CN116659598A - Transducer of adaptive ultrasonic lining reflective flowmeter - Google Patents
Transducer of adaptive ultrasonic lining reflective flowmeter Download PDFInfo
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- CN116659598A CN116659598A CN202210144980.7A CN202210144980A CN116659598A CN 116659598 A CN116659598 A CN 116659598A CN 202210144980 A CN202210144980 A CN 202210144980A CN 116659598 A CN116659598 A CN 116659598A
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
- G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
- G01F15/006—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus characterised by the use of a particular material, e.g. anti-corrosive material
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F15/00—Details of, or accessories for, apparatus of groups G01F1/00 - G01F13/00 insofar as such details or appliances are not adapted to particular types of such apparatus
- G01F15/14—Casings, e.g. of special material
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
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- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Measuring Volume Flow (AREA)
Abstract
The invention belongs to the technical field of sensors, and particularly relates to a transducer of an adaptive ultrasonic lining reflective flowmeter. The ultrasonic transducer aims at solving the defects that the traditional ultrasonic transducer is easily damaged by pressure mutation, the performance and consistency are affected by too thick adhesive layers between a ceramic wafer and a protection layer of the transducer, the transducer shell cannot be well adapted to the application of the traditional reflection type flowmeter, and the like, and the gap exists between the transducer shell and the technical guideline of the ultrasonic transducer; according to the invention, the transducer plastic material is selected, the impedance matching calculation of the thickness of the protective layer is adopted, the thin adhesive layer is obtained in a way of accommodating welding points by using the annular grooves, and the independent positioning double-sealing transducer structure with positioning and sealing separated is established.
Description
Technical Field
The invention belongs to the technical field of sensors, and particularly relates to a transducer of an adaptive ultrasonic lining reflective flowmeter.
Background
In the era of big data of the internet of things, artificial intelligence and industrial automatic control, the full-electronic mode flowmeter gradually replaces a mechanical or electromechanical combined mode flowmeter for the field of raw water, heat and gas supply metering of industry and people, and the full-electronic mode flowmeter has become an irreversible big trend.
In recent years, ultrasonic flow meters have been gaining attention and popularity in the industry, which have advantages of good compatibility with different diameters, low pressure loss, high accuracy, wide range ratio, high reliability, no abrasion devices, wide application to liquids and gases, and durability and economy.
The small-caliber ultrasonic flowmeter is composed of a time difference integrating circuit, and three aspects of a transducer and a transducer mounting mode, wherein the minimum value of measurable flow of a certain determined flowmeter base table is determined by the resolution of a time difference measuring chip; the latter two aspects determine the comprehensive performance and measurement quality index of the ultrasonic flowmeter, wherein the core of the measurement quality index of the flowmeter is measurement accuracy and measurement range ratio.
Transducers are key devices in ultrasonic flow meters that function as transduction transforms either high frequency electrical signals into high frequency acoustic waves, or received high frequency acoustic waves into electrical signals. The core component in the ultrasonic transducer is piezoelectric ceramic PZT mainly composed of lead zirconate titanate. Among them, the piezoelectric ceramic PZT-8 has superior performance and is widely applied to the field of fluid measurement. When the PZT-8 receives sound pressure of sound waves, the interior is mechanically deformed and polarized, and positive and negative charges are formed on the two opposite surfaces; when an electric field is applied to the opposite surfaces of the PZT-8, the inside of the PZT-8 is also physically deformed, and if a high-frequency electric field is applied, the deformation of the piezoelectric ceramics is combined with the action of an object to generate ultrasonic waves. The former effect is called positive piezoelectric effect, and the latter is called negative piezoelectric effect.
After PZT-8 is manufactured into ceramic plates with certain thickness and diameter, silver plating is required to be carried out on two sides of the piezoelectric plate, electrodes are led out, and the ceramic plates are comprehensively matched and protected by materials so as to be convenient to install and fix, and the PZT-8 is particularly applied to liquid. Therefore, the piezoelectric ceramic chip is conventionally packaged by a shell, and after the piezoelectric ceramic chip and the shell are packaged by welding leads, the piezoelectric ceramic chip can be called an ultrasonic transducer.
In the overall structure of an ultrasonic flow meter, for a low power circuit powered by a battery, matching of the ultrasonic transducer needs to take into account two factors: 1) The transducer is connected with the time difference circuit, and equivalent electrical impedance matching is needed, so that the circuit high-frequency electric signal source can provide larger power output for the transducer; the high-frequency electric signals converted from the received high-frequency sound wave voltage have better receiving reactance matching so as to obtain voltage response with better amplitude; 2) The transducer itself is driven by the high-frequency electric signal, and the intensity of the ultrasonic sound pressure generated by vibration and the intensity of the high-frequency electric signal converted from the received high-frequency sound pressure must also have high conversion efficiency. The second aspect factor can be attributed to the acoustic impedance matching between the piezoelectric ceramic sheet and the package housing. In other words, after the equivalent electrical impedance matching between the circuit and the transducer has been performed, the acoustic impedance matching between the piezoelectric ceramic sheet and the package housing needs to be solved; taking the transmitted sound wave as an example, acoustic impedance matching is a key element for determining the distance of propagation of the ultrasonic wave generated by the transducer and the useful waveform form of the generated ultrasonic wave.
The key factors can be understood as follows: for the same driving circuit, after the transducer is packaged, acoustic resistance is well matched, and acoustic waves are far propagated; and the receiving party converts the received sound wave into an electrical signal with regular form and large amplitude, which is more beneficial to the application of the large-caliber flowmeter with a far transducer distance; in addition, after the acoustic wave signals are received by the transducer, the piezoelectric ceramic plate is rapidly vibrated, the amplitude of the converted electric signal head wave is large, so that a timing circuit is easily and accurately triggered, and a circuit time difference module is started to accurately time.
In 2012-2017, as the international companies such as AMS, D-FLOW, TI and the like successively push out more advanced ultrasonic time difference timing chips, the resolution of the chips reaches 5-11 ps, the application requirements of water and gas metering are completely met, and the ultrasonic flowmeter starts to be applied and popularized along with the breakthrough of the basic technology. Currently, the performance of ultrasonic transducers is a bottleneck in ultrasonic flow meter applications that needs to be addressed and improved.
For manufacturing an ultrasonic transducer, according to theoretical deduction and practice, in combination with the characteristics of an ultrasonic lining reflective flowmeter, nine technical guidelines are provided, and the method is summarized as follows:
(1) Optimizing acoustic impedance matching selection principles of the acoustic conduction packaging material: the acoustic impedance of the acoustic wave of the material for packaging the piezoelectric ceramic plate is equal to or close to the square root of the sum of the dielectric impedances at two sides of the acoustic wave, so that the acoustic impedance matching can be achieved or close to that of the acoustic wave, and excellent acoustic wave transmissivity can be obtained.
(2) Acoustic impedance matching adapts to the principle of maximization of acoustic transmissivity: according to different material characteristics, the encapsulation thickness of the encapsulation material is deduced and calculated in the sound wave propagation direction so as to adapt to acoustic impedance matching, and the thickness of the material with poor acoustic impedance matching is reduced as much as possible, namely the acoustic impedance matching is ignored, so that the negative influence of the material with poor acoustic impedance matching is reduced;
(3) In order to reduce the loss of sound waves in the conduction process, the principle of reducing the number of matching layers as much as possible should be adopted: the more matching layers, the greater the attenuation of the acoustic wave. For example, in order to bond the encapsulation material to the ceramic sheet, it is generally necessary to glue the glue layer, which is a third matching material, and for the wavelength of the sound wave in the glue layer, if its thickness is not negligible, it must participate in acoustic impedance matching, and in addition, the thicker glue layer easily contains micro bubbles, which will cause serious imbalance in the conduction of the sound wave. Therefore, in order to reduce the adverse effect of the glue layer on the matching, the thinner the glue layer should be, the better, typically less than 0.1mm.
(4) The principle that the maximum effective sound wave generation area is ensured while the electrode outgoing line is convenient is that the two sides of the piezoelectric ceramic plate of the transducer are provided with: the two surfaces of the piezoelectric ceramic sheet are plated with silver to form two electrodes, and electrode lead wires are usually welded on the silver plating surface of the ceramic for ensuring the reliability of electrical contact. After the lead wires are welded, the areas of the silver plating surfaces of the two ceramics are not reduced as much as possible so as to ensure the sound wave intensity.
