JP5548834B1 - Ultrasonic flow meter - Google Patents

Abstract

The present invention provides an ultrasonic flowmeter that transmits and receives a high-frequency ultrasonic beam efficiently and stably and exhibits excellent measurement accuracy based on the number of high-frequency measurements.
A ceramic disk-shaped piezoelectric element is laminated between an acoustic impedance matching layer made of glass epoxy resin and a vibration absorbing layer made of silicon rubber. The thickness d1 is set thinner than the thickness d2 of the disk-shaped piezoelectric element 141, and the thickness d3 of the vibration absorbing layer 143 is set larger than the thickness d2 of the disk-shaped piezoelectric element 141, so that the acoustic impedance matching layer 142 is obtained. An ultrasonic flowmeter 100 that smoothly propagates an ultrasonic beam generated from the disk-shaped piezoelectric element 141 toward the pipe end sealing region 111 a of the straight tube 110.
[Selection] Figure 2

Description

  The present invention obtains the fluid velocity in the measurement conduit from the time difference between the time that the ultrasonic beam generated from the piezoelectric element propagates from the upstream side to the downstream side of the measurement conduit and the time that it propagates from the downstream side to the upstream side. The present invention relates to a time difference type ultrasonic flowmeter that obtains the flow rate in a straight tube by multiplying the cross-sectional area of the straight tube by velocity, and in particular, a device for polishing and cleaning silicon wafers in the manufacturing process of semiconductors and liquid crystals The present invention relates to an ultrasonic flowmeter for measuring various chemical liquids used in liquid crystal manufacturing apparatuses, raw materials in food production lines and chemical production lines, liquids such as chemical liquids handled in storage and mixing processes.

  Conventionally, as a time difference type ultrasonic flowmeter, a flow passage body including a measurement flow passage for measuring the flow rate of fluid is formed in a part of the flow passage through which the fluid flows, and a flow rate detector main body made of resin containing a sensor unit; There is an ultrasonic flow rate detector provided with a pair of ultrasonic piezoelectric elements arranged to face each other across a measurement flow path (for example, Patent Document 1).

  The sensor unit of the flow rate detector main body in this ultrasonic flow rate detector includes a disk-shaped ultrasonic piezoelectric element made of ceramics, an acoustic matching layer disposed on the front surface thereof, a side and a rear side of the ultrasonic piezoelectric element. It is composed of a surrounding housing, a rubber O-ring, and a fluororesin-coated lead wire connected to the ultrasonic piezoelectric element.

Japanese Patent Laying-Open No. 2011-38862 (refer to claim 1, FIG. 1 in particular)

  However, in the sensor unit in the conventional ultrasonic flow rate detector, the acoustic matching layer is disposed on the front surface of the ultrasonic piezoelectric element. However, when the ultrasonic beam passes through the acoustic matching layer, the acoustic vibration is generated in the acoustic matching layer. There is a problem that the signal intensity is weakened by being absorbed, and the S / N ratio of ultrasonic transmission / reception deteriorates to hinder flow rate measurement.

  Further, the fluid generates turbulent vortices at both ends of the measurement flow path, and the movement of the turbulent vortices hinders the propagation of the ultrasonic beam. There is a problem that the / N ratio further deteriorates and an error occurs in measurement accuracy.

  Furthermore, in the conventional ultrasonic flow rate detector, it takes a considerable time until the acoustic vibration of the ultrasonic piezoelectric element is attenuated, and the number of times the ultrasonic beam is generated per unit time cannot be increased. There is a problem in that beam transmission / reception is inefficient and improvement in measurement accuracy based on the number of high-frequency measurements cannot be expected.

  Therefore, the present invention solves the above-mentioned problems of the prior art, that is, the object of the present invention is to efficiently transmit and receive a high-frequency ultrasonic beam efficiently and based on a high-frequency measurement count. It is to provide an ultrasonic flowmeter that exhibits excellent measurement accuracy.

  The invention according to claim 1 includes a fluororesin straight circular pipe through which a fluid to be measured flows, an inflow pipe communicating with one end of the straight circular pipe at a predetermined inflow angle, and the other end of the straight pipe An outflow pipe communicating with a predetermined outflow angle, a pair of inflow side measurement heads and outflow side measurement heads extending to one end and the other end of the straight pipe and facing each other, and the inflow side measurement head And a ceramic disk-shaped piezoelectric element that is embedded in each of the outflow side measuring heads and alternately transmits and receives an ultrasonic beam along the central axis of the straight tube, and is generated from the disk-shaped piezoelectric element. The fluid velocity in the straight tube is obtained from the time difference between the time that the ultrasonic beam propagates from the upstream side to the downstream side of the straight tube and the time that the ultrasonic beam propagates from the downstream side to the upstream side. Multiply the cross-sectional area to find the flow rate in the straight pipe In the difference type ultrasonic flowmeter, the ceramic disk-shaped piezoelectric elements are arranged orthogonally to the central axis of the straight tube and formed at one end and the other end of the straight tube, respectively. Laminated between an acoustic impedance matching layer made of glass epoxy resin facing the pipe line end sealing region and a vibration absorbing layer made of silicon rubber facing the disc-shaped piezoelectric element, and the acoustic impedance The matching layer is set to be thinner than the disc-shaped piezoelectric element, and the vibration absorbing layer is set to be thicker than the disc-shaped piezoelectric element. Is.

  In the invention according to claim 2, in addition to the configuration of the ultrasonic flowmeter according to claim 1, the thickness of the pipe end sealing region formed in the straight circular pipe is the disk-shaped piezoelectric element. The above-mentioned problem is solved by setting the thickness to be thicker than the above-described thickness.

  In addition to the configuration of the ultrasonic flowmeter according to claim 2, the invention according to claim 3 is a glycerin that integrally adheres an acoustic impedance matching layer to a pipe end sealing region of the straight tube. The layer is provided between the pipe end sealing region of the straight tube and the acoustic impedance matching layer, thereby solving the above-described problem.

  In the invention according to claim 4, in addition to the configuration of the ultrasonic flowmeter described in claim 3, the pipe inner diameter of the straight circular pipe and the circular diameter of the disk-shaped piezoelectric element are set to be substantially the same. Thus, the above-described problems are solved.

  According to the fifth aspect of the invention, in addition to the configuration of the ultrasonic flowmeter according to the fourth aspect, a cylindrical holding member that holds a peripheral portion of the disc-shaped piezoelectric element includes the inflow side measuring head and the outflow side. The above-described problem is solved by providing an acoustic cavity provided in the side measuring head and allowing acoustic vibration of the disk-shaped piezoelectric element along the central axis of the disk-shaped piezoelectric element. .

