Flow meter

Abstract

To provide a flowmeter capable of more accurately performing measurement under space saving.SOLUTION: A flowmeter includes an orifice arranged on a flow path and a pressure measurement unit arranged on each of an upstream side and a downstream side of the orifice. The orifice includes: a disk-shaped orifice body centered about a central axis of the flow path; a central hole unit opening to a section including a center of the orifice body; and a plurality of peripheral hole units arranged so as to surround the central hole unit from an outer peripheral side. When distance from an edge of an outer peripheral side of the orifice body to the peripheral hole unit located closest to the outer peripheral side is defined as A, distance from the central hole unit to the peripheral hole unit is defined as B, and a diameter of the central hole unit and the peripheral hole unit are defined as C, C≤A≤B is satisfied.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a flow meter. [Background technology]

[0002] As a device for measuring the flow rate of a fluid flowing through a flow path, a flow meter using an orifice is known (for example, Patent Document 1 below). The flow meter described in Patent Document 1 below includes an orifice (restriction) in which one hole is formed, and pressure sensors arranged upstream and downstream of the orifice. The flow rate of the fluid can be obtained by measuring the differential pressure of the fluid before and after the orifice with the pressure sensor.

[0003] However, when using such a flow meter, in order to avoid the effects of drift and swirling flows and perform accurate measurements, it is necessary to place the orifice in a straight portion of the flow path, i.e., at a position spaced a predetermined distance from any bends or curves in the flow path. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-107090 Summary of the Invention [Problem to be solved by the invention]

[0005] However, providing a straight portion of the flow path as described above may lead to an increase in the space required for laying the piping and an increase in the construction costs of the facility.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a flow meter that is capable of performing more accurate measurement in a small space. [Means for solving the problem]

[0007] In order to solve the above problems, a flow meter according to the present disclosure includes an orifice disposed in a flow path, and pressure measuring units disposed on the upstream side and downstream side of the orifice, the orifice having a disk-shaped orifice body centered on a central axis of the flow path, a central hole portion opening in a portion of the orifice body including the center, and a plurality of peripheral holes disposed so as to surround the central hole portion from an outer periphery side, most From the outer peripheral edge to the peripheral hole The point closest to the outermost edge of the edge of The distance to the central hole is A. Center of From the peripheral hole portion The point closest to the outermost edge of the edge of When the distance to the central hole is B and the diameter of the central hole and the peripheral hole is C, < A≦B holds true. A flow meter according to the present disclosure includes an orifice disposed in a flow path, and pressure measuring units disposed respectively on the upstream and downstream sides of the orifice, the orifice having a disk-shaped orifice body centered on a central axis of the flow path, a central hole opening to a portion of the orifice body including the center, and a plurality of peripheral holes disposed to surround the central hole from the outer periphery, wherein A is the distance from the outermost edge of the orifice body to a point among the edges of the peripheral holes that is closest to the outermost edge, B is the distance from the center of the central hole to a point among the edges of the peripheral holes that is closest to the outermost edge, and C is the diameter of the central hole and the peripheral holes, whereby C≦A≦B is satisfied, and the peripheral holes are arranged at intervals in the circumferential direction about the central axis, and include a plurality of medium diameter holes having a diameter smaller than that of the central hole, and small diameter holes arranged at intervals in the circumferential direction on the outer periphery of the plurality of medium diameter holes and having a diameter smaller than that of the medium diameter holes. A flow meter according to the present disclosure includes an orifice disposed in a flow path, and pressure measuring units disposed upstream and downstream of the orifice, the orifice having a disk-shaped orifice body centered on a central axis of the flow path, a central hole opening to a portion of the orifice body including the center, and a plurality of peripheral holes disposed to surround the central hole from the outer periphery, wherein A is the distance from the outermost edge of the orifice body to a point among the edges of the peripheral holes that is closest to the outermost edge, B is the distance from the center of the central hole to a point among the edges of the peripheral holes that is closest to the outermost edge, and C is the diameter of the central hole and the peripheral holes, whereby C≦A≦B holds, and the peripheral holes are arranged at intervals in the circumferential direction about the central axis and at intervals in the radial direction, and have a plurality of rows of small diameter holes having a diameter smaller than that of the central hole. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a flow meter that is capable of performing more accurate measurements in a small space. [Brief description of the drawings]

