Flow rate calculation device and method for calculating flow rate

Abstract

To calculate the flow rate of a fluid while avoiding increase of size of the whole device even when the flow rate of the fluid is large.SOLUTION: A flow rate calculation device is for calculating the flow rate of a fluid flowing in a main flow passage, and includes: a specific flow passage and a bypass flow passage branching from a main flow passage and dividing a fluid; a first fluid resistive element provided in the specific flow passage; a second fluid resistive element provided in the bypass flow passage; a container arranged in the downstream side of the first fluid resistive element in the specific flow passage; a pressure sensor for detecting the pressure in the container; and a flow rate calculation unit for calculating the flow rate of a first branch fluid branching into the specific flow passage on the basis of change of the pressure in the container and calculating the flow rate of the fluid flowing in the main flow passage on the basis of the calculated flow rate of the first branch fluid and the flow division ratio of the first flow fluid resistive element and the second fluid resistive element.SELECTED DRAWING: Figure 1

Description

[Technical field] 【0001】 The present invention relates to a flow rate calculation device and a flow rate calibration method. [Background technology] 【0002】 Conventionally, the RoR (Rate of Rise) method has been known as one method for measuring the flow rate of a fluid. The RoR method is a method in which a fluid (e.g., gas) is made to flow from a test object (e.g., a flow control device) into an evacuated container, and the flow rate is calculated from the pressure rise rate inside the container using the state equation of the fluid. For example, Patent Document 1 discloses an apparatus for verifying the flow rate of a fluid using the RoR method. [Prior art documents] [Patent documents] 【0003】 [Patent Document 1] International Publication No. 2018 / 111725 Summary of the Invention [Problem to be solved by the invention] 【0004】 However, when using the RoR method, if the flow rate of the fluid to be verified increases, a large (large-capacity) container must be prepared accordingly, which increases the size of the entire apparatus. 【0005】 The present invention has been made to solve the above problems, and its object is to provide a flow rate calculation device and a flow rate calibration method that can calculate the flow rate of a fluid while avoiding an increase in the size of the entire device, even when the flow rate of the fluid is large. [Means for solving the problem] 【0006】 A flow rate calculation device according to one aspect of the present invention is a flow rate calculation device that calculates a flow rate of a fluid flowing through a main flow path, and includes a specific flow path and a bypass flow path branching off from the main flow path and into which the fluid is diverted, a first fluid resistance element provided in the specific flow path, a second fluid resistance element provided in the bypass flow path, a container arranged downstream of the first fluid resistance element in the specific flow path, a pressure sensor that detects the pressure in the container, and a flow rate calculation unit that calculates the flow rate of a first branched fluid diverted to the specific flow path based on a change in the pressure in the container, and calculates the flow rate of the fluid flowing through the main flow path based on the calculated flow rate of the first branched fluid and a diversion ratio determined according to the first fluid resistance element and the second fluid resistance element. 【0007】 A flow rate calculation method according to another aspect of the present invention includes the steps of: calculating the flow rate of a first branched fluid flowing through a specific flow path based on a change in pressure in a container arranged downstream of a first fluid resistance element in the specific flow path when a fluid flowing through a main flow path is diverted into a specific flow path and a bypass flow path branched off from the main flow path; and calculating the flow rate of the fluid flowing through the main flow path based on the calculated flow rate of the first branched fluid and a diversion ratio determined depending on the first fluid resistance element and a second fluid resistance element provided in the bypass flow path. Effect of the Invention 【0008】 According to the present invention, even when the flow rate of a fluid is large, it is possible to calculate the flow rate of the fluid while avoiding an increase in the size of the entire device. [Brief description of the drawings] 【0009】 [Figure 1] 1 is an explanatory diagram showing a schematic configuration of a flow rate calculation device according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a perspective view showing an example of a configuration of a pressure loss element. [Diagram 3] FIG. 4 is an exploded perspective view showing another configuration example of the pressure loss element. [Figure 4] FIG. 2 is a block diagram showing a detailed configuration of a control arithmetic device. [Diagram 5] 4 is a flowchart showing the flow of each step in a flow rate calculation method. [Figure 6] FIG. 4 is an explanatory diagram showing another configuration of the flow rate calculation device. [Figure 7] FIG. 11 is an explanatory diagram showing still another configuration of the flow rate calculation device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 【0010】 Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following description, the side into which a fluid flows with respect to any component of a flow rate calculation device is also referred to as the upstream side or primary side, and the side into which a fluid flows with respect to the component is also referred to as the downstream side or secondary side. 