Low-temperature temperature measuring device and low-temperature temperature measuring method based on thermal molecular pressure difference

Abstract

The present application relates to the technical fields of low temperature measurement, in particular to a low temperature temperature measuring device and method based on thermal molecular pressure difference. The low temperature temperature measuring device comprises: a reference part, which is set as a metal shell with a first chamber; a measuring part, which is set as a metal shell with a second chamber; a connecting capillary, which is arranged between the reference part and the measuring part; a pressure gauge, which is installed on the reference part; and a thermometer, which is installed on the reference part; wherein one end of the connecting capillary is communicated with the first chamber, the other end of the connecting capillary is communicated with the second chamber to form a closed system, and helium is filled in the closed system as a working medium which freely flows between the first chamber and the second chamber. In the present application, the measuring part is set as a passive metal cavity, which can avoid self-heating to cause interference to the temperature of the target to be measured, and the reference end is away from the target to be measured, which can avoid the measurement value from being interfered by a magnetic field.

Description

Technical Field

[0001] This invention relates to the field of cryogenic measurement technology, and in particular to a cryogenic temperature measuring device and method based on thermomolecular pressure difference. Background Technology

[0002] In cutting-edge scientific and technological fields such as quantum computing, cryogenic physics, and aerospace, accurate measurement of extremely low temperature environments (such as the mK temperature range) is crucial.

[0003] Currently, the most commonly used low-temperature thermometers are resistance thermometers, such as Cernox and RuO2 (ruthenium dioxide). However, existing resistance thermometry techniques suffer from two inherent drawbacks when applied to extreme conditions such as extremely low temperatures and strong magnetic fields: One is the self-heating effect. Resistance thermometers require an excitation current to measure their resistance value, and this current inevitably generates Joule heat on the sensor. Although this power is extremely small (typically in the range of pW to nW), in extremely low-temperature environments at the mK level, this amount of heat is sufficient to cause significant temperature rise disturbances to the measured object (such as a quantum bit chip), leading to measurement distortion.

[0004] Secondly, there is the magnetoresistive effect. The resistance of most resistance thermometers changes with the strength of the applied magnetic field, a phenomenon known as magnetoresistive effect. This causes their readings to be severely inaccurate in strong magnetic field research equipment (such as dilution refrigerators), requiring complex and time-consuming magnetic field correction.

[0005] Although traditional gas thermometers are based on the fundamental laws of thermodynamics, they suffer from complex sources of error, such as "dead volume," in low-temperature applications, making correction extremely difficult and hindering precise measurements. Summary of the Invention

[0006] This invention aims to solve the technical problems existing in related technologies. To this end, this invention proposes a low-temperature temperature measuring device and method based on thermomolecular pressure difference, in order to solve the problem that existing low-temperature thermometers cannot accurately measure low-temperature targets due to self-heating effects and magnetic field interference.

[0007] In a first aspect, the present invention provides a low-temperature temperature measuring device based on thermomolecular pressure difference, comprising: a reference unit, configured as a metal housing having a first chamber; The measuring unit is configured as a metal housing with a second chamber; A capillary tube is connected and disposed between the reference section and the measuring section; A pressure gauge is installed on the reference unit; A thermometer is installed on the reference unit; One end of the connecting capillary tube is connected to the first chamber, and the other end of the connecting capillary tube is connected to the second chamber to form a closed system. The closed system is filled with helium gas as a working medium that flows freely between the first chamber and the second chamber.

[0008] According to the present invention, a cryogenic temperature measuring device based on thermomolecular pressure difference is provided, wherein the equivalent channel diameter of the connecting capillary is much smaller than the mean free path of helium molecules, so that the connecting capillary becomes a free molecular flow region of helium.

[0009] According to the present invention, a low-temperature temperature measuring device based on thermomolecular pressure difference is provided, wherein the connecting capillary adopts a structure of multiple microchannel arrays; Alternatively, the connecting capillary may have a porous structure.

[0010] According to the present invention, a low-temperature temperature measuring device based on thermomolecular pressure difference is provided, wherein the material of the connecting capillary has heat insulation properties to avoid heat transfer between the reference part and the measuring part.