(5) The principle of minimizing the disturbance of the useless sound wave of the transducer is as follows: the piezoelectric ceramic sheet has two sides capable of emitting sound wave, but opposite directions, the reflected wave of sound wave emitted by the back side should be managed to prevent superposition interference to influence the sound wave emitted by the front side.
(6) The transducer adapts to the optimization principles of flow meter application performance: the structure of the transducer is suitable for the installation requirement of the transducer in the flowmeter, and the purpose of maximizing the range ratio is facilitated; the range ratio of the flowmeter is determined by the projection distance, namely the sound path, of the distance between the mounting positions of the pair of transducers in the flowmeter in the fluid flow direction, so that the structure of the transducers and the mounting of the transducers are convenient for adapting to the principle of maximizing the sound path of the flowmeter, and in doing so, a larger range ratio can be obtained theoretically. The simple deduction of the theory is as follows:
Wherein: q (Q) 3 Is the common flow rate of a certain caliber flowmeter, Q 1 In order to meet the minimum flow required by certain metering precision, 3 is a known quantity related to the metering time difference and the sound velocity of the flowmeter, L is the distance from the opposite surfaces of two transducers in an ultrasonic flowmeter pipeline to the water flow direction, alpha is the included angle (alpha is an acute angle, when alpha=0, the connecting line of the two transducers is consistent with the water flow direction, cos (alpha) =1) of the connecting line of the two transducers in the water flow direction of the flowmeter pipeline; from the above equation, the inter-transducer range is proportional to the meter range ratio.
(7) Sealing and positioning separation principle of the transducer: if the sealing of the transducer is integral with the positioning, for example the sealing ring is used both for sealing and for positioning, the positioning surface is offset if the sealing ring is deformed. The deformation of the sealing ring causes the deflection of the positioning surface, so that the deflection of the sounding surface direction causes the weakening or invalidation of the intensity of the sound wave received by the paired transducers, and the flowmeter cannot measure.
(8) The transducer has the impact resistance principle: the structure of the transducer is required to be capable of resisting the transducer failure caused by deformation of the sound wave sound emitting surface material or separation of the ceramic plate due to vibration or pressure mutation after the transducer is installed in the flowmeter, and in addition, the installed sealing ring cannot cause vibration of the sound emitting surface of the transducer when the pipeline vibrates.
(9) Transducer performance consistency principles; the packaging process is standardized, namely the welding point rule and the gluing thickness consistency are good, so that acoustic impedance matching is not affected, and then the consistency of the electric parameters of the transducers is good, thereby facilitating detection and interchange matching among the transducers.
The prior art still has drawbacks or deficiencies in contrast to the nine technical guidelines for ultrasonic transducers described above.
Patent grant bulletin number: CN 202471148U discloses a transducer, which is formed by using a metal layer as a shell protection layer of a piezoelectric ceramic sound-producing surface, and claim 3 shows that the matching thickness of the protection layer is less than or equal to 0.1mm. In practical application, in order to neglect the existence of a metal layer, the piezoelectric ceramic PZT-8 has better acoustic impedance matching and bandwidth guarantee, and the thickness of the metal layer is usually selected to be a stainless steel thin layer of 0.05 mm. The sound guide surface is formed by gluing a metal layer in a thin metal packaging mode and a piezoelectric ceramic plate; however, when a large positive and negative pressure change occurs in the pipeline where the flowmeter is located, the thin metal layer is easily separated from the ceramic plate or deformed by external suction force, so that a tiny vacuum or air layer (micron level) is formed between the ceramic plate and the thin metal layer, and the transducer can fail accordingly, contrary to the principle (8); in addition, the transducer shown in fig. 2 of the patent is in a 'convex' shape, and the front end side surface of the transducer is sealed and positioned by a sealing ring, which is contrary to the principle (7).
Patent application publication No.: CN 103487097A discloses a transducer, which is formed by using a metal layer as a shell protection layer of a piezoelectric ceramic sound-producing surface, contrary to principle (8); as is clear from fig. 1, the welding points of the two electrodes on the ceramic plate are on the silver plating surface (positive electrode) on the back of the ceramic plate, which is contrary to principle (4), the patent transducer is in a 'convex' shape, the front end side surface of the patent transducer is provided with a sealing ring for sealing and positioning, and the principle (7) is contrary to the principle.
Patent grant bulletin number: CN 203648820U discloses a lead mode of electrode of ceramic plate of transducer, as can be clearly seen from fig. 6, the negative electrode (front, ultrasonic wave generation and acoustic wave propagation surface) of ceramic plate of transducer is led to the welding lead wire of positive electrode (rear, i.e. opposite to front) of ceramic plate through side surface of ceramic plate, and the leads of two electrodes are on one electrode surface (positive electrode surface), so that the sound-producing surface of positive electrode of ceramic plate is reduced, and the principle (4) is contrary.
Patent grant bulletin number: CN 204944595U discloses a plastic encapsulated transducer, as can be clearly seen from fig. 1 and 2, the inner surface of the transducer housing has 4 supporting steps, which are used as positioning surfaces of the ceramic sheet, in this way, the adhesive bonding surface between the ceramic sheet and the housing is thicker, an acoustic impedance matching layer is formed, and in the implementation process, bubbles are easily contained in the adhesive, which is contrary to the principle (3).
Patent grant publication CN 205209565U discloses a measuring tube section for a reflective meter, and it can be seen that the two transducer mounting holes are relatively centered, the sound path is short, and the sound path cannot be maximized without departing from principle (6), so that the measuring range ratio is low.
In summary, for a reflective flowmeter suitable for ultrasonic fluid measurement and metering, the prior art cannot meet the above requirements for nine technical guidelines for ultrasonic transducer manufacturing; in terms of the installation of the transducer outline matching flowmeter, the common mode is only a 'convex' shape and the sealing ring and positioning are integrated, and in terms of the installation of the transducer, the maximization of transducer spacing is not considered sufficiently, namely the installation mode is not beneficial to the maximization of sound path, and the goal of obtaining a large range ratio R is not achieved yet.
For an ultrasonic transducer, how to provide a transducer which is adapted to an ultrasonic reflection type flowmeter according to nine technical guidelines for transducer manufacturing is the technical objective to be achieved herein.
Disclosure of Invention
From the above analysis of the prior art ultrasonic transducer patent, it is known that (1) if a metal layer is used as a casing protection layer for the piezoelectric ceramic sound emitting surface in order to adapt to acoustic resistance adaptation, the defect that the impedance cannot be matched is ignored, and the metal layer can only be selected as a thin film. In practical application, if instantaneous positive and negative pressure impact (such as sudden interruption of high-speed flowing fluid or breakage of a pressurized pipeline) is generated in the pipeline, particularly, tension generated by the negative pressure can cause deformation or detachment (not falling) of a metal film of the transducer, air is introduced between the matching layer and the surface of the ceramic plate or vacuum is generated (such as generation of a micron-sized gap), acoustic impedance matching of the matching layer can be permanently damaged, and the transducer is scrapped; (2) For the electrode lead mode of the ceramic plate of the transducer, if the negative electrode (front surface and sound-producing surface) of the ceramic plate is led to the welding lead wire of the positive electrode (rear surface) of the ceramic plate through the side surface of the ceramic plate, the leads of the two stages are arranged on one electrode surface (positive electrode surface), and in this mode, although the welding of the lead wire is convenient, the sound-producing surface of the positive electrode of the ceramic plate is reduced, in other words, the effective electroacoustic conversion efficiency is reduced according to the diameter size of the ceramic plate of the transducer, so that the sound wave propagation distance is shortened; (3) In order to maintain the integrity of the front and rear silver plated surfaces of the ceramic sheet, after the lead-out wires are soldered to the surface of the positive electrode (the front surface of the ceramic sheet) (the solder lead-out wires are currently the most reliable), the solder joint height needs to be set aside to keep the ceramic surface flat during gluing, so that the inner surface of the transducer housing is provided with support posts or steps for positioning the ceramic sheet plane, which results in thicker adhesive bonding surface between the ceramic sheet and the housing, typically greater than 0.5mm. The thicker adhesive layer inevitably forms a new acoustic impedance matching layer, and tiny bubbles (in the order of microns) are not easy to remove, and as the propagation speed of sound waves in gas and solid is several times different, the deviation greatly affects the performance of the transducer and the consistency thereof (the amplitude of the sound waves is attenuated), so that the parameters of the transducer need to be strictly screened and matched to be convenient to apply, and the workload is increased; (4) The convex transducer has the sealing ring matched with the front part of the convex transducer, so that the sealing effect and the positioning effect of the sound emitting surface of the transducer are realized, if the sealing ring is deformed, the sealing effect and the propagation direction of sound waves are influenced, and the water leakage of the flowmeter and the difficulty in receiving sound wave signals are caused; (5) The existing reflection type has the problems that two transducer mounting holes are relatively centered, the sound path is short, and the measuring range is lower than R.
