Thermal flowmeter

Abstract

To provide a thermal flowmeter having a wide rangeability.SOLUTION: The thermal flowmeter comprises: diaphragms 4, 5 formed using a passage wall (first passage wall 6) of a fluid passage 2; and a plurality of sensor chips for flowrate measurement (first to third sensor chips 11-13) which are disposed, with a space therebetween, to the wall surface of the passage wall side by side in a direction in which the fluid flows. Passage wall constituting the diaphragms 4, 5 (first and second slant parts 6d, 6e of the first passage wall 6) are inclined such that the passage sectional area is gradually reduced as it goes toward the direction in which the fluid flows. The plurality of sensor chips are disposed respectively at a plurality of positions of the fluid passage 2 differing in the flow velocity of the fluid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a thermal flow meter in which a sensor chip is provided downstream of a restriction in a fluid passage. [Background technology]

[0002] The sensor chip of the thermal flow sensor used in the thermal flow meter is generally known to be a silicon substrate on which multiple platinum resistance temperature detectors and heaters are formed using semiconductor microfabrication technology. There are two methods for obtaining the flow rate of a fluid using a thermal flow sensor: one is to obtain the heat distribution using a temperature sensor placed upstream and downstream of the heater and convert it into a flow rate, and the other is to convert the power consumption of the heater into a flow rate value.

[0003] A conventional thermal flow sensor is described in, for example, Patent Document 1. The thermal flow sensor disclosed in Patent Document 1 includes a restriction formed in a fluid passage and a sensor chip provided downstream of the restriction. The restriction is formed so that the cross-sectional area of ​​the passage gradually decreases toward the downstream side in the direction of fluid flow. By providing the restriction in this way, the approach distance can be shortened, and the device can be made more compact. The approach distance is the length from the entrance of the fluid passage to the developed flow. The thermal flow meter is configured to measure the flow velocity of the fluid before the flow is developed or the fluid that will become the developed flow by using the thermal flow sensor, and to obtain the flow rate by multiplying this flow velocity by the cross-sectional area of ​​the fluid passage. Since the sensor chip of the thermal flow sensor has a lower limit and an upper limit for the measurable flow velocity, a sensor chip that is compatible with the flow velocity of the fluid flowing through the fluid passage is adopted when installing it in the fluid passage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3385307 Summary of the Invention [Problem to be solved by the invention]

[0005] The sensor chip used in conventional thermal flow sensors has a limited range of measurable flow velocities, so when the flow velocity of the fluid flowing through the fluid passage falls below the measurable flow velocity, the measurement accuracy decreases. For this reason, conventional thermal flow meters have a problem of narrow rangeability.

[0006] An object of the present invention is to provide a thermal flow meter having wide rangeability. [Means for solving the problem]

[0007] In order to achieve this object, the thermal flow meter of the present invention comprises a throttle formed using a passage wall of a fluid passage, and a plurality of sensor chips for measuring flow rate arranged at intervals on the wall surface of the passage wall in the direction of fluid flow, the passage wall constituting the throttle is inclined so that the cross-sectional area of ​​the passage gradually decreases toward the downstream side in the direction of fluid flow, and the sensor chips are provided at a plurality of positions in the fluid passage where the flow speed of the fluid is different.

[0008] The present invention may be such that, in the thermal flow meter, the orthogonal is provided at a plurality of positions spaced apart in the direction of fluid flow, a passage wall extending parallel to the direction of fluid flow is connected to the downstream end of the orthogonal, and the sensor chip is provided at the boundary between the passage wall extending parallel to the direction of fluid flow and the downstream end of the orthogonal.

[0009] In the thermal flow meter of the present invention, the plurality of sensor chips may be provided on one passage wall that constitutes the throttle, inclined at a constant gradient.

[0010] In the thermal flow meter of the present invention, a cross section of the fluid passage may be rectangular, and the sensor chips may be provided on a passage wall that defines one side of the rectangle. Effect of the Invention

