JP2009281900A - Ultrasonic flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flow meter capable of improving measurement accuracy compared to conventional flow meters. <P>SOLUTION: In the ultrasonic flow meter 10, lead wire holding sections 83, 83 are formed at the distal end of sensor holders 40, 40, and an intermediate part of lead wire 55 extending from an ultrasonic sensor 50 is press-fitted in holding slits 85, 85 formed at the lead wire holding sections 83, 83. Noise waves leaked from the ultrasonic sensor 50 are transmitted to a sensor holder 40 directly or via the lead wire holding section 83. A cylindrical body 410 of each of the sensor holders 40, 40 is structured into a bellows cylinder, and the length of propagation route of the noise waves is longer than ever. The timing when the receiving side of the ultrasonic sensor 50 receives the noise waves can thus be sufficiently delayed compared to the timing when the ultrasonic waves propagated through a fluid in a measurement tube 31 are received. Measurement accuracy can be improved compared to conventional flow meters. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultrasonic flowmeter, and in particular, the inside of a meter case is partitioned into an upstream flow channel and a downstream flow channel by a partition wall, and a pair of openings is provided at both ends of a measurement tube penetrating the partition wall. It is related with what provided the ultrasonic sensor of no.

As shown in FIG. 6, a conventional ultrasonic flowmeter of this type is integrally provided with sensor holding portions 2 and 2 at both ends of a measuring tube 1, and the ultrasonic sensors 3 and 2 are respectively attached to the sensor holding portions 2 and 2. 3 is held (for example, see Patent Document 1). In addition, in order to take out the ultrasonic reception signal to the arithmetic processing unit 7 provided outside the meter case 6, lead wires 4 and 4 extending from the ultrasonic sensors 3 and 3 penetrate the meter case 6 in an airtight state. The terminal pins 5 and 5 were connected.
JP 2006-337059 (FIG. 1)

  However, in the conventional ultrasonic flowmeter described above, in addition to the ultrasonic wave propagating through the fluid flowing in the measurement tube 1, noise waves propagating through the sensor holding portions 2 and 2 and the tube wall of the measurement tube 1 are not received on the receiving side. The ultrasonic sensor 3 may receive the signal. Conventionally, as a countermeasure, a vibration isolating member such as rubber is interposed between the sensor holding portions 2 and 2 and the ultrasonic sensors 3 and 3, but when the temperature becomes low, the vibration isolating member becomes hard and noise waves are generated. There was a problem that the damping effect was reduced. Further, a noise wave propagating through the lead wire 4 is generated at a low temperature. This is probably because the resin covering the core wire of the lead wire 4 becomes hard.

  Since these noise waves are received by the ultrasonic sensor 3 prior to the ultrasonic wave that has propagated the fluid, the reception timing of the ultrasonic wave that has propagated the fluid becomes unclear, and the propagation time of the ultrasonic wave that has propagated the fluid, As a result, it was difficult to accurately measure the flow rate of the fluid.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ultrasonic flowmeter capable of improving the measurement accuracy from the conventional level.

  In order to achieve the above object, an ultrasonic flowmeter according to the invention of claim 1 is characterized in that the inside of a meter case having an inlet into which a fluid flows and an outlet from which the fluid flows out is separated from an upstream channel and a downstream by a partition wall. In an ultrasonic flowmeter that is divided into a side channel and has a pair of ultrasonic sensors facing the openings at both ends of the measurement tube that penetrates the partition wall, it has a cylindrical shape that covers the outside of the measurement tube A pair of cylindrical holders that extend in opposite directions from both the front and back sides of the partition wall, each tip projecting forward from the measurement tube, and holding the ultrasonic sensor away from the opening at the end of the measurement tube and the meter case A terminal pin that penetrates the meter case in an airtight state, an insulated wire that connects between the ultrasonic sensor and the terminal pin, and a wire that is provided at the tip of the cylindrical holder and is in close contact with and held in the middle of the insulated wire Holding part and For example, having the features a pair of cylindrical holder, where the irregularities in the axial direction has a continuous bellows-like cylindrical structure.

  The invention according to claim 2 is characterized in that, in the ultrasonic flowmeter according to claim 1, the electric wire holding portion is made of an elastomer.