【0011】 [1. Configuration of the flow rate calculation device] 1 is an explanatory diagram showing a schematic configuration of a flow rate calculation device 1 of this embodiment. The flow rate calculation device 1 calculates the flow rate of a fluid F flowing out of a flow control device 100 and flowing through a main flow path L0 by a method described later. Then, the flow rate calculation device 1 diagnoses the flow rate control device 100 based on the calculated flow rate and the set flow rate of the fluid F flowing out of the flow control device 100, and performs calibration as necessary. As the above-mentioned fluid F, for example, a material gas used in a semiconductor manufacturing process can be assumed. 【0012】 The flow rate control device 100 is a device that flows a fluid F into the main flow path L0, and is a device that is a diagnostic target (Device Under Test) by the flow rate calculation device 1. The flow rate control device 100 is, for example, configured as a mass flow controller that controls the flow rate of the fluid F, but is not limited to this example. 【0013】 The flow rate calculation device 1 includes a specific flow path L1 and a bypass flow path L2. The specific flow path L1 and the bypass flow path L2 are provided by branching off from the main flow path L0. The fluid F that flows out of the flow control device 100 and flows through the main flow path L0 is branched off into the specific flow path L1 and the bypass flow path L2. In this specification, the term "branched" refers to a fluid being branched off and flowing. Hereinafter, the fluid that branches off from the main flow path L0 to the specific flow path L1 is also referred to as a first branched fluid F1, and the fluid that branches off from the main flow path L0 to the bypass flow path L2 is also referred to as a second branched fluid F2. That is, the fluid F is branched off into the first branched fluid F1 and the second branched fluid F2 at the branch point between the specific flow path L1 and the bypass flow path L2, and then flows through the specific flow path L1 and the bypass flow path L2, respectively. 【0014】 The specific flow path L1 and the bypass flow path L2 join downstream of a container TA (described later) disposed in the specific flow path L1, and are connected to a joining line L3. The joining line L3 is connected to a pump PU. Therefore, the bypass flow path L2 is provided between the main flow path L0 and the joining line L3 so as to bypass the container TA of the specific flow path L1. 【0015】 The flow rate calculation device 1 further includes a first fluid resistance element RE1 and a second fluid resistance element RE2. The first fluid resistance element RE1 is provided in the specific flow path L1. The second fluid resistance element RE2 is provided in the bypass flow path L2. 【0016】 The first fluid resistance element RE1 and the second fluid resistance element RE2 are composed of, for example, a pressure loss element PL (see FIG. 2). The pressure loss element PL refers to an element that causes pressure loss (energy loss) to a fluid. The first fluid resistance element RE1 is provided in the specific flow path L1, and therefore causes a pressure loss to the first branch fluid F1 flowing through the specific flow path L1. The second fluid resistance element RE2 is provided in the bypass flow path L2, and therefore causes a pressure loss to the second branch fluid F2 flowing through the bypass flow path L2. 【0017】 For example, when flow path resistance is generated, a pressure loss is given to the fluid. When a pressure loss is given to the fluid, for example, the flow rate of the fluid decreases under the same pressure conditions. For this reason, the pressure loss element PL functions as an element that limits the flow rate, that is, a fluid resistance element that provides resistance when the fluid flows. Hereinafter, the pressure loss element PL constituting the first fluid resistance element RE1 is also referred to as the first pressure loss element PL1, and the pressure loss element PL constituting the second fluid resistance element RE2 is also referred to as the second pressure loss element PL2. 【0018】 2 is a perspective view showing one configuration example of the pressure loss element PL. The pressure loss element PL is configured to have a flow path forming member 10 and a covering member 20. The covering member 20 may be provided as necessary. 【0019】 The flow passage forming member 10 is made of ceramics such as quartz, alumina, zirconia, or silicon nitride, and is formed into a cylindrical shape. The flow passage forming member 10 has at least one flow passage 10a (hereinafter also referred to as resistance flow passage 10a) that serves as a resistance. The resistance flow passage 10a penetrates the flow passage forming member 10 in the axial direction and is formed to have a circular cross section. When the covering member 20 is provided, the covering member 20 is made of a metal that is at least lower in hardness than ceramics, such as stainless steel or a nickel-based alloy. Such a pressure loss element PL is also called a ceramic restrictor, meaning that it is a restrictor made of at least ceramics. 【0020】 The flow resistance of the pressure loss element PL is determined based on the aspect ratio and the number of resistance flow paths 10a. The aspect ratio refers to the ratio of the length dimension in the axial direction to the diameter dimension of the resistance flow path 10a. Therefore, when the aspect ratio of the resistance flow path 10a is constant, the flow resistance of the pressure loss element PL can be easily adjusted by changing the number of resistance flow paths 10a. Therefore, the flow rate of the fluid flowing through the pressure loss element PL can be easily adjusted by changing the number of resistance flow paths 10a. 