阅读说明：本技术 基于压力检测的质量流量控制方法及装置 (mass flow control method and device based on pressure detection ) 是由 何漫丽 牟昌华 王瑞 于 2018-10-31 设计创作，主要内容包括：本发明公开了一种基于压力检测的质量流量控制方法及装置。该方法包括：检测气体通道中的喉口前端流道的压力和喉口后端流道的压力；计算所述喉口后端流道的压力和所述喉口前端流道的压力的比值；判断所述比值是否小于设定临界值,如是,则计算气体通道输出的气体流量值,根据所计算的气体流量值与预期流量值的偏差值调整气体通道的气体入口处的控制阀的开度,使气体通道输出的流量值达到所述预期流量值；如否,则气体通道不输出流量。本发明基于喉口两端流道的压力判断气体的流动状态,以准确计算在不同压力状态下的气体流量；并针对不同的流动状态设置相应的控制方式,实现了对气体质量流量的精确控制。(the invention discloses a mass flow control method and device based on pressure detection. The method comprises the following steps: detecting the pressure of a flow passage at the front end of the throat opening and the pressure of a flow passage at the rear end of the throat opening in the gas passage; calculating the ratio of the pressure of the flow passage at the rear end of the throat to the pressure of the flow passage at the front end of the throat; judging whether the ratio is smaller than a set critical value or not, if so, calculating a gas flow value output by the gas channel, and adjusting the opening of a control valve at a gas inlet of the gas channel according to the deviation value of the calculated gas flow value and an expected flow value to enable the flow value output by the gas channel to reach the expected flow value; if not, the gas channel does not output flow. The invention judges the flowing state of the gas based on the pressure of the flow channels at the two ends of the throat so as to accurately calculate the gas flow under different pressure states; and corresponding control modes are set for different flow states, so that the accurate control of the gas mass flow is realized.)

1. a mass flow control method based on pressure detection is characterized by comprising the following steps:

Detecting the pressure of a flow passage at the front end of the throat opening and the pressure of a flow passage at the rear end of the throat opening in the gas passage;

Calculating the ratio of the pressure of the flow passage at the rear end of the throat to the pressure of the flow passage at the front end of the throat;

judging whether the ratio is smaller than a set critical value or not, if so, calculating a gas flow value output by the gas channel, and adjusting the opening of a control valve at a gas inlet of the gas channel according to the deviation value of the calculated gas flow value and an expected flow value to enable the flow value output by the gas channel to reach the expected flow value; if not, the gas channel does not output flow.

2. the pressure sensing based mass flow control method of claim 1, wherein the set critical value R is calculated according to equation (1):

R＝(2/(r+1)) (1)

wherein r is the specific heat ratio of the gas.

3. the pressure sensing based mass flow control method of claim 1, wherein when the ratio is less than the set threshold value, a gas flow value Qc is calculated according to equation (2):

wherein p1 is the pressure of the throat front end runner, r is the specific heat ratio of the gas, Mw is the molar mass of the gas, T1 is the temperature at the inlet of the throat front end runner, A is the throat cross-sectional area, and C is a constant.

4. The mass flow control method based on pressure detection as claimed in claim 1, wherein the cross-sectional area of the inlet of the throat front end flow passage and the cross-sectional area of the throat satisfy the relation (3):

(A1/A)＝1/Mal·(2/(r+1)·(1+r-1)/2·Mal)) (3)

a1 is the cross-sectional area of the inlet of the flow channel at the front end of the throat, A is the cross-sectional area of the throat, Ma1 is the Mach number at the position of the throat, and r is the specific heat ratio of the gas.

5. The pressure-sensing-based mass flow control method according to claim 3, further comprising closing the control valve at the gas inlet of the gas channel and calculating a zero-point leakage, specifically comprising:

When the ratio is not less than the set critical value, calculating the gas flow value Qc according to the formula (4):

Wherein p2 is the pressure of the throat rear end runner, Ma is Mach number, Ma is obtained by calculation according to the formula (5):

6. A mass flow control device based on pressure sensing, comprising:

The gas channel comprises a throat, a throat front end flow channel and a throat rear end flow channel;

the first pressure sensor and the second pressure sensor are used for respectively detecting the pressure of the flow passage at the front end of the throat and the pressure of the flow passage at the rear end of the throat;

a control unit that outputs a control signal based on detection results of the first pressure sensor and the second pressure sensor;

The control valve is arranged at a gas inlet of the gas channel, and the opening degree of the control valve is controlled by a control signal of the control unit;

The control unit calculates the ratio of the pressure of the flow passage at the rear end of the throat to the pressure of the flow passage at the front end of the throat and judges whether the ratio is smaller than a set critical value or not; if so, the control unit calculates a gas flow value, outputs a control signal according to a deviation value of the calculated gas flow value and an expected flow value to adjust the opening of the control valve, and controls the gas flow entering the gas channel so that the output value at the outlet of the gas channel reaches the expected flow value; if not, the gas channel does not output flow.