  The invention according to claim 3 is the ultrasonic flowmeter according to claim 1 or 2, wherein the meter case is provided with a pin insertion hole through which the terminal pin passes, and a gap between the pin insertion hole and the terminal pin is provided. It is characterized by being hermetically sealed with an elastomer.

  According to a fourth aspect of the present invention, in the ultrasonic flowmeter according to any one of the first to third aspects, the pair of cylindrical holders or partition walls are made of a resin containing bubbles or particles. Has characteristics.

  According to a fifth aspect of the present invention, in the ultrasonic flowmeter according to any one of the first to fourth aspects, the pair of cylindrical holders are made of different parts having a material different in acoustic impedance from the partition wall and fixed to the partition wall. It has the characteristics in that place.

  The invention of claim 6 is characterized in that in the ultrasonic flowmeter according to any one of claims 1 to 5, the measurement tube is made of metal or ceramic.

[Invention of Claim 1]
According to the first aspect of the present invention, the inside of the meter case is partitioned by the partition wall into the upstream channel and the downstream channel, and is communicated by the measurement tube penetrating the partition wall. All of the fluid that flows into the upstream flow path of the meter case from the inlet of the meter case passes through the measurement pipe and flows into the downstream flow path. Then, the flow velocity of the fluid passing through the measurement tube is calculated based on the propagation time of the ultrasonic waves transmitted and received between the pair of ultrasonic sensors, and the flow rate is calculated by multiplying the flow velocity by the cross-sectional area of the measurement tube. Is done.

  Here, in the ultrasonic flowmeter of the present invention, the pair of ultrasonic sensors are respectively held by the pair of cylindrical holders covering the outside of the measurement tube, so that the noise wave is a pair of cylindrical shapes. Communicate with the holder. In addition, the middle part of the insulated wire connected between the ultrasonic sensor and the terminal pin is in close contact with and held by the wire holding portion provided at the tip of the cylindrical holder, from the ultrasonic sensor to the insulated wire. The transmitted noise wave is transmitted from the wire holding part to the cylindrical holder.

  On the other hand, since each cylindrical holder has a bellows cylindrical structure, the propagation path length of the noise wave propagating through the cylindrical holder is longer than before. Thereby, the reception timing of the noise wave can be sufficiently delayed with respect to the reception timing of the ultrasonic wave propagated through the fluid in the measurement tube. Further, the noise wave transmitted through the insulated wire is attenuated by being escaped from the wire holding portion to the cylindrical holder in the middle. As a result, the reception timing of the ultrasonic wave propagated through the fluid can be clarified, and the measurement accuracy of the propagation time of the ultrasonic wave propagated through the fluid, and hence the measurement accuracy of the flow rate can be improved as compared with the prior art. .

  Here, in order to efficiently transmit the noise wave transmitted through the insulated wire to the cylindrical holder, it is preferable that the wire holding portion is made of hard resin (for example, hard urethane resin) or metal.

[Invention of claim 2]
According to the invention of claim 2, since the electric wire holding part is made of an elastomer, the noise wave transmitted from the ultrasonic sensor to the insulated electric wire can be absorbed and attenuated by the electric wire holding part.

  The noise wave that could not be absorbed by the wire holding part is transmitted to the cylindrical holder, but even in that case, the ultrasonic wave that propagates the fluid in the measurement tube by using the bellows cylinder structure of each cylindrical holder. The reception timing can be sufficiently delayed. In order to efficiently absorb the noise wave transmitted through the insulated wire, the elastomer constituting the wire holding part is excellent in vibration damping performance and cold resistance (it is hard to cure even at low temperatures), for example, silicone rubber (silicone rubber) ) Is preferred.

[Invention of claim 3]
According to the invention of claim 3, since the gap between the pin insertion hole of the meter case and the terminal pin is sealed with the elastomer, the noise wave can be absorbed and attenuated here. The elastomer is preferably one having excellent vibration damping performance and low gas permeability, such as acrylonitrile butadiene rubber (NBR).

[Invention of claim 4]
According to invention of Claim 4, since a noise wave repeats reflection with the bubble or granular material contained in resin which comprises a cylindrical holder or a partition wall, propagation of a noise wave can be prevented and attenuated. Here, the shape of the granular material is not particularly limited. Specifically, it may be spherical, fibrous, needle-shaped or plate-shaped.

