Passive piston type gas micro-flow calibration system and method based on image method

Abstract

The invention discloses a gas micro-flow calibration system and method based on an image method.The system is composed of a metering piston unit, a driving piston unit, a calibration pipeline and the like, the metering piston unit mainly comprises a metering cylinder barrel, a metering piston, a camera, a photoelectric switch and the like, and the metering cylinder barrel is vertically arranged; and the metering piston and the metering cylinder barrel are dynamically sealed by a mercury ring. The metering cylinder barrel is provided with a calibration starting section and a calibration stopping section, and the two photoelectric switches and the two cameras are installed at the corresponding positions of the starting section and the stopping section respectively. During calibration, gas flows through the calibrated flowmeter and then enters the metering cylinder barrel, when the metering piston reaches the starting section and the ending section, the photoelectric switch senses and triggers the camera to take pictures, images are analyzed to determine the accurate position and displacement of the metering piston at the starting moment and the ending moment, and the volume and the flow of exhausted gas are obtained. According to the invention, the movement position and time of the metering piston in the small-size metering cylinder barrel can be accurately measured, and verification and calibration of a gas micro-flow sensor or flowmeter can be realized.

Description

Technical Field

[0001] The invention belongs to the field of gas flow measurement, and in particular relates to a passive piston type gas micro-flow calibration system and method based on an image method. Background Art

[0002] High-precision measurement technology for tiny gas flows is widely used in semiconductors, biomedicine, environmental monitoring, chemical industry, precision equipment and other fields. Especially in some key processes of semiconductor manufacturing, the measurement and control of tiny gas flows is particularly important.

[0003] At present, the gas micro-flow rate has reached 5mL / min, but there is a lack of calibration technology for flow rates less than 10mL / min at home and abroad. For flow meters working at 10mL / min and below, how to ensure their measurement accuracy and traceability is an urgent problem to be solved.

[0004] The passive piston flow standard device is more suitable for gas micro-flow calibration. The quantities directly measured in this method are generally piston displacement and time. There are two specific implementation methods: 1) Determine the time interval of the piston passing through two fixed sections with known distances on the cylinder, and use a photoelectric switch to trigger the timing; 2) Use a laser interferometer or laser rangefinder to measure the piston displacement in real time, and collect displacement and time data at the same time, so as to obtain the displacement and time interval of the piston passing through two sections of the cylinder. However, these two methods each have certain problems. In the photoelectric switch method, since the posture of the piston during operation cannot be guaranteed to be consistent every time, there is a certain uncertainty in the triggering time of the photoelectric switch, which introduces a large timing error; for the method of real-time measurement of piston displacement, the laser interferometer is expensive and complicated to operate. The laser rangefinder is not suitable for piston displacement measurement in a smaller diameter cylinder, because its transmitting and receiving probes are separated and easily affected by the light reflection angle, so the effective displacement range that can be measured is relatively small, which cannot meet the needs of piston displacement measurement in a slender cylinder. Summary of the invention

[0005] In order to solve the above technical problems existing in the prior art, the present invention provides a passive piston type gas micro flow calibration system and method based on an image method, and the specific technical solution is as follows: A passive piston type gas micro-flow calibration system based on image method consists of four parts: metering piston unit, calibration pipeline, driving piston unit and data acquisition and control unit. Among them: The metering piston unit consists of a metering cylinder, a metering piston, a mercury ring, a lower photoelectric switch, an upper photoelectric switch, a limit switch, a starting camera, an ending camera, a scale ruler, a connecting end, a metering cavity pressure sensor, and a metering cavity temperature sensor. The metering cylinder is placed vertically, with the upper end opening to the atmosphere. A mercury ring is used to dynamically seal the metering piston and the metering cylinder. The cross-sectional dimensions of the metering cylinder are accurately determined by measurement. The metering cylinder is provided with calibration start and end sections, and scale lines are marked. The distance between the two scale lines is accurately determined by measurement. The lower photoelectric switch and the starting camera are aligned with the starting section, and the upper photoelectric switch and the ending camera are aligned with the ending section. The lower photoelectric switch is connected to the trigger port of the starting camera, and the upper photoelectric switch is connected to the trigger port of the ending camera.

[0006] The calibration pipeline includes the flow meter to be tested, the flow meter inlet valve, the filter, the metering piston inlet valve and the drain valve.

[0007] The driving piston unit includes a driving cylinder, a driving piston, a stepping motor, a driving cylinder pressure sensor, a driving cylinder temperature sensor and a driving piston inlet valve.

