Clamp-type ultrasonic flow meter

Abstract

[Problem] To provide a clamp-type ultrasonic flow meter that allows for easy positioning of the piezoelectric element installed in an ultrasonic transducer, suppresses subsequent misalignment, and maintains good acoustic characteristics. [Solution] The clamp-type ultrasonic flow meter uses ultrasound to measure the flow rate of fluid flowing in a piping system. A positioning recess (66) for positioning the piezoelectric element (62) is formed on the inclined surface of the wedge (61) on which the piezoelectric element (62) is installed in the ultrasonic transducer. Furthermore, the side of the positioning recess (66) has an outwardly expanding inclination. Acoustic grease is applied between the positioning recess (66) and the piezoelectric element (62), and the piezoelectric element (62) is fixed to the positioning recess (66) by pressing the retaining member (64) of the piezoelectric element (62) through a backing layer member (63) with a buffer function.

Description

Clamp-on ultrasonic flowmeter The present invention relates to a clamp-type ultrasonic flowmeter which uses ultrasound to measure the flow rate of a fluid flowing in a pipe. Conventionally, ultrasonic flowmeters are known that use ultrasound to measure the flow rate of fluid flowing through pipes. These ultrasonic flowmeters transmit and receive ultrasound between a piezoelectric element located upstream of the pipe and a piezoelectric element located downstream of the pipe, measuring the flow rate of the fluid flowing through the pipe based on the difference in transmission time. As such an ultrasonic flowmeter, an ultrasonic flowmeter of an oblique injection method is known (for example, refer to Patent Document 1). An ultrasonic flowmeter of an oblique injection method transmits and receives ultrasonic waves obliquely to the pipe between a small piezoelectric element provided on the upstream side of the pipe and a small piezoelectric element provided on the downstream side of the pipe, and measures the flow rate of the fluid flowing in the pipe based on the transmission time difference. In addition, an ultrasonic flowmeter of an oblique injection method can install the piezoelectric element on the pipe in a clamping manner. The clamping method is a method in which the piezoelectric element can be installed on an existing pipe without cutting the pipe. [Prior Technical Document] [Patent Document] [Patent Document 1] Japanese Patent Application Laid-Open No. 2021-15090 [Problems to be solved by the invention] While clamp-on ultrasonic flowmeters utilize ultrasonic transducers, adhesives have traditionally been used to attach the piezoelectric element to the transducer wedge. This adhesive structure can generate thermal stress due to low and high temperatures, potentially causing cracking or peeling of the piezoelectric element. Therefore, the use of acoustic paste to attach the piezoelectric element to the wedge's slope has been considered. However, the use of acoustic paste can cause the piezoelectric element to shift position due to vibration or shock after assembly, leading to deterioration in ultrasonic reception and transmission characteristics. The present invention has been completed in view of the above-mentioned problems, and its purpose is to provide a clamp-type ultrasonic flowmeter that can easily position the piezoelectric element installed in the ultrasonic transducer, suppress subsequent misalignment, and maintain good acoustic characteristics. [Technical Means for Solving the Problem] To solve the above-mentioned problems and achieve the purpose, the clamp-on ultrasonic flowmeter of the present invention uses ultrasound to measure the flow rate of a fluid flowing in a pipe. The clamp-on ultrasonic flowmeter is characterized in that a positioning recess for positioning the piezoelectric element is formed on the inclined surface of the wedge on which the piezoelectric element of the ultrasonic transducer is mounted. Furthermore, the present invention is characterized in that, in the above invention, the side surface of the positioning recess has an inclination that expands toward the periphery. Furthermore, the present invention is characterized in that, in the above invention, acoustic paste is applied between the positioning recess and the piezoelectric element, and the piezoelectric element is fixed to the positioning recess by pressing a fixing member of the piezoelectric element through a back layer member having a buffering function. [Effects of the Invention] In the present invention, the piezoelectric element mounted on the ultrasonic transducer can be easily positioned, and subsequent misalignment can be suppressed while maintaining good acoustic characteristics. Hereinafter, an embodiment of the clamp-type ultrasonic flowmeter of the present invention will be described in detail with reference