A device for measuring virial coefficient based on continuous expansion method

Abstract

The present disclosure provides a virial coefficient measurement device based on the continuous expansion method. In the device, a gas source, multiple expansion chambers, and an exhaust unit are connected in series in sequence; the measurement module controls the exhaust unit to open all the stop valves at the beginning of the measurement to first evacuate the expansion chamber; then all the stop valves are closed, and starting from the expansion chamber closest to the gas source, a fixed amount of gas provided by the gas source is sequentially introduced into each expansion chamber by controlling the stop valve, so that each expansion chamber is gradually connected in the order of connection; each time a new expansion chamber is connected, the pressure gauge and the thermostat data are recorded. After completing the inflation of all the expansion chambers, a linear fit is performed using the recorded data, and the two coefficients of the fitting line are the two virial coefficients. The present invention can obtain the first virial coefficient and the second virial coefficient applicable to different gases in the static expansion method, ensuring the accurate calibration of the vacuum gauge by the static expansion method.

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum metrology, and in particular to a device for accurately measuring virial coefficients. Background Art

[0002] In vacuum metrology, the static expansion method is used to calibrate rough and low vacuum measuring instruments. The basic principle of the static expansion method is based on the Boyle-Maliott theorem, which states that under isothermal conditions, a certain amount of gas obeys the equation pV=C, where p is the gas pressure, V is the volume occupied by the gas, and C is a constant. The static expansion method requires that the gas temperature remain constant during the calibration process, which places high demands on the environmental conditions of the calibration laboratory. Currently, strict isothermal conditions are difficult to achieve during static expansion method calibration, so the virial coefficient is used to modify the static expansion method formula.

[0003] For a certain amount of gas, its state can be described by three parameters: p, V, and T, satisfying pVnRT, that is, p is the gas pressure, V is the volume occupied by the gas, n is the number of moles, R is the gas constant, and T is the temperature. Since the isothermal condition is not met during static expansion, the actual gas state A is the first virial coefficient, B is the second virial coefficient, Vm is the molar volume, VmV / n, Vm expands with volume.

[0004] In order to achieve accurate calibration of a rough low vacuum measuring instrument using a static expansion method, the present invention measures the first virial coefficient and the second virial coefficient so as to correct the calibration result of the static expansion method. Summary of the Invention

[0005] In view of this, the present invention provides a virial coefficient measuring device based on the continuous expansion method to realize the measurement of the first virial coefficient and the second virial coefficient applicable to different gases in the static expansion method, ensuring the accurate calibration of the vacuum gauge by the static expansion method, and solving the technical difficulties in the field of vacuum testing technology in my country for the accurate value transmission and traceability of capacitance film vacuum gauges, magnetic levitation rotor vacuum gauges, ionization vacuum gauges, thermal conductivity vacuum gauges, etc.

[0006] In order to solve the above technical problems, the present invention is implemented as follows.

[0007] A virial coefficient measuring device based on a continuous expansion method comprises a gas source, M expansion chambers, a pressure gauge, an air pumping unit, and a measuring module; M is an integer greater than or equal to 3; the gas source, each expansion chamber, and the air pumping unit are connected in series; a shut-off valve is provided between the gas source and the expansion chamber, between each expansion chamber, and between the expansion chamber and the air pumping unit; the expansion chamber, the shut-off valve, and the pressure gauge are placed in a constant temperature box to maintain a constant temperature during measurement; the pressure gauge is selected to indicate the same pressure value for various gases of the same volume in the same expansion chamber at the same temperature;

[0008] The measuring module connects each gas source, each shut-off valve, pressure gauge and vacuum unit; the measuring module controls the vacuum unit to open all the shut-off valves at the beginning of the measurement to evacuate the expansion chamber first; then close all the shut-off valves, and start from the expansion chamber closest to the gas source, by controlling the shut-off valves, introduce a fixed amount of gas provided by the gas source into each expansion chamber in sequence, so that each expansion chamber is gradually connected in the connection order; each time a new expansion chamber is connected, the pressure gauge reading p is recorded after the pressure stabilizes. m The temperature of the thermostat is T m ; The gas state at the current stage is expressed as:

[0009]

[0010] Assume that the dependent variable of the current stage is Independent variable

[0011] Among them, V i is the volume of the i-th expansion chamber, n is the number of moles, R is the gas constant, Vm m is the molar volume, m means that the first m expansion chambers are currently connected;

[0012] After completing the inflation of all expansion chambers, the dependent variables y1~y M and independent variables x1 to x M Perform linear fitting to obtain the linear function ya+bx, where a is the value of the first virial coefficient A, and b is the value of the second virial coefficient B.