  In the invention according to claim 6, in addition to the configuration of the ultrasonic flowmeter described in claim 5, the lid member that elastically presses the cylindrical holding member toward the disk-shaped piezoelectric element includes: The problem described above is solved by being screwed into the opening end portions formed in the inflow side measurement head and the outflow side measurement head.

  According to the seventh aspect of the present invention, in addition to the configuration of the ultrasonic flowmeter according to the sixth aspect, the inflow pipe and the outflow pipe are arranged in the same direction at one end and the other end of the straight circular pipe. The above-described problems are solved by arranging in a U-shape and communicating with the straight pipe.

  According to the eighth aspect of the present invention, in addition to the configuration of the ultrasonic flowmeter according to the sixth aspect, the inflow pipe and the outflow pipe are alternately arranged at one end and the other end of the straight circular pipe. Thus, the above-described problems are solved by communicating with the straight pipe.

  In addition to the configuration of the ultrasonic flowmeter described in claim 7 or claim 8, the invention according to claim 9 is configured such that the disk-shaped piezoelectric element has a thickness of 1 mm and a circular diameter of 10 mm, and the ultrasonic beam When the frequency is 2 MHz, the thickness of the acoustic impedance matching layer is set to 0.5 mm, and the thickness of the vibration absorbing layer is set to 4 mm, thereby solving the above-described problem. .

  The ultrasonic flowmeter of the present invention includes a fluororesin straight circular pipe through which a fluid to be measured flows, an inflow pipe communicating with one end of the straight circular pipe at a predetermined inflow angle, and the other end of the straight circular pipe. An outflow pipe communicating at a predetermined outflow angle; a pair of inflow side measurement heads and outflow side measurement heads extending to one end and the other end of the straight circular pipe and facing each other; It is generated from the disk-shaped piezoelectric element by being equipped with a ceramic disk-shaped piezoelectric element that is embedded in the outflow side measuring head and alternately transmits and receives ultrasonic beams along the central axis of the straight tube The fluid velocity in the straight tube is obtained from the time difference between the time that the ultrasonic beam propagates from the upstream side to the downstream side of the straight tube and the time that it propagates from the downstream side to the upstream side. Multiply the area to find the flow rate in the straight pipe It not only can, it is possible to obtain the specific effect as described below.

  That is, according to the ultrasonic flowmeter of the present invention, the disk-shaped piezoelectric element made of ceramic is disposed orthogonally to the central axis of the straight circular pipe and has one end of the straight circular pipe and Laminated between an acoustic impedance matching layer made of glass epoxy resin facing the pipe end sealing region formed on the other end and a vibration absorbing layer made of silicon rubber facing the disc-shaped piezoelectric element. Therefore, the acoustic impedance matching layer gradually reduces the sudden change in acoustic impedance that tends to occur between the disk-shaped piezoelectric element and the pipe end sealing region of the straight tube. The ultrasonic beam generated from the disk-shaped piezoelectric element can be smoothly propagated toward the pipe end sealing region of the straight tube, and the vibration absorbing layer attenuates the acoustic vibration of the disk-shaped piezoelectric element early. Absorb Therefore, the number of generation of the ultrasonic beam per unit time between the inflow side measurement head and the outflow side measurement head can be greatly increased. As a result, the ultrasonic beam can be transmitted and received efficiently and stably. The accuracy of the measurement average value can be improved by increasing the number of measurements.

  And since the thickness of the acoustic impedance matching layer is set to be smaller than the thickness of the disk-shaped piezoelectric element, irregular reflection at the pipe end sealing region of the straight pipe having a different acoustic impedance from that of the disk-shaped piezoelectric element is caused. Since the waveform is reduced and the waveform is stabilized, transmission and reception of the ultrasonic beam can be stabilized. On the other hand, when the thickness of the acoustic impedance matching layer is thicker than the thickness of the disk-shaped piezoelectric element, the acoustic intensity is absorbed when the ultrasonic beam passes through the acoustic impedance matching layer, so that the signal intensity is weakened. The S / N ratio of ultrasonic transmission / reception is remarkably deteriorated, and the measurement accuracy is deteriorated.

  In addition, since the thickness of the vibration absorbing layer is set to be thicker than the thickness of the disk-shaped piezoelectric element, the acoustic vibration can be converged early and the next ultrasonic wave can be transmitted. The number of measurements associated with the number of occurrences per unit time greatly increases, and the accuracy of the response and the measurement average value can be significantly improved. On the other hand, when the thickness of the vibration absorbing layer is thinner than the thickness of the disk-shaped piezoelectric element, the acoustic vibration does not converge early and the next ultrasonic wave cannot be transmitted. The number of times of measurement associated with the number of hits is reduced, and the accuracy of the response and the measurement average value is deteriorated.

  According to the ultrasonic flowmeter of the invention of claim 2, in addition to the effect of the invention of claim 1, the thickness of the pipe end sealing region formed in the straight pipe is disc-shaped piezoelectric. By setting the thickness thicker than the thickness of the element, the temporal deformation of the pipe-end sealing region pressed by a certain pressing force from the disk-shaped piezoelectric element is suppressed, and the disk-shaped piezoelectric elements The relative arrangement relationship is maintained on the central axis perpendicular to the central axis over a long period of time, and the disk-shaped piezoelectric elements are arranged so as to face each other in parallel. Since wetting of chemical substances of the fluid under measurement into the fluororesin in the pipe end sealing area, which tends to occur, is suppressed, the propagation of the ultrasonic beam in the pipe end sealing area is ensured smoothly, and measurement accuracy is improved. It can be maintained for a long time. On the other hand, when the thickness of the pipe end sealing region formed in the straight circular pipe is thinner than the thickness of the disk-shaped piezoelectric element, the pipe pressed by the disk-shaped piezoelectric element with a constant pressing force The passage end seal area is susceptible to shape deformation over time, and the chemical substance of the fluid to be measured wets in the fluoro resin in the pipe end seal area due to the characteristics of the fluoro resin during long-term measurement. For this reason, the propagation of the ultrasonic beam in the pipe end sealing region is hindered, and the measurement accuracy is deteriorated.

  According to the ultrasonic flowmeter of the invention of claim 3, in addition to the effect of the invention of claim 2, the acoustic impedance matching layer is integrally adhered to the pipe end sealing region of the straight pipe. Since the glycerin layer to be provided is provided between the acoustic impedance matching layer and the pipe end sealing region of the straight tube, each surface of the pipe end sealing region of the straight tube and the acoustic impedance matching layer Since the gap between each other that tends to occur due to roughness is eliminated, the degree of adhesion between the two can be improved and the transmission / reception of the ultrasonic beam can be improved.

