Ultrasonic flow meter with lens combination

Abstract

The present invention discloses an ultrasonic flow meter (100), which includes a housing (108) for attachment to a fluid pipe (160). A first piezoelectric element (128) coupled to a transmitter (Tx 111) and a receiver (Rx 112) is configured to emit ultrasonic waves in an axial direction perpendicular to a horizontal plane defined by the piezoelectric element. A lens assembly is in a lower housing portion (108b), the lens assembly is radially positioned outside the first piezoelectric element, the lens assembly includes an annular refocusing lens (130), the refocusing lens is configured to redirect the received radial ultrasonic waves to travel in an axial direction perpendicular to the horizontal plane, and has a thickness distribution, the thickness distribution is configured to serve as a matching layer for reducing multiple reflections within the lower housing portion. A disc-shaped second lens (140) is below the refocusing lens and is configured to redirect the radial ultrasonic waves to travel in the axial direction.

Description

Technical Field

[0001] The disclosed embodiments of the present invention relate to ultrasonic flow meters. Background Art

[0002] Ultrasonic meters (USMs), also known as ultrasonic flow meters (UFMs), are becoming increasingly popular for fluid flow metering because they are able to measure a wide range of different flow rates, cause minimal pressure drop, and have non-moving parts, thereby providing less mechanical maintenance and better reliability. The key hardware component in a USM is a piezoelectric element comprising a piezoelectric crystal or piezoelectric ceramic. As known in physics, the piezoelectric effect is the ability of certain materials to generate an electrical charge in response to an applied mechanical stress.

[0003] For flow metering applications, two or more piezoelectric element-based transducers transmit and receive ultrasonic signals to and from the fluid flowing in the pipe through a fully or partially encapsulated housing. In industries such as oil and gas, there are still challenges in obtaining high ultrasonic signal quality and reliability. For industrial applications, high pressure (gauge pressure) flow can reach 200 bar or more, while for commercial applications, low and medium pressures are generally between 0.1 bar and 40 bar, such as 1 bar to 20 bar.

[0004] Commercial and / or urban gas distribution networks typically face performance degradation when conventional USMs are used at low and medium pressures, because the lower the pressure, the lower the gas density, and the higher the attenuation of the ultrasonic signal. Therefore, when the USM is operated at relatively low pressures, there is a lower signal-to-noise ratio (SNR) and reduced detectability, reliability and / or stability of the USM. Turbine meters are currently the next best alternative (NBA) to USMs, but mechanical movement and a narrow turndown ratio or measurement range make it difficult for turbine meters to serve the commercial gas distribution market, primarily because businesses in cities (such as restaurants and hotels) may have large differences between peaks and troughs in gas usage, where gas velocities (VoG) generally vary between 0.1 m / s and 25 m / s. Therefore, urban or commercial gas distribution networks have a high demand for USMs. Summary of the invention

[0005] This Summary is provided to introduce a brief selection of disclosed concepts in a simplified form, which are further described below in the Detailed Description including the provided figures. This Summary is not intended to limit the scope of the claimed subject matter.

[0006] The disclosed aspects of the present invention recognize that, in general, USM signal quality can be degraded by a variety of different factors. These USM signal degradation factors include the operating mode of the piezoelectric element, the surrounding housing (or casing) that produces large amplitudes, and persistent ringing effects that can destroy useful signal detectability and system sensitivity. Ringing effects that persist for a long time increase the minimum measurement range (blind zone), which is considered to be unfavorable for short-range measurements, especially in small-sized USMs, while matching and mismatch processing mechanisms cause signal loss and multiple reflections. Incorrect filling and backing materials can cause back coupling that increases the noise level, which reduces the SNR. Low or medium pressure of the fluid can cause severe attenuation effects on the signal amplitude, dust and dirt contamination on the piezoelectric transducer can cause a reduction in the SNR due to increased noise levels, and unwanted strong signals can saturate the low noise amplifier (LNA) of the receiver used to amplify the generally weak received ultrasonic signal.

[0007] The disclosed USM has features that generally address all of these USM signal quality degradation factors described above in one design, with an emphasis on being configured for relatively more difficult applications for low and medium pressure fluid flow sensing, generally between 0.1 bar and 40 bar, as described above, since high pressure applications may be less difficult due to the enhanced received signal quality resulting from lower attenuation / damping effects. Thus, conventional high pressure transducer designs will generally be unsuitable for such low and medium pressure applications in terms of signal quality, especially for compressible fluids (such as natural gas), which may cause considerable attenuation / damping to the signal traveling through the transducer, such that the transducer path will not function properly, resulting in low signal quality or failure of the USM's flow measurement.

