An apparatus for intermittently dispensing a low abundance gas

Abstract

The application relates to an intermittent low-abundance gas preparation device, which comprises an air flow pipeline, a first mass flow rate controller, a second mass flow rate controller, a gas storage tank, a sample tank, an air pump and a vacuum pump, a first air inlet and a second air inlet are arranged on the air flow pipeline, the first air inlet and the second air inlet are respectively connected with first and second air sources to be mixed, the gas storage tank is communicated with the air flow pipeline, the sample tank is communicated with the gas storage tank through the air pump, the vacuum pump is communicated with the air flow pipeline, the first mass flow rate controller is arranged between the first air inlet and the gas storage tank on the air flow pipeline, and the second mass flow rate controller is arranged between the second air inlet and the gas storage tank on the air flow pipeline. The intermittent low-abundance gas preparation device can reduce the waste of expensive air sources in the preparation process.

Description

Technical Field

[0001] This invention belongs to the field of gas mixing technology, specifically relating to a device for intermittently preparing low-abundance gases. Background Technology

[0002] The preparation of a gas mixture of a certain concentration can be achieved using methods such as static weighing, static volumetric methods, or dynamic methods. The static weighing method involves weighing specific masses of gas separately and then mixing them to obtain a gas mixture of a certain concentration. The static volumetric method involves introducing the gases to be mixed into containers of known volume at the same temperature, controlling the gas pressure in each container to control the amount of gas contained therein, and finally mixing the gases to obtain a gas mixture of a certain concentration. The dynamic method involves controlling the volumetric or mass flow rate of the gases to be mixed, mixing them during continuous flow to obtain a gas mixture of a certain concentration, which is generally prepared and used immediately.

[0003] However, the above mixing method usually requires additional mechanical equipment for stirring in order to mix the gases evenly, and there is some waste when preparing standard gases of expensive rare gases with a certain low element abundance. Summary of the Invention

[0004] In view of the shortcomings of existing designs, the purpose of this invention is to provide an apparatus for intermittent preparation of low-abundance gases to reduce the waste of expensive gas sources during the preparation process.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: an apparatus for intermittently preparing low-abundance gases, comprising: an airflow pipeline, a first mass flow rate controller, a second mass flow rate controller, a gas storage tank, a sample container, a gas pump, and a vacuum pump. The airflow pipeline has a first inlet and a second inlet, which are respectively connected to a first gas source and a second gas source to be mixed. The gas storage tank is connected to the airflow pipeline to transport the gases from the first and second gas sources to the gas storage tank for mixing. The sample container is connected to the gas storage tank via the gas pump. The vacuum pump is connected to the airflow pipeline. The first mass flow rate controller is located between the first inlet and the gas storage tank on the airflow pipeline, and the second mass flow rate controller is located between the second inlet and the gas storage tank on the airflow pipeline. The first and second mass flow rate controllers sequentially control the gases from the first and second gas sources to enter the gas storage tank at a preset volume.

[0006] Furthermore, the device for intermittently preparing low-abundance gas also includes a first filter and a second filter. The first filter is disposed on the gas flow pipeline connecting the first air inlet and the first mass flow rate controller, and the second filter is disposed on the gas flow pipeline connecting the second air inlet and the second mass flow rate controller.

[0007] Furthermore, the gas flow pipeline is equipped with a first shut-off valve, a second shut-off valve, a fifth shut-off valve, a sixth shut-off valve, a seventh shut-off valve, and a ninth shut-off valve. The first shut-off valve is located between the first air inlet and the first filter; the second shut-off valve is located between the second air inlet and the second filter; the fifth shut-off valve is located between the first mass flow rate controller and the gas storage tank; the sixth shut-off valve is located between the second mass flow rate controller and the gas storage tank; the seventh shut-off valve is located between the gas storage tank and the air pump; and the ninth shut-off valve is located between the air pump and the sample container.