[0013] Preferably, the pressure gauge is connected to the expansion chamber closest to the gas source.

[0014] Preferably, the gas source provides multiple independent high-purity gases, and the purity of the gas sample is guaranteed not to change during the process of being introduced into the expansion chamber.

[0015] Preferably, the stop valves are all made of metal and have an internal and external leakage rate of less than 1×10 -9 Pam 3 / s.

[0016] Preferably, the expansion chamber is a metal container of known volume, the volume of each expansion chamber is the same or different, the minimum volume is not less than 0.1L, and the maximum volume is not more than 100L.

[0017] Preferably, the vacuum unit (14) makes the vacuum background in the device no greater than 1×10 -3 Pa.

[0018] Preferably, the constant temperature box (15) controls the temperature of the environment in the box with an accuracy of 0.01°C during the measurement process, and the temperature fluctuation is less than ±0.01°C.

[0019] Preferably, there are five expansion chambers.

[0020] Beneficial effects:

[0021] The present invention proposes a virial coefficient measuring device based on the continuous expansion method, which realizes the accurate measurement of the first virial coefficient and the second virial coefficient applicable to different gases in the static expansion method, corrects the non-isothermal situation in the actual calibration process, and ensures the accurate calibration of the vacuum gauge by the static expansion method; due to the use of a pressure gauge with no discrimination effect, the measurement of the virial coefficients of different gases can be realized; and solves the technical difficulties in the field of vacuum testing technology in my country for the accurate value transmission and traceability of capacitance film vacuum gauges, magnetic levitation rotor vacuum gauges, ionization vacuum gauges, thermal conductivity vacuum gauges, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the virial coefficient measurement device based on the continuous expansion method of the present invention. DETAILED DESCRIPTION

[0023] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0024] The present invention provides a device for measuring virial coefficients based on the continuous expansion method, such as Figure 1 As shown, the measurement device includes a gas source 1, M expansion chambers 3, 6, 8, 10, and 12, an exhaust unit 14, and a measurement module. The gas source 1, each expansion chamber, and the exhaust unit 14 are connected in series. Shutoff valves 2, 5, 7, 9, 11, and 13 are installed between the gas source 1 and the expansion chambers, between each expansion chamber, and between the expansion chambers and the exhaust unit 14. The expansion chambers, shutoff valves, and pressure gauges are placed in a constant temperature box 15 to maintain a constant temperature during measurement. The measurement module connects the gas sources 1, each shutoff valve, pressure gauge 4, and exhaust unit 14 to implement measurement data acquisition, device control, and measurement calculations.

[0025] Manometer 4 should be non-discriminatory for various gases. That is, the pressure readings for the same amount of various gases in the same expansion chamber at the same temperature should be the same, enabling measurement of the virial coefficients of different gases. For example, a capacitance diaphragm vacuum gauge, commonly used in vacuum measurement, can be used. In a preferred embodiment, manometer 4 is connected to the expansion chamber closest to gas source 1. This allows a single manometer to perform all measurements, avoiding inconsistencies caused by using multiple manometers.

[0026] The gas source 1 can provide multiple independent high-purity gases, and the purity of the gas sample is guaranteed not to change during the process of being introduced into the expansion chamber 3.

[0027] The stop valves are all made of metal and the internal and external leakage rate is less than 1×10 -9 Pam 3 / s to ensure the accuracy of the data.

[0028] The expansion chamber is a metal container of known volume. The volume of each expansion chamber can be the same or different, with the minimum volume not less than 0.1L and the maximum not greater than 100L. There should be at least three expansion chambers. The more expansion chambers there are, the more accurate the calculated virial coefficient will be in theory. However, more expansion chambers require higher sealing and precision of the pipelines and components to avoid unnecessary attenuation. Therefore, through experiments, five expansion chambers were determined to be the optimal number.