[0009] [Figure 1] 1 is an overall configuration diagram showing a configuration of a flow meter according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a front view of an orifice according to an embodiment of the present disclosure. [Diagram 3] FIG. 2 is an enlarged cross-sectional view of a main portion of an orifice according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is an explanatory diagram showing the state of fluid flow before and after an orifice according to an embodiment of the present disclosure. [Diagram 5] FIG. 13 is a front view illustrating a modified example of an orifice according to an embodiment of the present disclosure. [Figure 6] FIG. 13 is a front view illustrating a further variation of an orifice according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Flow meter configuration) A flow meter 100 according to an embodiment of the present disclosure will be described below with reference to Fig. 1 to Fig. 4. The flow meter 100 is a device for measuring the flow rate of a fluid flowing through a flow path 90. As shown in Fig. 1, the flow meter 100 includes an orifice 10, a pressure measuring unit 20, and a calculation unit 30.

[0011] (Orifice configuration) The flow passage 90 is a straight pipe having a circular cross section. The orifice 10 is provided at a midpoint of the flow passage 90. As shown in Fig. 2, the orifice 10 is disk-shaped and centered on the central axis O of the flow passage 90. The orifice 10 has a disk-shaped orifice body 11, a central hole 12 formed in the orifice body 11, and a plurality of peripheral holes 13.

[0012] The central hole 12 is a circular hole formed in a portion including the central axis O, and penetrates the orifice body 11 in the direction of the central axis O. The center of the central hole 12 and the central axis O coincide with each other. Note that "coincidence" here refers to substantial coincidence, and slight manufacturing errors are allowed.

[0013] A plurality of peripheral holes 13 are formed around the central hole 12 so as to surround the central hole 12 from the outer periphery. In this embodiment, six peripheral holes 13 are formed around the central hole 12 at equal intervals, each at an angle of 60°. The distances from the central hole 12 to the respective peripheral holes 13 are equal to each other. In addition, the distances from the wall surface of the flow path 90 to the peripheral holes 13 are constant among the multiple peripheral holes 13. Furthermore, twelve peripheral holes 13 are formed around these six peripheral holes 13 at equal intervals so that the whole is a regular hexagon. The diameter of the peripheral hole 13 is the same as the diameter of the central hole 12. In addition, when one of the central hole 12 and the peripheral hole 13 is used as a reference, the distances to the other one of the central hole 12 and the peripheral hole 13 are equal to each other regardless of which hole is used as a reference. It should be noted that the terms "equal" and "same" used herein refer to substantial equality and sameness, and slight manufacturing errors are permitted.

[0014] Here, the distance from the inner wall of the flow path 90 (i.e., the outer peripheral edge 11a of the orifice body 11) to the peripheral hole portion 13 located on the outermost side is defined as A. Furthermore, the distance from the center of the central hole portion 12 to the peripheral hole portion 13 located on the outermost side is defined as B. Furthermore, the diameter of the central hole portion 12 and the peripheral hole portion 13 is defined as C. In this case, the relationship C≦A≦B is established. In other words, the peripheral hole portion 13 located on the outermost side is formed at a position sufficiently separated from the inner wall of the flow path 90.

[0015] Furthermore, here, a regular hexagonal region defined by the twelve peripheral holes 13 located on the outer periphery side is referred to as a hole formation region 14. The ratio of the area of ​​this hole formation region 14 to the cross-sectional area of ​​the flow path 90 is set to be 0.16 or more and 0.80 or less. In this way, the hole formation region 14 is formed to be sufficiently small compared to the cross-sectional area of ​​the flow path.