[Invention of claim 5]
According to the configuration of the fifth aspect, the noise wave is reflected at the interface between the partition wall constituted by different parts and each cylindrical holder due to the difference in acoustic impedance thereof, so that the propagation of the noise wave is prevented and attenuated. Can be made. Here, the partition wall is preferably made of polyacetal resin, and the cylindrical holder is preferably made of urethane resin. Further, if the cylindrical holder is made of resin and the partition wall is made of metal (for example, aluminum) instead of resin, the difference in acoustic impedance with the cylindrical holder can be increased, which is more effective.

[Invention of claim 6]
According to invention of Claim 6, the change of the cross-sectional area of a measuring tube by a temperature change can be prevented. In addition, when using metal, in order to flow a fluid smoothly, it is preferable to use a seamless drawing tube or extrusion tube.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
Reference numeral 10 in FIG. 1 is an ultrasonic flowmeter of the present invention, and is in the middle of a pipeline (not shown) through which a fluid (liquid or gas, specifically, hydrogen gas or helium gas having a relatively high acoustic velocity) flows. Is attached. The ultrasonic flowmeter 10 includes a measuring assembly 30 housed in a metal meter case 20.

  The meter case 20 includes a case main body 21 that is open at both ends, and case lids 22 and 22 that close both openings of the case main body 21, and a measurement assembly 30 is inserted through one of the openings of the case main body 21. The ultrasonic flow meter 10 is configured by closing both openings of the case body 21 with the case lids 22 and 22. The case lids 22 and 22 are detachably fixed to the case main body 21 by fixing brackets (not shown).

  Inside the meter case 20, a measuring assembly housing chamber 23 for storing the measuring assembly 30 is provided. The measuring assembly housing chamber 23 has a cylindrical structure as a whole.

  The side surface of the meter case 20 (specifically, the case body 21) is provided with a fluid inlet 24A (corresponding to the “inlet” of the present invention) and a fluid outlet 24B (corresponding to the “outlet” of the present invention). It has been. The fluid inflow port 24A and the fluid outflow port 24B are provided side by side at a position closer to the center of the meter case 20 in the axial direction. Although not shown, female spiral portions for screwing and connecting the meter case 20 to the middle of the pipeline are formed on the inner peripheral surfaces of the fluid inlet port 24A and the fluid outlet port 24B.

  The case body 21 is electrically connected to a pair of ultrasonic sensors 50, 50 housed inside the meter case 20 and an arithmetic processing unit 90 provided outside the meter case 20. A pair of hermetic terminals 80, 80 are assembled. The airtight terminal 80 has a structure in which the terminal pin 81 penetrates the meter case 20 in an airtight state. Specifically, pin insertion holes 29 and 29 are formed through the case main body 21 at positions closer to the center in the axial direction, and the terminal pins 81 and 81 pass through the pin insertion holes 29 and 29, and the pin insertion holes. 29 and the terminal pin 81 are sealed in an airtight state by a sealing member 82. The general sealing member 82 is made of glass. In this embodiment, the sealing member 82 is made of an elastomer having excellent vibration damping performance and low gas permeability (specifically, acrylonitrile butadiene rubber or butyl rubber). A lead wire 55 extending from the ultrasonic sensor 50 is connected to an inner end portion of the meter case 20 in the terminal pin 81, and an arithmetic processing unit 90 is directly or electrically connected to an outer end portion of the meter case 20. Connected through. The pin insertion holes 29 and 29 (airtight terminals 80 and 80) are provided side by side on both sides of the partition wall 35 described below.

  A partition wall 35 is provided at an intermediate portion in the axial direction of the measurement assembly housing chamber 23. The partition wall 35 divides the measurement assembly storage chamber 23 into two chambers at an intermediate position between the fluid inlet 24A and the fluid outlet 24B. That is, the metering assembly storage chamber 23 is partitioned into an upstream channel 25 that communicates with the fluid inlet 24A and a downstream channel 26 that communicates with the fluid outlet 24B.

  The partition wall 35 is a molded product of resin (specifically, polyacetal resin), for example, and is provided integrally with the weighing assembly 30. The partition wall 35 has a disk shape having substantially the same diameter as the inner diameter of the measuring assembly housing chamber 23 (see FIG. 3A). An O-ring groove 35 </ b> A is formed on the outer peripheral surface of the partition wall 35 (see FIG. 3B), and the O-ring 37 fitted into the partition wall 35 and the inside of the weighing assembly housing chamber 23 The space between the peripheral surface is sealed.