[0008] Furthermore, a vacuum pumping pipeline is also provided on the airflow pipeline, and the vacuum pump is connected to the airflow pipeline through the vacuum pumping pipeline. A third shut-off valve, a fourth shut-off valve, and an eighth shut-off valve are sequentially provided on the vacuum pumping pipeline along the first air inlet and the second air inlet toward the vacuum pump.

[0009] Furthermore, the device for intermittently configuring low-abundance gas also includes a first absolute pressure transmitter, a second absolute pressure transmitter, a fourth absolute pressure transmitter, a fifth absolute pressure transmitter, and a high-precision composite vacuum gauge. The first absolute pressure transmitter is disposed on the gas flow line between the first shut-off valve and the first filter, the second absolute pressure transmitter is disposed on the gas flow line between the second shut-off valve and the second filter, the high-precision composite vacuum gauge and the fourth absolute pressure transmitter are both disposed on the gas storage tank, and the fifth absolute pressure transmitter is disposed on the sample tank.

[0010] Furthermore, the airflow duct is made of stainless steel with an outer diameter of 1 / 8 inch.

[0011] Furthermore, both the first and second filters are made of stainless steel and are 1 / 8-inch in size.

[0012] Furthermore, both the gas storage tank and the sample container are made of stainless steel and have a volume of 500 mL.

[0013] Furthermore, the connection points between the airflow pipes are welded using tee or cross joints.

[0014] Furthermore, both the first mass flow rate controller and the second mass flow rate controller are connected to the airflow pipeline via VCR.

[0015] The advantages of this invention are as follows: When the gas storage tank and its connected pipelines are under a low to medium vacuum, a certain amount of gas from a first gas source is introduced using a first mass flow rate controller. This rapidly and uniformly disperses the gas within the storage tank and its connected pipelines. Then, a second high-precision mass flow rate controller slowly introduces gas from a second gas source, mixing it with the gas already uniformly dispersed in the first gas source within the storage tank and its connected pipelines, thus obtaining a gas with the target element abundance. Therefore, the mixing of the two gases does not require additional mechanical stirring. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a device for intermittently preparing low-abundance gases. Detailed Implementation

[0017] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0018] like Figure 1 As shown, the present invention provides an apparatus for intermittently preparing low-abundance gases, comprising an airflow pipeline, a first mass flow rate controller R1, a second mass flow rate controller R2, a gas storage tank C1, a sample container C2, an air pump P1, and a vacuum pump P2. The airflow pipeline has a first inlet I1 and a second inlet I2, which are respectively connected to a first gas source and a second gas source to be mixed. The gas storage tank C1 is connected to the airflow pipeline to transport the gases from the first and second gas sources to the gas storage tank C1 for mixing. The sample container C2 is connected to the gas storage tank C1 via the air pump P1. The vacuum pump P2 is connected to the airflow pipeline to evacuate the apparatus for intermittently preparing low-abundance gases. The first mass flow rate controller R1 is located at the first inlet I1 of the airflow pipeline. Between the first gas source and the gas storage tank C1, the second mass flow rate controller R2 is set between the second air inlet I2 and the gas storage tank C1 on the gas flow pipeline, so that the gas in the first gas source and the second gas source enters the gas storage tank C1 in a preset volume through the first mass flow rate controller R1 and the second mass flow rate controller R2 in sequence.

[0019] Understandably, before mixing, the device is first evacuated using vacuum pump P2. Then, the gases from the first and second gas sources are sequentially controlled to enter the gas storage tank C1 at preset volumes. The gas from the first gas source is rapidly and evenly dispersed within the gas storage tank C1 and its connected pipes. Next, the gas from the second gas source mixes with the gas from the first gas source, which has already been evenly dispersed within the gas storage tank C1 and its connected pipes, to obtain the gas with the target element abundance. Therefore, the mixing of the two gases does not require additional mechanical stirring.

[0020] Furthermore, the device for intermittently preparing low-abundance gas also includes a first filter F1 and a second filter F2. The first filter F1 is disposed on the gas flow line connecting the first air inlet I1 and the first mass flow rate controller R1, and the second filter F2 is disposed on the gas flow line connecting the second air inlet I2 and the second mass flow rate controller R2.

