JP2005252771A - Method of manufacturing matching member, ultrasonic sensor, and flow measuring device of fluid using the ultrasonic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve uniformity of density distribution in a matching member by filling hollow spheres having reduced electrostatic properties, without maldistribution in the matching member, consisting of a mixture of the hollow spheres and a binding material. <P>SOLUTION: A matching member forming tool 5 is provided on a pedestal 3, an accommodating body 4 accommodating the hollow spheres 11, having reduced electrostatic charge performance, is mounted on this tool 5, the pedestal 3 is dropped to a receiving base 10 in this state to collide with the pedestal 3, and the filling rate of the hollow spheres 11 is improved by vibration generated this time. After that, the binding material 13 is mixed and hardened. In this way, since the hollow spheres 11 in the accommodating body 4 are filled without unevenness, the density of the matching member 18 becomes uniform, and using this as an acoustic matching layer 19 for an ultrasonic sensor improves the performance thereof. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a matching member, an ultrasonic sensor using the same for an acoustic matching layer, and a gas or liquid fluid flow measurement device using the ultrasonic sensor.

  Conventionally, a method of manufacturing an alignment member used for an acoustic matching layer of an ultrasonic sensor includes, for example, an alignment member 31 made of a mixture of a hollow sphere 29 and a resin 30 and a cylindrical member as shown in FIG. A pair of load cases 32 was molded, and then cut into a thickness corresponding to a quarter wavelength of the resonance frequency of the piezoelectric body as shown in FIG.

  As shown in FIG. 7C, the acoustic matching layer 33 is placed on a piezoelectric vibrator 34 to form an ultrasonic vibrator (see Patent Document 1).

In addition, as for an alignment member made of a mixture of a glass balloon and a resin, there has been disclosed one in which bubbles having a particle diameter smaller than the wavelength of ultrasonic waves generated from a piezoelectric body are formed in a resin (see Patent Document 2).
Japanese Examined Patent Publication No. 6-101880 JP 11-215594 A

  However, this conventional manufacturing method has a problem that the hollow spheres are aggregated when the hollow spheres are charged, and the dispersion in the alignment member is not uniform. This is because when the hollow spheres are stored for a predetermined period, the hollow spheres become charged due to friction between the hollow spheres and the influence of the container that is easily charged with static electricity. It will not be done.

  Therefore, as shown in FIG. 7B, each of the acoustic matching layer groups in which the cylindrical members are cut to a predetermined thickness has different ratios between the hollow spheres and the resin, so that an acoustic matching layer having a non-uniform density is created. There was a problem.

  Moreover, it is very difficult to mix bubbles having a particle diameter smaller than the wavelength of the ultrasonic wave into the resin, and the size of the bubbles to be mixed cannot be controlled.

  Furthermore, the density of the acoustic matching layer created by mixing bubbles in the resin differs depending on the number of creation, and a constant acoustic impedance cannot be obtained.

  The present invention solves the above-described conventional problems, and can produce a matching member with reduced density variation, and also includes an ultrasonic sensor using the matching member as an acoustic matching layer and the ultrasonic sensor. An object of the present invention is to provide a flow measuring apparatus.

  In order to achieve the above object, the present invention fills a hollow sphere whose chargeability is reduced by applying vibration to the inside of the storage body, and then mixes the binding material to surround the hollow sphere with the binding material. By doing so, the hollow spheres are uniformly filled in the storage body, and the density can be made uniform.

  According to the method for manufacturing an alignment member of the present invention, the hollow spheres are reliably and uniformly filled, and can have a stable density. An ultrasonic sensor using the alignment member as an acoustic matching layer is provided. The performance and, as a result, a fluid flow measuring device equipped with this ultrasonic sensor can remarkably improve its accuracy.

  In the first invention, the hollow spheres with reduced chargeability are housed in the housing body, and are filled by vibration, and then the binding material is mixed to surround the hollow spheres with the binding material. Is.

  Since the chargeability of the hollow spheres is reduced, the hollow spheres are not filled into the storage body while agglomerating or repelling each other, so that the hollow spheres are not unevenly distributed in the storage body, and the density of the alignment member is uniform in any part it can.

  According to the second aspect of the invention, the hollow sphere is left in a conductive container for a predetermined time and then filled into the storage body.

