A lower limit is 5×10 -18 Pa•m 3 / s flow meter and its use method

Abstract

The present invention relates to a method with a lower limit of 5×10 ‑18 Pa·m 3 / s flowmeter and its use method, the standard gas flowmeter includes: a molecular flow conductance gas extraction module, including a first gas cylinder, a first valve, a second valve, a first vacuum chamber, a third valve and a first high vacuum pump unit, a fourth valve, a first standard flow conductance element, a fifth valve, a first vacuum gauge and a second vacuum gauge; a pressure gas extraction module, including a second gas cylinder, an eighth valve, a seventh valve, a sixth valve, a third vacuum chamber, a ninth valve and a second high vacuum pump unit, a fifth vacuum gauge and a sixth vacuum gauge; a molecular flow conductance gas supply module, including a second vacuum chamber, a tenth valve, a second standard flow conductance element, an eleventh valve, a fourth vacuum chamber, a twelfth valve, a third high vacuum pump unit, a thirteenth valve, a third vacuum gauge, a fourth vacuum gauge and a seventh vacuum gauge. The device of the present invention is simple, low-cost, and easy to operate, and can extend the lower limit of the standard gas flow rate to 10 ‑18 Order of magnitude.

Description

Technical Field

[0001] The present invention relates to the technical field of vacuum measurement detection and gas flow measurement under vacuum conditions, and in particular to a method with a lower limit of 5×10 -18 Pa·m 3 / s flow meter and its use method. Background Art

[0002] Most ultra-sensitive leak detectors use a standard leak as a reference standard to calibrate the leak detection results. A standard gas flow meter can replace the standard leak and provide a standard gas flow rate during the calibration of the leak detector. The lower limit of the current gas micro-flow rate provided to the vacuum environment is 5×10 -16 Pa·m 3 / s, can be obtained by a fixed conductance flow meter (see "A (10 -5 -10 -16 )Pa·m 3 / s Standard Gas Flow Meter Design", 2021). The principle is that under molecular flow conditions, the gas flow rate reaching a unit cross section can be calculated by the formula Q = (P1-P2)·C, where P1 is the pressure at the inlet of the standard flow conductance element, and P2 is the pressure at the outlet. In general, the value of P1 is much larger than the value of P2, so the previous formula can be approximately equivalent to Q = P1·C. Therefore, it can be seen from this formula that in order to obtain an extremely small flow rate Q, it is necessary to reduce the inlet pressure P1 of the standard flow conductance element or the conductance value C of the standard flow conductance element. The current minimum lower limit that a standard flow conductance element can reach is 10 -10 m 3 / s level, so if we want to further extend the lower limit of the tiny gas flow rate Q, we can only reduce P1 as much as possible.

[0003] The inlet pressure P1 of the standard flow conductance element is usually accurately measured by a thin film capacitor vacuum gauge, and the lower limit of accurate measurement is about 10Pa. After the gas measured by the thin film capacitor vacuum gauge is expanded and attenuated, the lower limit of pressure can be extended to 10 - 6 Pa level, but the background vacuum requirement is relatively high, usually reaching 10 -8 Pa level, it is generally difficult to obtain such a low background vacuum, so the lower limit of partial pressure can be extended by preparing a standard mixed gas. The principle is to introduce the prepared standard mixed gas into the vacuum chamber through a standard flow guide element. In the molecular flow state, the interaction between the two gas molecules can be ignored. In this way, as long as the partial pressure of the target gas in the standard mixed gas is calculated, the target gas flow rate at the outlet of the standard flow guide element can be obtained.

[0004] The standard mixed gas is generally prepared by the standard small volume pressure sampling method. The lower limit of the preparation ratio of the standard mixed gas prepared by this method is η = 5 × 10 -8 At this ratio, according to Q = P1·η·C, the minimum gas flow rate can be calculated to be 5×10 -17 Pa·m 3 / s, which is only one order of magnitude longer than the lower limit of standard gas flow meters in the prior art. Summary of the invention

[0005] In order to solve the technical deficiencies of the standard gas flowmeter used in the vacuum environment in the above-mentioned prior art, the purpose of the present invention is to provide a standard gas flowmeter used in a vacuum environment and a method of using the same, extending the lower limit of the traditional fixed conductance standard gas flowmeter, and having the advantages of simple equipment, low cost, and easy operation.

[0006] In order to achieve the above-mentioned object, the present invention provides a method with a lower limit of 5×10 -18 Pa·m 3 / s flowmeter, comprising a molecular flow guide gas intake module, a pressure gas intake module and a molecular flow guide gas supply module.

[0007] The molecular flow gas extraction module comprises a first gas cylinder, a first valve, a second valve, a third valve, a fourth valve, a fifth valve, a first standard flow guide element, a first vacuum chamber and a first high vacuum pump unit. The first vacuum chamber is provided with a first vacuum gauge and a second vacuum gauge.

[0008] The pressure gas extraction module comprises a second gas cylinder, a sixth valve, a seventh valve, an eighth valve, a ninth valve, a third vacuum chamber and a second high vacuum pump unit. The third vacuum chamber is provided with a fifth vacuum gauge and a sixth vacuum gauge.