[0021] It is understood that the first filter F1 and the second filter F2 intercept solid impurities carried in the gas flowing to the first mass flow rate controller R1 and the second mass flow rate controller R2, thereby preventing the first mass flow rate controller R1 and the second mass flow rate controller R2 from being blocked and ensuring that they are in good working condition.

[0022] Furthermore, the gas flow pipeline is equipped with a first shut-off valve V1, a second shut-off valve V2, a fifth shut-off valve V5, a sixth shut-off valve V6, a seventh shut-off valve V7, and a ninth shut-off valve V9. The first shut-off valve V1 is located between the first air inlet I1 and the first filter F1; the second shut-off valve V2 is located between the second air inlet I2 and the second filter F2; the fifth shut-off valve V5 is located between the first mass flow rate controller R1 and the gas storage tank C1; the sixth shut-off valve V7 is located between the second mass flow rate controller R2 and the gas storage tank C1; the seventh shut-off valve V7 is located between the gas storage tank C1 and the air pump P1; and the ninth shut-off valve V9 is located between the air pump P1 and the sample container C2.

[0023] Furthermore, a vacuum pumping pipeline is also provided on the airflow pipeline. The vacuum pump P2 is connected to the airflow pipeline through the vacuum pumping pipeline. The vacuum pumping pipeline is provided with a third shut-off valve V3, a fourth shut-off valve V4 and an eighth shut-off valve V8 in sequence along the first air inlet I1 and the second air inlet I2 toward the vacuum pump P2.

[0024] In this embodiment, multiple shut-off valves can be used to open or close the airflow pipeline at their corresponding positions, thereby controlling the flow of airflow within the pipeline.

[0025] It is understood that the first shut-off valve V1 and the second shut-off valve V2 can regulate the gas flow rate, controlling the gas to flow slowly towards the first mass flow rate controller R1 and the second mass flow rate controller R2, thus preventing a surge in pressure within the pipeline that could damage either the first mass flow rate controller R1 or the second mass flow rate controller R2. For example, during the gas distribution process, at the downstream end of the first mass flow rate controller R1 or the second mass flow rate controller R2 ( Figure 1 The pressure of the air passages on the right side of R1 and R2 is related to the pressure of the air passages at their front ends ( Figure 1 Before the pressure on the left side of R1 and R2 equalizes, closing the fifth shut-off valve V5 or the sixth shut-off valve V6 can prevent gas from flowing back to the front end of the first mass flow rate controller R1 or the second mass flow rate controller R2.

[0026] It is understandable that during the vacuuming process of the device, the first mass flow rate controller R1, the second mass flow rate controller R2 and the air pump P1 are all de-energized and shut down. Opening the third shut-off valve V3 and the fourth shut-off valve V4 can vacuum the air path at the front end of the first mass flow rate controller R1 and the second mass flow rate controller R2 together. Opening the ninth shut-off valve V9 can vacuum the sample container C2 together.

[0027] It is understandable that during the gas mixing process, closing the third shut-off valve V3 and the fourth shut-off valve V4 can prevent the mixed gas from flowing back to the gas path at the front end of the first mass flow rate controller R1 or the second mass flow rate controller R2; after the gas mixing is completed, during the process of transferring the mixed gas from the gas storage tank C1 to the sample tank C2 through the gas pump P1, closing the ninth shut-off valve V9 can prevent the gas from flowing back from the sample tank C2 to the gas path on the left side of the gas pump P1.

[0028] Furthermore, the device for intermittently configuring low-abundance gases also includes a first absolute pressure transmitter G1, a second absolute pressure transmitter G2, a fourth absolute pressure transmitter G4, a fifth absolute pressure transmitter G5, and a high-precision composite vacuum gauge G3. The first absolute pressure transmitter G1 is installed on the gas flow line between the first shut-off valve V1 and the first filter F1, the second absolute pressure transmitter G2 is installed on the gas flow line between the second shut-off valve V2 and the second filter F2, the high-precision composite vacuum gauge G3 and the fourth absolute pressure transmitter G4 are both installed on the gas storage tank C1, and the fifth absolute pressure transmitter G5 is installed on the sample tank C2.