  Since the hollow sphere contacts with the conductive container and is neutralized during standing, the chargeability is reduced, and the original high fluidity can be restored without aggregation of the hollow spheres. It can be filled while being dispersed.

  In the third aspect of the invention, the inside of the storage body is filled after the antistatic agent is applied to the hollow sphere.

  As described above, since the antistatic agent is applied to the surface of the hollow sphere, the surface chargeability due to the friction between the hollow spheres can be reduced, and aggregation of the hollow spheres does not occur. Therefore, it can be filled while being evenly dispersed in the storage body.

  According to a fourth aspect of the present invention, a housing body is provided in an alignment member creation jig supported by a pedestal, and the housing body is filled with hollow spheres by applying vibration to the alignment member creation jig via a vibration device. In addition, the pedestal, the alignment member creation jig, and the storage body are electrically connected, and the vibration exciter is grounded.

  Thus, by applying vibration to the storage body, the hollow spheres filled in the storage body are stacked without gaps, and the storage body filled with the hollow spheres is electrically grounded. These hollow spheres also do not aggregate. Therefore, the hollow spheres can be uniformly dispersed in the storage body without being unevenly distributed.

  According to the fifth aspect of the present invention, a plurality of storage bodies are arranged on an alignment member creation jig, and a large number of alignment members can be created at a time, which is rational.

  In the sixth invention, the bonding material is a thermosetting resin compound, which is easy to mix with the hollow sphere and hardens by heating after mixing. can do.

  In the seventh aspect of the invention, the mixture is hardened after mixing the binding material into the hollow sphere, and the entire containing body containing the mixture can be heated without taking out the mixture. Since it can be prepared and after heat curing, the alignment member can be easily taken out from the storage body.

  In the eighth invention, the hollow sphere contains a glass composition, and an alignment member can be prepared by mixing with a binding material while maintaining a hollow state. The hollow state of the hollow sphere is maintained and can contribute to stabilization of the matching layer density.

  In the ninth aspect of the invention, the matching member created by the above method is used as an acoustic matching layer of the ultrasonic sensor, and variations in characteristics among the individual ultrasonic sensors can be suppressed.

  A tenth aspect of the invention includes a cylindrical case having a top portion and a side wall portion, a piezoelectric body fixed to the inner wall surface of the top portion, and a matching layer disposed on the outer wall surface of the top portion via an adhesive layer. A sonic sensor was constructed.

  By doing so, the matching layer can efficiently propagate the vibration from the piezoelectric body into the gas as a sound wave.

  In an eleventh aspect, at least a pair of the ultrasonic sensors are arranged in the fluid flow direction, and the velocity of the fluid is detected based on the ultrasonic propagation time between the ultrasonic sensors.

  In a twelfth aspect of the invention, the flow rate is calculated based on the obtained fluid velocity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
In FIG. 1, four guide pillars 2 erected from four corners of a rectangular base 1 support a pedestal 3 so as to be movable up and down.

  An alignment member creation jig 5 having a storage body 4 is attached to the pedestal 3, and a circular storage chamber 6 is formed in the storage body 4.

  The pedestal 3 is locked at a predetermined height position of the guide column 2 via a lock device 7. When compressed air is sent through the flexible tube 8, the lock device 7 is released and falls due to its own weight. A switch 9 controls the flow of compressed air and operates the lock device 7. There is a cradle 10 fixed to the base 1 at the drop position of the pedestal 3.

  The manufacturing process of the alignment member will be described with reference to FIG.

  A glass hollow sphere 11 is accommodated in the storage chamber 6 of the storage body 4. The hollow spheres 11 each have a particle size of 10 to 100 um, and the average particle size is about 60 um. The true density is about 0.14 to 0.18 g / cm3.

  The hollow sphere 11 made of glass has a lighter specific gravity than other fillers, has heat resistance and impact resistance, and can improve physical properties such as dimensional stability and moldability when used as a filler.

  The composition of the glass used is borosilicate glass. The hollow sphere 11 made of glass is formed by melting a raw material such as silicon oxide, boric acid, calcium carbonate, sodium carbonate, sodium sulfate, etc. at a high temperature of 1000 ° C. or more to form a glass containing a large amount of sulfur, After the pulverization, the glass fine powder is dispersed and retained in the flame, so that the sulfur component is foamed as a foaming agent component.