  According to the ultrasonic flowmeter of the invention of claim 4, in addition to the effect of the invention of claim 3, the tube inner diameter of the straight circular tube and the circle diameter of the disk-like piezoelectric element are set to be substantially the same. As a result, the ultrasonic beam generated from the disk-shaped piezoelectric element is sufficiently amplified without being irregularly reflected in the straight tube, and the ultrasonic beam is alternately transmitted and received. An ultrasonic beam can be transmitted and received with high sensitivity between the measurement head and each other.

  According to the ultrasonic flowmeter of the fifth aspect of the invention, in addition to the effect of the fourth aspect of the invention, the cylindrical holding member that holds the peripheral edge portion of the disk-shaped piezoelectric element has the inflow side measuring head. And in the outflow side measuring head, the disk-shaped piezoelectric element is reliably positioned with respect to the acoustic impedance matching layer without hindering the vibration of the disk-shaped piezoelectric element. A stable flow rate measurement is possible, and excellent durability as a flow meter can be exhibited.

  Since the cylindrical holding member includes the acoustic cavity, acoustic vibration of the disk-shaped piezoelectric element is allowed and amplified, so that ultrasonic waves are generated between the inflow side measurement head and the outflow side measurement head. The beam can be transmitted with high sensitivity.

  According to the ultrasonic flowmeter of the invention of claim 6, in addition to the effect of the invention of claim 5, the lid member is screwed into the opening end portions formed in the inflow side measurement head and the outflow side measurement head. By being attached, the cylindrical holding member is elastically pressed toward the disk-shaped piezoelectric element and is securely held, and internal stress that tends to occur in the disk-shaped piezoelectric element depends on the degree of screwing. Since it is absorbed elastically, it is possible to stably measure the flow rate over a long period of time, and to exhibit excellent durability as a flow meter.

  According to the ultrasonic flowmeter of the invention of claim 7, in addition to the effect of the invention of claim 6, the inflow pipe and the outflow pipe are the same at one end and the other end of the straight circular pipe. The U-shaped arrangement from the direction minimizes the installation space between the inflow pipe and the outflow pipe for the straight circular pipe in the weighing work area, so it is easy to avoid installation interference with other peripheral devices. Thus, excellent operability can be exhibited.

  According to the ultrasonic flowmeter of the invention of claim 8, in addition to the effect of the invention of claim 6, the inflow pipe and the outflow pipe are alternately arranged at one end and the other end of the straight circular pipe. This makes it easy to place either the inflow pipe or the outflow pipe upwards in any measuring configuration in the measurement work area, and the bubbles of the fluid to be measured, which tends to stay in the straight circular pipe, are directly removed. Since it becomes easy to deaerate from one of the one end and the other end of the circular tube, it is possible to transmit and receive with high sensitivity the ultrasonic beam due to bubble failure that tends to occur between the inflow side measurement head and the outflow side measurement head. it can.

  According to the ultrasonic flowmeter of the invention of claim 9, in addition to the effects of the invention of claim 7 or claim 8, the disk-shaped piezoelectric element has a thickness of 1 mm and a circle diameter of 10 mm, and an ultrasonic beam The thickness of the acoustic impedance matching layer is set to 0.5 mm and the thickness of the vibration absorbing layer is set to 4 mm, so that the acoustic impedance matching layer is a disc-shaped piezoelectric element. Since the stable waveform propagates while suppressing the influence of a large difference in acoustic impedance between the pipe end sealing region and the pipe end sealing region, the ultrasonic beam can be transmitted with high sensitivity. On the other hand, when the thickness of the acoustic impedance matching layer becomes thinner than 0.5 mm, the effect of the acoustic impedance matching layer is reduced, and the acoustic impedance between the disk-shaped piezoelectric element and the pipe end sealing region is reduced. However, if the thickness of the acoustic impedance matching layer exceeds 0.5 mm, acoustic vibration will not occur when the ultrasonic beam passes through the acoustic impedance matching layer. It is absorbed by the acoustic impedance matching layer, the signal intensity becomes weak, the S / N ratio of ultrasonic transmission / reception deteriorates, and the measurement accuracy deteriorates.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front sectional view showing an outline of an ultrasonic flowmeter according to a first embodiment of the present invention. The principal part enlarged view in the inflow side of the ultrasonic flowmeter shown with the code | symbol 2 of FIG. (A) (B) is a figure which shows the waveform of the ultrasonic wave received when changing the magnitude relationship between the thickness of an acoustic impedance matching layer, and the thickness of a disk-shaped piezoelectric element. (A) (B) is a figure which shows the waveform of the ultrasonic wave received when changing the magnitude relationship of the thickness of a vibrational absorption layer, and the thickness of a disk-shaped piezoelectric element. Front sectional drawing which shows the outline of the ultrasonic flowmeter which is 2nd Example of this invention. Front sectional drawing which shows the outline of the ultrasonic flowmeter which is 3rd Example of this invention. Front sectional drawing which shows the outline of the ultrasonic flowmeter which is 4th Example of this invention.

  The present invention includes a straight circular pipe made of fluororesin that allows a fluid to be measured to flow, an inflow pipe communicating with one end of the straight pipe at a predetermined inflow angle, and a predetermined outflow angle at the other end of the straight circular pipe. An outflow pipe that communicates with each other, a pair of inflow side measurement heads and outflow side measurement heads that extend to one end and the other end of the straight circular pipe and face each other, and these inflow side measurement heads and outflow side measurement heads And a ceramic disk-shaped piezoelectric element that alternately transmits and receives an ultrasonic beam along the central axis of the straight tube, and the ultrasonic beam generated from the disk-shaped piezoelectric element is a straight tube. The fluid velocity in the straight pipe is obtained from the time difference between the time to propagate from the upstream side to the downstream side and the time to propagate from the downstream side to the upstream side. Time difference type ultrasonic flowmeter for determining flowing flow rate In this case, the ceramic disk-shaped piezoelectric element is disposed orthogonally to the central axis of the straight tube and faces the pipe end sealing regions formed at one end and the other end of the straight tube, respectively. The acoustic impedance matching layer is laminated between the acoustic impedance matching layer made of glass epoxy resin and the vibration absorbing layer made of silicon rubber facing the disk-shaped piezoelectric element, and the thickness of the acoustic impedance matching layer is set to be smaller than the thickness of the disk-shaped piezoelectric element. The thickness of the vibration absorbing layer is set to be thicker than the thickness of the disk-shaped piezoelectric element, and the high-frequency ultrasonic beam is transmitted and received efficiently and exhibits excellent measurement accuracy based on the number of high-frequency measurements. If so, the specific form may be any form.