[0009] The molecular flow conductance gas supply module includes a second vacuum chamber, a fourth vacuum chamber, a tenth valve, an eleventh valve, a twelfth valve, a thirteenth valve, a second standard flow conductance element and a third high vacuum pump unit. The second vacuum chamber is equipped with a third vacuum gauge and a fourth vacuum gauge, and the fourth vacuum chamber is equipped with a seventh vacuum gauge.

[0010] The connection relationship between the first vacuum chamber, the second vacuum chamber and the third vacuum chamber is: the first vacuum chamber is connected to the second vacuum chamber through the fourth valve, the first standard flow conductance element and the fifth valve connected in sequence; the third vacuum chamber is connected to the second vacuum chamber through the sixth valve; the fourth vacuum chamber is connected to the second vacuum chamber through the tenth valve, the second standard flow conductance element and the eleventh valve connected in sequence.

[0011] According to one aspect of the present invention, the volumes of the three vacuum chambers are all constant, the volume U1 of the first vacuum chamber is 5L, the volume U2 of the second vacuum chamber is 5L, the volume U3 of the third vacuum chamber is 1L, and the volume U4 of the fourth vacuum chamber is 5L.

[0012] According to one aspect of the present invention, the second valve and the seventh valve are both fine-tuning valves for controlling the pressure of the corresponding vacuum chamber to rise slowly.

[0013] According to one aspect of the present invention, the second vacuum gauge, the fourth vacuum gauge and the sixth vacuum gauge are a combination of capacitance film vacuum gauges, and the pressure measurement range is 1×10 5 The first vacuum gauge, the third vacuum gauge, the fifth vacuum gauge and the seventh vacuum gauge are composite monitoring vacuum gauges with a pressure measurement range of 1×10 5 Pa~1×10 -8 Pa.

[0014] According to one aspect of the present invention, the conductance value C1 of the first standard conductance element ranges from 10 - 8 Pa·m 3 / s~10 -10 Pa·m 3 / s, the conductance value C2 of the second standard conductance element ranges from 10 -8 Pa·m 3 / s~10 -10 Pa·m 3 / s.

[0015] According to one aspect of the present invention, the first high vacuum pump, the second high vacuum pump and the third high vacuum pump are all combinations of molecular pumps and vortex dry pumps.

[0016] According to one aspect of the present invention, a method as described in any one of the above technical solutions with a lower limit of 5×10 -18 Pa·m 3 The method for using the flow meter of / s includes the following steps:

[0017] Step S1: measuring the background pressure P of the first vacuum chamber, the second vacuum chamber, the third vacuum chamber and the fourth vacuum chamber 01 , P 02 , P 03 , P 04 ;

[0018] Step S2: Introduce the gas from the first gas cylinder into the first vacuum chamber, so that the pressure in the first vacuum chamber reaches P1, and then introduce the gas in the first vacuum chamber into the second vacuum chamber through the first standard flow guide element, which is recorded as the molecular flow gas extraction time t. The amount of gas obtained by the molecular flow gas extraction module can be calculated as M1 = (P1-P 01 )·C1·t.

[0019] Step S3: Introduce the gas in the second gas cylinder into the third vacuum chamber, so that the pressure in the third vacuum chamber reaches P3, and then expand the gas in the third vacuum chamber into the second vacuum chamber through the sixth valve, and make the pressure in the second vacuum chamber reach P2 after one or more expansion samplings to obtain a standard mixed gas. It can be calculated that after two samplings, the amount of gas in the second vacuum chamber is M2 = (P2-P 02 )·V2, the preparation ratio of the standard mixed gas is η=M1 / M2.

[0020] Step S4: Adjust the pressure in the second vacuum chamber so that the gas in the second vacuum chamber reaches a molecular flow state (≤1000 Pa). At this time, the pressure in the second vacuum chamber is P 21 Then, the standard mixed gas is introduced into the fourth vacuum chamber through the second standard flow guide element, and the flow rate Q of the trace gas in the standard mixed gas can be calculated. x =(P 21 -P 02 )·η·C2;

[0021] Wherein, C1 is the conductance value of the first standard conductance element (f1); C2 is the conductance value of the second standard conductance element (f2).

[0022] According to one aspect of the present invention, step S1 includes the following sub-steps:

[0023] Step S11: opening the third valve, the fourth valve, the fifth valve, the sixth valve, the ninth valve, the tenth valve, the eleventh valve and the twelfth valve, and simultaneously starting the first high vacuum pump unit, the second high vacuum pump unit and the third high vacuum pump unit;

[0024] Step S12: Turn on the first vacuum gauge, the third vacuum gauge, the fifth vacuum gauge and the seventh vacuum gauge, and then turn on the second vacuum gauge, the fourth vacuum gauge and the sixth vacuum gauge (when starting the capacitive film vacuum gauge for the first time, it should be preheated for more than 12 hours, and zeroed when the pressure in the corresponding vacuum chamber reaches the ultimate vacuum degree);

[0025] Step S13: When the readings of the first vacuum gauge, the third vacuum gauge, the fifth vacuum gauge and the seventh vacuum gauge reach 1×10 -6 When the pressure is below Pa, the displayed pressure value is recorded as P 01 , P 02 , P 03 , P 04 , and close the fourth valve, the fifth valve, the tenth valve and the eleventh valve.

