JP2008267848A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter which are provided with ultrasonic transducers arranged in parallel with the flow of a fluid so that a stagnant part is not produced in the fluid, controls the phase of an ultrasonic wave to be emitted from an ultrasonic transducer, and can emit an ultrasonic wave in a direction forming an acute angle (less than 90°) with the radiation surface of the ultrasonic transducer. <P>SOLUTION: The ultrasonic flowmeter is provided with a passage 30 where a fluid to be measured flows, a pair of ultrasonic elements 10, 20 arranged on the upstream side and on the downstream side with the passage 30 between, and a flow rate operation section 15 for calculating the flow rate of the fluid to be measured based on propagation time of an ultrasonic wave transmitted and received by the ultrasonic elements 10, 20. Each ultrasonic wave transmitting/receiving surface (acoustic matching layer 13, or 23) of the ultrasonic elements 10, 20 is arranged in parallel with a wall surface of the passage 30, and the ultrasonic flowmeter is equipped with delay circuits 14, 24 for delaying the transmission or reception of the ultrasonic wave for each block divided in the thickness direction of the ultrasonic elements 10, 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic flow meter, and more particularly, to an ultrasonic flow meter used for fluid flow velocity and flow rate measurement using ultrasonic waves, detection of minute leakage, and the like.

  Conventionally, in order to measure the flow velocity of a gas flowing through a pipeline, as shown in FIG. 6, at least one pair of ultrasonic transducers 100 and 200 are arranged along the flow on the upstream side and the downstream side so as to face the flow. They are arranged with a constant inclination θ (see, for example, Patent Document 1).

As a flow rate calculation method of such an ultrasonic flowmeter, the flow velocity of the fluid to be measured flowing inside the flow path is V, the velocity of the ultrasonic wave in the fluid is C, and the angle between the flow direction of the fluid and the propagation direction of the ultrasonic pulse is Let θ. Furthermore, when the ultrasonic transducer 100 arranged on the upstream side is used as a transmitter and the ultrasonic transducer 200 arranged on the downstream side is used as a receiver, the ultrasonic pulse emitted from the ultrasonic transducer 100 is transmitted between ultrasonic elements ( If the time for propagation between the ultrasonic transducers 100 and 200 is T1, the following equation is established.
1 / T1 = (C + V cos θ) / L (1)
Conversely, when the ultrasonic transducer 100 arranged on the upstream side is used as a receiver and the ultrasonic transducer 200 arranged on the downstream side is used as a transmitter, between the ultrasonic elements (between the ultrasonic transducers 100 and 200). When the propagation time is T2, the following equation is established.
1 / T2 = (C−V cos θ) / L (2)

From the propagation times T1 and T2, the flow velocity V of the fluid to be measured is obtained from the following equation.
2V cos θ / L = (1 / T1) − (1 / T2)
V = L / 2 cos θ * ((1 / T1) − (1 / T2)) (3)
Then, the flow rate Q can be calculated from the following equation using the obtained flow velocity V and the cross-sectional area S of the flow path.
Q = V * S (4)
Japanese Patent No. 3824236

  However, in such an arrangement, as shown in FIG. 6, there are places where the fluid always stagnates (fluid stagnation portions 101 and 201 in the figure), and this influence reduces the flow velocity accuracy. Further, since the state of flowing into the fluid stagnation portions 101 and 201 also changes depending on the flow rate, there is a problem that a stable and accurate flow velocity cannot be obtained.

Moreover, as a means for reducing the influence on the fluid stagnation parts 101 and 201, there is an idea of arranging a mesh-like member at a level that does not affect the ultrasonic measurement and reducing the inflow. In this case, it is necessary to newly provide the mesh member 300, which increases the cost and concerns about the characteristic difference due to assembly.
In addition, when the flow rate is increased, the flow turbulence increases, and ultrasonic waves are reflected or refracted by the increased vortex and the reception level of the ultrasonic waves is lowered. Therefore, it is difficult to reduce the drive input in ultrasonic transmission / reception. there were.

  The present invention has been made in view of the above circumstances, and an ultrasonic transducer is arranged in parallel to the flow of fluid so that a stagnation portion of fluid does not occur, and an ultrasonic wave emitted from the ultrasonic transducer is not generated. An object of the present invention is to provide an ultrasonic flowmeter that can control the phase and emit ultrasonic waves in a direction at an acute angle (less than 90 °) from the radiation surface of the ultrasonic transducer.