To sum up, to overcome the drawbacks of the prior art, a transducer with high quality, high performance and stability, suitable for fluid measurement application of a flowmeter, must 1) start from a packaging material with a correct piezoelectric ceramic plate selected, so that the front end of the transducer has enough thickness, and acoustic impedance matching is facilitated and acoustic propagation intensity is guaranteed to be close to the maximum value under the condition of guaranteeing positive and negative pressure impact resistance; 2) In order to ensure the integrity of the two electrode surfaces of the ceramic wafer, the difficult problem that the height of the adhesive surface is directly influenced by the height of the welding point of the lead-out wire of the cathode electrode at the front end of the traditional ceramic wafer is solved, namely, the adhesive layer can be as thin as possible to be ignored and does not participate in the harsh requirement of acoustic impedance matching, and tiny bubbles contained in the adhesive layer are easily reduced or removed, so that the performance of the transducer and the consistency of batches of the transducer are ensured; 3) The shape of the transducer protection shell is changed, so that the transducer can be accurately positioned and can be installed in the flowmeter, has good sealing performance, and can be conveniently matched with the optimized range ratio R of the ultrasonic reflection flowmeter.
In order to further explain the technical scheme, the scheme takes the acoustic wave propagation theory as guidance, and provides the following relation deduction and application conclusion for the selection of ultrasonic transducer matching materials and the determination of matching thickness parameters:
The theory that the piezoelectric ceramic plate is matched with the packaging material layer is deduced:
when the size of the vibration sound-producing surface of the piezoelectric ceramic body is far larger than the sound wave wavelength, the longitudinal wave sound wave emitted by the piezoelectric ceramic body can be considered as a beam of directional plane wave, and only the transmission of the sound pressure and the sound intensity of the plane wave can be analyzed and deduced under the condition of conforming to three basic equations of an ideal fluid medium, namely a motion equation, a continuity equation and an object state equation.
As shown in figure 2, the sound wave propagates from medium 1 and enters medium 2 and medium 3, assuming that the sound wave is vertically incident and the acoustic characteristic impedance of the three mediums are different, the thickness of the second medium is D, the sound wave can generate transmission and reflection on the interface, P0 is set as the sound pressure of the incident wave, P r For reflected wave sound pressure, P t For the transmission wave sound pressure, then the sound pressure transmission coefficient T can be deduced by the sound pressure P representing the sound wave propagation characteristics p Sound intensity transmission coefficient T I The effective transmission of the sound wave propagating in the medium is obtained (the reflection of the sound wave at the interface is not discussed here).
By definition, the transmission coefficient T of sound pressure p ：
In the above, p 1t 、p 3t Is the transmission sound pressure of the sound wave in the medium 1 and the medium 3; z is Z 1 、Z 2 、Z 3 Characteristic impedances for medium 1, medium 2 and medium 3; k (K) 2 The number of circles of the sound wave in the medium 2; d is the thickness of the medium 2, j is a complex expression.
Transmission coefficient T of sound intensity I ：
Transform the above equation:
from the variation of the matching layer thickness D, the following transmission coefficient conclusions of sound intensities can be obtained:
1) When (when)When (I)>
That is, when the ultrasonic waves are vertically incident on the middle thin layer with different media at two sides, if the thickness of the thin layer is an integral multiple of half wavelength, the sound intensity transmittance of the transmitted thin layer is irrelevant to the properties of the thin layer. In this case, the transmitted wave between the piezoelectric ceramic sheet and the protective case is generally smaller than the maximum value.
2) When (when)And->When there is T I =1, i.e. the ultrasound wave is completely transmitted, there is theoretically no reflected wave, which also reveals the optimal choice of matching layer thickness and material characteristic impedance for conventional transducer packaging.
3) When D is less than lambda, there are alsoI.e. the transmitted sound intensity is independent of the nature of the lamina and only of the acoustic impedance of the medium on the two sides.
(II) if the transducer is placed in water, the relation between the piezoelectric ceramic plate and various packaging materials and matching states thereof:
for the application of ultrasonic flowmeter in water metering field, piezoelectric ceramic material PZT-8 packaged transducer is placed in water medium for application matching, its material characteristic impedance Z 3 The transducer emits at a frequency of 1MHz, and in order to allow the acoustic wave to be transmitted entirely (the reflected wave is 0), the thickness of the matching layer is theoretically one-fourth of the wavelength of the acoustic wave in the matching layer, and as can be seen from the above equation (C), the transmission coefficient of acoustic energy varies with the characteristic impedance of the matching material, as shown in fig. 3.
Fig. 3 is interpreted as follows:
A. b is two intersection points of the curve and the straight line, and C is the best matching point when the acoustic energy transmission coefficient is 1.
(1) The horizontal straight line in fig. 3 indicates the magnitude of the acoustic energy transmission coefficient value when the piezoelectric ceramic is not provided with the matching layer;
(2) The graph in FIG. 3 shows the dependence of the transmission coefficient value of acoustic energy on the characteristic impedance of the matching material after the piezoelectric ceramic is added to the matching layer;
(3) When matching the characteristic impedance Z of the material 2 At point B Z 1 With point A Z 3 The addition of the matching layer effectively increases the acoustic energy radiation efficiency of the transducer when the value is takenWhen the matching effect reaches the best point C, the acoustic energy transmission coefficient is 1.
(4) When matching the characteristic impedance Z of the material 2 Greater than Z 1 (point B) or less than Z 3 When the value of the point A is taken, the impedance mismatch between the piezoelectric ceramic and water can be caused by adding the matching layer, and the transmission coefficient of sound energy is smaller than that of the situation without adding the matching layer.
(III) application analysis of piezoelectric ceramic wafer matching with certain packaging materials in water:
(the values of various material parameters are taken as reference values as follows)
For water Z w : sound speed c=1500 m/s; density ρ=1.0×10 3 kg/m 3 ；ρc＝1.5×10 6 MKS (Ruili)
For PZT-8,Z pzt : sound speed c=4100 m/s; density ρ=6.50×10 3 kg/m 3 ；ρc＝26.6 ×10 6 MKS (Ruili)
For some PPS, Z pps : sound speed c=3000 m/s; density ρ=1.7x10 3 kg/m 3 ；ρc＝5.1 ×10 6 MKS (Ruili)
For stainless steel, Z s : sound speed c=5660 m/s; density ρ=7.90×10 3 kg/m 3 ；ρc＝44.7 ×10 6 MKS (Ruili)
Application analysis:
1) When matching the characteristic impedance Z of the material 2 Equal to Z pzt Or Z is w When the value is taken, the added matching layer is equivalent to the absence, and the matching performance is poor.
2) When matching the characteristic impedance Z of the material 2 Greater than Z p2t Or less than Z w When the piezoelectric ceramic is valued, the impedance mismatch between the piezoelectric ceramic and water can be caused by adding the matching layer, and the transmission coefficient of sound energy is smaller than that of the situation without adding the matching layer. Due to the characteristic impedance Z of stainless steel s Characteristic impedance Z greater than PZT-8 pzt In order for the stainless steel not to seriously affect the impedance matching with PZT-8, the stainless steel matching layer must be as thin as possible, as in patent grant publication No.: CN 202471148U discloses a transducer, which uses a metal layer as a shell protection layer of a piezoelectric ceramic sound-producing surface, and claim 3 shows that the matching thickness of the metal protection layer is less than or equal to 0.1mm. In practical application, the thickness of the metal layer is determined according to the transmission coefficient of sound intensity when the conclusion is 3, namely D < lambda, and in practical application, 0.05mm is usually selected. When D is less than lambda, although the metal protective layer can be ignored and does not influence the matching, according to the transmission coefficient conclusion 3 of sound intensity, the characteristic impedance matching is related to the characteristic impedance of the medium at two sides, and the matching is poor; moreover, in such applications, once the pressure within the pipe changes dramatically, the thin stainless steel layer is highly susceptible to deformation or damage from changing squeeze and pull forces, resulting in transducer failure.