7. A pressure sensing based mass flow control device according to claim 6, wherein the control unit calculates the set threshold R according to equation (1):

R＝(2/(r+1)) (1)

Wherein r is the specific heat ratio of the gas.

8. A pressure sensing based mass flow control device according to claim 6, wherein when the ratio is less than the set threshold, the control unit calculates a gas flow value Qc according to equation (2):

Wherein p1 is the pressure of the throat front end runner, r is the specific heat ratio of the gas, Mw is the molar mass of the gas, T1 is the temperature at the inlet of the throat front end runner, A is the throat cross-sectional area, and C is a constant.

9. The pressure-sensing-based mass flow control device according to claim 6, wherein the cross-sectional area of the throat front end flow passage at the inlet and the cross-sectional area of the throat satisfy the relation (3):

(A1/A)＝1/Mal·(2/(r+1)·(1+r-1)/2·Mal)) (3)

A1 is the cross-sectional area of the inlet of the flow channel at the front end of the throat, A is the cross-sectional area of the throat, Ma1 is the Mach number at the position of the throat, and r is the specific heat ratio of the gas.

10. a pressure sensing based mass flow control device according to claim 8, wherein the control unit further calculates a zero point leakage when the control valve is in a closed state, in particular by:

when the ratio is not less than the set critical value, the control unit calculates a gas flow value Qc according to formula (4):

Wherein p2 is the pressure of the throat rear end runner, Ma is Mach number, Ma is obtained by calculation according to the formula (5):

11. A pressure sensing based mass flow control device according to claim 6, wherein the first and second pressure sensors each comprise a thermistor for sensing the temperature of the gas.

Technical Field

The invention relates to the field of gas flow control, in particular to a mass flow control method and device based on pressure detection.

Background

Mass Flow Controllers (MFCs) are gas flow control devices that provide high precision and rapid response, and are used in many fields, such as semiconductor and integrated circuit processes, specialty materials, chemical industry, petroleum industry, medicine, environmental protection, and vacuum, for research and production.

In the semiconductor field, especially in the key processes of the semiconductor process, such as etching, etc., the gas mass flow controller has high requirements on the aspects of precision, zero drift, response time, gas cleanliness, etc.

the main performance indexes of the mass flow controller comprise control precision, response speed, stability, repeatability, consistency and the like.

The operating principles of widely used gas mass flow controller products worldwide are mainly thermal type and differential pressure type.

Thermal MFCs were the earliest mass flow controllers and were most widely used. The MFC with the principle is obviously influenced by the temperature and mainly comprises the following two aspects: (1) before use, the electric heating device needs to be electrified and preheated for several minutes or even dozens of minutes so as to enable the zero point of the electric heating device to reach a stable state; the instability of the zero point causes the reduction of the precision and the repeatability of the controller; (2) thermal MFC response time is longer due to the relatively slow gas temperature change. Differential pressure MFCs achieve flow through a flow controller based on low reynolds number laminar flow, the flow being proportional to the pressure differential. The MFC based on the principle has high control precision, high response speed and relatively complex laminar flow structure, but is difficult to machine and manufacture, and the consistency is obviously influenced by the machining precision. Therefore, it is desirable to develop a gas mass flow control method and apparatus that has high accuracy, fast response, and a simple and reliable structure.

The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides a mass flow control method and a mass flow control device based on pressure detection, which ensure the flow accuracy in each pressure state by judging the gas flow state.

according to one aspect of the invention, a method of mass flow control based on pressure sensing is provided. The method comprises the following steps:

detecting the pressure of a flow passage at the front end of the throat opening and the pressure of a flow passage at the rear end of the throat opening in the gas passage;

Calculating the ratio of the pressure of the flow passage at the rear end of the throat to the pressure of the flow passage at the front end of the throat;

Judging whether the ratio is smaller than a set critical value or not, if so, calculating a gas flow value output by the gas channel, and adjusting the opening of a control valve at a gas inlet of the gas channel according to the deviation value of the calculated gas flow value and an expected flow value to enable the flow value output by the gas channel to reach the expected flow value; if not, the gas channel does not output flow.

preferably, the set critical value R is calculated according to formula (1):

R＝(2/(r+1)) (1)

Wherein r is the specific heat ratio of the gas.

