High-precision constant voltage control device and system

Abstract

The application relates to the technical field of pressure control, and provides a high-precision constant-pressure control device and system, wherein a first mass flowmeter and a second mass flowmeter are arranged, the gas flow value allowed to pass through the second mass flowmeter is smaller than the gas flow value allowed to pass through the first mass flowmeter, the working gas flow difference generated between the first mass flowmeter and the second mass flowmeter enters a lower space of a piston pressure gauge and a constant-pressure cavity, the working gas pressure in the lower space of the piston pressure gauge and the constant-pressure cavity is stabilized, a controller adjusts the gas flow value allowed to pass through the second mass flowmeter by taking the piston height measured by a displacement sensor as a feedback signal of pressure control, the pressure control precision of the whole device is prevented from being affected due to working gas leakage in the lower space of the piston pressure gauge, and the high precision and high sensitivity of pressure control of the whole device are improved.

Description

Technical Field

[0001] This invention relates to the field of pressure control technology, specifically to a high-precision constant pressure control device and system. Background Technology

[0002] A constant pressure device is a device that can provide a stable pressure environment. It is a basic piece of equipment required for some experimental environments and is commonly used in chemical reaction experiments, petrochemical fields, and scientific experiments.

[0003] The pressure control accuracy in a constant pressure device depends on the accuracy of the pressure gauge used. Constant pressure devices typically use high-accuracy, high-stability piston pressure gauges to monitor pressure. The piston pressure gauge consists of a cylinder and a piston. The piston is slidably mounted in the cylinder and divides the cylinder into an upper space and a lower space. The working gas to be measured is introduced into the lower space, and a standard weight is placed in the upper space. After the piston reaches the equilibrium position, the obtained pressure value is used as a feedback signal to control the pressure of the constant pressure device.

[0004] However, due to the tiny gap between the piston and cylinder of the piston pressure gauge, the working gas in the space below the piston will leak and be lost through this gap, resulting in unstable pressure measured by the piston pressure gauge. Furthermore, the working gas transmission process will experience continuous pulse fluctuations in gas pressure, affecting the pressure control accuracy of the constant pressure device. Summary of the Invention

[0005] This invention provides a high-precision constant pressure control device and system, which solves or at least partially solves the problems existing in the prior art.

[0006] A first aspect of the present invention provides a high-precision constant pressure control device, comprising:

[0007] Gas transmission pipelines;

[0008] A first mass flow meter and a second mass flow meter are sequentially installed on the gas transmission pipeline along the gas transmission direction, and at least the gas flow rate allowed to pass through the second mass flow meter is adjustable;

[0009] A piston pressure gauge includes a cylinder and a piston, the piston being slidably disposed within the cylinder, the piston dividing the cylinder into an upper space and a lower space;

[0010] Constant pressure chamber;

[0011] The gas transmission pipeline between the first mass flow meter and the second mass flow meter is connected to the lower space of the piston pressure gauge and the constant pressure chamber, respectively.

[0012] A displacement sensor is used to measure the height of the piston;

[0013] The controller is electrically connected to the displacement sensor and the second mass flow meter to adjust the gas flow rate allowed through the second mass flow meter according to the change in the height of the piston.

[0014] The high-precision constant pressure control device provided by the present invention further includes:

[0015] An auxiliary monitoring unit, which includes auxiliary pipelines and pressure measuring devices;

[0016] The gas transmission pipeline between the first mass flow meter and the second mass flow meter is connected to the auxiliary pipeline;

[0017] The pressure measuring device is installed on the auxiliary pipeline and is used to measure the pressure inside the auxiliary pipeline.

[0018] According to the high-precision constant pressure control device provided by the present invention, the auxiliary monitoring unit further includes a first buffer cavity disposed on the auxiliary pipeline.

[0019] According to the high-precision constant pressure control device provided by the present invention, the pressure measuring device includes:

[0020] The first pressure sensor and the second pressure sensor are sequentially installed on the auxiliary pipeline.

[0021] According to the high-precision constant pressure control device provided by the present invention, a three-way valve is provided on the gas transmission pipeline between the first mass flow meter and the second mass flow meter, the three-way valve including a first end, a second end and a third end;

[0022] The first end is connected to the outlet end of the first mass flow meter, and the second end is connected to the inlet end of the second mass flow meter.