[0029] Furthermore, the airflow duct is made of 304 stainless steel with an outer diameter of 1 / 8 inch.

[0030] Furthermore, the first shut-off valve V1, the second shut-off valve V2, the third shut-off valve V3, the fourth shut-off valve V4, the fifth shut-off valve V5, the sixth shut-off valve V6, the seventh shut-off valve V7, the eighth shut-off valve V8, and the ninth shut-off valve V9 are all needle-type shut-off valves made of 304 stainless steel with a specification of "1 / 8 inch to 1 / 8 inch".

[0031] Furthermore, both the first filter F1 and the second filter F2 are made of 304 stainless steel and are 1 / 8-inch size filters.

[0032] Furthermore, both the gas storage tank C1 and the sample tank C2 are made of 304 stainless steel and have a volume of 500mL.

[0033] Furthermore, the first mass flow rate controller R1 has a range of 0 to 0.5 sccm, a range controllability ratio of 200:1, an accuracy of ±(0.4% of reading + 0.2% of full scale), a preheating time of <1s, a response time of <100ms, an operating temperature of -10℃ to 60℃, a maximum operating pressure of 1MPa (gauge pressure), and a built-in LCD display that can simultaneously display mass flow rate, volumetric flow rate, temperature (accuracy ±0.75℃), pressure (accuracy ±0.5% of reading (>1atm) or ±0.07PSIA (<1atm)), medium, and setpoint.

[0034] Furthermore, the second mass flow rate controller R2 has a range of 0–100 sccm, a range controllability ratio of 10000:1, an accuracy of ±0.6% of the reading or ±0.1% of the full scale (whichever is greater), a preheating time of <1 s, a response time of <100 ms, an operating temperature of -10℃ to 60℃, a maximum operating pressure of 1 MPa (gauge pressure), and a built-in LCD display that can simultaneously display mass flow rate, volumetric flow rate, temperature (accuracy ±0.75℃), pressure (accuracy ±0.5% of the reading (>1 atm) or ±0.07 PSIA (<1 atm)), medium, and setpoint.

[0035] Furthermore, the high-precision composite vacuum gauge G3 adopts a diaphragm resistance high-precision composite vacuum gauge with a measurement range of 0.01Pa to 150000Pa, a measurement accuracy of ±1% of the reading for 3000Pa to 150000Pa, a measurement accuracy of ±10% of the reading for 0.1Pa to 3000Pa, and a measurement accuracy of ±15% of the reading for 0.01Pa to 0.1Pa. The measurement repeatability is 1% across the entire range, the response time is <100ms, the operating temperature is 0℃ to 50℃, and the maximum pressure is 200kPa.

[0036] Furthermore, the first absolute pressure transmitter G1, the second absolute pressure transmitter G2, the fourth absolute pressure transmitter G4, and the fifth absolute pressure transmitter G5 are silicon-type absolute pressure transmitters. The measurement range of the first absolute pressure transmitter G1, the fourth absolute pressure transmitter G4, and the fifth absolute pressure transmitter G5 is 0–200 kPa, the measurement range of the second absolute pressure transmitter G2 is 0–400 kPa, the overall accuracy (nonlinearity, repeatability, hysteresis) is ±0.1% of full scale, the response time is ≤2 ms, and the operating temperature is -20℃ to 80℃.

[0037] Furthermore, the air pump P1 is a miniature diaphragm air pump with a maximum vacuum of -97kPa, a working flow rate of 2.0L / min to 7.0L / min, and an operating ambient temperature of -10℃ to 50℃.

[0038] Furthermore, vacuum pump P2 is a two-stage rotary vane vacuum pump with a pumping speed of 0.5 L / s and an ultimate vacuum of 0.067 Pa.