  That is, the specific communication form of the straight circular pipe, the inflow pipe, and the outflow pipe in the ultrasonic flowmeter of the present invention is a pair of opposite ends that extend to one end and the other end of the straight circular pipe, respectively. As long as the inflow side measurement head and the outflow side measurement head can be provided in any communication form, any communication form may be used.For example, a predetermined inflow angle of the inflow pipe communicating with one end of the straight circular pipe, The predetermined outflow angle of the outflow pipe communicating with the other end of the straight pipe is 30 ° unless excessive turbulent vortices occur at one end and the other end of the straight pipe or a flow failure occurs. Any angle that communicates at 45 °, 90 °, etc. is acceptable. Also, regarding the layout of the inflow pipe and the outflow pipe with respect to the straight circular pipe, the inflow pipe and the outflow pipe are connected to one end and the other end of the straight circular pipe. In the U-shape from the same direction Those are location, or of what is staggered, such as Z-shaped, may be any.

  The specific materials of the straight circular pipe, the inflow pipe, and the outflow pipe used in the ultrasonic flowmeter of the present invention should be a fluorine resin excellent in chemical resistance, heat resistance, weather resistance, transparency, and electrical characteristics. In particular, when PFA (tetrafluoroethylene / perfluoroalkyl / vinyl ether copolymer) is used, not only is the shape of the straight tube excellent, but the sound speed in the PFA is the sound speed of the fluid to be measured. Therefore, it is preferable that the ultrasonic beam is prevented from being transmitted to a pipe such as a straight tube and becoming a noise source.

  Regarding the specific material of the acoustic impedance matching layer used in the ultrasonic flowmeter of the present invention, a sudden change in acoustic impedance that tends to occur between the disk-shaped piezoelectric element and the pipe end sealing region of the straight circular pipe is staged. It is only necessary that the ultrasonic beam can be smoothly propagated and the ultrasonic wave can be smoothly propagated. For example, the glass cloth is made to have a density that is about halfway between the density of the disk-shaped piezoelectric element and the straight tube. A glass epoxy resin or the like in which the density is adjusted by mixing small bubbles when the epoxy resin is impregnated is more preferable.

  The fluid to be measured with the ultrasonic flowmeter of the present invention includes, for example, various chemicals used in devices for polishing and cleaning silicon wafers in liquid crystal manufacturing processes, liquid crystal manufacturing devices, and food manufacturing lines. And liquids such as chemicals used in raw materials, storage and mixing processes in chemical production lines.

Below, the ultrasonic flowmeter 100 which is 1st Example of this invention is demonstrated based on FIG. 1 thru | or FIG.
Here, FIG. 1 is a front sectional view showing an outline of the ultrasonic flowmeter 100 according to the first embodiment, and FIG. 2 is a main part on the inflow side of the ultrasonic flowmeter 100 indicated by reference numeral 2 in FIG. 3A is an enlarged view, and FIG. 3A shows a waveform of an ultrasonic wave received by the disk-shaped piezoelectric element 141 when the thickness d1 of the acoustic impedance matching layer 142 is thinner than the thickness d2 of the disk-shaped piezoelectric element 141. FIG. 3B is a diagram showing a waveform of an ultrasonic wave received by the disk-shaped piezoelectric element 141 when the thickness d1 of the acoustic impedance matching layer 142 is thicker than the thickness d2 of the disk-shaped piezoelectric element 141. 4A is a diagram showing a waveform of an ultrasonic wave received by the disk-shaped piezoelectric element 141 when the thickness d3 of the vibration absorbing layer 143 is thicker than the thickness d2 of the disk-shaped piezoelectric element 141. FIG. 4B shows that the thickness d3 of the vibration absorbing layer 143 is Is a diagram showing an ultrasonic wave received by the plate-like piezoelectric thin disc-shaped piezoelectric element 141 when than the thickness d2 of the element 141.

As shown in FIG. 1, the ultrasonic flowmeter 100 according to the first embodiment of the present invention includes a fluororesin straight tube 110 made of PFA, a fluororesin inflow pipe 120 made of PFA, and a PFA. An outflow pipe 130, a pair of inflow side measuring heads 140 and outflow side measuring heads 150, and a disk-shaped piezoelectric element 141 made of ceramic, also called a piezoelectric element.
Among these, the straight circular tube 110 is provided so as to circulate a liquid which is an example of a fluid to be measured.
Further, the inflow pipe 120 is disposed so as to communicate with one end 111 of the straight circular pipe 110 at a predetermined inflow angle.
Similarly, the outflow pipe 130 is disposed so as to communicate with the other end 112 of the straight circular pipe 110 at a predetermined outflow angle.

In this embodiment, the inflow pipe 120 communicates with one end 111 of the straight pipe 110 at 90 degrees, and the outflow pipe 130 communicates with the other end 112 of the straight pipe 110 from the same side as the inflow pipe 120 at 90 degrees, The straight circular pipe 110, the inflow pipe 120, and the outflow pipe 130 are arranged in a U-shape.
Further, the straight circular pipe 110, the inflow pipe 120, and the outflow pipe 130 are integrally formed of a fluororesin.
The pair of inflow side measurement heads 140 and outflow side measurement heads 150 are disposed so as to extend to one end 111 and the other end 112 of the straight tube 110 and to face each other.
The inflow side measuring head 140 and the outflow side measuring head 150 are also formed integrally with the straight circular pipe 110, the inflow pipe 120, and the outflow pipe 130, and are made of PFA having excellent moldability.
The disk-shaped piezoelectric element 141 is provided in each of the inflow side measurement head 140 and the outflow side measurement head 150 so as to alternately transmit and receive the ultrasonic beam along the central axis C of the straight tube 110. .

Then, the ultrasonic flowmeter 100 receives an ultrasonic beam generated from the disk-shaped piezoelectric element 141 by a calculation unit such as a converter (not shown) electrically connected to the inflow side measurement head 140 and the outflow side measurement head 150. The liquid velocity in the straight tube 110 is obtained from the time difference between the time of propagation from the upstream side to the downstream side of the straight tube 110 and the time of propagation from the downstream side to the upstream side, and the cross-sectional area of the straight tube 110 is obtained from this liquid velocity. And the flow rate of the liquid to be measured flowing in the straight pipe 110 is calculated.
In this embodiment, since the configuration of the inflow side measuring head 140 and the configuration of the outflow side measuring head 150 are the same, the configuration of the inflow side measuring head 140 will be described with reference to FIG. Detailed description of the configuration is omitted.

