RU7742U1 - ACOUSTIC Piezoelectric transducer of ultrasonic flow meter - Google Patents

Abstract

1. An acoustic piezoelectric transducer of an ultrasonic flow meter containing a multifaceted sound duct that has an installation face mounted on a pipeline, a measuring face with a piezoelectric element mounted on it, made at an acute angle to the installation face, and ultrasound-reflecting faces made so that the first reflecting face is perpendicular to the mounting face , the second reflective face is perpendicular to the first reflective face, and the third reflective face forms an acute angle with the second reflective face, creating together with the second reflecting face, an acoustic trap for ultrasonic waves reflected from the installation face, characterized in that the angle between the second and third reflecting faces is determined from the expression 0 <β <L, where β is the angle between the second and third reflecting faces; α is the angle between measuring and installation faces. 2. The piezoelectric transducer according to claim 1, characterized in that the fourth and fifth reflecting faces are introduced into the sound duct, creating, together with the mounting face, a second acoustic trap, the fourth reflecting face being perpendicular to the mounting face, the fifth reflecting face being made perpendicular to the fourth reflecting face and forming with the measuring face the angle is 180-α, and the angle between the second and third reflective faces is determined from the expressions 0 <β <α; α <β <90.l

Description

JUSTIC SECURITY TRANSMITTER

J ULTRA DRIVE.

The present log model relates to measuring technique and can be used to measure the flow rate and flow rate of the substance by the ultrasonic method.

The acoustic piezoelectric transducer of an ultrasonic flow meter is known to be installed on the external surface of a pipeline, containing a sound duct made in the form of a polyhedron with reflective surfaces, a pye30 element is installed on one of its faces, and this face is made at an acute angle to the other face of the sound duct installed on the pipeline. (A.S. USSR} 2II8I3 MKI: 42 e 23/05, 1965). The sound conduit of such a transducer is made of a material having a lower ultrasound velocity than the material of the pipeline wall.

Such converters ... along with the advantages of U1i (the absence of obstacles to the flow, the absence of pressure and energy losses, the possibility of installing the converters on a working pipeline without dismantling it and stopping the process) also have disadvantages. These include significant reverberation noise, especially when reflecting ultrasonic waves from reflective surfaces and when reflecting from a sound duct - pipe wall interface.

Closest to the proposed acoustic piezoelectric transducer of an ultrasonic flow meter is a transducer (Ermolov I.N. Theory and practice of ultrasonic testing. - M .: Mechanical Engineering, I98I.- 240 p.), Containing a sound duct with an acoustic trap, which is formed by reflecting edges made at an acute angle to each other.

The disadvantage of this converter is the insufficient suppression of reverberation interference.

Reverberation interference occurs because acoustic signals trapped in an acoustic trap after reflections in it return to the sound duct and fall onto the piezo plate. This effect is especially significant in sound ducts made of materials with low ultrasound absorption.

The inventive utility model of an acoustic piezoelectric transducer of an ultrasonic flowmeter is aimed at reducing the level of reverberation noise.

The technical result of the refinement of the utility model is to reduce the distortion of the useful signal and increase the measurement accuracy.

To solve this problem, an acoustic piezoelectric transducer of an ultrasonic flow meter is proposed, which contains a multifaceted sound duct, which has an installation face installed on the pipeline, a measuring face with a piezoelectric element mounted on it, made at an acute angle to the installation face, reflecting ultrasound faces, made so that the first reflecting the face is perpendicular to the installation face, the second reflective face is perpendicular to the first reflective face, and the third reflective face forms a sharp the angle with the second reflecting face, creating, together with the second reflecting face, an acoustic trap, characterized in that the angle between the second and third reflecting faces is determined from the expression:

About J3 (ts

 - the angle between the second and third reflecting faces, ob - the angle between the measuring and installation faces.

The fourth and fifth reflecting faces are introduced into the sound duct, creating, together with the mounting face, a second acoustic trap, moreover

crash, the fifth reflective face is perpendicular to the fourth reflective face and forms an angle 180 - with the measuring face. , and the angle of the mead of the second and third reflection} with the edges is determined from the expression: o,. . R

At the same time, along with solving problems, it is possible to solve the problem of increasing mechanochemical strength and reliability of the converter.

The utility model is illustrated by drawings. On $ ig. I, 2, 3, 4, 5, 6 schematically depict sound ducts with practical traps with different angles of the second and third reflective elongation and the directions of propagation of ultrasonic waves in them. Game I depicts a sound pipe with one acoustic trap and an angle between the second and third intersections and the reflection and rpabuiTvniJ3 0 °. On the . 2 depicts a third-named utility model with one acoustic trap at an angle. Fet.Z depicts a sound pipe with one oh sound trap and angle. Figure 4 shows a sound pipe with one acoustic trap and angle: .j3 90. On $ EG. 5 shows a sound pipe with one acoustic trap and angle jS 90. Per kg 6 depicts the claimed utility model with doors and acoustic traps and angle cL f 90.