  A measurement tube insertion hole 36 is formed at the center of the partition wall 35 and the measurement tube 31 passes therethrough. The measuring tube 31 is, for example, a straight pipe made of metal or ceramic, and has a circular tubular shape with a constant inner diameter and outer diameter. Specifically, it is composed of a seamless aluminum or aluminum alloy pipe that has been drawn or drawn. Since the measurement pipe 31 is made of metal, it is possible to prevent a change in the cross-sectional area of the flow path 31A of the measurement pipe 31 due to a temperature change of the fluid.

  As shown in FIG. 3B, the measurement tube insertion hole 36 includes a small diameter portion 36A having the same diameter as the outer diameter of the measurement tube 31, and a large diameter portion 36B larger in diameter than the small diameter portion 36A. An O-ring 38 is fitted inside the portion 36B. The O-ring 38 seals between the outer peripheral surface of the measurement tube 31 and the inner peripheral surface of the measurement tube insertion hole 36 (see FIG. 1). Note that the O-ring 38 can also prevent the measurement tube 31 from rattling or misalignment in the axial direction.

  As shown in FIG. 1, the measuring tube 31 penetrating the partition wall 35 extends from a position closer to one end to a position closer to the other end in the axial direction of the measuring assembly housing chamber 23. The upstream flow path 25 and the downstream flow path 26 are connected only by the flow path 31 </ b> A in the measurement pipe 31. That is, all the fluid that has flowed into the upstream flow path 25 from the fluid inlet 24A of the meter case 20 passes through the measurement pipe 31 (flow path 31A) and flows to the downstream flow path 26.

  A pair of ultrasonic sensors 50 and 50 are arranged at both ends in the axial direction of the measurement assembly housing chamber 23. The ultrasonic sensors 50 and 50 are disposed coaxially with the measurement tube 31 and are disposed opposite to each other with the flow channel 31 </ b> A of the measurement tube 31 interposed therebetween.

  The ultrasonic sensor 50 has a structure in which a flange 52 projects laterally from the rear end portion of the flat cylindrical sensor main body 51, and the front end surface of the sensor main body 51 is an ultrasonic transmission / reception surface 51A.

  Although not shown, the sensor body 51 includes a piezoelectric element (vibrator) inside the outer shell case, and a lead wire 55 is connected to the piezoelectric element. The lead wire 55 is an “insulated electric wire” in which a metal conductive wire (core wire) is covered with a coating material of an insulating resin (for example, polyvinyl chloride). The outer shell case is filled with resin in a state where the piezoelectric element and the metal conductor of the lead wire 55 are soldered so that the piezoelectric element and the metal conductor do not come into contact with the fluid flowing in the meter case 20. It is sealed (resin mold). The resin filled in the outer shell case does not hinder the vibration of the piezoelectric element.

  The lead wire 55 is pulled out from the rear surface of the ultrasonic sensor 50 and connected to the terminal pin 81 of the airtight terminal 80 described above. Although not shown, the connecting portion between the lead wire 55 and the terminal pin 81 is also covered with a resin-sealed or heat-shrinkable tube so that the metal conductor and the terminal pin 81 do not come into contact with the fluid flowing in the meter case 20. ing.

  By the way, each ultrasonic sensor 50, 50 is held at a position away from both openings of the measurement tube 31 and the inner surface of the meter case 22. In order to hold the ultrasonic sensors 50, 50 at such positions, the measuring assembly 30 is provided with a pair of sensor holders 40, 40 (corresponding to the “cylindrical holder” of the present invention).

  The pair of sensor holders 40, 40 are arranged symmetrically across the partition wall 35 and have the same shape. That is, the sensor holder 40 extends in opposite directions along the measurement tube 31 from both the front and back surfaces (left and right surfaces in FIG. 1) of the partition wall 35, and has a cylindrical shape covering the outer peripheral surface of the measurement tube 31. Yes. Here, the sensor holders 40 and 40 are molded articles made of a resin (for example, hard foamed urethane resin) that has different acoustic impedance from the partition wall 35 and contains bubbles.