Patent grant bulletin number: CN 204944595U discloses a plastic encapsulated transducer, as can be clearly seen from fig. 1 and 2, the inner surface of the transducer housing has 4 supporting steps, which are used as positioning surfaces of the ceramic sheet, and this is to avoid the height of the soldering point of the negative electrode lead, so the adhesive bonding surface between the ceramic sheet and the housing is thicker. The ceramic plates of the transducer are usually required to be connected by gluing, but if the glue layer is too thick, the characteristic impedance of the glue layer needs to be matched with materials such as PZT-8, PPS and the like; secondly, the adhesive with thickness is easy to contain bubbles and is not easy to be removed, which can seriously affect the sound propagation characteristics (the propagation speed of sound in the adhesive is several times of that of sound in the air), and the consistency of the transducer is difficult to ensure, so that the thinner the adhesive layer is, the better the thinner the adhesive layer is, namely D is less than lambda.
3) If PPS is selected as the matching layer of the piezoelectric ceramic and the adhesive layer is thin and negligible, then Z is the factor of pps Value at Z pzt And Z w So according to equation (C), as long as d= (2 n-1) is satisfiedThen there is transmitted wave sound intensity T I In a matched state if Z is achieved 2 Approach->The matching effect is better.
4) The manufacture of transducer outer shells using engineering plastics such as PPS, PEEK is the primary direction of transducer application today.
Because acoustic characteristic impedance represented by PPS and PEEK is easy to be matched with piezoelectric ceramics and water materials, the characteristics are stable, and the external structure can be changed according to different installation requirements in application, so that different types of flowmeters can be better matched, and the metering parameters of the flowmeter are optimized.
The invention starts from nine technical guidelines proposed by the scheme and theoretical deduction of matching relation of ultrasonic transducers, improves and upgrades important aspects such as impedance matching characteristics of piezoelectric ceramics and a protective shell, adhesive thickness, installation adaptation of electrode leads and transducers and a flowmeter base table, and the like, and seeks to solve the problems of poor adaptability of the existing metal thin-layer transducer protective shell, too thick adhesive layer of an engineering plastic shell, poor durability of sealing and positioning of the transducer shell and the flowmeter base table, and provides the following technical scheme:
(1) Manufacturing an acoustic characteristic impedance matching material of the transducer housing body from engineering plastic such as PPS, PEEK, PSF and accurately calculating the matching thickness of the material;
(2) The thickness of the adhesive layer is reduced to the thinnest, namely, the welding point of the negative electrode of the piezoelectric ceramic is arranged at the edge of the ceramic sheet, and an annular groove for arranging the welding point of the electrode lead tin is reserved at the front end of the inner side of the transducer shell, so that the adhesive thickness between the piezoelectric ceramic of the transducer and the inner side of the front end of the outer protective shell is smaller than 0.1mm, and the air in the adhesive can be effectively discharged;
(3) An outgoing line channel of a ceramic wafer negative electrode lead is arranged at the inner side edge of the transducer shell, so that outgoing lines are facilitated;
(4) The back of the piezoelectric ceramic piece of the transducer is provided with an air or sound absorption layer, and delays or absorbs reflected waves;
(5) By utilizing the plastic characteristic of engineering plastics, the transducer with the independent positioning double-sealing structure is provided, the external structure of the original convex transducer shell with the single-sealing structure is changed, so that the convex transducer shell is sealed, positioned and separated, and the characteristic requirement of an ultrasonic reflection type flowmeter can be more conveniently adapted;
the implementation of the technical scheme has the remarkable advantages that: (1) Engineering plastics such as PPS, PEEK, PSF material is selected for the outer shell of the transducer, and the thickness of the matching layer is accurately calculated according to the characteristic impedance adaptation theory of the piezoelectric ceramic matching layer, so that the characteristic impedance relationship of the matching layer is as close as possibleThe maximum transmission amplitude of the sound wave is achieved, and the sound wave can propagate farther; (2) The arrangement of the mounting groove capable of accommodating the welding point of the piezoelectric ceramic cathode has the advantages that the adhesive layer is thin, the air in the adhesive layer is easily discharged, and the consistency of the parameters of the transducer is improved; (3) The outgoing line channel of the ceramic wafer negative electrode lead is arranged in the transducer, so that outgoing lines are convenient, and the standardization of the packaging process is facilitated; (4) The back (positive electrode) of the piezoelectric ceramic piece of the transducer is reserved with The air or sound absorption layer prevents reflected waves from interfering forward emitted waves of the transducer; (5) The application of engineering plastics ensures that the external structure of the transducer shell can be better matched with the base meter of the flowmeter in the aspects of positioning and sealing, thereby improving the overall performance of the flowmeter;
the invention relates to a transducer adapting to an ultrasonic lining reflective flowmeter, which is characterized by comprising an independent positioning double-sealing structure transducer adapting to the reflective flowmeter and an ultrasonic reflective flowmeter provided with the independent positioning double-sealing structure transducer. The transducer with the independent positioning double-sealing structure comprises a transducer shell structural member and an internal assembly; the ultrasonic reflection type flowmeter comprises an equal-diameter metal outer tube, a transducer fixing seat, a positioning boss, a transducer, a flow guiding and reflecting surface fixing support, a rectifying tube, a fixing nut, an instrument box and the like. The middle part of the transducer shell structural member is provided with a blind hole which is of a cylindrical structure; the internal components comprise a piezoelectric ceramic piece, a switching PCB and the like; the bottom of the blind hole is a bottom plane, and the outer ring of the bottom plane is an annular groove; the piezoelectric ceramic plate is adhered to the bottom plane, two sides of the piezoelectric ceramic plate are provided with two electrodes, namely a negative electrode and a positive electrode, a negative electrode outgoing line and a positive electrode outgoing line are welded on the piezoelectric ceramic plate and are electrically connected to the transfer PCB, a signal wire of the transducer is welded on the positive electrode surface of the transfer PCB, and the signal wire is led out from the upper part of the transducer through a middle through hole of a fixing nut and is electrically connected with the integrating circuit PCB in the instrument box; the ultrasonic reflection type flowmeter base outer tube is an equal-diameter metal outer tube, the transducer fixing seat is arranged on the equal-diameter metal outer tube and is positioned at two ends of the inner side of the equal-diameter metal outer tube thread, and the equal-diameter metal outer tube and the transducer fixing seat are connected through laser welding; the transducer is arranged in the transducer fixing seat, a positioning boss is arranged in the transducer fixing seat, the transducer with an independent positioning double-sealing structure is positioned on the positioning boss, and a sealing ring on the transducer is sealed with the inner side of the transducer fixing seat; the appearance structure of the transducer is improved, so that the transducer is installed and positioned and sealed separately, and the ultrasonic lining reflection type flowmeter can be effectively adapted; the guide and reflecting surface fixing support in the lining reflective flowmeter base table and the rectifying tube are integrated through gluing or laser welding, so that the distance between the two reflecting surfaces of the ultrasonic wave can be kept permanently unchanged, and the two transducer fixing seats can be respectively close to the inner side of the equal-diameter metal outer tube thread as much as possible, so that the effective sound path between the two transducers is maximized, and therefore, according to the technical guideline (6), the measuring range ratio of the reflective flowmeter can be maximized, and the flowmeter has a wider fluid metering measuring range.
As shown in fig. 4 and 5, the inside of the structural member of the transducer housing is a blind hole, the bottom of the blind hole is a bottom plane, and the blind hole is used for bonding the piezoelectric ceramic plate, in order to make the bonding adhesive layer between the piezoelectric ceramic plate and the bottom plane of the blind hole as thin as possible, an annular groove is arranged on the outer ring of the bottom plane of the blind hole, and the annular groove is used for accommodating the welding point of the negative electrode lead-out wire at the edge of the piezoelectric ceramic plate; the depth of the annular groove is larger than the height of the welding point of the negative electrode outgoing line of the piezoelectric ceramic piece, so that the negative electrode plane of the piezoelectric ceramic piece and the plane at the bottom of the blind hole can be tightly adhered, the adhesive layer is thin, and bubbles cannot be reserved in the adhesive layer. From the above-mentioned transmission coefficient of sound intensity, it is known that when D < lambda, there isI.e. the transmitted sound intensity is independent of the nature of the lamina and is only related to the acoustic impedance of the medium at the two sides, the glue layer does not participate in acoustic impedance matching.
