RU2766105C2 - High-temperature bending moment sensor for vortex flowmeters - Google Patents

Abstract

FIELD: sensors.

SUBSTANCE: invention relates to vortex flowmeters for liquids, gas or steam, in particular, to bending moment sensors for recording the frequency of vortices formed in the flow of a liquid, gas or steam behind the bluff body. A distinctive feature of the described sensor for vortex flowmeters consists in the fact that, according to the invention, the bottom constitutes a membrane, the diameter whereof is equal to the inner diameter of the bottom and exceeds the thickness thereof by at least 10 times, the wedge body at the point of connection with the bottom has a cylindrical neck, the diameter whereof does not exceed 1/3 of the inner diameter of the bottom, the bottom on the inner side is connected with a fastener of the piezoelectric unit with a transverse dimension not exceeding 1/3 of the inner diameter of the bottom and a height not exceeding 1/5 of the longer side of the piezoelectric plates. The fastener of the piezoelectric plates can constitute a cylindrical protrusion, coaxial with the body, provided with two flats parallel to the plane of symmetry dividing the wedge of the wedge wing in half; or the fastener of the piezoelectric plates can constitute a hollow thin-wall cylinder located coaxially with the body of the sensor.

EFFECT: increase in the level of sensitivity and the intrinsic resonant frequency of mechanical oscillations of the body of the sensor due to the structural change of the body with respect to reducing the length of the oscillating part thereof and the fastening unit of the piezoelectric plates for more efficient transformation of the bending deformations of the membrane into bending deformations of the piezoelectric plates.

3 cl, 4 dwg, 1 tbl

Description

The invention relates to vortex flowmeters for liquid, gas or vapor, in particular to bending moment sensors used and designed to record the frequency of vortices generated in a liquid, gas or vapor flow behind a shedder body.

Known Asymmetric bending moment sensor for high-temperature vortex flowmeters (RU 2 688 876, IPC H01L41 / 08, pub. 08/15/2016), having an outer plate, one end of which is attached to the end of a cylindrical body, the other end is free, and the plate thickness linearly decreases from of the fixed end to the free end with an angle between the planes equal to 2…4°, which perceives the variable bending moment of the pressure force from the side of the vortices and causes variable body deformations, and one or more piezoelectric elements located in the body cavity and converting the bending moment into an alternating electrical signal, the frequency of which is equal to the frequency of occurrence of vortices, characterized in that, in order to expand the temperature range through the use of high-temperature piezomaterials, characterized by small values of the piezoelectric modulus d ₃₁ , but acceptable values of the piezoelectric modulus d ₃₃ , the transducer geometry is changed so that its sensitive element has a e a set of coaxial piezoelectric discs polarized in thickness and installed in a cylindrical cavity, the axis of which is displaced relative to the plane of the outer plate, due to which the bending deformations of this plate transmitted through the membrane cause compression-tension stresses along the axis of the piezoelectric discs, which are converted into an electrical signal proportional to piezoelectric module d ₃₃ , output by means of a cable to devices that fix its frequency.

This technical solution has disadvantages. The main disadvantage is the low sensitivity of the sensor, which is due to the violation of the symmetry of the structure. As a result of this violation of symmetry, the bending moment of the pressure force from the side of the vortices and causing variable deformations of the body will act on a set of piezoelectric disks, mainly causing compressive stresses when the outer plate is deflected to one side and the membrane is bent, while when the outer plate is deflected to the other side of the tensile stress on the disk set will not be applied. In this case, the compressive stress will only weaken. Thus, the efficiency of such a design is at least twice as low as compared to a symmetrical design solution.

Also known is a bending moment sensor for vortex flowmeters (Piezo Sensor for Vortex Flowmeter, "Tms Electronic Co. Ltd", Anhui, China.), containing a hollow cylindrical metal case ending on one side with a wedge-shaped wing, and on the other side with a sealed input with a coaxial a cable having a shield and a center conductor connected to a piezoelectric assembly located inside the housing.