【0021】 In addition, a fluid resistance element (flow restrictor) used in a differential pressure type flow control device (mass flow controller) can also be suitably used as the pressure loss element PL. Fig. 3 is an exploded perspective view showing the schematic configuration of a flow restrictor as another configuration example of the pressure loss element PL. 【0022】 The flow restrictor is an element that generates a pressure difference (differential pressure) between two pressure sensors included in the mass flow controller. As shown in the figure, the flow restrictor has a structure in which circular slit plates 31 and circular slit covering plates 32 are alternately laminated. The slit plates 31 and the slit covering plates 32 are made of a metal such as stainless steel (Steel Use Stainless). In other words, the flow restrictor is a restrictor made of a metal. 【0023】 The slit plate 31 has a first through hole 31a penetrating the center in the thickness direction and a plurality of slits 31b formed radially from the center. The slit covering plate 32 has a second through hole 32a penetrating the center in the thickness direction. The outer diameter of the slit covering plate 32 is smaller than the outer diameter of the slit plate 31, and the inner diameter is larger than the inner diameter of the slit plate 31. 【0024】 By stacking the slit plate 31 and the slit covering plate 32, the inner end of the slit 31b becomes the start of the resistance flow path, and the outer end of the slit 31b becomes the end of the resistance flow path. Also, the first through hole 31a of the slit plate 31 and the second through hole 32a of the slit covering plate 32 form a through hole that penetrates the center of the flow restrictor along the stacking direction. The above-mentioned through hole serves as a fluid introduction portion. 【0025】 The number of the resistance flow paths is changed by changing the number of stacked slit plates 31 and slit covering plates 32. Therefore, similar to the case of the ceramic restrictor, the flow rate of the fluid flowing through the flow restrictor can be easily adjusted by changing the number of stacked plates. 【0026】 The pressure loss element PL is not limited to the ceramic restrictor and flow restrictor described above. Any element that can restrict the flow rate of a fluid by applying a pressure loss to the fluid can be used as the pressure loss element PL. In this respect, even an element such as an orifice can be used as the pressure loss element PL. 【0027】 As shown in FIG. 1, the flow rate calculation device 1 further includes a main flow path pressure sensor P1, a container TA, a specific flow path pressure sensor P2, a temperature sensor T, a bypass flow path pressure sensor P3, a control valve CV, a first on-off valve V1, and a second on-off valve V2. 【0028】 The main flow path pressure sensor P1 (main flow path pressure detection unit) measures the pressure of the fluid flowing through the main flow path L0. The container TA is a tank located downstream of the first fluid resistance element RE1 in the specific flow path L1. The first branch fluid F1 flowing through the specific flow path L1 flows into the container TA. The specific flow path pressure sensor P2 detects the pressure inside the container TA. The temperature sensor T detects the gas temperature inside the container TA. Note that if the gas temperature inside the container TA is equivalent to the temperature of the outer wall surface or inner wall surface of the container TA, the temperature sensor T may detect the temperature of the outer wall surface or inner wall surface of the container TA. 【0029】 The bypass flow path pressure sensor P3 is disposed downstream of the second fluid resistance element RE2 in the bypass flow path L2 and measures the pressure of the second branch fluid F2 flowing through the second fluid resistance element RE2. The control valve CV is provided to control the flow rate of the second branch fluid F2 flowing through the bypass flow path L2 via the second fluid resistance element RE2. The control valve CV is formed of, for example, an electromagnetic proportional valve, but may be formed of another valve (flow rate control valve). 【0030】 The first on-off valve V1 is located downstream of the container TA in the specific flow path L1 and opens and closes the flow path. The second on-off valve V2 is located downstream of the second fluid resistance element RE2, particularly downstream of the control valve CV, in the bypass flow path L2 and opens and closes the flow path. The first on-off valve V1 and the second on-off valve V2 are, for example, pneumatic valves, but may be other valves. 【0031】 The flow rate calculation device 1 further includes a control arithmetic unit COM. The control arithmetic unit COM is configured by, for example, a computer including a central processing unit (CPU). The control arithmetic unit COM performs various calculations based on detection signals output from the instruments (main flow path pressure sensor P1, specific flow path pressure sensor P2, temperature sensor T, bypass flow path pressure sensor P3) included in the flow rate calculation device 1, and controls the valves (control valve CV, first on-off valve V1, second on-off valve V2) included in the flow rate calculation device 1. 【0032】 Fig. 4 is a block diagram showing a detailed configuration of the control arithmetic device COM. The control arithmetic device COM includes a control unit 50 and a storage unit 60. The control arithmetic device COM further includes an input unit (e.g., a keyboard, a mouse, a touch panel), a display unit (e.g., a liquid crystal display device), a communication unit (e.g., a connector, an adapter), etc., but since the input unit etc. are not essential components in this embodiment, they are not shown in Fig. 4. 