As shown in fig. 1 and 5, the negative electrode lead-out wire of the piezoelectric ceramic plate is led to the adapting PCB from the side surface of the ceramic plate, so that the lead-out wire of the negative electrode is led out for space convenience, and two symmetrical inner outwards protruding structures are arranged at the positions of the blind holes in the structural member of the transducer, namely the side surfaces of the inner walls of the tubular structures corresponding to the negative electrode lead-out wire ends and the positive electrode lead-out wire ends of the piezoelectric ceramic plate, so that the lead-out wire is conveniently connected to the adapting PCB, and the protruding structures are always led to the bottom of the annular groove of the lower end from the upper end of the blind holes in the tubular structures.
As shown in FIG. 5, in order to maintain a 1-3 mm distance between the transfer PCB and the positive electrode of the piezoelectric ceramic plate, in the cylindrical structure inner wall of the transducer housing structural member, the space at the upper end is wider and the lower end is up toThe annular groove is narrow in one section (the passing of the ceramic wafer negative electrode lead-out wire can be met), and a height positioning surface for installing the transfer PCB is formed at the joint of the annular groove and the ceramic wafer negative electrode lead-out wire, and the transfer PCB is installed on the height positioning surface; after being driven by high-frequency electric signals, the piezoelectric ceramic plate vibrates in two directions of a positive direction (a ceramic plate negative electrode) and a negative direction (a ceramic plate positive electrode) simultaneously to generate ultrasonic waves, so that the position of a normal high-positioning surface, namely a distance between the switching PCB and the piezoelectric ceramic plate positive electrode, is kept to be 1-3 mm in order to prevent reflected waves in the reverse direction from interfering and overlapping forward waves, and the reflected waves on the switching PCB are delayed. For example, after 1MHz sound wave is reflected at 1mm pitch, it takes 5.9X10 time to pass 2mm distance (reflected wave) -6 Seconds (in air), whereas the ceramic plate forward wave (negative) takes about 10 hours to transmit a complete wave in the PPS matching layer -6 Second (1 micro), so that the reflected wave will not interfere with the first 5 waves of the forward wave, if the time difference circuit needs to sample more integer waves in the accuracy calculation, the distance between the transfer PCB and the positive electrode of the piezoelectric ceramic plate needs to be pulled apart, so that the reflected wave has more delay; if asphalt is filled between the positive electrode of the piezoelectric ceramic plate and the switching PCB, the asphalt can fully absorb and reduce reflected wave energy, and any reflected wave will not interfere with forward wave; thus, for calculation of the reflection interval by using more waves, accuracy of timing will be ensured.
As shown in fig. 1 and 5, symmetrical convex structures of the PCB are arranged on two sides of the outer circle of the transfer PCB and are correspondingly fixed on the positioning surface; the middle of the convex structure of the transfer PCB is provided with a PCB convex structure slit penetrating through the transfer PCB, so that the lead-out wires of the positive electrode and the negative electrode of the piezoelectric ceramic chip can conveniently pass through and be welded on the transfer PCB.
As shown in fig. 5, the matching layer thickness of the transducer housing structural member matching the piezoelectric ceramic sheet should be calculated and valued as follows: from conclusion 2 of the sound intensity transmission coefficient, if the transducer is to be placed in water, the engineering plastic material is chosen so that its characteristic impedance Z is as high as possible 2 To approach or equalAnd, in addition, the processing unit,calculate the matching layer thickness D whenThe matching is optimal, the thickness D is usually a plurality of values, the values can be generally enough to meet the requirement that the maximum positive and negative pressure difference exists in the pipeline, for example, for a 2MHz ceramic wafer and a phi 8mm ceramic wafer, the thickness D of the protection layer PPS is calculated according to the above, the matching value which is larger than 1mm can be conventionally selected according to different pressure requirements in the pipeline, the transmission coefficient of the ultrasonic sound intensity after matching is larger, and the acoustic wave energy is far propagated.
The transducer shell structural member is manufactured by injection molding of engineering plastics such as PPS, PEEK, PSF and other acoustic characteristic impedance matching materials; the rectifying tube is manufactured by injection molding of engineering plastic PPS, PPO, PPA, PA 66.
As shown in fig. 7, the two fixing brackets of the diversion and reflection surface are respectively positioned at two ends of the inner side of the equal-diameter metal outer tube, namely a water inlet end and a water outlet end in the equal-diameter metal outer tube; the guide cap is arranged at the water inlet and the water outlet of the guide and reflecting surface fixing bracket, so that the guide and reflecting surface fixing bracket plays a role in guiding fluid and reduces water resistance; a reflection surface forming 45 degrees with the horizontal is arranged on one side of a rectifying tube tightly matched with a flow guiding and reflection surface fixing support, the reflection surface is made of metal or ceramic materials, a U-shaped sound path structure is formed between two independent positioning double-sealing structure transducer surfaces, and the middle section is an effective sound path.
The connection between the diversion and reflection surface fixing support and the rectifying tube is that: the flow guiding and reflecting surface fixing support and the rectifying tube are in butt joint through the concave-convex structure, epoxy resin glue is coated and fixed at the butt joint position, after the glue is dried, the flow guiding and reflecting surface fixing support and the rectifying tube can be permanently fixed, namely the distance between the two independent flow guiding and reflecting surfaces of the reflecting surface fixing support in the equal-diameter metal outer tube is fixed, the structure can achieve high consistency of flow meter assembly and mass production, and flow meter calibration time is reduced. In addition, because the two independent transducer fixing seats are close to the inner sides of the pipe threads at the outer sides of the two ends of the equal-diameter metal outer pipe, the ultrasonic reflection surfaces are correspondingly close to the two ends of the inner side of the equal-diameter metal outer pipe as much as possible, and according to the technical guideline (6), the sound range, namely the range ratio, of the ultrasonic lining reflection type flowmeter is maximized.
As shown in fig. 6 and 7, the transducer with the independent positioning double-sealing structure is installed in the transducer fixing seat, the positioning flange is positioned on the positioning boss, two sealing rings are applied to seal the inner side of the transducer fixing seat, the high positioning and sealing separation of the transducer are achieved, the deformation of the sealing rings can not influence the high-low change of the positioning flange, namely the deflection of the angle of the sound emitting surface of the transducer, and the long-term stability of ultrasonic signals is effectively ensured.
As shown in fig. 6, the fixing nut compresses and fixes the transducer through the elastic washer below the fixing nut and the sealing ring above the fixing nut, so as to fix and seal the transducer with an independent positioning double-sealing structure; the rectifying tube fixing screw plays a role in fixing the rectifying tube.
As shown in fig. 6 and 7, the positive electrode surface of the transfer PCB is welded with a transducer signal wire, and the signal wire is electrically connected with the integrating circuit PCB through the central hole of the fixing nut and through the inside of the instrument box.
As shown in fig. 6, the cylindrical structure of the lower case of the instrument box is tightly matched with the outer diameter of the circular transducer fixing seat, namely, the instrument box is tightly fixed by the fixing nut.
The independent positioning double-sealing structure transducer and the assembled reflection structure thereof form a complete U-shaped ultrasonic acoustic path reflection type flowmeter, and the two independent transducer fixing seats and the independent positioning double-sealing structure transducer installed in the flowmeter are arranged as close as possible to the two ends of the equal-diameter metal outer tube; the distance between the two ultrasonic wave reflecting surfaces arranged in the equal-diameter metal outer tube is permanently fixed, so that the measuring range ratio of the reflective flowmeter can be maximized, the performance is kept unchanged for a long time, namely, the flowmeter has a wider fluid metering range; in addition, the ultrasonic sound path, namely the range of the flowmeter is higher than the consistency of R, so that the ultrasonic reflection flowmeter is beneficial to mass production and quick calibration, and can improve the production efficiency.
In summary, the invention successfully overcomes the technical defects of the prior ultrasonic transducer, and through theoretical deduction and practical application to the conclusion thereof, the performance of the ultrasonic transducer can be greatly improved, and the ultrasonic transducer is suitable for an ultrasonic reflection type flowmeter structure with larger measuring range ratio and high batch consistency. Compared with the prior art, the transducer with the brand new structure has outstanding substantive characteristics and progress, and is characterized in that:
first, it is proposed to analyze and deduce the sound pressure and transmittance of the sound intensity of plane wave under the condition of following three basic equations of ideal fluid medium, namely motion equation, continuity equation and object state equation, and obtain the sound intensity transmittance coefficient T I The matching thickness of the intermediate medium layer can be applied and analyzed to obtain 3 conclusions of the matching layer and the transmitted wave sound intensity under three conditions, and the performance of the transducer can be improved by the rule.