[0011] A low-temperature temperature measuring device based on thermomolecular pressure difference according to the present invention further includes: A vacuum pump unit, connected to the reference unit, is used to evacuate the sealing system; A helium cylinder, connected to the reference unit, is used to supply helium to the sealing system.

[0012] According to the present invention, a low-temperature temperature measuring device based on thermomolecular pressure difference is provided, wherein the reference part is made of oxygen-free copper and the measuring part is made of oxygen-free copper.

[0013] Secondly, the present invention also provides a low-temperature temperature measurement method, employing any of the aforementioned low-temperature temperature measurement devices based on thermomolecular pressure difference, the low-temperature temperature measurement method comprising: S1. Calibrate the cryogenic temperature measuring device and obtain the volume V1 of the first chamber, the volume V2 of the second chamber, and the total number of helium molecules N in the sealed system. total Or the equivalent characteristic constant C=N total ×k B ; S2. Install the calibrated low-temperature measuring device onto the low-temperature target to be measured, so that the measuring part is in contact with the low-temperature target to maintain a consistent temperature, and place the reference part in a high-temperature environment, waiting for the helium in the first chamber and the helium in the second chamber to reach thermodynamic equilibrium. S3. Obtain the first pressure P1 and the first temperature T1 in the first chamber using a pressure gauge and a thermometer, and then use the mass conservation model and the thermomolecular pressure difference model to calculate the temperature T2 in the second chamber.

[0014] According to a low-temperature temperature measurement method provided by the present invention, the calibration of the low-temperature temperature measuring device includes: A vacuum pump assembly is used to evacuate the sealed system consisting of the first chamber, the connecting capillary tube, and the second chamber. The measuring unit is placed at a known and stable standard temperature point. Helium is introduced into the closed system using a helium cylinder. After the helium reaches thermodynamic equilibrium within the closed system, the pressure P of the first chamber under calibrated conditions is collected. 1,cal and temperature T 1,cal ; First, based on the free molecular flow model: Calculate the pressure P in the second chamber under calibration conditions. 2,cal Then, according to the mass conservation model: Calculate the characteristic constant C of the closed system.

[0015] According to a cryogenic temperature measurement method provided by the present invention, placing the measuring unit at a known and stable standard temperature point includes: immersing the measuring unit in liquid nitrogen contained in a cryogenic Dewar flask to ensure that the second chamber is at temperature T under calibration conditions. 2,cal Stablize.

[0016] According to a low-temperature temperature measurement method provided by the present invention, the calculation of the temperature T2 of the second chamber using a mass conservation model and a thermomolecular pressure difference model includes: Substituting the first pressure P1 and the first temperature T1 into Equation 1: And Formula 2: The temperature T2 of the second chamber was calculated.

[0017] The above-described one or more technical solutions of this invention have at least one of the following technical effects: The measuring unit is configured as a passive metal cavity. Upon contact with the target, it ensures that the temperature of the gas in the second chamber matches the temperature of the target. By measuring the gas pressure and temperature in the first chamber and applying the principles of gas thermodynamics and kinetics, the temperature of the gas in the second chamber can be obtained. This avoids measurement errors caused by the self-heating interference of the excitation current with the target. Simultaneously, the thermometer and pressure gauge are positioned in the reference unit, away from the target, to prevent interference from the magnetic field near the target.

[0018] In addition to the technical problems solved by the present invention, the technical features of the technical solutions constituted by the present invention, and the advantages brought about by the technical features of these technical solutions as described above, other technical features of the present invention and the advantages brought about by these technical features will be further explained in conjunction with the accompanying drawings, or will be learned through the practice of the present invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram illustrating the calibration of the low-temperature temperature measuring device provided in an embodiment of the present invention.

[0021] Figure label: 1. Reference unit; 2. Helium; 3. Connecting capillary tube; 4. Cryogenic Dewar; 5. Liquid nitrogen; 6. Measuring unit; 7. Pressure gauge; 8. Thermometer; 9. Three-way valve; 10. Vacuum pump assembly; 11. Gas connection pipeline; 12. Helium cylinder. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] In an embodiment of the present invention, a low-temperature temperature measuring device based on thermomolecular pressure difference is described.