【0033】 The control unit 50 includes a main control unit 51, a flow rate calculation unit 52, and an equipment diagnosis unit 53. The main control unit 51 controls the operation of each unit of the control arithmetic device COM, and outputs a control signal for controlling the valves of the flow rate calculation device 1. 【0034】 The flow rate calculation unit 52 calculates the flow rate of the fluid F flowing through the main flow path L0 based on the detection signals output from the above-mentioned meters of the flow rate calculation device 1. Specifically, the flow rate calculation unit 52 has a specific flow path measurement unit 52a, a bypass flow path control unit 52b, a division ratio calculation unit 52c, and a main flow path calculation unit 52d. 【0035】 The specific flow path measuring unit 52a measures the flow rate of the first branched fluid F1 branched to the specific flow path L1 by using the RoR method. The bypass flow path control unit 52b controls the control valve CV arranged in the bypass flow path L2. The branch flow ratio calculation unit 52c calculates the ratio (branch flow ratio) between the flow rate of the first branched fluid F1 branched from the main flow path L0 to the specific flow path L1 and the flow rate of the second branched fluid F2 branched from the main flow path L0 to the bypass flow path L2. The main flow path calculation unit 52d calculates the flow rate of the fluid F flowing through the main flow path L0 by using the flow rate of the first branched fluid F1 and the above branch flow ratio. The method of calculating the above flow rates will be described in detail later. 【0036】 The device diagnostic unit 53 diagnoses the flow control device 100 that flows the fluid F into the main flow path L0. The flow control device 100 may become unable to control the flow rate according to the set flow rate due to aging, clogging of the flow path, some kind of malfunction, etc. For this reason, the device diagnostic unit 53 periodically diagnoses whether the flow control device 100 is able to control the flow rate according to the set flow rate based on the flow rate calculated by the flow rate calculation unit 52. 【0037】 The storage unit 60 is a memory that stores the operation program of the control unit 50, as well as various information (detected measurement values) included in the detection signals output from the above-mentioned instruments of the flow rate calculation device 1, information about the first fluid resistance element RE1 and the second fluid resistance element RE2 (e.g., information about the number of resistance flow paths), etc. Such a storage unit 60 can be composed of, for example, a hard disk, an SSD (solid state drive), an optical disk, a magnetic disk, or a non-volatile memory. 【0038】 As shown in FIG. 1, the flow rate calculation device 1 further includes a main flow path thermometer T0. The main flow path thermometer T0 measures the temperature of the fluid F flowing through the main flow path L0. The main flow path thermometer T0 is provided to acquire temperature information required for calculation of the RoR method when correcting the flow rate of the fluid F flowing through the main flow path L0. The correction of the flow rate will be described in "4. Supplementary Information" below. When correcting the flow rate, strictly speaking, information on the temperature and pressure upstream of the first fluid resistance element RE1 in the specific flow path L1 and the temperature and pressure upstream of the second fluid resistance element RE2 in the bypass flow path L2 are required, but these can be substituted by the detection value (pressure Pr1) of the main flow path pressure sensor P1 and the detection value of the main flow path thermometer T0. 【0039】 [2. Flow rate calculation method] Fig. 5 is a flowchart showing the flow of each step in the flow rate calculation method of this embodiment. The flow rate calculation method of this embodiment will be described below with reference to Figs. 1 to 5. Note that, below, an example will be described in which flow restrictors are used as the first fluid resistance element RE1 and the second fluid resistance element RE2. Note that even when ceramic restrictors are used as the first fluid resistance element RE1 and the second fluid resistance element RE2, the flow rate calculation method described below can be applied. 【0040】 (S1: Vacuum drawing process) First, the first on-off valve V1 and the second on-off valve V2 are both opened, and the pump PU is driven to evacuate the inside of the container TA until the set pressure is reached. At this time, the outflow of the fluid F from the flow control device 100 to the main flow path L0 is stopped, but the evacuation may be performed while the fluid F is being allowed to flow. Also, the inside of the container TA does not need to be a strict vacuum. In other words, the set pressure may be a pressure at which the pressure rise rate can be calculated using the RoR method described below. 【0041】 (S2; ​​Fluid supply process) Next, the fluid F is caused to flow from the flow control device 100 to the main flow path L0 at a set flow rate Q0. Since the first on-off valve V1 and the second on-off valve V2 are open, the fluid F is diverted to the specific flow path L1 and the bypass flow path L2. After the flow rate of the first branched fluid F1 becomes stable, the first on-off valve V1 is closed. Note that the second on-off valve V2 is left open. 