The acoustic piezoelectric transducer (I1, I, 2, 3, 4, 5, 6) consists of a sound pipe - I, a piezoelectric element - 2, heated on a radiating face - 3, made at an angle oL to the installation face - 4,

loaded on the pipe wall - 5, the first reflective face - 6, the second reflective face - 7

and the third reflective face - 8, forming an acoustic trap with the second reflective face. The acoustic transducer shown in FIG. 6 additionally throws a fourth reflecting face 9 and a fifth reflecting face - 10, which form an acoustic trap with a mounting face of the intruder.

works as follows.

On the opposite walls of the pipeline, two identical acoustic piezoelectric transducers are installed, which probe the investigated MEV flow with ultrasonic pulsagly directed at an angle relative to the flow velocity vector. Sounding is made in the direction and towards a stream. The ultrasonic signal emitted by the piezoelectric element 2 of the first transducer through the sound pipe I and the wall of the pipe 5 comes into the stream under study. The extent to which a flow signal travels depends on the flow rate. An ultrasonic signal, passing the flow acquires information about its speed and passing through the opposite wall of the pipe 5, the sound pipe I is received by the piezoelectric element 2 of the second transducer. The signals emitted by the second transducer propagate in a similar way. The piezoelectric elements of the transducers are reversible i.e. work both in pe} imie radiation and in the mode of receiving ultrasonic signals. The angle of introduction of ultrasound into the flow is determined by the acoustic parameters of the controlled medium, the walls of the pipeline, the material of the sound duct and the angle of the sound duct between the measuring and installation faces.

As can be seen from FIG. I, 2, 3, 4, 5, 6, radiated into the sound duct I

ultrasonic wave / transducer 2, / arrival & 1T on the installation face 4 at an angle

slip e

  , (I)

 - the angle meg / do normal to the front of the ultrasonic wave that came from the piezoelectric element, and the installation face.

Once an ultrasonic wave hits an installation face, it partially passes into the pipeline wall, and then into the stream under investigation, and is partially reflected and propagates into the sound duct under the sliding edge to the installation face. Then, at a glancing angle, the wave falls on the first reflecting face, is reflected from it and at a glancing angle 9

falls onto the second reflective face. Reflected from the second reflecting face, the wave hits the third reflecting face, and depending on the angle A between the second and third reflecting granules, the angles of incidence of the wave on the third reflecting face are different and the waves reflected from it propagate differently.

If / E FIG. I), the third reflective face is parallel to the second reflective face and the wave, reflected from the second reflective face at a glide angle), comes to the third reflective face at the same angle, is reflected from it and comes to the second reflective face at the same angle. Reflected several times between these faces, the wave loses part of its energy and returns to the weakened sound duct. This is the basis for the action of the acoustic trap. The attenuated wave returned to the sound duct from the acoustic trap normal to the radiating face and, when incident on the piezoelectric element, excites the reverberation signal

If J3 оС then, as can be seen from figure 2., the wave propagates to the second reflecting face in the same way as in the previous case. Then reflected under the fragile slip F from the second reflecting wave comes on the third reflecting face at a sliding angle V, which is determined from the expression:

) is the angle between the normal to the wave front and the third reflecting

side.

Having reflected from the third reflecting face, the wave under the fragility comes to the second reflecting face:

, Sz)

) 90- оС + fi (2) waves repeatedly coming to the second reflecting face. The wave reflected from the second reflecting face at a gliding angle i falls onto the third reflecting face: i.-5R (4) (/ I is the angle between the third reflecting face and the normal to the wave front coming from the acoustic trap. The wave reflected from the third reflecting face goes into the sound duct and reflected from the first and second reflective faces, returns to the acoustic louvoupe, where it fades after repeated reflections. On the element 30, the wave does not return and does not excite the reverberation signal. If | 3. - about (Fig. 3), then, as follows from expression (2 ), the ultrasonic wave is incident on the third reflecting face perpendicularly ()) 90) and reflected from it along the same path it returns to the piezoelectric element and excites a significant reverberation signal. If / 3 o, then the ultrasonic wave, reflected from the second reflecting face (Fig. 4), falls onto the third reflecting face at an angle j): V) i / 6) (5) Having reflected from it at the same angle, the wave returns to the sound duct and it comes to the second reflecting face at an angle I: I-30 +, (6) i is the angle between the normal to the ultrasonic wave coming from the acoustic trap and the second reflecting face. Reflected from the second reflective face, the ultrasonic wave falls on the first reflective face at an angle (:

, (7)

iP is the angle between the normal to the front of the ultrasonic wave that came from the acoustic trap and the first reflecting face.