  In order to solve the above-mentioned problems, the invention of claim 1 includes a channel through which a fluid to be measured flows, a pair of ultrasonic elements disposed on the upstream side and the downstream side across the channel, and the pair of ultrasonic elements. An ultrasonic flowmeter comprising flow rate calculation means for calculating a flow rate of the fluid to be measured based on a propagation time of ultrasonic waves transmitted and received by the acoustic wave element, wherein the pair of ultrasonic elements includes the pair of ultrasonic elements. Each ultrasonic transmission / reception surface of the ultrasonic element is arranged in parallel with the wall surface of the flow path, and the ultrasonic flowmeter transmits or receives ultrasonic waves for each block divided in the thickness direction of the pair of ultrasonic elements. It is characterized by comprising delay means for delaying.

  According to a second aspect of the present invention, in the first aspect of the present invention, the delay unit sequentially delays the divided blocks of the ultrasonic element on the transmission side when transmitting and receiving ultrasonic waves by the pair of ultrasonic elements. In addition to being driven, the divided blocks of the receiving-side ultrasonic element are received in order in the same delay time as the transmitting-side ultrasonic element.

  The invention of claim 3 is the invention of claim 1 or 2, wherein each of the pair of ultrasonic elements has one piezoelectric element bonded to one acoustic matching layer and one in the thickness direction of the piezoelectric element. The above-mentioned slit is formed.

  According to a fourth aspect of the present invention, in the first or second aspect of the present invention, each of the pair of ultrasonic elements is integrally configured by bonding a plurality of independent piezoelectric elements to one acoustic matching layer. It is characterized by that.

  According to the present invention, the ultrasonic transducer is arranged in parallel to the fluid flow so as not to generate a stagnation portion of the fluid, the phase of the ultrasonic wave emitted from the ultrasonic transducer is controlled, and the radiation surface of the ultrasonic transducer Can emit an ultrasonic beam at an oblique angle with respect to the flow, without disturbing the flow, and without reducing the transmission / reception efficiency of the ultrasonic wave. The fluid flow rate can be calculated.

  Hereinafter, preferred embodiments of the ultrasonic flowmeter of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the part which has the same function in each embodiment, and repeated description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a diagram illustrating an arrangement example of ultrasonic elements included in the ultrasonic flowmeter of the present invention. In the figure, reference numeral 10 denotes an ultrasonic element (hereinafter referred to as an ultrasonic transducer). The ultrasonic transducer 10 includes a packing (damper) member 11, a piezoelectric element 12, and an acoustic matching layer 13. Similarly, the ultrasonic transducer 20 that forms a pair with the ultrasonic transducer 10 includes a packing (damper) member 21, a piezoelectric element 22, and an acoustic matching layer 23. In the case of this example, it is assumed that the fluid to be measured flows in the flow path 30 at the flow velocity V in the direction of the arrow in the figure.

  The pair of ultrasonic transducers 10 and 20 are disposed on the upstream side and the downstream side with the flow path 30 through which the fluid to be measured flows, and each ultrasonic transmission / reception surface of the ultrasonic transducer 10 and the ultrasonic transducer 20. (In other words, the acoustic matching layers 13 and 23) are arranged in parallel with the wall surface of the flow path 30. In other words, the ultrasonic transmission / reception surfaces of the ultrasonic transducer 10 and the ultrasonic transducer 20 are arranged at positions parallel to the flow of the fluid to be measured flowing through the flow path 30, and constitute a part of the wall surface of the flow path 30. is doing. As described above, the ultrasonic transmission / reception surfaces of the upstream ultrasonic transducer 10 and the downstream ultrasonic transducer 20 are arranged so as to be parallel to the direction of the flow of the fluid to be measured. Generation of the fluid stagnation part (triangular region) shown can be prevented.

  In FIG. 1, when the propagation length between a pair of ultrasonic transducers is L and the radiation beam directivity angle is θ, the flow velocity V can be obtained from the above-described equation (3). For example, when transmitting an ultrasonic wave, the position of the adjacent piezoelectric element transmitted with a delay of td or 2td is received with a delay equal to the delay time when receiving the ultrasonic wave. The propagation time is only the delay, and the shortest time of the sound wave at the propagation length L is equal.

  When the phase-controlled ultrasonic waves from a pair of ultrasonic transducers are directed at a certain angle θ relative to the direction of their arrangement, the same-phase ultrasonic waves are attached at a pseudo constant angle θ. It is the same as the treatment of. It is assumed that the ultrasonic waves that propagate with a delay of td and 2td at the time of driving are synthesized with an equal delay considering the delay at the time of reception, as if the same ultrasonic waves arrived at the same time with the delay time canceled. Can be handled.