[0024] like Figure 1 As shown, the low-temperature temperature measuring device mainly includes a reference part 1, a measuring part 6, and a connecting capillary tube 3.

[0025] The reference section 1 is configured as a metal housing having a first chamber. The measuring section 6 is configured as a metal housing having a second chamber. A connecting capillary tube 3 is disposed between the reference section 1 and the measuring section 6.

[0026] Pressure gauge 7 is installed in the reference part 1. Thermometer 8 is installed in the reference part 1.

[0027] One end of the connecting capillary tube 3 is connected to the first chamber, and the other end of the connecting capillary tube 3 is connected to the second chamber to form a closed system. The closed system is filled with helium gas 2 as a working medium that flows freely between the first chamber and the second chamber.

[0028] Specifically, the reference section 1 is made of a material with high thermal conductivity to improve the heat exchange efficiency between the gas in the first chamber and the external environment, ensuring that the gas temperature is the same as the external environment. Preferably, the reference section 1 is made of oxygen-free copper. The reference section 1 is made of a material with high thermal conductivity to ensure that the temperature of the gas in the second chamber is completely consistent with the temperature of the target being measured. Preferably, the measuring section 6 is made of oxygen-free copper.

[0029] The thermometer 8 is installed above the reference part 1 and communicates with the first chamber to measure the first temperature T1 inside the first chamber.

[0030] Pressure gauge 7 is installed above reference part 1 and communicates with the first chamber to measure the first pressure P1 in the first chamber.

[0031] Furthermore, the low-temperature temperature measuring device also includes a data processor. The data processor is electrically connected to the thermometer 8 and the pressure gauge 7, respectively, and is used to collect the first pressure P1 and the first temperature T1 in the first chamber, and calculate the temperature T2 of the second chamber according to the built-in model.

[0032] When measuring a low-temperature target using a low-temperature temperature measuring device, the reference unit 1 is placed in a high-temperature environment, and the measuring unit 6 is brought into thermal contact with the low-temperature target to be measured. Then, after the sealed system reaches thermodynamic equilibrium, the first pressure P1 and the first temperature T1 within the first chamber are obtained. The temperature value T2 of the target can then be obtained by calculation using a data processor.

[0033] Furthermore, for mK-level cryogenic measurements, helium-3 is preferred as the working medium because it maintains a sufficiently high vapor pressure at even lower temperatures and does not condense. For K-level temperature measurements, helium-4 can be used to reduce costs.

[0034] In this embodiment, the measuring unit 6 is configured as a passive metal cavity. After contacting the target, it can make the temperature of the gas in the second chamber the same as the temperature of the target. By measuring the gas pressure and temperature in the first chamber and applying the thermodynamics and kinetics of the gas, the temperature of the gas in the second chamber can be obtained, avoiding measurement errors caused by the self-heating interference of the excitation current on the target. At the same time, the thermometer 8 and pressure gauge 7 are placed in the reference unit 1, which can be far away from the target to prevent the magnetic field near the target from interfering with the thermometer 8 and pressure gauge 7.

[0035] Based on the above embodiments, another embodiment of the present invention introduces a low-temperature temperature measuring device based on thermomolecular pressure difference.

[0036] The low-temperature temperature measuring device calculates the second temperature T2 based on the mass conservation relationship and the thermomolecular pressure difference relationship, using the collected first temperature T1 and first pressure P1.

[0037] The equivalent channel diameter of the connecting capillary 3 is much smaller than the mean free path of helium 2 molecules, so that the connecting capillary 3 becomes a free molecular flow region of helium 2.

[0038] Specifically, the inner diameter d of the connecting capillary 3 is designed to be sufficiently small, such that within the target working pressure and temperature range, the mean free path λ of helium 2 molecules is much greater than the inner diameter d, i.e., the Knudsen number Kn = λ / d is much greater than 1. This results in the collision frequency of gas molecules with the channel wall within the connecting capillary 3 being much higher than the collision frequency between them.

[0039] In this region, the thermomolecular pressure difference relationship has a definite physical form, namely: .

[0040] Meanwhile, the mass conservation relationship of the low-temperature temperature measuring device can be expressed (when the capillary volume is ignored) as follows: The data processor can obtain the second temperature T2 by simultaneously solving these two equations.