[0026] According to one aspect of the present invention, step S2 includes the following sub-steps:

[0027] Step S21: closing the third valve, opening the first valve and slowly adjusting the second valve to introduce the gas in the first gas cylinder into the first vacuum chamber;

[0028] Step S22: When the pressure in the first vacuum chamber reaches 10Pa~1×10 5 When the vacuum gauge is within the range of Pa, the first valve and the second valve are closed, and after the indicated value of the second vacuum gauge is stable, it is recorded as P1;

[0029] Step S23: close the sixth valve, then open the fourth valve and the fifth valve in sequence, introduce the gas in the first vacuum chamber into the second vacuum chamber through the first standard flow conductance element, and calculate the intake time from the moment the fifth valve is opened, which ranges from 100s to 1000s. After the intake is completed, quickly close the fourth valve and the fifth valve, and record it as the molecular flow conductance intake and extraction time t.

[0030] According to one aspect of the present invention, step S3 includes the following sub-steps:

[0031] Step S31: closing the ninth valve, opening the eighth valve and slowly adjusting the seventh valve to slowly introduce the gas in the second gas cylinder into the third vacuum chamber;

[0032] Step S32: When the pressure in the third vacuum chamber reaches 10Pa~1×10 5 Pa range, close the seventh valve and the eighth valve, and after the indicated value of the sixth vacuum gauge stabilizes, record its indicated value as P3;

[0033] Step S33: Open the sixth valve to introduce the gas in the third vacuum chamber into the second vacuum chamber, so that the pressure in the second vacuum chamber reaches 10Pa to 1×10 5 Pa range, close the sixth valve, and after the indicated value of the fourth vacuum gauge stabilizes, record it as P2;

[0034] Step S34: Calculate the mixing ratio of the standard mixed gas in the second vacuum chamber as follows:

[0035]

[0036] According to one aspect of the present invention, in step S4, the following sub-steps are included:

[0037] Step S41: Open the thirteenth valve, adjust the pressure in the second vacuum chamber to 10Pa-1000Pa, that is, let the gas in the second vacuum chamber reach a molecular flow state, close the thirteenth valve, and after the indication value of the fourth vacuum gauge stabilizes, record it as P 21 ;

[0038] Step S42: closing the twelfth valve, opening the tenth valve and the eleventh valve, and introducing the standard mixed gas in the second vacuum chamber into the fourth vacuum chamber;

[0039] Step S43: Calculate the trace gas flow rate of the standard mixed gas introduced into the fourth vacuum chamber as Q x =(P 21 -P 02 )·η·C2.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The standard mixed gas was configured by combining the molecular flow conductance gas extraction module and the pressure gas extraction module, and then a method with a lower limit of 5×10 -18 Pa·m 3 / s standard gas flowmeter. The device accurately samples the target gas and other gases based on the molecular conductance method and the static expansion method, mixes the two gases evenly in the second vacuum chamber to obtain a standard mixed gas, and then provides the standard gas flow to the vacuum chamber through the second standard conductance element. According to the reference standard, the background pressure and gas pressure of the first vacuum chamber, the second vacuum chamber, the third vacuum chamber and the fourth vacuum chamber are measured respectively. The flow rate of the trace gas in the standard mixed gas provided to the fourth vacuum chamber can be calculated from the conductance values ​​of the first standard conductance element and the second standard conductance element and the volume of the second vacuum chamber.

[0042] The present invention breaks through the bottleneck that the lower limit of the traditional standard gas flow meter provided under vacuum conditions is difficult to extend, solves the problem that the lower limit of the inlet pressure of the flow element provided by the traditional fixed conductance method for providing standard gas flow is difficult to extend, and proposes a method of coupling the fixed conductance method by configuring a standard mixed gas to increase the lower limit of the standard gas flow provided under vacuum conditions from the currently reported 5×10 -16 Pa·m 3 / s extended to 5×10 -18 Pa·m 3 / s. The method of the present invention has the advantages of simple equipment, low cost, convenient operation, low flow meter lower limit, etc., and provides an effective means for further solving the measurement and value traceability of gas flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 Schematic diagram of the structure of a flow meter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The description of the embodiments of this specification should be combined with the corresponding drawings, which should be considered as part of the complete specification. In the drawings, the shape or thickness of the embodiments may be enlarged and indicated for simplification or convenience. Furthermore, the parts of each structure in the drawings will be described separately. It is worth noting that the elements not shown in the drawings or not described in words are in a form known to ordinary technicians in the relevant technical field.

[0046] The description of the embodiments herein and any reference to directions and orientations are only for the convenience of description and are not to be construed as any limitation on the scope of protection of the present invention. The following description of the preferred embodiments may involve combinations of features, which may exist independently or in combination, and the present invention is not particularly limited to the preferred embodiments. The scope of the present invention is defined by the claims.

[0047] like Figure 1 As shown, the lower limit of the vacuum environment of the embodiment of the present invention is 5×10 -18 Pa·m 3 / s standard gas flow meter, including: molecular flow guide gas intake module, pressure gas intake module and molecular flow guide gas supply module.

[0048] The molecular flow guide gas extraction module includes the first gas cylinder Gas1, the first valve V1, the second valve V2, the third valve V3, the fourth valve V4, the fifth valve V5, the first standard flow guide element f1, the first vacuum chamber VC1 and the first high vacuum pump unit Pump1. The first vacuum chamber VC1 is equipped with the first vacuum gauge G1 and the second vacuum gauge G2.