  FIG. 2 is a diagram illustrating a configuration example of a piezoelectric element included in the ultrasonic transducer according to the first embodiment of the present invention. FIG. 2A shows an integrated piezoelectric element, and FIG. 2B shows a state where the integrated piezoelectric element and the acoustic matching layer are bonded and bonded together. As shown in FIGS. 2A and 2B, the piezoelectric element 12 having a square shape is formed with one or more slits S in the thickness direction. In the case of this example, the piezoelectric element 12 is divided into three blocks by the two slits S, and each of the blocks 1, 2, and 3 vibrates longitudinally in the thickness direction almost independently. As a result, vibration from each of the blocks 1, 2, 3 propagates to the common acoustic matching layer 13, and the ultrasonic waves are radiated independently from substantially the center position of each of the blocks 1, 2, 3. Can do.

  FIG. 3 is a diagram illustrating a configuration example of the ultrasonic flowmeter according to the first embodiment of the present invention. In the figure, the ultrasonic flowmeter is connected to the ultrasonic transducer 10 and the ultrasonic transducer 10, and a delay circuit 14 that delays transmission or reception of ultrasonic waves for each of the blocks 1, 2, and 3 constituting the piezoelectric element 12. An ultrasonic transducer 20, a delay circuit 24 connected to the ultrasonic transducer 20, and delaying the transmission or reception of the ultrasonic wave for each of the blocks 1 ′, 2 ′ and 3 ′ constituting the piezoelectric element 22; A flow rate calculation unit 15 connected to the delay circuit 24 and corresponding to the flow rate calculation means of the present invention for calculating the flow rate of the fluid to be measured based on the propagation time of the ultrasonic waves transmitted and received by the ultrasonic transducers 10 and 20; Prepare.

  The delay circuits 14 and 24 correspond to the delay means of the present invention. When transmitting and receiving ultrasonic waves by the pair of ultrasonic transducers 10 and 20, for example, the divided blocks 1 and 2 of the ultrasonic transducer 10 on the transmission side are used. , 3 are driven in order in order to transmit ultrasonic waves, and the divided blocks 1 ′, 2 ′, 3 ′ of the ultrasonic transducer 20 on the receiving side are sequentially switched with the same delay time as the ultrasonic transducer 10 on the transmitting side. Configured to receive late.

  That is, as shown in FIG. 3, the piezoelectric element 12 is divided into three blocks 1, 2, and 3, and each of the blocks 1, 2, and 3 is each independently provided with a delay circuit 14 (delay circuits a, b, and c). Specifically, a delay circuit a is connected to the piezoelectric block 1 constituting the upstream ultrasonic transducer 10, a delay circuit b is connected to the piezoelectric block 2, and a delay circuit c is connected to the piezoelectric block 3. When transmitting ultrasonic waves from each of the piezoelectric blocks 1, 2, 3, first, a driving voltage is applied to the piezoelectric block 1 from the outside, and then the adjacent piezoelectric block 2 is driven with a delay of a predetermined time td. The adjacent piezoelectric block 3 is driven with a delay of a fixed time td ′ (= 2td).

  On the other hand, in the ultrasonic transducer 20 on the downstream side, a delay circuit a 'is connected to the piezoelectric block 1', a delay circuit b 'is connected to the piezoelectric block 2', and a delay circuit c 'is connected to the piezoelectric block 3'. . Then, the ultrasonic wave from the ultrasonic transducer 10 is first received by the piezoelectric block 1 ', and thereafter received by the piezoelectric block 2' with a delay of a certain delay time td by the delay circuit b ', and finally, the delay circuit c. 'Is delayed by a fixed delay time td' (= 2td) and received by the piezoelectric block 3 '. The ultrasonic signals received by the piezoelectric blocks 1 ', 2', 3 'are added and synthesized independently.

  In this way, the ultrasonic radiation surface of the ultrasonic transducer can be arranged without being inclined with respect to the flow of the fluid to be measured, so it is possible to eliminate the stagnation part (triangular region) of the fluid, and the influence of inflow due to the flow rate Since the measurement error can be remarkably reduced by eliminating the above, highly accurate and stable flow velocity measurement becomes possible.