[0016] The ratio of the area of ​​the central hole 12 to the area of ​​the peripheral hole 13 in the hole formation region 14 (hole ratio) is 0.40 or more and 0.90 or less.

[0017] Furthermore, the ratio of the diameter C of the central hole 12 and the peripheral hole 13 to the diameter of the flow passage 90 is not less than 0.1 and not more than 0.15.

[0018] As shown in FIG. 3, the thickness D (dimension in the direction of the central axis O) of the orifice body 11 is 0.1C or more and 0.5C or less, relative to the diameter C of the central hole 12 and the peripheral hole 13.

[0019] 3, the edge 12a facing the upstream side of the central hole 12 and the edge 13a facing the upstream side of the peripheral hole 13 are not chamfered and have corners. On the other hand, a chamfered portion 15 is formed only on the edge 12b facing the downstream side of the central hole 12 and the edge 13b facing the downstream side of the peripheral hole 13. The opening area of ​​the chamfered portion 15 gradually increases from the upstream side to the downstream side.

[0020] (Configuration of pressure measurement unit and calculation unit) 1 again, one pressure measuring unit 20 for measuring static pressure in the flow path 90 is provided on each of the upstream and downstream sides of the orifice 10. As an example of the pressure measuring unit 20, a pressure sensor that measures static pressure and transmits the measured value as an electric signal to the calculation unit 30 is used. Based on the value received from the pressure measuring unit 20, the calculation unit 30 calculates the differential pressure between the upstream and downstream sides of the orifice 10, and further derives the flow rate of the fluid in the flow path 90 based on this differential pressure.

[0021] (Action and effect)

[0022] Incidentally, when using such a flowmeter 100, in order to perform accurate measurement while avoiding the influence of drift and swirling flow, it is necessary to place the orifice 10 in a straight portion of the flow path 90. In other words, it is necessary to place the orifice 10 at a position a predetermined distance away from the bent or curved portion of the flow path 90. However, providing a long straight portion in the flow path 90 as described above may lead to an increase in the installation space for piping and an increase in the construction cost of the facility. Therefore, in this embodiment, a central hole portion 12 and peripheral holes 13 are formed in the orifice 10.

[0023] According to the above configuration, as shown in Fig. 4, a single jet is formed in the center of the flow path 90 by the flow that has passed through the central hole 12. The flow that has passed through the peripheral holes 13 is stabilized as if entrained by this jet. For this reason, even if a bent or curved portion of the flow path 90 is provided on the upstream side of the orifice 10 (that is, a swirling flow or drift is formed on the upstream side), the flow field on the downstream side of the orifice 10 is made uniform, making it possible to perform accurate flow rate measurement in a small space.

[0024] Furthermore, in the above-mentioned orifice 10, when the distance from the outer peripheral edge of the orifice body 11 to the peripheral hole portion 13 located on the outermost side is defined as A, the distance from the central hole portion 12 to the peripheral hole portion 13 is defined as B, and the diameter of the central hole portion 12 and the peripheral hole portion 13 is defined as C, then C≦A≦B holds.

[0025] According to the above configuration, it is possible to ensure the distance from the wall surface of the flow path 90 to the peripheral holes 13. This suppresses flow turbulence caused by the jet flowing out of the peripheral holes 13 colliding with the wall surface. As a result, it is possible to make the pressure distribution in the circumferential direction uniform. This makes it possible to perform more accurate flow rate measurement.

[0026] In the above-described orifice 10, the ratio of the area of ​​the hole formation region 14 defined by the central hole portion 12 and the multiple peripheral hole portions 13 to the cross-sectional area of ​​the flow passage 90 is 0.16 or more and 0.80 or less.