[0008] Aspects disclosed herein include an ultrasonic flow meter comprising a housing including an upper housing portion and a lower housing portion for attachment to a fluid pipe. A piezoelectric element coupled to a transmitter and a receiver is configured to emit an ultrasonic wave in an axial direction perpendicular to a horizontal plane defined by the piezoelectric element. A lens assembly is in the lower housing portion, the lens assembly comprising an annular refocusing lens positioned radially outside a first piezoelectric element, the refocusing lens being configured to redirect received radial ultrasonic waves traveling in an axial direction, and having a thickness distribution configured to serve as a matching layer for reducing multiple reflections within the lower housing portion. A flat disc-shaped second lens is below the refocusing lens, the refocusing lens comprising an outer portion radially outside a first piezoelectric element, the first piezoelectric element being configured to redirect radial ultrasonic waves traveling in an axial direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1Ais a block diagram of an exemplary USM installed for flow measurement of a fluid flowing in a pipe according to an exemplary embodiment, wherein the USM includes a first piezoelectric element and a second piezoelectric element to implement indirect path (reflection path) sensing.

[0010] Figure 1B An exemplary arrangement of the disclosed refocusing lens and the second lens relative to the piezoelectric element within the lower housing portion is shown.

[0011] Figure 2A A direct path configuration is shown implemented with a first USM having a first piezoelectric element and a second USM having a second piezoelectric element, wherein the respective USMs are located on opposite sides of the tube, with faces of the respective piezoelectric elements pointing towards each other.

[0012] Figure 2B An indirect path configuration is shown having a first USM having a first piezoelectric element and a second USM having a second piezoelectric element, wherein the respective USMs are located on the same side of the tube.

[0013] Figure 3 A cross-sectional view of an exemplary USM with a refocusing lens and a half-wavelength lens is shown according to an exemplary embodiment.

[0014] Figure 4 A cross-sectional view of an exemplary USM with a refocusing lens and a half-wavelength lens with an outer housing variation according to an exemplary embodiment is shown. The USM shown has a large interior space filled with damping material.

[0015] Figure 5 A cross-sectional view of an exemplary USM having a refocusing lens and a second lens showing yet another outer housing variation is shown according to an exemplary embodiment. DETAILED DESCRIPTION

[0016] The disclosed embodiments are described with reference to the accompanying drawings, wherein the same reference numerals are used to refer to similar or equivalent elements in all drawings. The drawings are not drawn to scale, and they are provided only to illustrate the aspects disclosed herein. Several disclosed aspects are described below with reference to exemplary applications for illustration. It should be understood that many specific details, relationships, and methods are set forth to provide a complete understanding of the embodiments disclosed herein.

[0017] However, it will be readily appreciated by those skilled in the relevant art that the disclosed embodiments may be practiced without one or more of the specific details or by other methods. In other cases, well-known structures or operations are not shown in detail to avoid obscuring the aspects disclosed herein. The present disclosure is not limited by the order of the actions or events shown, because certain actions may occur in different orders and / or simultaneously with other actions or events. In addition, not all of the actions or events shown are necessary to implement the methods according to the present disclosure.

[0018] Additionally, the terms "coupled to" or "coupled with..." (etc.) as used herein without further qualification are intended to describe either an indirect or direct electrical connection. Thus, if a first device is "coupled" to a second device, the connection may be through a direct electrical connection, where only parasitics exist in the path; or through an indirect electrical connection via intermediary items including other devices and connections. For indirect coupling, the intermediary items generally do not modify the information of the signal, but may adjust its current level, voltage level, and / or power level.

[0019] Figure 1A is a block diagram of a USM 100 including at least the disclosed lens combination, including a refocusing lens 130 and a second lens 140, and generally also including a plurality of other features described above for overcoming USM signal quality degrading factors, mounted within a meter body for use in ultrasonic-based flow measurement of a fluid flowing in a segment of a tube 160. The USM 100 is shown to include an outer housing 108 (also referred to as a casing) providing a meter body having a piezoelectric element pair shown therein, the piezoelectric element pair including a first piezoelectric element shown as T1 and a second piezoelectric element T2 spaced apart from each other by a distance shown as d on the same side of the tube 160, the USM implementing a reflected path (indirect path) sensing configuration. The disclosed USM may also have only a single piezoelectric element, such as described below Figure 2A The housing 108 may include brass, titanium, or an aluminum alloy, such as aluminum 6061 including magnesium and silicon as its primary alloying elements.