[0049] The pressure gas extraction module includes a second gas cylinder Gas2, a sixth valve V6, a seventh valve V7, an eighth valve V8, a ninth valve V9, a third vacuum chamber VC3 and a second high vacuum pump unit Pump2. The third vacuum chamber VC3 is equipped with a fifth vacuum gauge G5 and a sixth vacuum gauge G6.

[0050] The molecular flow conductance gas supply module includes the second vacuum chamber VC2, the fourth vacuum chamber VC4, the tenth valve V10, the eleventh valve V11, the twelfth valve V12, the thirteenth valve V13, the second standard flow conductance element f2 and the third high vacuum pump unit Pump3. The third vacuum gauge G3 and the fourth vacuum gauge G4 are installed on the second vacuum chamber VC2, and the seventh vacuum gauge G7 is installed on the fourth vacuum chamber VC4.

[0051] In this embodiment, the connection relationship between the various components is as follows: the first vacuum chamber VC1 is connected to the second vacuum chamber VC2 through the fourth valve V4, the first standard flow conductance element f1 and the fifth valve V5 which are connected in sequence; the third vacuum chamber VC3 is connected to the second vacuum chamber VC2 through the sixth valve V6; the fourth vacuum chamber VC4 is connected to the second vacuum chamber VC2 through the tenth valve V10, the second standard flow conductance element f2 and the eleventh valve V11 which are connected in sequence.

[0052] In this embodiment, the leakage rate at the connection interface between the components should be less than 1×10 -11 Pa·m 3 / s(e.g. 5.5×10 -12 Pa·m 3 / s).

[0053] In a preferred embodiment of the present invention, the gas in the first gas cylinder Gas1 is He with a purity of 99.9999%, and the gas in the second gas cylinder Gas2 is N2 with a purity of 99.9999%.

[0054] In a preferred embodiment of the present invention, the second valve V2 and the seventh valve V7 are both fine-tuning valves for controlling the pressure of the vacuum chamber to rise slowly.

[0055] In a preferred embodiment of the present invention, the volume U1 of the first vacuum chamber VC1 is 5L, the volume U2 of the second vacuum chamber VC2 is 5L, the volume U3 of the third vacuum chamber VC3 is 1L, and the volume U4 of the fourth vacuum chamber VC4 is 5L.

[0056] In the preferred embodiment of the present invention, the second vacuum gauge G2, the fourth vacuum gauge G4 and the sixth vacuum gauge G6 are all capacitance film vacuum gauge combinations, and the pressure measurement range is 1×10 5The first vacuum gauge G1, the third vacuum gauge G3, the fifth vacuum gauge G5 and the seventh vacuum gauge G7 are composite monitoring vacuum gauges with a pressure measurement range of 1×10 5 Pa~1×10 -8 Pa.

[0057] In a preferred embodiment of the present invention, the first high vacuum pump unit Pump1, the second high vacuum pump unit Pump2 and the third high vacuum pump unit Pump3 are all combinations of turbomolecular pumps (TMP1-TMP3) and vortex dry pumps (RP1-RP3), which can obtain a vacuum of less than 1×10 -6 The ultimate vacuum degree of Pa.

[0058] In a preferred embodiment of the present invention, the conductance value C1 of the first standard conductance element f1 ranges from 10 -8 m 3 / s~10 -10 ·m 3 / s, the conductance value C2 of the second standard conductance element f2 ranges from 10 -8 m 3 / s~10 -10 m 3 / s(e.g. C1=3.6×10 -10 ·m 3 / s, C2=2.1×10 -10 ·m 3 / s).

[0059] In a preferred embodiment of the present invention, all components are subjected to high-temperature dehydrogenation or high-temperature baking degassing treatment to reduce the impact on the background vacuum.

[0060] The embodiment of the present invention further provides a method for using the above device, comprising the following steps:

[0061] Step S1: Measure the background pressure P of the first vacuum chamber VC1, the second vacuum chamber VC2, the third vacuum chamber VC3 and the fourth vacuum chamber VC4 01 , P 02 , P 03 , P 04 ;

[0062] Step S2: Introduce the He in the first gas cylinder Gas1 into the first vacuum chamber VC1, so that the pressure in the first vacuum chamber reaches P1, and then introduce the He in the first vacuum chamber VC1 into the second vacuum chamber VC2 through the first standard flow guide element f1, and the molecular flow gas extraction time is recorded as t. It can be calculated that the He obtained by the molecular flow gas extraction module is M1 = (P1-P 01 )·C1·t.

[0063] Step S3: Introduce N2 from the second gas cylinder Gas2 into the third vacuum chamber VC3, so that the pressure in the third vacuum chamber VC3 reaches P3, and then expand the N2 in the third vacuum chamber VC3 into the second vacuum chamber VC2 through the sixth valve V6. After one or more expansion samplings, the pressure in the second vacuum chamber VC2 reaches P2, and a standard mixed gas of He and N2 is obtained. It can be calculated that after two samplings, the amount of gas in the second vacuum chamber VC2 is M2 = (P2-P 02 )·V2, the proportion of He in the standard mixed gas, that is, the preparation ratio, can be obtained as η=M1 / M2.