[0027] According to the above-mentioned configuration, it is possible to ensure a sufficient distance from the wall surface of the flow path 90 to the peripheral holes 13. This suppresses flow turbulence caused by the jet flowing out of the peripheral holes 13 colliding with the wall surface. As a result, it is possible to further uniformize the pressure distribution in the circumferential direction.

[0028] In addition, the ratio of the central hole portion 12 to the peripheral hole portions 13 in the hole formation region 14 is not less than 0.40 and not more than 0.90.

[0029] According to the above configuration, the ratio of the central hole portion 12 and the peripheral hole portion 13 is optimized, and the flow field of the jet on the downstream side of the orifice 10 can be further stabilized. On the other hand, if the above ratio is deviated, the interval (pitch) between the holes becomes too large or too small, and the flow formed between the holes develops, which may disturb the flow field. According to the above configuration, such a possibility can be reduced.

[0030] Furthermore, in the above configuration, the ratio of the diameter of the central hole 12 and the peripheral hole 13 to the diameter of the flow passage 90 is 0.1 or more and 0.15 or less.

[0031] According to the above configuration, the ratio between the diameter of the central hole 12 and the peripheral hole 13 and the diameter of the flow passage is optimized, and the flow field of the jet on the downstream side of the orifice 10 can be further stabilized.

[0032] Furthermore, when the diameter of the central hole 12 and the peripheral hole 13 is C, the thickness D of the orifice 10 is 0.1C or more and 0.5C or less.

[0033] According to the above configuration, the thickness D of the orifice 10 is optimized, thereby reducing the possibility that the separation of the flow generated on the inner wall surface of the central hole 12 and the peripheral hole 13 will reattach to the wall surface. This makes it possible to obtain a sufficient pressure loss due to the orifice 10. Therefore, it becomes possible to perform more accurate flow rate measurement.

[0034] Furthermore, chamfered portions 15 are formed only on the downstream-facing edges 12b, 13b of the central hole 12 and the peripheral hole 13.

[0035] According to the above-mentioned configuration, the chamfered portion 15 can further reduce the possibility that the separation of the flow generated on the inner wall surface of the central hole 12 and the peripheral hole 13 will reattach to the wall surface, thereby further increasing the pressure loss through the orifice 10.

[0036] (Other embodiments) The above describes the embodiment of the present disclosure. Various changes and modifications can be made to the above configuration without departing from the gist of the present disclosure. For example, in the above embodiment, an example in which a total of two rows of peripheral holes 13 are formed counting from the central hole 12 has been described. However, the configuration of the peripheral holes 13 is not limited to the above, and it is possible to form only one row of peripheral holes 13 from the central hole 12, or to form three or more rows of peripheral holes 13.

[0037] More specifically, as shown in Fig. 5, the peripheral hole portion 13 may have a configuration including medium diameter hole portions 13a located relatively on the inner circumferential side and small diameter hole portions 13b located on the outer circumferential side. The medium diameter hole portions 13a have a smaller diameter than the central hole portion 12, and a plurality of the medium diameter hole portions 13a are arranged at intervals in the circumferential direction of the central axis O. The small diameter hole portions 13b have an even smaller diameter than the medium diameter hole portions 13a, and a greater number of the small diameter hole portions 13b are arranged in the circumferential direction than the medium diameter hole portions 13a.

[0038] According to this configuration, the small diameter hole portion 13b can uniformize the pressure distribution in the circumferential direction on the outer circumferential side of the flow path 90. On the other hand, in the region on the inner circumferential side of the small diameter hole portion 13b, the flow rate can be ensured by the medium diameter hole portion 13a having a larger diameter than the small diameter hole portion 13b.

[0039] As a further modified example, as shown in Fig. 6, it is also possible to adopt a configuration in which the peripheral hole portion 13 does not have the medium diameter hole portion 13a, but has only a plurality of rows of small diameter hole portions 13b. In this case, the small diameter hole portions 13b having the same diameter are arranged in two rows at intervals on the inner and outer circumferential sides.