[0023] The high-precision constant pressure control device provided by the present invention further includes:

[0024] A four-way valve, comprising a fourth end, a fifth end, a sixth end, and a seventh end;

[0025] The fourth end is connected to the third end of the three-way valve, the fifth end is connected to the constant pressure chamber, the sixth end is connected to the lower space of the piston pressure gauge, and the seventh end is connected to the auxiliary pipeline.

[0026] The high-precision constant pressure control device provided by the present invention further includes:

[0027] A gas cylinder connected to the gas transmission pipeline;

[0028] A pressure reducing valve is provided on the gas transmission pipeline between the gas cylinder and the first mass flow meter;

[0029] The second buffer chamber is located on the gas transmission pipeline between the pressure reducing valve and the first mass flow meter.

[0030] According to the high-precision constant pressure control device provided by the present invention, the outlet end of the second mass flow meter is connected to the first mechanical pump, and the first mechanical pump is used to pump air from the outlet end of the second mass flow meter.

[0031] According to the high-precision constant pressure control device provided by the present invention, the upper space of the piston pressure gauge is connected to a second mechanical pump, and the second mechanical pump is used to evacuate the upper space of the piston pressure gauge.

[0032] A second aspect of the present invention provides a constant pressure control system, including the high-precision constant pressure control device as described above.

[0033] Beneficial Effects: The high-precision constant pressure control device provided by this invention includes a gas transmission pipeline, a first mass flow meter, a second mass flow meter, a piston pressure gauge, a constant pressure chamber, a displacement sensor, and a controller. By setting the first and second mass flow meters, and setting the allowable gas flow rate of the second mass flow meter to be less than that of the first mass flow meter, the working gas flow difference generated between the first and second mass flow meters is used in the lower space of the piston pressure gauge and the constant pressure chamber. After pressure stabilization and flow restriction by the first and second mass flow meters, the gas entering the piston pressure gauge can be controlled. The working gas pressure in the lower space and the constant pressure chamber is stable, and the gas transmission pipeline between the lower space of the piston pressure gauge, the constant pressure chamber, and the first and second mass flow meters are connected, with equal gas pressure. The pressure value measured by the piston pressure gauge is the pressure value in the constant pressure chamber. The controller uses the piston height measured by the displacement sensor as the feedback signal for pressure control to adjust the allowable gas flow rate of the second mass flow meter. This avoids the pressure control accuracy of the entire device being affected by working gas leakage in the lower space of the piston pressure gauge, thereby improving the high precision and high sensitivity of the pressure control of the entire device.

[0034] Furthermore, the constant pressure control system provided by the present invention also possesses the various advantages described above due to the high-precision constant pressure control device described above. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the high-precision constant pressure control device in an embodiment of the present invention.

[0037] Figure label:

[0038] 1. Gas transmission pipeline; 2. First mass flow meter; 3. Second mass flow meter; 4. Piston pressure gauge; 5. Constant pressure chamber; 6. Displacement sensor; 7. Auxiliary pipeline; 8. First buffer chamber; 9. First pressure sensor; 10. Second pressure sensor; 11. Three-way valve; 12. Four-way valve; 13. First valve; 14. Gas cylinder; 15. Second valve; 16. Pressure reducing valve; 17. Second buffer chamber; 18. First mechanical pump; 19. Second mechanical pump; 20. Vacuum pump; 21. Temperature control box. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] In the description of this invention, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0043] A constant pressure device is a device that can provide a stable pressure environment. It is a basic piece of equipment required for some experimental environments and is commonly used in chemical reaction experiments, petrochemical fields, and scientific experiments.

[0044] The pressure control accuracy in a constant pressure device depends on the accuracy of the pressure gauge used. Constant pressure devices typically use high-accuracy, high-stability piston pressure gauges to monitor pressure. The piston pressure gauge consists of a cylinder and a piston. The piston is slidably mounted in the cylinder and divides the cylinder into an upper space and a lower space. The working gas to be measured is introduced into the lower space, and a standard weight is placed in the upper space. After the piston reaches the equilibrium position, the obtained pressure value is used as a feedback signal to control the pressure of the constant pressure device.

[0045] However, due to the tiny gap between the piston and cylinder of the piston pressure gauge, the working gas in the space below the piston will leak and be lost through this gap, resulting in unstable pressure measured by the piston pressure gauge. Furthermore, the working gas transmission process will experience continuous pulse fluctuations in gas pressure, affecting the pressure control accuracy of the constant pressure device.