[0020] Although USM 100 is shown as implementing a reflective path sensing configuration, it is also possible to implement Figure 2A A direct path configuration is shown, in which there is a first USM 100a having a first piezoelectric element and a second USM 100b having a second piezoelectric element, wherein the respective USMs are alternatively located on opposite sides of a tube 160, with the faces of the respective piezoelectric elements 128 pointing toward each other. As is known in the art, the piezoelectric element 128 generally has a disc shape, which is a flat, thin, circular object that, due to its thin nature, can be considered to provide a horizontal plane that is radial in the USM, i.e., perpendicular to the actual direction of the ultrasound waves emitted by the USM. Figure 2BThe reflective (indirect) path configuration in is shown as being implemented with a first USM 100c having a first piezoelectric element 128 and a second USM 100d having a second piezoelectric element 128, wherein the respective USMs are now located on the same side of the tube 160.

[0021] The USM 100 is attached to the tube 160 and is generally inserted into the tube 160 using a gas-tight and high pressure resistant mechanism, or is configured as a clamping device mounted on the exterior of the tube 160. Figure 1A , but piezoelectric elements T1 and T2 may each have their own separate packaging chamber (see below). Figure 3 An internal packaging (isolation) chamber 129 is shown, which encapsulates the piezoelectric element and is shown as also encapsulating the refocusing lens 130.

[0022] The piezoelectric elements T1 and T2 employ piezoelectric crystals or piezoelectric ceramics which are set into vibration when a pulse voltage signal (received from a transmitter) is applied to their piezoelectric elements, thereby generating ultrasonic waves. In operation, ultrasonic pulses are alternately emitted by one of the piezoelectric element pair and received by the other piezoelectric element in the piezoelectric element pair required for flow measurement.

[0023] The angled axial signal path Figure 1A As is known in the art, a USM may include Figure 1A More than 2 piezoelectric elements T1 and T2 are shown, typically from two to as many as 16 piezoelectric elements. USM 100 includes a transmitter (Tx) 111 and a receiver (Rx) 112, or instead of separate Tx and Rx as shown, there may be a single transceiver, coupled to T2 and T1 respectively by a digitally controlled multiplexer (MUX) 115, which enables piezoelectric elements T2 and T1 to exchange (alternate) transmit and receive roles, so that at one time Tx 111 is turned on and at another time Rx 112 is turned on. The tube 160 in operation has a fluid therein, which is a liquid or a gas, such as natural gas. The fluid may be at a low or medium pressure, typically between 0.1 bar and 40 bar, such as 1 bar to 20 bar.

[0024] The USM 100 also generally includes a controller 120, which generally includes a microprocessor, a digital signal processor (DSP), or a microcontroller unit (MCU), having an associated memory shown as "MEM" 124, which can store code for algorithms including algorithms for implementing the disclosed fluid velocity measurement method. The controller 120 is coupled to the Tx 111 and Rx 112, and is also coupled to control the MUX 115. The controller 120 is also configured to switch the Tx and Rx roles in a specified time slot.

[0025] However, as is known in the art, the algorithm executed by the controller 120 may be implemented in hardware or in software. With respect to hardware-based implementations, the algorithm equations may be converted into digital logic gate patterns, such as using VHDL (hardware description language), which may then be implemented using a programmable device, such as a field programmable gate array (FPGA) or a complex programmable logic device (CPLD) or a dedicated application-specific integrated circuit (ASIC), to implement the logic gate patterns. With respect to software-based implementations, the code for the algorithm is generally stored in a memory, such as the memory 124 that may be implemented by the controller 120.

[0026] Figure 1A Also shown is a human machine interface (HMI) 126 coupled to the controller 120, which may include a keyboard and display if deemed necessary. The HMI 126 may be used by an operator to adjust operating parameters of the USM.

[0027] The USM 100 also includes a disclosed lens arrangement, which can be better seen in the following description. Figure 1B , where the piezoelectric element is now shown as 128. Figure 1B 1 is a cross-sectional view showing an exemplary arrangement in the lower housing portion 108b showing the disclosed refocusing lens 130 and the disclosed second lens 140 generally comprising the bottom section of the lower housing portion 108b, and how they are positioned relative to each other and relative to the piezoelectric element 128. Both the axial direction and the radial direction are shown. The radial direction is the same as the direction of the horizontal plane defined by the piezoelectric element 128, wherein the piezoelectric element 128 as described above is generally disk-shaped.

[0028] Figure 1B Also shown are backfill and damping material 135 on top of the damping and compensation layer 168 , the matching and insulation layer 155 below and on the sides of the piezoelectric element 128 , and side damping 172 including a lower housing portion and between the matching and insulation layer 155 and the damping and compensation layer 168 .