[0011] According to the present invention, even if the flow velocity is too low to be measured by the sensor chip arranged on the upstream side of the fluid passage, the flow velocity of the fluid increases as the fluid passes through the restriction, and the increased flow velocity falls within the range of flow velocities that can be measured by the downstream sensor chip, making it possible to measure the flow velocity of the fluid by the downstream sensor chip. Therefore, a thermal flow meter with wide rangeability can be provided by using multiple sensor chips. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing the basic configuration of a thermal flow meter according to the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of the fluid passage as viewed from the direction in which the fluid flows. [Diagram 3] FIG. 3 is a schematic diagram showing a flow velocity distribution when a fluid flows through a fluid passage having a throttle. [Figure 4] FIG. 4 is a cross-sectional view showing a measurement example in which the sensor chip to be used is changed depending on the flow rate. [Diagram 5] FIG. 5 is a cross-sectional view showing a specific embodiment of the thermal flow sensor. [Figure 6] FIG. 6 is a cross-sectional view showing a modified example of the thermal type flow sensor. [Figure 7] FIG. 7 is a cross-sectional view of the fluid passage as viewed from the direction in which the fluid flows. [Figure 8] FIG. 8 is a cross-sectional view showing a modified example of the thermal type flow sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of a thermal flow meter according to the present invention will be described in detail with reference to FIG. The thermal flow meter 1 shown in Fig. 1 is configured using a thermal flow sensor 3 including a fluid passage 2. A fluid such as a gas or liquid flows through the fluid passage 2 in the direction indicated by arrow A in Fig. 1 (from left to right in Fig. 1).

[0014] Two orifices 4, 5 are provided in a fluid passage 2 shown in Fig. 1. These orifices 4, 5 are provided at a plurality of positions aligned at predetermined intervals in the direction of fluid flow. The flow velocity of the fluid increases as the fluid passes through the orifices 4, 5. In Fig. 1, the increase in the flow velocity as the fluid passes through the orifices is represented by arrows A to C of different sizes. The flow velocity indicated by arrow B is faster than the flow velocity indicated by arrow A and slower than the flow velocity indicated by arrow C.

[0015] The fluid passage 2 is formed so that the cross section of the passage has a rectangular shape, as shown in Fig. 2. The cut position of Fig. 2 is the position shown by line II-II in Fig. 1. The above-mentioned two throttles 4, 5 are provided in a passage wall that is one side of a rectangle. More specifically, the two throttles 4, 5 are formed by using the first passage wall 6, which is the lowest one in FIG. 2, among the first to fourth passage walls 6-9 that form the fluid passage 2.

[0016] As shown in FIG. 1, the first passage wall 6 has first to third parallel portions 6a to 6c extending parallel to the direction in which the fluid flows, and first and second inclined portions 6d, 6e that define the throttles 4, 5 between the first to third parallel portions 6a to 6c. The first inclined portion 6d is formed between the first parallel portion 6a and the second parallel portion 6b, and the second inclined portion 6e is formed between the second parallel portion 6b and the third parallel portion 6c. The first inclined portion 6d and the second inclined portion 6e are inclined so that the passage cross-sectional area gradually decreases toward the downstream side in the fluid flow direction.

[0017] 1, the inclination angle of the first inclined portion 6d with respect to the fluid flow direction is smaller than the inclination angle of the second inclined portion 6e. The inclination angles of the first inclined portion 6d and the second inclined portion 6e can be changed as appropriate. The second to fourth passage walls 7 to 9 have flat wall surfaces and extend parallel to the direction in which the fluid flows. The second passage wall 7 is provided at a position opposite to the first passage wall 6, and the third and fourth passage walls 8 and 9 connect the first passage wall 6 and the second passage wall 7.

[0018] A first sensor chip 11 for measuring flow rate is provided on the first parallel portion 6a, and a second sensor chip 12 for measuring flow rate is provided on the second parallel portion 6b. A third sensor chip 13 for measuring flow rate is provided on the third parallel portion 6c. That is, the first to third sensor chips 11 to 13 are provided at a plurality of positions in the fluid passage 2 where the flow speed of the fluid is different. These first to third sensor chips 11 to 13 are arranged so as not to create any step between them and the wall surfaces of the first to third parallel portions 6a to 6c, as shown in Figures 1 and 2. The positions of the first to third sensor chips 11 to 13 in the direction in which the third passage wall 8 and the fourth passage wall 9 are aligned may be in the center as shown in Figure 2, or may be offset so as to be closer to the third passage wall 8 or the fourth passage wall 9.

[0019] The first sensor chip 11 is positioned downstream of the first parallel portion 6a and in the vicinity of the upstream side of the orifice 4, and is configured to measure the flow velocity of a fluid that has a flat flow velocity distribution with almost no velocity boundary layer in the fluid passage 2. In general, the flow of a fluid in a passage is classified into a "flat flow before development", a "flow during development", and a "flow after development" as shown in FIG. 3. In the middle of the orifice 14 provided in the upstream portion on the leftmost side in FIG. 3 and immediately after the orifice 14, the flow velocity is flat with almost no velocity boundary layer on the inner wall surface (flat flow before development), as indicated by the flow velocity arrows. The flow of the fluid that has passed through the orifice 14 and flowed into the passage 15 with a constant passage diameter passes through the inlet section L (a state in which the flow becomes a developing flow) where a laminar boundary layer (velocity boundary layer) 16 is generated, and becomes a laminar flow 17 that has reached equilibrium (flow after development). The flow velocity distribution after equilibrium is stabilized at the flow velocity distribution indicated by the parabola in FIG. 3.