This technical solution is also not without drawbacks. The main disadvantage is the low sensitivity of the sensor, given in the description of technical characteristics (https://tmselec.en.ec21.com/Piezo_Sensor_for_Vortex_Flowmeter--4083813_4083855.html). Another drawback is the low natural resonant frequency of the mechanical vibrations of the sensor housing, due to its geometry (the long cantilever part of the housing that goes into the measured flow).

The closest to the claimed technical solution is a vortex flowmeter sensor bending moment sensor for high-temperature vortex flowmeters (RU 2608331, IPC G01F1 / 32, pub. 01/17/2017 ), containing an outer plate attached to the end of a cylindrical body, perceiving a variable bending moment of the pressure force from sides of the vortices and causing variable deformations of the body, and a piezoelectric element in the form of a hollow cylinder of piezoelectric ceramics polarized in the radial direction, installed in the cavity of the body and rigidly connected to it, the outer cylindrical surface of the piezoelectric element being covered with a solid electrode, and on the inner surface the electrode is cut into two parts along the generatrix along the plane coinciding with the plane of the outer plate, due to which an alternating electrical signal arises between the inner electrodes with a frequency of vortex formation proportional to the flow velocity, taken by means of a cable, signal the conductors of which are connected to the internal electrodes of the piezoelectric element, contact elements are introduced into the internal cavity of the piezoelectric element in the form of two cylindrically curved metal plates, preliminarily welded to the cable conductors, separated from each other by an insulator plate, pressed against the internal electrodes of the piezoelectric element by elastic forces that provide electrical contact between the electrodes of the piezoelectric element and communication line.

This technical solution also has disadvantages. One of the disadvantages is the insufficiently high sensitivity of the sensor, which is obviously associated with the use of a hollow cylinder made of piezoelectric ceramics, which has a more stable geometry with respect to axial bending compared to, for example, rectangular elements.

Another disadvantage is that the bending moment of the pressure force from the Karman vortices formed behind the shedding body in the medium flow, perceived by the outer plate attached to the body, falls on the middle region of the cylindrical body, in the inner cavity of which there is a piezoelectric element in the form of a hollow cylinder made of piezoelectric ceramics. In this case, the natural resonant frequency of mechanical vibrations is determined and limited from above by the total length of the outer plate and part of the housing from the plane of its fixation to the free end of the outer plate. This, in turn, is the reason for limiting the upper limit of the dynamic range of measured costs (https://www.piezoelectric.ru/Products/FlowSensors/SensorsBendingMoment.php).

The technical problem is to develop a bending moment sensor for vortex flowmeters capable of operating at high temperatures and pressures of the measured medium of flowing liquid and gas flows and having high sensitivity and an increased natural resonant frequency of mechanical vibrations of the body, which will expand the dynamic range of measured flow rates. The range of measured frequencies of oscillations of the wedge-shaped wing of the sensor, due to the influence of the vortices of the moving medium, lies in the frequency range from units, or tens of hertz, to 2-3 kilohertz. The amplitudes of these oscillations are significantly less than the amplitude of the body oscillations at their own resonant frequencies. Therefore, the overlap of the range of measured frequencies and the natural resonance frequency lead to a malfunction of the flow meter and, accordingly, to limit the dynamic range of the measured flow rates. For this reason, it is desirable that the natural resonant frequency of the sensor housing would be significantly higher than the maximum measurable frequencies.

The technical result consists in increasing the level of sensitivity and natural resonant frequency of mechanical vibrations of the sensor housing by changing the design of the housing in relation to reducing the length of its oscillating part and the piezoelectric plate fixation unit for more efficient transformation of the membrane bending deformations into bending deformations of the piezoelectric plates.