[0029] The lens arrangement includes a refocusing lens 130 and a second lens 140, both of which are positioned in the lower housing portion 108b, wherein the refocusing lens 130 is radially outside the first piezoelectric element 128, and an outer portion of the second lens 140 is radially outside the first piezoelectric element 128. The second lens 140 is generally disk-shaped, which is generally a solid disk, and is positioned below the refocusing lens 130, wherein ultrasound signals are transmitted (e.g., emitted and optionally also received) through the inner portion of the second lens 140.

[0030] As is known in the art, during operation of the USM 100, when the piezoelectric element 128 vibrates, both p-waves and s-waves are generated having a slope including an inflection point in the radial direction. The refocusing lens 130 is configured to redirect radial ultrasonic waves from the first piezoelectric element 128 to provide diffraction or an inflection point, thereby redirecting these radial ultrasonic waves in the axial direction to reduce signal loss.

[0031] As is known in acoustics, the thickness of the matching layer is generally equal to one quarter of the acoustic wavelength (λ / 4) to minimize reflections at the front side of the matching layer, thereby favoring the transmitted wave. Having found the optimal impedance value, the next determination is to find a material with that specific impedance. The known Mason model, which is a theoretical matching layer modeling algorithm, can be used. It is also possible to find the most suitable thickness by using computer numerical simulations or comparative tests.

[0032] The second lens 140 is also used to redirect the radial ultrasound waves it receives to travel more directionally in the axial direction. The nominal central diameter of the second lens 140 is generally λ / 2 (which may generally be ±20%), and the nominal thickness of the second lens 140 is also generally determined by acoustic impedance matching considerations to provide a matching layer as with the refocusing lens 130. The second lens 140 may have a nominal thickness of λ / 20 (which may generally be ±20%) to provide an impedance matching layer, which is determined to be the optimal acoustic matching thickness based on the results of comparative tests performed by the inventors for a specific set of operating conditions.

[0033] Where the diameter of the second lens 140 is a disk surface of the bottommost portion of the housing specified as generally about λ / 2, and its thickness is about λ / 20, by these two defined geometric parameters, the bottommost portion of the housing acts as a lens to redirect the acoustic waves received in the USM, such as where the same piezoelectric elements alternate in pairs as transmitters or receivers. Thus, the bottommost flat surface of the housing provides an additional new function as an acoustic lens.

[0034] As is known in the art, during operation, when the piezoelectric element 128 is controlled to vibrate, both a p-wave (also called a compression wave) and an s-wave (also called a secondary wave) are generated having a slope including an inflection point in the radial direction, wherein resonance may occur when the radial spacing (the outer diameter of the piezoelectric element 128 to the inner wall of the lower housing portion 108b) is too narrow, so that standing waves may be generated.

[0035] The refocusing lens 130 is generally shaped to have a right triangle cross section (see Figure 1B) and is configured to redirect the received ultrasonic wave away in the axial direction, which is perpendicular to the horizontal plane of the piezoelectric element 128 as described above, so that no standing acoustic wave is generated. Specifically, the inflection point and diffraction / inflection point of the received radial ultrasonic wave provided by the refocusing lens 130 are used to overcome the acoustic impedance mismatch of the housing generally including metal or metal alloy and gas (such as air, natural gas or nitrogen), which has a large impedance difference compared to the thermal insulation layer 155, which is shown as being positioned between the piezoelectric element 128 and the refocusing lens 130 and the second lens 140.

[0036] With respect to flow velocity measurements, acoustic pulses from piezoelectric elements T1 and T2 travel through tube 160 like a ferryman crossing a river. In the absence of fluid flowing in tube 160, the acoustic pulses propagate at the same speed in both directions. If the fluid in tube 160 has a flow velocity different from zero, then the acoustic pulses traveling downstream with the fluid flow (from T1 to T2) will move faster, while those traveling upstream against the fluid flow (from T2 to T1) will move slower. Thus, the downstream travel time "t" is longer than it would be if the fluid were not moving. AB " will be shorter, and the upstream travel time "t BA " will be longer. Time of flight (TOF) in this article refers to the travel time of a directly measured signal, or indirect measurement methods such as system cross-correlation based on Tx signals or post-processing based cross-correlation can also be used to determine the travel time. The formula below shows the calculation principle and represents the travel time, fluid velocity and the speed of sound in the fluid as a function of the path length and the angle of the path relative to the tube 160.

[0037]

[0038]

[0039] Where: t ABn is the downstream travel time of path n between the piezoelectric element T1 shown as A in the formula and the piezoelectric element T2 shown as B in the formula.