  One sensor holder 40 can be divided into a pair of holder structures 41 and 41 sandwiching the measuring tube 30 from the side (see FIG. 2, in which only one holder structure 41 is shown. It is composed by fixing them together. Specifically, the pair of holder structures 41, 41 has a structure in which the sensor holder 40 is vertically divided along the axial direction, and has the same shape. By making the pair of holder constituting bodies 41, 41 into the same shape, it is possible to share a molding die.

  As shown in FIGS. 1 and 3B, “L” -shaped hooks 39 protruding in the axial direction of the measuring tube 31 and bent at right angles are formed on both the front and back surfaces of the partition wall 35. As shown in FIG. 1 and FIG. 2, an engagement groove 44 having an “L” shape corresponding to the shape of the hook 39 is recessed and formed on the combined surface of each holder component 41. . Then, the pair of holder structures 41, 41 are engaged in a state in which they are moved and united in a direction orthogonal to the axial direction (a direction in which the combined surfaces are brought closer to each other, a direction orthogonal to the paper surface of FIG. 1). When the groove 44 and the hook 39 are engaged with each other, the movement of the holder constituting bodies 41 and 41 (sensor holder 40) in the axial direction is restricted. In this combined state, the holder constituting bodies 41 and 41 are fixed to each other with a fixing bracket (such as a screw) (not shown), and the sensor holder 40 is fixed to the partition wall 35.

  Each part of the sensor holder 40 will be described. As shown in FIG. 2, the sensor holder 40 includes a cylindrical body 410 that extends from the partition wall 35 along the axial direction of the measurement tube 31 and covers the outer peripheral surface of the measurement tube 31. A flange wall 420 is integrally formed at an end of the cylindrical body 410 on the partition wall 35 side (hereinafter referred to as “base end” as appropriate), and an end on the opposite side (hereinafter referred to as “tip end”). A plurality of sensor holding portions 430 for holding the ultrasonic sensor 50 are integrally formed.

  The flange wall 420 protrudes laterally from the base end of the cylindrical body 410 and has a disk shape smaller than the inner diameter of the partition wall 35 and the meter case 20, and is directed to the front and back surfaces of the partition wall 35. (See FIG. 1).

  For example, four sensor holders 430 are provided in one sensor holder 40, and the four sensor holders 430 cooperate to hold one ultrasonic sensor 50. In FIGS. 1 and 2, only three of the four sensor holding portions 430 are shown.

  The sensor holding portion 430 extends in a cantilever shape from the distal end portion of the cylindrical body 410 in the axial direction of the measurement tube 31 (direction away from the opening of the measurement tube 31). Specifically, an arm portion 431 extending in the axial direction of the measurement tube 31 from the distal end portion of the cylindrical body 410 and a pair of sandwiching walls 432 and 432 projecting from the distal end portion of the arm portion 431 toward the ultrasonic sensor 50. The flange 52 of the ultrasonic sensor 50 is clamped between the clamping walls 432 and 432 in the thickness direction.

  Among the sensor holders 40, the cylindrical body 410 has a bellows cylinder structure in which irregularities are continuous along the axial direction. As shown in FIG. 2, the cross section of the cylindrical body 410 has a rectangular wave shape. More specifically, a plurality of annular recesses 412 are formed at equal intervals in the axial direction on the outer peripheral surface of the cylindrical body 410, and an annular projection 413 is formed in which both sides of the annular recesses 412 are relatively convex. At the same time, an annular recess 414 is formed in a portion of the inner peripheral surface of the cylindrical body portion 410 where the annular protrusion 413 is formed, and an annular recess 412 on the outer peripheral surface of the cylindrical body portion 410 and an inner peripheral surface thereof. The annular recesses 414 have a structure in which the sensor holders 40 are alternately arranged adjacent to each other in the axial direction. In the present embodiment, the depths of the annular recesses 412 and 414 are larger than the width dimension.

  A lead wire holding portion 84 (corresponding to the “electric wire holding portion” of the present invention) that is in close contact with the middle portion of the lead wire 55 extending from the ultrasonic sensor 50 is integrally formed at the tip of each sensor holder 40, 40. ing. The lead wire holding portion 84 is provided in any one of the four sensor holding portions 430. As shown in FIG. 4, the lead wire holding portion 84 protrudes from the arm portion 431 of the sensor holding portion 430 to the side opposite to the holding walls 432 and 432, and is formed in a slit 85 formed in the lead wire holding portion 84. The middle part of the lead wire 55 is sandwiched in a press-fitted state. Here, the lead wire 55 is placed inside the measuring assembly housing chamber 23 so as not to contact the meter case 20 (the case main body 21 and the case lid bodies 22 and 22) and the sensor holder 40 except for the portion press-fitted into the slit 85. It is being circulated. As described above, the lead wire holding portion 84 is integrally formed with the sensor holder 40 and is made of the same material (hard urethane resin) as the sensor holder 40.