[0040] According to such a configuration, the pressure distribution on the outer periphery side of the flow passage 90 can be made more uniform in the circumferential direction by the plurality of rows of small diameter holes 13b.

[0041] <Additional Notes> The flow meter 100 described in each embodiment can be understood, for example, as follows.

[0042] (1) A flowmeter 100 according to a first embodiment includes an orifice 10 disposed on a flow path 90, and pressure measuring units 20 disposed on the upstream and downstream sides of the orifice 10. The orifice 10 has a disk-shaped orifice body 11 centered on a central axis O of the flow path 90, a central hole portion 12 opening to a portion of the orifice body 11 including the center, and a plurality of peripheral hole portions 13 disposed to surround the central hole portion 12 from the outer periphery. When the distance from an outer periphery edge 11a of the orifice body 11 to the peripheral hole portion 13 located on the outermost side is A, the distance from the central hole portion 12 to the peripheral hole portion 13 is B, and the diameters of the central hole portion 12 and the peripheral hole portion 13 are C, C≦A≦B holds.

[0043] According to the above configuration, a single jet is formed at the center of the flow path 90 by the flow that has passed through the central hole 12. The flow that has passed through the peripheral hole 13 is stabilized as if entrained by this jet. Therefore, even if a bent or curved part of the flow path is provided upstream of the orifice 10, the flow field downstream of the orifice 10 is uniformized, making it possible to perform accurate flow measurement. In addition, according to the above configuration, the distance from the wall surface of the flow path 90 to the peripheral hole 13 can be secured. This suppresses flow turbulence caused by the jet flowing out of the peripheral hole 13 colliding with the wall surface. As a result, the pressure distribution in the circumferential direction can be uniformized.

[0044] (2) In the flow meter 100 according to the second aspect, the peripheral holes are arranged at equal distances from the central hole.

[0045] According to the above-described configuration, the pressure distribution in the circumferential direction around the central hole 12 can be made more uniform.

[0046] (3) In the flowmeter 100 according to the third aspect, the distance from the wall surface of the flow passage 90 to the peripheral hole portion 13 is constant among the multiple peripheral hole portions 13 .

[0047] According to the above configuration, it is possible to ensure the distance from the wall surface of the flow path 90 to the peripheral holes 13. This suppresses flow turbulence caused by the jet flowing out of the peripheral holes 13 colliding with the wall surface. As a result, it is possible to uniformize the pressure distribution in the circumferential direction.

[0048] (4) In the flowmeter 100 of the fourth aspect, the peripheral hole portion 13 includes a plurality of medium diameter hole portions 13a arranged at intervals in the circumferential direction about the central axis O and having a diameter smaller than that of the central hole portion 12, and small diameter hole portions 13b arranged at intervals in the circumferential direction on the outer periphery of the plurality of medium diameter hole portions 13a and having a diameter smaller than that of the medium diameter hole portions 13a.

[0049] According to the above configuration, the small diameter hole portion 13b can uniformize the pressure distribution in the circumferential direction on the outer circumferential side of the flow passage 90. On the other hand, in the region on the inner circumferential side of the small diameter hole portion 13b, the flow rate can be ensured by the medium diameter hole portion 13a having a diameter larger than that of the small diameter hole portion 13b.

[0050] (5) In the flow meter 100 according to the fifth aspect, the peripheral holes have multiple rows of small diameter holes that are arranged at intervals in the circumferential direction and in the radial direction about the central axis, and have a smaller diameter than the central hole.

[0051] According to the above-described configuration, the pressure distribution on the outer periphery side of the flow passage 90 can be made more uniform in the circumferential direction by the plurality of rows of small diameter holes 13b.

[0052] (6) In the flowmeter 100 according to the sixth aspect, the central hole portion and the peripheral hole portion have the same diameter, and when one of the central hole portion and the peripheral hole portion is used as a reference, the distance from the central hole portion to the other one of the peripheral hole portion is equal to the distance from the other one of the central hole portion and the peripheral hole portion.