[0040] t BAn is the upstream travel time of path n between piezoelectric elements A and B.

[0041] L n is the straight-line length of the acoustic path n between the two piezoelectric elements T1 (A) and T2 (B).

[0042] Φ n is the angle of path n relative to the tube.

[0043] v n is the uncorrected raw velocity of the fluid measured by the piezoelectric element of path n.

[0044] c n is the speed of sound in the fluid measured by the piezoelectric element of path n.

[0045] Figure 3 A cross-sectional view of an exemplary USM 300 having a disclosed refocusing lens 130 and a second lens 140 according to an exemplary embodiment is shown. The operating wavelength of the USM is generally in the range of 10 mm to 30 mm. The outer housing 108 is as shown in FIG. Figure 1A shown. Figure 3 The upper housing portion 108a is attached to the lower housing portion 108b. The chamber connection threads 117 are Figure 3 108a is shown coupled to the lower housing portion 108b. The housing 108 is configured as a separate upper housing portion 108a and a lower housing portion 108b, which reduces the amount of air bubbles introduced when fill materials (such as the damping layer 165, the damping and compensation layer 168, and the backfill and damping material 135) that are generally added in liquid form are added to the interior of the housing 108 using conventional long tubes, as well as the difficulty of filling the interior of the housing 108 in production, and also enables the adjustment of joints in the air space (air interface) between the upper housing portion 108a and the lower housing portion 108b to mitigate undesirable back coupling of signals from the front to the back and then back to the front of the USM 300.

[0046] The housing 108 may include a metallic material or a non-metallic material. The upper housing portion 108a has attachment features shown as mounting connection threads 109 for attachment to a pipe having fluid herein. With respect to terminology, the top of the USM 300 is the side of the USM having the threads 109, as shown in FIG. Figure 3 As shown, the O-ring 113 is below the thread 109, which is on the opposite side relative to the piezoelectric element 128, and the bottom of the USM 300 is the end with the piezoelectric element 128, which is the front acoustic active end for the required acoustic transmission and reception directions, wherein the bottom (front end) of the USM 300 is designed to be positioned downwardly inside the tube of the meter body, as shown in FIG. Figure 2A and Figure 2B 1. The piezoelectric element 128 is shown in the lower housing portion 108b. However, the piezoelectric element 128 may also be in the boundary area between the upper housing portion 108a and the lower housing portion 108b. The piezoelectric element 128 is coupled to a transceiver (Tx 111 / Rx 112) as shown in FIG. 1, which may be located in an electronics housing (not shown) along with the controller 120.

[0047] Above the piezoelectric element 128 is a damping layer 165, which generally includes a material with a low density such as a porous foam or a polymer, and a damping and compensation layer 168, which generally also includes a material with a low density such as a porous foam or a polymer. The layer thickness of the damping layer 165 is generally about λ / 2 in the rearward axial direction toward the upper housing portion 108a. The piezoelectric element 128 is surrounded by a matching and insulation layer 155, which generally includes a composite material with low thermal conductivity, such as epoxy resin glass or thermoplastic composite foam. There is also a side damping layer 172 outside the damping and compensation layer 168 and partially above the matching and insulation layer 155 above the piezoelectric element 128 and the damping layer 165.

[0048] The refocusing lens 130 is configured according to the vibration mode of the piezoelectric element 128 and the arrangement of the piezoelectric element 128 in the housing (lower housing portion 108b). The refocusing lens 130 is shown in the triangular space between the matching and temperature insulation layer 155 and the lower housing portion 108b, and may include an adhesive epoxy mixed with a hardener to fill the gap between the metal lower housing 108b and the matching and temperature insulation layer 155. The filling material using the adhesive compound not only bonds two different materials without a void, but also seals the gap in a specified shape so that the refocusing lens 130 can be formed in the gap.

[0049] The refocusing lens 130 as described above may be shaped as a right triangle, may provide a hypotenuse angle generally greater than or equal to 20 degrees defined by the gap present in the structure, and a central width (thickness) of about 1 / 50 wavelength, which is a relatively small thickness, typically less than 1 mm. Therefore, most of the ultrasound signal leaking toward the sides of the USM 300 between the refocusing lens 130 and the λ / 8 wall of the lower housing portion 108b will be reflected by the refocusing lens 130 and the λ / 8 thick housing wall to not interfere with the signal traveling forward at the bottom of the USM 300 (which is the acoustically active front end).

[0050] Figure 3 Also shown is an internal packaging chamber 129 that encapsulates the piezoelectric element 128, which is also shown as encapsulating a refocusing lens 130. A second lens 140, which is typically a portion (bottom portion) of the housing, is outside the packaging chamber 129.