[0046] In this embodiment of the invention, by setting a first mass flow meter and a second mass flow meter, and setting the allowable gas flow rate of the second mass flow meter to be less than that of the first mass flow meter, the working gas flow difference generated between the first and second mass flow meters is used in the lower space of the piston pressure gauge and the constant pressure chamber. After pressure stabilization and flow restriction by the first and second mass flow meters, the working gas pressure entering the lower space of the piston pressure gauge and the constant pressure chamber can be stabilized. Furthermore, the lower space of the piston pressure gauge, the constant pressure chamber, and the gas transmission pipeline between the first and second mass flow meters are connected, and the gas pressures are equal. The gas pressure value measured by the piston pressure gauge is the gas pressure value in the constant pressure chamber. The controller uses the piston height measured by the displacement sensor as the feedback signal for pressure control to adjust the allowable gas flow rate of the second mass flow meter, avoiding the impact of working gas leakage in the lower space of the piston pressure gauge on the pressure control accuracy of the entire device, thereby improving the high precision and high sensitivity of the pressure control of the entire device.

[0047] The following is combined with Figure 1 This invention describes a high-precision constant pressure control device and system.

[0048] like Figure 1 As shown, the high-precision constant pressure control device provided in some embodiments of the present invention includes a gas transmission pipeline 1, a first mass flow meter 2, a second mass flow meter 3, a piston pressure gauge 4, a constant pressure chamber 5, a displacement sensor 6, and a controller. The gas transmission pipeline 1 is used to transmit working gas. The first mass flow meter 2 and the second mass flow meter 3 are sequentially arranged on the gas transmission pipeline 1 along the direction of gas transmission, and at least the gas flow rate allowed by the second mass flow meter 3 is adjustable. Both the first mass flow meter 2 and the second mass flow meter 3 can measure the actual gas flow rate and can also set the allowed flow rate.

[0049] The piston pressure gauge 4 includes a cylinder and a piston. The piston is slidably disposed within the cylinder, dividing the cylinder into an upper space and a lower space. The gas transmission pipeline 1 between the first mass flow meter 2 and the second mass flow meter 3 is connected to the lower space of the piston pressure gauge 4 and the constant pressure chamber 5, respectively, ensuring that the gas pressure in the lower space of the piston pressure gauge 4, the constant pressure chamber 5, and the gas transmission pipeline 1 are equal. In practical applications, part of the gas transmission pipeline 1, the first mass flow meter 2, the second mass flow meter 3, and the piston pressure gauge 4 are placed on an operating platform to stabilize the gas pressure among them. The constant pressure chamber 5 can be a cavity structure of various materials and shapes, applicable to various constant pressure environments. The displacement sensor 6 is used to measure the piston height. The piston height measured by the displacement sensor 6 is used as the feedback signal for pressure control. The displacement sensor 6 can be a laser displacement meter. The controller is electrically connected to the displacement sensor 6 and the second mass flow meter 3 to adjust the allowable gas flow rate of the second mass flow meter 3 according to the change in piston height.

[0050] The first mass flow meter 2 is used to control the gas flow rate entering the constant pressure chamber 5. In application, it can be set to a constant value. The specific value is adjusted according to parameters such as the range of the first mass flow meter 2 and the second mass flow meter 3, the measured pressure of the piston pressure gauge 4, and the required pressure of the constant pressure chamber 5. The second mass flow meter 3 is used to control the gas flow rate exiting the constant pressure chamber 5. The gas flow rate allowed by the second mass flow meter 3 is less than the gas flow rate allowed by the first mass flow meter 2. The controller dynamically adjusts the gas flow rate allowed by the second mass flow meter 3 according to the piston height signal of the piston pressure gauge 4 fed back by the displacement sensor 6. Since the flow rate allowed by the second mass flow meter 3 is always less than the flow rate allowed by the first mass flow meter 2, the pressure between the first mass flow meter 2 and the second mass flow meter 3 is kept stable. That is to say, the total pressure difference between the lower space of the piston pressure gauge 4, the constant pressure chamber 5, and the gas transmission pipeline 1 between the first mass flow meter 2 and the second mass flow meter 3 is the pressure difference between the first mass flow meter 2 and the second mass flow meter 3.