  As shown in FIG. 2, in the inflow side measuring head 140, a disk-shaped piezoelectric element 141 made of ceramic, an acoustic impedance matching layer 142 made of glass epoxy resin, a vibration absorbing layer 143 made of silicon rubber, A glycerin layer 144, a fluororesin cylindrical holding member 146, a substrate 147, and a rubber O-ring 148 are provided. Has been.

  The disk-shaped piezoelectric element 141 is arranged orthogonally to the central axis C of the straight circular tube 110 and warps by an electrical signal (voltage) sent from the substrate 147 via the conductor L as the transmitting-side disk-shaped piezoelectric element 141. An ultrasonic beam is transmitted by vibrating at a resonance frequency. On the other hand, the receiving-side disk-shaped piezoelectric element 141 is configured to receive and vibrate an ultrasonic beam transmitted from the transmitting-side disk-shaped piezoelectric element, and to transmit an electric signal (voltage) to the substrate 147 through the lead L. Has been.

The acoustic impedance matching layer 142 faces the pipe end sealing region 111a formed at one end 111 of the straight tube 110, and is disposed between the pipe end sealing region 111a and the disk-shaped piezoelectric element 141. Has been.
The acoustic impedance of the acoustic impedance matching layer 142 is set between the acoustic impedance of the duct end sealing region 111a and the acoustic impedance of the disk-shaped piezoelectric element 141.

  In short, the acoustic impedance matching layer 142 is arranged so that the density of the disk-shaped piezoelectric element 141 and the pipe end sealing are such that the ultrasonic beam transmitted from the disk-shaped piezoelectric element 141 is well transmitted to the pipe end sealing region 111a. A thin layer in which small bubbles are mixed in the glass so that the density is intermediate to the density of the stop region 111a, and the acoustic impedance between the disk-shaped piezoelectric element 141 and the pipe end sealing region 111a is adjusted. The purpose is to alleviate sudden changes.

The vibration absorbing layer 143 is disposed on the opposite side to the acoustic impedance matching layer 142 side in the disk-shaped piezoelectric element 141. The vibration absorbing layer 143 has viscoelasticity and is provided to stop vibration early. The vibration absorbing layer 143 also has a role of covering the disk-shaped piezoelectric element 141 and preventing the disk-shaped piezoelectric element 141 from being deteriorated by air or moisture.
The glycerin layer 144 is formed of glycerin applied between the pipe end sealing region 111 a and the acoustic impedance matching layer 142.
The cylindrical holding member 146 holds the substrate 147 therein, and the tip is in contact with the peripheral portion 141a of the disk-shaped piezoelectric element 141.

The O-ring 148 is disposed between the cylindrical holding member 146 and the lid member 149. The O-ring 148 is a buffer material for keeping the pressing force against the disk-shaped piezoelectric element 141 at a predetermined magnitude.
The lid member 149 has a screw structure to keep pressing the O-ring 148.
The pressing force is adjusted by screwing the lid member 149 to the opening end 145 formed in the inflow side measuring head 140.

In the present embodiment, as described above, the disk-shaped piezoelectric element 141 made of ceramic is disposed orthogonally to the central axis C of the straight tube 110 and is formed at one end 111 of the straight tube 110. The acoustic impedance matching layer 142 made of glass epoxy resin facing the pipe end sealing region 111a and the vibration absorbing layer 143 made of silicon rubber facing the disc-shaped piezoelectric element 141 are laminated.
As a result, the acoustic impedance matching layer 142 gradually reduces a sudden change in acoustic impedance that tends to occur between the disk-shaped piezoelectric element 141 and the pipe end sealing region 111a of the straight pipe 110.
Further, the vibration absorbing layer 143 attenuates and absorbs the acoustic vibration of the disk-shaped piezoelectric element 141 at an early stage.

Further, the thickness d1 (that is, thickness 0.5 mm) of the acoustic impedance matching layer 142 is set to be thinner than the thickness d2 (that is, thickness 1 mm) of the disc-shaped piezoelectric element 141.
As a result, as shown in FIG. 3A, irregular reflection at the pipe end sealing region 111a of the straight pipe 110 having an acoustic impedance different from that of the disk-shaped piezoelectric element 141 is reduced, and reception is performed by the disk-shaped piezoelectric element 141. The waveform is stable with a clean spindle shape.
In short, the signal strength is sufficiently strong, the S / N ratio of ultrasonic transmission / reception is sufficiently high, and the measurement accuracy can be improved, so that a turbulent vortex is generated on the flow path of the liquid to be measured. This is particularly effective when the ultrasonic flowmeter 100 is used.

Here, the horizontal axis of FIG. 3A indicates the time when the transmission-side disk-shaped piezoelectric element 141 transmits an ultrasonic beam to 0, and the vertical axis indicates the reception-side disk-shaped piezoelectric element. 141 shows the magnitude of an electric signal (voltage) generated by receiving an ultrasonic beam.
In addition, the “clean spindle-shaped” waveform is a line (as shown in FIG. 3A) in which the amplitude of vibration monotonously increases and reaches a peak, and then attenuates monotonously and indicates a change in amplitude ( (Not shown) refers to a waveform having a spindle shape.

It is desirable that the change in amplitude increases as soon as possible and attenuates as soon as possible.
This is because the waveform when the receiving disk-shaped piezoelectric element 141 receives the ultrasonic beam becomes a “clean spindle shape”, so that the time at the peak of the waveform and the voltage are over a predetermined time period. The time from when the transmitting disk-shaped piezoelectric element 141 transmits an ultrasonic beam to the moment when the receiving disk-shaped piezoelectric element 141 receives the ultrasonic beam is This is because the measurement can be performed with high accuracy, and as a result, the accuracy of the flow rate measurement can be improved.

On the other hand, for reference, when the thickness d1 of the acoustic impedance matching layer 142 is larger than the thickness d2 of the disk-shaped piezoelectric element 141, the ultrasonic beam is converted into the acoustic impedance as shown in FIG. When passing through the matching layer 142, the acoustic vibration is almost absorbed and the signal intensity is weakened, and the amplitude of the vibration does not monotonously increase / decrease, resulting in a distorted waveform where the location of the peak is not clear.
Therefore, the S / N ratio of ultrasonic transmission / reception is significantly deteriorated, and the flow rate measurement accuracy is deteriorated.