  In addition, by forming slits in the thickness direction of the piezoelectric element, the piezoelectric element is divided into a plurality of pieces and the adjacent vibrations can be substantially separated, so that each piezoelectric element can vibrate substantially equally. It is possible to efficiently radiate a plurality of ultrasonic waves to a space independently.

  In addition, the piezoelectric elements divided into a plurality by the slits are vibrated with their phases shifted independently from each other, so that the phase-shifted ultrasonic signal is the direction of the receiving-side ultrasonic transducer as a target. Therefore, even if the ultrasonic radiation surfaces are parallel to each other, it is possible to efficiently transmit ultrasonic waves.

  In addition, the ultrasonic transducer can be placed parallel to the fluid flow as described above, eliminating the fluid stagnation part (triangular region) and significantly reducing measurement errors due to the flow rate. Measurement is possible.

  Here, as shown in FIG. 2, the piezoelectric element 12 included in the pair of ultrasonic transducers 10 is an integrated piezoelectric element that is separated into three blocks by two slits provided at a certain depth in the thickness direction. Configured as An acoustic matching layer 13 having a certain thickness is adhered to the surface on which the slit is formed, and a damper (packing) member (not shown) is filled on the surface on the opposite side. It goes without saying that the ultrasonic transducer 20 that is paired with the ultrasonic transducer 10 is similarly configured.

  As shown in FIG. 3, the ultrasonic transducers 10 and 20 attached to the upstream side and the downstream side of the flow path 30 are arranged so that the ultrasonic radiation surfaces of the acoustic matching layers 13 and 23 are parallel to the flow of the fluid to be measured. Furthermore, they are arranged at positions facing each other with a certain distance in the flow direction. The pair of ultrasonic transducers 10 and 20 includes piezoelectric elements 12 and 22 divided into three blocks, respectively. The piezoelectric elements 12 and 22 are externally connected via damper members 11 and 21 on the back surface. Delay circuits 14 and 24 are connected to each other independently.

  As described above, in the case of the ultrasonic transducer 10 on the upstream side, the piezoelectric block 1 constituting the piezoelectric element 12 has the delay circuit a, the piezoelectric block 2 has the delay circuit b, and the piezoelectric block 3 has the delay circuit c. Connected. When transmitting ultrasonic waves from each of the piezoelectric blocks 1, 2 and 3, a driving voltage is applied to the piezoelectric block 1 from the outside, and then the adjacent piezoelectric block 2 is driven with a delay of a certain time td, and further, a certain time td. The adjacent piezoelectric block 3 is driven with a delay of ′ (= 2td).

  As a result, the wavefront w1 of the ultrasonic wave transmitted from the piezoelectric block 1, the wavefront w2 due to the piezoelectric block 2 propagated later, and the wavefront w3 due to the piezoelectric block 3 propagated further later are synthesized and in phase. The wavefront w is delayed in time and reaches the ultrasonic wave receiving surface of the acoustic matching layer 23 provided in the ultrasonic transducer 20 on the downstream side.

  In the case of the ultrasonic transducer 20 on the downstream side, piezoelectric blocks 1 ′, 2 ′, 3 ′ are provided for receiving the ultrasonic waves propagated through the acoustic matching layer 23, and a delay circuit a ′ is provided in the piezoelectric block 1 ′. A delay circuit b 'is connected to the piezoelectric block 2', and a delay circuit c 'is connected to the piezoelectric block 3'. Here, the signal is first received by the piezoelectric block 1 ′, then received by the piezoelectric block 2 ′ with a delay of a certain delay time td by the delay circuit b ′, and finally the constant delay time td by the delay circuit c ′. It is received by the piezoelectric block 3 'with a delay of' (= 2td). These ultrasonic signals are electrically added separately. Thereby, the ultrasonic signals transmitted from the upstream ultrasonic transducer 10 and received by the piezoelectric blocks of the downstream ultrasonic transducer 20 can be synthesized at a constant time interval.

  Next, an operation (operation 2) opposite to the above operation (operation 1) is performed. That is, operation 2 is an operation in which ultrasonic waves are transmitted from the ultrasonic transducer 20 on the downstream side and received by the ultrasonic transducer 10 on the upstream side. Then, by repeating these operations 1 and 2 alternately and repeatedly, the flow rate can be calculated by measuring and calculating the flow velocity of the fluid to be measured flowing through the flow path 30.

  As described above, in addition to the operation that alternately repeats the operations 1 and 2, for example, after the operation 1 is repeated a plurality of times, the ultrasonic waves are transmitted and received in a set in which the opposite operation 2 is repeated a plurality of times. It may be.