【0042】 (S3; CV control process) By closing the first on-off valve V1 at S2, the first branched fluid F1 flows into the container TA. This causes the pressure in the container TA to rise. At this time, the flow rate calculation unit 52 (particularly the bypass flow path control unit 52b) controls the control valve CV so that the pressure Pr3 downstream of the second fluid resistance element RE2 measured by the bypass flow path pressure sensor P3 coincides with or approaches the pressure Pr2 in the container TA detected by the specific flow path pressure sensor P2. 【0043】 By the above control, the relationship between the pressure on the primary side and the pressure on the secondary side of the fluid resistance element becomes the same or approaches the same for the specific flow path L1 and the bypass flow path L2. Therefore, the flow division ratio S can be easily expressed as the ratio between the number of resistance flow paths constituting the first fluid resistance element RE1 and the number of resistance flow paths constituting the second fluid resistance element RE2. 【0044】 The above-mentioned branch ratio S indicates the relative flow rate (S) of the first branch fluid F1 branched to the specific flow path L1, with the flow rate of the fluid F flowing through the main flow path L0 being 1 (reference). In other words, since the flow rate of the second branch fluid F2 branched to the bypass flow path L2 is (1-S), the branch ratio S is expressed as S=S / {S+(1-S)}. 【0045】 For example, when the aspect ratio of the resistance flow path is constant and the ratio between the number of resistance flow paths constituting the first fluid resistance element RE1 and the number of resistance flow paths constituting the second fluid resistance element RE2 is 1:10, the ratio of the flow rates flowing through the first fluid resistance element RE1 and the second fluid resistance element RE2 is 1:10. Therefore, the division ratio S is S=1 / (1+10). The flow rate calculation unit 52 (particularly the division ratio calculation unit 52c) calculates the division ratio S based on information (here, information on the number of resistance flow paths constituting the first fluid resistance element RE1 and the number of resistance flow paths constituting the second fluid resistance element RE2) previously stored in, for example, the storage unit 60. Note that, in order to reduce errors in the division ratio due to manufacturing errors of the fluid resistance elements, it is desirable to actually flow a fluid to obtain an actual division ratio in advance and correct a theoretical division ratio determined based on the number of resistance flow paths. 【0046】 (S4: Flow rate calculation process of the first branched fluid) Next, the flow rate calculation unit 52 (particularly the specific flow path measurement unit 52a) calculates the flow rate Q1 of the first branched fluid F1 branched to the specific flow path L1 based on the RoR method, that is, based on the pressure change in the container TA. For example, it is assumed that the pressure in the container TA increases by ΔP (Pa) during a time Δt (sec). In this case, the flow rate calculation unit 52 can calculate the flow rate Q1 based on the following formula (A) using the RoR method. Q1=(ΔP / Δt)×(V / RT)×C (A) In formula (A), V is the volume (L) of the container TA, T is the gas temperature inside the container TA detected by the temperature sensor or the temperature (K) of the outer or inner wall of the container TA, R is the gas constant, and C is the correction coefficient. Multiplying by the correction coefficient C allows conversion to mass flow rate or volumetric flow rate, changes to the reference temperature, etc. The compression coefficient, which is a physical property value, is also included in the correction coefficient C. 【0047】 (S5: Calculation process of the fluid flow rate in the main flow path) Next, the flow rate calculation unit 52 (particularly the main flow path calculation unit 52d) calculates the flow rate Q of the fluid F flowing through the main flow path L0 based on the calculated flow rate Q1 of the first branch fluid calculated in S4 and the above-mentioned branch ratio S determined according to the first fluid resistance element RE1 and the second fluid resistance element RE2. Specifically, the flow rate calculation unit 52 can calculate the flow rate Q based on the following formula (B). Q = Q1 / S (B) 【0048】 (S6: Fluid control device diagnostic process) Finally, the device diagnosis unit 53 diagnoses the flow control device 100 based on the set flow rate Q0 when the flow control device 100 flows out the fluid F and the flow rate Q of the fluid F flowing through the main flow path L0 calculated by the flow calculation unit 52. For example, if there is a difference of a predetermined value or more between the set flow rate Q0 and the actual flow rate Q, the device diagnosis unit 53 can determine that the flow control device 100 has deteriorated with age, the flow path has become clogged, or there is some kind of failure. In this case, the device diagnosis unit 53 can output a control signal for calibrating the outflow flow rate to the flow control device 100 to operate the flow control device 100 appropriately. 【0049】 As described above, the flow rate calculation unit 52 calculates the flow rate Q of the fluid F flowing through the main flow path L0 based on the calculated flow rate Q1 of the first branch fluid F1 and the branch ratio S (S4, S5). As a result, even if the flow rate of the fluid F is large, the flow rate Q of the fluid F can be calculated using a container TA large enough to allow a portion of the fluid F (first branch fluid F1) to flow in. Therefore, it is not necessary to prepare a large-capacity container TA to calculate the flow rate Q. As a result, the flow rate Q of the fluid F flowing through the main flow path L0 can be calculated while avoiding an increase in the size of the entire device. 