The technical result of the proposed solution is achieved by the fact that in the bending moment sensor for vortex flowmeters of liquid or gas, containing a hollow cylindrical metal case, ending on the one hand with a bottom connected to the wedge-shaped wing, and on the other hand, with a sealed input with two coaxial cables having screen and center conductors connected to a piezoelectric assembly located inside the housing, and representing a pair of rectangular piezoelectric plates with parallel planes, polarized in thickness, having surfaces metallized along the planes and fixed to the body along its two narrow sides, according to the invention, the bottom is a membrane, the diameter of which is equal to the inner diameter of the bottom and exceeds its thickness, at least 10 times, the wedge-shaped wing connected to the outer surface of the bottom at its thickened base at the junction with the bottom has a cylindrical neck, the diameter of which does not exceed 1/3 of the inner diameter of the bottom, on the inside the bottom in its center is connected to a piezoelectric assembly retainer having a transverse dimension not exceeding 1/3 of the inner diameter of the bottom and a height not exceeding 1/5 of the long side of the piezoelectric plates.

The technical result of the proposed solution according to claim 2 is achieved by the fact that the latch of the piezoelectric plates is a cylindrical ledge coaxial with the body, having two flats parallel to the plane of symmetry dividing the wedge of the wedge-shaped wing in half;

The technical result of the proposed solution according to claim 3 is achieved by the fact that the latch of the piezoelectric plates is a hollow thin-walled cylinder located coaxially with the sensor housing.

The piezoelectric plates can be bonded to the body along their two narrow sides with a high temperature adhesive.

The invention is illustrated by drawings, where:

- figure 1 shows the general design of the claimed invention; the sensor is installed in the measuring tube, side and top views;

- figure 2 shows the design of the sensor installed in the measuring tube; view in which the axis of the pipe is normal to the surface of the pattern;

- figure 3 shows the design options for the retainer of the piezoelectric plates;

- figure 4 shows an image of the sensor in three positions, in which, under the influence of the pressure of the vortices, the wedge-shaped wing bends to the left and right, or remains in a neutral position.

In the drawings (figure 1 - figure 4) positions indicate:

1 - metal case,

2 - bottom,

3 - wedge-shaped wing,

4 - measuring pipe,

5 - sealed input,

6 - coaxial cable,

7 - screen explorer,

8 - central conductor,

9 - piezoelectric assembly,

10 - piezoelectric plates,

11 - high temperature adhesive,

12 - cylindrical neck,

13 - piezoelectric assembly retainer,

14 - wrap body,

15 - cylindrical protrusion from the inside of the bottom;

16 - flats on a cylindrical ledge;

17 - hollow thin-walled cylinder.

A bending moment sensor for vortex flowmeters of liquid or gas, containing a hollow cylindrical metal case 1, ending on one side with a bottom 2 connected to a wedge-shaped wing 3, which goes into the measuring tube 4, and on the other hand, with a sealed inlet 5 with two coaxial cables 6 having screen 7 and central 8 conductors connected to the piezoelectric node 9 located inside the housing 1, and representing a pair of rectangular piezoelectric plates 10 with parallel planes, polarized in thickness, having surfaces metallized along the planes and fixed to the body along its two narrow sides with a high-temperature adhesive 11, the bottom 2 is a membrane, the diameter of which is equal to the inner diameter of the bottom 2 and exceeds its thickness by at least ten times, the wedge-shaped wing 3 connected to the outer surface of the bottom 2 at its thickened base at the junction with the bottom 2 has a cylindrical neck 12, the diameter of which does not exceed one third of the inner diameter of the bottom 2, on the inside the bottom 2 in its center is connected to the latch 13 of the piezoelectric assembly 9, having a transverse dimension not exceeding one third of the inner diameter of the bottom 2 and a height not exceeding one fifth of the long side of the piezoelectric plates 10. In the measuring tube 4 in front of the wedge-shaped wing 3 sensors 14, which is a source of vortex formations (Karman vortices) that create alternating (from each plane of the wing 3) pressure on the wing 3 of the sensor with a frequency proportional to the velocity of the liquid or gas flow.