[0008] The data acquisition and control unit mainly includes a data acquisition control module and a computer. The limit switch is connected to the input signal port of the data acquisition control module. The metering chamber pressure sensor, the metering chamber temperature sensor, the drive cylinder pressure sensor, the drive cylinder temperature sensor and the stepper motor are connected to the data acquisition control module. The two cameras are connected to the computer. The data acquisition control module is connected to the computer.

[0009] The metering cylinder is made of transparent glass, and the starting and ending sections of the metering cylinder are respectively provided with scale rulers for geometric calibration of camera images. The starting and ending images collected by the computer contain images of the scale rulers, based on which the proportional relationship between pixels and actual physical dimensions can be obtained.

[0010] The main function of the lower photoelectric switch and the upper photoelectric switch is to trigger the camera to take pictures as an external signal. When the metering piston passes the installation position of the photoelectric switch, the metering piston blocks the light source, and the photoelectric switch receiving end generates a level signal change, thereby triggering the camera to take pictures.

[0011] The metering chamber temperature and pressure sensor is used to detect the gas temperature and pressure in the metering cylinder so as to make temperature and pressure corrections to the volume flow; the driving cylinder temperature and pressure sensor is used to detect the pressure temperature in the driving cylinder and monitor the system working parameters.

[0012] The limit switch is used to prevent the metering piston from rushing out of the metering cylinder when it moves upward. When the metering piston reaches the limit switch position, the limit switch induction triggers the stepping motor to stop rotating, and the gas in the metering pipeline stops flowing.

[0013] The functions of the drain valve are, firstly, to discharge the gas in the metering tube and the metering pipeline so that the metering piston falls to the lowest position, and, secondly, to discharge the gas when the pipeline is purged.

[0014] The working principle of the system is: the computer program controls the stepper motor to drive the piston to move, pushing the gas to flow through the flow meter to enter the metering cylinder, and the gas pushes the metering piston to move at a constant speed from bottom to top. When the metering piston reaches the starting section, the lower photoelectric switch senses and triggers the starting camera to take a photo to obtain the starting image; when the metering piston reaches the ending section, the upper photoelectric switch senses and triggers the ending camera to take a photo to obtain the ending image. The starting image and the ending image taken are collected by the computer, and the time corresponding to the two images is recorded, which is called the starting time and the ending time. The time interval between the two photos Δ t The starting and ending images are analyzed to determine the starting and ending positions of the metering piston and obtain the working displacement of the metering piston. L (i.e. the distance between the starting and ending positions of the metering piston), combined with the cross-sectional area of ​​the metering cylinder A Calculate the gas volume V , and then the volume flow rate is obtained, Q = V / Δ t , thereby realizing the verification and calibration of the flow meter being tested. Beneficial Effects

[0015] 1. The image method is used to determine the starting position and ending position of the metering piston, as well as the corresponding starting time and ending time, to obtain the working displacement and time interval. It has the characteristics of accurate measurement, and the equipment is simple and reliable.

[0016] 2. The cylinder piston method is used to drive the gas flow in the tube, which has the advantages of a large flow rate variation range, accurate and fast flow rate setting, and stable airflow, and the system is easy to automate.

[0017] 3. Using two cameras, the start and end, can obtain high-resolution images, and the start and end positions can be measured with high accuracy.

[0018] The passive piston type gas micro-flow calibration system and method based on the image method of the present invention solves the problem of being unable to measure or inaccurately measuring in the current passive piston type gas micro-flow standard device, and can realize the calibration of gas micro-flow below 10mL / min. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the passive piston type gas micro flow calibration system based on the image method; Figure 2 This is a schematic diagram of an example system using nitrogen as the calibration medium; Figure 3 This is a schematic diagram of the metering piston movement.