[0041] Furthermore, the connecting capillary 3 adopts a structure of multiple microchannel arrays; or, the connecting capillary 3 adopts a porous structure.

[0042] The material used to make the connecting capillary tube 3 has heat insulation properties, which is used to avoid heat transfer between the reference part 1 and the measuring part 6, thereby establishing and maintaining a significant and stable temperature difference at both ends of the connecting capillary tube 3.

[0043] The housing connecting the capillary tube 3 is made of a material with low thermal conductivity to minimize heat leakage from the reference section 1 to the measuring section 6. Preferably, the housing connecting the capillary tube 3 is made of stainless steel or a copper-nickel alloy.

[0044] Furthermore, the cryogenic temperature measuring device also includes a vacuum pump assembly 10 and two helium cylinders.

[0045] Vacuum pump assembly 10 is connected to the reference unit 1 and is used to evacuate the sealing system. Helium cylinder 2 is connected to the reference unit 1 and is used to supply helium gas 2 to the sealing system.

[0046] Specifically, the vacuum pump unit 10 is connected to the reference unit 1 via a three-way valve 9, and is used to evacuate the closed system consisting of the reference unit 1, the connecting capillary tube 3 and the measuring unit 6.

[0047] Helium cylinder 2 is connected to reference unit 1 via gas connection pipe 11 and three-way valve 9, and is used to fill the closed system consisting of reference unit 1, connecting capillary tube 3 and measuring unit 6 with helium gas 2.

[0048] The low-temperature measuring device in this embodiment measures the low-temperature target based on the thermodynamics and kinetics of the gas. Since the measuring unit 6 has the same temperature as the low-temperature target, any tiny temperature change of the low-temperature target will cause the helium gas 2 to redistribute between the first chamber and the second chamber, thereby causing a significant change in the first pressure in the first chamber, making the low-temperature measuring device extremely sensitive.

[0049] Furthermore, by placing the active electrical measuring components (pressure gauge 7 and thermometer 8) on the high-temperature reference part 1, the low-temperature temperature measuring device can eliminate the need for complex low-temperature wiring and a precision low-temperature resistance bridge, simplifying the structure of the measuring device, and can provide accurate temperature readings in a strong magnetic field environment, thus solving the magnetoresistive effect problem.

[0050] Furthermore, in another embodiment of the present invention, a low-temperature temperature measurement method is described. This measurement method is applied to the low-temperature temperature measurement device in any of the above embodiments.

[0051] Low-temperature measurement methods include: S1. Calibrate the cryogenic temperature measuring device and obtain the volume V1 of the first chamber, the volume V2 of the second chamber, and the total number N of helium 2 molecules in the sealed system. total Or the equivalent characteristic constant C=N total ×k B ; S2. Install the calibrated low-temperature measuring device onto the low-temperature target to be measured, so that the measuring part 6 is in contact with the low-temperature target to maintain a consistent temperature, and place the reference part 1 in a high-temperature environment, waiting for the helium 2 in the first chamber and the helium 2 in the second chamber to reach thermodynamic equilibrium. S3. Obtain the first pressure P1 and the first temperature T1 in the first chamber through pressure gauge 7 and thermometer 8, and then use the mass conservation model and the thermomolecular pressure difference model to calculate the temperature T2 of the second chamber.

[0052] Specifically, the calibration of the low-temperature measuring device includes: The vacuum pump assembly 10 is used to evacuate the closed system consisting of the first chamber, the connecting capillary tube 3, and the second chamber. The measuring unit 6 is placed at a known and stable standard temperature point. Helium 2 is introduced into the closed system using helium cylinder 2. After the helium 2 reaches thermodynamic equilibrium within the closed system, the pressure P of the first chamber under the calibration condition is collected. 1,cal and temperature T 1,cal ; First, based on the free molecular flow model: Calculate the pressure P in the second chamber under calibration conditions. 2,cal Then, according to the mass conservation model: Calculate the characteristic constant C of the closed system.

[0053] Preferably, to improve the sensitivity of the low-temperature measuring device, the ratio of the volume V1 of the first chamber to the volume V2 of the second chamber can be optimized according to the low-temperature measurement range. The larger the V1 / V2 ratio, the higher the sensitivity of the low-temperature measuring device to the extremely low-temperature region.