In this way, by oscillating the piezoelectric elements divided into a plurality by the slits with their phases shifted independently from each other, the ultrasonic signals shifted in phase can be converted into ultrasonic waves on the receiving side that are positionally shifted as targets. It is possible to concentrate and bias in the direction of the transducer, and at the same time, even when receiving ultrasonic waves, by receiving delayed ultrasonic waves while shifting the phase, it is possible to improve transmission and reception efficiency, high accuracy and stability Can be measured.
In addition, since the sound pressure can be increased by concentrating individual ultrasonic waves, power consumption can be reduced.

(Second Embodiment)
FIG. 4 is a diagram illustrating a configuration example of a piezoelectric element included in an ultrasonic transducer according to the second embodiment of the present invention. 4A shows a separation-type piezoelectric element, and FIG. 4B shows a state in which the separation-type piezoelectric element and an acoustic matching layer are bonded and bonded together. As shown in FIGS. 4A and 4B, the acoustic matching layer 13 having a certain thickness is adhered to the upper surface of the plurality of piezoelectric elements 1, 2, and 3 that are spatially separated into three. It is configured by filling a damper material (not shown) on the opposite surface.

  In the case of the present embodiment, the piezoelectric element 12 is divided into three blocks by three rectangular piezoelectric elements 1, 2, 3 that are originally separated, and each of the blocks 1, 2, 3 is independently in the thickness direction. It vibrates longitudinally. Thereby, similarly to the configuration of FIG. 2, the vibration from each of the blocks 1, 2, 3 propagates to the common acoustic matching layer 13, and from the substantially central position of each block 1, 2, 3, Ultrasonic waves can be emitted independently. It goes without saying that the ultrasonic transducer 20 that is paired with the ultrasonic transducer 10 is similarly configured.

  FIG. 5 is a diagram illustrating a configuration example of an ultrasonic flowmeter according to the second embodiment of the present invention. In the figure, the ultrasonic flowmeter includes an ultrasonic transducer 10, a delay circuit 14, an ultrasonic transducer 20, a delay circuit 24, and a flow rate calculation unit 15, similarly to the configuration of FIG. 3. In the case of this embodiment, each of the pair of ultrasonic transducers is integrally configured by bonding a plurality of independent piezoelectric elements to one acoustic matching layer. The other basic configuration is the same as that of the first embodiment.

  That is, the ultrasonic transducers 10 and 20 attached to the upstream side and the downstream side of the flow path 30 are attached so that the ultrasonic radiation surfaces of the acoustic matching layers 13 and 23 are parallel to the flow of the fluid to be measured. It arrange | positions in the position facing a predetermined distance apart in the flow direction. The pair of ultrasonic transducers 10 and 20 includes piezoelectric elements 12 and 22 each formed of three blocks. The piezoelectric elements 12 and 22 are externally connected via damper members 11 and 21 on the back surface. Delay circuits 14 and 24 are connected to each other independently.

  In the case of the upstream ultrasonic transducer 10, a delay circuit a is connected to the piezoelectric block 1 constituting the piezoelectric element 12, a delay circuit b is connected to the piezoelectric block 2, and a delay circuit c is connected to the piezoelectric block 3. When transmitting ultrasonic waves from each of the piezoelectric blocks 1, 2 and 3, a driving voltage is applied to the piezoelectric block 1 from the outside, and then the adjacent piezoelectric block 2 is driven with a delay of a certain time td, and further, a certain time td. The adjacent piezoelectric block 3 is driven with a delay of ′ (= 2td).

  As a result, the wavefront w1 of the ultrasonic wave transmitted from the piezoelectric block 1, the wavefront w2 due to the piezoelectric block 2 propagated later, and the wavefront w3 due to the piezoelectric block 3 propagated further later are synthesized and in phase. The wavefront w is delayed in time and reaches the ultrasonic wave receiving surface of the acoustic matching layer 23 provided in the ultrasonic transducer 20 on the downstream side.