to the drawings. However, this embodiment is not intended to limit the present invention. <Overall Structure> Figure 1 is a perspective view of a clamp-type ultrasonic flowmeter 1 according to an embodiment of the present invention. Furthermore, Figure 2 is an exploded perspective view of the clamp-type ultrasonic flowmeter 1 shown in Figure 1 . Furthermore, Figure 3 is a longitudinal sectional view of the clamp-type ultrasonic flowmeter 1 shown in Figure 1 . As shown in Figures 1 to 3 , the clamp-type ultrasonic flowmeter 1 clamps a pipe 100 through which fluid flows from both sides by means of a main body-side pipe mounting portion 30 and an external pipe mounting portion 20 mounted on a main body 10 of the device, thereby measuring the flow rate of the fluid. The clamp-type ultrasonic flowmeter 1 includes ultrasonic transducers 5 and 6 facing each other. These transducers 5 and 6 transmit and receive ultrasonic signals to and from the fluid in the pipe 100. Piezoelectric elements 52 and 62 are mounted on the inclined surfaces of wedges 51 and 61, respectively, and transmit and receive ultrasonic signals obliquely toward the pipe 100 from the lower surfaces of the wedges 51 and 61 through the acoustic coupler rubber 40. The clamp-on ultrasonic flowmeter 1 measures flow rate by clamping the pipe 100. For example, ultrasonic transducer 5 transmits ultrasonic signal L1, which is reflected and returned once by the pipe 100 by ultrasonic transducer 6. The propagation time of ultrasonic signal L1 is measured. Subsequently, ultrasonic transducer 6 transmits ultrasonic signal L2, which is reflected and returned once by the pipe 100 by ultrasonic transducer 5. The propagation time of ultrasonic signal L2 is measured. The flow rate of the fluid is then calculated based on the propagation time difference between ultrasonic signals L1 and L2, thereby determining the flow rate per unit time. Alternatively, the flow rate can be calculated as the cumulative flow rate. In this case, the temperature of the fluid across the pipe 100 is measured by the temperature measuring unit 7 installed in the device body 10, thereby performing temperature correction for the flow rate. Furthermore, the ultrasonic signals L1 and L2 are set to pass through the axis of the pipe 100 . The device body 10 includes an operation unit 2, a display unit 3, and a cable connection unit 4. The device body 10 also includes a control unit (not shown). The operation unit 2 is an input interface for inputting various types of information, and information is input by selecting pre-set information. The display unit 3 is an output interface for outputting various types of information, such as displaying the flow rate [liters / min], displaying the accumulated flow rate [liters], and displaying the status [normal / abnormal]. The cable connection unit 4 is a connection unit for connecting a cable, which includes an external power supply line and a signal line between the device and the external device. The control unit controls the transmission and reception of the ultrasonic transducers 5 and 6 according to the instructions of the operation unit 2, calculates the flow rate based on the transmission time difference and the temperature measured by the temperature measuring unit 7, displays the result and status on the display unit 3, and outputs them to the outside through the cable connection unit 4. <Acoustic Coupler Rubber> Figure 4 is a perspective view of the main body-side piping mounting portion 30 as viewed from an oblique bottom. Figure 5 is a top view of the main body-side piping mounting portion 30. Figure 6 is a cross-sectional view taken along line AA of the main body-side piping mounting portion 30 shown in Figure 5. Figure 7 shows the acoustic coupler rubber 40 mounted on the main body-side piping mounting portion 30. The acoustic coupler rubber 40 is an elastomeric rubber that serves as an acoustic coupler and ensures acoustic coupling between the ultrasonic receiving and receiving surfaces of the ultrasonic transducers 5 and 6 and the piping 100. Conventional acoustic coupler rubbers have a three-dimensional structure that covers the wedges of the ultrasonic transducers, but in this embodiment, they have a flat plate structure. As shown in Figures 4 to 7 , the main body-side piping mounting portion 30 is formed with six screw positioning holes 34 for positioning screws 33 used for mounting on the device body 10. Four screw holes 31a, used to clamp the piping 100 with the external piping mounting portion 20 using the screws 23, are formed in the four flanges 31. Furthermore, piping positioning recesses 32 are formed at the ends in the ±Y directions. Here, the main body-side piping mounting portion 30 has an opening 36 formed in the center, through which the ultrasonic transducers 5 and 6's ultrasonic receiving surfaces protrude in the -Z direction. Four