Second, from the conclusion 3 that the transmitted sound intensity is independent of the properties of the thin layer when the matching layer thickness D < λ, and is related only to the acoustic impedance of the medium at both sides, the thickness of the adhesive layer applied between the piezoelectric ceramic sheet and the matching layer should be as thin as possible. Therefore, in order to solve the situation that the bonding is affected by welding spots on the negative electrode lead of the piezoelectric ceramic plate, an annular groove is formed in the outer ring of the bottom plane of the blind hole of the cylindrical structure in the middle of the structural part of the transducer shell, and the height of the welding spots of the electrode lead wire for accommodating the negative electrode of the piezoelectric ceramic plate can be met, so that the negative electrode of the piezoelectric ceramic plate and a bonding adhesive layer between matching layers can be made to be very thin and closely attached, the influence of impedance matching of the adhesive layer and the influence of bubbles contained in a thicker adhesive layer are avoided, and the consistency of the transducer is good.
Thirdly, the inner wall of the cylindrical structure of the transducer shell structural member with the independent positioning double-sealing structure is provided with a height positioning surface for mounting the switching PCB, and the height positioning surface, namely, the space between the switching PCB and the positive electrode of the piezoelectric ceramic plate is kept between 1 and 3mm, so that reflected waves on the back surface of the piezoelectric ceramic plate can be prevented from interfering with the front surface waves, and the accuracy of detection waves is improved.
Fourth, the outer shell of the transducer is made of engineering plastics such as PPS, PEEK, PSF, and the appearance structure is of an independent positioning double-sealing structure, so that the shell is convenient to be made into an adaptive ultrasonic reflection type flowmeter structure besides being favorable for impedance matching with the piezoelectric ceramic plates, and the positioning and sealing of the transducer are separated and are of a double-sealing ring structure, so that the durability and reliability of the reflection type flowmeter are more stable.
Fifth, the flow guiding and reflecting surface fixing support and rectifying tube are made by injection molding of engineering plastic PPS, PPO, PPA, PA, the flow guiding and reflecting surface fixing support and rectifying tube are in butt joint and fixed by epoxy resin glue in concave-convex structure, and permanent fixation is formed between the flow guiding and reflecting surface fixing support and rectifying tube.
Sixth, according to conclusion 2 of sound intensity transmission coefficient, the thickness of the matching layer of the material matched with the piezoelectric ceramic plate can be accurately calculated, if the transducer is applied in water, the material of engineering plastic is selected to make the characteristic impedance Z as much as possible 2 To approach or equalAnd, the matching layer thickness D is calculated asThus, the sound intensity transmission coefficient of the ultrasonic wave is larger, and the sound wave energy propagates farther.
Seventh, fixing the independently positioned double-seal structure transducer: the fixing nut presses and fixes the transducer through the elastic washer below the fixing nut and the sealing ring above the fixing nut, so that the transducer is fixed and sealed.
Eighth, the fixing of the instrument box is simple and stable: the cylindrical structure of the lower shell of the instrument box is matched with the outer diameter of the circular transducer fixing seat, and the instrument box is tightly pressed and fixed through a fixing nut.
Drawings
FIG. 1 is a schematic diagram of a self-contained dual seal structure transducer adapted for an ultrasonic liner reflective flow meter;
FIG. 2 is a schematic illustration of sound pressure transmission and reflection of sound waves through three media of different impedance;
FIG. 3 is a schematic diagram of impedance matching when sound waves penetrate through a piezoelectric ceramic plate, different matching mediums and water;
FIG. 4 is a cross-sectional view of a self-contained dual seal structure transducer adapted for an ultrasonic liner reflective flow meter;
FIG. 5 is a cross-sectional exploded view of a separately positioned dual seal construction transducer assembly;
FIG. 6 is a cross-sectional view of a transducer mounting structure for an adaptive ultrasonic liner reflective flow meter;
FIG. 7 is a cross-sectional view of an adaptive ultrasonic liner reflective flowmeter structure;
in the figure:
11. an isodiametric metal outer tube; 12. a transducer mount; 121. positioning the boss; 441. butt joint of concave-convex structures; 41. a fixing nut; 42. an elastic washer; 13. a rectifying tube fixing seat; 44 rectifying tube; 131. a rectifying tube fixing screw; 33, a transducer shell structural member; 330. a matching layer; 3301. an annular groove; 3302. a bottom plane; 3303. a positioning surface; 339. an outwardly protruding structure; 3304. a cylindrical structure; 3305. positioning the convex edge; 3306. a groove; 3307 inclined plane; 331. a piezoelectric ceramic sheet; 3311. welding points; 3312. a negative electrode lead; 3313. a positive electrode lead; 332. switching the PCB;3321. switching PCB welding points; 3322 pcb male structure; 3323 PCB male structural slot; 36. a seal ring; 333. a signal line; 22. a guide and reflecting surface fixing bracket; 220, a diversion cap; 221. a reflecting surface; 2211. a concave-convex structure; 55. an instrument box; 554. a lower shell tubular structure of the instrument box; 551. a display screen; 552. integrating a circuit PCB;553. and a battery.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples.
Example 1:
the embodiment is a transducer of an adaptive DN15 ultrasonic lining reflective flowmeter, and is characterized by comprising an independent positioning double-sealing structure transducer of an adaptive reflective flowmeter and an ultrasonic reflective flowmeter provided with the independent positioning double-sealing structure transducer. The independent positioning double-sealing structure transducer comprises a transducer shell structural member 33 and an internal component; the ultrasonic reflection type flowmeter comprises an equal-diameter metal outer tube 11, a transducer fixing seat 12, a positioning boss 121, an independent positioning double-sealing structure transducer, a diversion and reflection surface fixing bracket 22, a rectifying tube 44, a fixing nut 41, an instrument box 55 and the like. A blind hole is formed in the middle of the transducer shell structural member, and the blind hole is of a cylindrical structure 3304; the internal components include a piezoelectric ceramic chip 331 and a transfer PCB 332, etc.; the bottom of the blind hole is a bottom plane 3302, and the outer ring of the bottom plane is an annular cavity 3301; the piezoelectric ceramic plate is adhered on the bottom plane, two sides of the piezoelectric ceramic plate are two electrodes, namely a negative electrode and a positive electrode, a negative electrode lead-out wire 3312 and a positive electrode lead-out wire 3313 are welded on the piezoelectric ceramic plate and are electrically connected to the transfer PCB 332, a signal wire 333 of a transducer is welded on the positive electrode surface of the transfer PCB, the signal wire is led out through a middle through hole of the fixing nut 41 above the transducer, and the signal wire is electrically connected with the integrating circuit PCB 552 in the instrument box 55; the ultrasonic reflection type flowmeter base outer tube is an equal-diameter metal outer tube 11, a transducer fixing seat 12 is arranged on the equal-diameter metal outer tube, the transducer fixing seat and the transducer fixing seat are positioned at two ends of the inner side of a thread of the equal-diameter metal outer tube, and the two are connected by laser welding; the transducer with the independent positioning double-sealing structure is arranged in the transducer fixing seat 12, a positioning boss 121 is arranged in the transducer fixing seat, the transducer with the independent positioning double-sealing structure is positioned on the positioning boss, and a sealing ring 36 on the transducer is sealed with the inner side of the transducer fixing seat 12; the appearance structure of the transducer is improved, so that the transducer is installed and positioned and sealed separately, and the ultrasonic lining reflection type flowmeter can be effectively adapted; the guiding and reflecting surface fixing support in the lining reflecting flowmeter base table and the rectifying tube are integrated through gluing or laser welding, so that the distance between the two reflecting surfaces of the ultrasonic wave can be kept permanently unchanged, the two transducer fixing seats can be respectively close to the inner side of the equal-diameter metal outer tube thread as much as possible, and the effective sound path between the two transducers is maximized, therefore, according to the technical guideline (6), the measuring range ratio of the reflecting flowmeter can be maximized, and the flowmeter has a wider fluid metering measuring range.