【0050】 In particular, the flow rate calculation unit 52 calculates the flow rate Q based on the above-mentioned formula (B) (S5). Even when the flow rate Q is large, by using formula (B) that defines the relationship between the flow rate Q1, the split flow ratio S, and the flow rate Q, the flow rate Q can be reliably calculated without increasing the size of the container TA. 【0051】 In addition, since the flow rate calculation unit 52 controls the control valve CV as shown by S3, the flow division ratio S can be easily set by the ratio of the numbers of the resistance flow paths. In addition, the flow division ratio S can be easily adjusted by adjusting the number of the resistance flow paths. 【0052】 The first fluid resistance element RE1 and the second fluid resistance element RE2 are each a pressure loss element PL. This allows a fluid resistance element such as a ceramic restrictor or a throttle to be used as the pressure loss element PL. In addition, a flow restrictor used in a differential pressure type mass flow controller can also be used as the pressure loss element PL. 【0053】 Incidentally, it is preferable that the first fluid resistance element RE1 and the second fluid resistance element RE2 are composed of the same type of element. For example, it is preferable that both the first fluid resistance element RE1 and the second fluid resistance element RE2 are composed of ceramic restrictors. Alternatively, it is preferable that both the first fluid resistance element RE1 and the second fluid resistance element RE2 are composed of flow restrictors. In this case, even if the pressure on the downstream side of the fluid resistance element changes, the pressure loss (energy loss) given to the branched fluid can be made the same in the specific flow path L1 and the bypass flow path L2. This can reduce the risk that the flow division ratio S will vary due to a change in the pressure on the downstream side of the fluid resistance element. As a result, the flow rate Q of the main flow path L0 can be calculated with stable accuracy using the flow division ratio S. 【0054】 3. Other configurations of the flow rate calculation device Fig. 6 is an explanatory diagram showing another configuration of the flow rate calculation device 1. The flow rate calculation device 1 in Fig. 6 has the same configuration as that in Fig. 1, except that a pressure control device UR is disposed in the position of the control valve CV in Fig. 1. The pressure control device UR incorporates the control valve CV and pressure gauge P4 in Fig. 1. With this pressure control device UR, it is possible to control the flow rate of the fluid (the pressure of the fluid flowing through the flow path) by controlling the control valve CV based on the detection value of the pressure gauge P4. 【0055】 Even with the configuration of Fig. 6, it is possible to realize pressure control similar to S3 of Fig. 5. That is, the flow rate calculation unit 52 controls the control valve CV of the pressure control device UR to make the pressure Pr3 downstream of the second fluid resistance element RE2 coincident with or approach the pressure Pr2 in the container TA detected by the specific flow path pressure sensor P2. As a result, it is possible to obtain the same effect as above, that is, to easily adjust the division ratio S. It is considered that the pressure detection value of the pressure gauge P4 built into the pressure control device UR is equal to the pressure Pr3. 【0056】 In the configuration of Fig. 6, the pressure is adjusted by controlling the control valve CV of the pressure control device UR so that the pressure Pr3 downstream of the second fluid resistance element RE2 coincides with or approaches the pressure Pr2 in the container TA detected by the specific flow path pressure sensor P2. However, a table or a relational expression may be set in advance that indicates the relationship between the flow rate and pressure between the main flow path pressure sensor P1 and the specific flow path pressure sensor P2 in each branch flow path, and between the main flow path pressure sensor P1 and the bypass flow path pressure sensor P3. In this case, the difference in the pressure values ​​of the branch flow paths can be corrected without controlling the control valve CV as described above (even without the control valve CV), thereby achieving the same purpose. 【0057】 [4. Other configurations of the flow rate calculation device] Fig. 7 is an explanatory diagram showing yet another configuration of the flow rate calculation device 1. The flow rate calculation device 1 in Fig. 7 has the same configuration as the flow rate calculation device 1 in Fig. 1, except that critical nozzles are used as the first fluid resistance element RE1 and the second fluid resistance element RE2, and the bypass flow path pressure sensor P3 and the control valve CV are deleted. Also, the flow rate calculation method is the same as the method shown in Fig. 5, except that the process of S3 is deleted. 【0058】 The first fluid resistance element RE1 is composed of a first critical nozzle CN1. The second fluid resistance element RE2 is composed of a second critical nozzle CN2. The first critical nozzle CN1 and the second critical nozzle CN2 may have exactly the same characteristics (shape, size, minimum diameter) or may have different characteristics. 