In the present embodiment, the thickness d3 (that is, the thickness of 4 mm) of the vibration absorbing layer 143 is set to be thicker than the thickness d2 (that is, the thickness of 1 mm) of the disk-shaped piezoelectric element 141.
As a result, as shown in FIG. 4A, the acoustic vibrations converge early and the next ultrasonic wave can be transmitted.

On the other hand, for reference, when the thickness d3 of the vibration absorbing layer 143 is thinner than the thickness d2 of the disk-shaped piezoelectric element 141, vibration absorption by the vibration absorbing layer 143 is prevented as shown in FIG. It is insufficient and the acoustic vibration does not converge early, and the next ultrasonic wave cannot be transmitted.
Therefore, the number of times of measurement associated with the number of times the ultrasonic beam is generated per unit time is reduced, and the accuracy of the response and the measurement average value is deteriorated.

Returning to FIG. 2, further technical features will be described.
In the present embodiment, the thickness d4 (that is, thickness 3 mm) of the pipe end sealing region 111a formed in the straight circular pipe 110 is set to be thicker than the thickness d2 (that is, thickness 1 mm) of the disk-shaped piezoelectric element 141. ing.
As a result, the temporal deformation of the pipe end sealing region 111a is suppressed, and the relative positional relationship between the disk-shaped piezoelectric elements 141 and 141 is maintained on the central axis and perpendicular to the central axis over a long period of time. In addition, the disk-shaped piezoelectric elements 141 and 141 are arranged so as to face each other in parallel, and the liquid into the fluororesin in the pipe end sealing region 111a that tends to be generated due to the characteristics of the fluororesin. Wetting of chemical substances is suppressed.

On the other hand, for reference, when the thickness d4 of the pipe end sealing region 111a formed in the straight circular pipe 110 is smaller than the thickness d2 of the disk-shaped piezoelectric element 141, the disk-shaped piezoelectric element 141 The pipe-end sealing region 111a that is pressed with a constant pressure becomes susceptible to form deformation over time, the parallelism between the disk-shaped piezoelectric elements is broken, and it is caused by the characteristics of the fluororesin during long-term measurement. As a result, the liquid chemical substance wets in the fluororesin in the pipeline end sealing region 111a.
For this reason, the propagation of the ultrasonic beam in the pipeline end sealing region 111a is obstructed, and the measurement accuracy is deteriorated.

In the present embodiment, as described above, the glycerin layer 144 is provided between the acoustic impedance matching layer 142 and the pipe end sealing region 111a of the straight pipe 110.
Then, the glycerin layer 144 integrally adheres the acoustic impedance matching layer 142 to the duct end sealing region 111a of the straight pipe 110.
This eliminates a gap between the pipe end sealing region 111a of the straight circular pipe 110 and the acoustic impedance matching layer 142, which tends to occur due to the surface roughness.

In the present embodiment, the tube inner diameter r1 of the straight circular tube 110 and the circle diameter r2 of the disc-shaped piezoelectric element 141 are set to be substantially the same.
Here, “substantially the same” means that the difference between the two is less than 2 mm.
Thereby, the ultrasonic beam generated from the disk-shaped piezoelectric element 141 is sufficiently amplified without being irregularly reflected in the straight tube 110, and the ultrasonic beam is alternately transmitted and received.

A cylindrical holding member 146 is provided in the inflow side measuring head 140 and the outflow side measuring head 150, and is in contact with only the peripheral portion 141a so as to hold the peripheral portion 141a of the disc-shaped piezoelectric element 141.
As a result, the disk-shaped piezoelectric element 141 is reliably positioned with respect to the acoustic impedance matching layer 142 without hindering the vibration of the disk-shaped piezoelectric element 141.
Further, the cylindrical holding member 146 includes an acoustic cavity S.
Thereby, the acoustic vibration of the disk-shaped piezoelectric element 141 is allowed and amplified.
That is, the cylindrical holding member 146 presses only the peripheral portion 141a of the disc-shaped piezoelectric element 141 so that the central portion of the disc-shaped piezoelectric element 141 vibrates.

A lid member 149 is screwed to the open end 145 of the inflow side measuring head 140.
Thereby, the cylindrical holding member 146 is elastically pressed toward the disc-shaped piezoelectric element 141 and is securely held.
Furthermore, internal stress that tends to occur in the disk-shaped piezoelectric element 141 is elastically absorbed in accordance with the degree of screwing.
In the present embodiment, the lid member 149 presses the cylindrical holding member 146 toward the disc-shaped piezoelectric element 141 through an O-ring 148 that is elastically deformed.
Thereby, the magnitude | size of the pressing force which the cylindrical holding member 146 contacts the peripheral part 141a of the disk-shaped piezoelectric element 141, and presses this peripheral part 141a becomes a moderate magnitude | size.
Here, the “appropriate size” means the magnitude of the pressing force that can position the disk-shaped piezoelectric element 141 without adversely affecting the vibration of the disk-shaped piezoelectric element 141.

The inflow pipe 120 and the outflow pipe 130 are arranged in a U shape from the same direction at one end 111 and the other end 112 of the straight circular pipe 110.
Thereby, the installation space of the inflow pipe 120 and the outflow pipe 130 with respect to the straight circular pipe 110 in the measurement work area is minimized.

In this embodiment, when the disk-shaped piezoelectric element 141 has a thickness of 1 mm, a circular diameter (r2) of 10 mm, and the frequency of the ultrasonic beam is 2 MHz, the thickness d1 of the acoustic impedance matching layer 142 is 0.5 mm. In addition, the thickness d3 of the vibration absorbing layer 143 is set to 4 mm.
Thereby, the acoustic impedance matching layer 142 suppresses the influence of a large difference in acoustic impedance between the disk-shaped piezoelectric element 141 and the pipe line end sealing region 111a, and a stable waveform propagates.

  On the other hand, for reference, when the disk-shaped piezoelectric element 141 has a thickness of 1 mm, a circular diameter (r2) of 10 mm, and the frequency of the ultrasonic beam is 2 MHz, the thickness d1 of the acoustic impedance matching layer 142 is 0.5 mm. When the thickness becomes thinner, the effect of the acoustic impedance matching layer 142 is reduced, and the influence of a large difference in acoustic impedance between the disk-shaped piezoelectric element 141 and the pipe end sealing region 111a remains, and a stable waveform is obtained. It will interfere with transmission. On the other hand, when the thickness d1 of the acoustic impedance matching layer 142 exceeds 0.5 mm, the acoustic vibration is absorbed by the acoustic impedance matching layer 142 when the ultrasonic beam passes through the acoustic impedance matching layer 142, and the signal intensity is weak. Thus, the S / N ratio of ultrasonic transmission / reception deteriorates and the measurement accuracy decreases.