[0054] Furthermore, placing the measuring unit 6 at a known and stable standard temperature point includes immersing the measuring unit 6 in liquid nitrogen 5 contained in a cryogenic Dewar 4 to ensure that the second chamber is at the calibrated temperature T. 2,cal Stablize.

[0055] The calculation of the temperature T2 of the second chamber using the mass conservation model and the thermomolecular pressure difference model includes: Substituting the first pressure P1 and the first temperature T1 into Equation 1: And Formula 2: The temperature T2 of the second chamber was calculated.

[0056] Specifically, the process of measuring the temperature of mK-level cryogenic targets using a cryogenic temperature measuring device is as follows: Step 1, System Preparation and Calibration: Charge the system with a known total number of molecules N. total Helium 2, or calibrating the equivalent system characteristic constant C=N total ×k B .

[0057] Vacuum the sealed system: Open the three-way valve 9, start the vacuum pump group 10, and perform high-vacuum exhaust on the sealed system consisting of the reference part 1, the connecting capillary tube 3 and the measuring part 6.

[0058] Establish a calibration point: Place the measuring unit 6 at a known and stable standard temperature point. For example, immerse the measuring unit 6 in liquid helium of a cryogenic Dewar 4 until its temperature stabilizes at T. cal =4.20K.

[0059] Gas filling and equilibration: Turn off vacuum pump unit 10, open the valve of helium cylinder 2, and slowly fill the closed system with helium 2 through three-way valve 9 until pressure gauge 7 shows a suitable pressure (e.g., P1 = 20.0 Pa). Wait for the closed system to reach complete thermodynamic equilibrium.

[0060] Sealing: Close the three-way valve 9 to disconnect the sealed system from the vacuum pump group 10 and the helium cylinder 2, forming a permanently sealed system containing a known total number of molecules.

[0061] Data collection and calibration: After the closed system stabilizes, simultaneously read the readings of thermometer 8 and pressure gauge 7, and record the high-temperature parameter under calibration conditions: T 1,cal =295.0K and P 1,cal =20.0Pa.

[0062] Calculate the characteristic constant C: First, calculate the low-temperature pressure P under the calibration state according to the thermomolecular pressure difference formula. 2,cal : Then, the characteristic constant C=N of the system is calculated according to the mass conservation formula. total ×k B : .

[0063] Step Two: System Installation and Balancing Installation: Remove the calibrated measuring unit 6 from the calibration environment (such as liquid helium) and install it onto the cryogenic target to be measured. For example, the mK sample stage of a dilution refrigerator.

[0064] Cooling and Equilibrium: The refrigeration unit is activated, causing the measuring unit 6 to cool down along with the low-temperature target. The reference unit 1 remains in a high-temperature environment, waiting for the entire closed system to reach a new thermodynamic equilibrium.

[0065] Step 3: Data Collection Real-time monitoring: Once the system stabilizes at the unknown low temperature T2, the data processor begins to monitor the high-temperature end T1 and P1 in real time using thermometer 8 and pressure gauge 7.

[0066] Record instantaneous values: Suppose that the instantaneous values ​​collected at this moment are T1=296.0K and P1=8.50Pa.

[0067] Step 4: Temperature Calculation Substituting into the equations: The data processor calls the characteristic constant C stored in step one and the P1 and T1 values ​​collected in step three, and substitutes them into the system of equations: Solve for T2: Solve simultaneously using the data processor.

[0068] Output result: The data processor finally outputs the measured temperature T2 = 12.2mK.

[0069] Cycle: Steps three and four are continuously repeated to achieve real-time, self-heating-free, and magnetic field-resistant temperature monitoring of the low-temperature target. The temperature can also be compared and verified with the calibrated low-temperature thermometer mounted on the measurement unit.

[0070] Furthermore, the characteristic constant C of the closed system can also be determined by weighing. Specifically, the vacuum state mass of the thermomolecular pressure difference cryogenic temperature measuring device is... m 0 and the mass after filling with working gas m p Change Δ m = m p - m The ratio of 0 to molar mass is determined. C = N A ×Δ m / M ,in N A is Avogadro's constant.