[0051] During operation, the working gas enters the gas transmission pipeline 1 for transmission, then enters the first mass flow meter 2 for pressure stabilization and flow restriction. Afterward, it enters the lower space of the piston pressure gauge 4, the constant pressure chamber 5, and the second mass flow meter 3. Since the flow rate allowed by the second mass flow meter 3 is less than that allowed by the first mass flow meter 2, the working gas intercepted between the first mass flow meter 2 and the second mass flow meter 3 is evenly distributed in the lower space of the piston pressure gauge 4, the constant pressure chamber 5, and the gas transmission pipeline 1 between the first mass flow meter 2 and the second mass flow meter 3. The gas pressure in these three places is equal. After the working gas enters the lower space of the piston pressure gauge 4, the piston will float. After the piston reaches the equilibrium position, the gas pressure measured by the piston pressure gauge 4 is the gas pressure value in the constant pressure chamber 5 at this time. The change in piston height can sensitively reflect the gas pressure fluctuations in the space below the piston. Therefore, the piston height measured by displacement sensor 6 is used as the feedback signal for pressure control. The controller adjusts the gas flow rate of the second mass flow meter 3 according to this feedback signal. By dynamically adjusting the gas flow rate of the second mass flow meter 3, the pressure in the constant pressure chamber 5 is controlled to maintain a constant pressure. At the same time, the rise and fall of the piston of piston pressure gauge 4 compensates for and buffers the pressure changes in the lower space, that is, it can reduce the amplitude of pressure changes in the lower space and stabilize the pressure.

[0052] In this embodiment, by setting a first mass flow meter 2 and a second mass flow meter 3, and setting the allowable gas flow rate of the second mass flow meter 3 to be less than the allowable gas flow rate of the first mass flow meter 2, the working gas flow difference generated between the first mass flow meter 2 and the second mass flow meter 3 is used in the lower space of the piston pressure gauge 4 and the constant pressure chamber 5. After the pressure stabilization and flow restriction of the first mass flow meter 2 and the second mass flow meter 3, the working gas pressure entering the lower space of the piston pressure gauge 4 and the constant pressure chamber 5 can be stabilized. Furthermore, the gas transmission pipeline 1 between the lower space of the piston pressure gauge 4, the constant pressure chamber 5, and the first mass flow meter 2 and the second mass flow meter 3 is connected, and the gas pressure is equal. The gas pressure value measured by the piston pressure gauge 4 is the gas pressure value in the constant pressure chamber 5. The controller uses the piston height measured by the displacement sensor 6 as the feedback signal for pressure control to adjust the allowable gas flow rate of the second mass flow meter 3, avoiding the impact of working gas leakage in the lower space of the piston pressure gauge 4 on the pressure control accuracy of the entire device, thereby improving the high accuracy and high sensitivity of the pressure control of the entire device.

[0053] Continue as Figure 1As shown, the high-precision constant pressure control device also includes an auxiliary monitoring unit for monitoring the gas pressure within the constant pressure chamber 5. A pressure measuring device is installed on the auxiliary pipeline to measure the pressure within it. Specifically, the auxiliary monitoring unit includes an auxiliary pipeline 7 and a pressure measuring device. The auxiliary pipeline 7 is connected to the constant pressure chamber 5, the lower space of the piston pressure gauge 4, and the gas transmission pipeline 1 between the first mass flow meter 2 and the second mass flow meter 3. This means that the gas pressure within these four locations is equal. The pressure measuring device measures the pressure within the auxiliary pipeline, which is equivalent to measuring the pressure within the lower space of the piston pressure gauge 4 and the constant pressure chamber 5. The pressure measuring device measures the pressure in real time to obtain higher accuracy in pressure changes and also reflects pressure fluctuations within the pipeline.

[0054] In order to further stabilize the air pressure changes in the pipeline, in some embodiments of the present invention, the auxiliary monitoring unit further includes a first buffer cavity 8, which is disposed on the auxiliary pipeline and located at the end of the auxiliary pipeline, that is, the end away from the piston pressure gauge 4. The first buffer cavity 8 has a certain volume and is used to stabilize the air pressure in the pipeline and reduce air pressure fluctuations. The size of the first buffer cavity 8 can be adjusted according to the magnitude of the disturbance to the air pressure in the pipeline and the actual air pressure fluctuation.

[0055] Continue as Figure 1 As shown, in order to improve the measurement accuracy of the pressure measuring device, in some embodiments of the present invention, the pressure measuring device includes a first pressure sensor 9 and a second pressure sensor 10, which are sequentially disposed on the auxiliary pipeline 7. The first pressure sensor 9 is disposed close to the first buffer cavity 8, and the second pressure sensor 10 is disposed on the side of the first pressure sensor 9 away from the first buffer cavity 8. In order to avoid the inherent drift of the temperature measuring device over time, which makes the absolute value of the pressure measurement inaccurate, two pressure sensors are used for comparison in this embodiment to improve the measurement accuracy. In this embodiment, there can also be two or more pressure sensors to obtain higher pressure change accuracy and reflect the pipeline pressure fluctuation.