  In the ultrasonic flow meter 100 according to the first embodiment of the present invention thus obtained, the disk-shaped piezoelectric element 141 made of ceramic is arranged orthogonally to the central axis C of the straight tube 110. At the same time, the acoustic impedance matching layer 142 made of glass epoxy resin and the disc-shaped piezoelectric element 141 face the pipe end sealing regions (111a) formed at the one end 111 and the other end 112 of the straight tube 110, respectively. The acoustic impedance matching layer 142 is set to have a thickness d1 thinner than the thickness d2 of the disc-shaped piezoelectric element 141, and the thickness d3 of the vibration absorbing layer 143 is set to be between the vibration absorbing layer 143 made of silicon rubber. The ultrasonic impedance generated by the acoustic impedance matching layer 142 from the disk-shaped piezoelectric element 141 is set by being thicker than the thickness d2 of the disk-shaped piezoelectric element 141. The number of times the ultrasonic beam is generated per unit time between the inflow side measurement head 140 and the outflow side measurement head 150 can be smoothly propagated toward the pipe end sealing region 111a of the straight tube 110. As a result, the ultrasonic beam can be transmitted and received efficiently and stably, and the accuracy of the response and the measurement average value can be significantly improved.

  Further, since the thickness d4 of the pipe end sealing region 111a formed in the straight circular pipe 110 is set to be thicker than the thickness d2 of the disc-shaped piezoelectric element 141, the ultrasonic wave in the pipe end sealing region 111a is set. The propagation of the beam can be ensured smoothly, and the measurement accuracy can be maintained over a long period of time.

  Further, the glycerin layer 144 that integrally adheres the acoustic impedance matching layer 142 to the pipe end sealing region 111a of the straight pipe 110 is provided with the acoustic impedance matching layer 142 and the pipe end sealing area 111a of the straight pipe 110. The degree of adhesion between the two is improved, and the transmission / reception of the ultrasonic beam can be improved.

  Further, since the inner diameter r1 of the straight circular tube 110 and the circular diameter r2 of the disk-shaped piezoelectric element 141 are set to be substantially the same, the inflow side measuring head 140 and the outflow side measuring head 150 are super A sound beam can be transmitted and received with high sensitivity.

  Further, a cylindrical holding member 146 that holds the peripheral edge 141 a of the disk-shaped piezoelectric element 141 is provided in the inflow side measuring head 140 and the outflow side measuring head 150, and is along the central axis C of the disk-shaped piezoelectric element 141. By providing the acoustic cavity S that allows acoustic vibration of the disc-shaped piezoelectric element 141, it is possible to measure the flow rate stably over a long period of time, and to exhibit excellent durability as a flow meter. The ultrasonic beam can be transmitted with high sensitivity between the side measuring head 140 and the outflow side measuring head 150.

  Further, since the lid member 149 is screwed to the opening end 145 formed in the inflow side measuring head 140 and the outflow side measuring head 150, the flow rate can be stably measured over a long period of time and is excellent as a flowmeter. Durability can be demonstrated.

  Furthermore, since the inflow pipe 120 and the outflow pipe 130 are arranged in a U shape from the same direction at one end 111 and the other end 112 of the straight circular pipe 110, installation interference with other peripheral devices is also possible. It becomes easy to avoid and excellent operability can be exhibited.

  When the disk-shaped piezoelectric element 141 has a thickness of 1 mm, a circular diameter (r2) of 10 mm, and the frequency of the ultrasonic beam is 2 MHz, the thickness d1 of the acoustic impedance matching layer 142 is set to 0.5 mm, Since the thickness d3 of the vibration absorbing layer 143 is set to 4 mm, the effect is enormous, such that the ultrasonic beam can be transmitted with high sensitivity.

Next, an ultrasonic flowmeter 200 according to the second embodiment of the present invention will be described with reference to FIG.
Here, FIG. 5 is a front sectional view showing an outline of the ultrasonic flowmeter 200 of the second embodiment of the present invention.

  The ultrasonic flowmeter 200 of the second embodiment is obtained by arranging the ultrasonic flowmeter 100 of the first embodiment with respect to the straight pipe 110 on the opposite side of the outflow pipe 130. The ultrasonic flow meter 100 is the same as the ultrasonic flow meter 100, and therefore, detailed description of the common items is omitted, and only the reference numbers of the 200th series having the last two digits are attached.

In the ultrasonic flowmeter 200 of the second embodiment, as shown in FIG. 5, the inflow pipe 220 and the outflow pipe 230 are alternately arranged at one end 211 and the other end 212 of the straight circular pipe 210. This is a so-called Z-shaped ultrasonic flow meter 200.
This makes it easy for either the inflow pipe 220 or the outflow pipe 230 to be arranged upward in any measuring form in the measurement work area, and in the liquid to be measured that tends to stay in the straight pipe 210. Air bubbles can be easily degassed from either one end 211 or the other end 212 of the straight tube 210.

  In the ultrasonic flowmeter 200 according to the second embodiment of the present invention thus obtained, the inflow pipe 220 and the outflow pipe 230 are alternately arranged at one end 211 and the other end 212 of the straight circular pipe 210. As a result, it is possible to transmit an ultrasonic beam due to bubble failure that tends to occur between the inflow side measuring head 240 and the outflow side measuring head 250 with high sensitivity.

Subsequently, an ultrasonic flowmeter 300 according to a third embodiment of the present invention will be described with reference to FIG.
Here, FIG. 6 is a front sectional view showing an outline of the ultrasonic flowmeter 300 of the third embodiment of the present invention.

  In the ultrasonic flowmeter 300 of the third embodiment, the inflow angle of the inflow pipe 120 with respect to the straight pipe 110 and the outflow angle of the outflow pipe 130 with respect to the straight pipe 110 of the ultrasonic flowmeter 100 of the first embodiment are set to 45 degrees. Since many elements are the same as those of the ultrasonic flowmeter 100 of the first embodiment, detailed explanations are omitted for the common items, and only the numbers in the 300 series with the last two digits are attached. To do.

In the ultrasonic flowmeter 300 of the third embodiment, as shown in FIG. 6, the inflow pipe 320 communicates with one end 311 of the straight pipe 310 at 45 degrees, and the outflow pipe 330 is also directly connected from the same side as the inflow pipe 320. It communicates with the other end 312 of the circular tube 310 at 45 degrees.
Thereby, compared with the case where the inflow pipe and the outflow pipe communicate with each other at 90 degrees with respect to the straight circular pipe, the liquid to be measured flows smoothly at the communication portion, and the turbulent vortex of the liquid to be measured is reduced, or The generation of this turbulent vortex is suppressed.
As a result, the measurement accuracy of the liquid to be measured can be improved, and the effect is enormous.