[0064] Step S4: Adjust the pressure in the second vacuum chamber VC2 so that the gas in the second vacuum chamber VC2 reaches a molecular flow state (≤1000Pa). At this time, the pressure in the second vacuum chamber VC2 is P 21 Then, the standard mixed gas of He and N2 is introduced into the fourth vacuum chamber VC4 through the second standard flow conduction element f2, and the flow rate Q of the trace gas in the standard mixed gas can be calculated. He =(P 21 -P 02 )·η·C2.

[0065] In a preferred embodiment of the present invention, step S1 includes the following sub-steps:

[0066] Step S11: Record the temperature and humidity under the test environment conditions as 21.1°C and 50% respectively. Open the third valve V3, the fourth valve V4, the fifth valve V5, the sixth valve V6, the ninth valve V9, the tenth valve V10, the eleventh valve V11 and the twelfth valve V12, and start the first fore-stage pump RP1, the second fore-stage pump RP2 and the third fore-stage pump RP3 at the same time to perform rough pumping on the four vacuum chambers;

[0067] Step S12: Turn on the first vacuum gauge G1, the second vacuum gauge G2, the third vacuum gauge G3, the fourth vacuum gauge G4, the fifth vacuum gauge G5, the sixth vacuum gauge G6 and the seventh vacuum gauge G7. When the indication values ​​of the first vacuum gauge G1 (e.g., 8.6Pa), the third vacuum gauge G3 (e.g., 8.8Pa), the fifth vacuum gauge G5 (9.4Pa) and the seventh vacuum gauge G7 (8.2Pa) all reach below 10Pa, start the first molecular pump TMP1, the second molecular pump TMP2 and the third molecular pump TMP3 to perform high vacuum extraction on the four vacuum chambers;

[0068] Step S13: When the readings of the first vacuum gauge G1, the third vacuum gauge G3, the fifth vacuum gauge G5 and the seventh vacuum gauge G7 reach 1×10 -6 When the pressure is below Pa, the displayed pressure value is recorded as P 01 (e.g. 8.7×10-7 Pa), P 02 (e.g. 9.6×10 -7 Pa), P 03 (e.g. 8.5×10 -7 Pa), P 04 (e.g. 9.8×10 -7 Pa), and close the fourth valve V4, the fifth valve V5, the tenth valve V10 and the eleventh valve V11.

[0069] In a preferred embodiment of the present invention, step S2 includes the following sub-steps:

[0070] Step S21: close the third valve V3, open the first valve V1 and slowly adjust the second valve V2 to introduce He in the first gas cylinder Gas1 into the first vacuum chamber VC1;

[0071] Step S22: When the pressure in the first vacuum chamber VC1 reaches 10Pa~1×10 5 Pa range, close the first valve V1 and the second valve V2, and after the indication value of the second vacuum gauge G2 stabilizes, record it as P1 (e.g. 10Pa);

[0072] Step S23: close the sixth valve V6, then open the fourth valve V4 and the fifth valve V5 in sequence, introduce the gas in the first vacuum chamber VC1 into the second vacuum chamber VC2 through the first standard flow conduction element f1, and calculate the gas intake time from the moment the fifth valve V5 is opened, and the gas intake time ranges from 100s to 1000s. After the gas intake is completed, quickly close the fourth valve V4 and the fifth valve V5, and record the gas extraction time t (e.g., t=350s).

[0073] In a preferred embodiment of the present invention, step S3 includes the following sub-steps:

[0074] Step S31: close the ninth valve V9, open the eighth valve V8 and slowly adjust the seventh valve V7 to slowly introduce the N2 in the second gas cylinder Gas2 into the third vacuum chamber VC3;

[0075] Step S32: When the pressure in the third vacuum chamber VC3 reaches 10Pa~1×10 5 Pa range, close the seventh valve V7 and the eighth valve V8, and wait until the sixth vacuum gauge G6 indicates a stable value, and record its indicated value as P3 (e.g. 1×10 5 Pa);

[0076] Step S33: The gas in the third vacuum chamber VC3 is introduced into the second vacuum chamber VC2 through the sixth valve V6, so that the pressure in the second vacuum chamber VC2 reaches 10Pa~1×10 5Pa range, close the sixth valve V6, and wait for the fourth vacuum gauge G4 to indicate a stable value, and record it as P2 (for example, after multiple sampling of N2, P2 = 1 × 10 5 Pa);

[0077] Step S34: Calculate the standard mixed gas ratio of He and N2 in the second vacuum chamber VC2 as follows:

[0078]

[0079] In a preferred embodiment of the present invention, step S4 includes the following sub-steps:

[0080] Step S41: Open the thirteenth valve V13, adjust the pressure in the second vacuum chamber VC2 to 10Pa-1000Pa, that is, let the gas in the second vacuum chamber VC2 reach the molecular flow state, close the thirteenth valve V13, and after the indication value of the fourth vacuum gauge G4 stabilizes, record it as P 21 (e.g. 10Pa);

[0081] Step S42: close the twelfth valve V12, open the tenth valve V10 and the eleventh valve V11, and introduce the standard mixed gas of He and N2 in the second vacuum chamber VC2 into the fourth vacuum chamber VC4 through the second standard flow conduction element f2;

[0082] Step S43: Calculate the trace gas flow rate of the standard mixed gas of He and N2 introduced into the fourth vacuum chamber VC4 as Q He =(P 21 -P 02 )·η·C2.