【0059】 The critical nozzle has a property that when the pressure reduction on the secondary side progresses and the flow velocity of the fluid flowing through the narrowing (throat) of the critical nozzle reaches the sonic speed (critical state), no matter how much the pressure on the downstream side of the nozzle is reduced, the flow velocity of the fluid passing through the throat does not exceed the sonic speed, and the flow velocity is fixed at the sonic speed. Therefore, when a critical nozzle is used, the flow rate of the fluid passing through the critical nozzle is determined only by the pressure on the primary side, regardless of the pressure on the secondary side of the critical nozzle, in the critical state (under critical conditions). That is, in the example of FIG. 7, the flow rate of the fluid passing through the critical nozzle is determined depending on the pressure Pr1 of the main flow path pressure sensor P1. Specifically, in the critical state, the flow rate of the fluid passing through the critical nozzle is calculated by the following formula 1. 【0060】 【number】 【0061】 In formula 1, qt is the theoretical mass flow rate of the fluid (kg / s), At is the cross-sectional area of ​​the throat of the critical nozzle (m 2 ), Cc is the critical constant, Ps is the stagnation pressure (Pa), Na is the molar mass of the fluid (kg / mol), Ru is the universal gas constant (J / K mol), and Ts is the stagnation temperature (K). The critical constant Cc is expressed by the following equation 2, where κ is the specific heat ratio. 【0062】 【number】 【0063】 When the mass flow rate, which indicates the actual flow rate of the fluid, is qm (kg / s), the discharge coefficient Cd is expressed by the following equation 3. 【0064】 【number】 【0065】 Therefore, by measuring the stagnation pressure Ps with the main flow path pressure sensor P1, with the other parameters known, the theoretical value qt of the mass flow rate can be calculated from equations 1 and 2, and the actual flow rate (mass flow rate qm) of the critical nozzle can be obtained by multiplying the theoretical value qt by the discharge coefficient Cd in equation 3. 【0066】 Meanwhile, the above formula 1 is composed of the eigenvalues ​​of the critical nozzle and the physical properties of the fluid (gas) for parameters other than Ps (stagnation pressure). Therefore, when various gases are flowing, if Ps is the same, the ratio of the flow rates through each critical nozzle can be known even if the flow rates through each critical nozzle are not known. Therefore, when a critical nozzle is used, the flow division ratio S can be calculated using the above flow ratio. For example, if the flow ratio of the fluid flowing through the first critical nozzle CN1 and the fluid flowing through the second critical nozzle CN2 is m:n, the flow division ratio S can be expressed as S=m / (m+n). 【0067】 Therefore, when the first fluid resistance element RE1 is configured with the first critical nozzle CN1 and the second fluid resistance element RE2 is configured with the second critical nozzle CN2, it is not necessary to perform step S3 in FIG. 5 to obtain the division ratio S. In other words, the division ratio S can be obtained without controlling the pressure downstream of the second fluid resistance element RE2 to match the pressure inside the container TA. Therefore, it is not necessary to provide the bypass flow path pressure sensor P3 and the control valve CV in the bypass flow path L2 to obtain the division ratio S. As a result, the flow rate Q of the fluid F can be calculated with a simpler configuration and in a simpler manner than that in FIG. 1. 【0068】 [4. Supplementary Information] In the configuration shown in FIG. 1 etc., when the first on-off valve V1 downstream of the container TA is closed, the pressure Pr2 in the container TA rises. Accordingly, it is considered that the pressure Pr1 detected by the upstream main flow path pressure sensor P1 also rises. By performing a correction in which the flow rate Q calculated in accordance with the pressure rise in the specific flow path L1 is added with the flow rate ΔQ calculated in accordance with the pressure rise in the upstream main flow path L0, the flow rate Q' (=Q+ΔQ) of the flow control device 100 can be calculated with higher accuracy. The flow rate ΔQ can be expressed by the volume of the flow path connecting the flow control device 100 and the two fluid resistance elements (the first fluid resistance element RE1, the second fluid resistance element RE2). The volume can be obtained by calculating V by setting P=Pr1 in the above-mentioned formula (A). 【0069】 [5. Program] The control arithmetic unit COM of the flow rate calculation device 1 of this embodiment can be configured by a computer in which an operating program (application software) is installed. The above program can be read and executed by a computer (for example, the control unit 50), thereby operating each part of the control unit 50 (the main control unit 51, the flow rate calculation unit 52, the device diagnosis unit 53) to execute each of the above-mentioned processes (each step). Such a program is acquired by, for example, downloading from an external source via a network and stored in a memory (storage unit 60). The above program may be recorded in a computer-readable recording medium such as a CD-ROM (Compact Disk-Read Only Memory), and the program may be read from the recording medium and stored in the memory. That is, the flow rate calculation program of this embodiment is a program for causing a computer to execute each step in the above-mentioned flow rate calculation method of this embodiment. The recording medium of this embodiment is a computer-readable recording medium in which the above-mentioned flow rate calculation program is recorded. 【0070】 Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to this, and the invention can be expanded or modified without departing from the spirit of the invention. [Industrial Applicability] 【0071】 The present invention can be used in a system for inspecting or diagnosing a flow control device such as a mass flow controller. [Explanation of symbols] 【0072】 1 Flow rate calculation device 52 Flow rate calculation section 53 Equipment Diagnosis Department 100 Flow control equipment CN1 First critical nozzle CN2 Second critical nozzle CV Control Valve F fluid F1 First branch fluid F2 Second branch fluid L0 main flow path L1 Specific flow path L2 Bypass flow path P1 Main flow path pressure sensor (main flow path pressure detection part) P2 Specific flow path pressure sensor P3 Bypass flow pressure sensor PL Pressure loss element PL1 First pressure loss element PL2 Second pressure loss element RE1 First fluid resistance element RE2 Second fluid resistance element S Shunt ratio TA container UR Pressure Control Device