Subsequently, an ultrasonic flowmeter 400 according to a fourth embodiment of the present invention will be described with reference to FIG.
Here, FIG. 7 is a front sectional view showing an outline of the ultrasonic flowmeter 400 of the fourth embodiment of the present invention.

  In the ultrasonic flowmeter 400 of the fourth embodiment, the inflow angle of the inflow pipe 220 to the straight pipe 210 and the outflow angle of the outflow pipe 230 to the straight pipe 210 of the ultrasonic flowmeter 200 of the second embodiment are set to 45 degrees. Since many elements are the same as those of the ultrasonic flowmeter 200 of the second embodiment, detailed explanations are omitted for the common items, and only the 400th series code having the same last two digits is attached. To do.

In the ultrasonic flowmeter 400 of the fourth embodiment, as shown in FIG. 7, the inflow pipe 420 communicates with one end 411 of the straight circular pipe 410 at 45 degrees, and the outflow pipe 430 is opposite to the inflow pipe 420. To the other end 412 of the straight tube 410 at 45 degrees.
Thereby, compared with the case where the inflow pipe and the outflow pipe communicate with each other at 90 degrees with respect to the straight circular pipe, the liquid flows smoothly at the communication portion, and the turbulent vortex of the liquid becomes smaller. The generation of vortices is suppressed, and one of the inflow pipe 420 and the outflow pipe 430 is easily arranged upward, and bubbles in the liquid that tends to stay in the straight pipe 410 are removed from the straight pipe 410. It becomes easy to deaerate from either one end 411 or the other end 412.
As a result, the measurement accuracy of the liquid can be improved, and the effect is enormous.

100, 200, 300, 400 ... Ultrasonic flowmeters 110, 210, 310, 410 ... Straight pipes 111, 211, 311, 411 ... One end 111a ... Pipe end sealing region 112 212, 312, 412... The other end 120, 220, 320, 420 ・ ・ ・ the inflow pipe 130, 230, 330, 430 ・ ・ ・ the outflow pipe 140, 240, 340, 440 ・ ・ ・ the inflow side measuring head 141 ... disk-shaped piezoelectric element 141a ... peripheral part 142 ... acoustic impedance matching layer 143 ... vibration absorption layer 144 ... glycerin layer 145 ... opening end 146 ... cylindrical holding member 147 ... Substrate 148 ... O-ring 149 ... Lid members 150, 250, 350, 450 ... Outflow side measuring head C ... Center axis d1 ... Acoustic impedance matching layer thickness d2 ... Disc-shaped piezoelectric element thickness d3 ... Vibration absorbing layer thickness d4 ... Pipe end sealing region thickness L ... Conductor r1・ ・ ・ Pipe inner diameter r2 of straight pipe ・ ・ ・ Circle diameter S of disk-shaped piezoelectric element ・ ・ ・ Acoustic cavity

Claims (9)

A fluororesin straight circular pipe for circulating the fluid to be measured, an inflow pipe communicating with one end of the straight circular pipe at a predetermined inflow angle, and an outflow communicating with the other end of the straight circular pipe at a predetermined outflow angle A pipe, a pair of inflow side measurement heads and outflow side measurement heads extending to one end and the other end of the straight circular tube and facing each other, and inflow side measurement heads and outflow side measurement heads, respectively. And a ceramic disk-shaped piezoelectric element that alternately transmits and receives an ultrasonic beam along the central axis of the straight pipe, and the ultrasonic beam generated from the disk-shaped piezoelectric element is The fluid velocity in the straight pipe is obtained from the time difference between the time propagating from the upstream side to the downstream side and the time propagating from the downstream side to the upstream side, and the fluid velocity is multiplied by the cross-sectional area of the straight pipe. Time difference type ultrasonic flowmeter for determining flowing flow rate Oite,
The ceramic disk-shaped piezoelectric element is disposed orthogonally to the central axis of the straight pipe and faces a pipe end sealing region formed at one end and the other end of the straight pipe, respectively. Laminated between an acoustic impedance matching layer made of glass epoxy resin and a vibration absorbing layer made of silicon rubber facing the disk-shaped piezoelectric element,
The thickness of the acoustic impedance matching layer is set to be thinner than the thickness of the disk-shaped piezoelectric element,
The ultrasonic flowmeter according to claim 1, wherein a thickness of the vibration absorbing layer is set to be greater than a thickness of the disk-shaped piezoelectric element.   The ultrasonic flowmeter according to claim 1, wherein a thickness of a pipe end sealing region formed in the straight circular pipe is set to be thicker than a thickness of the disk-shaped piezoelectric element.   A glycerin layer for integrally adhering the acoustic impedance matching layer to the pipe end sealing region of the straight pipe is provided between the pipe end sealing region of the straight pipe and the acoustic impedance matching layer. The ultrasonic flowmeter according to claim 2, wherein   The ultrasonic flowmeter according to claim 3, wherein the inner diameter of the straight circular tube and the diameter of the disk-shaped piezoelectric element are set to be substantially the same.   A disc-shaped piezoelectric element is provided along the central axis of the disc-shaped piezoelectric element, wherein a cylindrical holding member that holds a peripheral portion of the disc-shaped piezoelectric element is provided in the inflow side measuring head and the outflow side measuring head The ultrasonic flowmeter according to claim 4, further comprising an acoustic cavity that allows acoustic vibrations of the ultrasonic flowmeter.   A lid member that elastically presses a cylindrical holding member toward the disk-shaped piezoelectric element is screwed to an opening end formed in the inflow side measurement head and the outflow side measurement head. The ultrasonic flowmeter according to claim 5.   7. The inflow pipe and the outflow pipe are arranged in a U-shape from the same direction at one end and the other end of the straight circular pipe and communicate with the straight circular pipe. The described ultrasonic flowmeter.   The ultrasonic flowmeter according to claim 6, wherein the inflow pipe and the outflow pipe are alternately arranged at one end and the other end of the straight circular pipe and communicate with the straight circular pipe.   When the disk-shaped piezoelectric element has a thickness of 1 mm, a circular diameter of 10 mm, and the frequency of the ultrasonic beam is 2 MHz, the thickness of the acoustic impedance matching layer is set to 0.5 mm, and the vibration absorption layer The ultrasonic flowmeter according to claim 7 or 8, wherein the thickness is set to 4 mm.