  The hollow sphere 11 is put into the storage chamber 6 of the storage body 4 little by little, and each time the base 3 of the alignment member creating jig 5 to which the storage body 4 is attached is dropped onto the receiving base 10. As a result, the hollow sphere 11 is filled into the storage chamber 6 by drop impact vibration. The storage chamber 6 is filled with the hollow sphere 11 while repeating this process several times to several tens of times.

  Here, the hollow sphere 11 made of glass has a high fluidity because its outer wall surface forms a coating layer of a surface modifying material.

  After the upper and lower filters 12 are installed in the storage chamber 6 of the storage body 4 filled with the hollow spheres 11 as shown in FIG. 2 (a), the binding material 13 is supplied as shown in FIG. 2 (b). Impregnate.

  Here, an epoxy resin which is a thermosetting resin compound was used as the bonding material 13.

  This is because the epoxy resin has a small change in the shape of the resin after curing and is excellent in long-term stability. Above all, since the affinity with the surface of the hollow sphere 11 is high, the binding force with the hollow sphere 11 is stably improved. To do.

The epoxy resin used is a two-component curable epoxy resin. The main agent is a bisphenol A type liquid epoxy resin, and the curing agent is tetrahydromethylphthalic anhydride. The main agent and the curing agent were mixed at an optimum mixing ratio and used as an epoxy resin. The specific gravity is about 1.0 to 1.2 g / cm ³ . However, the two-part curable epoxy resin is not particularly limited here, and one-part curable epoxy resin may be used if the purpose is achieved.

  In order to impregnate the binding material 13, a suction jig 15 provided with a suction port 14 is installed. In FIG. 2B, only one suction port 14 of the suction jig 15 is provided, but the number of suction ports 14 is not limited to one, and a plurality of suction ports may be provided.

  The aligning member creation jig 5 in which the storage chamber 6 of the storage body 4 is filled with the hollow sphere 11 is placed in a container 16 viewed with a bonding material 13 made of epoxy resin. The filter 12 installed on the lower side of the storage chamber 6 is for preventing the hollow sphere 11 therein from leaking, and the filter 12 provided on the upper side does not suck the hollow sphere 11 together when the binding material 13 is sucked. Because. Here, filter paper was used for the filter 12. Note that the material is not particular as long as the purpose of the filter 12 described above is achieved.

  Then, as shown in FIG. 2B, the bonding material 13 in the container 16 is sucked by the vacuum pump 17 from the suction port 14 of the suction jig 15. In this way, under the low-pressure atmosphere, voids existing between the hollow spheres 11 are removed, and the bonding material 13 is filled in between them. As a result, the binding material 13 is applied around the hollow sphere 11 in the storage chamber 6.

  When the bonding material 13 is sucked, it is desirable that the atmosphere and the matching layer forming jig 5 are set to a temperature at which the bonding material 13 is not cured and a temperature at which the viscosity of the bonding material 13 is lowered. Can be implemented efficiently.

  When an epoxy resin is used as the bonding material 13, the curing condition is that the temperature is raised from room temperature, 80 ° C. × 2 h, 120 ° C. × 2 h, and then a 150 ° C. × 1 h curing profile. Suction was performed at 60 ° C., which is lower than the crystallization temperature.

  After impregnating the binding material 13 in the storage chamber 6 filled with the hollow spheres 11 in this way, after taking out the storage body 4 containing the mixture of the hollow spheres 11 and the binding material 13 as shown in FIG. The entire housing 4 is heated to heat and cure the bonding material 13.

  The cured mixture is cooled to room temperature and taken out of the storage body 4 using a bar-shaped jig or the like as shown in FIG.

  Although there is only one storage chamber 6 of the storage body 4 shown in FIG. 2, if a large number of storage chambers 6 are provided as shown in FIG. 3, a large number of alignment members 17 can be taken out at a time.

  Next, as shown in FIG. 2 (e), the matching member 18 is cut into a predetermined thickness by a dicing apparatus or the like to obtain a target acoustic matching layer 19.

  In the present embodiment, the hollow sphere 11 filled in the storage chamber 6 of the storage body 4 is left in the metal container before the filling step, and the amount to be filled is taken out from the metal container.