As shown in fig. 4 and 5, the transducer housing structure 33 is blind,the blind hole is of a cylindrical structure 3304, the bottom of the blind hole is a bottom plane 3302 and is used for bonding the piezoelectric ceramic piece 331, in order to make the bonding adhesive layer between the piezoelectric ceramic piece and the bottom plane of the blind hole as thin as possible, an annular groove 3301 is arranged on the outer ring of the bottom plane of the blind hole and is used for accommodating a welding point 3311 of a negative electrode lead-out wire 3312 at the edge of the piezoelectric ceramic piece; the depth of the annular cavity 3301 is larger than the height of the welding point 3311 of the negative electrode outgoing line of the piezoelectric ceramic plate, so that the negative electrode plane of the piezoelectric ceramic plate and the bottom plane 3302 of the blind hole can be tightly adhered, the adhesive layer is thin, and bubbles cannot be reserved in the adhesive layer. From the above-mentioned transmission coefficient of sound intensity, it is known that when D < lambda, there isI.e. the transmitted sound intensity is independent of the nature of the lamina and is only related to the acoustic impedance of the medium at the two sides, the glue layer does not participate in acoustic impedance matching.
As shown in fig. 1 and 5, the negative electrode lead-out wire 3312 of the piezoelectric ceramic plate 331 is led to the adapting PCB 332 from the side surface of the piezoelectric ceramic plate, in order to have a space for facilitating the lead-out of the negative electrode lead-out wire, two symmetrical inner outward protruding structures 339 are provided in the blind hole in the transducer housing structure 33, i.e. the inner wall of the tubular structure 3304 corresponds to the side surface positions of the negative electrode lead-out wire and the positive electrode lead-out wire of the piezoelectric ceramic plate, so as to facilitate the connection of the negative electrode lead-out wire 3312 and the positive electrode lead-out wire 3313 to the adapting PCB 332, and the protruding structures are led from the upper end of the blind hole in the tubular structure to the bottom of the lower annular groove 3301.
As shown in fig. 5, in order to maintain a 1-3 mm distance between the adaptor PCB 332 and the positive electrode of the piezoelectric ceramic chip 331, in the inner wall of the cylindrical structure 3304 of the transducer housing structural member 33, in the structure 339 protruding from the inside to the outside, the space located at the upper end is wider, the lower end is narrower to the annular groove (only the passing of the negative electrode lead wire of the ceramic chip can be satisfied), and a height positioning surface 3303 for installing the adaptor PCB 332 is formed at the junction between the adaptor PCB and the annular groove, and the adaptor PCB is installed on the height positioning surface; after being driven by high-frequency electric signals, the piezoelectric ceramic plate vibrates on the two surfaces to face forward (the negative electrode of the ceramic plate) and reverseThe ultrasonic waves are generated in both directions (the positive electrode of the ceramic plate), so that the position of the height locating surface 3303 is usually kept at a distance of 1-3 mm between the transfer PCB and the positive electrode of the piezoelectric ceramic plate in order to prevent the interference of the reflected waves in the opposite direction and the superposition of the forward waves, and the reflected waves on the transfer PCB are delayed. For example, in this embodiment, a 2MHz frequency ceramic wafer is selected, and the time taken for the acoustic wave to pass through a 2mm distance (reflected wave) after being reflected at a 1mm pitch is 5.9X10 -6 Second (in air) and ceramic plate forward wave (negative), the time taken to transmit a complete wave in PPS matching layer is about 0.5 x 10 -6 Second (0.5 microseconds), so the reflected wave will not interfere with the first 11.7 waves of the forward wave, if the time difference circuit needs to sample more integer waves in the accuracy calculation, the distance between the switching PCB and the positive electrode of the piezoelectric ceramic plate needs to be pulled apart, so that the reflected wave has more delay; if asphalt is filled between the positive electrode of the piezoelectric ceramic plate and the transfer PCB, the asphalt can fully absorb and reduce reflected wave energy, and any reflected wave will not interfere with forward wave.
As shown in fig. 1 and 5, symmetrical PCB convex structures 3322 are provided on both sides of the outer circle of the adapting PCB 332, and are correspondingly fixed on the positioning surface 3303; a PCB convex structure slot 3323 penetrating through the transfer PCB is arranged in the middle of the convex structure 3322 of the transfer PCB, and the positive electrode lead 3313 and the negative electrode lead 3312 of the piezoelectric ceramic chip pass through and are welded on the transfer PCB 332.
As shown in fig. 5, the matching layer 330 of the transducer housing structure 33 to which the piezoelectric ceramic piece 331 is matched needs to be computationally matched: from conclusion 2 of the sound intensity transmission coefficient, if the transducer is to be placed in water, the engineering plastic material is chosen so that its characteristic impedance Z is as high as possible 2 To approach or equalAnd, the matching layer thickness D is calculated as +. > The matching is optimal, the thickness D is usually provided with a plurality of values, and the values are generally enough to meet the condition that the pipeline is not deformed when the maximum positive pressure difference and the maximum negative pressure difference exist in the pipeline.
Actual computing application of the embodiment:
if the transducer is to be placed in water for application, the matching material of the piezoceramic wafer is selected from a PPS, then for water Z w : sound speed c=1500 m/s; density ρ=1.0×10 3 kg/m 3 ；ρc＝1.5×10 6 MKS for PZT-8,Z pzt : sound speed c=4100 m/s; density ρ=6.50×10 3 kg/m 3 ；ρc＝26.6 ×10 6 MKS for certain PPS, Z pps : sound speed c=3000 m/s; density ρ=1.7x10 3 kg/m 3 ；ρc＝5.1 ×10 6 MKS here Z pps ＝5.1×10 6 MKS, butAs can be seen from FIG. 3, the transmission coefficient of 5.1 is already close to the maximum value of 6.3, and the matching performance of the PPS is better.
For a 2MHz acoustic wave propagating in PPS, λ=c/f=3000/(2×10) 6 )＝1.5mm
The method can obtain: when n=2, d=1.125 mm: n=3, d=1.875 mm: n=4, d=2.625 mm, so that one of the thicknesses can be selected to be suitable according to the practical pressure working condition of the flowmeter, for example, the pipeline pressure is 2MPa, the diameter of the ceramic plate in the embodiment is phi 8mm, and the matching layer thickness d=2.625 mm is selected according to application experience.
The transducer housing structure 33 is injection molded from an acoustic characteristic impedance matching material such as an engineering plastic PPS, PEEK, PSF; the rectifying tube 44 is manufactured by injection molding of engineering plastic PPS, PPO, PPA, PA.
As shown in fig. 7, two fixing brackets 22 for guiding and reflecting surface are respectively positioned at two ends of the inner side of the equal-diameter metal outer tube 11, namely at the water inlet and the water outlet of the equal-diameter metal outer tube; the guide cap 220 is arranged at the water inlet and the water outlet of the guide and reflecting surface fixing bracket, plays a role in guiding fluid and reduces water resistance; the invention relates to a U-shaped sound path structure formed between two independent positioning double-sealing structure transducer surfaces, wherein one side of a rectifying tube is tightly matched with a flow guiding and reflecting surface fixing support, a reflecting surface 221 which forms an angle of 45 degrees with the horizontal is arranged on one side of the rectifying tube, the reflecting surface is made of metal or ceramic materials and is used for reflecting sound waves emitted or received by the transducer at an angle of 90 degrees.
The connection between the guide and reflecting surface fixing support 22 and the rectifying tube 44 is as follows: the flow guiding and reflecting surface fixing support and the rectifying tube are butted by the concave-convex structure 441, epoxy resin glue is coated and fixed at the butted position, after the glue is dried, the flow guiding and reflecting surface fixing support and the rectifying tube can be permanently fixed, namely, the distance between two independent flow guiding and reflecting surfaces 221 of the reflecting surface fixing support 22 in the equal-diameter metal outer tube 11 is fixed, the structure can achieve high consistency of flow meter assembly and batch production, and the flow meter calibration time is reduced. In addition, since the two independent transducer holders 12 are located close to the inner side of the pipe threads on the outer sides of the two ends of the equal-diameter metal outer pipe, the ultrasonic reflection surface 221 is located as close as possible to the two ends of the inner side of the equal-diameter metal outer pipe, and the acoustic path, that is, the range ratio of the ultrasonic lining reflection type flowmeter is maximized as is known from the technical guideline (6).
As shown in fig. 6 and 7, the transducer with the independent positioning double-sealing structure is installed in the transducer fixing seat 12, the positioning convex edge 3305 is positioned on the positioning boss 121, two independent sealing rings 36 are used for sealing the inner side of the transducer fixing seat 12, the high positioning and sealing separation of the transducer are achieved, the deformation of the sealing rings can not affect the high-low change of the positioning convex edge, namely the deflection of the angle of the sound emitting surface of the transducer, and the long-term stability of ultrasonic signals is effectively ensured.