[0020] As shown in FIG. 1, the second sensor chip 12 is provided in the second parallel portion 6b at the boundary with the downstream end of the upstream throttle 4 (the downstream end of the first inclined portion 6d). The third sensor chip 13 is provided in the boundary portion of the third parallel portion 6c with the downstream end of the downstream throttle 5 (the downstream end of the second inclined portion 6e).

[0021] The fluid flows along the orifices 4, 5 (the first inclined portion 6d and the second inclined portion 6e), thereby preventing the phenomenon in which the flow rate decreases due to contact with the wall surface. Therefore, at the boundary portions between the downstream ends of the orifices 4, 5 (the first inclined portion 6d and the second inclined portion 6e) and the second and third parallel portions 6b, 6c, the flow rate distribution is uniform, the velocity boundary layer on the inner wall surface of the flow path is eliminated, and the flow of the fluid is uniform (flat). Therefore, the second sensor chip 12 and the third sensor chip 13 measure the flow rate of the fluid in such a uniform state.

[0022] The first to third sensor chips 11 to 13 may be conventionally well-known sensor chips for thermal flow sensors. The first to third sensor chips 11 to 13 may have the same measurable flow velocity range, or may have different measurable flow velocity ranges. When the first to third sensor chips 11 to 13 have different measurable flow velocity ranges, the second sensor chip 12 has a higher measurable flow velocity than the first sensor chip 11, and the third sensor chip 13 has a higher measurable flow velocity than the second sensor chip 12.

[0023] As shown in Fig. 1, the first to third sensor chips 11-13 are each connected to a calculation unit 18 of the thermal flow meter 1, and send the measured flow velocities as signals to the calculation unit 18. The calculation unit 18 calculates the flow rate by multiplying the flow velocities measured by the first to third sensor chips 11-13 by the passage cross-sectional area of ​​the fluid passage 2 in which the first to third sensor chips 11-13 are provided. A display unit 19 is connected to the calculation unit 18. The display unit 19 displays the flow rate calculated by the calculation unit 18.

[0024] When measuring the flow rate of a fluid using the first to third sensor chips 11 to 13, it is necessary to select an optimal value from the output values ​​of the first to third sensor chips 11 to 13. For this reason, it is desirable to confirm in advance the measurable flow rate ranges for each of the first to third sensor chips 11 to 13, and to switch the sensor chip to be used according to the flow rate range to be measured. When this configuration is adopted, it becomes possible to measure a large flow rate with the first sensor chip 11, a medium flow rate with the second sensor chip 12, and a minute flow rate with the third sensor chip 13. The calculation unit 18 can be provided with a function of selecting such output values ​​of the first to third sensor chips 11 to 13.

[0025] When the flow velocity of the fluid flowing through the portion of the fluid passage 2 corresponding to the first parallel portion 6a falls below the flow velocity that can be measured by the first sensor chip 11, the first sensor chip 11 cannot measure the flow velocity accurately. However, the flow velocity of the fluid flowing through the portion of the fluid passage 2 corresponding to the second parallel portion 6b is higher than the flow velocity of the portion corresponding to the first parallel portion 6a. Therefore, the second sensor chip 12 can measure the flow velocity that could not be measured by the first sensor chip 11. Similarly, the third sensor chip 13 can measure the flow velocity that could not be measured by the second sensor chip 12.

[0026] On the other hand, if the first to third sensor chips 11 to 13 have the same measurable flow velocity range, the measurement value of the sensor chip whose flow velocity is outside the flow velocity range will be significantly different from the measurement values ​​of the other sensor chips, resulting in an error. Therefore, in this case, the flow rate can be calculated using the measurement value of the sensor chip that is not causing an error.

[0027] Here, a measurement example in which a large flow rate, a medium flow rate, and a small flow rate are measured using the first to third sensor chips 11 to 13, which have the same measurable flow rate range, will be described with reference to Figures 4(A) to (C). In Figures 4(A) to (C), the flow rate of the fluid is indicated by the length of the arrow and a flow rate value that is a numerical value of the flow rate for convenience. Here, the range of flow rates that can be measured by the first to third sensor chips 11 to 13 will be described as flow rate values ​​of 8 to 10.