  The configuration of the ultrasonic flowmeter 10 of the present embodiment is as described above. Next, the effect of this embodiment is demonstrated. When the ultrasonic flowmeter 10 is connected in the middle of a pipeline (not shown), the fluid flows into the upstream flow path 25 of the meter case 20. All of the fluid that has flowed into the upstream flow path 25 passes through the measurement pipe 31 and flows into the downstream flow path 26, and is discharged from the downstream flow path 26 to the downstream side of the pipeline. At this time, transmission / reception of ultrasonic waves is performed between the pair of ultrasonic sensors 50, 50 in both the forward direction along the fluid flow and the reverse direction. That is, the propagation time in the forward direction and the reverse direction is detected by propagating ultrasonic waves using the fluid flowing through the measurement tube 31 as a propagation medium. Then, based on the propagation time (specifically, the reciprocal difference in propagation time), the flow velocity of the fluid is calculated, and the flow rate is calculated by multiplying the flow velocity by the cross-sectional area of the flow path 31A of the measurement tube 31.

  Incidentally, since the sensor holders 40 and 40, the lead wires 55 and 55, and the meter case 20 are in direct or indirect contact with the ultrasonic sensor 50, they can be ultrasonic propagation media. And the ultrasonic wave which uses these as a propagation medium is a noise wave unrelated to the flow velocity of the fluid which flows through the inside of the measurement tube 31.

  Specifically, the noise wave is directly transmitted from the sensor holding unit 430 to the sensor holder 40. Alternatively, it is transmitted from the ultrasonic sensor 50 to the sensor holder 40 via the lead wire 55 from the lead wire holding portion 84 held in close contact with the lead wire 55. The noise wave that has propagated through the lead wire 55 escapes from the lead wire holding portion 84 to the sensor holder 40 and attenuates. Further, since the sealing member 82 of the hermetic terminal 80 is made of an elastomer having excellent vibration damping performance, the noise wave can be attenuated here as well. As described above, the noise wave transmitted through the lead wire 55 does not reach the meter case 20 or is sufficiently attenuated even if it reaches, so the reception timing of the ultrasonic wave propagating through the fluid by the noise wave is unclear. It does n’t happen.

  Now, as described above, the noise wave is transmitted to the sensor holder 40 directly or via the lead wire 55. On the other hand, according to the ultrasonic flowmeter 10 of the present embodiment, since the cylindrical body 410 of each sensor holder 40, 40 has a bellows cylinder structure, the propagation path length of the noise wave is longer than the conventional one. . Thereby, the timing at which the reception-side ultrasonic sensor 50 receives the noise wave can be sufficiently delayed with respect to the reception timing of the ultrasonic wave propagated through the fluid in the measurement tube 31. In other words, since the noise wave is not superimposed when receiving the ultrasonic wave propagated in the fluid, the reception timing of the ultrasonic wave propagated in the fluid can be clarified, the measurement accuracy of the propagation time of the ultrasonic wave propagated in the fluid, As a result, the measurement accuracy of the flow rate can be improved as compared with the prior art. In addition, the noise wave is reflected while propagating through the sensor holders 40 and 40 due to the bellows structure, and the propagation path length of the noise wave is extended, so that the noise wave is attenuated more than before. .

  In the present embodiment, the sensor holders 40, 40 and the partition wall 35 are configured as separate parts and are formed of materials having different acoustic impedances. Noise waves are reflected at the interface, preventing propagation. Further, the sensor holders 40, 40 are made of resin containing bubbles (specifically, urethane foam resin), and the noise waves are repeatedly reflected by the bubbles, so that the propagation of the noise waves can be prevented and attenuated. it can. The resin constituting the partition wall 35 may contain bubbles, or the resin constituting the partition wall 35 or the sensor holders 40, 40 may contain inorganic or organic powder (filler), or the resin. The noise wave can be reflected at the interface between the powder and the granular material, and the same effect is obtained. Here, the shape of the granular material is not particularly limited. For example, it may be spherical, fibrous, needle-shaped or plate-shaped.