claws 35 are formed around this opening 36, extending vertically in the -Z direction. The protrusion of the ultrasonic receiving surfaces in the -Z direction from the opening 36 is equal to the thickness of the opening 36. The bent ends of the claws 35 face the ±X directions. The acoustic coupler rubber 40 has four engagement holes 41 formed at positions corresponding to the claws 35. The tip of the claw 35 is bent at a position corresponding to the thickness of the acoustic coupler rubber 40. By engaging the claws 35 with the engagement holes 41, the acoustic coupler rubber 40 is mounted on the main body-side piping mounting portion 30. In this manner, the acoustic coupler rubber 40 abuts against the ultrasonic wave receiving surfaces of the ultrasonic transducers 5 and 6. Furthermore, by sandwiching the piping 100, the acoustic coupler rubber 40 is in close contact with the ultrasonic wave receiving surfaces of the ultrasonic transducers 5 and 6. Specifically, the acoustic coupler rubber 40 is mounted by, for example, engaging the two claws 35 in the +X direction with the two engagement holes 41 in the +X direction of the acoustic coupler rubber 40. Thereafter, the acoustic coupler rubber 40 is pulled in the -X direction to engage the two claws 35 in the -X direction with the two engagement holes 41 in the -X direction of the acoustic coupler rubber 40. This causes the acoustic coupler rubber 40 to contact the ultrasonic receiving and transmitting surfaces of the ultrasonic transducers 5 and 6. The acoustic coupler rubber 40 of this embodiment has a flat plate structure, making it easy to control surface roughness and vulcanization conditions. The use of molds is unnecessary, minimizing material unevenness and ensuring excellent acoustic properties. Furthermore, the lack of molds reduces costs. Furthermore, the acoustic coupler rubber 40 is easy to handle due to its flat plate structure. Installation can be completed simply by engaging the claws 35 with the engagement holes 41, making assembly and removal operations simple. <Opening of the External Pipe Mounting Portion> If the pipe 100 is made of resin, the ultrasonic signal will also be reflected by the external pipe mounting portion 20. Therefore, as shown in Figure 8(a), the ultrasonic signal L1 reflected by the pipe 100 and the ultrasonic signal L1' reflected by the external pipe mounting portion 20 overlap, reaching the ultrasonic transducer 6. This can reduce the accuracy of flow velocity measurement. In this regard, in this embodiment, an opening 22 is formed at the location where the ultrasonic signal is reflected on the outer pipe mounting portion 20 (see Figure 2). The opening 22 is U-shaped, corresponding to the shape of the pipe, and is provided at the pipe abutment portion 21 that contacts and clamps the pipe 100. As a result, as shown in Figure 8(b), the ultrasonic signal L1' reflected by the outer pipe mounting portion 20 disappears, and the ultrasonic transducer 6 only receives the ultrasonic signal L1 reflected by the pipe 100, thereby improving the accuracy of flow velocity measurement. Furthermore, the shape of the opening 22 can be arbitrary, as long as the location where the ultrasonic signal is reflected is an opening. <Ultrasonic Transducer> Conventionally, adhesives were used to attach piezoelectric elements to the wedges of ultrasonic transducers. This adhesive structure can generate thermal stress due to low and high temperatures, leading to adhesive delamination. Therefore, the use of acoustic paste to attach the piezoelectric element to the inclined surface of the wedge was considered. However, the use of acoustic paste can cause the piezoelectric element to shift position due to vibration or shock after assembly, deteriorating ultrasonic transmission and reception characteristics. Figure 9 is a front view of the ultrasonic transducer 6. Figure 10 is an exploded perspective view of the ultrasonic transducer 6. Figure 11 is a longitudinal sectional view of the ultrasonic transducer 6. Figure 12 is a sectional view taken along line BB of the ultrasonic transducer 6 shown in Figure 11. As shown in Figures 9 to 12, the ultrasonic transducer 6 has a positioning recess 66 formed on the slope of the wedge 61 on which the piezoelectric element 62 is mounted. This recess 66 is recessed to match the shape of the piezoelectric element 62 and allows the piezoelectric element 62 to be positioned at a predetermined position on the slope of the wedge 61. Acoustic paste is applied to the mounting surface of the piezoelectric element 62 and placed in the positioning recess 66. Any excess acoustic paste applied to the mounting surface of the piezoelectric element 62 is wiped off. Here, the side surfaces of the positioning recess 66 are inclined so as to expand outward. Specifically, as shown in Figures 11 and 12, the side surfaces of the positioning recess 66 are