[0053] According to the above-described configuration, the pressure distribution and the flow rate distribution in the region including the central hole portion and the peripheral hole portion can be made uniform.

[0054] (7) In the flowmeter 100 according to the seventh aspect, the ratio of the area of ​​the hole formation region 14 defined by the central hole portion 12 and the multiple peripheral hole portions 13 to the cross-sectional area of ​​the flow path 90 is 0.16 or more and 0.80 or less.

[0055] According to the above configuration, it is possible to ensure the distance from the wall surface of the flow path 90 to the peripheral holes 13. This suppresses flow turbulence caused by the jet flowing out of the peripheral holes 13 colliding with the wall surface. As a result, it is possible to uniformize the pressure distribution in the circumferential direction.

[0056] (8) In the flowmeter 100 according to the eighth aspect, the ratio of the central hole portion 12 to the peripheral hole portions 13 in the hole formation region 14 is not less than 0.40 and not more than 0.90.

[0057] According to the above-mentioned configuration, the ratio of the central hole portion 12 to the peripheral hole portion 13 is optimized, and the flow field of the jet on the downstream side of the orifice 10 can be further stabilized.

[0058] (9) In the flowmeter 100 according to the ninth aspect, the ratio of the diameter of the central hole 12 and the peripheral hole 13 to the diameter of the flow passage 90 is not less than 0.1 and not more than 0.15.

[0059] According to the above configuration, the ratio between the diameter of the central hole portion 12 and the peripheral hole portion 13 and the diameter of the flow passage 90 is optimized, and the flow field of the jet on the downstream side of the orifice 10 can be further stabilized.

[0060] (10) In the flowmeter 100 according to the tenth aspect, when the diameter of the central hole 12 and the peripheral hole 13 is C, the thickness of the orifice 10 is not less than 0.1C and not more than 0.5C.

[0061] According to the above-mentioned configuration, the thickness of the orifice 10 is optimized, which reduces the possibility that the separation of the flow generated on the inner wall surface of the central hole 12 and the peripheral hole 13 will reattach to the wall surface. This makes it possible to obtain a sufficient pressure loss through the orifice 10.

[0062] (11) In the flowmeter 100 according to the eleventh aspect, the chamfered portions 15 are formed only on the downstream-facing edges 12b, 13b of the central hole 12 and the peripheral hole 13.

[0063] According to the above configuration, the chamfered portion 15 is formed only on the downstream edges 12b, 13b of the central hole 12 and the peripheral holes 13, which further reduces the possibility that the flow separation occurring on the inner wall surfaces of the central hole 12 and the peripheral holes 13 will reattach to the wall surfaces. This further increases the pressure loss through the orifice 10. [Explanation of symbols]

[0064] 100 flow meter 90 Flow Path 10 Orifice 11 Orifice body 11a edge 12 Center hole 13 Peripheral holes 13a Medium diameter hole 13b Small diameter hole 14 Pore formation area 15 Chamfered part 20 Pressure measurement section 30 Arithmetic section

Claims

1. an orifice disposed on the flow path; pressure measuring units disposed on the upstream side and downstream side of the orifice, respectively; Equipped with The orifice is a disk-shaped orifice body having a center on a central axis of the flow passage; a central hole portion that opens into a portion of the orifice body that includes the center; a plurality of peripheral holes arranged so as to surround the central hole from an outer periphery side; having A flow meter in which C<A≦B holds, where A is the distance from the outermost edge of the orifice body to the point among the edges of the peripheral hole portion located on the outermost side that is closest to the outermost edge, B is the distance from the center of the central hole portion to the point among the edges of the peripheral hole portion that is closest to the outermost edge, and C is the diameter of the central hole portion and the peripheral hole portion.

2. 2. The flow meter according to claim 1, wherein the peripheral holes are arranged at equal distances from the central hole.