Usually, the hollow sphere 11 is put in a plastic bag in a corrugated cardboard or a predetermined container and is sent in large quantities (at least about 1 kg or more) from the manufacturer. From there, the amount of the alignment member to be manufactured during a predetermined period is divided in advance and stored in the container.

  In the case of this embodiment, about 100 g of the hollow sphere 11 is divided into a predetermined container from the amount sent from the manufacturer, dried in a constant temperature layer at about 100 ° C. for 1 hour, and then placed in a metal container. It was. The metal container material is SUS316.

  The daily average density change of the acoustic matching layer 19 manufactured by the method of the present embodiment was compared with the daily average density change of the acoustic matching layer 19 when the separated hollow sphere 11 was stored in a resin container. The material of the resin container is polypropylene.

  In addition, the manufacturing method used the jig | tool shown to Fig.1 (a), dropped the base 3 from 70 mm in height, and filled the storage chamber 6 of the storage body 4 with the hollow sphere 11. FIG. The number of storage chambers 6 was 17, and the inner diameter of each storage chamber 6 was about 10 mm and the length was about 50 mm. The hollow sphere 11 used at one time with this jig is about 9.5 g. Since the amount to be subdivided at one time is about 100 g, about 10 lots are manufactured to use up this subdivided amount. This time, the alignment member was manufactured at a rate of one lot per day. The used hollow sphere 11 is a glass hollow sphere.

  The measurement result of the average density change is shown in FIG. As shown in FIG. 4, the average density of the alignment members manufactured every day varies greatly depending on the material of the storage container. The average density of the alignment members using the hollow spheres 11 that are subdivided and stored in the resin container increases the density manufactured every day, whereas the average density of the alignment members manufactured in the hollow spheres 11 stored in the SUS container Is stable.

  Of course, the same result as FIG. 4 was obtained for the average density of the matching layer cut and extracted from the matching member.

  Further, the amount of static electricity of the hollow sphere 11 in the storage container was measured with an electrostatic tester. The static electricity amount of the hollow sphere 11 was measured and compared in the storage container every time it was used for each production lot.

For the measurement of the amount of static electricity, 3M Static Sencor (product number 709) was used.
The result is shown in FIG.

  As shown in FIG. 5, it was found that the static electricity amount of the hollow sphere 11 stored in the polypropylene container was large from about 10 times to about 100 times compared with the static electricity amount stored in the SUS container.

From the above results, the hollow spheres stored in the resin container have a high chargeability. This is because the surface resistivity of the resin container is extremely high (about 10 ¹⁶ Ω or more), and the hollow spheres stored in the resin container are affected and the hollow spheres are aggregated or repelled (very small gaps). Is considered to have occurred). When the storage chamber 6 is filled with the hollow spheres in this state, when the inside of the storage chamber 6 is microscopically captured, a portion where the presence of the hollow spheres 11 is rough is formed opposite to the portion where the hollow spheres 11 are aggregated. Therefore, the proportion of the bonding material 13 in the portion where the hollow sphere 11 is rough increases.

  Compared with the hollow sphere 11, the specific gravity of the bonding material 13 is about 10 times larger. For this reason, compared to the case where the hollow spheres 11 are evenly filled in the storage chamber 6, the proportion of the binding material 13 in the storage chamber 6 is increased, so that the mixture of the hollow sphere 11 and the binding material 13 is used. The density of a certain alignment member 18 is increased.

  Further, each acoustic matching layer 19 obtained with a predetermined thickness from the matching member 18 may have different proportions of the composition component of the matching layer, such as when the proportion of the coupling material 13 is large or small. It is done. For this reason, the variation in the density of each acoustic matching layer 19 becomes large, or the characteristic variation when incorporated as an ultrasonic sensor is affected.

  The acoustic matching layer of the present embodiment has a stable density because the mixing ratio of the hollow sphere 11 and the binding material 13 is constant. In addition, the matching layer density for each production lot is also stabilized.

  This is because the influence of the chargeability is reduced because the hollow sphere 11 is neutralized, so that the high fluidity inherently retained by the hollow sphere 11 during filling is not impaired. Are stacked and filled. Thus, an acoustic matching layer having a stable density can be manufactured by this manufacturing method.