Preferably, when said ratio is less than said set threshold value, the gas flow value Qc is calculated according to formula (2):

Wherein p1 is the pressure of the throat front end runner, r is the specific heat ratio of the gas, Mw is the molar mass of the gas, T1 is the temperature at the inlet of the throat front end runner, A is the throat cross-sectional area, and C is a constant.

preferably, the cross-sectional area of the inlet of the throat front end flow passage and the cross-sectional area of the throat satisfy the relation (3):

(A1/A)＝1/Mal·(2/(r+1)·(1+r-1)/2·Mal)) (3)

A1 is the cross-sectional area of the inlet of the flow channel at the front end of the throat, A is the cross-sectional area of the throat, Ma1 is the Mach number at the position, and r is the specific heat ratio of the gas.

Preferably, the method further comprises closing the control valve at the gas inlet of the gas channel and calculating the zero point leakage amount, and specifically comprises:

when the ratio is not less than the set critical value, calculating the gas flow value Qc according to the formula (4):

Wherein p2 is the pressure of the throat rear end runner, Ma is Mach number, Ma is obtained by calculation according to the formula (5):

according to another aspect of the present invention, a mass flow control device for pressure sensing is provided. The device includes:

the gas channel comprises a throat, a throat front end flow channel and a throat rear end flow channel;

The first pressure sensor and the second pressure sensor are used for respectively detecting the pressure of the flow passage at the front end of the throat and the pressure of the flow passage at the rear end of the throat;

A control unit that outputs a control signal based on detection results of the first pressure sensor and the second pressure sensor;

The control valve is arranged at a gas inlet of the gas channel, and the opening degree of the control valve is controlled by a control signal of the control unit;

The control unit calculates the ratio of the pressure of the flow passage at the rear end of the throat to the pressure of the flow passage at the front end of the throat and judges whether the ratio is smaller than a set critical value or not; if so, the control unit calculates a gas flow value, outputs a control signal according to a deviation value of the calculated gas flow value and an expected flow value to adjust the opening of the control valve, and controls the gas flow entering the gas channel so that the output value at the outlet of the gas channel reaches the expected flow value; if not, the gas channel does not output flow.

Preferably, the control unit calculates the set critical value R according to formula (1):

R＝(2/(r+1)) (1)

wherein r is the specific heat ratio of the gas.

Preferably, when said ratio is less than said set threshold, said control unit calculates a gas flow value Qc according to formula (2):

wherein p1 is the pressure of the throat front end runner, r is the specific heat ratio of the gas, Mw is the molar mass of the gas, T1 is the temperature at the inlet of the throat front end runner, A is the throat cross-sectional area, and C is a constant.

preferably, the cross-sectional area of the inlet of the throat front end flow passage and the cross-sectional area of the throat satisfy the relation (3):

(A1/A)＝1/Mal·(2/(r+1)·(1+r-1)/2·Mal)) (3)

A1 is the cross-sectional area of the inlet of the flow channel at the front end of the throat, A is the cross-sectional area of the throat, Ma1 is the Mach number at the position, and r is the specific heat ratio of the gas.

preferably, when the control valve is in the closed state, the control unit further calculates a zero-point leakage amount, specifically, the zero-point leakage amount is calculated by:

When the ratio is not less than the set critical value, the control unit calculates a gas flow value Qc according to formula (4):

Wherein p2 is the pressure of the throat rear end runner, Ma is Mach number, Ma is obtained by calculation according to the formula (5):

preferably, the first and second pressure sensors each comprise a thermistor for detecting the temperature of the gas.

The invention judges the flowing state of the gas based on the pressure of the flow channels at the two ends of the throat so as to accurately calculate the gas flow under different pressure states; and corresponding control modes are set for different flow states, so that the accurate control of the gas mass flow is realized.

furthermore, the flow state of the gas is judged by using the critical condition of sonic flow, so that the flow accuracy under each pressure state is ensured.

the method of the present invention has other features and advantages which will be apparent from or are set forth in detail in the accompanying drawings and the following detailed description, which are incorporated herein, and which together serve to explain certain principles of the invention.

drawings

the above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings, in which like reference numerals generally represent like parts.