  Here, if the propagation path length of the noise wave is simply extended, a sensor holding part for holding the ultrasonic sensor may be integrally formed at both ends of the measurement pipe, and the measurement pipe has a bellows cylinder structure. With such a configuration, irregularities are formed on the inner surface of the measurement tube and the fluid flow is disturbed, which may adversely affect measurement accuracy. On the other hand, in the ultrasonic flowmeter 10 of the present embodiment, the measurement pipe 31 is a straight pipe, and the sensor holders 40 and 40 that hold the ultrasonic sensors 50 and 50 are configured as separate parts from the measurement pipe 31. Since the sensor holders 40 and 40 have a bellows cylinder structure, the propagation path length of the noise wave can be extended as compared with the conventional one without disturbing the flow of the fluid passing through the measurement tube 31, and the measurement accuracy can be improved. .

[Second Embodiment]
The present embodiment is different from the first embodiment in that the lead wire holding portion is made of an elastomer capable of absorbing noise waves. Since other configurations are the same as those in the first embodiment, the same reference numerals are given to the same configurations, and duplicate descriptions are omitted.

  As shown in FIG. 5, a recessed recess 86 is formed in any one of the four sensor holding portions 430 (arm portions 431) at the distal end portion of the sensor holder 40. The depressed recess 86 has a structure in which the outer surface of the arm portion 431 is depressed, and the middle portion of the lead wire 55 is received in a state of not contacting the inner surface of the depressed recess 86. In this state, the depressed recess 86 is filled with an elastomer (specifically, silicone rubber) excellent in vibration damping performance and cold resistance, and the lead wire holding portion 87 is configured by the elastomer. As a result, the lead wire 55 penetrates the lead wire holding portion 87 and is in close contact with the lead wire holding portion 87.

  According to the present embodiment, the noise wave transmitted from the ultrasonic sensor 50 to the lead wire 55 is absorbed and attenuated by the lead wire holding portion 87. Thereby, the noise wave transmitted through the lead wire 55 can be made difficult to be transmitted to the sensor holder 40 and the meter case 20.

  Even if the lead wire holding portion 87 does not completely absorb the noise wave and is transmitted to the sensor holder 40, the sensor holder 40 has a bellows cylinder structure. The reception timing of the ultrasonic wave that has propagated the fluid can be sufficiently delayed.

  Even if the lead wire holding portion 87 does not completely absorb the noise wave, it can be sufficiently attenuated, and the sealing member 82 of the airtight terminal 80 can be further attenuated. Since the noise wave transmitted through the lead wire 55 does not reach the meter case 20 or is sufficiently attenuated even if it reaches, the reception timing of the ultrasonic wave propagating through the fluid by the noise wave becomes unclear. It does n’t happen. Therefore, according to the present embodiment, the measurement accuracy can be improved as in the first embodiment.

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.

  (1) In the above embodiment, the sensor holders 40 and 40 are connected and fixed to the partition wall 35 by the concave-convex engagement of the L-shaped hook 39 and the engagement groove 44, but the flange wall 420 of the sensor holder 40 is fixed. You may fix to the partition wall 35 with the screw penetrated and screwed to the partition wall 35.

  (2) In the above embodiment, the outer peripheral surface of the measuring tube 31 and the inner peripheral surface of the sensor holders 40 and 40 are slightly separated from each other (see FIG. 1), but they may be in close contact with each other. In order to prevent noise waves from being transmitted from the sensor holder 40 to the measurement tube 31, it is preferable to provide a gap between them. However, even if they are in close contact, the measurement tube 31 is made of metal and the sensor If the holder 40 is made of resin, the noise wave is reflected at the interface due to the difference in acoustic impedance, so that the propagation of the noise wave from the sensor holder 40 to the measurement tube 31 can be prevented.

  (3) In the above embodiment, the partition wall 35 is provided integrally with the weighing assembly 30, but may be formed integrally with the meter case 20.