[0071] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0072] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0073] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0074] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms are not limited to the same embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-temperature temperature measurement method, characterized in that, Applied to cryogenic temperature measurement devices based on thermomolecular pressure differences, cryogenic temperature measurement methods include: S1. Calibrate the low-temperature measuring device to obtain the volume V1 of the first chamber, the volume V2 of the second chamber, and the total number N of helium (2) molecules in the sealed system. total Or the equivalent characteristic constant C=N total ×k B ; S2. Install the calibrated low-temperature measuring device onto the low-temperature target to be measured, so that the measuring part (6) is in contact with the low-temperature target to maintain a consistent temperature, and place the reference part (1) in a high-temperature environment, waiting for the helium (2) in the first chamber and the helium (2) in the second chamber to reach thermodynamic equilibrium. S3. Obtain the first pressure P1 and the first temperature T1 in the first chamber through the pressure gauge (7) and the thermometer (8), and then use the mass conservation model and the thermomolecular pressure difference model to calculate the temperature T2 of the second chamber. The cryogenic temperature measuring device based on thermomolecular pressure difference includes: The reference part (1) is configured as a metal housing having a first chamber; The measuring unit (6) is configured as a metal housing with a second chamber; A capillary tube (3) is connected and disposed between the reference part (1) and the measuring part (6); Pressure gauge (7) is installed on the reference unit (1); Thermometer (8) is installed on the reference unit (1); One end of the connecting capillary tube (3) is connected to the first chamber, and the other end of the connecting capillary tube (3) is connected to the second chamber to form a closed system. The closed system is filled with helium gas (2) as a working medium that flows freely between the first chamber and the second chamber.

2. The low-temperature temperature measurement method according to claim 1, characterized in that, The equivalent channel diameter of the connecting capillary (3) is much smaller than the mean free path of the helium (2) molecules, so that the connecting capillary (3) becomes a free molecular flow region of helium (2).

3. The low-temperature temperature measurement method according to claim 2, characterized in that, The connecting capillary (3) adopts a structure of multiple microchannel arrays; Alternatively, the connecting capillary (3) may have a porous structure.

4. The low-temperature temperature measurement method according to claim 3, characterized in that, The material used to make the connecting capillary (3) has heat insulation properties to prevent heat transfer between the reference part (1) and the measuring part (6).

5. The low-temperature temperature measurement method according to claim 4, characterized in that, Also includes: A vacuum pump assembly (10) is connected to the reference unit (1) and is used to evacuate the sealing system; A helium (2) bottle, connected to the reference part (1), is used to supply helium (2) to the sealing system.

6. The low-temperature temperature measurement method according to claim 1, characterized in that, The reference part (1) is made of oxygen-free copper, and the measuring part (6) is made of oxygen-free copper.

7. The low-temperature temperature measurement method according to any one of claims 1 to 6, characterized in that, The calibration of the low-temperature measuring device includes: The vacuum pump assembly (10) is used to evacuate the closed system consisting of the first chamber, the connecting capillary tube (3), and the second chamber; The measuring unit (6) is placed at a known and stable standard temperature point. Helium (2) is introduced into the closed system using a helium (2) cylinder. After the helium (2) reaches thermodynamic equilibrium in the closed system, the pressure P of the first chamber under the calibration condition is collected. 1,cal and temperature T 1,cal ; First, based on the free molecular flow model: Calculate the pressure P in the second chamber under calibration conditions. 2,cal Then, according to the mass conservation model: Calculate the characteristic constant C of the closed system.

8. The low-temperature temperature measurement method according to claim 7, characterized in that, The step of placing the measuring unit (6) at a known and stable standard temperature point includes immersing the measuring unit (6) in liquid nitrogen (5) contained in a cryogenic Dewar (4) to ensure that the second chamber is at the calibrated temperature T. 2,cal Stablize.

9. The low-temperature temperature measurement method according to claim 8, characterized in that, The calculation of the temperature T2 of the second chamber using the mass conservation model and the thermomolecular pressure difference model includes: Substituting the first pressure P1 and the first temperature T1 into Equation 1: And Formula 2: The temperature T2 of the second chamber was calculated.

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