[0028] (A) When a large flow rate flows through the fluid passage 2; When a large flow rate (flow velocity value is 10) flows, measurement is performed by the first sensor chip 11 disposed in the first parallel section 6a, which has the largest passage cross-sectional area. Since the range of flow velocities that can be measured by the first sensor chip 11 is suited to the flow velocity of a large flow rate fluid, the flow velocity of the fluid at a large flow rate can be measured by the first sensor chip 11.

[0029] (B) When a medium flow rate flows through fluid passage 2; At a medium flow rate (flow velocity value 7), the flow velocity is low and the first sensor chip 11 provided in the first parallel portion 6a cannot measure the flow velocity with high accuracy. The flow that was at a medium flow rate in the first parallel portion 6a increases in flow velocity as the passage cross-sectional area is reduced by the orifice 4 and passes through the second parallel portion 6b. In FIG. 4(B), the flow velocity increases from 7 to 9. In this case, the flow velocity of the fluid passing through the second parallel portion 6b falls within the range of flow velocities that can be measured by the second sensor chip 12, and the second sensor chip 12 can measure the flow velocity at a medium flow rate with high accuracy.

[0030] (C) When a small flow rate flows through fluid passage 2; When a small flow rate (flow rate value 4) flows, the flow rate is too low to be accurately measured by the first sensor chip 11 provided on the first parallel portion 6a or the second sensor chip 12 provided on the second parallel portion 6b. The flow rate of the fluid, which was at a small flow rate when passing through the first parallel portion 6a, increases when passing through the orifice 4, and then further increases when passing through the orifice 5. In FIG. 4(C), the flow rate value increases from 4 to 6 to 8. In this case, the flow rate when the fluid passes through the third parallel portion 6c falls within the range of flow rates that can be measured by the third sensor chip 13, so that the flow rate at the time of the small flow rate can be accurately measured by the third sensor chip 13.

[0031] In the thermal flowmeter 1 configured in this manner, even if the flow velocity cannot be measured by the upstream sensor chip (first and second sensor chips 11 and 12) because the flow velocity is too low, the flow velocity increases due to the orifices 4 and 5, and the flow velocity of the fluid having a flat flow velocity distribution with almost no velocity boundary layer on the inner wall surface during or immediately after the orifice can be measured with high accuracy by the downstream sensor chip (second and third sensor chips 12 and 13). Therefore, according to this embodiment, a thermal flowmeter with wide rangeability and a shortened fluid passage can be provided.

[0032] The thermal flow sensor used in the thermal flow meter of the present invention can be configured as shown in Figures 5 to 8. In Figures 5 to 8, members that are the same as or equivalent to those described in Figures 1 and 2 are given the same reference numerals and detailed descriptions thereof will be omitted as appropriate. 5 has two sensor chips 12, 13 housed inside a housing that forms a fluid passage 2. The upstream end of housing 22 that forms fluid passage 2 is connected to upstream piping 24 via upstream joint 23. The downstream end of housing 22 is connected to downstream piping 26 via downstream joint 25.

[0033] The upstream end of the fluid passage 2 formed in the housing 22 is formed so that the passage cross-sectional area gradually increases from the connection with the upstream joint 23 toward the downstream side. The passage cross-sectional area is gradually increased by inclining the wall surface of the first passage wall 6 and the wall surface of the second passage wall 7 opposed to the first passage wall 6. The first passage wall 6 is formed with an upstream restrictor 4 and a downstream restrictor 5, similarly to the case of adopting the form shown in Fig. 1. No sensor chip is provided on the first parallel portion 6a of the first passage wall 6.

[0034] 5, even if the second sensor chip 12 cannot measure the flow velocity because the flow velocity is low, the flow velocity of the fluid increases due to the downstream throttle 5 and has a flat flow velocity distribution with almost no velocity boundary layer on the inner wall surface during or immediately after throttle, and the flow velocity can be measured with high accuracy by the third sensor chip 13. Therefore, this embodiment also provides a thermal flow meter with wide rangeability and a shortened fluid passage.

[0035] The fluid passage 2 of the thermal type flow sensor 31 shown in Fig. 6 is formed to have a rectangular cross section as shown in Fig. 7. The break position in Fig. 7 is the position shown by line VII-VII in Fig. 6. The first passage wall 6 of this fluid passage 2 has an inclined portion 32 that is inclined at a constant gradient. The second to fourth passage walls 7 to 9 have flat wall surfaces and extend in the direction in which the fluid flows. The inclined portion 32 of the first passage wall 6 is inclined so that the passage cross-sectional area gradually decreases toward the downstream side in the fluid flow direction. In this thermal type flow sensor 31, a throttle 33 is formed by the inclined portion 32 of the first passage wall 6.