[0020] Reference numerals in the figure: 1-metering piston unit; 2-calibration pipeline; 3-driving piston unit; 4-data acquisition and control unit; 101-metering cylinder; 102-metering piston; 103-mercury ring; 104-lower photoelectric switch; 105-upper photoelectric switch; 106-limit switch; 107-start camera; 108-end camera; 109-scale ruler; 110-connection terminal; 111-metering chamber pressure sensor; 112-metering chamber temperature sensor; 201 - flow meter under test; 202 - flow meter inlet valve; 203 - filter; 204 - metering piston inlet valve; 205 - bypass valve; 301 - drive cylinder; 302 - drive piston; 303 - stepper motor; 304 - drive cylinder pressure sensor; 305 - drive cylinder temperature sensor; 306 - drive cylinder inlet valve; 401 - data acquisition control module; 402 - computer; 501 - nitrogen cylinder; 502 - pressure regulating tank; 503 - cylinder switch valve; 504 - pressure regulating valve. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0022] like Figure 1 As shown, the passive piston type gas micro-flow calibration system based on the image method of the present invention is divided into a metering piston unit 1, a calibration pipeline 2, a driving piston unit 3 and a data acquisition and control unit 4; wherein the metering piston unit 1 includes a metering cylinder 101, a metering piston 102, a mercury ring 103, a lower photoelectric switch 104, an upper photoelectric switch 105, a limit switch 106, a start camera 107, an end camera 108, a scale ruler 109, a connecting end 110, a metering cavity pressure sensor 111 and a metering cavity temperature sensor 112; the calibration pipeline 2 includes a flow meter 201 to be tested, a flow meter inlet valve 202, a filter 203, a metering piston inlet valve 204 and an exhaust valve 205; the driving piston unit 3 includes a driving cylinder 301, a driving piston 302, a stepping motor 303, a driving cylinder pressure sensor 304, a driving cylinder temperature sensor 305 and a driving piston inlet valve 306; the data acquisition and control unit 4 mainly includes a data acquisition control module 401 and a computer 402.

[0023] like Figure 2 As shown, this system uses nitrogen as an example of a calibration medium. The nitrogen supply pipeline mainly includes a nitrogen cylinder 501, a pressure regulating tank 502, a cylinder switch valve 503 and a pressure regulating valve 504. The nitrogen supply pipeline is connected to the inlet of the driving cylinder 301.

[0024] The metering cylinder 101 is made of transparent glass and placed vertically. The gap between the metering piston 102 and the metering tube 101 is about 0.1mm. The two are dynamically sealed with a mercury ring 103. The upper end of the metering tube 101 is open to the atmosphere. The metering cylinder 101 is set with a calibration start and end section, and the scale lines are marked. The distance between the two scale lines is L s Accurately measure the inner diameter of the measuring cylinder for devices with an upper flow rate of 20 mL / min D About 12mm, L s About 100mm.

[0025] like Figure 3 As shown, the metering piston movement image is shown. When the metering piston 102 reaches the starting section or the ending section, the photoelectric switch senses and triggers the camera to take a photo to obtain the metering piston movement image. The starting image and the ending image are collected by the computer, and the time corresponding to the two images is recorded. The time interval between the two photos is Δ t .like Figure 3 As shown, taking the upper edge of the metering piston as a reference, the distance between the upper edge of the piston and the scale line in the image is Δ L , define when the piston top is above the scale line Δ L is positive, otherwise it is negative, and is recorded as Δ in the starting image L 1, denoted as Δ in the termination image L 2, then the working displacement of the metering piston is L = L s -Δ L 1+Δ L 2. If the cross-sectional area of ​​the metering cylinder is A , then the volume of gas flowing during the measurement period is V = AL , volume flow rate, Q = V / Δ t .

[0026] The steps for calibration using this example are: 1) System initialization. The metering piston 102 is in the lowest position. When the exhaust valve 205 is open, the metering piston 102 will slowly drop to the lowest position due to gravity; turn on the power of the equipment, run the computer 402 system acquisition and control software; drive the piston 302 to the rightmost position.

[0027] 2) Pipeline purging. Close the metering piston inlet valve 204, set the pressure regulating valve 504 to a suitable pressure, open the drain valve 205 and the flow meter inlet valve 202, move the drive piston 302 to the leftmost position, open the drive cylinder inlet valve 306 and the gas cylinder switch valve 503 for purging, and the purging time shall not be less than 2 minutes. Note: The purging process can also be completed by driving the piston to drive the gas flow.

[0028] 3) Calibration test. First, the driving cylinder is inhaled, the driving piston inlet valve 306 is opened, the flow meter inlet valve 202 is closed, and the driving piston 302 moves from the leftmost side to the right to inhale nitrogen into the driving cylinder 301; then the driving piston inlet valve 306 and the exhaust valve 205 are closed, the flow meter inlet valve 202 and the metering piston inlet valve 204 are opened, and the driving piston 302 moves to the left at a uniform speed, pushing the gas in the tube to flow through the flow meter 201 to be tested and into the metering cylinder 101, thus realizing flow calibration.

[0029] The above description is only the basic idea and method of the present invention, and does not limit the patent of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related fields, are also included in the patent protection scope of the present invention.