FIG. 1 illustrates a flow diagram of a method of mass flow control based on pressure sensing, according to an exemplary embodiment of the present invention;

FIG. 2 illustrates a schematic diagram of a mass flow control device based on pressure sensing, according to an exemplary embodiment of the present invention;

Fig. 3 shows a block diagram of the apparatus shown in fig. 2.

description of reference numerals:

10 gas channel

11 throat

12 throat front end runner

13 throat rear end flow channel

14 gas inlet

15 gas outlet

20 first pressure sensor

30 second pressure sensor

40 control unit

50 control valve

51 valve body

52 control valve drive unit

60, a housing.

Detailed Description

the invention will be described in more detail below with reference to the accompanying drawings. While the preferred embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

FIG. 1 illustrates a pressure sensing based mass flow control method according to an exemplary embodiment of the present invention, which mainly includes steps S1-S5; fig. 2 shows a schematic view of a corresponding mass flow control device.

in step S1, the pressure p1 of the throat front end flow path and the pressure p2 of the throat rear end flow path in the gas passage are detected.

the throat in the gas channel is shown in fig. 2, which forms the narrowest part of the gas channel. The flow channel at the front end of the throat is the part of the gas channel which is transited to the throat, and the flow channel at the rear end of the throat is the part of the throat which is transited to the gas channel.

in step S2, the ratio p2/p1 of the pressure p2 of the throat rear end flow passage and the pressure p1 of the throat front end flow passage is calculated.

In step S3, it is determined whether the ratio p2/p1 is less than a set threshold.

For the mass flow control device shown in fig. 2, the flow span is determined by the throat in the gas channel. The flow of gas through the throat can be divided into non-choked and choked flows by its mach number. Mach number Ma is a parameter that determines what state the gas is in, which is the ratio of the gas flow rate to the speed of sound through the gas at that state. The Mach number is calculated as follows:

When the ratio of the pressure p2 of the flow passage at the back end of the throat to the pressure of the flow passage at the back end of the throat

when p2/p1 > (2/(r +1)) r/(r-1), Ma <1, the gas is in a subsonic flow state, namely a non-blocking flow state, and the flow rate passing through the throat is in a nonlinear relation with the front end pressure p1 and the rear end pressure p2 of the flow channel; when p2/p1 is less than or equal to (2/(r +1)) r/(r-1), the gas flows at the throat at sonic speed, namely in a blocking flow state, and the flow rate through the throat is not influenced by the outlet pressure p2 at the rear end of the throat.

Therefore, the relationship between the ratio p2/p1 and the set threshold value R can be used as a condition for judging whether the gas blocks the flow. The set threshold value R is calculated by the formula (1):

R＝(2/(r+1)) (1)

wherein r is the specific heat ratio of the gas, which is the ratio of the constant pressure specific heat capacity and the constant volume specific heat capacity of the gas.

If the ratio p2/p1 is smaller than the predetermined threshold R, i.e. the gas is in a choked flow state at the throat, go to step S4; if the ratio p2/p1 is not less than the set threshold R, i.e. the gas is in a non-choked flow state at the throat, step S5 is performed.

In step S4, the gas flow rate value Qc outputted by the number of gas passages in the blocked flow state is first calculated.

Specifically, the gas flow value Qc may be calculated according to equation (2):

Wherein p1 is the pressure of the flow channel at the front end of the throat, r is the specific heat ratio of the gas, Mw is the molar mass of the gas, T1 is the temperature at the inlet of the flow channel at the front end of the throat, A is the cross-sectional area (i.e. the hydraulic area) of the throat, and C is a constant. Because of the influence of factors such as processing and manufacturing limitations, the actual flow and the theoretical calculated value have certain errors and can be corrected by calibrating and setting a constant C.

For example, the specific heat ratio R of gaseous phosphorus trifluoride (PF3) commonly used in the semiconductor industry is 1.165 at 101325Pa and 250 ℃, and the threshold value R is set to 0.575. Namely, if the detected pressure ratio of the flow passage at the rear end of the throat to the flow passage at the front end of the throat is smaller than the R value, the gas flow value is calculated according to the blocking flow state.

For a given expected flow rate value Qs outputted by the gas channel, a deviation Δ Q between the gas flow rate value Qc calculated in the blocked flow state and the expected flow rate value Qs is obtained as Qs-Qc, and the opening of the control valve at the gas inlet of the gas channel is adjusted according to the deviation, so that the flow rate value outputted by the gas channel reaches the given expected flow rate value Qs by changing the flow rate of the gas entering the gas channel. The control valve may be, but is not limited to, a piezoelectric valve.