Claims

[Claim 1] A flow rate calculation device for calculating the flow rate of a fluid flowing through a main channel, A specific channel and a bypass channel are provided, branching off from the main channel, through which the fluid is diverted. A first fluid resistance element provided in the aforementioned specific flow path, A second fluid resistance element is provided in the bypass channel, In the aforementioned specific flow path, a container is disposed downstream of the first fluid resistance element, A pressure sensor for detecting the pressure inside the container, A flow rate calculation device comprising: a flow rate calculation unit that calculates the flow rate of a first branch fluid that is diverted to the specified flow path based on the change in pressure inside the container, and calculates the flow rate of the fluid flowing through the main flow path based on the calculated flow rate of the first branch fluid and a diversion ratio determined according to the first fluid resistance element and the second fluid resistance element. [Claim 2] When the pressure sensor is used as a pressure sensor for a specific flow path, A bypass flow path pressure sensor is positioned downstream of the second fluid resistance element in the bypass flow path, The system further comprises a control valve that controls the flow rate of the second branch fluid flowing through the bypass channel via the second fluid resistance element, The flow rate calculation device according to claim 1, wherein the flow rate calculation unit controls the control valve so that the pressure downstream of the second fluid resistance element, measured by the bypass flow path pressure sensor, matches or approaches the pressure inside the container, detected by the specific flow path pressure sensor. [Claim 3] The pressure control device further includes the aforementioned control valve and pressure gauge, The flow rate calculation device according to claim 2, wherein the flow rate calculation unit controls the control valve of the pressure control device. [Claim 4] The flow rate calculation device according to claim 2 or 3, wherein the first fluid resistance element and the second fluid resistance element are pressure loss elements that impart pressure loss to the first branch fluid and the second branch fluid, respectively. [Claim 5] The flow rate calculation device according to claim 4, wherein the pressure drop element constituting the first fluid resistance element and the second fluid resistance element is a restrictor made of ceramics. [Claim 6] The flow rate calculation device according to claim 4, wherein the pressure drop elements constituting the first fluid resistance element and the second fluid resistance element are restrictors made of metal. [Claim 7] The flow rate calculation device according to claim 1, wherein the first fluid resistance element and the second fluid resistance element are critical nozzles. [Claim 8] The main flow path is further equipped with a pressure detection unit for the main flow path, The flow rate calculation device according to claim 7, wherein the flow rate calculation unit determines the flow division ratio based on the ratio of the flow rates of the fluids flowing through each critical nozzle, which is calculated using the pressure detected by the main flow path pressure detection unit, under critical conditions where the flow velocity of each fluid flowing through each critical nozzle constituting the first fluid resistance element and the second fluid resistance element is the speed of sound. [Claim 9] The system further includes an equipment diagnostic unit for diagnosing flow control equipment that discharges the fluid into the main flow path, The flow rate calculation device according to any one of claims 1 to 3, wherein the device diagnostic unit diagnoses the flow rate control device based on the set flow rate when the flow rate control device discharges the fluid and the flow rate of the fluid flowing through the main channel calculated by the flow rate calculation unit. [Claim 10] The flow rate calculation unit sets the flow division ratio to S and the calculated flow rate of the first branched fluid to Q1. Q = Q1 / S A flow rate calculation device according to any one of claims 1 to 3, which calculates the flow rate Q of the fluid flowing through the main channel by performing a calculation. [Claim 11] The process involves calculating the flow rate of the first branched fluid flowing through a specific channel when the fluid flowing through the main channel is divided into a specific channel and a bypass channel provided by branching off from the main channel, based on the change in pressure in a container located downstream of the first fluid resistance element in the specific channel, A flow rate calculation method comprising the step of calculating the flow rate of the fluid flowing through the main channel based on the calculated flow rate of the first branched fluid and the flow division ratio determined according to the first fluid resistance element and the second fluid resistance element provided in the bypass channel.

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