As shown in fig. 6 and 7, the fixing nut 41 compresses and fixes the independently positioned double-sealing structure transducer and the sealing ring at the upper part thereof through the elastic washer 42 at the lower part thereof, thereby playing a role in fixing and sealing the independently positioned double-sealing structure transducer; the rectifier tube fixing screw 131 plays a role in fixing the rectifier tube 44.
As shown in fig. 6 and 7, the positive electrode surface of the adaptor PCB 332 is soldered with a signal wire 333 of the transducer, and the signal wire is electrically connected to the integrating circuit PCB 552 through the central hole of the fixing nut 41 and through the inside of the instrument box 55.
As shown in fig. 6, the lower case cylindrical structure 554 of the instrument case is tightly fitted to the outer diameter of the circular transducer holder 12, i.e., the instrument case 55 is also pressed and fixed by the fixing nut 41.
The above-mentioned independent positioning double-seal structure transducer and its assembled reflective structure form a complete U-shaped ultrasonic acoustic path reflective flowmeter, and the two independent transducer fixing seats 12 of the flowmeter and the positions of the independent positioning double-seal structure transducer mounted in the flowmeter are set as close as possible to two ends of the equal-diameter metal outer tube 11; the distance between the two ultrasonic reflection surfaces 221 arranged in the equal-diameter metal outer tube is permanently fixed, so that the measuring range ratio of the reflective flowmeter can be maximized, the performance is kept unchanged for a long time, namely, the flowmeter has a wider fluid metering range; in addition, the ultrasonic sound path, namely the range of the flowmeter is higher than the consistency of R, so that the ultrasonic reflection flowmeter is beneficial to mass production and quick calibration, and can improve the production efficiency.
The transducer of the invention adapted to DN15 ultrasonic lining reflective flowmeter is implemented and applied by the above illustration, but is not limited to the specific embodiment, the theoretical deduction and application analysis of the matching thickness of the middle dielectric layer and the 3 conclusions of the obtained matching layer and the transmitted wave sound intensity are equally applicable to the transducer of the piezoelectric ceramic plates with different frequencies and the changed outer shell structure, and any modification or deformation based on the content of the invention is within the scope of the invention.
Claims (9)
1. The transducer of the adaptive ultrasonic lining reflective flowmeter is characterized by comprising an independent positioning double-sealing structure transducer of the adaptive reflective flowmeter and an ultrasonic reflective flowmeter provided with the independent positioning double-sealing structure transducer; the independent positioning double-sealing structure transducer comprises a transducer shell structural member (33) and an internal assembly; the ultrasonic reflection type flowmeter comprises an equal-diameter metal outer tube (11), a transducer fixing seat (12), a positioning boss (121), an independent positioning double-sealing structure transducer, a diversion and reflection surface fixing bracket (22), a rectifying tube (44), a fixing nut (41), an instrument box (55) and the like; the middle part of the transducer shell structure is provided with a blind hole, and the blind hole is of a cylindrical structure (3304); the internal components comprise a piezoelectric ceramic chip (331), a transfer PCB (332) and the like; the bottom of the blind hole is a bottom plane (3302), and the outer ring of the bottom plane is an annular groove (3301); the piezoelectric ceramic plate is adhered to the bottom plane, two sides of the piezoelectric ceramic plate are provided with two electrodes, namely a negative electrode and a positive electrode, a negative electrode outgoing line (3312) and a positive electrode outgoing line (3313) are welded on the piezoelectric ceramic plate and are electrically connected to the transfer PCB (332), a signal wire (333) of a transducer is welded on the positive electrode surface of the transfer PCB, the signal wire is led out through a middle through hole of a fixing nut (41) above the transducer, and the signal wire is electrically connected with the integrating circuit PCB (552) in the instrument box (55); the ultrasonic reflection type flowmeter base outer tube is an equal-diameter metal outer tube (11), a transducer fixing seat (12) and the like are arranged on the outer tube, and the outer tube and the transducer fixing seat are positioned at two ends of the equal-diameter metal outer tube and are connected through laser welding; the transducer with the independent positioning double-sealing structure is arranged in a transducer fixing seat (12), a positioning boss (121) is arranged in the transducer fixing seat, the transducer with the independent positioning double-sealing structure is positioned on the positioning boss, and a sealing ring (36) on the transducer is sealed with the inner side of the transducer fixing seat (12).
2. The transducer adapted to an ultrasonic lined reflective flowmeter of claim 1, wherein said annular recess is adapted to receive a weld (3311) of a negative electrode lead-out wire (3312) of a piezoelectric ceramic plate rim; the depth of the annular groove (3301) is greater than the height of the welding point (3311) of the negative electrode lead of the piezoelectric ceramic plate.
3. The transducer adapted to an ultrasonic lined reflective flowmeter of claim 1, wherein said piezoelectric ceramic sheet negative electrode lead (3312) is led from the side of the piezoelectric ceramic sheet (331) to the transit PCB (332); the two symmetrical inner and outwards protruding structures (339) are arranged at the side positions of the inner wall of the tubular structure (3304) corresponding to the ends of the negative electrode outgoing line (3312) and the positive electrode outgoing line (3313) of the piezoelectric ceramic plate in the blind hole in the transducer shell structural member (33), so that the negative electrode outgoing line (3312) and the positive electrode outgoing line (3313) can be conveniently connected to the transfer PCB (332), and the protruding structures are communicated to the bottom of the lower annular groove (3301) all the way from the upper end of the blind hole in the tubular structure.
4. The transducer of an adaptive ultrasonic lining reflective flowmeter of claim 3, wherein in the inward-outward protruding structure (339), a space at the upper end is wider, a section from the lower end to the annular groove is narrower, a positioning surface (3303) for mounting the height of the transfer PCB (332) is formed at the junction of the two, a space of 1-3 mm is kept between the positioning surface (3303) and the positive electrode of the piezoelectric ceramic plate (331), and the transfer PCB is mounted on the positioning surface.
5. The transducer adapted to an ultrasonic liner reflective flowmeter of claim 4, wherein said adapter PCB (332) has symmetrical PCB male structures (3322) on opposite sides of its outer circumference, and is correspondingly secured to said locating surface (3303); a PCB convex structure slit (3323) penetrating through the adapting PCB is formed in the middle of the adapting PCB convex structure (3322).
6. The transducer for an adaptive ultrasonic lining reflective flowmeter of claim 1, wherein the two guide and reflection surface fixing brackets (22) are respectively positioned at two ends of the inner side of the equal-diameter metal outer tube (11), the other side of the guide and reflection surface fixing bracket is provided with a guide cap (220), namely, the side of the rectifying tube (44) tightly matched with the guide and reflection surface fixing bracket is provided with a reflection surface (221) which is 45 degrees with the horizontal, and the reflection surface is made of metal or ceramic materials.
7. The transducer adapted to an ultrasonic lined reflective flowmeter of claim 1, wherein said transducer housing structure (33) is injection molded from an engineering plastic such as PPS, PEEK, PSF with a relatively matched acoustic characteristic impedance; the rectifying tube (44) is manufactured by injection molding of engineering plastic PPS, PPO, PPA, PA.
8. The transducer adapted to an ultrasonic lined reflective flowmeter of claim 1, wherein the connection between the baffle and reflector mounting bracket (22) and the rectifier tube (44): the diversion and reflection surface fixing support is in butt joint with the rectifying tube through a concave-convex structure (441), and epoxy resin glue is coated and fixed at the butt joint position.
9. The transducer adapted to an ultrasonic liner reflectometer as in claim 1, wherein the retaining nut (41) secures the independently positioned double seal structure transducer by compression against an underlying elastomeric washer (42); at the same time, the fixing nut (41) also presses and fixes the cylindrical structure (554) of the lower shell of the instrument box, and the cylindrical structure (554) of the lower shell of the instrument box is tightly matched with the outer diameter of the circular transducer fixing seat (12).
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210144980.7A CN116659598A (en) | 2022-02-18 | 2022-02-18 | Transducer of adaptive ultrasonic lining reflective flowmeter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210144980.7A CN116659598A (en) | 2022-02-18 | 2022-02-18 | Transducer of adaptive ultrasonic lining reflective flowmeter |
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| Publication Number | Publication Date |
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| CN116659598A true CN116659598A (en) | 2023-08-29 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202210144980.7A Pending CN116659598A (en) | 2022-02-18 | 2022-02-18 | Transducer of adaptive ultrasonic lining reflective flowmeter |
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| Country | Link |
|---|---|
| CN (1) | CN116659598A (en) |
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2022
- 2022-02-18 CN CN202210144980.7A patent/CN116659598A/en active Pending
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