[0051] The refocusing lens 130 is oriented generally annularly and is positioned radially outside the piezoelectric element 128, but lower in the lower housing portion 108b relative to the piezoelectric element 128, while the second lens 140 is generally below the refocusing lens 130. The second lens 140 as described above is generally a region of the lower housing portion 108b and is not a separate component. The housing region used to provide the second lens 140 can be disc-shaped, with a nominal center diameter of λ / 2 and a thickness of about λ / 20. Therefore, the refocusing lens 130 and the second lens 140 are configured so that ultrasonic waves from their own acoustic reflections and refractions are directed and / or redirected in an axial direction toward the fluid medium in the tube, where the so-called mismatch of the acoustic impedances of the different media is known to cause undesirable reflections back to the piezoelectric element 128.

[0052] Therefore, the 45-degree angle (given by Figure 3 The housing wall setting above the second lens 140 shown) does not interfere with the signal emitted by the piezoelectric element 128 from the lower housing portion 108b, which is the front acoustic active end of the USM 300, by redirecting the lateral waves to the front acoustic active end to avoid multiple reflections in a relatively small space and for canceling the standing resonant waves. The refocusing lens 130 is configured to cancel the leakage of ultrasonic waves reaching the housing wall, which generally includes metal, where the impedance discontinuity is more severe at the outer surface of the lower housing. This mismatch can also generate multiple reflections (standing waves) between the area of ​​the piezoelectric element 128 and the refocusing lens 130. Therefore, the λ / 8 housing wall thickness is intended to suppress the standing waves in this space to enhance the axial ultrasonic waves from the piezoelectric element 128.

[0053] As described above, the central diameter of the disk shape of the second lens 140 may be λ / 2±20%, where λ is the wavelength of the ultrasonic signal used for the sensing application, such as 10 mm to 30 mm, as described above. The material used for the second lens 140, which is generally part of the lower housing portion, may include metal or non-metal, but will generally be a metal that is considered to be well suited for housing materials in harsh environmental conditions, such as stainless steel or titanium. Figure 1B The outer region of the second lens 140 is shown to reduce radial ultrasound wave propagation perpendicular to the axial direction (ie, to cancel them out in anti-phase), and suppress the side lobes to make the ultrasound waves travel more directionally in the axial direction.

[0054] The refocusing lens 130 and the second lens 140 are generally partially concentric with each other, wherein the second lens 140 extends radially outside of the refocusing lens and is at least partially below the refocusing lens 130, which is generally shown as being completely below the refocusing lens 130. As described above, the piezoelectric element 128 is generally disk-shaped, and the refocusing lens 130 is generally a right-angled triangle ring radially outward of the piezoelectric element 128, and as described above, the second lens 140 is generally a segment of the lower housing portion 108b, which is generally disk-shaped and is positioned below the piezoelectric element 128 relative to the front face 128a of the piezoelectric element 128.

[0055] The lens material used for the refocusing lens 130 and the second lens 140 is generally selected to be suitable for low and medium pressure conditions up to 40 bar as described above, and the lens material should not be too soft to withstand the pressure conditions. For example, titanium, SS304, SS316, aluminum alloys or non-metallic materials (such as plastics) can be used, depending on the requirements of the fluid measurement conditions, such as corrosiveness or dust. This is why a 1 / 4λ matching layer is shown as the matching and thermal insulation layer 155, and the refocusing lens 130 is configured to redirect the sidelobe ultrasound to the front of the USM 300 and suppress multiple reflections that can occur within the generally metal rigid housing 108a, 108b.

[0056] Therefore, the refocusing lens 130 and the second lens 140 are used to redirect the received radial ultrasonic waves and prevent multiple reflections within the wall of the lower housing portion 108b. The refocusing lens 130 and the second lens 140 redirect the received radial ultrasonic waves in the axial direction toward their corresponding piezoelectric elements in the piezoelectric element pair. Figure 4 A cross-sectional view of an exemplary USM 400 is shown with an outer housing having a refocusing lens 130 and a second lens 140. The area shown as 179 is a fastener, such as comprising a heavy rubber ring.

[0057] Figure 5 A cross-sectional view of an exemplary USM 500 having a refocusing lens 130 and a second lens 140 according to an exemplary embodiment is shown, the exemplary USM having an outer housing variation. The outer housing variation shown eliminates the need for external components such as Figure 3 and Figure 4 The exterior steps shown are now Figure 5 The inner rear structure of the backfill and damping material 135 and 136 may include epoxy resin or room temperature vulcanized (RTV) rubber. The backfill and damping material 136 between the backfill and damping material 135 and the damping and compensation layer 168 is used to better fill the backfill and damping material 135 and reduce the reverse signal coupling. The backfill and damping material area 136 may be pre-formed, such as including rubber.