  In the case of the ultrasonic transducer 20 on the downstream side, piezoelectric blocks 1 ′, 2 ′, 3 ′ are provided for receiving the ultrasonic waves propagated through the acoustic matching layer 23, and a delay circuit a ′ is provided in the piezoelectric block 1 ′. A delay circuit b 'is connected to the piezoelectric block 2', and a delay circuit c 'is connected to the piezoelectric block 3'. Here, the signal is first received by the piezoelectric block 1 ′, then received by the piezoelectric block 2 ′ with a delay of a certain delay time td by the delay circuit b ′, and finally the constant delay time td by the delay circuit c ′. It is received by the piezoelectric block 3 'with a delay of' (= 2td). These ultrasonic signals are electrically added separately. Thereby, the ultrasonic signals transmitted from the upstream ultrasonic transducer 10 and received by the piezoelectric blocks of the downstream ultrasonic transducer 20 can be synthesized at a constant time interval.

  Next, an operation (operation 2) opposite to the above operation (operation 1) is performed. That is, operation 2 is an operation in which ultrasonic waves are transmitted from the ultrasonic transducer 20 on the downstream side and received by the ultrasonic transducer 10 on the upstream side. Then, by repeating these operations 1 and 2 alternately and repeatedly, the flow rate can be calculated by measuring and calculating the flow velocity of the fluid to be measured flowing through the flow path 30.

  As described above, in addition to the operation that alternately repeats the operations 1 and 2, for example, after the operation 1 is repeated a plurality of times, the ultrasonic waves are transmitted and received in a set in which the opposite operation 2 is repeated a plurality of times. It may be.

Thus, the vibration efficiency can be further improved by vibrating the plurality of mechanically separated piezoelectric elements with their phases shifted independently of each other.
In addition, it is possible to concentrate and bias the phase-shifted ultrasonic signals toward the target ultrasonic transducer on the target position, which is shifted in position, and at the same time shift the phase when receiving ultrasonic waves. However, by receiving the delayed ultrasonic wave, it is possible to increase the transmission / reception efficiency, and it is possible to perform highly accurate and stable flow velocity measurement.
In addition, since the sound pressure can be increased by concentrating individual ultrasonic waves, power consumption can be reduced.

It is a figure which shows the example of arrangement | positioning of the ultrasonic element with which the ultrasonic flowmeter of this invention is provided. It is a figure which shows the structural example of the piezoelectric element with which the ultrasonic transducer which concerns on the 1st Embodiment of this invention is provided. It is a figure which shows the structural example of the ultrasonic flowmeter which concerns on the 1st Embodiment of this invention. It is a figure which shows the structural example of the piezoelectric element with which the ultrasonic transducer which concerns on the 2nd Embodiment of this invention is provided. It is a figure which shows the structural example of the ultrasonic flowmeter which concerns on the 2nd Embodiment of this invention. It is a figure which shows arrangement | positioning of the ultrasonic element with which the conventional ultrasonic flowmeter is provided.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20, 100, 200 ... Ultrasonic transducer, 11, 21 ... Packing (damper) member, 12, 22 ... Piezoelectric element, 13, 23 ... Acoustic matching layer, 14, 24 ... Delay circuit, 15 ... Flow rate calculating part, 30 ... flow path, 101, 201 ... fluid stagnation part, 300 ... mesh member.

Claims (4)

Based on the flow path through which the fluid to be measured flows, a pair of ultrasonic elements disposed on the upstream side and the downstream side across the flow path, and the propagation time of ultrasonic waves transmitted and received by the pair of ultrasonic elements An ultrasonic flowmeter comprising a flow rate calculation means for calculating the flow rate of the fluid to be measured,
In the pair of ultrasonic elements, each ultrasonic transmission / reception surface of the pair of ultrasonic elements is arranged in parallel with the wall surface of the flow path,
The ultrasonic flowmeter comprises delay means for delaying transmission or reception of ultrasonic waves for each block divided in the thickness direction of the pair of ultrasonic elements.   2. The ultrasonic flowmeter according to claim 1, wherein the delay unit drives the divided blocks of the ultrasonic element on the transmission side with a delay in order when transmitting and receiving ultrasonic waves by the pair of ultrasonic elements. In addition, the ultrasonic flowmeter is characterized in that the divided blocks of the receiving-side ultrasonic element are sequentially received with the same delay time as the transmitting-side ultrasonic element.   The ultrasonic flowmeter according to claim 1 or 2, wherein each of the pair of ultrasonic elements has one piezoelectric element bonded to one acoustic matching layer, and one or more in the thickness direction of the piezoelectric element. An ultrasonic flowmeter, wherein a slit is formed.   3. The ultrasonic flowmeter according to claim 1, wherein each of the pair of ultrasonic elements is configured integrally by bonding a plurality of independent piezoelectric elements to one acoustic matching layer. The characteristic ultrasonic flowmeter.

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