In the decision under item 2. the latch 13 of the piezoelectric plates 8 is a cylindrical protrusion 15 coaxial with the body, having two flats 16 parallel to the plane of symmetry dividing the wedge of the wedge-shaped wing 3 in half.

In the solution according to claim 3 of the formula, the latch 13 of the piezoelectric plates 8 is a hollow thin-walled cylinder 17 located coaxially with the sensor housing 1.

The device works as follows.

The sensor is installed in the measuring tube 4 behind the bluff body 14 along the liquid or gas flow so that the plane of symmetry dividing the wedge of the wedge-shaped wing 3 in half is parallel to the axis of the measuring tube 4. A periodic sequence of vortices (see Fig.1) arising in the measuring pipe 4 behind the bluff body 14, causes in turn pressure on each of the planes of the wedge-shaped wing 3 of the bending moment sensor (see Fig.4) with a frequency equal to the reciprocal of the wing oscillation period and proportional to the velocity of the measured liquid or gas flow. Vibrations of the wing 3 cause bending deformations of the membrane, which is part of the bottom 2 of the sensor and through the latch of the piezoelectric assembly 13 (see Fig.2 - 4) are transmitted to the piezoelectric plates 10, causing their bending deformation. Bending deformations of the piezoelectric plates 10, due to the piezoelectric effect, induce the appearance of electric charges on the metallized surfaces of the piezoelectric plates 10, the metallized surfaces of each of which are electrically connected to the screen 7 and signal 8 conductors of the coaxial cables 6.

The electrical voltage taken from the output of the sensor is determined by the ratio of the induced charge to the total capacitance of the piezoelectric sensitive node 9 and the output cable 6.

An example of a specific design of the bending moment sensor.

The sensor housing, made of titanium, has a wedge-shaped wing 25 mm long. The hollow cylindrical channel of the sensor housing has a diameter of 5 mm and a depth of 14 mm, equal to the length of the piezoceramic plates. The width of the piezoceramic plates is 4mm. The diameter of the cylindrical neck of the wedge-shaped wing is chosen equal to the diameter of the hollow thin-walled cylinder (piezoelectric assembly retainer) and equal to 4 mm. The inner diameter of the bottom is 12 mm, and its thickness is 1 mm. The height of the piezoelectric assembly retainer was chosen to be 2.5 mm. In FIG. 3. options (corresponding to paragraphs 2 and 3 of the formula) for the execution of the piezoelectric plate retainer are given. The left part of the figure shows a variant of the piezoelectric plate retainer in the form of a cylindrical protrusion coaxial with the body, having two flats parallel to the plane of symmetry dividing the wedge-shaped wing wedge in half. The right side of the figure shows a variant of the piezoelectric plate retainer in the form of a hollow thin-walled cylinder located coaxially with the sensor body.

The piezoelectric plates are fixed in the sensor body with a high-temperature adhesive.

The connection of the screen and central conductors of coaxial cables to the metallized surfaces of the piezoelectric plates can be implemented, for example, using spot microwelding; in this example, this connection is carried out by high-temperature soldering.