In step S5, since the gas is in a non-choked flow state at the throat, the pressure condition at this time does not satisfy the use condition of the flow rate control, and therefore, the gas passage does not output the flow rate.

in this state, the gas flow rate value Qc is calculated according to the formula (4):

In the present embodiment, the zero point leak value can be calculated using the gas flow rate values calculated in the blocked flow state and the non-blocked flow state, contributing to improvement of safety.

when the control valve is closed, the flow output from the gas passage should be zero. Sometimes, however, for some reason, the flow rate may not be zero, and there is a zero-point flow rate, i.e., a zero-point leakage rate. At the moment, the pressure of the front end flow channel and the rear end flow channel of the throat is used for determining whether the gas is in a blocked flow state or a non-blocked flow state at the throat, then a formula for calculating the gas flow value is selected according to different states, and the calculated gas flow value is the zero leakage.

in this embodiment, the cross-sectional area a1 of the inlet of the throat front end channel and the cross-sectional area a of the throat are designed to obtain the sonic flow of the fluid at the throat, so as to obtain the linear relationship between the flow rate and the pressure at the throat front end, and obtain a smaller channel volume, so that the pressure in the throat front end channel can be rapidly detected, thereby shortening the response time.

Specifically, the cross-sectional area a1 at the inlet of the flow passage at the front end of the throat and the cross-sectional area a of the throat satisfy the relation (3):

(A1/A)＝1/Ma1·(2/(r+1)·(1+(r-1)/2·Ma1)) (3)

Where Ma1 is the mach number at the throat position, and r is the specific heat ratio of the gas.

the invention also provides a mass flow control device based on pressure detection. As shown in fig. 2, the apparatus includes a gas passage 10, a first pressure sensor 20, a second pressure sensor, a control unit 40, and a control valve 50.

The gas passage 10 includes a throat 11, a throat front end flow channel 12, a throat rear end flow channel 13, a gas inlet 14, and a gas outlet 15. The throat 11 forms the narrowest part of the gas channel, the throat front end flow passage 12 is the part of the gas channel which is transited to the throat 11, and the throat rear end flow passage 13 is the part of the throat 11 which is transited to the gas channel.

The first pressure sensor 20 and the second pressure sensor 30 detect the pressure of the throat front end flow path 12 and the pressure of the throat rear end flow path 13, respectively.

In one example, the first pressure sensor 20 and the second pressure sensor 30 are pressure sensors that can extract temperature signals.

Specifically, each of the first pressure sensor 20 and the second pressure sensor 30 includes a thermistor, and a pressure signal detected by the pressure sensor is output through the thermistor, and a change in gas temperature causes a change in resistance value, so that the gas temperature can be obtained by a change in resistance value of the thermistor. It will be appreciated by those skilled in the art that the temperature of the gas in the gas channel may also be obtained by providing a separate temperature sensor.

The control valve 50 includes a valve body 51 and a control valve driving unit 52, the valve body 51 being provided at the gas inlet 14 of the gas channel 10 with an opening degree controlling a flow rate flowing into the gas channel 10; the control valve driving unit 52 is connected between the valve body 51 and the control unit 40, and the control valve driving unit 52 controls the opening degree of the valve body 51 according to a control signal output from the control unit 40.

The specific structure of the mass flow control device based on pressure detection is shown in fig. 3, in which a housing 60 is also shown.

The mass flow control device based on pressure detection controls the output flow rate of the gas based on the above method.

in the present embodiment, the cross-sectional area a1 at the inlet of the throat front end flow channel 12 and the cross-sectional area a of the throat 11 are also designed to obtain the sonic flow of the fluid at the throat 11, so as to obtain the linear relationship between the flow rate and the pressure at the throat front end, and obtain a smaller flow channel volume, so that the first pressure sensor 20 can quickly detect the gas pressure in the throat front end flow channel 12, thereby shortening the response time.

Specifically, the cross-sectional area a1 at the inlet of the flow passage at the front end of the throat and the cross-sectional area a of the throat satisfy the relation (3):

(A1/A)＝1/Ma1·(2/(r+1)·(1+(r-1)/2·Ma1)) (3)

Where Ma1 is the mach number at the throat position, and r is the specific heat ratio of the gas.

In the embodiment, two throat structures with small flow and large flow can be designed, so that the device has a wide measuring range; by using the control valve with quick response characteristic and the control valve high-pressure driving system, the response time of the whole control device can be shortened by matching with a smaller fluid passage area.

having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.