Reflecting from the first reflecting face, the wave again comes to the third reflecting face at an angle) and reflecting from it comes to the second reflecting face at the angle and reflecting comes to the first reflecting face at an angle cL. Reflected from the first reflective face, the ultrasonic wave arrives at the installation face at an angle. After reflection from the installation face, the ultrasonic wave falls normal to the measuring face, exciting significantly attenuations on the piezoelectric element due to multiple reflections, the reverberation signal.

If j3 is 90, then as can be seen from Fig. 5, after reflection from the second reflecting face, the ultrasonic wave arrives at the third reflecting face at a glancing angle оС and reflecting from it comes to the first reflecting face also under the corner оС, and after reflection comes

to the installation face at an angle / Reflecting from the installation face

the wave falls normal to the measuring face and excites a significant reverberation signal.

Thus, only at angles between the second and third reflecting faces greater than zero and less than c, the reflected waves do not fall on the piezoelectric element and do not cause the appearance of reverberation signals. These angles are optical for sound ducts with one acoustic trap:

(9 J3 s; (8)

in sound ducts with an angle between the second and third reflecting faces large oС t, it is possible to additionally reduce the reverberation signals by introducing a second acoustic trap. Moreover, as can be seen from Fig.6, the waves from the first acoustic trap come to the installation

a face at an angle of slip E, deposit and fall onto the fifth reflecting face, and then reflected from it fall on the installation face, etc. In this case, the fourth and fifth reflecting faces, together with the installation face, form the second acoustic trap for the reverberating signals that came from the sound duct. According to the foregoing, for an acoustic duct with two acoustic traps, the angle between the second and third reflecting faces must satisfy the conditions (8 and 9).

° C J3 50 (9)

It should be noted that sound ducts with angles / / имеют have increased mechanical strength, which significantly imposes significant mechanical forces when the sound duct is pressed against the pipe wall to obtain good acoustic contact.

In practice, for example, at an angle o (. 45 for a sound pipe with one acoustic trap, the angle jS is selected in the range from O to 451 For a sound pipe with a two-wire acoustic pickup, angle JZ is selected in the intervals from O to 45 or from 45 to 90f Usually, the angle is selected in the middle these ranges, i.e. / 3 22.5 ° or A 652 ,.

In the manufacture of a sound duct from a material with little absorption of ultrasound, for example, from polyolide, with about 45, without acoustic traps (V 9C), the reverberation noise level was

- 15 dB. In the manufacture of a sound duct with one acoustic trap with J3 22, the level of reverse interference was 34 dB. In the manufacture of zvody zvod and one acoustic loshchpozhi with an angle

| 3 617 ,, the level of reverb interference is 27 dB. The introduction of a second acoustic trap in such a sound duct allows it to be reduced to 34 dB.

The use of additional measures to reduce the reverberation noise associated with an increase in the roughness of the reflecting faces, applying scattering grooves, and a sound absorber on them allows the proposed utility model to significantly reduce the reverberation noise, reduce distortion of the useful signal and improve the accuracy of ultrasonic measurements flow meters.

Experimental samples of the claimed acoustic piezoelectric transducer of an ultrasonic flow meter were made and preliminary tests were carried out.

Claims (2)

1. An acoustic piezoelectric transducer of an ultrasonic flow meter containing a multifaceted sound duct that has an installation face mounted on a pipeline, a measuring face with a piezoelectric element mounted on it, made at an acute angle to the installation face, and ultrasound-reflecting faces made so that the first reflecting face is perpendicular to the mounting face , the second reflective face is perpendicular to the first reflective face, and the third reflective face forms an acute angle with the second reflective face, creating together with the second reflecting face, an acoustic trap for ultrasonic waves reflected from the installation face, characterized in that the angle between the second and third reflecting faces is determined from the expression
0 ^° <β <L,
where β is the angle between the second and third reflective faces;
α is the angle between the measuring and installation faces. 2. The piezoelectric transducer according to claim 1, characterized in that the fourth and fifth reflecting faces are introduced into the sound duct, creating, together with the mounting face, a second acoustic trap, the fourth reflecting face being perpendicular to the mounting face, the fifth reflecting face being made perpendicular to the fourth reflecting face and forming the measuring face is an angle of 180 ^° -α, and the angle between the second and third reflective faces is determined from the expressions
0 ^° <β <α; α <β <90 ^° .l