[0056] To ensure the airtightness of the connection between the lower space of the piston pressure gauge 4, the constant pressure chamber 5, and the gas transmission pipeline 1 between the first mass flow meter 2 and the second mass flow meter 3, in some embodiments of the present invention, a three-way valve 11 is provided on the gas transmission pipeline 1 between the first mass flow meter 2 and the second mass flow meter 3. The three-way valve 11 includes a first end, a second end, and a third end, wherein the first end is connected to the outlet end of the first mass flow meter 2, and the second end is connected to the inlet end of the second mass flow meter 3. The airtightness of each connection point is improved by setting the three-way valve 11.

[0057] To ensure the airtightness of the connection between the auxiliary pipeline 7 and the constant pressure chamber 5, the lower space of the piston pressure gauge 4, and the gas transmission pipeline 1 between the first mass flow meter 2 and the second mass flow meter 3, in some embodiments of the present invention, a four-way valve 12 is also provided. The four-way valve 12 includes a fourth end, a fifth end, a sixth end, and a seventh end. The fourth end is connected to the third end of the three-way valve 11, the fifth end is connected to the constant pressure chamber 5, the sixth end is connected to the lower space of the piston pressure gauge 4, and the seventh end is connected to the auxiliary pipeline 7. A first valve 13 is also provided between the seventh end and the auxiliary pipeline 7 to control the opening and closing of the connection between the four-way valve 12 and the auxiliary pipeline 7.

[0058] In some embodiments of the present invention, the constant pressure control device further includes a gas cylinder 14, which stores a high-pressure working gas. The working gas includes, but is not limited to, any one of the elemental gases such as helium, argon, and nitrogen, or a mixture of any of the aforementioned elemental gases. The gas cylinder 14 serves as the gas source for the constant pressure control device. The gas cylinder 14 is connected to a second valve 15, which connects the gas cylinder 14 to the gas transmission pipeline 1. The second valve 15 controls the connection and disconnection between the gas cylinder 14 and the gas transmission pipeline 1. A pressure reducing valve 16 is also provided between the second valve 15 and the first mass flow meter 2. The pressure reducing valve 16 is installed on the gas transmission pipeline 1 between the gas cylinder 14 and the first mass flow meter 2. The pressure reducing valve 16 can reduce the pressure of the gas flowing out of the gas cylinder 14 and prevent high-pressure gas from directly impacting the first mass flow meter 2. A second buffer chamber 17 is also provided between the pressure reducing valve 16 and the first mass flow meter 2. The second buffer chamber 17 is installed on the gas transmission pipeline 1 between the pressure reducing valve 16 and the first mass flow meter 2. The second buffer chamber 17 can buffer the pressure of the gas flowing out of the pressure reducing valve 16 and provide a more uniform pressure environment for the first mass flow meter 2.

[0059] In order to ensure that the working gas flows out of the second mass flow meter 3 smoothly, in some embodiments of the present invention, the outlet end of the second mass flow meter 3 is connected to the first mechanical pump 18. The first mechanical pump 18 is used to pump air from the outlet end of the second mass flow meter 3. The first mechanical pump 18 can provide a low-pressure environment so that the working gas flows out of the second mass flow meter 3 smoothly. The pumping efficiency of the first mechanical pump 18 is set at 100-400 Pa, and more preferably 200 Pa or 300 Pa.

[0060] Since the working gas in the lower space of the piston pressure gauge 4 leaks into the upper space through the gap between the piston and the cylinder, it will increase the weight of the standard weight. In order to maintain the vacuum in the upper space of the piston pressure gauge 4 and improve the measurement accuracy of the piston pressure gauge 4, in some embodiments of the present invention, the upper space of the piston pressure gauge 4 is connected to the second mechanical pump 19, and the upper space of the piston pressure gauge 4 is evacuated by the second mechanical pump 19. Alternatively, a vacuum pump 20 can be set between the upper space of the piston pressure gauge 4 and the second mechanical pump 19. The vacuum pump 20 and the second mechanical pump 19 work together to promptly remove the gas leaking from the lower space to the upper space, maintain the high vacuum environment in the upper space of the piston pressure gauge 4, and maintain the gas pressure in the upper space of the piston pressure gauge 4 at about 0.4 Pa.