[0039] Furthermore, the connection points between the airflow pipes are welded using tees or crosses;

[0040] Each shut-off valve is connected to the gas flow line via a compression fitting or welding.

[0041] The first filter F1 and the second filter F2 are connected to the airflow pipeline by compression fittings or welding.

[0042] The first mass flow rate controller R1 and the airflow pipeline, and the second mass flow rate controller R2 and the airflow pipeline are all connected by VCRs;

[0043] The first absolute pressure transmitter G1, the second absolute pressure transmitter G2, and the fifth absolute pressure transmitter G5 are connected to the gas flow pipeline by thread or welding; the fourth absolute pressure transmitter G4 is connected to the gas storage tank C1 by thread or welding; and the high-precision composite vacuum gauge G3 is connected to the gas storage tank C1 by flange or welding.

[0044] The gas storage tank C1 is connected to the gas flow pipeline by compression fitting or welding.

[0045] Vacuum pump P2 is connected to the gas flow line via a flange;

[0046] The air pump P1 is connected to the airflow pipeline by a compression fitting or a flange.

[0047] The configuration process of the above-mentioned device will be illustrated with an example. Gas A in the first gas source is composed of isotopes n X and m X is composed of, where n The abundance (mole fraction) of X is 0.2699%, and gas B in the second gas source is composed of isotopes n X and m X is composed of, where m The abundance (mole fraction) of X is 99.9999%. The goal is to prepare using gas source A and gas source B. n To prepare 500 mL of gas (standard conditions) with an abundance of 1 ppm (0.0001%) of X, it is necessary to mix 0.1853 mL (standard conditions) of gas A with 499.8 mL (standard conditions) of gas B. At this point, the gas storage tank volume and the sample tank volume are both 500 mL.

[0048] First, connect the gas sources. Connect the gas sources of gas A and gas B to the device through the first air inlet I1 and the second air inlet I2 respectively, and keep both gas sources closed.

[0049] Next, the device is evacuated. The first shut-off valve V1 to the ninth shut-off valve V9 are opened, while the first mass flow rate controller R1 and the second mass flow rate controller R2 are kept de-energized and closed, and the gas pump P1 is de-energized and closed. The vacuum pump P2 is started. When the reading of the high-precision composite vacuum gauge G3 is lower than 0.1 Pa, the ninth shut-off valve V9, the seventh shut-off valve V7, the second shut-off valve V2, the first shut-off valve V1, the third shut-off valve V3, the fourth shut-off valve V4 and the eighth shut-off valve V8 are closed in sequence, and then the vacuum pump P2 is turned off.

[0050] Then, import 0.1853cm. 3 STD Gas A. Partially open the first shut-off valve V1 to slowly increase the pressure in the gas path at the front end of the first mass flow rate controller R1. Once the reading of the first absolute pressure transmitter G1 remains essentially constant, energize the first mass flow rate controller R1 and set its parameters to allow a flow rate of 0.1853 cm⁻¹. 3 STD After gas A is discharged, the valve automatically shuts off; after the first mass flow rate controller R1 finishes working, the fifth shut-off valve V5 is closed, and the reading of the high-precision composite hollow gas meter G3 is recorded.

[0051] Import 499.8cm 3 STD Gas B. Partially open the second shut-off valve V2 to slowly increase the pressure in the gas path before the second mass flow rate controller R2. Once the reading of the second absolute pressure transmitter G2 remains essentially constant, energize the second mass flow rate controller R2 and set its parameters to ensure a flow rate of 499.8 cm. 3 STD Gas B is automatically shut off; after the second mass flow rate controller R2 finishes working, the gas distribution is completed, and the readings of the high-precision composite hollow gas meter G3 and the fourth absolute pressure transmitter G4 are recorded.

