration system is set at 280 kPa, and controlled. ,but .

7. The automated high-precision ultra-low temperature control method according to claim 5, characterized in that, When the liquid nitrogen level in the liquid nitrogen tank is lower than the lower limit, the solenoid valve D first automatically closes to prevent liquid nitrogen from overflowing from the heat exchange tube into the gas nitrogen tank. Then, the solenoid valve A automatically opens, and liquid nitrogen from the storage tank is injected into the liquid nitrogen tank. The liquid nitrogen in the liquid nitrogen tank vaporizes, and the pressure increases. The solenoid valves B and E then automatically depressurize.

8. The automated high-precision ultra-low temperature control method according to claim 5, characterized in that, The liquid nitrogen level in the liquid nitrogen tank begins to rise. Since the pressure in the nitrogen storage tank is slightly higher than that in the liquid nitrogen tank, liquid nitrogen is pushed into the liquid nitrogen storage tank. The liquid nitrogen in the liquid nitrogen storage tank flows into the heat exchange tube. The liquid nitrogen levels in the liquid nitrogen tank and the heat exchange tube are level. When the liquid level rises to the upper limit, the solenoid valve A automatically closes first, the nitrogen storage tank stops injecting liquid nitrogen, and the pressure of the refrigeration system is maintained at the pressure relief value of the gas nitrogen tank. Then, the solenoid valve D automatically opens. During the process of the liquid nitrogen level in the liquid nitrogen tank rising from the lower limit to the upper limit, the liquid nitrogen in the liquid nitrogen tank will vaporize, causing the pressure in the liquid nitrogen tank to increase. The solenoid valves B and E automatically release the pressure.

9. The automated high-precision ultra-low temperature control method according to claim 5, characterized in that, During the refrigeration process, the liquid nitrogen in the liquid nitrogen tank is continuously consumed, causing the liquid nitrogen to vaporize and the pressure to increase. The solenoid valves B and E automatically release the pressure. After the liquid nitrogen in the liquid nitrogen tank is consumed to a level below the lower limit, the solenoid valve D first automatically closes, and then the solenoid valve A automatically opens to replenish the liquid nitrogen in the liquid nitrogen tank. This process will cause the temperature of the liquid nitrogen tank to drop to -186.0℃.

10. The automated high-precision ultra-low temperature control method according to claim 5, characterized in that, The control process is divided into automatic mode and manual mode. After setting all parameters, in automatic mode, the refrigeration device can automatically and orderly complete the refrigeration and low temperature maintenance process. In all processes, the pressure set in the liquid nitrogen tank and gas nitrogen tank is maintained by depressurizing through the solenoid valve.

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