  In addition, although the SUS container was used as the metal container that was subdivided and stored this time, the material is not particularly limited as long as it is a conductive container having an effect of removing the charge from the hollow sphere 11. For example, a resin container or a resin bag subjected to antistatic processing by blending carbon fiber or the like, or a resin container or resin bag subjected to antistatic processing to reduce the surface specific resistance value may be used. Furthermore, it is not a hindrance to achieve the object of the present invention to obtain a static elimination effect by placing an electrostatic mat under the container.

  Moreover, before filling the hollow sphere 11 into the storage chamber 6 of the storage body 4, it is possible to prevent aggregation and repulsion of the hollow sphere 11 due to static electricity generated by applying an antistatic agent and friction between the hollow spheres. It is.

  Even when a mixture of ethyl alcohol and a cationic surfactant is applied to the hollow sphere 11 by spraying before filling the container 4, the aggregation of the hollow sphere 11 is reduced and the fluidity of the hollow sphere 11 is improved. The density of the acoustic matching layer 19 taken out from the matching member 18 manufactured by the hollow sphere 11 may vary from 0.50 to 0.53 regardless of where the manufacturing lots are collected or from any of the matching members 18 having different manufacturing lots. As shown, an acoustic matching layer 19 having a stable density range can be obtained.

  Further, the vibration exciter that vibrates the alignment member creation jig 5 including the storage body 4 can also neutralize the hollow spheres 11 filled in the storage chamber 6 by grounding, and even between the hollow spheres 11 during the vibration filling process. Aggregation and repulsion can be prevented, and it contributes greatly to filling the storage chamber 6 evenly without gaps. For this reason, it is desirable that the vibration exciter is made of an electrical conductor.

  If the container 4 and the alignment member creation jig are electrical conductors, the grounding portion can be grounded by taking out the lead wire from the base 1 or the pedestal 3 of the vibration device and grounding it. As a result, the vibrating device itself can also be reduced in chargeability, so that the hollow spheres 11 are evenly distributed and filled in the housing 4, and the density-stable acoustic matching layer 19 can be obtained.

  In addition, the vibration exciter of this Embodiment 1 loads the alignment member preparation jig | tool 5 containing the storage body 4 filled with the hollow sphere 11 as shown in FIG. 1 on the base 3, and falls from the predetermined height with the base 3 together. The method of filling the hollow sphere 11 with the impact acceleration applied to the cradle 10 is not a method for filling the hollow sphere 11 with this method.

  For example, the hollow sphere 11 with reduced chargeability is evenly filled by a method of filling the storage body 4 with a vibration device that applies longitudinal vibration or lateral vibration with a predetermined frequency and a predetermined amplitude.

(Embodiment 2)
FIG. 6 shows an ultrasonic sensor using the acoustic matching layer 19 obtained by the first embodiment.

  The cylindrical case 20 made of a conductive material has a top portion 21, and the piezoelectric body 22 is bonded to the inner wall surface of the top portion 21 and the acoustic matching layer 19 is bonded to the outer wall surface. The lower open portion of the cylindrical case 20 is closed by a terminal plate 24 connected to one terminal 23.

  The other terminal 25 passes through the terminal plate 24 via an electrical insulating material 26 and is connected to a conductor 27 that contacts the lower surface of the piezoelectric body 22. A plurality of vertical grooves 28 are formed in the piezoelectric body 22.

  When a voltage is applied to the piezoelectric body 22 from the terminals 23 and 25 via the conductor 27, the piezoelectric body 22 vibrates due to a piezoelectric phenomenon.

  6 vibrates at about 500 KHz, and the vibration is transmitted from the case 20 to the acoustic matching layer 19, and the vibration of the acoustic matching layer 19 propagates to the gas as a sound wave.

  In the acoustic matching layer created by the conventional manufacturing method, since the dispersion of the hollow spheres therein is not constant, the wavelength of vibration propagating from the piezoelectric body through the case shifts inside the acoustic matching layer. As a result, the transmission / reception sensitivity of the ultrasonic sensor decreases.

  On the other hand, the acoustic matching layer 19 of the present embodiment has a uniform density because the hollow spheres therein are uniformly dispersed, so the wavelength of vibration does not shift the phase inside the acoustic matching layer. The oscillation wave can be stably oscillated in the measurement fluid, and the transmission / reception sensitivity characteristic of the ultrasonic sensor can be maintained without deteriorating.