[0083] Theoretically, if the pressure of the first vacuum chamber VC1 is P1 = 10Pa, the conductance value of the first standard conductance element f1 is C1 = 1×10 -10 ·m 3 / s, the conductance value of the second standard conductance element f2 is C2=1×10 -10 m 3 / s, the molecular flow gas extraction time is t = 100s, and the pressure of the second vacuum chamber VC2 is P2 = 1×10 5 Pa, volume U2 = 5 × 10 -3 m 3 , we can calculate the minimum mixing ratio of the standard mixed gas η=2×10 -10 If the pressure in the second vacuum chamber VC2 is P 21 =10Pa, the lower limit of the trace gas flow rate of the standard mixed gas introduced into the fourth vacuum chamber VC4 is 2×10 -19 Pa·m 3 / s. According to the lower limit of the flow rate, it can be calculated that the number of trace gas molecules in the standard mixed gas passing through the second standard flow conductance element f2 per second is about 49. However, this is almost impossible in the actual experiment. Due to the uncertainty of the movement of gas molecules, it is impossible to guarantee that there are dozens of stable gas molecules passing through the standard flow conductance element per second. Therefore, according to actual experience, the molecular flow conductance gas extraction time is extended to t = 350s, and the lower limit of the preparation ratio is set to 5×10 -9 , then the lower limit of the standard flow meter is 5×10 -18 Pa·m 3 / s. Thus, the flow rate of the standard mixed gas of He and N2 provided to the fourth vacuum chamber VC4 is calculated to be Q He =5.3×10 -18 Pa·m 3 / s.

[0084] In a preferred embodiment of the present invention, it also includes:

[0085] Step S5: After the standard mixed gas flow of He and N2 is provided to the fourth vacuum chamber VC4, the tenth valve V10 and the eleventh valve V11 are closed, and the three high vacuum pump groups and all vacuum gauges are closed, and the test is completely completed.

[0086] The lower limit of the vacuum environment of the present invention is 5×10 -18 Pa·m 3 / s standard gas flowmeter, which adopts the combination of molecular conductance gas extraction module and pressure gas extraction module to configure standard mixed gas, and then obtains the standard gas flowmeter based on fixed conductance method. The device of the present invention accurately samples He and N2 based on molecular conductance method and static expansion method respectively, mixes the two gases evenly in the second vacuum chamber VC2 to obtain a standard mixed gas of He and N2, and then provides the standard gas flow to the fourth vacuum chamber VC4 through the second standard conductance element f2. According to the reference standard, the background pressure and gas pressure of the first vacuum chamber VC1, the second vacuum chamber VC2, the third vacuum chamber VC3 and the fourth vacuum chamber VC4 are measured respectively, and the flow rate Q of He in the standard mixed gas provided to the fourth vacuum chamber VC4 can be calculated by the conductance value C1 of the first standard conductance element f1, the conductance value C2 of the second standard conductance element f2 and the volume U2 of the second vacuum chamber VC2. He . Thus, the minimum He flow rate Q He =5×10 -18 Pa·m 3 / s.

[0087] The present invention overcomes the bottleneck that the traditional standard gas flow meter based on the fixed flow conductance method is difficult to break through the lower limit of the flow rate, and extends the lower limit of the standard gas flow rate to 5×10-18 Pa·m 3 / s, which has the advantages of simple equipment, low cost and easy operation, and further solves the calibration and value traceability problems of leak detectors.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A lower limit is 5×10 -18 Pa·m 3 / s flow meter, characterized in that, It includes a molecular flow air intake module, a pressure air intake module and a molecular flow air supply module; The molecular flow gas guide module comprises a first gas cylinder (Gas1), a first valve (V1), a second valve (V2), a first vacuum chamber (VC1), a third valve (V3), a first high vacuum pump unit (Pump1), a fourth valve (V4), a first standard flow guide element (f1) and a fifth valve (V5); a first vacuum gauge (G1) and a second vacuum gauge (G2) are installed on the first vacuum chamber (VC1); The pressure gas extraction module comprises a second gas cylinder (Gas2), an eighth valve (V8), a seventh valve (V7), a sixth valve (V6), a third vacuum chamber (VC3), a ninth valve (V9) and a second high vacuum pump unit (Pump2), and a fifth vacuum gauge (G5) and a sixth vacuum gauge (G6) are installed on the third vacuum chamber (VC3); The molecular flow conductance gas supply module comprises a second vacuum chamber (VC2), a tenth valve (V10), a second standard flow conductance element (f2), an eleventh valve (V11), a fourth vacuum chamber (VC4), a twelfth valve (V12), a third high vacuum pump unit (Pump3) and a thirteenth valve (V13); a third vacuum gauge (G3) and a fourth vacuum gauge (G4) are installed on the second vacuum chamber (VC2); and a seventh vacuum gauge (G7) is installed on the fourth vacuum chamber (VC4); The first high vacuum pump assembly (Pump1) includes a first molecular pump (TMP1) and a first backing pump (RP1), the second high vacuum pump assembly (Pump2) includes a second molecular pump (TMP2) and a second backing pump (RP2), and the third high vacuum pump assembly (Pump3) includes a third molecular pump (TMP3) and a third backing pump (RP3); In the molecular flow gas guide module, the first gas cylinder (Gas1), the first valve (V1), the second valve (V2), the first vacuum chamber (VC1), the third valve (V3) and the first high vacuum pump unit (Pump1) are connected in sequence, and the first gas cylinder (Gas1), the first valve (V1), the second valve (V2), the first vacuum chamber (VC1), the fourth valve (V4), the first standard flow guide element (f1) and the fifth valve (V5) are connected in sequence; In the pressure gas extraction module, the second gas cylinder (Gas2), the eighth valve (V8), the seventh valve (V7), the third vacuum chamber (VC3), the ninth valve (V9) and the second high vacuum pump unit (Pump2) are connected in sequence; the second gas cylinder (Gas2), the eighth valve (V8), the seventh valve (V7), the third vacuum chamber (VC3) and the sixth valve (V6) are connected in sequence; In the molecular flow conductance gas supply module, the second vacuum chamber (VC2), the tenth valve (V10), the second standard flow conductance element (f2), the eleventh valve (V11), the fourth vacuum chamber (VC4), the twelfth valve (V12) and the third high vacuum pump unit (Pump3) are connected in sequence; the thirteenth valve (V13) is installed on the second vacuum chamber (VC2); The second vacuum chamber (VC2) is connected to the fifth valve (V5), the sixth valve (V6) and the tenth valve (V10).