[0052] Finally, perform the gas transfer. Open the seventh shut-off valve V7, energize and start the gas pump P1. The gas pump P1 will pump the gas from the gas storage tank C1 and the gas circuit connected to it to the sample tank C2. When the reading of the fifth absolute pressure transmitter G5 remains basically unchanged, record the reading of the fifth absolute pressure transmitter G5, close the seventh shut-off valve V7, turn off the gas pump P1, close the valve on the sample tank, and remove the sample tank. The gas transfer is now complete.

[0053] As can be seen from the above embodiments, the present invention, by introducing a certain amount of gas from a first gas source into the gas storage tank and its connected pipeline under a low to medium vacuum using a first mass flow rate controller, rapidly and uniformly disperses the gas within the gas storage tank and its connected pipeline. Then, a second high-precision mass flow rate controller slowly introduces gas from a second gas source, mixing it with the gas already uniformly dispersed in the first gas source within the gas storage tank and its connected pipeline, thus obtaining a gas with the target element abundance. Therefore, the mixing of the two gases does not require additional mechanical stirring.

[0054] The mass or volume (standard conditions) of the introduced gas is determined by the set flow rate and operating time of the mass flow rate controller, and is not affected by ambient temperature or gas pressure.

[0055] The mass flow rate controller used can automatically control the mass or volume of the introduced gas (under standard conditions) without the need for manual timing.

[0056] Generally, the amount of gas in the first gas source is small (the gas source pressure is around atmospheric pressure) and the price is expensive. When the device is in a low to medium vacuum state, the gas in the first gas source is introduced first to ensure that the pressure difference before and after the mass flow rate controller is higher than its minimum working pressure difference.

[0057] Before introducing the gas from the first gas source, the pipelines before and after the mass flow rate controller are simultaneously evacuated. This avoids replacing the air in the pipelines with the expensive gas from the first gas source, thus preventing waste of gas resources. Simultaneously, the sample container can be evacuated during the device's vacuum pretreatment process, ensuring that the prepared gas is not contaminated by air during transfer. Furthermore, using an air pump to complete the transfer of the prepared gas reduces the amount of residual gas within the device, minimizing gas resource waste.

[0058] If necessary, the amount of each gas introduced can be calculated by observing the changes in the readings of the high-precision vacuum gauge and absolute pressure transmitter on the gas storage tank before and after the introduction of each gas. Therefore, the device ensures the accuracy of the prepared gas abundance through multiple safeguards, including a high-precision mass flow rate controller, a high-precision vacuum gauge, and an absolute pressure transmitter.

[0059] The methods and systems described in this invention are not limited to the embodiments described in the specific implementation. Other implementation methods derived by those skilled in the art based on the technical solutions of this invention also fall within the scope of technical innovation of this invention.

Claims

1. A method for intermittently preparing low-abundance gases, characterized in that, The apparatus used includes: The system comprises an airflow pipeline, a first mass flow rate controller, a second mass flow rate controller, a gas storage tank, a sample container, an air pump, and a vacuum pump. The airflow pipeline has a first air inlet and a second air inlet, which are respectively connected to a first gas source and a second gas source to be mixed. The gas storage tank is connected to the airflow pipeline to transport gases from the first and second gas sources to the gas storage tank for mixing. The sample container is connected to the gas storage tank via the air pump. The airflow pipeline also includes a vacuum pump, which is connected to the airflow pipeline. The first mass flow rate controller is located between the first air inlet and the gas storage tank on the airflow pipeline, and the second mass flow rate controller is located between the second air inlet and the gas storage tank on the airflow pipeline. The first and second mass flow rate controllers sequentially control the gases from the first and second gas sources to enter the gas storage tank at a preset volume. By introducing a certain amount of gas from a first gas source into the gas storage tank and its connected pipeline under a low to medium vacuum using a first mass flow rate controller, the gas from each individual gas source is relatively small, thus quickly and evenly dispersing within the gas storage tank and its connected pipeline. Then, gas from a second gas source is slowly introduced using a second mass flow rate controller, mixing with the gas from the first gas source already evenly dispersed within the gas storage tank and its connected pipeline, to obtain the gas with the target element abundance. After gas preparation, a gas pump draws the gas from the gas storage tank and its connected gas lines to the sample tank. By analyzing the changes in the readings of the high-precision vacuum gauge and absolute pressure transmitter on the gas storage tank before and after each gas introduction, the amount of each gas introduced is calculated. The accuracy of the prepared gas abundance is ensured through multiple safeguards provided by the high-precision mass flow rate controller, the high-precision vacuum gauge, and the absolute pressure transmitter.