  Furthermore, the ultrasonic sensor is used in a fluid flow measuring device. That is, at least a pair of ultrasonic sensors are arranged on the upstream side and the downstream side in the fluid flow direction of the flow path, and the time until the ultrasonic wave transmitted from one ultrasonic sensor is received by the other ultrasonic sensor, The ultrasonic propagation time can be detected and the fluid flow rate can then be measured.

  In addition, the flow rate can be measured by calculating by involving elements such as the cross-sectional area of the flow path based on the flow velocity. As described above, since the ultrasonic sensor has high performance, the flow velocity and / or flow rate can be measured with high accuracy.

  As described above, the manufacturing method of the matching member according to the present invention, the ultrasonic sensor using the matching member as an acoustic matching layer, and the fluid flow measuring device using the ultrasonic sensor include the matching member and the acoustic matching layer. It can be manufactured at a uniform density, and the performance of the ultrasonic sensor using this acoustic matching layer can be improved. Furthermore, the accuracy of the fluid flow measurement device equipped with this ultrasonic sensor can be remarkably increased. Therefore, it can be applied to uses such as gas and liquid fluid flow measuring devices.

(A) Front view at the time of non-operation of the alignment member manufacturing apparatus in Embodiment 1 of the present invention, (b) Top view of a storage body for filling a hollow sphere, (c) Embodiment 1 of the present invention View of the alignment member manufacturing apparatus at the time of operation Manufacturing process diagram (A) The perspective view of the alignment member preparation jig | tool which shows other embodiment of this invention, (b) The perspective view of the storage body Graph showing density change of alignment member Graph showing static electricity comparison of hollow spheres Cross-sectional view of an ultrasonic sensor using the matching layer of the present invention Manufacturing process diagram of conventional alignment members

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Base 4 Storage body 5 Alignment member preparation jig 6 Storage chamber 10 Base 11 Hollow sphere 13 Binding material 19 Acoustic matching layer 20 Shaped case 21 Top part 22 Piezoelectric body

Claims (12)

A hollow sphere having reduced chargeability is housed in a housing body, and is filled by vibration, and then the hollow sphere is surrounded by the binding material by mixing the binding material, thereby producing a matching member. Method. 2. The method for manufacturing an alignment member according to claim 1, wherein the hollow sphere is left in the conductive container for a predetermined time and then filled into the housing. The method for manufacturing an alignment member according to claim 1, wherein an antistatic agent is applied to the hollow sphere and then the inside of the container is filled. A container is provided in the alignment member creation jig supported by the pedestal, and the hollow body is filled in the storage body by applying vibration to the alignment member creation jig via a vibration device, and the pedestal and The method for manufacturing an alignment member according to claim 1, wherein the alignment member creation jig and the storage body are electrically connected, and the vibration exciter is grounded. The manufacturing method of the alignment member of Claim 4 which has arrange | positioned the several accommodating body to the alignment member preparation jig | tool. The method for manufacturing an alignment member according to claim 1, wherein the binding material is a thermosetting resin compound. The method for manufacturing an alignment member according to claim 1 or 6, wherein the mixture is cured after the bonding material is mixed into the hollow sphere. The method for manufacturing an alignment member according to claim 1, wherein the hollow sphere includes a glass composition. The ultrasonic sensor provided with the matching member created with the manufacturing method of the matching member of any one of Claims 1-8 as an acoustic matching layer. The cylindrical case having a top part and a side wall part, a piezoelectric body fixed to the inner wall surface of the top part, and an acoustic matching layer installed on the outer wall surface of the top part via an adhesive layer. Ultrasonic sensor. 11. A fluid flow measuring device comprising: at least a pair of the ultrasonic sensors according to claim 9 or 10 arranged in a fluid flow direction, wherein the fluid velocity is detected based on an ultrasonic propagation time between the ultrasonic sensors. A flow measurement of a fluid in which at least a pair of the ultrasonic sensors according to claim 10 or 11 are arranged in a fluid flow direction, and a flow rate is measured based on a velocity of the fluid obtained by an ultrasonic propagation time between the ultrasonic sensors. apparatus.

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