[0036] A plurality of sensor chips 34, 35 are provided on one passage wall (inclined portion 32 of first passage wall 6) constituting this throttle 33. In the thermal flow sensor 31 shown in Fig. 6, the upstream sensor chip 34 and the downstream sensor chip 35 are arranged so as to be spaced apart at a predetermined interval in the direction of fluid flow. The upstream sensor chip 34 and the downstream sensor chip 35 are positioned at the center of the inclined portion 32 in a direction perpendicular to the direction of fluid flow (the direction in which the third passage wall 8 and the fourth passage wall 9 are aligned), and are arranged so as not to create a step between them and the wall surface of the inclined portion 32.

[0037] When the fluid flows along the inclined portion 32 of the first passage wall 6, the phenomenon in which the flow velocity decreases due to contact with the wall surface of the inclined portion 32 is suppressed. Therefore, in the passage (inside the orifice 33) where the inclined portion 32 forms part of the wall surface, the fluid flows with a flat flow velocity distribution with almost no velocity boundary layer. As a result, the upstream sensor chip 34 and the downstream sensor chip 35 measure the flow velocity of the fluid with a flat flow velocity distribution with almost no velocity boundary layer.

[0038] 6 and 7, when the flow velocity of the fluid falls below the flow velocity that can be measured by the upstream sensor chip 34, the flow velocity of the fluid whose flow velocity has been increased by the restrictor 33 can be measured with high accuracy by the downstream sensor chip 35. Therefore, also in this embodiment, it is possible to provide a thermal flowmeter having a wide rangeability and a shortened fluid passage.

[0039] 8 is provided with an inclined portion 37 inclined at a constant gradient on the second passage wall 7. This inclined portion 37 is formed to be symmetrical with the inclined portion 32 of the first passage wall 6 with respect to the center line CL of the fluid passage 2 extending in the fluid flow direction between the first passage wall 6 and the second passage wall 7. Even if the fluid passage 2 is formed as shown in Figure 8, it is possible to provide a thermal flow meter that has wide rangeability and a shortened fluid passage, just as when the configuration shown in Figures 6 and 7 is adopted.

[0040] In each of the above-described embodiments, an example has been shown in which multiple sensor chips 11-13, 34, 35 are provided on one passage wall (first passage wall 6) of the fluid passage 2 having a rectangular cross-sectional shape. When this configuration is adopted, it becomes possible to form the first passage wall 6 separately from the second to fourth passage walls 7-9, and therefore the task of assembling the multiple sensor chips 11-13, 34, 35 to the first passage wall 6 can be easily performed. Note that the cross-sectional shape of the fluid passage 2 is not limited to a rectangle and may be, for example, a circle. [Explanation of symbols]

[0041] 1...thermal flow meter, 2...fluid passage, 4, 5, 33...throttle, 6...first passage wall (passage wall), 6a to 6c...first to third parallel portions, 6d, 6e...first and second inclined portions, 11...first sensor chip, 12...second sensor chip, 13...third sensor chip, 32...inclined portion.

Claims

1. a restriction formed by a passage wall of the fluid passage; a plurality of sensor chips for measuring flow rate, the sensor chips being arranged at intervals in a direction in which the fluid flows on a wall surface of the passage wall; the passage wall constituting the throttle is inclined so that the passage cross-sectional area gradually decreases toward the downstream side in the fluid flow direction, The thermal flow meter is characterized in that the sensor chip is provided at a plurality of positions in the fluid passage where the fluid flow speed differs.

2. 2. The thermal flow meter according to claim 1, The throttles are provided at a plurality of positions spaced apart from one another in the direction of fluid flow, A passage wall extending parallel to the direction of fluid flow is connected to the downstream end of the throttle, 13. A thermal flow meter, comprising: a passage wall extending parallel to a direction in which a fluid flows; a downstream end of the restrictor, the passage wall being provided at a boundary between the passage wall and the downstream end of the restrictor;

3. 2. The thermal flow meter according to claim 1, 13. A thermal flow meter, comprising: a plurality of said sensor chips provided on one passage wall constituting said throttle, said sensor chips being inclined at a constant gradient.

4. In the thermal flow meter according to any one of claims 1 to 3, The cross-sectional shape of the fluid passage is rectangular, A thermal flow meter, characterized in that the plurality of sensor chips are provided on a passage wall that defines one side of the rectangle.

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