Claims

1. A passive piston type gas micro-flow calibration system based on an image method, comprising a metering piston unit (1), a calibration pipeline (2), a driving piston unit (3) and a data acquisition and control unit (4), characterized in that: The metering piston unit (1) comprises a metering cylinder (101), a metering piston (102), a mercury ring (103), a lower photoelectric switch (104), an upper photoelectric switch (105), a limit switch (106), a start camera (107), an end camera (108), a scale ruler (109), a connecting end (110), a metering cavity pressure sensor (111), and a metering cavity temperature sensor (112); the calibration pipeline (2) comprises a flow meter to be tested (201), a flow meter inlet valve (202), a flow meter pressure sensor (111), and a flow meter temperature sensor (112). filter (203), a metering piston inlet valve (204) and an exhaust valve (205); the driving piston unit (3) comprises a driving cylinder (301), a driving piston (302), a stepping motor (303), a driving cylinder pressure sensor (304), a driving cylinder temperature sensor (305) and a driving piston inlet valve (306); the data acquisition and control unit (4) comprises a data acquisition control module (401) and a computer (402), and the data acquisition control module (401) is communicatively connected to the computer (402); The metering cylinder (101) is placed vertically, with an upper opening for communicating with the atmosphere, and a mercury ring (103) is used to form a dynamic seal between the metering piston (102) and the metering cylinder (101). The metering cylinder (101) is provided with a calibration start and end section, and scale lines are marked, and the distance between the two scale lines is accurately determined. The lower photoelectric switch (104) and the upper photoelectric switch (105) are respectively aligned with the start section and the end section, and the start camera (107) and the end camera (108) are respectively aligned with the start section and the end section.

2. According to the image-based passive piston gas micro-flow calibration system of claim 1, it is characterized by: The lower photoelectric switch (104) is connected to the trigger port of the starting camera (107), and the upper photoelectric switch (105) is connected to the trigger port of the ending camera (108).

3. The passive piston type gas micro flow calibration system based on image method according to claim 1 is characterized by: The limit switch (106) is connected to the input signal port of the data acquisition control module (401).

4. The passive piston type gas micro flow calibration system based on image method according to claim 1 is characterized by: The metering chamber pressure sensor (111), the metering chamber temperature sensor (112), the driving cylinder pressure sensor (304), the driving cylinder temperature sensor (305), and the stepping motor (303) are communicatively connected to the data acquisition control module (401).

5. A calibration method for a passive piston type gas micro-flow calibration system based on an image method according to any one of claims 1 to 4, characterized in that: During calibration, the gas flows through the flow meter (201) to be tested and enters the metering cylinder (101), and the metering piston (102) moves at a uniform speed from bottom to top; when the metering piston (102) reaches the starting section, the lower photoelectric switch (104) senses and triggers the starting camera (107) to take a picture, thereby obtaining a starting image; when the metering piston (102) reaches the ending section, the upper photoelectric switch (105) senses and triggers the ending camera (108) to take a picture, thereby obtaining a ending image; the taken starting image and ending image are collected by a computer (402), and the time corresponding to the two images is recorded, which is called the starting time and the ending time, and the time interval Δ between the two pictures is t The two images are analyzed to determine the exact position of the metering piston (102) at the start and end time, and its exact displacement is obtained. L , combined with the cross-sectional area of ​​the metering cylinder (101) A Calculate the gas volume V , and then the volume flow rate is obtained, Q = V / Δ t .

6. The calibration method according to claim 5, characterized in that: The starting section and the ending section of the metering cylinder (101) are respectively provided with scale rulers (109) for geometric calibration of the camera image; the starting image and the ending image captured by the computer 402 contain images of the scale ruler (109) to obtain the relationship between the pixel and the actual physical size.

7. The calibration method according to claim 5, characterized in that: During the calibration process, the cylinder-piston method is used to drive the gas flow; first, the driving cylinder is inhaled, the driving piston inlet valve (306) is opened, the flow meter inlet valve (202) is closed, the driving piston (302) moves from the leftmost side to the right, and the gas medium is sucked into the driving cylinder (301), and then the calibration is started, the driving piston inlet valve (306) and the bypass valve (205) are closed, the flow meter inlet valve (202) and the metering piston inlet valve (204) are opened, and the stepping motor (303) drives the driving piston (302) to move to the left at a uniform speed, pushing the gas in the tube to flow through the flow meter (201) to be tested and enter the metering cylinder (101), thereby realizing flow calibration.

8. The calibration method according to claim 5, characterized in that: During the calibration preparation phase, the pipeline is purged as follows: when the metering piston (102) is at the lowest position, the metering piston inlet valve (204) is closed, the drain valve (205) and the flow meter inlet valve (202) are opened, and the piston (302) is driven to push the air flow in the pipeline to flow and drain.

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