inclined outward relative to a plane perpendicular to the bottom surface S of the positioning recess 66. Therefore, the side surfaces of the piezoelectric element 62 do not contact the wedge 61, and the vibration characteristics of the piezoelectric element 62 are not deteriorated. However, the piezoelectric element 62 is attached to the wedge 61 through acoustic paste, so there is a possibility of misalignment. Therefore, a back layer with a cushioning function such as sponge is arranged on the back of the piezoelectric element 62 as a back layer member 63, and the piezoelectric element 62 is pressed by a fixing member 64 through the back layer member 63. The fixing member 64 is attached to the wedge 61 by a screw 65, thereby fixing the piezoelectric element 62 to the positioning recess 66. Furthermore, corresponding to the position of the lead wire L10 of the piezoelectric element 62, a notch 63a is formed in the back layer member 63, and a notch 64a is formed in the fixing member 64. Although the ultrasonic transducer 6 has been described, the ultrasonic transducer 5 is also similar. In this embodiment, since the piezoelectric element is not bonded with an adhesive, there is no risk of peeling. The acoustic paste maintains acoustic properties, and the positioning recess secures the piezoelectric element. Furthermore, since the piezoelectric element is secured with a fixture, subsequent misalignment is prevented. Furthermore, since the side surfaces of the positioning recess are inclined toward the periphery, the vibration characteristics of the piezoelectric element are not degraded. Furthermore, while this embodiment uses an acoustic paste, an adhesive could also be used. Furthermore, in the above embodiment, the ultrasonic transducers 5 and 6 are provided on one device body 10 side. However, within the applicable range, the ultrasonic transducers 5 and 6 may be separated and arranged to face each other via a pipe to perform flow measurement. The present invention is not limited to the above-described embodiments, and can of course be freely modified within the scope not departing from the gist of the present invention. 1: Clamp-type ultrasonic flowmeter 2: Operation unit 3: Display unit 4: Cable connection unit 5, 6: Ultrasonic converter 7: Temperature measurement unit 10: Device body 20: External piping mounting unit 21: Piping contact unit 22: Opening 23, 33, 65: Screw 30: Main body side piping mounting unit 31: Flange 31a: Screw hole 32: Piping positioning recess 34: Screw positioning hole 35: Claw 36: Opening 40: Acoustic coupler rubber 41: Engaging hole 51, 61: Wedge 52, 62: Piezoelectric element 66: Positioning recess 63: Back layer member 63a, 64a: Notch 64: Fixing member 100: Piping L1, L1', L2: Ultrasonic signal L10: Wire S: Bottom [Figure 1] A perspective view of a clamp-type ultrasonic flowmeter according to an embodiment of the present invention. [Figure 2] An exploded perspective view of the clamp-type ultrasonic flowmeter shown in Figure 1. [Figure 3] A longitudinal sectional view of the clamp-type ultrasonic flowmeter shown in Figure 1. [Figure 4] A perspective view of the main body side piping mounting portion as viewed from an oblique bottom. [Figure 5] A top view of the main body side piping mounting portion. [Figure 6] A sectional view taken along line AA of the main body side piping mounting portion shown in Figure 5. [Figure 7] A diagram showing the state in which the acoustic coupler rubber is mounted on the main body side piping mounting portion. [Figure 8] A diagram illustrating the reflection of ultrasonic signals caused by the presence or absence of an opening. [Figure 9] A front view of the ultrasonic transducer. [Figure 10] An exploded perspective view of the ultrasonic transducer. [Figure 11] A longitudinal sectional view of the ultrasonic transducer. [Figure 12] A sectional view taken along line BB of the ultrasonic transducer shown in Figure 11. 61: Wedge 62: Piezoelectric element 63: Back layer component 63a:Incision 64:Fixer 64a:Incision 65: Screw 66: Positioning recess L10: Wire

Claims

1. A clamp-type ultrasonic flow meter that uses ultrasound to measure the flow rate of fluid flowing in a piping system, characterized in that a positioning recess for positioning the piezoelectric element is formed on the inclined surface of the ultrasonic transducer where a wedge for mounting a piezoelectric element is installed; the side of the positioning recess has an outwardly expanding inclination; acoustic grease is applied between the positioning recess and the piezoelectric element; and the piezoelectric element is directly fixed to the positioning recess by pressing the fixing member of the piezoelectric element through a back member with a buffer function, without the side of the piezoelectric element contacting the positioning recess.

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