[0058] In summary, the main features used in the disclosed USM to address USM signal quality degradation factors are:

[0059] 1. A lens combination including a refocusing lens 130, both radially outside of the piezoelectric element, together with a second lens 140 in the lower housing portion 108b redirects radial ultrasound waves in the axial direction with an inflection slope and with a diffraction / inflection point to overcome the mismatch between the typical metal comprising the lower housing portion 108b and the fluid in the tube which may have a large impedance difference. Acoustic impedance is the product of the material density and the speed of sound. Conventionally, a so-called matching layer with a thickness of 1 / 4λ is used, wherein for the disclosed USM, except in Figures 3 to 5 In addition to the conventional 1 / 4λ matching layer indicated as the matching and temperature-isolating layer 155, a refocusing lens 130 and a second lens 140 are placed, and the impedance ratio of the matching layer is Where Zc is the acoustic impedance of the piezoelectric element 128, and Zp is the acoustic impedance of the fluid medium. For example, if Zc=35MRayl, and Zp=0.0004MRayl (Zp value of air), then Zm is approximately equal to 0.11MRayl for good impedance matching with air (the impedance of natural gas is approximately 1.3 greater than that of air at the same pressure and density), but such impedance ratios are difficult to achieve for solid and rigid materials. The disclosed refocusing lens 130 together with the disclosed second lens 140 can solve this problem.

[0060] 2. The encapsulation chamber 129 encapsulating the piezoelectric element 128 maximizes forward ultrasonic radiation efficiency while withstanding fluid pressure. The encapsulation chamber 129 may include a foam material. Alternatives to foam include polymers, epoxies, or generally any type of material having an impedance that is well matched to the impedance of the piezoelectric element 128 and relative to air.

[0061] 3. The wall of the lower housing portion 108b may have a wall thickness of λ / 8±15% (as shown in FIG. 2 to FIG. Figure 4 as shown) to cancel standing waves and also redirect (partial) reflections at a specified angle (e.g., a calculated angle and tolerance (range)), such as 45 degrees ± 5 degrees.

[0062] 4. The temperature insulation layer 155 is generally a composite material with low thermal conductivity, so as to protect the conventional crystal material (-20°C to +60°C) of the piezoelectric element from the large temperature changes that may exist in the field, such as -40°C to +85°C, when the piezoelectric element 128 includes a piezoelectric crystal.

[0063] 5. The generally disk-shaped piezoelectric element 128 as described may include a ceramic material with a relatively large diameter to thickness ratio of >10, which is specifically configured for radial mode vibration to increase its efficiency while reducing multiple modes. This provides high system sensitivity and signal efficiency, enables the use of low voltages to more easily meet intrinsic safety requirements, and is designed to be driven by batteries by providing low power consumption.

[0064] 6. A special arrangement screwed on the inner or outer wall, including something together with wiring pins to the printed circuit board (PCB) for signal excitation and the receiving circuit. The piezoelectric element 128 and the PCB are generally connected by cables with positive terminals, negative terminals and ground terminals. When adding filling material from the back side of the backfill and damping material 135, a negative pressure will generally be generated, making it difficult to push the backfill and damping material 135 into the housing. If the material has a viscous form or is in liquid form, it may be more difficult to push the backfill and damping material into the housing due to internal bubbles. Make the housing in two parts (upper part and lower part, such as Figure 1A , Figure 1B and Figure 3 108a and 108b in FIG. 1 ) makes the backfill and damping material 135 filling process easier, more controllable and more flexible to also mitigate possible back coupling.

[0065] An exemplary assembly sequence for manufacturing the disclosed USM is now provided. In a first step, the piezoelectric element 128 can be bonded to the thermal insulation layer 155, which lines the lower housing portion 108b and is therefore above the second lens 140, which is a core assembly step that generally requires special attention to operating conditions such as temperature, preload, dust and static electricity. In a second step, the damping layer 165 can be poured on top of the piezoelectric element 128 when in liquid form. In a third step, the above components can be assembled together with the side damping layer 172, and then the damping and compensation layer 168 can be poured therein when in liquid form.