2. The method for intermittently preparing low-abundance gases as described in claim 1, characterized in that: The device further includes a first filter and a second filter, wherein the first filter is disposed on the airflow pipeline connecting the first air inlet and the first mass flow rate controller, and the second filter is disposed on the airflow pipeline connecting the second air inlet and the second mass flow rate controller. The first and second filters intercept solid impurities carried in the gas flowing to the first and second mass flow rate controllers, preventing the first and second mass flow rate controllers from becoming clogged.

3. The method for intermittently preparing low-abundance gases as described in claim 2, characterized in that: The gas flow pipeline is equipped with a first shut-off valve, a second shut-off valve, a fifth shut-off valve, a sixth shut-off valve, a seventh shut-off valve, and a ninth shut-off valve. The first shut-off valve is located between the first air inlet and the first filter; the second shut-off valve is located between the second air inlet and the second filter; the fifth shut-off valve is located between the first mass flow rate controller and the gas storage tank; the sixth shut-off valve is located between the second mass flow rate controller and the gas storage tank; the seventh shut-off valve is located between the gas storage tank and the air pump; and the ninth shut-off valve is located between the air pump and the sample container. The first and second shut-off valves can regulate the gas flow rate and control the gas to flow slowly towards the first and second mass flow rate controllers, preventing the pressure in the pipeline from surging and causing damage to the first or second mass flow rate controllers; closing the fifth or sixth shut-off valve can prevent the gas from flowing back to the front end of the first or second mass flow rate controllers.

4. The method for intermittently preparing low-abundance gases as described in claim 3, characterized in that: The vacuum pipeline is provided with a third shut-off valve, a fourth shut-off valve and an eighth shut-off valve in sequence along the first air inlet and the second air inlet toward the vacuum pump. During the vacuuming process, the first mass flow rate controller, the second mass flow rate controller, and the air pump are all powered off and shut down. The third and fourth shut-off valves are opened to evacuate the air paths at the front ends of the first and second mass flow rate controllers together. The ninth shut-off valve is opened to evacuate the sample container together.

5. The method for intermittently preparing low-abundance gases as described in claim 4, characterized in that: The device further includes a first absolute pressure transmitter, a second absolute pressure transmitter, a fourth absolute pressure transmitter, a fifth absolute pressure transmitter, and a high-precision composite vacuum gauge. The first absolute pressure transmitter is disposed on the gas flow line between the first shut-off valve and the first filter. The second absolute pressure transmitter is disposed on the gas flow line between the second shut-off valve and the second filter. The high-precision composite vacuum gauge and the fourth absolute pressure transmitter are both disposed on the gas storage tank. The fifth absolute pressure transmitter is disposed on the sample tank.

6. The method for intermittently preparing low-abundance gases as described in claim 5, characterized in that... : The airflow duct is made of stainless steel with an outer diameter of 1 / 8 inch.

7. The method for intermittently preparing low-abundance gases as described in claim 6, characterized in that... : Both the first and second filters are made of stainless steel and are 1 / 8-inch in size.

8. The method for intermittently preparing low-abundance gases as described in claim 7, characterized in that: Both the gas storage tank and the sample container are made of stainless steel and have a volume of 500 mL.

9. The method for intermittently preparing low-abundance gases as described in claim 8, characterized in that: The connection points between the airflow pipes are welded using tee or cross joints.

10. The method for intermittently preparing low-abundance gases as described in claim 1, characterized in that: Both the first mass flow rate controller and the second mass flow rate controller are connected to the airflow pipeline via VCR.

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