  (4) The partition wall 35 and the sensor holders 40 and 40 may be made of materials having different acoustic impedances, and are not limited to the combination of polyacetal resin and urethane resin as in the above embodiment. For example, the partition wall 35 may be made of metal (for example, aluminum). When the partition wall 35 is made of aluminum and the sensor holder 40 is made of polyurethane resin, the transmittance of ultrasonic waves at the interface between the partition wall 35 and the sensor holder 40 is about 50%. Therefore, the sensor holder 40, the partition wall 35, and the sensor holder 40 Noise wave can be attenuated to about 1/4.

  (5) In the first embodiment, the lead wire holding portion 84 is made of the same hard resin (hard urethane resin) as the sensor holder 40, but is an elastomer (for example, silicone rubber) that is a separate part from the sensor holder 40. If it comprises, it has an effect equivalent to the said 2nd Embodiment. Further, in the second embodiment, if the depressed recess 86 is filled with the hard resin that efficiently propagates the noise wave instead of the lead wire holding portion 87, the same effect as that of the first embodiment is obtained.

  (6) In the above embodiment, an elastomer such as rubber is interposed between the flange 52 of the ultrasonic sensor 50 and the sandwiching walls 432 and 432 of the sensor holding unit 430 so that the ultrasonic sensor 50 directly passes to the sensor holder 40. The propagating noise wave may be attenuated.

  (7) In the above embodiment, the noise wave may be attenuated by the resin filled in the outer shell case of the ultrasonic sensor 50.

  (8) Of the pair of sensor holders 40, 40, provided with positioning projections that protrude inward from the tip of the cylindrical body 410 and are engaged with both end faces of the measurement tube 31, the measurement tube 31 is pivoted. It can be positioned and retained in the direction.

1 is a cross-sectional plan view of an ultrasonic flowmeter according to an embodiment of the present invention. Plan view of the holder structure as seen from the split surface side (A) Front view of partition wall, (B) Side sectional view Partial enlarged sectional view of the sensor holder Partial expanded sectional view of the sensor holder of the ultrasonic flowmeter concerning a 2nd embodiment. Cross section of a conventional ultrasonic flowmeter

Explanation of symbols

10 Ultrasonic flow meter 20 Meter case 24A Fluid inlet (inlet)
24B Fluid outlet (exit)
25 Upstream channel 26 Downstream channel 29 Pin insertion hole 31 Measuring tube 35 Partition wall 40 Sensor holder (tubular holder)
50 Ultrasonic sensor 55 Lead wire (insulated wire)
80 Airtight terminal 81 Terminal pin 82 Sealing member 84, 87 Lead wire holding portion (wire holding portion)
85 slit 90 arithmetic processing unit

Claims (6)

The inside of the meter case having an inlet through which the fluid flows and an outlet through which the fluid flows out is divided into an upstream flow channel and a downstream flow channel by a partition wall, and 1 is provided at the openings at both ends of the measurement tube penetrating the partition wall. In an ultrasonic flowmeter equipped with a pair of ultrasonic sensors facing each other,
Forming a cylindrical shape covering the outside of the measurement tube and extending in opposite directions from both the front and back surfaces of the partition wall, each tip protrudes forward from the measurement tube, and the ultrasonic sensor is connected to the end of the measurement tube. A pair of cylindrical holders held away from the opening and the meter case;
A terminal pin penetrating the meter case in an airtight state;
An insulated wire connected between the ultrasonic sensor and the terminal pin;
An electric wire holding part provided at the tip of the cylindrical holder and in close contact with and held in the middle of the insulated wire;
2. The ultrasonic flowmeter according to claim 1, wherein the pair of cylindrical holders has a bellows cylindrical structure in which irregularities are continuous in an axial direction.   The ultrasonic flowmeter according to claim 1, wherein the electric wire holding portion is made of an elastomer.   The meter case has a pin insertion hole through which the terminal pin penetrates, and a gap between the pin insertion hole and the terminal pin is sealed in an airtight state by an elastomer. 2. The ultrasonic flowmeter according to 2.   The ultrasonic flowmeter according to any one of claims 1 to 3, wherein the pair of cylindrical holders or the partition walls are made of a resin containing bubbles or particles.   5. The ultrasonic flowmeter according to claim 1, wherein the pair of cylindrical holders are made of different parts having a material different in acoustic impedance from the partition wall and fixed to the partition wall. 6. .   The ultrasonic flowmeter according to claim 1, wherein the measurement tube is made of metal or ceramic.

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