The efficiency of the bending moment sensor is largely determined, along with the properties of piezoceramic elements, its geometric characteristics, as well as the elastic properties of the materials used. In particular, the use of an axisymmetric disk membrane for transforming the bending vibrations of a wedge-shaped wing into bending vibrations of piezoelectric plates makes it possible to increase the sensitivity of the sensor in comparison with the design; bending vibrations of the cylindrical sensor housing are used. The thickness of the membrane, which for this technical solution does not exceed 1/10 of its diameter, was chosen based on experimental data on optimizing the geometric characteristics of the sensor housing. Optimization was carried out according to the coefficient of conversion of mechanical stresses into electrical ones, while maintaining the strength characteristics of the bottom. The cylindrical neck of the wedge-shaped wing connected to the bottom from the outside, as well as the piezoelectric assembly retainer connected to the bottom from the inside, have close transverse dimensions not exceeding 1/3 of the inner diameter of the bottom. This parameter was also found experimentally and determines the ratio of dimensions between the loaded section of the membrane, which mechanically connects the neck of the wedge-shaped wing, the membrane, the piezoelectric assembly retainer, and the free section of the membrane, which is subjected to bending vibrations. With such a ratio of dimensions, the loaded section provides reliable fixation of the piezoelectric assembly and, at the same time, the free section provides the membrane oscillation amplitude close to the maximum. The height of the latch of the piezoelectric assembly is chosen not to exceed 1/5 of the long side of the piezoelectric plate. This value, as experiments show, is sufficient for rigid fixation of the ends of the piezoelectric plates with a membrane and with a wedge-shaped wing and, at the same time, the central part of the piezoelectric plate, free from external mechanical load, has a sufficient area for transformation into an electric signal of the bending moment transmitted from the bending membrane when the wedge-shaped wing deviates from the middle position under the influence of pressure from the vortices of the moving measured flow.

Drawings in Fig.4. explain the principle of transferring elastic deformations to piezoelectric plates through a membrane from a wedge-shaped wing, which oscillates under the influence of alternating pressures from the side of the flow vortices to one and the other of its planes.

Table 1 shows a comparison of the experimental characteristics of the proposed device and published data on the characteristics of the prototype and one of the analogues.

For the purpose of the greatest correctness of comparisons for the experiment, samples of the proposed device with the length of the wedge-shaped wing and the type of piezoceramics used, corresponding to the prototype, were made. The operating temperature of the compared samples is also chosen identical to 350°C.

Table 1.

Character -
Ristic
Sensor Wedge-shaped wing length, mm Ceramic type Working temperature, ° С Feelings
capacity, mV/g Sensitivity, nK/Nm resonant
Frequency, kHz The claimed device 25 CFTS 21 350 32 80 6.0 Protopip 108MT (LLC "Piezoelectric" Rostov-on-Don)
25
CFTS 21
350
12
thirty
3.1 Analog Piezoelectric sensor for vortex flowmeter ("Tms Electronic Co. Ltd", China.)
25
-
350
0.1
0.25
2.2

Table 1 shows that with other identical parameters (operating temperature, wedge-shaped wing length), the characteristics of the proposed device compare favorably with the prototype and analogue. The sensitivity of the proposed device is 2.5 times higher in comparison with the prototype and more than 300 times higher in comparison with the analogue. Own resonant frequency of mechanical vibrations of the proposed device is two times higher than that of the prototype and 2.7 times higher than the resonant frequency of the analogue.

Claims (3)

1. Bending moment sensor for vortex flowmeters of liquid or gas, containing a hollow cylindrical metal case, ending on one side with a bottom connected to a wedge-shaped wing, and on the other side with a sealed input with two coaxial cables having screen and center conductors connected to a piezoelectric assembly located inside the body and representing a pair of rectangular piezoelectric plates with parallel planes, polarized in thickness, having surfaces metallized along the planes and fixed to the body along its two narrow sides with a high-temperature adhesive,different in thatthat the bottom is a membrane, the diameter of which is equal to the inner diameter of the bottom and exceeds its thickness by at least 10 times; /3 of the inner diameter of the bottom, on the inner side the bottom in its center is connected to a piezoelectric assembly retainer having a transverse dimension not exceeding 1/3 of the inner diameter of the bottom and a height not exceeding 1/5 of the long side of the piezoelectric plates. 2. The bending moment sensor according to claim 1, characterized in that the latch of the piezoelectric plates is a cylindrical protrusion coaxial with the body, having two flats parallel to the plane of symmetry dividing the wedge of the wedge-shaped wing in half. 3. The bending moment sensor according to claim 1, characterized in that the piezoelectric plate retainer is a hollow thin-walled cylinder located coaxially with the sensor body.

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