[0061] To further improve the measurement accuracy of each component and reduce the impact of temperature changes on the measurement, components that are easily affected by temperature are placed in the temperature control chamber 21. As a further preferred option, for example, the first pressure sensor 9, the second pressure sensor 10, the piston pressure gauge 4, the displacement sensor 6, the first mass flow meter 2, the second mass flow meter 3, the second buffer chamber 17, and part of the gas transmission pipeline 1 can be placed in the temperature control chamber 21. The temperature control chamber 21 can maintain a relatively stable set temperature to reduce the impact of temperature fluctuations on the instrument's working state. The set temperature of the temperature control chamber 21 includes, but is not limited to, 24.5℃. The constant pressure chamber 5 can be placed in a pressure-stable experimental environment chamber, which includes, but is not limited to, room temperature, low temperature, and extremely low temperature environments.

[0062] Secondly, this invention also provides a constant pressure control system, including the high-precision constant pressure control device provided in any of the above embodiments. The derivation process of the beneficial effects of the constant pressure control system in this invention is largely similar to the derivation process of the beneficial effects of the high-precision constant pressure control device described above, and therefore will not be repeated here.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-precision constant pressure control device, characterized in that, include: Gas transmission pipeline (1); The first mass flow meter (2) and the second mass flow meter (3) are sequentially installed on the gas transmission pipeline (1) along the gas transmission direction, and at least the gas flow rate allowed to pass through the second mass flow meter (3) is adjustable; A piston pressure gauge (4) includes a cylinder and a piston, wherein the piston is slidably disposed in the cylinder and the piston divides the cylinder into an upper space and a lower space; Constant pressure chamber (5); The gas transmission pipeline (1) between the first mass flow meter (2) and the second mass flow meter (3) is connected to the lower space of the piston pressure gauge (4) and the constant pressure chamber (5), respectively. Displacement sensor (6) is used to measure the height of the piston; The controller is electrically connected to the displacement sensor (6) and the second mass flow meter (3) to adjust the gas flow rate allowed by the second mass flow meter (3) according to the change in the height of the piston; An auxiliary monitoring unit is provided, comprising an auxiliary pipeline (7) and a pressure measuring device; the gas transmission pipeline (1) between the first mass flow meter (2) and the second mass flow meter (3) is connected to the auxiliary pipeline (7); the pressure measuring device is provided on the auxiliary pipeline (7) and is used to measure the pressure in the auxiliary pipeline (7); The gas transmission pipeline (1) between the first mass flow meter (2) and the second mass flow meter (3) is provided with a three-way valve (11), which includes a first end, a second end and a third end; the first end is connected to the outlet end of the first mass flow meter (2) and the second end is connected to the inlet end of the second mass flow meter (3).

2. The high-precision constant pressure control device according to claim 1, characterized in that, The auxiliary monitoring unit also includes a first buffer cavity (8), which is located on the auxiliary pipeline (7).

3. The high-precision constant pressure control device according to claim 1 or 2, characterized in that, The pressure measuring device includes: The first pressure sensor (9) and the second pressure sensor (10) are sequentially installed on the auxiliary pipeline (7).

4. The high-precision constant pressure control device according to claim 1, characterized in that, Also includes: A four-way valve (12), the four-way valve (12) including a fourth end, a fifth end, a sixth end and a seventh end; The fourth end is connected to the third end of the three-way valve (11), the fifth end is connected to the constant pressure chamber (5), the sixth end is connected to the lower space of the piston pressure gauge (4), and the seventh end is connected to the auxiliary pipeline (7).

5. The high-precision constant pressure control device according to claim 1, characterized in that, Also includes: Gas cylinder (14) is connected to the gas transmission pipeline (1); A pressure reducing valve (16) is provided on the gas transmission pipeline (1) between the gas cylinder (14) and the first mass flow meter (2); The second buffer chamber (17) is located on the gas transmission pipeline (1) between the pressure reducing valve (16) and the first mass flow meter (2).

6. The high-precision constant pressure control device according to claim 1, characterized in that, The outlet of the second mass flow meter (3) is connected to the first mechanical pump (18), which is used to pump air from the outlet of the second mass flow meter (3).

7. The high-precision constant pressure control device according to claim 1 or 6, characterized in that, The upper space of the piston pressure gauge (4) is connected to the second mechanical pump (19), which is used to pump air from the upper space of the piston pressure gauge (4).

8. A constant pressure control system, characterized in that, Includes the high-precision constant pressure control device as described in any one of claims 1-7.

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