2. A method according to claim 1 with a lower limit of 5×10 -18 Pa·m 3 / s flow meter, characterized in that, The leakage rate at the connection interface between each component is less than 1×10 -11 Pa·m 3 / s.

3. A method according to claim 1 with a lower limit of 5×10 -18 Pa·m 3 / s flow meter, characterized in that, The second valve (V2) and the seventh valve (V7) are both fine-tuning valves for controlling the pressure of the corresponding vacuum chamber to rise slowly.

4. A method according to claim 1 with a lower limit of 5×10 -18 Pa·m 3 / s flow meter, characterized in that, The volume U1 of the first vacuum chamber (VC1) is 5L, the volume U2 of the second vacuum chamber (VC2) is 5L, the volume U3 of the third vacuum chamber (VC3) is 1L, and the volume U4 of the fourth vacuum chamber (VC4) is 5L.

5. A method according to claim 1 with a lower limit of 5×10 -18 Pa·m 3 / s flow meter, characterized in that, The second vacuum gauge (G2), the fourth vacuum gauge (G4) and the sixth vacuum gauge (G6) are all capacitance film vacuum gauge combinations, and the pressure measurement range is 1×10 5 Pa~10Pa, measurement accuracy is better than 0.5%; The first vacuum gauge (G1), the third vacuum gauge (G3), the fifth vacuum gauge (G5) and the seventh vacuum gauge (G7) are all composite monitoring vacuum gauges with a pressure measurement range of 1×10 5 Pa~1×10 -8 Pa.

6. A method according to claim 1 with a lower limit of 5×10 -18 Pa·m 3 / s flow meter, characterized in that, The first high vacuum pump unit (Pump1), the second high vacuum pump unit (Pump2) and the third high vacuum pump unit (Pump3) obtain a limit vacuum degree in a range of less than 1×10 -6 Pa.

7. A method according to claim 1 with a lower limit of 5×10 -18 Pa·m 3 / s flow meter, characterized in that, The range of the conductance value C1 of the first standard conductance element (f1) is 10 -8 m 3 / s~10 -10 ·m 3 / s, the range of the conductance value C2 of the second standard conductance element (f2) is 10 -8 m 3 / s~10 -10 m 3 / s.

8. A method according to claim 1 with a lower limit of 5×10 -18 Pa·m 3 / s flow meter, characterized in that, All components are treated with high-temperature dehydrogenation or high-temperature baking degassing to reduce the impact on the background vacuum.

9. A method for using the flow meter according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step S1: Measure the background pressure P of the first vacuum chamber (VC1), the second vacuum chamber (VC2), the third vacuum chamber (VC3) and the fourth vacuum chamber (VC4). 01 , P 02 , P 03 , P 04 ; Step S2: Introduce the gas in the first gas cylinder (Gas1) into the first vacuum chamber (VC1) so that the indication value of the second vacuum gauge (G2) reaches P1, where the range of P1 is 10Pa~1×10 5 Pa; then the gas in the first vacuum chamber (VC1) is introduced into the second vacuum chamber (VC2) through the first standard flow guide element (f1), and the molecular flow guide gas extraction time is recorded as t, where t ranges from 100s to 1000s; the amount of gas extracted by the molecular flow is calculated to be M1 = (P1-P 01 )·C2·t; Step S3: Introduce the gas from the second gas cylinder (Gas2) into the third vacuum chamber (VC3) so that the indication value of the sixth vacuum gauge (G6) reaches P3, where the range of P3 is 10Pa~1×10 5 Pa, and then expand the gas in the third vacuum chamber (VC3) into the second vacuum chamber (VC2) through the sixth valve (V6), and after one or more expansion samplings, the indication value of the fourth vacuum gauge (G4) reaches P2, wherein the range of P2 is 10Pa~1×10 5 Pa, a standard mixed gas is prepared; after two samplings, the gas volume in the second vacuum chamber (VC2) is M2 = (P2-P 02 )·V2, then the proportion of trace gas in the standard mixed gas is obtained, which is η=M1 / M2; Step S4: Adjust the pressure in the second vacuum chamber (VC2) so that the gas in the second vacuum chamber (VC2) reaches a molecular flow state, and the indication value of the fourth vacuum gauge (G4) is P 21 , where P 21 The range of the standard mixed gas is 10Pa to 1000Pa, and then the standard mixed gas is introduced into the fourth vacuum chamber (VC4) through the second standard flow guide element (f2). The flow rate of the trace gas in the standard mixed gas is Q x =(P 21 -P 02 )·η·C2; Wherein, C1 is the conductance value of the first standard conductance element (f1); C2 is the conductance value of the second standard conductance element (f2).