[0066] In a fourth step, the above components may be assembled within the lower housing portion 108b, which is a core assembly step and requires special attention to the bottom and side couplings, such as paying attention to fully mating joints so that no air gaps are left, such as filling the gaps with matching and thermal insulation layers 155. A fifth step may include assembling the upper housing 108a to the lower housing portion 108b, shown above as chamber connection threads 117. In a sixth step, the backfill and damping material 135 may be poured into the housing while in liquid form, paying attention to the cables in the middle and the bonding wells. In the sixth step, as described above, the liquid material will be converted to a solid while avoiding air bubbles.

[0067] Although various disclosed embodiments have been described above, it should be understood that they are presented by way of example only and not limitation. Many changes may be made to the disclosed embodiments according to the disclosure herein without departing from the spirit or scope of the present disclosure. Therefore, the breadth and scope of the present disclosure should not be limited by any of the above-described embodiments. On the contrary, the scope of the present disclosure should be limited according to the following claims and their equivalents.

[0068] Although the disclosed embodiments have been shown and described with respect to one or more specific embodiments, equivalent changes and modifications will occur to others skilled in the art upon reading and understanding this specification and the accompanying drawings. Although a particular feature may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired or advantageous for any given or particular application.

Claims

1. An ultrasonic flow meter, comprising: an outer housing having an upper housing portion attached to a lower housing portion, wherein the upper housing portion has attachment features for attachment to a tube adapted to flow a fluid therein; at least a first piezoelectric element having a planar surface defining a horizontal plane coupled to the transmitter and the receiver, wherein the first piezoelectric element is configured to emit ultrasonic waves of an operating wavelength λ in an axial direction perpendicular to the horizontal plane; A lens assembly, wherein the lens assembly is in the lower housing portion, and the lens assembly comprises: an annular refocusing lens positioned radially outside the first piezoelectric element, the refocusing lens being configured to redirect received radial ones of the ultrasound waves to travel in the axial direction for reducing signal loss, and a second lens having a flat disk shape, the second lens being positioned below the refocusing lens, the second lens comprising an outer portion radially outside the first piezoelectric element, the first piezoelectric element being configured to redirect the received radial ultrasonic waves among the ultrasonic waves to travel in the axial direction, the second lens having a thickness distribution, the thickness distribution being configured to serve as a matching layer for reducing multiple reflections within the lower housing portion.

2. The ultrasonic flow meter of claim 1 further comprising an internal packaging chamber, wherein both the first piezoelectric element and the refocusing lens are within the packaging chamber.

3. The ultrasonic flow meter of claim 1, wherein the first piezoelectric element is disc-shaped, and wherein the lower housing portion has a wall area at an angle of 45°±5 degrees relative to the horizontal plane, and a thickness of λ / 8±20%. 4 . The ultrasonic flow meter of claim 1 , wherein the first piezoelectric element comprises a disc-shaped piezoelectric ceramic having a diameter to thickness ratio of at least 10. The ultrasonic flow meter according to claim 1 , wherein a central diameter of the second lens is λ / 2±20%.

6. A method of ultrasonic fluid flow sensing, the method comprising: An ultrasonic flow meter is provided, the ultrasonic flow meter comprising a housing having an upper housing portion attached to a lower housing portion, wherein the upper housing portion has an attachment feature for attaching to a tube for flowing a fluid therein, wherein the ultrasonic flow meter comprises at least a first piezoelectric element having a planar surface defining a horizontal plane coupled to a transmitter and a receiver; and a lens combination lens in the lower housing portion, the lens combination lens comprising an annular refocusing lens positioned radially outside the first piezoelectric element, and a flat disk-shaped second lens positioned below the refocusing lens, the second lens comprising an outer portion positioned radially outside the first piezoelectric element; The transmitter forces the first piezoelectric element to emit ultrasonic waves of a working wavelength λ mainly in an axial direction perpendicular to the horizontal plane; wherein the refocusing lens is configured to redirect received radial ultrasonic waves among the ultrasonic waves to travel in the axial direction to reduce signal loss, and The outer portion of the second lens is configured to redirect the received radial ultrasonic waves among the ultrasonic waves to travel in the axial direction, and the second lens has a thickness distribution, which is configured to serve as a matching layer to reduce multiple reflections within the lower housing portion.

7. The method of claim 6, wherein the first piezoelectric element is disc-shaped, and wherein the lower housing portion has a wall area at an angle of 45°±5 degrees relative to the horizontal plane and a thickness of λ / 8±20%.

8. The method of claim 6, wherein the first piezoelectric element comprises a disk-shaped piezoelectric ceramic having a diameter to thickness ratio of at least 10.

9. The method of claim 6, wherein the refocusing lens has a triangular cross-section, and wherein the second lens utilizes a bottom section of the lower housing portion.

10. The method of claim 6, wherein the pressure of the fluid is between 1 bar and 20 bar.

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