3. 3. The flow meter according to claim 1, wherein a distance from an inner circumferential surface of the flow passage to the peripheral hole portion is constant among the plurality of peripheral hole portions.

4. The peripheral hole portion is a plurality of medium diameter holes arranged at intervals in a circumferential direction about the central axis and having a diameter smaller than that of the central hole; small diameter hole portions arranged at intervals in a circumferential direction on an outer circumferential side of the plurality of medium diameter hole portions, the small diameter hole portions having diameters smaller than those of the medium diameter hole portions; 4. The flow meter according to claim 1, further comprising:

5. The peripheral hole portion is 4. The flow meter according to claim 1, further comprising a plurality of rows of small diameter holes arranged at intervals in a circumferential direction about the central axis and arranged at intervals in a radial direction, the small diameter holes having a diameter smaller than that of the central hole.

6. The central hole and the peripheral hole have the same diameter, 4. The flow meter according to claim 1, wherein when one of the central hole portion and the peripheral hole portion is used as a reference, the distance to the other of the central hole portion and the peripheral hole portion is equal to each other.

7. 7. The flow meter according to claim 1, wherein a ratio of an area of ​​a hole formation region defined by the central hole and the plurality of peripheral hole portions to a cross-sectional area of ​​the flow path is 0.16 or more and 0.80 or less.

8. 8. The flowmeter according to claim 7, wherein a ratio of the central hole portion to the peripheral hole portion in the hole formation region is 0.40 or more and 0.90 or less.

9. 7. The flowmeter according to claim 6, wherein a ratio of the diameter of said central hole and said peripheral hole to the diameter of said flow passage is 0.1 or more and 0.15 or less.

10. 7. The flowmeter according to claim 6, wherein the thickness of said orifice is 0.1C or more and 0.5C or less, where C is a diameter of said central hole and said peripheral hole.

11. The flowmeter according to claim 1 , wherein chamfers are formed only on edges of the central hole and the peripheral hole that face downstream.

12. An orifice disposed on a flow path; pressure measuring units disposed on the upstream side and downstream side of the orifice, respectively; Equipped with The orifice is a disk-shaped orifice body having a center on a central axis of the flow passage; a central hole portion that opens into a portion of the orifice body that includes the center; a plurality of peripheral holes arranged so as to surround the central hole from an outer periphery side; having where A is the distance from the outermost edge of the orifice body to the point among the edges of the peripheral hole portions located on the outermost side that is closest to the outermost edge, B is the distance from the center of the central hole portion to the point among the edges of the peripheral hole portions that is closest to the outermost edge, and C is the diameter of the central hole portion and the peripheral hole portion, C≦A≦B is satisfied, The peripheral hole portion is a plurality of medium diameter holes arranged at intervals in a circumferential direction about the central axis and having a diameter smaller than that of the central hole; small diameter hole portions arranged at intervals in a circumferential direction on an outer circumferential side of the plurality of medium diameter hole portions, the small diameter hole portions having diameters smaller than those of the medium diameter hole portions; A flow meter having a

13. An orifice disposed on a flow path; pressure measuring units disposed on the upstream side and downstream side of the orifice, respectively; Equipped with The orifice is a disk-shaped orifice body having a center on a central axis of the flow passage; a central hole portion that opens into a portion of the orifice body that includes the center; a plurality of peripheral holes arranged so as to surround the central hole from an outer periphery side; having where A is the distance from the outermost edge of the orifice body to the point among the edges of the peripheral hole portions located on the outermost side that is closest to the outermost edge, B is the distance from the center of the central hole portion to the point among the edges of the peripheral hole portions that is closest to the outermost edge, and C is the diameter of the central hole portion and the peripheral hole portion, C≦A≦B is satisfied, The peripheral hole portion is A flowmeter having a plurality of rows of small diameter holes spaced apart in a circumferential direction about said central axis and spaced apart in a radial direction, said small diameter holes having a diameter smaller than that of said central hole.

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