[0029] Preferably, the constant temperature box 15 is selected to ensure that the temperature control accuracy of the environment in the box is 0.01°C and the temperature fluctuation is less than ±0.01°C during the measurement process, so as to ensure stable temperature control.

[0030] Preferably, the vacuum unit 14 makes the vacuum background in the device no greater than 1×10 -3 Pa.

[0031] The device implements the Virial coefficient measurement scheme as follows: the measurement module controls the vacuum unit 14 to open all the stop valves at the beginning of the measurement to first evacuate the expansion chamber, then close all the stop valves, and then start from the expansion chamber closest to the gas source, by controlling the stop valves, to sequentially introduce a fixed amount of gas provided by the gas source 1 into each expansion chamber of known volume, so that each expansion chamber is gradually connected in the order of connection; after each new expansion chamber is connected, assuming that the currently connected expansion chamber is the mth expansion chamber, the pressure gauge 4 reading p is recorded after the pressure stabilizes. m The temperature of the thermostat is T m ; The gas state at the current stage is expressed as:

[0032]

[0033] Assume that the dependent variable of the current stage is Independent variable

[0034] Among them, V i is the volume of the i-th expansion chamber, is the sum of the capacities of the first m expansion chambers that have been opened; n is the number of moles, R is the gas constant, Vm m is the molar volume,

[0035] After completing the inflation of all expansion chambers, the dependent variables y1~y M and independent variables x1 to x MPerform linear fitting to obtain the linear function ya+bx, where a is the value of the first virial coefficient A, and b is the value of the second virial coefficient B.

[0036] The following example includes five expansion chambers to describe the implementation scheme of the present invention in detail. The method includes the following steps:

[0037] Step 1: Turn on the constant temperature box 15 and keep the temperature fluctuation less than ±0.01°C during the measurement process.

[0038] Step 2: Open all stop valves 5, 7, 9, 11, and 13, and use the vacuum unit 14 to evacuate all expansion chambers 3, 6, 8, 10, and 12 until the vacuum reading on the pressure gauge 4 is less than 1×10 -3 Pa.

[0039] Step 3: Close all stop valves 5, 7, 9, 11, and 13, open stop valve 2, and introduce the high-purity gas from gas source 1 into expansion chamber 3 with a known volume of V1. Based on the reading of pressure gauge 4, determine that the pressure is stable and then close valve 2. Record the pressure gauge 4 reading p1 and the constant temperature chamber reading T1. The gas state at this time is expressed by formula (1), where Vm1 is the molar volume, n is the number of moles, and R is the gas constant.

[0040]

[0041] Step 4: Open stop valve 5 and introduce the high-purity gas from expansion chamber 3 into expansion chamber 6, whose volume is known as V2. After the pressure stabilizes, record the pressure gauge 4 reading as p2 and the thermostat temperature reading as T2. The gas state at this point is expressed by equation (2), where Vm2 is the molar volume.

[0042]

[0043] Step 5: Open stop valve 7 and introduce the high-purity gas from expansion chamber 6 into expansion chamber 8, whose volume is known as V3. After the pressure stabilizes, record the pressure gauge 4 reading as p3 and the thermostat temperature reading as T3. The gas state at this point is expressed by equation (3), where Vm3 is the molar volume.

[0044]

[0045] Step 6: Open stop valve 9 and introduce the high-purity gas from expansion chamber 8 into expansion chamber 10, whose volume is known as V4. After the pressure stabilizes, record the pressure gauge 4 reading as p4 and the thermostat temperature reading as T4. The gas state at this point is expressed by equation (4), where Vm4 is the molar volume.

[0046]

[0047] Step 7: Open shutoff valve 11 and introduce the high-purity gas from expansion chamber 10 into expansion chamber 12, which has a known volume of V5. After the pressure stabilizes, record the pressure gauge 4 reading p5 and the thermostat temperature reading T5. The gas state at this point is expressed by equation (5), where Vm5 is the molar volume.

[0048]

[0049] Step 8: Solve.