10. The method of use according to claim 9, characterized in that: The step S1 comprises the following sub-steps: Step S11: opening the third valve (V3), the fourth valve (V4), the fifth valve (V5), the sixth valve (V6), the ninth valve (V9), the tenth valve (V10), the eleventh valve (V11) and the twelfth valve (V12), and simultaneously starting the first fore-stage pump (RP1), the second fore-stage pump (RP2) and the third fore-stage pump (RP3) to perform rough pumping on the four vacuum chambers; Step S12: turning on the first vacuum gauge (G1), the second vacuum gauge (G2), the third vacuum gauge (G3), the fourth vacuum gauge (G4), the fifth vacuum gauge (G5), the sixth vacuum gauge (G6) and the seventh vacuum gauge (G7); when the indicated values ​​of the first vacuum gauge (G1), the third vacuum gauge (G3), the fifth vacuum gauge (G5) and the seventh vacuum gauge (G7) all reach below 10Pa, starting the first molecular pump (TMP1), the second molecular pump (TMP2) and the third molecular pump (TMP3) to perform high vacuum extraction on the four vacuum chambers; Step S13: When the readings of the first vacuum gauge (G1), the third vacuum gauge (G3), the fifth vacuum gauge (G5) and the seventh vacuum gauge (G7) reach 1×10 -6 When the pressure is below Pa, the displayed pressure value is P 01 , P 02 , P 03 , P 04 , and close the fourth valve (V4), the fifth valve (V5), the tenth valve (V10) and the eleventh valve (V11).

11. The method of use according to claim 9, characterized in that: The step S2 comprises the following sub-steps: Step S21: closing the third valve (V3), opening the first valve (V1) and slowly adjusting the second valve (V2) to introduce the gas in the first gas cylinder (Gas1) into the first vacuum chamber (VC1); Step S22: When the pressure in the first vacuum chamber (VC1) reaches 10Pa~1×10 5 When the vacuum level is within the range of Pa, the first valve (V1) and the second valve (V2) are closed, and the indicated value of the second vacuum gauge (G2) is recorded as P1 after it stabilizes; Step S23: close the sixth valve (V6), open the fourth valve (V4) and the fifth valve (V5) in sequence, introduce the gas in the first vacuum chamber (VC1) into the second vacuum chamber (VC2) through the first standard flow conduction element (f1), calculate the gas extraction time from the moment the fifth valve (V5) is opened, and after the gas intake is completed, quickly close the fourth valve (V4) and the fifth valve (V5), and record the gas extraction time t, which ranges from 100s to 1000s.

12. The method of use according to claim 9, characterized in that: The step S3 comprises the following sub-steps: Step S31: closing the ninth valve (V9), opening the eighth valve (V8) and slowly adjusting the seventh valve (V7), and slowly introducing the gas in the second gas cylinder (Gas2) into the third vacuum chamber (VC3); Step S32: When the pressure in the third vacuum chamber (VC3) reaches 10Pa~1×10 5 When the vacuum level is within the range of Pa, the seventh valve (V7) and the eighth valve (V8) are closed, and after the indicated value of the sixth vacuum gauge (G6) is stabilized, the indicated value is recorded as P3; Step S33: Open the sixth valve (V6) to introduce the gas in the third vacuum chamber (VC3) into the second vacuum chamber (VC2), so that the pressure in the second vacuum chamber (VC2) reaches 10Pa to 1×10 5 Pa range, then close the sixth valve (V6), and wait for the indicated value of the fourth vacuum gauge (G4) to stabilize and record it as P2; Step S34: Calculate the mixing ratio of the standard mixed gas in the second vacuum chamber (VC2), the formula is:

13. The method of use according to claim 9, characterized in that: The step S4 comprises the following sub-steps: Step S41: Open the thirteenth valve (V13), adjust the pressure in the second vacuum chamber (VC2) to 10Pa-1000Pa, close the thirteenth valve (V13), and record the indicated value of the fourth vacuum gauge (G4) as P after it stabilizes. 21 ; Step S42: closing the twelfth valve (V12), opening the tenth valve (V10) and the eleventh valve (V11), and introducing the standard mixed gas in the second vacuum chamber (VC2) into the fourth vacuum chamber (VC4) through the second standard flow guide element (f2); Step S43: Calculate the trace gas flow rate of the standard mixed gas introduced into the fourth vacuum chamber (VC4) as Q x =(P 21 -P 02 )·η·C2.

14. The method of use according to claim 9, characterized in that: The step S4 further includes: Step S5: After the standard mixed gas flow rate is provided to the fourth vacuum chamber (VC4), the tenth valve (V10) and the eleventh valve (V11) are closed, and the three high vacuum pump groups and all vacuum gauges are closed, and the test is completely completed.

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