[0050] make,

[0051] Take y1, y2, y3, y4, y5 as dependent variables and x1, x2, x3, x4, x5 as independent variables, and perform linear fitting on the 5 sets of data to obtain the linear function ya+bx, then a is the value of the first virial coefficient A, and b is the value of the second virial coefficient B.

[0052] The present invention is based on a virial coefficient measurement scheme of the continuous expansion method, which can correct the temperature inconsistency in the actual calibration process to realize the measurement of the first virial coefficient and the second virial coefficient applicable to different gases in the static expansion method, thereby ensuring the accurate calibration of the vacuum gauge by the static expansion method, and solving the technical difficulties in the field of vacuum testing technology in my country for the accurate value transmission and traceability of capacitance film vacuum gauges, magnetic levitation rotor vacuum gauges, ionization vacuum gauges, thermal conductivity vacuum gauges, etc.

[0053] The above specific embodiments merely illustrate the design principles of the present invention. The shapes and names of the components described herein may vary and are not limiting. Therefore, those skilled in the art may modify or substitute equivalents for the technical solutions described in the above embodiments. Such modifications and substitutions, without departing from the inventive spirit and technical solutions of the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A virial coefficient measuring device based on the continuous expansion method, characterized in that: The measuring device comprises a gas source (1), M expansion chambers (3, 6, 8, 10, 12), a pressure gauge (4), an air pumping unit (14), and a measuring module; M is an integer greater than or equal to 3; the gas source (1), each expansion chamber, and the air pumping unit (14) are sequentially connected in series; stop valves (2, 5, 7, 9, 11, 13) are provided between the gas source (1) and the expansion chambers, between each of the expansion chambers, and between the expansion chambers and the air pumping unit (14); the expansion chambers, the stop valves, and the pressure gauge are arranged in a constant temperature box (15) to maintain a constant temperature during the measurement process; the pressure gauge is selected to have the same pressure indication value for various gases of the same volume in the same expansion chamber at the same temperature; The measuring module is connected to each gas source (1), each stop valve, pressure gauge (4) and the vacuum unit (14); the measuring module controls the vacuum unit (14) to open all the stop valves at the beginning of the measurement to first evacuate the expansion chamber; then close all the stop valves, and starting from the expansion chamber closest to the gas source, a fixed amount of gas provided by the gas source (1) is sequentially introduced into each expansion chamber by controlling the stop valves, so that each expansion chamber is gradually connected in the connection order; each time a new expansion chamber is connected, the pressure gauge (4) reading is recorded after the pressure stabilizes And the constant temperature box temperature is ; The gas state at the current stage is expressed as: Assume that the dependent variable of the current stage is , independent variable ; in, For the i The volume of the expansion chamber, n is the number of moles, R is the gas constant, is the molar volume, ; m Indicates that the current connection m expansion chamber; After completing the inflation of all expansion chambers, the dependent variables of M stages are and independent variables Perform linear fitting to obtain a linear function ,but is the value of the first virial coefficient A, The second virial coefficient is B The value of .

2. The measuring device according to claim 1, characterized in that The pressure gauge (4) is connected to the expansion chamber closest to the gas source (1).

3. The measuring device according to claim 1, characterized in that The gas source (1) provides multiple independent high-purity gases, and the purity of the gas sample is guaranteed not to change during the process of being introduced into the expansion chamber (3).

4. The measuring device according to claim 1, characterized in that The stop valves are all made of metal and the internal and external leakage rate is less than 1×10 -9 Pam 3 / s.

5. The measuring device according to claim 1, characterized in that The expansion chamber is a metal container with a known volume. The volume of each expansion chamber is the same or different, with the minimum volume not less than 0.1L and the maximum volume not greater than 100L.

6. The measuring device according to claim 1, characterized in that The vacuum unit (14) pumps air to ensure that the vacuum level in the device is no greater than 1×10 -3 Pa.

7. The measuring device according to claim 1, characterized in that The constant temperature box (15) controls the temperature of the environment in the box with an accuracy of 0.01°C during the measurement process, and the temperature fluctuation is less than ±0.01°C.

8. The measuring device according to claim 1, characterized in that There are five expansion chambers.

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